Biological Fuel Cells: Fundamental to Applications 0323857116, 9780323857116

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BIOLOGICAL FUEL CELLS

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BIOLOGICAL FUEL CELLS Fundamental to Applications Edited by

MOSTAFA RAHIMNEJAD Biofuel and Renewable Energy Research Center, Chemical Engineering Department, Babol Noshirvani University of Technology, Babol, Mazandaran, Iran

Elsevier Radarweg 29, PO Box 211, 1000 AE Amsterdam, Netherlands The Boulevard, Langford Lane, Kidlington, Oxford OX5 1GB, United Kingdom 50 Hampshire Street, 5th Floor, Cambridge, MA 02139, United States Copyright © 2023 Elsevier Inc. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Details on how to seek permission, further information about the Publisher’s permissions policies and our arrangements with organizations such as the Copyright Clearance Center and the Copyright Licensing Agency, can be found at our website: www.elsevier.com/permissions. This book and the individual contributions contained in it are protected under copyright by the Publisher (other than as may be noted herein). Notices Knowledge and best practice in this field are constantly changing. As new research and experience broaden our understanding, changes in research methods, professional practices, or medical treatment may become necessary. Practitioners and researchers must always rely on their own experience and knowledge in evaluating and using any information, methods, compounds, or experiments described herein. In using such information or methods they should be mindful of their own safety and the safety of others, including parties for whom they have a professional responsibility. To the fullest extent of the law, neither the Publisher nor the authors, contributors, or editors, assume any liability for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions, or ideas contained in the material herein. ISBN: 978-0-323-85711-6 For information on all Elsevier publications visit our website at https://www.elsevier.com/books-and-journals

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Contents

Contributors

PART 1

xi

Constituents, structure, materials and measurement with conceptual, practical and economical views

1. Introduction to biological fuel cell technology

3

Mostafa Rahimnejad 1.1 Background 1.2 Basic principles 1.3 Potential feedstocks for MFCs 1.4 BFC’s classification 1.5 Conclusions References

2. Microbiological concepts of MFCs

3 5 10 15 20 21

29

Mostafa Rahimnejad 2.1 Introduction 2.2 Exoelectrogenic microorganisms 2.3 Electrotrophic microorganisms 2.4 Electron transport mechanisms 2.5 Factors affecting the electron transfer mechanism 2.6 Mechanism of biofilm formation in MFCs 2.7 Factors affecting biofilm formation and performance 2.8 Genetic approaches for improving the performance of MFCs 2.9 Conclusions References

3. Anode electrodes in MFCs

29 29 38 39 44 45 46 53 54 54

67

Mostafa Rahimnejad 3.1 Introduction 3.2 Necessities of anode materials 3.3 Anolytes 3.4 Anode-assisted electrochemical catalysis 3.5 Anode materials 3.6 Surface modification of MFC anode materials 3.7 Conclusions References

67 67 71 73 75 78 85 85 v

vi

Contents

4. Cathode electrodes in MFCs

93

Mostafa Rahimnejad 4.1 Introduction 4.2 Cathode concepts 4.3 Cathodic structures in MFC 4.4 Cathode requirements in MFCs 4.5 Cathodic surface treatment 4.6 Catholytes 4.7 Enzyme immobilization methods for biocathodes 4.8 Cathode catalysts: Conventional, photo, and biocatalysts 4.9 Conclusions References

93 93 98 100 103 105 106 110 116 116

5. Energy and power measurement methods in MFCs

127

Mostafa Rahimnejad 5.1 Introduction 5.2 Power indicators 5.3 Electrochemical methods 5.4 Biofilm characterization methods 5.5 Conclusions References

127 129 131 141 143 143

6. MFC designing and performance

147

Mostafa Rahimnejad 6.1 Introduction 6.2 MFC configurations 6.3 Different modes of operation in MFCs 6.4 Kinetic analysis and modeling of MFCs 6.5 MFCs at a larger laboratory scale 6.6 Pilot-scale MFC designs 6.7 Conclusions References

7. Separators and membranes

147 147 160 162 166 167 168 169

177

Mostafa Rahimnejad 7.1 Introduction 7.2 Membrane types for MFCs 7.3 Membrane requirements in MFCs 7.4 Conclusions References

177 177 198 202 203

Contents

8. Supercapacitive microbial fuel cells

213

Federico Poli, Francesca Soavi, and Carlo Santoro 8.1 Introduction 8.2 High surface area capacitive electrodes in MFCs 8.3 Supercapacitive microbial fuel cells 8.4 Pseudocapacitive MFC electrodes 8.5 Conclusions References

213 214 217 220 221 222

9. MFCs’ challenges and their potential solutions

225

Mostafa Rahimnejad 9.1 Introduction 9.2 Voltage losses 9.3 How can biofilm formation cause voltage losses? 9.4 Biofouling formation principles 9.5 Biofouling development on membrane and cathode surfaces 9.6 Biofouling assessment methods 9.7 Driving factors of biofouling 9.8 How to overcome fouling challenges 9.9 Conclusions References

10. MFCs’ commercialization and economic analysis

225 226 227 229 231 232 233 234 240 241

249

Mostafa Rahimnejad 10.1 Introduction 10.2 Field trials of MFCs 10.3 Cost-effective MFC resources 10.4 Commercialization requirements 10.5 Large-scale implementation 10.6 Conclusions References

PART 2

249 251 258 260 263 264 265

MFCs’ applications

11. Electricity generation

273

Mostafa Rahimnejad 11.1 Introduction 11.2 Bioelectricity generation in MFC systems 11.3 Power generation in EFC systems

273 273 287

vii

viii

Contents

11.4 Practical implementation of MFC technology for power generation 11.5 Conclusions References

12. Application of biological fuel cell in wastewater treatment

288 291 292

301

Nahid Navidjouy, Fatemeh Soltani, and Mostafa Rahimnejad 12.1 MFCs vs other available options 12.2 Principles of wastewater treatment via MFCs 12.3 Preference of MFCs vs other WWTP 12.4 Expansion of microbial fuel cell research in wastewater treatment 12.5 Mechanisms and reactions of MFC 12.6 Microbial communities for bioanode 12.7 Application of microbial fuel cells in various wastewater treatments 12.8 MFC Integration with other processes in wastewater treatment plants 12.9 Integration of MFC with electro-Fenton technology (BEF) 12.10 Future perspective 12.11 Conclusions References

13. Biohydrogen generation and MECs

301 301 302 302 303 306 307 311 311 316 316 317

321

Mostafa Rahimnejad 13.1 Introduction 13.2 MEC fundamentals 13.3 Theoretical yields of MEC systems 13.4 MEC Challenges and promising solutions 13.5 MEC operation 13.6 MEC Performance 13.7 Conclusions References

14. CO2 reduction and MES

321 322 324 324 332 340 341 341

351

Mostafa Rahimnejad 14.1 Introduction 14.2 Basic principles of MECs utilized for CO2 capture 14.3 MES microbial community 14.4 MES products 14.5 Requirements for MES operation 14.6 MES scale-up 14.7 Conclusions References

351 351 354 354 358 361 364 365

Contents

15. Bioremediation by MFC technology

373

Mehri Shabani, Bita Roshanravan, Habibollah Younesi, Maxime Ponti e, Sang-Hyun Pyo, and Mostafa Rahimnejad 15.1 Types of microbial fuel cells for bioremediation of pollutants 15.2 Applications of MFC for sludge remediation 15.3 Bioremediation of chromium released from industrial wastewater using MFC 15.4 Bioremediation of landfill leachates and municipal wastewater via MFC 15.5 MFC-assisted biodegradation of azo dyes 15.6 Bioremediation of hydrocarbons and their derivatives 15.7 Removal of heavy metals 15.8 Mechanism and thermodynamic of metal bioelectrodeposition 15.9 Removal of other pollutants References

16. MFC-based biosensors

373 382 383 383 384 384 385 400 406 407

419

Hoda Ezoji and Mostafa Rahimnejad 16.1 Measurement and sensors 16.2 Types of sensors 16.3 Recognition element 16.4 Transducer 16.5 Classification of chemical sensors 16.6 Biosensors and their classification 16.7 Biosensors applications 16.8 Self-powered biosensors 16.9 MFC-based biosensors 16.10 Conclusions References

419 419 421 422 422 424 429 429 430 435 435

17. Sediment microbial fuel cell (SMFCs)

439

Atieh Zabihollahpoor and Mostafa Rahimnejad 17.1 SMFCs and constructed wetland (CW) associated with it 17.2 Photosynthetic sediment microbial fuel cells (PSMFCs) 17.3 SMFCs and removal of heavy metals References

18. Future applications of biological fuel cells

439 455 456 456

463

Tahereh Jafary, Anteneh Mesfin Yeneneh, Muna Al Hinai, Mimi Hani Abu Bakar, and Mostafa Rahimnejad 18.1 Introduction 18.2 Robotics

463 463

ix

x

Contents

18.3 Powering low-energy devices 18.4 MFCs powering remote sensors 18.5 Paper-based MFC devices 18.6 Urine-based MFC 18.7 Concluding remarks Acknowledgment References Index

466 468 473 478 480 481 481 487

Contributors

Muna Al Hinai Engineering Department, International Maritime College Oman, National University of Science and Technology, Muscat, Oman Mimi Hani Abu Bakar Fuel Cell Institute, Universiti Kebangsaan Malaysia, Bandar Baru Bangi, Malaysia Hoda Ezoji Faculty of Research and Development of Energy and Environment, Research Institute of Petroleum Industry (RIPI), Tehran, Iran Tahereh Jafary Engineering Department, International Maritime College Oman, National University of Science and Technology, Muscat, Oman Nahid Navidjouy Department of Environmental Health Engineering, School of Public Health, Urmia University of Medical Sciences, Urmia, Iran Federico Poli Department of Chemistry “Giacomo Ciamician” Alma Mater Studiorum, Universita` di Bologna, Bologna, Italy Maxime Pontie Group of Analysis & Processes (GA&P), Faculty of Science, University of Angers, Angers, France Sang-Hyun Pyo Division of Biotechnology, Department of Chemistry, Center for Chemistry and Chemical Engineering, Lund University, Lund, Sweden Mostafa Rahimnejad Biofuel and Renewable Energy Research Center, Chemical Engineering Department, Babol Noshirvani University of Technology, Babol, Mazandaran, Iran Bita Roshanravan Department of Environmental Science, Faculty of Natural Resources, Tarbiat Modares University, Tehran, Iran Carlo Santoro Department of Material Science, Universita` degli Studi di Milano-Bicocca, Milan, Italy

xi

xii

Contributors

Mehri Shabani ESAIP La Salle, CERADE, Graduate School of Engineering, Saint-Barthelemy d’Anjou; Group of Analysis & Processes (GA&P), Faculty of Science, University of Angers, Angers, France Francesca Soavi Department of Chemistry “Giacomo Ciamician” Alma Mater Studiorum, Universita` di Bologna, Bologna, Italy Fatemeh Soltani Department of Environmental Health Engineering, School of Public Health, Urmia University of Medical Sciences, Urmia, Iran Anteneh Mesfin Yeneneh Engineering Department, International Maritime College Oman, National University of Science and Technology, Muscat, Oman Habibollah Younesi Department of Environmental Science, Faculty of Natural Resources; Department of Renewable Energy, Faculty of Interdisciplinary Science and Technology, Tarbiat Modares University, Tehran, Iran Atieh Zabihollahpoor Biofuel and Renewable Energy Research Center, Chemical Engineering Department, Babol Noshirvani University of Technology, Babol, Mazandaran, Iran

PART 1

Constituents, structure, materials and measurement with conceptual, practical and economical views

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CHAPTER 1

Introduction to biological fuel cell technology Mostafa Rahimnejad

Biofuel and Renewable Energy Research Center, Chemical Engineering Department, Babol Noshirvani University of Technology, Babol, Mazandaran, Iran

1.1 Background Energy consistently impacts the quality of life and plays a crucial role in the development of modern society. Energy can be obtained from renewable or nonrenewable sources (Fig. 1.1). Nonrenewable energy possesses cumulative share of world energy consumption including fossil fuels (oil, coal, and natural gas) and nuclear energy. As reported in Statistical Review of World Energy, fossil fuels provide more than 80% of total energy on the Earth (Fig. 1.2). Although fossil fuels are prime energy providers, the risks of carbon dioxide emission, air pollution, global warming, and health problems restrict their applications [1,2]. Furthermore, due to population growth and energy crisis [3] there is an immense need to develop alternative energy sources. Renewable energy sources comprising solar energy, wind energy, biomass energy, geothermal energy, wave energy, and hydro energy are established around the world as green and cost-effective power suppliers (Fig. 1.3). However, there are some drawbacks in reliability of the generated power as to meteorological conditions and financial constraints. From feasibility assessment provided in the literature, it can be concluded that biomass has the potential to provide significant economic opportunities for energy conservation. Biomass is one of the most abundant renewable energy available. Chemical energy embedded within bulk biomass can be converted into electricity using bioelectrochemical systems. Agricultural residue, animal waste, energy crops, and food processing wastewater are well-known biomass options for electricity production. Interest in biological fuel cells (BFCs) increased when NASA utilized biocatalytic devices to turn organic waste into electrical power on space missions. BFCs transform electrical energy of organics into electrical energy carried out either with enzymes or microorganisms as biocatalysts. As a matter of fact, enzymatic-based fuel cells (EFCs) have some advantages such as biocompatibility, good occurring under mild conditions as well as being specific and hierarchical in performance. However, enzymatic life time is limited and there are some practical problems associated with enzyme Biological Fuel Cells https://doi.org/10.1016/B978-0-323-85711-6.00002-3

Copyright © 2023 Elsevier Inc. All rights reserved.

3

4

Biological fuel cells

Fig. 1.1 Types of energy sources.

Fig. 1.2 Primary global energy consumption 2019.

operating conditions. Enzyme stability enhancement is possible, although it requires additional operating costs. Microbial fuel cells (MFCs) are known as bioelectrochemical systems in which microorganisms actively participate in direct conversion of chemical energy embedded within organic materials into sustainable electrical energy. MFCs are primarily utilized for bioelectricity production. Being economically feasible and an eco-friendly approach, MFCs provide immense potential as an alternative to the uncontrolled use of fossil fuels

Introduction to biological fuel cell technology

Fig. 1.3 Renewable electricity generation 2017. (Reported by International Renewables Energy Agency (IRENA).)

(Fig. 1.4). There are a wide variety of carbonaceous substrates for MFC operation such as pure organic compounds, synthetic feedstocks, biomass, and domestic and industrial wastewater. Recent studies have developed MFC constructs for simultaneous wastewater treatment and power generation (Fig. 1.5). The electrical power is prognosticated to partially cover energy demand of wastewater treatment plants [4]. The process includes microbial decomposition of substrates, aiming at sustained electron flows to provide a valuable green electrical current. Chapter 12 deals with applications and challenges of MFCs as novel wastewater treatment systems. In situ electrochemical biosensing is another potential application of MFCs. Recently, significant progress has been made in the development of MFC-based biosensors for monitoring biochemical oxygen demand (BOD) and toxicity in the environment. The application of MFCs as biosensors are discussed Chapter 16. Despite significant advancement in MFC technology, its commercialization remained a challenge due to its low revenue per unit energy [5]. Chapter 6 provides an overview of practical designs of MFCs, scale-up parameters, and limitations in large-scale application of MFCs. This chapter presents an introduction to MFCs, their basic principles, classifications, and a brief evaluation of potential feedstocks.

1.2 Basic principles 1.2.1 Microbial decomposition of organic materials Decomposition means biocatalytic breakdown of raw organic materials into CO2, water, mineral nutrients, and energy. In the past 10–15 years, global energy crisis has captured the attention of researchers for energy recovery from organic waste through microbial/

5

Fig. 1.4 Comparison of operational characteristics between MFCs and chemical fuel cells (CFCs).

Introduction to biological fuel cell technology

Fig. 1.5 MFC a green energy supplier of wastewater treatment plants.

enzymatic electrochemical reactions, among which microbial catalysts are preferred due to their economic feasibility, and more sustainable biocatalytic activity of microorganisms. In MFCs, microbes are used as catalysts for electrochemical reactions. Microbes have excellent capacity to generate electricity. The choice of microbial community is dependent on the type of substrate and operating conditions [6,7]. MFCs cover a broad range of biodegradable organic substrates that alter the degradation kinetics and affect the operational conditions [8]. Until now, various groups of microorganisms (such as bacteria, microalgae, fungi, and yeast) have been shown to be capable of biocatalytic function in MFC systems. Different kinds of microorganisms used in MFC operation are discussed in detail in Chapter 2.

1.2.2 Working principles of MFCs As a biological technology, MFCs integrate cathode and anode materials with microorganisms to achieve electricity generation. MFCs utilize a strategy that includes the microbial conversion of chemical energy of organic and inorganic compounds into electricity [9,10]. MFCs require four components, an anodic electrode within which electrons, protons, and other metabolites are produced through anaerobic oxidation of substrates, a cathodic electrode for collecting the electrons by an electron acceptor material, a membrane for physical separation of the electrodes and mediating proton diffusion to the cathode electrodes, and an external circuit allowing electron flow from anode to cathode.

7

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Biological fuel cells

Cathodic and anodic chambers contain electrolytes that play a vital role in electron and proton transportation within MFCs. Chapters 3–5 discuss recent advances in anode, cathode, and separator materials used in MFC systems. Microbes decompose organic substrates in anodic chamber to provide electron and proton flows. Electrons migrate toward the cathode via an external circuit, while the protons are transported from anode to cathode through electrolytes. At cathodic chamber, the collected particles are combined with oxygen to produce water. Oxygen is a conventional electron acceptor capable of providing high oxidation potential and offering a clean final product (water). MFC technology has a high energy conversion efficiency and a reduced level of undesired by-products [11,12]. However, there are some disadvantages of using MFCs. For instance, one drawback is that there has been electron mediating limitation between microbial cells and exogenous electrodes, restricting the choice of available materials. Thus, further studies are required to improve the performance of MFCs. Following the use of galvanic cells as a way of electricity production, it is necessary to look at standard cell potential of electrodes involved in MFCs. To date various redox reactions have been coupled to generate electron flows (Table 1.1). Studies show that a wide range of biodegradable organic substances can be oxidized within the anode chambers. The substrates can be of natural or synthetic origin, including sugars, organic acids [8] or even domestic and industrial waste. Oxygen reduction reaction (ORR) is the most prevalent redox couple in MFCs. Generally, ORR is a logical way to achieve positive redox potential at cathodes because of limitless availability of oxygen in the air. However, ORR has some unappealing performances, such as poor oxygen solubility in electrolytes. Alternative materials such as hexacyanoferrate and ferri-/ferrocyanide do not have solubility issues and possess faster reduction kinetics, but they are not ideal candidates as cathode materials due to the toxicity and lack of sustainability [13]. A simple example of cathodic and anodic reactions is as follows: Anodic reaction : C6 H12 O6 + 6H2 O ! 6CO2 + 24H+ + 24e

E 0 ¼ 0:014 V (1.1a)

Cathodic reaction : 6O2 + 24H+ + 24e ! 12H2 O E 0 ¼ 1:23 V The overall reaction : C6 H12 O6 + 6O2 ! 6CO2 + 6H2 O + electricity

(1.1b)

ðΔG ¼ 1438 kJ=molÞ (1.1c)

The Gibbs free energy confirms that the process is thermodynamically favorable [14]. The overall standard potential is thermodynamically predictable using the Nernst equation (Eq. 1.2). E cell,t ¼ E0cell 

RT ln Qr , zF

(1.2)

Introduction to biological fuel cell technology

Table 1.1 Anodic and cathodic reactions involved in MFCs. Anode reactions

E0’ at pH 7 (V vs SHE)

AQDSH2/AQDS HS−/SO42− HS−/S Methane/HCO3− Oil and grease C8H16O/HCO3− Acetate/HCO3− Propionate/HCO3− Ethanol/HCO3−

− 0.18 −.217 −0.27 −0.25 −0.29

wastewater C10H19O3N/HCO3− Protein C16H24O5N4/HCO3− Lactate/HCO3− Pyruvate/HCO3− Methanol/HCO3− H2/H+

−0.33

Glucose/HCO3− NADH/NAD+ Neural redred/neutral redox Cysteine/cystine Methyl viologenred/methyl viologenox

−0.43 − 0.32 −0.33 −0.34 −0.44

−.029 −0.29 −0.33

Microbial Fuel Cell Oxygen/H2O ClO3−/Cl− ClO4−/Cl− Fe3+/ Fe2+ NO3−/N2

−0.15

−0.20

E0’ at pH 7 (V vs SHE) +0.82 +0.81 +0.81 +0.77 +0.75

C2H4Cl2/C2H4 C2Cl4/C2HCl3 C2HCl3/cis- C2H2Cl2

+0.739 +0.574 +0.550

Oxygen/H2O

+0.51

C2H4Cl2/C2H4

+0.45

NO3−/N2 Cr2O72−/Cr3+ NO3−/NH4+ [Fe(CN)6]3−/[Fe(CN)6]4−

+0.433 +0.365 +0.36 +0.36

−0.35

NO2−/NO NO2−/NH4+ O2 (gas)/H2O2

+0.35 +0.34 +0.26

−0.40

SeO42−/Se HSeO3−/Se

+0.322 +0.26

O2 (gas)/H2O2 Fumarate2−/succinate2−

+0.26 +0.03

0.8

−0.25

−0.333 −0.34 −0.37 − 0.39 −0.41

Cathode reaction

−0.30

−0.45

0.6

0.5

0.4

0.3

0.2

0.1 −0.50

0

E 0cell ¼ E 0red,cathode  E 0red,anode

(1.3)

A positive standard cell potential (E0cell) indicates the need for an external power source. Contrary to this is when possessing a positive cell potential. Galvanic cells have spontaneous release of electrons and, therefore, negative Gibbs free energy (ΔG, J/mol). ΔG0 ¼ z  F  E0

(1.4)

The Gibbs free energy resulting from material oxidation of microbes is ultimately converted into electric power. However, the power production of MFCs is strongly

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dependent on the types of the microorganisms and operation conditions, where a part of the Gibbs free energy can be used for catabolic activities of microbes and other undesired losses of energy [15,16]. The rest of the free energy may be used for power generation. Findings suggest that sustainable function of MFCs is correlated with the balance between the amount of energy that is consumed for catabolic activities of microbes and energy being converted into electrical energy. The results from the studies confirm the involvement of respiration and fermentation pathways in microbes’ energy conversion. In respiratory cycle, fuel glucose undergoes glycolysis, Krebs cycle, electron transport chain, and oxidative phosphorylation steps under aerobic conditions. Besides respiration, fermentation has also demonstrated great potential in improving electricity production under anaerobic conditions. MFC requires an ideal working volume (VMFC, m3) to promote voltage generation. The required volume can be easily calculated using the following equation: V MFC ¼ Q  tHRT

(1.5)

where Q is organic material flow rate (m3/h) and tHRT is the time required to achieve desired power density.

1.3 Potential feedstocks for MFCs The MFC is an electro-biological cell that fulfills its function through microbial oxidation of substrates. Different substrates ranging from pure compounds to complex mixture of organics can be employed as feasible power sources in MFCs (Table 1.2). Table 1.2 Comparative efficacy of different substrates for power generation in MFCs. Source of substrate

Organism

Power density (mW/m2)

Ref.

3600

[17]

476.19 32.16 1400 1240 2030 1520 17.2 170 7.3 109 55

[18] [19] [20] [21] [21] [21] [22] [23] [24] [7] [25]

Pure organics D-Glucose D-Galactose Fructose L-Rhamnose D-Mannose D-Arabinose D-Ribose Lactose Sucrose Maltose Starch Cellulose

Mixed bacterial culture from anaerobic sludge Gluconobacter oxydans Saccharomyces cerevisiae Enteromorpha prolifera Mixed bacterial culture Mixed bacterial culture Mixed bacterial culture Anaerobic sludge Anaerobic sludge Corynebacterium sp. Anaerobic sludge Rumen microbes

Introduction to biological fuel cell technology

Table 1.2 Comparative efficacy of different substrates for power generation in MFCs—cont’d Power density (mW/m2)

Ref.

Mixed bacterial culture Mixed bacterial culture Mixed bacterial culture Domestic wastewater Domestic wastewater Wastewater Wastewater Domestic wastewater Sludge from domestic wastewater treatment plant Mixed bacterial culture Mixed bacterial culture Mixed bacterial culture Mixed bacterial culture Mixed bacterial culture Anaerobic sludge Sludge from domestic wastewater treatment plant Domestic wastewater Domestic wastewater Domestic wastewater Domestic wastewater Domestic wastewater Domestic wastewater Domestic wastewater Domestic wastewater Sediment samples Activated sludge wastewater wastewater Sediments

1480 2770 2050 739 835 62 444 820 0.25

[26] [26] [26] [27] [27] [27] [27] [27] [28]

1490 1690 2110 2030 2350 31.3 0.11

[29] [29] [29] [29] [29] [30] [28]

556 768 592 718 727 595 601 686 39 173 309 260 34.8

[31] [31] [31] [31] [31] [31] [31] [31] [32] [33] [34] [34] [35,36]

Anaerobic sludge

40

[37]

Digester effluent Sediment Municipal wastewater

26  24 84  10 2.19

[38] [39] [40]

Sewage water Wastewater

88,990 124

[41] [42]

Anaerobic sludge

657.8

[43]

Source of substrate

Organism

Galacturonic acid Glucuronic acid Gluconic acid Lactic acid Acetic acid Formic acid Succinic acid Ethanol Glycerol Mannitol Sorbitol Xylitol Arabitol Ribitol Phenol Glycine Alanine Serine Lysine Histidine Arginine Asparagine Aspartic acid Glutamic acid Cysteine Quinoline Acetate Butyrate Propionate, lactate, succinate Ethanol and methanol Sulfide Chitin Nitrate Solid waste

Vegetable waste Wheat straw hydrolysate Food waste leachate

Continued

11

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Biological fuel cells

Table 1.2 Comparative efficacy of different substrates for power generation in MFCs—cont’d Source of substrate

Organism

Power density (mW/m2)

Ref.

Human waste Corn stover Furfural Vegetable waste Cattle dung Cheese whey Municipal solid waste Potato waste Fruit and vegetable waste Food waste Food (composite) waste Landfill leachate

Anaerobic sludge Municipal wastewater Anaerobic and aerobic sludge UASB sludge Biogas slurry Digested sludge Granular sludge Anaerobic consortia Compost

70.8 14.89 W/m3 103 W/m3 2.72 W/m3 0.22 W/m3 1.3 W/m3 0.71 W/m3 0.39 W/m3 71.43 W/m3

[44] [45] [46] [47] [48] [49] [50] [51] [52]

Composite chemical wastewater Composite chemical wastewater

207 W/m3 107.9 W/m3

[53] [53]

Municipal leachate

20.9 W/m3

[54]

Wastewater Fish market wastewater plant supernatant Seed bacteria of animal carcass wastewater Activated sludge and coal tar wastewater Mixed anaerobic sludge Activated sludge and sea food wastewater Mixed cultures and a pure strain of Shewanella oneidensis Acetobacter aceti and Gluconobacter roseus Anaerobic digestor sludge Anaerobic sludge Activated sludge

72 4.5

[34] [55]

2.19 W/m3

[56]

4.5

[57]

297.6 358.8

[58] [59]

13 mA/m2

[60]

3.8 W/m3 10 mA/m2 42 mA/m2 0.302 mA/cm2

[61] [62] [63] [64]

Anaerobic consortia Equalization basin

245.3 mA/m2 0.05 mA/cm2

[65] [66]

Mixture of anaerobic and aerobic sludge Geobacter sulfurreducence

14  1 W/m3

[67]

70.8 W/m3

[68]

Phosphate-buffered basal medium

622 mW/m2

[69]

Organic materials

Domestic wastewater Fishery wastewater Animal carcass wastewater Coal tar wastewater Piggery wastewater Seafood wastewater Agriculture wastewater Bad wine wastewater Brewery and bakery Cheese whey Chocolate industry wastewater Distillery wastewater Food processing wastewater Hospital wastewater Human feces wastewater Palm oil effluent with acetate

Introduction to biological fuel cell technology

Table 1.2 Comparative efficacy of different substrates for power generation in MFCs—cont’d Power density (mW/m2)

Ref.

Anaerobic digestor sludge Anaerobic consortia Mixed culture of aerobic and anaerobic microorganisms Starch wastewater

125 mA/m2 177.36 W/cm3 0.018 mA/m2

[62] [70] [71]

0.09 mA/cm2

[72]

Wastewater Digester effluent Protein rich wastewater

0.015 mA/cm2 48 W/m3 80  1 mW/m2

[73] [74] [75]

Wastewater

1.61

[76]

Source of substrate

Organism

Paper wastewater Pharmaceutical Real urban wastewater Starch processing wastewater Swine wastewater Potato producing Meat packing industry Beer brewery wastewater

Carbohydrates, sugar acids, organic acids, esters, alcohols, and amino acids are the most widely used organic compounds for power production. However, the use of pure compounds is limited to laboratory-scale investigation [77]. High production costs and limited availability of pure organics have restricted their pilot-scale and large-scale applications. A wide range of waste materials including solid waste, liquid wastewater, and synthetic wastewater can be used as low-cost substrates. Compared with pure compounds, the objective of the process is simultaneous water treatment and energy production [78]. The treating process produces less sludge (anaerobic macerate) which can be used for soil enrichment. Furthermore, MFC exhibits a high performance in COD removal without using chemicals and, as the most important features, in case of civil and industrial wastewater the produced energy can cover waste treatment costs [79–81]. The excellent power density is closely correlated with operational conditions, such as pH, temperature, substrate concentration, organic loading rate (OLR), hydraulic retention time (HRT), type of microorganism, parallel or serial connection, and static magnetic field [82–85].

1.3.1 Pure organics Accumulating evidence demonstrates that organic compounds are potential substrates of power generation in MFCs. Oxidation of these complex materials have been linked to decreased pollutant load, enhanced microbial growth, improved water purity, and electricity generation [86,87]. Compared with complex organic substrates, simple defined substrates, such as monomers of carbohydrate, protein, and lipid, are required for fundamental MFC studies [8].

13

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Glucose, fructose, and sucrose are simple materials that can be used as a source of electricity. Glucose mediates higher electricity production as compared to other simple organics, although up to 5 g/L glucose concentration correlates with an inhibitory effect on metabolic activity of microbes [88]. Proteus vulgaris [89], Rhodoferax ferrireducens [90]. Escherichia coli [91], Geobacter sulfurreducens [92], and Saccharomyces cerevisiae [93] have been shown as effective microbes that oxidize glucose into electricity. Compared with glucose, fructose produces relatively lower electrical power [7]. Furthermore, it was demonstrated that aerobic oxidation of fructose and other substrates mediates higher electricity generation other than anaerobic condition [94] due to high level of key proteins regulating Krebs cycle and Entner-Doudoroff (ED) pathways. Sucrose is an additional carbon source for MFCs [95–97]. The effectiveness of sucrose in power generation depends on the status of microorganisms. For instance, power density of 0.52 mW/m2 was observed for dual-chambered membraneless anaerobic cathode [96], while 10.13 mW/m2 [95] and 148.76 mW/m2 [97] have been reported for aerobic cathode. As a conventional end product of various microbial pathways, acetate induces alternative metabolic conversions [97]. Such conversions suppress current generation and have been confirmed to decrease the resulted power density from 309 to 220 mW/m2 [98]. However, there are some evidence on power density increment up to 362 mW/m2 from acetate conversion to bioethanol in MFC apparatus [99]. Ironically, when comparing glucose and acetate as substrates for bioelectricity generation, higher power densities have been reported with acetate [98,100]. Besides simple defined substrates, several complex synthetic materials have shown potential for power production in MFCs. The substrates have been used to determine whether or not natural complex substrates available such as starch, cellulose/lignocelluloses, butyrate/propionate, methanol/ethanol, glycerol, and phenol can be utilized for microbial electricity production. For instance, 1.16 g of starch residue have exhibited a high capacity in power density generation (502 mW/m2) using E. coli as a biocatalyst [101], and up to 143 mW/m2 power density has been reported from cellulosic substrate mediated by Clostridium cellulolyticum [102]. Butyrate and propionate exhibited less power generation capacity as compared with glucose [103]. Pure glycerol resulted in a 0.06 mW/cm2 maximum power density in one culture system [104]. However, maximum power density of 2.15 mW/m2 has been reported for Shewanella oneidensis and Klebsiella pneumoniae coculture system [105].

1.3.2 Solid wastes Simultaneous electricity production supplies energy-intensive removal of organics. MFC-based technologies can effectively remove solid wastes that are difficult to be recycled by conventional methods. Specifically, the objective of the process is organic loading removal for high power consumption rate. Cellulose and hemicellulose are

Introduction to biological fuel cell technology

the major components of the solid waste and particularly active participants of bioelectricity generation. Although, the presence of such complex materials can be detrimental to electrogenic bacteria, multiple pretreatment methods such as mechanical, thermal, chemical, and biological strategies are required to hydrolyze them into low-molecular weight compounds [106]. The performance of the operation is determined via volumetric power densities and COD removal efficiencies. Regarding the substrate chemistry, energy-generating yield of MFCs varies from 2 to 100 W/m3 with the COD removal capacities in the range 40%–90%.

1.3.3 Organic materials MFCs are known to reduce operational costs of the wastewater treatment plants [107]. The technology provides high energy generation from a wide range of wastewater [49] and less secondary sludge production during the process. Preventing from stringent aseptic conditions and using multiple substrates, mixed microbial cultures are utilized to inoculate MFCs. A range of 3–5 g/L is reported as an effective COD range for MFCs’ function. Municipal wastewater is characterized as low energy-content feedstock and is relatively easy to treat. However, high BOD content of 2000 mg/L observed in industrial and agricultural wastewater can be treated under anaerobic conditions. Accumulating evidence demonstrates that for treatment of highstrength wastewater, integration of MFCs with other wastewater treatment technologies have been known to improve energy recovery by 30%–40% and removal efficiencies by 70%–90% [108–110]. Observations suggest that energy recovery from wastewater might be interrupted due to the presence of alternative electron acceptors, such as nitrate, nitrite, and sulfate. On the other hand, high carbohydrate content of feedstocks as well as low concentration of ammonia nitrogen are known to be involved in high power density production. For instance, high carbohydrate content and low concentrations of organic nitrogen have been reported for food processing wastewater [111,112]. Electricity production from this type of wastewater lies in the range of 2–260 kWh/ton depending on different BOD contents of the feedstock. It has been demonstrated that 46 and 1960 MW of electricity can be produced from milk dairy farms and high-strength dairy industry, respectively [113]. Livestock-related wastewater is another class of MFC feedstock with high COD content and nitrogen-containing components [114]. Because of high level of hardly biodegradable components, the efficacy of power production in this class of wastewater is limited.

1.4 BFC’s classification BFCs can be broadly classified into those related to the microorganisms and those related to concentrated enzymes. Microorganism-based BFCs include photosynthetic MFCs (PMFCs), microbial desalination cells (MDCs), and sediment microbial fuel cells (SMFCs) (Fig. 1.6).

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Fig. 1.6 Classification of MFCs based on their working principles: (A) the overall design of microorganism-based BFCs, (B) algal MFC, (C) MDC, (D) SMFC, and (E) plant MFC.

1.4.1 MFCs 1.4.1.1 Photosynthetic MFCs In photosynthetic MFCs (PMFCs), sunlight is converted into electricity through metabolic reactions. The innovative technologies based on a combination of sunlight and microbial powers have been an effective strategy for improved voltage generation.

Introduction to biological fuel cell technology

The most attention has been focused on microscopic photosynthetic organisms, because they can grow in a broad range of aquatic habitats. Several microalgae, cyanobacteria, and plant species have exhibited remarkable capacity to optimize voltage generation in PMFCs. The main limitation of the light-enhanced MFCs is overcoming the photosynthetic dark reactions which convert the products of the light reaction into carbohydrates. Plant MFCs Plant MFC is a sustainable technology aimed at bioelectricity generation through synergistic interaction between photosynthetic organism and heterotrophic bacteria [115]. PMFCs have been known as renewable energy sources because they have a clean conversion and circumvent the impacts of competition for arable land [116]. Vascular plants, rhizosphere electrochemical active bacteria, and electrically connected anodes and cathodes are the main components of PMFCs [117,118]. Around 70% of the fixed carbon resulted from photosynthesis process is extruded into rhizosphere in terms of rhizodeposits [119]. Rhizosphere-resident heterotrophic microorganisms oxidize the excreted materials into carbon dioxide and protons and transfer electrons to the anode [116]. The selection of plant type is dependent on the aim of the research. Among the plethora of plants, Spartina anglica generated the highest power output (679 mW/m2). The anode of a PMFC is suitable for the growth of bacteria that don’t produce electricity. This can suppress power production capacity of PMFCs. Algal MFCs In the past decade, algal MFC has been characterized as a novel technology to which a succession of solar irradiance conversion (up to 9%) has been applied. Given that algae have high growth rate, can be harvested all the year round, and have no competition with food and feed, studies suggest that algae should be sustainable feedstock for MFCs. In algal MFCs, proton induction of algal cells mediates CO2 fixation into a variety of cellular compounds. Case series have reported that algae can be applied at both cathode and anode for providing oxygen and substrate for bacterial growth, respectively. Algae have two different types of glucose metabolism: autotrophic and heterotrophic [120]. The heterotrophic growth mode poses some advantages over the autotrophic growth including high growth rate of the biomass due to high level of ATP production and high content of nitrogen and lipid contents. Furthermore, there is no requirement of specify bioreactor design. Although, for heterotrophic growth model the number of microalgae species available is limited, energy expenses are high, and there are some risks of contamination with other microorganisms [121]. Mixotrophic growth can be also exerted to combine photosynthetic metabolism and respiratory metabolism in order to assimilate organic carbon and carbon dioxide [122]. Heterotrophic organisms oxidize organic materials in anodic chamber to create electron flow and produce carbon dioxide, which are utilized by photosynthetic organisms in cathodic chamber to generate biomass, water, and oxygen [123]. During dark phase oxygen

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is consumed to oxidize organic materials and to produce energy [123]. Following reactions describe the anodic and cathodic biochemical reactions involved in algal MFCs [124]: C6 H12 O6 + 6H2 O ! 6CO2 + 24H+ + 24 e

(1.6a)

6CO2 + 12H+ + 12 e ! 6C6 H12 O6 + 3O2

(1.6b)

C6 H12 O6 + 6O2 ! 6CO2 + 6H2 O

(1.6c)

1.4.1.2 Microbial desalination cells (MDCs) The focus on absolute demand of drinking water because of rapid industrialization and population growth has increased awareness among researchers in determining sustainable and cost-effective technologies for freshwater production. International Desalination Association has reported active 18,426 desalination plants worldwide with operational capacity of 86.8 million m3per day. Conventional destination plants are energy intensive and consume 3.7–650 kWh energy per m3 of water desalination [125]. Moreover, since up to 60% of the desalination plants use fossil fuels as energy source [126], the emission of greenhouse gases and global warming could be additional drawbacks of conventional desalination plants. Microbial desalination cell (MDC) is important for simultaneous organic waste and wastewater treatment, water desalination, and electricity generation through oxidation of organics. The main evidence for advantages of MDCs comes from a study that confirms 90% desalination efficiency and 1.8 kWh energy production per m3 of water treatment [127]. Additionally, MDCs have been successfully employed for the production of valuable chemicals along with wastewater treatment [128,129], water softening [130], and denitrification [131]. Preacclimated inoculum provided from existing MFCs and inoculum from local wastewater treatment plants are usually required as microorganism seeds of MDCs [132,133]. During the desalination process increment in electrolyte conductivity and overall system performance depend on diffusion of cations and anions from desalination chamber toward cathodic and anodic chambers [134]. However, increase in Cl concentration may disturb microbial activities. Studies have demonstrated that exoelectrogenic community tolerates salinity of 41 g/L TSD though permanently loses its functionality at salinity of 46 g/L TDS [135]. Today, longer period of acclimation has been known as a possible technique for increment of salinity tolerance in microbes. Air cathode, biocathode, capacitive, photosynthetic, osmotic, stacked, resin packed, and upflow configurations are the most widely used laboratory-scale designs of MDCs [136,137]. To date, the use of MDCs in pilot- or full-scale studies have not been investigated and a more fundamental understanding of MDC process is required to circumvent design and operational challenges.

Introduction to biological fuel cell technology

1.4.1.3 Sediment microbial fuel cells (SMFCs) Eutrophication significantly increases the risk to environmental health. With an upward deposition of nutrient pollutants such as nitrogen and phosphorus into aquatic environment, the worldwide incidence of eutrophication is expected to increase. Eutrophication can have devastating consequences and is often associated with water blooms and bioturbation [138]. An improvement in the quality of eutrophication water can be achieved by removing pollutants from sediments. Sediment microbial fuel cells (SMFCs) have drawn a lot of attention as promising techniques that provide simultaneous heavy metal bioremediation and bioenergy production. Studies demonstrated the potential involvement of SMFCs in contaminant removal from submerged soil using clean energy [139]. Furthermore, findings suggest that SMFCs can simultaneously generate sustainable electrical energy along with wastewater decontamination. Low-cost operation and long-term power generation have been known as the most important advantages of SMFCs [140]. A simple SMFC consists of an anode electrode buried in an anaerobic sediment including exoelectrogens [141,142] and a cathode electrode immersed in the overlying water [143]. SMFC is a membrane-free technology in which electrons flow in an external circuit, while water enables proton transport between electrodes [144]. Poor organic content of sediments could be the sole obstacle of the method [145,146] which can be overcome through the use of sediment from eutrophic water body [147]. Electron transfer via conductive pili is a prominent microbial mechanism in SMFCs [148]. Firmicutes, Acidobacteria, Proteobacteria phylum, and yeast, fungi, and microalgae are five major groups of microorganisms capable of electricity generation in SMFCs [149]. It was anticipated that iron-reducing species including Shewanella spp. [150], Aeromonas hydrophila [151], Clostridium butyricum [152], Geobacter spp. [153], Rhodoferax ferrireducens [154], and Enterococcus gallinarum [155] have excellent electron exchange with electrodes. Additionally, some bacterial species such as Geobacter display supercapacitor and transistor properties due to their structural conductive polymers [156]. The integration of SMFCs with photosynthetic organisms, plant, and algae has increased the effectiveness of sediment remediation technique. The photosynthetic organism can produce oxygen and organics during the process which serve as electron acceptors and donors during the operation [157]. The incorporation of plants can improve the mass transfer rate between the anode and the electron donors, which subsequently increase the harvested energy by 7-fold and 18-fold [158,159]. Importantly, SMFCs have shown significant scale-up potential, although further studies are needed to develop this technology and intensify its applications.

1.4.2 Enzyme-based fuel cells (EFCs) Enzyme-based fuel cells (EFCs) are bioelectrochemical devices that convert organics into energy through catalyzing the oxidant-reductive reaction (Fig. 1.7). The main difference

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Fig. 1.7 A schematic representation of enzyme-based fuel cell.

between MFCs and EFCs lies in dissimilar enzyme concentration by which the efficacy of electricity production is determined. In MFCs, enzyme concentration is limited and their activity is correlated with microbial metabolism. Extraction of enzymes and using them with high degree of purity, therefore, have an important role in the increment of power output. Some studies have reported that the use of pure enzymes in either cathodes or anodes improves the diffusion of reactants and products. Additionally, enzymes possess high selectivity and compatibility, making them potential candidates for micropower suppliers of implanted medical devices [160,161]. However, there are some limitations in enzyme stability and survival [162]. Moreover, enzyme selectivity imposes additional operation costs for providing multiple sequential enzymes which are essential for the multistep oxidation of organic substrates and mediators that are necessary for electron transfer and product release [163,164]. Bilirubin oxidase [165] and laccase [166] are the enzymes most frequently used at cathode, and sugar-based enzymes like glucose oxidase [167] have been introduced as highly efficient enzymes employed at anodic electrode.

1.5 Conclusions MFCs offer real potential for green power generation, which can reduce global energy demand and solve the health-care crisis. Simultaneous wastewater treatment and power production is intended for this application. Despite considerable advances in the development of MFCs, there are several needs and challenges for improvement in power output from potential substrates. One such challenge is limited understanding of the involved microbial mechanisms and deprived progression in scale-up of the process. Addressing these challenges requires further studies on operating conditions, including influent COD concentration, HRT, feed pH, and specific organic loading rate.

Introduction to biological fuel cell technology

Nevertheless, the studies are often hindered by microbiological, technological, and economic challenges of the process. This book can serve as a tool for researchers to facilitate right direction of MFC processing toward large-scale industrial applications.

References [1] X. Zheng, W. Zhou, R. Wan, J. Luo, Y. Su, H. Huang, Y. Chen, Increasing municipal wastewater BNR by using the preferred carbon source derived from kitchen wastewater to enhance phosphorus uptake and short-cut nitrification-denitrification, Chem. Eng. J. 344 (2018) 556–564. [2] M. Rahimnejad, A. Adhami, S. Darvari, A. Zirepour, S.-E. Oh, Microbial fuel cell as new technology for bioelectricity generation: A review, Alexandria Eng. J. 54 (2015) 745–756. [3] F. Martins, C. Felgueiras, M. Smitkova´, Fossil fuel energy consumption in European countries, Energy Procedia 153 (2018) 107–111. [4] M. Rahimnejad, M. Asghary, M. Fallah, Microbial fuel cell (MFC): an innovative technology for wastewater treatment and power generation, Springer, Bioremediation of Industrial Waste for Environmental Safety, 2020, pp. 215–235. [5] H. Wang, J.-D. Park, Z.J. Ren, Practical energy harvesting for microbial fuel cells: a review, Environ. Sci. Technol. 49 (2015) 3267–3277. [6] M. Rahimnejad, N. Mokhtarian, G. Najafpour, A.A. Ghoreyshi, W.R.W. Dahud, Effective parameters on performance of microbial fuel cell, in: 2009 Second International Conference on Environmental and Computer Science, IEEE, 2009, pp. 411–415. [7] N. Mokhtarian, M. Rahimnejad, G. Najafpour, W.R.W. Daud, A. Ghoreyshi, Effect of different substrate on performance of microbial fuel cell, Afr. J. Biotechnol. 11 (2012) 3363–3369. [8] D. Pant, G. Van Bogaert, L. Diels, K. Vanbroekhoven, A review of the substrates used in microbial fuel cells (MFCs) for sustainable energy production, Bioresour. Technol. 101 (2010) 1533–1543. [9] J. Chouler, M. Di Lorenzo, Water quality monitoring in developing countries; can microbial fuel cells be the answer? Biosensors 5 (2015) 450–470. [10] M. Rahimnejad, G. Najafpour, Microbial fuel cells: a new source of power, Biochem. Eng. Biotechnol. (2011) 1–31. [11] H. Wang, Z.J. Ren, A comprehensive review of microbial electrochemical systems as a platform technology, Biotechnol. Adv. 31 (2013) 1796–1807. [12] T. Huggins, P.H. Fallgren, S. Jin, Z. Ren, Energy and performance comparison of microbial fuel cell and conventional aeration treating of wastewater, J. Microb. Biochem. Technol. S6 (2013). [13] K. Rabaey, P. Clauwaert, P. Aelterman, W. Verstraete, Tubular microbial fuel cells for efficient electricity generation, Environ. Sci. Technol. 39 (2005) 8077–8082. [14] S. Freguia, K. Rabaey, Z. Yuan, J.R. Keller, Syntrophic processes drive the conversion of glucose in microbial fuel cell anodes, Environ. Sci. Technol. 42 (2008) 7937–7943. [15] M. Lu, S.F.Y. Li, Cathode reactions and applications in microbial fuel cells: a review, Crit. Rev. Environ. Sci. Technol. 42 (2012) 2504–2525. [16] B.E. Logan, B. Hamelers, R. Rozendal, U. Schr€ oder, J. Keller, S. Freguia, P. Aelterman, W. Verstraete, K. Rabaey, Microbial fuel cells: methodology and technology, Environ. Sci. Technol. 40 (2006) 5181–5192. [17] K. Rabaey, G. Lissens, S.D. Siciliano, W. Verstraete, A microbial fuel cell capable of converting glucose to electricity at high rate and efficiency, Biotechnol. Lett. 25 (2003) 1531–1535. [18] S. Alferov, P. Minaicheva, V. Arlyapov, L. Asulyan, V. Alferov, O. Ponamoreva, A. Reshetilov, Bioanode for a microbial fuel cell based on Gluconobacter oxydans immobilized into a polymer matrix, Appl. Biochem. Microbiol. 50 (2014) 637–643. [19] H. Liu, S. Grot, B.E. Logan, Electrochemically assisted microbial production of hydrogen from acetate, Environ. Sci. Technol. 39 (2005) 4317–4320. [20] M. Wang, Z. Yan, B. Huang, J. Zhao, R. Liu, Electricity generation by microbial fuel cells fuelled with Enteromorpha prolifera hydrolysis, Int. J. Electrochem. Sci. 8 (2013) 2104–2111. [21] T. Catal, K. Li, H. Bermek, H. Liu, Electricity production from twelve monosaccharides using microbial fuel cells, J. Power Sources 175 (2008) 196–200.

21

22

Biological fuel cells

[22] G. Antonopoulou, K. Stamatelatou, S. Bebelis, G. Lyberatos, Electricity generation from synthetic substrates and cheese whey using a two chamber microbial fuel cell, Biochem. Eng. J. 50 (2010) 10–15. [23] Z. He, S.D. Minteer, L.T. Angenent, Electricity generation from artificial wastewater using an upflow microbial fuel cell, Environ. Sci. Technol. 39 (2005) 5262–5267. [24] M. Liu, Y. Yuan, L.-X. Zhang, L. Zhuang, S.-G. Zhou, J.-R. Ni, Bioelectricity generation by a Grampositive Corynebacterium sp. strain MFC03 under alkaline condition in microbial fuel cells, Bioresour. Technol. 101 (2010) 1807–1811. [25] H. Rismani-Yazdi, A.D. Christy, B.A. Dehority, M. Morrison, Z. Yu, O.H. Tuovinen, Electricity generation from cellulose by rumen microorganisms in microbial fuel cells, Biotechnol. Bioeng. 97 (2007) 1398–1407. [26] H. Friman, A. Schechter, Y. Ioffe, Y. Nitzan, R. Cahan, Current production in a microbial fuel cell using a pure culture of C upriavidus basilensis growing in acetate or phenol as a carbon source, Microb. Biotechnol. 6 (2013) 425–434. [27] P.D. Kiely, G. Rader, J.M. Regan, B.E. Logan, Long-term cathode performance and the microbial communities that develop in microbial fuel cells fed different fermentation endproducts, Bioresour. Technol. 102 (2011) 361–366. [28] C.-Y. Chen, T.-Y. Chen, Y.-C. Chung, A comparison of bioelectricity in microbial fuel cells with aerobic and anaerobic anodes, Environ. Technol. 35 (2014) 286–293. [29] T. Catal, S. Xu, K. Li, H. Bermek, H. Liu, Electricity generation from polyalcohols in single-chamber microbial fuel cells, Biosens. Bioelectron. 24 (2008) 849–854. [30] T.-S. Song, X.-Y. Wu, C.C. Zhou, Effect of different acclimation methods on the performance of microbial fuel cells using phenol as substrate, Bioprocess Biosyst. Eng. 37 (2014) 133–138. [31] Q. Yang, X. Wang, Y. Feng, H. Lee, J. Liu, X. Shi, Y. Qu, N. Ren, Electricity generation using eight amino acids by air–cathode microbial fuel cells, Fuel 102 (2012) 478–482. [32] B.E. Logan, C. Murano, K. Scott, N.D. Gray, I.M. Head, Electricity generation from cysteine in a microbial fuel cell, Water Res. 39 (2005) 942–952. [33] M.F. Arooj, S.-K. Han, S.-H. Kim, D.-H. Kim, H.-S. Shin, Continuous biohydrogen production in a CSTR using starch as a substrate, Int. J. Hydrog. Energy 33 (2008) 3289–3294. [34] B. Min, B.E. Logan, Continuous electricity generation from domestic wastewater and organic substrates in a flat plate microbial fuel cell, Environ. Sci. Technol. 38 (2004) 5809–5814. [35] D.E. Holmes, D.R. Bond, D.R. Lovley, Electron transfer by Desulfobulbus propionicus to Fe (III) and graphite electrodes, Appl. Environ. Microbiol. 70 (2004) 1234–1237. [36] D. Holmes, D. Bond, R. O’neil, C. Reimers, L. Tender, D. Lovley, Microbial communities associated with electrodes harvesting electricity from a variety of aquatic sediments, Microb. Ecol. 48 (2004) 178–190. [37] J.R. Kim, S.H. Jung, J.M. Regan, B.E. Logan, Electricity generation and microbial community analysis of alcohol powered microbial fuel cells, Bioresour. Technol. 98 (2007) 2568–2577. [38] K. Rabaey, K. Van de Sompel, L. Maignien, N. Boon, P. Aelterman, P. Clauwaert, L. De Schamphelaire, H.T. Pham, J. Vermeulen, M. Verhaege, Microbial fuel cells for sulfide removal, Environ. Sci. Technol. 40 (2006) 5218–5224. [39] F. Rezaei, T.L. Richard, R.A. Brennan, B.E. Logan, Substrate-enhanced microbial fuel cells for improved remote power generation from sediment-based systems, Environ. Sci. Technol. 41 (2007) 4053–4058. [40] C. Jiang, Q. Yang, D. Wang, Y. Zhong, F. Chen, X. Li, G. Zeng, X. Li, M. Shang, Simultaneous perchlorate and nitrate removal coupled with electricity generation in autotrophic denitrifying biocathode microbial fuel cell, Chem. Eng. J. 308 (2017) 783–790. [41] M.M. Javed, M.A. Nisar, B. Muneer, M.U. Ahmad, Production of bioelectricity from vegetable waste extract by designing a U-shaped microbial fuel cell, Pak. J. Zool. 49 (2017). [42] Y. Zhang, B. Min, L. Huang, I. Angelidaki, Generation of electricity and analysis of microbial communities in wheat straw biomass-powered microbial fuel cells, Appl. Environ. Microbiol. 75 (2009) 3389–3395. [43] X.M. Li, K.Y. Cheng, J.W. Wong, Bioelectricity production from food waste leachate using microbial fuel cells: effect of NaCl and pH, Bioresour. Technol. 149 (2013) 452–458. [44] D. Fangzhou, L. Zhenglong, Y. Shaoqiang, X. Beizhen, L. Hong, Electricity generation directly using human feces wastewater for life support system, Acta Astronaut. 68 (2011) 1537–1547.

Introduction to biological fuel cell technology

[45] X. Wang, Y. Feng, H. Wang, Y. Qu, Y. Yu, N. Ren, N. Li, E. Wang, H. Lee, B.E. Logan, Bioaugmentation for electricity generation from corn stover biomass using microbial fuel cells, Environ. Sci. Technol. 43 (2009) 6088–6093. [46] Y. Luo, G. Liu, R. Zhang, C. Zhang, Power generation from furfural using the microbial fuel cell, J. Power Sources 195 (2010) 190–194. [47] S.V. Mohan, G. Mohanakrishna, P. Sarma, Composite vegetable waste as renewable resource for bioelectricity generation through non-catalyzed open-air cathode microbial fuel cell, Bioresour. Technol. 101 (2010) 970–976. [48] G. Zhao, F. Ma, L. Wei, H. Chua, C.-C. Chang, X.-J. Zhang, Electricity generation from cattle dung using microbial fuel cell technology during anaerobic acidogenesis and the development of microbial populations, Waste Manag. 32 (2012) 1651–1658. [49] P.T. Kelly, Z. He, Understanding the application niche of microbial fuel cells in a cheese wastewater treatment process, Bioresour. Technol. 157 (2014) 154–160. € [50] A. Karluvalı, E.O. K€ oroglu, N. Manav, A.Y. C ¸ etinkaya, B. Ozkaya, Electricity generation from organic fraction of municipal solid wastes in tubular microbial fuel cell, Sep. Purif. Technol. 156 (2015) 502–511. [51] H. Du, F. Li, Size effects of potato waste on its treatment by microbial fuel cell, Environ. Technol. 37 (2016) 1305–1313. [52] J.M. Khudzari, B. Tartakovsky, G.V. Raghavan, Effect of C/N ratio and salinity on power generation in compost microbial fuel cells, Waste Manag. 48 (2016) 135–142. [53] R.K. Goud, P.S. Babu, S.V. Mohan, Canteen based composite food waste as potential anodic fuel for bioelectricity generation in single chambered microbial fuel cell (MFC): bio-electrochemical evaluation under increasing substrate loading condition, Int. J. Hydr. Energy 36 (2011) 6210–6218. [54] A.L. Va´zquez-Larios, O. Solorza-Feria, H.M. Poggi-Varaldo, R. de Guadalupe Gonza´lez-Huerta, M.T. Ponce-Noyola, E. Rı´os-Leal, N. Rinderknecht-Seijas, Bioelectricity production from municipal leachate in a microbial fuel cell: effect of two cathodic catalysts, Int. J. Hydrog. Energy 39 (2014) 16667–16675. [55] C.-Y. Lee, J.-H. Chen, Y.-Y. Cai, Bioelectricity generation and organic removal in microbial fuel cells used for treatment of wastewater from fish-market, J. Environ. Eng. Manage. 20 (2010) 173–180. [56] X. Li, N. Zhu, Y. Wang, P. Li, P. Wu, J. Wu, Animal carcass wastewater treatment and bioelectricity generation in up-flow tubular microbial fuel cells: effects of HRT and non-precious metallic catalyst, Bioresour. Technol. 128 (2013) 454–460. [57] H.I. Park, C. Wu, L.-S. Lin, Coal tar wastewater treatment and electricity production using a membrane-less tubular microbial fuel cell, Biotechnol. Bioprocess Eng. 17 (2012) 654–660. [58] Z. Ye, B. Zhang, Y. Liu, Z. Wang, C. Tian, Continuous electricity generation with piggery wastewater treatment using an anaerobic baffled stacking microbial fuel cell, Desalin. Water Treat. 55 (2015) 2079–2087. [59] H.L. Sun, Electricity generation from seafood wastewater in a single-and dual-chamber microbial fuel cell with CoTMPP oxygen-reduction electrocatalyst, J. Chem. Technol. Biotechnol. 87 (2012) 1167–1172. [60] V.R. Nimje, C.-Y. Chen, H.-R. Chen, C.-C. Chen, Y.M. Huang, M.-J. Tseng, K.-C. Cheng, Y.F. Chang, Comparative bioelectricity production from various wastewaters in microbial fuel cells using mixed cultures and a pure strain of Shewanella oneidensis, Bioresour. Technol. 104 (2012) 315–323. [61] K. Rengasamy, S. Berchmans, Simultaneous degradation of bad wine and electricity generation with the aid of the coexisting biocatalysts Acetobacter aceti and Gluconobacter roseus, Bioresour. Technol. 104 (2012) 388–393. [62] S. Velasquez-Orta, I. Head, T. Curtis, K. Scott, Factors affecting current production in microbial fuel cells using different industrial wastewaters, Bioresour. Technol. 102 (2011) 5105–5112. [63] K. Stamatelatou, G. Antonopoulou, A. Tremouli, G. Lyberatos, Production of gaseous biofuels and electricity from cheese whey, Ind. Eng. Chem. Res. 50 (2011) 639–644. [64] S.A. Patil, V.P. Surakasi, S. Koul, S. Ijmulwar, A. Vivek, Y. Shouche, B. Kapadnis, Electricity generation using chocolate industry wastewater and its treatment in activated sludge based microbial fuel cell and analysis of developed microbial community in the anode chamber, Bioresour. Technol. 100 (2009) 5132–5139.

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24

Biological fuel cells

[65] G. Mohanakrishna, S.K. Mohan, S.V. Mohan, Carbon based nanotubes and nanopowder as impregnated electrode structures for enhanced power generation: evaluation with real field wastewater, Appl. Energy 95 (2012) 31–37. [66] S. Oh, B.E. Logan, Hydrogen and electricity production from a food processing wastewater using fermentation and microbial fuel cell technologies, Water Res. 39 (2005) 4673–4682. [67] P. Aelterman, K. Rabaey, P. Clauwaert, W. Verstraete, Microbial fuel cells for wastewater treatment, Water Sci. Technol. 54 (2006) 9–15. [68] F. Du, B. Xie, W. Dong, B. Jia, K. Dong, H. Liu, Continuous flowing membraneless microbial fuel cells with separated electrode chambers, Bioresour. Technol. 102 (2011) 8914–8920. [69] B. Jong, P. Liew, M.L. Juri, B. Kim, A. Mohd, K. Dzomir, M.A. Leo, Performance and microbial diversity of palm oil mill effluent microbial fuel cell, Lett. Appl. Microbiol. 53 (2011) 660–667. [70] G. Velvizhi, S.V. Mohan, Biocatalyst behavior under self-induced electrogenic microenvironment in comparison with anaerobic treatment: evaluation with pharmaceutical wastewater for multi-pollutant removal, Bioresour. Technol. 102 (2011) 10784–10793. [71] M.A. Rodrigo, P. Can˜izares, J. Lobato, Effect of the electron-acceptors on the performance of a MFC, Bioresour. Technol. 101 (2010) 7014–7018. [72] N. Lu, S.-G. Zhou, L. Zhuang, J.-T. Zhang, J.-R. Ni, Electricity generation from starch processing wastewater using microbial fuel cell technology, Biochem. Eng. J. 43 (2009) 246–251. [73] B. Min, J. Kim, S. Oh, J.M. Regan, B.E. Logan, Electricity generation from swine wastewater using microbial fuel cells, Water Res. 39 (2005) 4961–4968. [74] K. Rabaey, W. Verstraete, Microbial fuel cells: novel biotechnology for energy generation, Trends Biotechnol. 23 (2005) 291–298. [75] J. Heilmann, B.E. Logan, Production of electricity from proteins using a microbial fuel cell, Water Environ. Res. 78 (2006) 531–537. [76] M. Lu, S. Chen, S. Babanova, S. Phadke, M. Salvacion, A. Mirhosseini, S. Chan, K. Carpenter, R. Cortese, O. Bretschger, Long-term performance of a 20-L continuous flow microbial fuel cell for treatment of brewery wastewater, J. Power Sources 356 (2017) 274–287. [77] M. Rahimnejad, G. Najafpour, A. Ghoreyshi, T. Jafari, F. Haghparast, Microbial fuel cell a reliable source for recovery of electrical power from synthetic wastewater, Linnaeus Eco-Tech (2010) 627–635. [78] F. Hejazi, A. Ghoreyshi, M. Rahimnejad, Simultaneous phenol removal and electricity generation using a hybrid granular activated carbon adsorption-biodegradation process in a batch recycled tubular microbial fuel cell, Biomass Bioenergy 129 (2019), 105336. [79] S. Puig, M. Serra, M. Coma, M. Balaguer, J. Colprim, Simultaneous domestic wastewater treatment and renewable energy production using microbial fuel cells (MFCs), Water Sci. Technol. 64 (2011) 904–909. [80] A. Capodaglio, D. Molognoni, E. Dallago, A. Liberale, R. Cella, P. Longoni, L. Pantaleoni, Microbial fuel cells for direct electrical energy recovery from urban wastewaters, Sci. World J. 2013 (2013). [81] T. Jafary, G. Najafpour, A. Ghoreyshi, F. Haghparast, M. Rahimnejad, H. Zare, Bioelectricity power generation from organic substrate in a microbial fuel cell using Saccharomyces cerevisiae as biocatalysts, Fuel Cells 4 (2011) 1182. [82] D. Akman, K. Cirik, S. Ozdemir, B. Ozkaya, O. Cinar, Bioelectricity generation in continuously-fed microbial fuel cell: effects of anode electrode material and hydraulic retention time, Bioresour. Technol. 149 (2013) 459–464. [83] G. Jadhav, M. Ghangrekar, Performance of microbial fuel cell subjected to variation in pH, temperature, external load and substrate concentration, Bioresour. Technol. 100 (2009) 717–723. [84] T. Jafary, M. Rahimnejad, A.A. Ghoreyshi, G. Najafpour, F. Hghparast, W.R.W. Daud, Assessment of bioelectricity production in microbial fuel cells through series and parallel connections, Energy Convers. Manag. 75 (2013) 256–262. [85] W.-W. Li, G.-P. Sheng, X.-W. Liu, P.-J. Cai, M. Sun, X. Xiao, Y.-K. Wang, Z.-H. Tong, F. Dong, H.-Q. Yu, Impact of a static magnetic field on the electricity production of Shewanella-inoculated microbial fuel cells, Biosens. Bioelectron. 26 (2011) 3987–3992. [86] D. Majumder, J.P. Maity, M.-J. Tseng, V.R. Nimje, H.-R. Chen, C.-C. Chen, Y.-F. Chang, T.-C. Yang, C.-Y. Chen, Electricity generation and wastewater treatment of oil refinery in microbial fuel cells using Pseudomonas putida, Int. J. Mol. Sci. 15 (2014) 16772–16786.

Introduction to biological fuel cell technology

[87] E. Dannys, T. Green, A. Wettlaufer, C. Madhurnathakam, A. Elkamel, Wastewater treatment with microbial fuel cells: a design and feasibility study for scale-up in microbreweries, J. Bioprocess Biotech. 6 (2016) 2. [88] H. Liu, T. Hu, G. Zeng, X. Yuan, J. Wu, Y. Shen, L. Yin, Electricity generation using p-nitrophenol as substrate in microbial fuel cell, Int. Biodeterior. Biodegradation 76 (2013) 108–111. [89] C. Thurston, H. Bennetto, G. Delaney, J. Mason, S. Roller, J. Stirling, Glucose metabolism in a microbial fuel cell. Stoichiometry of product formation in a thionine-mediated Proteus vulgaris fuel cell and its relation to coulombic yields, Microbiology 131 (1985) 1393–1401. [90] S.K. Chaudhuri, D.R. Lovley, Electricity generation by direct oxidation of glucose in mediatorless microbial fuel cells, Nat. Biotechnol. 21 (2003) 1229–1232. [91] V.D. D’souza Rohan, G. Rohan, B. Satish, Bioelectricity production from microbial fuel using Escherichia coli (glucose and brewery waste), Int. Res. J. Biol. Sci. 2 (2013) 50–54. [92] G.E. Oyiwona, J. Ogbonna, C.U. Anyanwu, S. Ishizaki, Z.-I. Kimura, S. Okabe, Oxidation of glucose by syntrophic association between Geobacter and hydrogenotrophic methanogens in microbial fuel cell, Biotechnol. Lett. 39 (2017) 253–259. [93] A. Ghoreyshi, T. Jafary, G. Najafpour, F. Haghparast, Effect of type and concentration of substrate on power generation in a dual chambered microbial fuel cell, in: World Renewable Energy CongressSweden; 8–13 May; 2011, Link€ oping University Electronic Press, Link€ oping, Sweden, 2011, pp. 1174–1181. [94] J.C. Biffinger, J.N. Byrd, B.L. Dudley, B.R. Ringeisen, Oxygen exposure promotes fuel diversity for Shewanella oneidensis microbial fuel cells, Biosens. Bioelectron. 23 (2008) 820–826. [95] M. Ghangrekar, V. Shinde, Performance of membrane-less microbial fuel cell treating wastewater and effect of electrode distance and area on electricity production, Bioresour. Technol. 98 (2007) 2879–2885. [96] G. Jadhav, Y. Jagtap, M. Ghangrekar, Dual-chambered membrane microbial fuel cell: limitation on potential difference, Int. J. Eng. Res. Technol. 2 (2013). [97] P. Zaveri, T. Modi, L. Parekh, A. Patel, S. Kureshi, N. Munshi, Performance analysis of separators in dual-chambered microbial fuel cell and treatment of combined industrial effluent of South Gujarat, in: Proceedings of the First International Conference on Recent Advances in Bioenergy Research, Springer, 2016, pp. 319–329. [98] K.-J. Chae, M.-J. Choi, J.-W. Lee, K.-Y. Kim, I.S. Kim, Effect of different substrates on the performance, bacterial diversity, and bacterial viability in microbial fuel cells, Bioresour. Technol. 100 (2009) 3518–3525. [99] G. Sun, A. Thygesen, A.S. Meyer, Acetate is a superior substrate for microbial fuel cell initiation preceding bioethanol effluent utilization, Appl. Microbiol. Biotechnol. 99 (2015) 4905–4915. [100] H.-S. Lee, P. Parameswaran, A. Kato-Marcus, C.I. Torres, B.E. Rittmann, Evaluation of energyconversion efficiencies in microbial fuel cells (MFCs) utilizing fermentable and non-fermentable substrates, Water Res. 42 (2008) 1501–1510. [101] E. Herrero-Herna´ndez, T. Smith, R. Akid, Electricity generation from wastewaters with starch as carbon source using a mediatorless microbial fuel cell, Biosens. Bioelectron. 39 (2013) 194–198. [102] Z. Ren, T.E. Ward, J.M. Regan, Electricity production from cellulose in a microbial fuel cell using a defined binary culture, Environ. Sci. Technol. 41 (2007) 4781–4786. [103] H. Liu, S. Cheng, B.E. Logan, Production of electricity from acetate or butyrate using a singlechamber microbial fuel cell, Environ. Sci. Technol. 39 (2005) 658–662. [104] V.R. Nimje, C.-Y. Chen, C.-C. Chen, H.-R. Chen, M.-J. Tseng, J.-S. Jean, Y.-F. Chang, Glycerol degradation in single-chamber microbial fuel cells, Bioresour. Technol. 102 (2011) 2629–2634. [105] C. Kim, Y.E. Song, C.R. Lee, B.-H. Jeon, J.R. Kim, Glycerol-fed microbial fuel cell with a co-culture of Shewanella oneidensis MR-1 and Klebsiella pneumonae J2B, J. Ind. Microbiol. Biotechnol. 43 (2016) 1397–1403. [106] J. Ariunbaatar, A. Panico, G. Esposito, F. Pirozzi, P.N. Lens, Pretreatment methods to enhance anaerobic digestion of organic solid waste, Appl. Energy 123 (2014) 143–156. [107] D. Pant, A. Singh, G. Van Bogaert, S.I. Olsen, P.S. Nigam, L. Diels, K. Vanbroekhoven, Bioelectrochemical systems (BES) for sustainable energy production and product recovery from organic wastes and industrial wastewaters, RSC Adv. 2 (2012) 1248–1263.

25

26

Biological fuel cells

[108] T. Chookaew, P. Prasertsan, Z.J. Ren, Two-stage conversion of crude glycerol to energy using dark fermentation linked with microbial fuel cell or microbial electrolysis cell, New Biotechnol. 31 (2014) 179–184. [109] S.B. Pasupuleti, S. Srikanth, S.V. Mohan, D. Pant, Continuous mode operation of microbial fuel cell (MFC) stack with dual gas diffusion cathode design for the treatment of dark fermentation effluent, Int. J. Hydr. Energy 40 (2015) 12424–12435. [110] J.L. Varanasi, S. Roy, S. Pandit, D. Das, Improvement of energy recovery from cellobiose by thermophillic dark fermentative hydrogen production followed by microbial fuel cell, Int. J. Hydr. Energy 40 (2015) 8311–8321. [111] W. Fuchs, H. Binder, G. Mavrias, R. Braun, Anaerobic treatment of wastewater with high organic content using a stirred tank reactor coupled with a membrane filtration unit, Water Res. 37 (2003) 902–908. [112] A. Gohil, G. Nakhla, Treatment of food industry waste by bench-scale upflow anaerobic sludge blanket-anoxic-aerobic system, Water Environ. Res. 78 (2006) 974–985. [113] A.P. Borole, C.Y. Hamilton, Energy production from food industry wastewaters using bioelectrochemical cells, in: Emerging Environmental Technologies, vol. II, Springer, 2010, pp. 97–113. [114] R.A. Hoffmann, M.L. Garcia, M. Veskivar, K. Karim, M.H. Al-Dahhan, L.T. Angenent, Effect of shear on performance and microbial ecology of continuously stirred anaerobic digesters treating animal manure, Biotechnol. Bioeng. 100 (2008) 38–48. [115] D.P. Strik, H. Hamelers, J.F. Snel, C.J. Buisman, Green electricity production with living plants and bacteria in a fuel cell, Int. J. Energy Res. 32 (2008) 870–876. [116] K. Wetser, E. Sudirjo, C.J. Buisman, D.P. Strik, Electricity generation by a plant microbial fuel cell with an integrated oxygen reducing biocathode, Appl. Energy 137 (2015) 151–157. [117] P. Bombelli, D.M.R. Iyer, S. Covshoff, A.J. McCormick, K. Yunus, J.M. Hibberd, A.C. Fisher, C.J. Howe, Comparison of power output by rice (Oryza sativa) and an associated weed (Echinochloa glabrescens) in vascular plant bio-photovoltaic (VP-BPV) systems, Appl. Microbiol. Biotechnol. 97 (2013) 429–438. [118] M. Helder, W.S. Chen, E.J. Van Der Harst, D.P. Strik, H.V. Hamelers, C.J. Buisman, J. Potting, Electricity production with living plants on a green roof: environmental performance of the plantmicrobial fuel cell, Biofuels Bioprod. Biorefin. 7 (2013) 52–64. [119] P. Chiranjeevi, G. Mohanakrishna, S.V. Mohan, Rhizosphere mediated electrogenesis with the function of anode placement for harnessing bioenergy through CO2 sequestration, Bioresour. Technol. 124 (2012) 364–370. [120] I. Karube, T. Takeuchi, D. Barnes, Biotechnological reduction of CO2 emissions, in: Modern Biochemical Engineering, Springer, 1992, pp. 63–79. [121] C. Yang, Q. Hua, K. Shimizu, Energetics and carbon metabolism during growth of microalgal cells under photoautotrophic, mixotrophic and cyclic light-autotrophic/dark-heterotrophic conditions, Biochem. Eng. J. 6 (2000) 87–102. [122] Y.K. Lee, Algal nutrition–heterotrophic carbon nutrition, in: Handbook of Microalgal Culture: Biotechnology and Applied Phycology, Blackwell Publishing, London, 2003, pp. 116–124. [123] A.G. del Campo, P. Can˜izares, M.A. Rodrigo, F.J. Ferna´ndez, J. Lobato, Microbial fuel cell with an algae-assisted cathode: a preliminary assessment, J. Power Sources 242 (2013) 638–645. [124] M. Zhou, H. He, T. Jin, H. Wang, Power generation enhancement in novel microbial carbon capture cells with immobilized Chlorella vulgaris, J. Power Sources 214 (2012) 216–219. [125] M. Mehanna, P.D. Kiely, D.F. Call, B.E. Logan, Microbial electrodialysis cell for simultaneous water desalination and hydrogen gas production, Environ. Sci. Technol. 44 (2010) 9578–9583. [126] V.G. Gude, N. Nirmalakhandan, S. Deng, Renewable and sustainable approaches for desalination, Renew. Sust. Energ. Rev. 14 (2010) 2641–2654. [127] K.S. Jacobson, D.M. Drew, Z. He, Efficient salt removal in a continuously operated upflow microbial desalination cell with an air cathode, Bioresour. Technol. 102 (2011) 376–380. [128] X. Chen, P. Liang, Z. Wei, X. Zhang, X. Huang, Sustainable water desalination and electricity generation in a separator coupled stacked microbial desalination cell with buffer free electrolyte circulation, Bioresour. Technol. 119 (2012) 88–93. [129] S. Chen, H. Luo, G. Liu, R. Zhang, H. Wang, B. Qin, Y. Hou, Integrated utilization of seawater using a five-chamber bioelectrochemical system, J. Membr. Sci. 444 (2013) 16–21.

Introduction to biological fuel cell technology

[130] K.S. Brastad, Z. He, Water softening using microbial desalination cell technology, Desalination 309 (2013) 32–37. [131] Y. Zhang, I. Angelidaki, A new method for in situ nitrate removal from groundwater using submerged microbial desalination–denitrification cell (SMDDC), Water Res. 47 (2013) 1827–1836. [132] Y. Kim, B.E. Logan, Series assembly of microbial desalination cells containing stacked electrodialysis cells for partial or complete seawater desalination, Environ. Sci. Technol. 45 (2011) 5840–5845. [133] D. Zhuwei, L. Qinghai, T. Meng, L. Shaohua, L. Haoran, Electricity generation using membrane-less microbial fuel cell during wastewater treatment, Chin. J. Chem. Eng. 16 (2008) 772–777. [134] H. Luo, P. Xu, T.M. Roane, P.E. Jenkins, Z. Ren, Microbial desalination cells for improved performance in wastewater treatment, electricity production, and desalination, Bioresour. Technol. 105 (2012) 60–66. [135] Y. Kim, B.E. Logan, Simultaneous removal of organic matter and salt ions from saline wastewater in bioelectrochemical systems, Desalination 308 (2013) 115–121. [136] S. Chen, G. Liu, R. Zhang, B. Qin, Y. Luo, Development of the microbial electrolysis desalination and chemical-production cell for desalination as well as acid and alkali productions, Environ. Sci. Technol. 46 (2012) 2467–2472. [137] C. Forrestal, P. Xu, P.E. Jenkins, Z. Ren, Microbial desalination cell with capacitive adsorption for ion migration control, Bioresour. Technol. 120 (2012) 332–336. [138] H. Xu, M. Xu, Y. Li, X. Liu, L. Guo, H. Jiang, Characterization, origin and aggregation behavior of colloids in eutrophic shallow lake, Water Res. 142 (2018) 176–186. [139] M. Rahimnejad, G. Najafpor, Z. Najafgholi, Sediment as new source of clean energy for bioelectricity production, Q. J. Sci. Kharazmi Univ. 14 (2015) 199–208. [140] R. Alipanahi, M. Rahimnejad, G. Najafpour, Improvement of sediment microbial fuel cell performances by design and application of power management systems, Int. J. Hydrog. Energy 44 (2019) 16965–16975. [141] S. Jung, J.M. Regan, Influence of external resistance on electrogenesis, methanogenesis, and anode prokaryotic communities in microbial fuel cells, Appl. Environ. Microbiol. 77 (2011) 564–571. [142] S.P. Jung, S. Pandit, Important factors influencing microbial fuel cell performance, in: Microbial Electrochemical Technology, Elsevier, 2019, pp. 377–406. [143] A. Zabihallahpoor, M. Rahimnejad, F. Talebnia, Sediment microbial fuel cells as a new source of renewable and sustainable energy: present status and future prospects, RSC Adv. 5 (2015) 94171–94183. [144] H. Zhang, D. Zhu, T.-S. Song, P. Ouyang, J. Xie, Effects of the presence of sheet iron in freshwater sediment on the performance of a sediment microbial fuel cell, Int. J. Hydr. Energy 40 (2015) 16566–16571. [145] N. Song, H.-L. Jiang, Effects of initial sediment properties on start-up times for sediment microbial fuel cells, Int. J. Hydrog. Energy 43 (2018) 10082–10093. [146] R. Alipanahi, M. Rahimnejad, Effect of different ecosystems on generated power in sediment microbial fuel cell, Int. J. Energy Res. 42 (2018) 4891–4897. [147] S.P. Jung, M.-H. Yoon, S.-M. Lee, S.-E. Oh, H. Kang, J.-K. Yang, Power generation and anode bacterial community compositions of sediment fuel cells differing in anode materials and carbon sources, Int. J. Electrochem. Sci. 9 (2014) 315–326. [148] Z. Najafgholi, M. Rahimnejad, G. Najafpour, Effect of electrolyte conductivity and aeration on performance of sediment microbial fuel cell, Journal of Renewable, Energy Environ. 2 (2015) 43–48. [149] R. Kumar, L. Singh, Z.A. Wahid, M.F.M. Din, Exoelectrogens in microbial fuel cells toward bioelectricity generation: a review, Int. J. Energy Res. 39 (2015) 1048–1067. [150] Y.A. Gorby, S. Yanina, J.S. McLean, K.M. Rosso, D. Moyles, A. Dohnalkova, T.J. Beveridge, I.S. Chang, B.H. Kim, K.S. Kim, Electrically conductive bacterial nanowires produced by Shewanella oneidensis strain MR-1 and other microorganisms, Proc. Natl. Acad. Sci. 103 (2006) 11358–11363. [151] C.A. Pham, S.J. Jung, N.T. Phung, J. Lee, I.S. Chang, B.H. Kim, H. Yi, J. Chun, A novel electrochemically active and Fe (III)-reducing bacterium phylogenetically related to Aeromonas hydrophila, isolated from a microbial fuel cell, FEMS Microbiol. Lett. 223 (2003) 129–134. [152] H.S. Park, B.H. Kim, H.S. Kim, H.J. Kim, G.T. Kim, M. Kim, I.S. Chang, Y.K. Park, H.I. Chang, A novel electrochemically active and Fe (III)-reducing bacterium phylogenetically related to Clostridium butyricum isolated from a microbial fuel cell, Anaerobe 7 (2001) 297–306.

27

28

Biological fuel cells

[153] K.P. Nevin, H. Richter, S. Covalla, J. Johnson, T. Woodard, A. Orloff, H. Jia, M. Zhang, D. Lovley, Power output and columbic efficiencies from biofilms of Geobacter sulfurreducens comparable to mixed community microbial fuel cells, Environ. Microbiol. 10 (2008) 2505–2514. [154] K.B. Ghoreishi, M. Ghasemi, M. Rahimnejad, M.A. Yarmo, W.R.W. Daud, N. Asim, M. Ismail, Development and application of vanadium oxide/polyaniline composite as a novel cathode catalyst in microbial fuel cell, Int. J. Energy Res. 38 (2014) 70–77. [155] G. Kim, M. Hyun, I. Chang, H. Kim, H. Park, B. Kim, S. Kim, J. Wimpenny, A.J. Weightman, Dissimilatory Fe (III) reduction by an electrochemically active lactic acid bacterium phylogenetically related to Enterococcus gallinarum isolated from submerged soil, J. Appl. Microbiol. 99 (2005) 978–987. [156] N.S. Malvankar, M. Vargas, K.P. Nevin, A.E. Franks, C. Leang, B.-C. Kim, K. Inoue, T. Mester, S.F. Covalla, J.P. Johnson, Tunable metallic-like conductivity in microbial nanowire networks, Nat. Nanotechnol. 6 (2011) 573–579. [157] D.-B. Wang, T.-S. Song, T. Guo, Q. Zeng, J. Xie, Electricity generation from sediment microbial fuel cells with algae-assisted cathodes, Int. J. Hydrog. Energy 39 (2014) 13224–13230. [158] L.D. Schamphelaire, L.V.D. Bossche, H.S. Dang, M. H€ ofte, N. Boon, K. Rabaey, W. Verstraete, Microbial fuel cells generating electricity from rhizodeposits of rice plants, Environ. Sci. Technol. 42 (2008) 3053–3058. [159] R.A. Timmers, M. Rothballer, D.P. Strik, M. Engel, S. Schulz, M. Schloter, A. Hartmann, B. Hamelers, C. Buisman, Microbial community structure elucidates performance of Glyceria maxima plant microbial fuel cell, Appl. Microbiol. Biotechnol. 94 (2012) 537–548. [160] S. Calabrese Barton, J. Gallaway, P. Atanassov, Enzymatic biofuel cells for implantable and microscale devices, Chem. Rev. 104 (2004) 4867–4886. [161] S. Kerzenmacher, J. Ducree, R. Zengerle, F. Von Stetten, Energy harvesting by implantable abiotically catalyzed glucose fuel cells, J. Power Sources 182 (2008) 1–17. [162] M. Osman, A. Shah, F. Walsh, Recent progress and continuing challenges in bio-fuel cells. Part I: Enzymatic cells, Biosens. Bioelectr. 26 (2011) 3087–3102. [163] D. Sokic-Lazic, R.L. Arechederra, B.L. Treu, S.D. Minteer, Oxidation of biofuels: fuel diversity and effectiveness of fuel oxidation through multiple enzyme cascades, Electroanal.: Int. J. Devot. Fundam. Pract. Aspects Electroanal. 22 (2010) 757–764. [164] P. Kar, H. Wen, H. Li, S.D. Minteer, S.C. Barton, Simulation of multistep enzyme-catalyzed methanol oxidation in biofuel cells, J. Electrochem. Soc. 158 (2011) B580. [165] R.J. Lopez, S. Babanova, Y. Ulyanova, S. Singhal, P. Atanassov, Improved interfacial electron transfer in modified bilirubin oxidase biocathodes, ChemElectroChem 1 (2014) 241–248. [166] P. Scodeller, R. Carballo, R. Szamocki, L. Levin, F. Forchiassin, E.J. Calvo, Layer-by-layer selfassembled osmium polymer-mediated laccase oxygen cathodes for biofuel cells: the role of hydrogen peroxide, J. Am. Chem. Soc. 132 (2010) 11132–11140. [167] F. Barrie`re, P. Kavanagh, D. Leech, A laccase–glucose oxidase biofuel cell prototype operating in a physiological buffer, Electrochim. Acta 51 (2006) 5187–5192.

CHAPTER 2

Microbiological concepts of MFCs Mostafa Rahimnejad

Biofuel and Renewable Energy Research Center, Chemical Engineering Department, Babol Noshirvani University of Technology, Babol, Mazandaran, Iran

2.1 Introduction Electroactive microorganisms play an important role in the power output of microbial fuel cells (MFCs). Such microorganisms have various applications in MFC technology that include energy production, wastewater treatment, biosensing of toxic materials, water distillation, and chemical production [1,2]. A vast array of anaerobic and aerobic microbes are recognized as potential electroconductive microbes [3]. However, there have been some limited reports on the use of aerobics and facultative aerobics [4,5]. Exoelectrogens and electrotrophs are two main classes of electroconductive microbes incorporated in different types of bioelectrochemical systems (BES) as biocatalysts. Substantial research over the past two decades has characterized the significance of electron exchange between the outer cell surface and the cell interior to overall BES performance, suggesting that direct electron transfer and indirect electron transfer regulate metabolic functions of MFCs. As an essential part of microbial electrochemical technologies, exoelectrogens transfer electrons to the electrode surface, while electrotrophs derive electrons from the electrodes [1]. For direct electron transfer, shuttling between the cell and the electrode surface is greatly affected by outer membrane cytochromes and conductive extensions [2]. Indirect electric transfer, on the other hand, is mediated by either selfproduced mediators such as flavins and humic substances or added mediators or electron shuttles. This chapter focuses on characteristic features and function of exoelectrogens and electrotrophs as the main microorganism types in MFCs. We discuss the growing diversity of electroactive microorganisms and their remarkable electronic capabilities that open up possible avenues for electrochemical devices.

2.2 Exoelectrogenic microorganisms Exoelectrogens have gained increasing interest in MFCs, as they can contribute electrons to the anode either directly via c-type cytochromes, pili, or nanowires [3] or indirectly through artificial mediators or secreted natural mediators (e.g., flavins and pyocyanin) [4,5]. Initially, bacterial species were dominant exoelectrogenic species in MFC systems. However, following technological innovations, emerging attention has shifted to Biological Fuel Cells https://doi.org/10.1016/B978-0-323-85711-6.00010-2

Copyright © 2023 Elsevier Inc. All rights reserved.

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eukaryotes and archaea that can also generate high power densities. Various factors such as alkalinity, temperature, nutrient availability, type of electron acceptor, and mediator concentration can regulate the actual electrogenic capability of microbes in MFCs [6,7]. Table 2.1 summarizes the major exoelectrogenic microbes used as MFC biocatalysts.

2.2.1 Pioneering microbial communities 2.2.1.1 Bacterial involvement in MFCs Bacteria have drawn a lot of attention as promising exoelectrogens [3]. Proteobacteria species and phototrophs have possessed utilities in MFC applications. Proteobacteria Geobacter species: Incorporation of the Geobacter species into the anodic chamber is an attractive MFC design that combines organic compound oxidation with bioremediation processes [64]. Geobacter species can be used for concomitant degradation of petroleum compounds and metal reduction [65]. Geobacter sulfurreducens has been utilized to reach a significant power density from acetate oxidation due to its high coulombic efficiency and ease of electron transferring via type-IV pili and c-type cytochromes [3,10,66]. For instance, highly electroconductive networks of Geobacter sulfurreducens PCA and Geobacter sulfurreducens KN400 have been provided power densities of 1.88 and 3.9 W m2, respectively [67,68]. However, Geobacter sulfurreducens suffers alterations in the metabolism of aromatic hydrocarbons. To incorporate new function into MFC, Geobacter sulfurreducens has been used to metabolize aromatic compounds [64,69] with Fe(III) [70]. In addition to c-type cytochromes and type IV pili, NHL repeat-containing protein and pili glycosylation involved genes are important for metal reduction by Geobacter metallireducens [13]. Shewanella species: Shewanella, a facultative anaerobic bacterial species, can be used as MFC biocatalysts to generate electron flows, via either direct electron transfer (DET) or mediated electron transfer (MET). Shewanella putrefaciens and Shewanella oneidensis DSP10 are capable of producing power in a mediator-less MFC [18,19]. Maximum power density of 3 W m 2 was reported for Shewanella oneidensis DSP10. Biffinger et al. demonstrated the incorporation of DET and MET in the power output of Shewanella oneidensis-driven MFCs [22]. In Shewanella oneidensis, MET is conducted by flavin secretion of microbes, which enables electron transference from cell surface c-type cytochromes to the electrode surface [4,5], while DET is formed by direct contact between the cell surface and the anode either by cell surface c-type cytochromes or by nanowires [71]. As another member, a power density of 1326 mW m 2 was reported for Shewanella oneidensis [72]. Studies show that a single cell of Shewanella oneidensis MR-1 can mediate an electron flow from the cell surface to the anode surface at a rate of 1.3  106 e cell 1 s 1 [73]. Pseudomonas species: Pseudomonas aeruginosa, a facultative anaerobic bacterium, showed MET property in electricity production using MFC technology [14,15,74].

Microbiological concepts of MFCs

Table 2.1 The major exoelectrogenic microbes used as an MFC biocatalyst.

Category

Biocatalyst

Substrate

Proteobacteria

Geobacter sulfurreducens Geobacter metallireducens Pseudomonas aeruginosa Shewanella putrefaciens Shewanella oneidensis DSP10 Shewanella oneidensis MR-1 Shewanella loihica PV-4 Escherichia coli

Acetate, H2

Desulfobulbus propionicus Geothrix fermentans Paracoccus denitrificans and Paracoccus pantotrophus Rhodoferax ferrireducens Tolumonas osonensis Ochrobactrum anthropi

Firmicutes

Phototrophic bacteria

Klebsiella pneumoniae Arcobacter butzleri Clostridium butyricum Clostridium beijerinckii Rhodopseudomonas palustris DX-1

Acetate, benzoate

Maximum current/power density

References

0.418– 0.866 W m 2 0.04 W m 2

[8–11] [12,13]

2

2.6 mW m

[14–16]

Glucose, yeast extract Lactate, pyruvate, formate Lactate

10.2 mW m 2– 4.40 W m 2 1.5 W m 2

Lactate

10 W m

Lactate

0.497 W m

Glucose, yeast extract Lactate, pyruvate, ethanol Acetate Sulfide acetate

0.1–0.6 W m

– 47 W m

Glucose

31 mA m

Lactate

0.424 W m

Acetate lactate, propionate, butyrate, glucose, sucrose, cellobiose, glycerol, ethanol Glucose

89 mW m

2

[34]

3.64 W m

3

[35–37]

Acetate Starch

296 mW L 1 1–1.3 mA cm

Volatile fatty acids, yeast extract, thiosulfate

2.72 W m

2

[20–22] [22,23]

2

[24,25] 2

2

28 mA m

[17–19]

[26–29] [30] [30] [31]

3

2

[32] 2

2

[33]

2

[38] [39]

[40]

Continued

31

Table 2.1 The major exoelectrogenic microbes used as an MFC biocatalyst—cont’d

Category

Yeast

Maximum current/power density

Biocatalyst

Substrate

Rhodobacter sphaeroides

Succinate, propionate, ammonia, nitrite, nitrate, glutamate Glucose

3Wm

Glucose

Glucose

2.12 mW m 2 4.48 mW m 2 40 mW m 3 146.71 mW m 12.9 mW m 2 20.2 mW m 2 2 mW m 2 80 mW m 2 148 mW m 2 120 mW m 2 138 mW m 2 344 mW m 2 400 mW m 2 80 mW m 2 500 mW m 2 3 mW m 2 60 mW m 2 1500 mW m 2

Glucose

283 mW m

Glucose

13.6 mW m

Lactose

2.7 mW m

Lactose

33 mW m

D-Glucose

2.8 mW m

D-Xylose

8 mW m

D-Glucose

31 mW m 39 mW m 32 mW m 22 mW m 14 mW m

Saccharomyces cerevisiae Saccharomyces cerevisiae Saccharomyces cerevisiae Saccharomyces cerevisiae

Glucose Glucose

Saccharomyces cerevisiae

Glucose

Saccharomyces cerevisiae Saccharomyces cerevisiae

Glucose

Saccharomyces cerevisiae Saccharomyces cerevisiae Saccharomyces cerevisiae PTCC 5269 Saccharomyces cerevisiae displaying GOx Saccharomyces cerevisiae Saccharomyces cerevisiae displaying CDH Saccharomyces cerevisiae displaying GOx Saccharomyces cerevisiae S. cerevisiae displaying PDH

Glucose

Dextrose

D-Xylose L-Arabinose D-Cellobiose D-Galactose

References

3

[41]

2

65 mW m

[42]

2

2

2

2

2

2

[43] [44] 3

[45]

[45]

[46] [47]

[48] [49] [50]

[51]

[52] [52]

[52]

[52] 2 2 2 2 2

[52]

Microbiological concepts of MFCs

Table 2.1 The major exoelectrogenic microbes used as an MFC biocatalyst—cont’d

Category

Biocatalyst

Saccharomyces cerevisiae Saccharomyces cerevisiae Saccharomyces cerevisiae Saccharomyces cerevisiae Saccharomyces cerevisiae Saccharomyces cerevisiae Saccharomyces cerevisiae Candida melibiosica 2491

Substrate

Maximum current/power density

Synthetic wastewater Glucose

25.51 mW m

Glucose

60 mW m 2 133 mW m 2 0.414 mW m 2 mW m 2 33 mW m 2

Glucose Glucose Glucose Glucose

Candida melibiosica

Fructose YPfru YPfru YPfru

Candida melibiosica

Fructose

Arxula adeninivorans Candida sp. IR11

Dextrose and glucose Glucose rejected wastewater

3 mW m

References 2

2

[53] [54] [50]

2

[55] [56]

20 mW m 2 15.4 mW m 2 30.46 mW m 2

[57] [58]

60 mW m 3 180 mW m 3 185 mW m 3 20 mW m 2 46 mW m 2 89 mW m 2 113 mW m 2 137 mW m 2 640 mW m 2 36 mW m 2 720 mW m 2 390 mW m 2 28 mW m 2 1030 mW m 2 20.6 mW m 2

[59]

[60]

[61]

[62] [63]

As expected, incorporation of sophorolipid biosurfactant to the system accelerated the electron dynamics by 1.7 and 2.6 times through enhancing cell membrane permeability and promoting pyocyanin production [75]. Nonnative phenazines also showed a several fold power output increment [76]. The expression level or the profile of mediators synthesized by Pseudomonas aeruginosa could be tuned by genetic engineering, resulting in promoted electrical power production [16]. Escherichia coli species: Escherichia, a facultative anaerobe, can be conveniently engineered due to the abundance of genome sequence information. Moreover, Escherichia

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Biological fuel cells

coli has shown excellent adaptation to a broad range of environmental conditions and therefore can act as a promising biocatalyst for MFCs. Escherichia coli provides significant power density through the secretion of its own redox mediators [77]. For instance, Escherichia coli HB101 possessed a power density of 760 mW m 2 using self-made electron mediators [27,78]. Moreover, genetically engineered Escherichia coli BL-21 exhibited a significant increment in power density associated with the activation of the riboflavin biosynthetic pathway [79]. Clostridium species: Clostridium butyricum EG3, an obligate anaerobe, showed power production capacity through the fermentation of complex organic compounds. Clostridium beijerinckii is another member of the Clostridium genus which enables it to produce power by anaerobic digestion of starch, molasse, glucose, or lactate [39]. Rhodoferax ferrireducens: Rhodoferax, a facultative anaerobic bacterium, showed good power production performance without the need for redox mediators. Interestingly, Rhodoferax ferrireducens could be a potential biocatalyst of long-term MFC operation due to stability of the bacterial growth assisted by energy obtained from the electron transfer process [32]. Tolumonas osonensis: Tolumonas has shown a fascinating capacity in oxidizing a variety of substrates such as glucose, lactose, maltose, arabinose, acetate, lactate, and glycerol. For instance, in a Tolumonas osonensis-assisted MFC, a maximum power density of 424 mW m 2 was reported using lactate as the substrate [33]. Ochrobactrum anthropi: Ochrobactrum, an obligate aerobe, can be used to generate power from organics including acetate, lactate, propionate, butyrate, glucose, sucrose, cellobiose, glycerol, and ethanol, although opportunistic properties have restricted its power production applications in MFC systems [30].

Phototrophic bacteria Phototrophic bacteria can be used in MFCs as electron suppliers for other biocatalysts, anodic reaction catalyzers (photoheterotrophic microorganisms), and oxygen suppliers (photoautotrophic microorganisms) [80]. For instance, Anabaena and Synechocystis (cyanobacterial species) have been used in the MFC as biocatalysts, and HNQ (an artificial redox mediator) was utilized to shuttle electrons to the anode. However, the approach suffers from particular properties of the artificial redox mediator such as high price, toxicity, and unsustainability, impairing the development of cyanobacteria-assisted MFCs [81]. An electroconductive network composed of phototrophic Rhodopseudomonas palustris DX-1, isolated from an anodic community, exhibited a significant amount of electrical power production (2720 mW m 2), compared to the mixed cultures in the same MFC system [45]. Rhodopseudomonas palustris DX-1 can utilize a wide range of substrates for power production including volatile fatty acids, yeast extract, glycerol, thiosulfate, and

Microbiological concepts of MFCs

whole cells of the cyanobacterium Arthrospira maxima [40,82]. Furthermore, the addition of Rhodopseudomonas to a phototrophic consortium have increased the power density by eightfold [83]. Hydrogen production by photosynthetic bacteria, during bacterial metabolism [48,49], can also provide a natural electron mediator for electron shuttle between the microbes and the anode. Confirming the correlation between photosynthesis and MFC activity, Cho and coworkers reported a power density of 3 W m 3 in light and 0.008 W m 3 in the dark, using H2-producing Rhodobacter sphaeroides and platinum as an electrocatalyst [84]. 2.2.1.2 Exoelectrogenic eukaryotes Yeast can coordinate with an anode to accomplish power production from various substrates. Yeast-based MFCs can produce power density in the range of several mW m 2 to several W m 2. In terms of mechanism, yeast mediates electron transfer from substrates to an anode electrode either directly by redox-active enzymes or indirectly via chemical mediators. The commonly used yeasts in MFCs are as follows: Saccharomyces cerevisiae: Various characteristics, such as being biocompatible, cost-effective, and convenient to cultivate and genetic manipulation, have made Saccharomyces cerevisiae a potential microbe community for MFC systems [48,50]. Saccharomyces cerevisiae can utilize both MET [85] and DET for power production. However, the mechanisms of DET exhibited by Saccharomyces cerevisiae have not been thoroughly understood. Power density in the range of 20–2440 mW m 2 has been proven for Saccharomyces cerevisiae-mediated MFCs [54,57,85,86]. Hansenula anomala: Hansenula can contribute to the current production through oxidizing glucose in the anodic chamber of MFCs. Direct electron transfer mechanisms are mediated by redox enzymes present in the outer membrane of the yeast [87]. Candida sp.: Candida melibiosica 2491, a yeast strain, possesses a promoted phytase activity appropriate for degradation of phosphorus compounds of plant tissues. Candida melibiosica has a good oxidation-reduction potential, that is, the ability to transfer electrons without the addition of chemical mediators [59]. The maximum power output of 60 mW m 3 has been obtained from Candida melibiosica-based MFCs using fructose as the substrate. Yeast cell growth and the rate of substrate digestion are accompanied by the rate of electron production. More importantly, the energy density of Candida melibiosica-based MFCs in the presence of exogenous mediators was also studied [60]. It has been reported that incorporation of methylene blue promotes current production from 20 to 640 mW m 2 through enhancement in electron-transfer kinetics. Arxula adeninivorans: It has been widely accepted that Arxula adeninivorans has a sustained growth at high temperatures, high salinity, and various pHs. The power density of Arxula adeninivorans has been studied using a continuous mode mediatorless double-chamber MFC [62]. Arxula adeninivorans mediated sufficient electron flows

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Biological fuel cells

through the secretion of a soluble electroactive molecule. Additionally, 2,3,5,6-tetramethyl-1,4-phenylenediamine and KMnO4 can be used as anodic and cathodic mediators for increment of power production in adeninivorans-based MFCs [51]. 2.2.1.3 Mixed culture in MFCs Developing mixed microbial communities is a practical strategy for advancement of MFC technology. In mixed communities, synergistic interactions are reported between the aerobe and anaerobe consortia. Photosynthetic organisms are investigated as a biocatalyst of anoxygenic mixed-MFC systems [88]. Mixed microalgae can be utilized as anode biocatalysts to generate electricity from sewage and dissolved oxygen introduced as a limiting factor of microalgae electrogenic activity [89]. It was found that higher electricity generation resulted under illumination as compared to dark conditions. Mixed communities use a combination of metabolic pathways through which the desired degradation of complex substrates is carried out. Because of this, the use of mixed communities is more convenient than those of pure culture-driven systems, particularly when complex wastewater is used as the substrate. A higher rate of power production was reported for a mixed culture biofilm compared to a pure culture biofilm in the same device [90]. As expected, a two times higher electron transfer potential was concluded from the enriched consortia compared to pure Geobacter sulfurreducens. In addition, mixed communities remain metabolically active in robust environments, making them a promising inoculum for recalcitrant waste treatment. However, the abundant groups of methanogens and nonexoelectrogens can significantly attenuate the energy efficiency of MFCs. Instability of the mixed culture is another issue, affecting the power output of the system [14].

2.2.2 Sources of exoelectrogens Electroactive microorganisms isolated from the anode surface of MFCs or natural sources can facilitate the power production of MFC systems, thereby enhancing the rate of the electron shuttle to the anode electrode. However, the majority of them belong to the anaerobic class of bacteria. Accumulated evidence showed that wastewater treatment plants, marine and aquatic sediments, soil, and activated sludge are the richest sources of electroconductive microbes [91]. 2.2.2.1 Natural sources Significant progress has been made to isolate electroactive organisms from terrestrial and aquatic habitats. Upon material diversity, natural environments can be settled by different groups of active microorganisms. For example, composted organic matter is introduced as a natural source for γ-Proteobacteria, while soil is rich in Proteobacteria, Firmicutes, and Actinobacteria species [92]. While considering terrestrial superiority in terms of

Microbiological concepts of MFCs

preferred microorganisms, the microbes isolated from anaerobic environments usually exhibited advantages over those from aerial habitats. Aquatic habitats like marine or coastal environments can be used as abundant sources of electrochemically active microorganisms [91]. Electrogenic bacteria were used in sediment MFCs to provide autonomous oceanographic or environmental sensors at marine or coastal regions which can report air temperature, pressure, relative humidity, and water temperature on site [93]. For example, isolated Geobacter sulfurreducens is known as the most appropriate organism to study sediment MFCs [94]. 2.2.2.2 Artificial sources Similar to natural sources, industrial or domestic effluents are also suitable sources of electroconductive organisms due to the abundance of organics. Starchy wastewater, municipal wastewater, and domestic wastewater were offered noticeable inoculum suppliers [91,95]. Apart from these, inoculum sources of MFCs can be readily extended to hazardous wastes such as petroleum-hydrocarbon contaminated soils [96], landfill leachate [97], and fly ash from the thermal power plant [98]. The dominant microbial community after inoculation depends on the source of action. For instance, β-Proteobacteria and δ-Proteobacteria are the observed dominant species of the inoculum isolated from anaerobic sludge, while Firmicutes is the major participant of the microbial community obtained from starch processing wastewater [99]. Likewise, Aspergillus luchuensis is the dominant species of municipal wastewater exhibiting a high removal efficacy for diclofenac [95].

2.2.3 Strategies for studying exoelectrogens Today, a wide variety of exoelectrogens are frequently utilized as focused and controlled biocatalysts of MFCs. In particular, the efficacy of these microorganisms in electricity generation depends on the microbial isolation source and MFC operating conditions. Several microbiological and electrochemical assessments are considered as excellent methods for selection of suitable sources of microbial communities and operational conditions [100]. The assessments aim to cover various MFC configurations, their application in energy generation, wastewater treatment and biosensing, and other associated challenges. 2.2.3.1 Microbiological methods Microbiological techniques are administrated to investigate specific microbial communities with the goal of achieving the desired characterization. The application of a microbiological approach is a central strategy to obtain morphological, physiological, and biochemical characteristics of exoelectrogenic species. Considering the recent approaches, the most prevalent used isolation methods include the dilution-to-extinction method and plating techniques such as streaking, spreading, or pour plating. Additionally,

37

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Biological fuel cells

the most probable number method suggests the suitability of a mixed microbial community for MFC applications. The method is carried out through incubation of cultures followed by colony counting or microscopic counts. 2.2.3.2 Molecular methods The 16S rRNA-gene sequencing is a potential molecular method for assessment of microbiological parameters, mainly through a detailed understanding of pure bacterial species and mixed community dynamics. There are several other fingerprinting methods for studying the exoelectrogenic community dynamics in MFCs, including denaturing gradient gel electrophoresis, formation of clone libraries, fluorescence in situ hybridization, pyrosequencing, and DNA microarray. 2.2.3.3 Electrochemical methods Polarization techniques, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), etc. are used for the performance and kinetic study of MFCs [100]. Such techniques elucidate undergoing microbial reactions and electron transfer mechanisms. Polarization techniques ensure the effectiveness of designing power management circuits. EIS analysis is used for collecting data on the most influential resistance prevailing using Nyquists and Bode plots. CV has become an ideal tool for investigation of redox processes, electron discharge patterns, metabolic changes, and electron carriers.

2.3 Electrotrophic microorganisms Exoelectrotrophs are electroactive microbes that pull electrons from the cathode surface either by direct or indirect electron transfer mechanisms [101]. Electrotrophs can serve as natural available electron acceptors [102] and economic alternatives to oxygen-based electron acceptors in cathodes. Additionally, studies suggest the application of cathode biofilms in removal of environmental contaminants like nitrates, radioactive waste, toxic heavy metals. For instance, Ochrobactrum sp. X1, Ochrobactrum anthropi X7, Pseudomonas sp. X3, and Pseudomonas delhiensis X5 exhibited high capacity in Cd (II)-removal from the cathodic chamber of MECs [103]. There are two main types of biocathodes: aerobic and anaerobic. Oxygen and inorganic compounds, such as nitrates and sulfates, are utilized as final electron acceptors in aerobic and anaerobic biocathodes, respectively. Pseudomonas sp. and Desulfovibrio sp. are examples of anaerobic electrotrophs [102], and Pseudomonas aeruginosa, Pseudomonas putrefaciens, Escherichia coli, Enterobacter cloacae, and Bacillus subtilis are well-known aerobic electrotrophs [104]. The cathodic electron transfer mechanisms have not been well understood compared to the involved mechanisms at the anode, although the results provide evidence of indirect and direct electron transfer in the cathodic chamber [104].

Microbiological concepts of MFCs

These results show different redox potentials of cathodic mediators/cytochromes compared to the anode-based shuttles/cytochromes. Besides electrotrophic bacteria, fungi can function as a cathode biocatalyst through production of enzymes catalyzing the reduction of oxygen. For instance, Trametes versicolor enables electron exchange in the cathodic chamber by producing oxidative enzymes. Wu et al. [105] investigated the potential of laccase-secreting white-rot fungus Trametes versicolor in promoting MFC performance. Continuous laccase secretion improved the resulting power density. The method was viewed as a potential alternative for costconsuming laccase isolation and purification.

2.4 Electron transport mechanisms Electrical current is generated due to the sustainable oxidation of an electron donor and reduction of an electron acceptor within MFCs. The involved oxidation is carried out by electroconductive microbes, and the process starts with biological oxidation of organics, producing a flow of electrons and protons, which are then transported toward the cathode to mediate a sustained power generation. Cathodes and anodes can be incorporated as either soluble or solid-state electron acceptors or donors. For instance, Geobacter species favor Fe(III) oxides as an insoluble electron acceptor [106,107]. The use of an insoluble electron acceptor or donor is consistent with electron transference from an intracellular electron donor toward the extracellular electron acceptor. Exoelectrogens donate electrons to an electron acceptor, while electrotrophs uptake electrons from electron donors, mediating an electrical current. Several approaches use the interactions of microorganisms with electrodes [108], such as MFCs, microbial electrolysis cell, and microbial electrosynthesis (MES). In an MFC, chemical energy embedded within organics is converted into electrical energy. Interaction between the biological oxidation of substrate at the anode and the chemical or biochemical reduction processes at the cathode generates a spontaneous electrical current. For example, biological oxidation of substrates at the anode and chemical or biological oxygen reduction at the cathode are also used for wastewater treatment in MFCs [109]. On the other hand, in an MEC, an electrical energy input power is converted into chemical energy (biotic H2). Furthermore, the third application of microbe-electrode interactions is biological production of CH4 [110] at the cathode through MES.

2.4.1 Mechanisms for delivering electrons to an anode A large variety of mixed microbial communities, enriched from sediments, anaerobic digesters, and wastewater (sludge), have shown excellent electron-donor ability [67]. Similarly, several pure cultures are also used for electron flow preparation in the anodic chamber [111]. Due to the electrogenic capacity of reducing solid-state electron

39

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Biological fuel cells

Fig. 2.1 Electron transport mechanisms in MFCs. Mechanisms for delivering electrons to an anode (A). Mechanisms for electron uptake from cathodes (B).

acceptors, Fe(III) reducers are well-known electron donors [112]. However, some of them are weak in Fe(III) reduction [34]. DET and MET are known as the major mechanisms for delivering electrons to an anode (Fig. 2.1). Some exoelectrogens enable both DET and MET mechanisms. For instance, Geobacter sulfurreducens and Pseudomonas oneidensis are the most frequently used exoelectrogens at the anode [113,114]. Geobacter sulfurreducens reduces the anode through the direct electron transfer mechanism, while Pseudomonas oneidensis has become an efficient electron delivery vehicle using the mediated electron transfer mechanism, although

Microbiological concepts of MFCs

studies show that Geobacter sulfurreducens is also capable of developing electron mediators [115] and that Pseudomonas oneidensis can contribute to the direct electron transfer mechanism [116,117]. Direct electron transfer (DET). In exoelectrogenic bacteria, c-type cytochromes and pili (nanowires) are involved in direct electron transference to a solid-state electron acceptor [68,118]. c-Type cytochromes are multiheme proteins located on the outer membrane of the bacteria [118]. The most promising application of c-type cytochromes lies in their ability to transport respiratory electrons in bacterial species. It is worth noting that several studies have been done to thoroughly elucidate cytochrome involvement in bacterial electron conduction. For instance, it was demonstrated that Geobacter sulfurreducens and Pseudomonas oneidensis are DET model organisms that utilize the OMC pathway [119–121] and Mtr pathway [122,123], respectively, for electron induction. Some exoelectrogens are capable of nanowire-based electron transference. Nanowires have been proven to be efficient electron delivery tools. Generally, on the base of electron transfer mechanisms, microbial wires are subdivided into three categories: (1) nanowires that mediate π-π interactions, (2) cytochrome-decorated nanowires, and (3) cable bacteria. Type-IV pili have been employed by Geobacter sulfurreducens, where overlapping π-π orbitals found in aromatic amino acids mediate electrical conductivity [123–126]. The pili was capable of inducing electron conductivity in the range from 37 to 199 mS cm 1 at pH 2 [125,127]. The π-π interactions are determined by the choice of environmental conditions such as temperature and pH [121,125,127,128]. Cytochrome-decorated nanowires can also be developed to transfer electrons through the outer membrane of Shewanella oneidensis [125,129]. The Msh (mannose-sensitive hemagglutinin) pili have been prepared by Shewanella oneidensis and employed for electron hopping from the cell membrane to an electron acceptor [117]. Cable bacteria are the third type of bacterial nanowires that involves multiple cells. In a study, long conductive cables containing Desulfobulbaceae bacteria were developed to oxidize sulfide in marine sediments [130]. The study confirmed a sustained electron transfer from sulfide-oxidizing bacteria to oxygen-reducing bacteria [131]. Besides electroactive bacteria, significant progress has been made toward fungi-based MFCs for the desired power production abilities. It is via redox-active fungal proteins that direct electron transfer in the anodic chamber is carried out [132,133]. Yeast has recently emerged as a promising candidate in facilitating electron transfer in the anodic chamber through cytochrome c [134]. It has been demonstrated that white-rot—wood fungi can degrade lignin [135,136], xenobiotic compounds and dyes [137] through an extracellular oxidative ligninolytic enzymatic system mostly containing oxidoreductases, such as laccases (EC 1.10.3.2), manganese peroxidases (MnPs, EC 1.11.1.13), and lignin peroxidases (LiP, EC 1.11.1.14). Mediated electron transfer (MET). MET is acknowledged extracellular electron transfer [138]. Secretion of a soluble electron shuttle aims to exchange electrons between

41

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Biological fuel cells

outer-membrane cytochromes and electron acceptors. To provide a sustainable synthesis of endogenous electron shuttles, the concentration range of electron shuttles must be kept at low levels. Artificial mediators also present a unique electron transference potential during power production in MFCs. Synthesis of electron shuttles starts where the high thickness of the biofilm impairs DET mechanisms [139]. Several electrogenic bacteria are able to use exogenous electron shuttles; however, Shewanella oneidensis and Pseudomonas aeruginosa are known as the most efficient producers. Several studies proved the capability of Shewanella oneidensis in the secretion of electron shuttles such as flavin mononucleotide and riboflavin [15,140,141]. Naturally, MET exerts up to 75% of EET in Shewanella oneidensis [140]. Phenazine production, specifically pyocyanin and phenazine-1-carboxamide, is mainly performed in Pseudomonas aeruginosa KRP1 culture media [14,15]. In aerobic conditions, pyocyanin mediates electron transference from lipids and carbohydrates to oxygen [142], while in an anaerobic culture, pyocyanin uses iron as a terminal electron acceptor [143]. Redox potentials of 275, 150, and 30 mV were reported for phenazine-1-carboxylic acid, phenazine-1-carboxamide, and pyocyanin, respectively [144,145]. Additionally, it was demonstrated that the mediators secreted by P. aeruginosa can be further utilized by other microorganisms in mixed microbial communities [146]. Used riboflavin in Geobacter sulfurreducens, Geothrix fermentans, Clostridium, and Alkaliphilus spp. cultures [147–149], and used flavin-like compounds in Tinctura Ferri acetic and some Bacillus sp. [150] are other examples of MET mechanisms. To overcome restrictions of endogenous electron shutter secretion, such as biofilm thickness, artificial mediators and supplemental natural mediators have been used to increase power production in MFCs [104,151]. The extracellular electron transfer route was reported to be an important property for artificial mediator utilization in microorganisms such as Escherichia coli, Pseudomonas, Proteus, and Bacillus spp. [152]. Thionine, benzylviologen, 2,6-dichlorophenolindophenol, 2-hydroxy-1,4-naphthoquinone, phenothiazines, phenoxoazines, iron chelates, and neutral red are examples of this type of extracellular electron transfer [153]. Application of artificial mediators presents several drawbacks, such as restricted energy conserved for growth and cell maintenance [152], costly commercial-scale systems, and cause environmental health risks when released into the environment. Based on the secretion of chemical reactants, manganese peroxidases (MnPs), cellobiose dehydrogenase (CDH), and extracellular oxidative ligninolytic enzymes have opened up the possibility of MET in yeast. CDH, a N-glycosylated peptide with two domains, has also begun to show significant utility as an electron mediator [154,155]. CDH has two domains: a small cytochrome domain (CYT) and a C-terminal flavodehydrogenase domain (DH) [156,157]. CDH oxidizes carbohydrates such as cellobiose, lactose, maltose, and glucose [157,158]. During such a process, two electrons result in

Microbiological concepts of MFCs

the DH domain and are transferred to the CYT domain by internal electron transfer [159]. CYT is used to deliver electrons directly into the targeted anode. In MnPs, the heme prosthetic group oxidizes Mn2+ into Mn3+. The contribution of chelating agents such as oxalic acid stabilizes Mn3+ ions. The developed Mn3+ ions exhibit higher reactivity and can act like redox mediators in this system [160,161].

2.4.2 Mechanisms for electron uptake from cathodes Nowadays, there are multiple reports of mixed communities and pure cultures used for electron uptake from the cathode. Electroconductive organisms also have a role in electron uptake at the cathode called electrotrophs [101]. Generally, there are two distinct types of biocathodes: aerobic and anaerobic. In the former, oxygen is utilized as the final electron acceptor by aerobic electrotrophs such as Pseudomonas aeruginosa, Shewanella putrefaciens, Escherichia coli, Enterobacter cloacae, Bacillus subtilis, etc. [104], while in anaerobic conditions inorganic compounds are used as final electron acceptors. Geobacter sp. [162], Pseudomonas sp., and Desulfovibrio sp. are examples of anaerobic electrotrophs [102]. Studies confirmed the involvement of both DET and MET mechanisms in electrode uptake from the cathode [104]. For instance, metal oxidation pathways have been recently introduced as involved DET mechanisms at the cathode. Autotrophic Sideroxydans lithotrophicus ES-1 utilizes CymA, MtoA, MtoB, and MtoD proteins to uptake electrons from Fe(II) [163,164]. Similarly, in Rhodopseudomonas palustris, TIE-1 oxidizes PioA and PioB oxidize Fe(II) and transfer electrons to PioC in the periplasm [165]. Furthermore, Acidithiobacillus ferrooxidans and Leptospirillum also benefited from the transfer electrons across the periplasm [166,167]. In contrast to the pure culture, in case of mixed culture, the exact mechanisms of electron transfer reactions in mixed culture are still unknown [168]. Fungi contain multiple oxidative enzymes, contributing in the electron exchange between the cathode and the electron acceptor, mainly oxygen. The most frequently used subtype of fungus is laccase-secreting fungi. Laccase has shown an extraordinary potential in mediating oxidation/reduction mechanisms at the cathodic chamber [169,170]. Laccase-secreting fungi continuously secrete laccase within the cathodic chamber through which the possibility of the enzyme activity inhibition is declined. The power density of an MFC inoculated with Tinea versicolor increased from 40 to 50 mW m 3 to 320  30 mW m 3. Tinea versicolor attenuates laccase deactivation by converting glucose into acetate. In another study, the performance of a MFC was investigated using laccase-secreting Ganoderma lucidum BCRC 36123 to promote the power density and simultaneous degradation of azo dye acid orange 7 (AO7) [171]. Azo dyes are found in the textile and paper industry wastewaters. The maximum power density of 207.74 mW m 2 has been reported at an AO7 concentration of 500 mg L 1.

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Biological fuel cells

2.4.3 Interspecies electron transfer through conductive minerals Similar to pure cultures, DET and MET are well-known interspecies electron transfer mechanisms in the study of mixed microbial communities. DET aims at contributing to enhance electron exchange reactions between two bacterial species in both aerobic and anaerobic conditions referred to as direct interspecies electron transfer [172]. Examples are the reactions done in anaerobic digesters and MFCs utilized mixed cultures as a biocatalyst [173]. Moreover, the function of conductive minerals in interspecies electron transfer has been broadly studied [174]. Natural conductive minerals such as pyrite, magnetite, and hematite can facilitate MFC operation through enhancing interspecies electron transfer [174]. Research on iron oxide minerals for increment of current densities has also been done in the past few years [172]. The study reported a power density in the range of 100 MW cm 2 in the presence of G. sulfurreducens and Thiobacillus denitrificans as biocatalysts.

2.5 Factors affecting the electron transfer mechanism There are various microbiological and electrochemical factors that can affect chemical and metabolical reactions within MFCs [139]. These factors determine the overall energy output of MFCs. Some of these factors are the biofilm integrity, the structure and composition of electrodes, and the types of electrolyte and electron mediators, which are presented below.

2.5.1 Biofilm integrity The incidence of biofilm formation by possible orders of mono-/multilayered arrangement has been found as an effective parameter to determine the efficiency of DET and MET in MFCs. The biofilm affects the diffusion of substrate molecules toward the anode [175] and subsequently kinetics of the electron transfer mechanisms. Electroactive species involved in DET may suffer from the restricted delivery of waste and nutrients, where the arrangement of the microbes is poor, although indirect electron transfer can be limited due to the lack of effective transport of soluble and mobile carriers [176], affected by biofilm integrity. Biofilm integrity depends on the distribution of both electroactive and nonelectroactive microbes. Electroactive species have been reported to enhance electron exchange interactions, while the pretense of nonelectroactive microbes disrupts the electron exchange mechanisms via consuming organics and other electron donors/acceptors. To improve MFC efficacy, nonelectroactive microbes such as methanogens, aerobic organisms, hydrogen scavengers, and nitrate reducers can be eliminated from the system [177]. Generally, the electrocatalytic function of a biofilm is affected by the source, nature, and type of inoculum, influent concentration, operating conditions, and structure and composition of electrodes.

Microbiological concepts of MFCs

2.5.2 Structure and composition of electrodes Many different types of electrode architectures have been used in MFCs. Electrodes provide a promising support for biofilm formation, electron exchange mechanisms, and electron transfer toward the cathodic chamber. A number of electrodes have been developed to illustrate the pivotal role of electrode configurations in the microbial metabolism and electron transfer across the biofilm and electrode matrix, and the most widely used ones are the flat, packed, stuffed, and brush models. Moreover, the surface roughness of the electrode is involved in electron propagation [178]. The flow-over or flow-through electrodes are the mostly used ones because of their potential in facilitating the pH gradient and feed concentration, as well as eliminating nonelectroactive microbes. Carbon nanostructures are preferred due to their high surface area, supporting biofilm formation [179]. The composition of electrodes can also be used to guide the electron transfer mechanism. Today, the nanomodification of anode electrodes has been possible for the improvement of electrode function. Upon modification, electrodes work in tandem with microbes and transfer electrons to orchestrate a sustainable power generation. Electrode modification, in which the anode or the cathode is improved in the surface characteristics, conductivity, and chemical stability, remains the gold standard [180]. To address this need, multiple methods have been investigated, including pulse electro-deposition, impregnation, coating, and immobilization [85]. The modified electrodes have the ability to promote extracellular electron transfer and electron uptake.

2.5.3 Electrolyte and electron mediators The availability of electron carriers in the electrolyte and substrate properties requires robust assessment to validate effective electron transfer mechanisms [139]. The high concentrated influent increases the acetogenesis and methanogenesis mechanisms which impair the electrocatalytic performance. Similarly, continued research into electron transfer mediators might profoundly enhance MFC performance. In the majority of studies, mediators were either metabolically synthesized [181] or artificially added into electrode chambers [182]. However, the high concentration of mediators can lead to impaired electrodes because of toxicity and instability.

2.6 Mechanism of biofilm formation in MFCs Besides providing electron conductivity, the anode contributes to the biofilm formation associated with the electron transfer between microorganisms and the electrode. Biofilm formation requires the development of microbial associations on an inert surface followed by adherence to by microbial secreted polymers called exopolysaccharides (EPS). Natural biofilms might contain a variety of microbial species, including bacteria, fungi, algae, protozoa, etc. Quorum sensing provides cell-cell interactions within the biofilm matrix.

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Fig. 2.2 Mechanism of biofilm formation in MFCs. Fungal biofilm formation (A). Bacterial biofilm formation (B).

Today, biofilms are pivotal utilities of various bioremediation techniques, wastewater treatment, metal leaching, and bio-electrochemical systems. Biofilm formation includes a cascade of five stages (Fig. 2.2). In the first stage, microbes move toward a biotic surface [183] either by actively swimming or through other weak forces, including Brownian motion, gravitational and van der Waals forces, etc. Additionally, a continuous-flow condition could effectively bring the microbes closer to the electrode surface. The surface properties of the electrode are critical for the microorganism’s adhesion and viability. In the second stage, slender appendages of the cells, pili, fimbriae, and flagella provide a reversible attachment of the microbes on the surface. Subsequently, various phenotypic changes in the cells lead to irreversible microbial attachment on the material surface. Then the maturation of the biofilm occurs through microbial secretion of EPS. The types of microbial content are responsible for the different compositions of EPS [184]. Some studies have highlighted that the EPS matrix can provide physical and chemical stability for microorganisms under various environmental stresses.

2.7 Factors affecting biofilm formation and performance Biofilm is an interface between the anodic electrode and the environment, providing effective electron transfer from the microorganisms to the electrode. System

Microbiological concepts of MFCs

Fig. 2.3 Factors affecting electron transfer and biofilm formation in MFCs.

configuration, operating conditions, and biological parameters are involved in the biofilm format and performance [185] (Fig. 2.3).

2.7.1 System configuration Electrode material, type of membrane, and reactor design have been described as the three main structural components of MFCs, by far the most prevalent factors responsible for biofilm formation and the final power output. Electrode material. It has been demonstrated that electrode material is likely involved in effective anaerobic respiration through providing the substratum for biofilm growth and electron exchange. Carbon-based electrodes, polymer-based electrodes, and metal-based electrodes are the most prevalent materials [186–188]. However, the use of metal-based electrodes on a large scale is limited because of economic issues. It is becoming increasingly evident that the type of material determines the morphology of bioelectrodes, including porosity, hydrophobicity, conductivity, charge, etc. Studies have suggested the porosity of electrodes to be associated with providing more space for the attachment and growth of microbes. Moreover, electroactive microbes, which form conductive biofilms, are more selective toward the positively charged and hydrophilic electrodes [189].

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The most prevalent electroactive bacteria in nature, Gram-negative bacteria, offer the potential to enhance electrostatic interactions with the positively charged electrode surface. Additionally, the hydrophilic electrode surface has proved effective in the formation of hydrogen bonds that increase the attachment of the planktonic bacteria [189]. Several surface modification studies have surveyed the bacterial adhesion enhancement associated with electrode surface modification [190–192]. Increased current densities have also recently validated using surface modification approaches, including heat treatment, electrochemical oxidation, acid soaking, nanoparticle loading, etc. What is evident is that this increment in current density is driven by improvement in the surface area, improved biocompatibility, or improved electron transfer. While there are so many reports on biocompatible electrodes to date, the challenges in bacterial cell-electrode surface interactions and the lack of cost-effective surface modification techniques are still unsolved problems [193,194]. Type of membrane. MFC apparatus can be designed both with and without membranes. In MFCs, the membrane accounts for electroneutrality between the two chambers. Power output is significantly correlated with the type and surface characteristics of the membrane [195]. This indicates that there is the type of membrane that influences the type of ion transferred and validates the pH of the electrolytes. For instance, it is observed that the catholyte solution is dominated by Na+, K+, Ca2+, and Mg2+ cations instead of protons when using Nafion 117, increasing the pH at the cathode compared to the anode [196]. Such pH fluctuations in broad functionality likely affect the biofilm growth and structure. Reactor design. In addition to the functional features of the substrate, electrode, and membrane, there are many reactor design characteristics that can influence biofilm formation and performance, among which the scale of an MFC system is the most important one. It is known that a typical scale study of MFC systems has resulted in a wide range of reactor scale diversities, ranging from microliters up to 1000 L [197]. Generally, there are multiple factors that influence the electron exchange between the microbes and the electrode, including diffusion of substrates/products, electron transfer rate, and biofilm thickness, all of which are affected by the scale of the MFC systems. It is plausible to consider the differences in biofilm formation capacity between the microenvironment and other niches. Studies have reported a greater preference for biofilm formation in microenvironments [198], probably due to the higher throughput, shorter start-up times, and declined substrate consumption rate [199,200]. The major drawback of the miniature MFCs is the low current output that restricts their commercialization. For wastewater treatment and bioremediation applications, large-scale MFCs are required, which suggests that they contain highly electroactive species. Thus, most knowledge of the MFC systems has been obtained through screening of the electroactive species using miniature MFCs followed by their large-scale studies.

Microbiological concepts of MFCs

2.7.2 Operating parameters Since microorganisms and electrode materials can be affected by environmental conditions, different physiochemical parameters such as pH, temperature, substrate, and ion concentration should be adjusted to achieve the desired energy outputs [189]. pH: Anodic pH determines the overall power production and proton consumption. Anodic pH has become an essential operating parameter as it can directly affect biofilm formation and structure [201]. Alteration of microbial metabolism caused by sensitivity to the surrounding pH, because of changes in the cytoplasmic electrochemical gradient, is one of the major challenges facing the MFC. Besides this, the membrane potential and proton motive force are intensely affected by pH variation [201]. It was found that at neutral (7) or near-neutral (6–8) pH ranges, the MFC apparatus can effectively maintain the electrical potential. When used as a substrate, wastewater alters the pH at different time intervals, which leads to change in the microbial community and power outputs during MFC operation [201]. Therefore, monitoring the pH of the system periodically to sustain an optimum pH is proposed for improving the longevity of microbial communities. In a study, the efficiency of an MFC apparatus enriched with sulfate-reducing bacteria on voltage generation and Cu2+ removal from domestic wastewater at different pHs was investigated [202]. At 4–6 pH range, more than 90% of Cu2+ removal was reported within 12 h; however, the removal efficiency dropped to 55% at pH 3. Similarly, the produced voltage was reduced to 29% by decreasing the pH from 6 to 4. Furthermore, a 60% decrement in voltage was reported at pH 3. The results showed that the function of the sulfate-reducing bacteria is greatly affected by the pH of the electrolyte. The addition of an acid/alkali, the use of buffers, and the application of anion exchange membranes are gaining increasing attention as they offer the advantage of ideally mineralizing pH changes during the MFC operation. However, the addition of an acid/alkali is costly and the researches mostly use buffer [203] or anion exchange membranes [204] to overcome economic challenges. Temperature: Studies show that the growth and electrocatalytic activity of biofilms are also sensitive to temperature. Temperature variation can bring changes in biofilm physical integrity because it does alter the kinetics and thermodynamics of the anodic chamber’s reactions [205]. Furthermore, it was found that various microbial communities have different temperature preferences, namely psychrophiles (40°C), among which mesophiles are gaining increasing attention [206], as they are highly effective electroactive microbes. However, some psychrophiles and thermophiles also possess electroactive properties [207]. In a study, we evaluated the potential of temperature changes in the power generation and phenol removal efficiency of a mixed-culture biofilm [208]. A GAC-Adsorption/MFC combined system (GAMFC) was designed and inoculated with activated sludge prepared from an industrial wastewater treatment plant. To find the optimal temperature, the

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system was operated at 25°C, 30°C, 35°C, and 45°C. The highest removal percentage and power density were found at 35°C; however, the system performance decreased at 45°C. This was accompanied by the dominance of the thermophilic microbial community, possessing the maximum growth rate in the range of 35–40°C. Thus, temperature has a significant effect on the growth and electrocatalytic activity of biofilms. Substrate concentration: In MFCs, biofilms are subjected to diverse substrates, including simple sugars, complex carbohydrates, artificial and real wastewater, lignocellulosic biomass, etc. [209]. The nature and concentration of substrates determine the dominant functioning microbial community in the anodic chamber. Moreover, substrate concentration accounts for the power generation capacity and is linked to biofilm functionalities. In order to determine the influence of substrate type and concentration on the current density, we used an MFC system inoculated with Saccharomyces cerevisiae. The system was fed with either simple sugars (glucose, fructose, and sucrose) or complex carbohydrates (molasses and date syrup) with both high (10, 20, 30, and 40 g L 1) and low (1–7 g L 1) concentrations. It was found that power generation is consistent with the microbial growth rate. Date syrup and molasses were treated with acidic-basic hydrolysis and achieved maximum power densities of 65 and 59.97 mW m 2, respectively. As seen in Fig. 2.4, date syrup has a high potential of power production at 6 g L 1 concentration. However, compared with molasses, the earlier voltage drop was obtained for date syrup due to the higher rate of microbial oxidation. Sucrose is not suitable for power generation in fuel cells with Saccharomyces cerevisiae, but it is still capable of generating electrical power. It has been shown that high-range substrates are detrimental for microbial

Fig. 2.4 Power density production conducted by Saccharomyces cerevisiae at optimal concentrations of glucose, fructose, sucrose, date syrup, and molasses.

Microbiological concepts of MFCs

Table 2.2 Illustrating the impact of mixing and cathode aeration on potential current density in MFCs. Without agitation

Power density Current density

25 mW m 120 mA m

2 2

200 rpm

35 mW m 145 mA m

400 rpm 2 2

28 mW m 140 mA m

600 rpm 2 2

19 mW m 110 mA m

2 2

communities caused by the effect of substrate inhibition. Sufficient electron release from substrate oxidation tends to favor high coulombic efficiencies. The phenomenon is linked to the presence of intermediate compounds as a certain number of electrons can be consumed by such materials, reducing the overall power output. Furthermore, these intermediate compounds can be toxic for biofilm growth and negatively affect power generation. Other factors: The effects of external resistance, mixing and shear rate, and cathodic dissolved oxygen concentration on biofilm performance are also investigated [210]. Our results demonstrated that a minimum mixing rate is required to prevent from precipitation of biocatalysts and electron mediators, as seen in Table 2.2. Moreover, we confirmed the significant effect of cathode aeration on enhancing the overall current densities at the anode through supporting the kinetics of microbial reduction. However, some studies have reported that the use of oxygen as a terminal electron acceptor at the cathodic chamber can decrease biofilm activity. Such an issue is due to the oxygen diffusion from the cathode to the anode, which changes the microbial community dynamics toward facultative anaerobes that favor a low-oxygen environment. Moreover, controlling the anode potential would play a key role in increasing the electroconductivity of biofilms [211].

2.7.3 Biological parameters Type and source of inoculum, the growth rate of microorganisms, and the electron transfer mechanisms are the most influential factors which affect biofilm formation. Type and source of inoculum: Electroactive biofilms revolutionized the field of MFCmediated electricity production by providing electrogenic activities. Gram-negative bacteria are still the most prevalent used organisms [212]. The choice is on the basis of cell wall composition [213]. The lipopolysaccharide layer (the outermost layer of the cell wall in Gram-negative bacteria) contributes to providing negative charges on the cell membrane which interact with the surface charges on the electrodes. Biofilms can represent an ideal community of either monoculture or mixed species [214] given that the type of species determines the microcolonization of the organisms. The source of inoculum determines the nature of the biofilm and the dominant species in MFCs. For instance, wastewater, anaerobic sludge, and river/marine sediments are the frequently used sources of mixed species [215]. Mixed species are employed in

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wastewater treatment applications, while pure cultures are preferred for selective applications such as biosensors [216]. The outputs of MFCs are also associated with the number of electroactive species present. The more electroactive species there are, the more flux of protons and electrons is resulted in the substrate degradation process. Excellent results in terms of electron flows have been achieved with mixed culture biofilms compared to MFC systems containing pure cultures. However, the use of mixed communities is associated with major drawbacks such as inconsistency. Microbe-electrode interaction: As mentioned in Section 2.3, the desired MFC output takes advantage of the interaction between the microbes and the electrode surface. Such an interaction can be improved through the use of cathodic and anodic electron mediators. Despite the unique capability of exoelectrogens to transfer electrons from the anolyte to the solid electrodes, the low power output caused by the slow electron transfer between the bacteria and the anode is frequently reported as a major barrier of BES performance. Electron donors can be used to stimulate electron transfer between the exoelectrogens and the anode. In a study, we examined how electron donors can affect the electrochemical performance of the electrogenic biofilm. Saccharomyces cerevisiae and glucose were used as the biocatalyst and the substrate, respectively. As seen in Fig. 2.5, optimal concentrations of ferric iron (400 M mol L 1), thionine (500 M mol L 1), neutral red (200 M mol L 1), and methylene blue (300 M mol L 1) resulted in a sharp increment in

Fig. 2.5 Illustrating the impact of electron donors-including ferric iron, thionine, neutral red, and methylene blue—and electron acceptors—including potassium ferricyanide and potassium permanganate on the overall MFC power generation, using Saccharomyces cerevisiae as the biocatalyst.

Microbiological concepts of MFCs

electron conductivity and overall power generation, among which 250 M mol L 1 neutral red achieved the highest bioanode current density. Similarly, the role of electron acceptors on the overall cathodic performance and the resultant current density was investigated. Our study sought to use cathodic oxidizing agents to increase the potential electrical current production. As seen in Fig. 2.5, ferricyanide and permanganate showed a higher open circuit potential and increased power density in optimal concentrations of 250 and 500 M mol L 1, respectively. This could be attributed to the higher open circuit potential (OCP) provided by permanganate in the MFC. Inter- and intraspecies interactions: Researches have shown that mixed-culture biofilms utilize both direct and mediator-based electron transfer mechanisms to perform power generation [217]. Furthermore, interspecies interactions have been confirmed within electroactive mixed-cultures [218]. These interactions can increase the power generation capacity of MFCs [219]. For instance, it has been demonstrated that Quorum sensing is utilized for providing a communication link between different bacteria species. The advantages of Quorum sensing chemicals are enhancing the microbial coordination behavior and modulating the expression of biofilm-related genes [185]. Syntrophic interactions via bacterial nanowires can also perform electron conductivity [109]. Although the study of interspecies symbiotic interactions has been developed, especially in fermentative processes, the interactions still cannot meet the actual understanding in MFC cases. Hence, further investigations are required to study synergistic interactions within electroactive communities of MFC systems.

2.8 Genetic approaches for improving the performance of MFCs Genetic engineering of electroactive microorganisms has the advantage of high MFC performance. The goal of genetic manipulation is generally to modify metabolic pathways and to express enzymes and proteins with special properties and functions. Recent results show that genetic engineering of exoelectrogens exhibits fascinating electricity production associated with producing specific molecules. For instance, through genetic manipulation, Shewanella oneidensis MR-1 exhibits flavin biosynthesis at a similar range to that of Bacillus subtilis [220]. Moreover, it is possible to shift laboratory models such as Escherichia coli and Saccharomyces cerevisiae to exoelectrogenic microorganisms using genetic manipulation. These types of microbes are selected because they are known to be easily manipulated, their genome is well understood, and they possess fast and easy growth. In MFCs, metabolic engineering is associated with promoting the overall electron flux. Both NAD+ and NADH are major electron carriers in the cell. The ratio of NAD+/NADH plays critical roles in the enzymatic activity and energy flux of the microorganisms [220,221]. For MFCs, utilizing metabolic engineering methods in order to

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alter the NAD+/NADH ratio can increase the power generation density. In a study, engineering the NAD salvage pathway changed the ratio of NAD (H+) and NAD+/ NADH in Escherichia coli [222]. The NAD salvage pathway can recycle NAD+/NADH in the cell. By overexpression of the pncB gene, encoding the nicotinic acid phosphoribosyltransferase, the amount of NAD (H+) in a DH10B culture was doubled. Another strategy of metabolic engineering for improving MFC performance could be the triggered adhesion of exoelectrogens to the electrode surface. Kouzuma et al. studied the deletion of the SO3177 gene in Shewanella oneidensis, modulating the surface biosynthesis of formyltransferase [223]. The ΔSO3177 mutant resulted in 50% more current generation compared to the control. This example demonstrates the advantage of making a microbial hydrophobic surface as a result of polysaccharide capsule impairment, increasing microbial attachment to carbon-based electrodes. Enzyme and protein engineering utilize engineered pilin and protein immobilization to promote MFC efficiency. Bacterial pili are conductive structures that can be used for DNA transfer [224], DNA binding [225], surface attachment [226], cell-cell adhesion [227] and for exogenous electron transfer [9]. It was found that a broad application of engineering more conductive pili will be possible through the manipulation of π-π stacking interactions between aromatic amino acids at a folded state of pili [228]. A 500-fold increment in conductivity of the self-assembled pili confirmed the correlation between the pili conductivity and the aromatic residues along the axis.

2.9 Conclusions In the last two decades, the power output of MFCs has been significantly improved due to the increasing knowledge of electron transfer mechanisms. This is also because of beneficial researches on novel biocatalysts and electrocatalysts that are predicted as efficient electron transfer promoters in MFCs, although modulating sufficient power density has remained the main issue of MFC applications in energy storage and portable power supply. Studies on improvement of durability and using cost-effective components can contribute to MFC valuation and facilitate its commercialization.

References [1] Y.P. Afsharian, M. Rahimnejad, Functional dynamics of microbial communities in bioelectrochemical systems: the importance of eco-electrogenic treatment of complex substrates, Curr. Opin. Electrochem. 31 (2022), 100816. [2] B.S. Thapa, T. Kim, S. Pandit, Y.E. Song, Y.P. Afsharian, M. Rahimnejad, J.R. Kim, S.-E. Oh, Overview of electroactive microorganisms and electron transfer mechanisms in microbial electrochemistry, Bioresour. Technol. (2021) 126579. [3] R. Kumar, L. Singh, A. Zularisam, Exoelectrogens: recent advances in molecular drivers involved in extracellular electron transfer and strategies used to improve it for microbial fuel cell applications, Renew. Sustain. Energy Rev. 56 (2016) 1322–1336.

Microbiological concepts of MFCs

[4] N.J. Kotloski, J.A. Gralnick, Flavin electron shuttles dominate extracellular electron transfer by Shewanella oneidensis, MBio 4 (2013). [5] E.D. Brutinel, J.A. Gralnick, Shuttling happens: soluble flavin mediators of extracellular electron transfer in Shewanella, Appl. Microbiol. Biotechnol. 93 (2012) 41–48. [6] A.R. Rahmani, N. Navidjouy, M. Rahimnejad, S. Alizadeh, M.R. Samarghandi, D. Nematollahi, Effect of different concentrations of substrate in microbial fuel cells toward bioenergy recovery and simultaneous wastewater treatment, Environ. Technol. (2020) 1–9. [7] M. Shabani, M. Ponti
e, H. Younesi, M. Nacef, A. Rahimpour, M. Rahimnejad, R.M. Bouchenak Khelladi, Biodegradation of acetaminophen and its main by-product 4-aminophenol by Trichoderma harzianum versus mixed biofilm of Trichoderma harzianum/Pseudomonas fluorescens in a fungal microbial fuel cell, J. Appl. Electrochem. 51 (2021) 581–596. [8] D.R. Bond, D.R. Lovley, Electricity production by Geobacter sulfurreducens attached to electrodes, Appl. Environ. Microbiol. 69 (2003) 1548–1555. [9] G. Reguera, K.D. McCarthy, T. Mehta, J.S. Nicoll, M.T. Tuominen, D.R. Lovley, Extracellular electron transfer via microbial nanowires, Nature 435 (2005) 1098–1101. [10] G. Reguera, K.P. Nevin, J.S. Nicoll, S.F. Covalla, T.L. Woodard, D.R. Lovley, Biofilm and nanowire production leads to increased current in Geobacter sulfurreducens fuel cells, Appl. Environ. Microbiol. 72 (2006) 7345–7348. [11] N.T. Trinh, J.H. Park, B.-W. Kim, Increased generation of electricity in a microbial fuel cell using Geobacter sulfurreducens, Korean J. Chem. Eng. 26 (2009) 748–753. [12] B. Min, S. Cheng, B.E. Logan, Electricity generation using membrane and salt bridge microbial fuel cells, Water Res. 39 (2005) 1675–1686. [13] J.A. Smith, D.R. Lovley, P.-L. Tremblay, Outer cell surface components essential for Fe (III) oxide reduction by Geobacter metallireducens, Appl. Environ. Microbiol. 79 (2013) 901–907. [14] K. Rabaey, N. Boon, S.D. Siciliano, M. Verhaege, W. Verstraete, Biofuel cells select for microbial consortia that self-mediate electron transfer, Appl. Environ. Microbiol. 70 (2004) 5373–5382. [15] K. Rabaey, N. Boon, M. H€ ofte, W. Verstraete, Microbial phenazine production enhances electron transfer in biofuel cells, Environ. Sci. Technol. 39 (2005) 3401–3408. [16] Y.-C. Yong, Y.-Y. Yu, C.-M. Li, J.-J. Zhong, H. Song, Bioelectricity enhancement via overexpression of quorum sensing system in Pseudomonas aeruginosa-inoculated microbial fuel cells, Biosens. Bioelectron. 30 (2011) 87–92. [17] L. Yang, W. Deng, Y. Zhang, Y. Tan, M. Ma, Q. Xie, Boosting current generation in microbial fuel cells by an order of magnitude by coating an ionic liquid polymer on carbon anodes, Biosens. Bioelectron. 91 (2017) 644–649. [18] H.J. Kim, H.S. Park, M.S. Hyun, I.S. Chang, M. Kim, B.H. Kim, A mediator-less microbial fuel cell using a metal reducing bacterium, Shewanella putrefaciens, Enzyme Microb. Technol. 30 (2002) 145–152. [19] D. Park, J. Zeikus, Impact of electrode composition on electricity generation in a single-compartment fuel cell using Shewanella putrefaciens, Appl. Microbiol. Biotechnol. 59 (2002) 58–61. [20] B.R. Ringeisen, E. Henderson, P.K. Wu, J. Pietron, R. Ray, B. Little, J.C. Biffinger, J.M. JonesMeehan, High power density from a miniature microbial fuel cell using Shewanella oneidensis DSP10, Environ. Sci. Technol. 40 (2006) 2629–2634. [21] J.C. Biffinger, J. Pietron, R. Ray, B. Little, B.R. Ringeisen, A biofilm enhanced miniature microbial fuel cell using Shewanella oneidensis DSP10 and oxygen reduction cathodes, Biosens. Bioelectron. 22 (2007) 1672–1679. [22] J.C. Biffinger, J. Pietron, O. Bretschger, L.J. Nadeau, G.R. Johnson, C.C. Williams, K.H. Nealson, B.R. Ringeisen, The influence of acidity on microbial fuel cells containing Shewanella oneidensis, Biosens. Bioelectron. 24 (2008) 900–905. [23] A.K. Manohar, O. Bretschger, K.H. Nealson, F. Mansfeld, The use of electrochemical impedance spectroscopy (EIS) in the evaluation of the electrochemical properties of a microbial fuel cell, Bioelectrochemistry 72 (2008) 149–154. [24] T. Yin, H. Li, L. Su, S. Liu, C. Yuan, D. Fu, The catalytic effect of TiO2 nanosheets on extracellular electron transfer of Shewanella loihica PV-4, Phys. Chem. Chem. Phys. 18 (2016) 29871–29878.

55

56

Biological fuel cells

[25] C.M. Ding, M.L. Lv, Y. Zhu, L. Jiang, H. Liu, Wettability-regulated extracellular electron transfer from the living organism of Shewanella loihica PV-4, Angew. Chem. Int. Ed. 54 (2015) 1446–1451. [26] Y. Zou, C. Xiang, L. Yang, L.-X. Sun, F. Xu, Z. Cao, A mediatorless microbial fuel cell using polypyrrole coated carbon nanotubes composite as anode material, Int. J. Hydrogen Energy 33 (2008) 4856–4862. [27] T. Zhang, C. Cui, S. Chen, X. Ai, H. Yang, P. Shen, Z. Peng, A novel mediatorless microbial fuel cell based on direct biocatalysis of Escherichia coli, Chem. Commun. (2006) 2257–2259. [28] D.H. Park, J.G. Zeikus, Electricity generation in microbial fuel cells using neutral red as an electronophore, Appl. Environ. Microbiol. 66 (2000) 1292–1297. [29] Y. Qiao, C.M. Li, S.-J. Bao, Z. Lu, Y. Hong, Direct electrochemistry and electrocatalytic mechanism of evolved Escherichia coli cells in microbial fuel cells, Chem. Commun. (2008) 1290–1292. [30] D.E. Holmes, D.R. Bond, D.R. Lovley, Electron transfer by Desulfobulbus propionicus to Fe (III) and graphite electrodes, Appl. Environ. Microbiol. 70 (2004) 1234–1237. [31] K. Rabaey, K. Van de Sompel, L. Maignien, N. Boon, P. Aelterman, P. Clauwaert, L. De Schamphelaire, H.T. Pham, J. Vermeulen, M. Verhaege, Microbial fuel cells for sulfide removal, Environ. Sci. Technol. 40 (2006) 5218–5224. [32] S.K. Chaudhuri, D.R. Lovley, Electricity generation by direct oxidation of glucose in mediatorless microbial fuel cells, Nat. Biotechnol. 21 (2003) 1229–1232. [33] J. Luo, J. Yang, H. He, T. Jin, L. Zhou, M. Wang, M. Zhou, A new electrochemically active bacterium phylogenetically related to Tolumonas osonensis and power performance in MFCs, Bioresour. Technol. 139 (2013) 141–148. [34] Y. Zuo, D. Xing, J.M. Regan, B.E. Logan, Isolation of the exoelectrogenic bacterium Ochrobactrum anthropi YZ-1 by using a U-tube microbial fuel cell, Appl. Environ. Microbiol. 74 (2008) 3130–3137. [35] L. Zeng, L. Zhang, W. Li, S. Zhao, J. Lei, Z. Zhou, Molybdenum carbide as anodic catalyst for microbial fuel cell based on Klebsiella pneumoniae, Biosens. Bioelectron. 25 (2010) 2696–2700. [36] J. Menicucci, H. Beyenal, E. Marsili, R.A. Veluchamy, G. Demir, Z. Lewandowski, Procedure for determining maximum sustainable power generated by microbial fuel cells, Environ. Sci. Technol. 40 (2006) 1062–1068. [37] A. Rhoads, H. Beyenal, Z. Lewandowski, Microbial fuel cell using anaerobic respiration as an anodic reaction and biomineralized manganese as a cathodic reactant, Environ. Sci. Technol. 39 (2005) 4666–4671. [38] V. Fedorovich, M.C. Knighton, E. Pagaling, F.B. Ward, A. Free, I. Goryanin, Novel electrochemically active bacterium phylogenetically related to Arcobacter butzleri, isolated from a microbial fuel cell, Appl. Environ. Microbiol. 75 (2009) 7326–7334. [39] J. Niessen, U. Schr€ oder, F. Scholz, Exploiting complex carbohydrates for microbial electricity generation—a bacterial fuel cell operating on starch, Electrochem. Commun. 6 (2004) 955–958. [40] D. Xing, Y. Zuo, S. Cheng, J.M. Regan, B.E. Logan, Electricity generation by Rhodopseudomonas palustris DX-1, Environ. Sci. Technol. 42 (2008) 4146–4151. [41] Y. Cho, T. Donohue, I. Tejedor, M. Anderson, K. McMahon, D. Noguera, Development of a solarpowered microbial fuel cell, J. Appl. Microbiol. 104 (2008) 640–650. [42] A.L. Walker, C.W. Walker Jr., Biological fuel cell and an application as a reserve power source, J. Power Sources 160 (2006) 123–129. [43] D. Permana, D. Rosdianti, S. Ishmayana, S.D. Rachman, H.E. Putra, D. Rahayuningwulan, H.R. Hariyadi, Preliminary investigation of electricity production using dual chamber microbial fuel cell (dcMFC) with Saccharomyces cerevisiae as biocatalyst and methylene blue as an electron mediator, Procedia Chem. 17 (2015) 36–43. [44] A. Gunawardena, S. Fernando, F. To, Performance of a yeast-mediated biological fuel cell, Int. J. Mol. Sci. 9 (2008) 1893–1907. [45] E.T. Kasem, T. Tsujiguchi, N. Nakagawa, Effect of metal modification to carbon paper anodes on the performance of yeast-based microbial fuel cells part Ι: in the case without exogenous mediator, Key Eng. Mater. (2013) 76–81. Trans Tech Publ. [46] M. Christwardana, Y. Kwon, Yeast and carbon nanotube based biocatalyst developed by synergetic effects of covalent bonding and hydrophobic interaction for performance enhancement of membraneless microbial fuel cell, Bioresour. Technol. 225 (2017) 175–182.

Microbiological concepts of MFCs

[47] S. Wilkinson, J. Klar, S. Applegarth, Optimizing biofuel cell performance using a targeted mixed mediator combination, Electroanalysis 18 (2006) 2001–2007. [48] M. Rahimnejad, G.D. Najafpour, A.A. Ghoreyshi, F. Talebnia, G.C. Premier, G. Bakeri, J.R. Kim, S.-E. Oh, Thionine increases electricity generation from microbial fuel cell using Saccharomyces cerevisiae and exoelectrogenic mixed culture, J. Microbiol. 50 (2012) 575–580. [49] R. Ganguli, B. Dunn, Kinetics of anode reactions for a yeast-catalysed microbial fuel cell, Fuel Cells 9 (2009) 44–52. [50] M. Rahimnejad, A.A. Ghoreyshi, G. Najafpour, T. Jafary, Power generation from organic substrate in batch and continuous flow microbial fuel cell operations, Appl. Energy 88 (2011) 3999–4004. [51] S. Fishilevich, L. Amir, Y. Fridman, A. Aharoni, L. Alfonta, Surface display of redox enzymes in microbial fuel cells, J. Am. Chem. Soc. 131 (2009) 12052–12053. [52] I. Gal, O. Schlesinger, L. Amir, L. Alfonta, Yeast surface display of dehydrogenases in microbial fuelcells, Bioelectrochemistry 112 (2016) 53–60. [53] S.V. Raghavulu, R.K. Goud, P. Sarma, S.V. Mohan, Saccharomyces cerevisiae as anodic biocatalyst for power generation in biofuel cell: influence of redox condition and substrate load, Bioresour. Technol. 102 (2011) 2751–2757. [54] E.T. Sayed, T. Tsujiguchi, N. Nakagawa, Catalytic activity of Baker’s yeast in a mediatorless microbial fuel cell, Bioelectrochemistry 86 (2012) 97–101. [55] M. Rahimnejad, G. Najafpour, A. Ghoreyshi, M. Shakeri, H. Zare, Methylene blue as electron promoters in microbial fuel cell, Int. J. Hydrogen Energy 36 (2011) 13335–13341. [56] R. Arbianti, H. Hermansyah, T.S. Utami, N.C. Zahara, I. Trisnawati, E. Kristin, The usage of Saccharomyces cerevisiae in microbial fuel cell system for electricity energy production, Iran. J. Chem. Chem. Eng. 6 (2012) 814. [57] M. Rahimnejad, M. Ghasemi, G. Najafpour, M. Ismail, A. Mohammad, A. Ghoreyshi, S.H. Hassan, Synthesis, characterization and application studies of self-made Fe3O4/PES nanocomposite membranes in microbial fuel cell, Electrochim. Acta 85 (2012) 700–706. [58] N. Birjandi, H. Younesi, A.A. Ghoreyshi, M. Rahimnejad, Electricity generation, ethanol fermentation and enhanced glucose degradation in a bio-electro-Fenton system driven by a microbial fuel cell, J. Chem. Technol. Biotechnol. 91 (2016) 1868–1876. [59] Y. Hubenova, M. Mitov, Potential application of Candida melibiosica in biofuel cells, Bioelectrochemistry 78 (2010) 57–61. [60] S. Babanova, Y. Hubenova, M. Mitov, Influence of artificial mediators on yeast-based fuel cell performance, J. Biosci. Bioeng. 112 (2011) 379–387. [61] Y.V. Hubenova, R.S. Rashkov, V.D. Buchvarov, M.H. Arnaudova, S.M. Babanova, M.Y. Mitov, Improvement of yeast–biofuel cell output by electrode modifications, Ind. Eng. Chem. Res. 50 (2011) 557–564. [62] N.D. Haslett, F.J. Rawson, F. Barrie¨re, G. Kunze, N. Pasco, R. Gooneratne, K.H. Baronian, Characterisation of yeast microbial fuel cell with the yeast Arxula adeninivorans as the biocatalyst, Biosens. Bioelectron. 26 (2011) 3742–3747. [63] Y.-Y. Lee, T.G. Kim, K.-S. Cho, Isolation and characterization of a novel electricity-producing yeast, Candida sp. IR11, Bioresour. Technol. 192 (2015) 556–563. [64] D.R. Lovley, S.J. Giovannoni, D.C. White, J.E. Champine, E. Phillips, Y.A. Gorby, S. Goodwin, Geobacter metallireducens gen. nov. sp. nov., a microorganism capable of coupling the complete oxidation of organic compounds to the reduction of iron and other metals, Arch. Microbiol. 159 (1993) 336–344. [65] D.R. Bond, D.E. Holmes, L.M. Tender, D.R. Lovley, Electrode-reducing microorganisms that harvest energy from marine sediments, Science 295 (2002) 483–485. [66] T. Mehta, M.V. Coppi, S.E. Childers, D.R. Lovley, Outer membrane c-type cytochromes required for Fe (III) and Mn (IV) oxide reduction in Geobacter sulfurreducens, Appl. Environ. Microbiol. 71 (2005) 8634–8641. [67] K.P. Nevin, H. Richter, S. Covalla, J. Johnson, T. Woodard, A. Orloff, H. Jia, M. Zhang, D. Lovley, Power output and columbic efficiencies from biofilms of Geobacter sulfurreducens comparable to mixed community microbial fuel cells, Environ. Microbiol. 10 (2008) 2505–2514.

57

58

Biological fuel cells

[68] H. Yi, K.P. Nevin, B.-C. Kim, A.E. Franks, A. Klimes, L.M. Tender, D.R. Lovley, Selection of a variant of Geobacter sulfurreducens with enhanced capacity for current production in microbial fuel cells, Biosens. Bioelectron. 24 (2009) 3498–3503. [69] T. Zhang, T.S. Bain, K.P. Nevin, M.A. Barlett, D.R. Lovley, Anaerobic benzene oxidation by Geobacter species, Appl. Environ. Microbiol. 78 (2012) 8304–8310. [70] P.L. Tremblay, M. Aklujkar, C. Leang, K.P. Nevin, D. Lovley, A genetic system for Geobacter metallireducens: role of the flagellin and pilin in the reduction of Fe (III) oxide, Environ. Microbiol. Rep. 4 (2012) 82–88. [71] K.H. Nealson, A.R. Rowe, Electromicrobiology: realities, grand challenges, goals and predictions, J. Microbial. Biotechnol. 9 (2016) 595–600. [72] Z. Lv, Y. Chen, H. Wei, F. Li, Y. Hu, C. Wei, C. Feng, One-step electrosynthesis of polypyrrole/ graphene oxide composites for microbial fuel cell application, Electrochim. Acta 111 (2013) 366–373. [73] J.S. McLean, G. Wanger, Y.A. Gorby, M. Wainstein, J. McQuaid, S.I. Ishii, O. Bretschger, H. Beyenal, K.H. Nealson, Quantification of electron transfer rates to a solid phase electron acceptor through the stages of biofilm formation from single cells to multicellular communities, Environ. Sci. Technol. 44 (2010) 2721–2727. [74] W. Chen, X.-Y. Liu, C. Qian, X.-N. Song, W.-W. Li, H.-Q. Yu, An UV–vis spectroelectrochemical approach for rapid detection of phenazines and exploration of their redox characteristics, Biosens. Bioelectron. 64 (2015) 25–29. [75] H.-B. Shen, X.-Y. Yong, Y.-L. Chen, Z.-H. Liao, R.-W. Si, J. Zhou, S.-Y. Wang, Y.-C. Yong, P.-K. OuYang, T. Zheng, Enhanced bioelectricity generation by improving pyocyanin production and membrane permeability through sophorolipid addition in Pseudomonas aeruginosa-inoculated microbial fuel cells, Bioresour. Technol. 167 (2014) 490–494. [76] J. Jayapriya, V. Ramamurthy, Use of non-native phenazines to improve the performance of Pseudomonas aeruginosa MTCC 2474 catalysed fuel cells, Bioresour. Technol. 124 (2012) 23–28. [77] T. Zhang, C. Cui, S. Chen, H. Yang, P. Shen, The direct electrocatalysis of Escherichia coli through electroactivated excretion in microbial fuel cell, Electrochem. Commun. 10 (2008) 293–297. [78] T. Zhang, Y. Zeng, S. Chen, X. Ai, H. Yang, Improved performances of E. coli-catalyzed microbial fuel cells with composite graphite/PTFE anodes, Electrochem. Commun. 9 (2007) 349–353. [79] L. Tao, H. Wang, M. Xie, L. Thia, W.N. Chen, X. Wang, Improving mediated electron transport in anodic bioelectrocatalysis, Chem. Commun. 51 (2015) 12170–12173. [80] L. Xiao, Z. He, Applications and perspectives of phototrophic microorganisms for electricity generation from organic compounds in microbial fuel cells, Renew. Sustain. Energy Rev. 37 (2014) 550–559. [81] M. Rosenbaum, Z. He, L.T. Angenent, Light energy to bioelectricity: photosynthetic microbial fuel cells, Curr. Opin. Biotechnol. 21 (2010) 259–264. [82] A.E. Inglesby, D.A. Beatty, A.C. Fisher, Rhodopseudomonas palustris purple bacteria fed Arthrospira maxima cyanobacteria: demonstration of application in microbial fuel cells, RSC Adv. 2 (2012) 4829–4838. [83] X. Cao, X. Huang, N. Boon, P. Liang, M. Fan, Electricity generation by an enriched phototrophic consortium in a microbial fuel cell, Electrochem. Commun. 10 (2008) 1392–1395. [84] L.L. Beer, E.S. Boyd, J.W. Peters, M.C. Posewitz, Engineering algae for biohydrogen and biofuel production, Curr. Opin. Biotechnol. 20 (2009) 264–271. [85] Y. Hubenova, M. Mitov, Extracellular electron transfer in yeast-based biofuel cells: a review, Bioelectrochemistry 106 (2015) 177–185. [86] M. Rahimnejad, A. Ghoreyshi, G. Najafpour, H. Younesi, M. Shakeri, A novel microbial fuel cell stack for continuous production of clean energy, Int. J. Hydrogen Energy 37 (2012) 5992–6000. [87] D. Prasad, S. Arun, M. Murugesan, S. Padmanaban, R. Satyanarayanan, S. Berchmans, V. Yegnaraman, Direct electron transfer with yeast cells and construction of a mediatorless microbial fuel cell, Biosens. Bioelectron. 22 (2007) 2604–2610. [88] R. Chandra, G.V. Subhash, S.V. Mohan, Mixotrophic operation of photo-bioelectrocatalytic fuel cell under anoxygenic microenvironment enhances the light dependent bioelectrogenic activity, Bioresour. Technol. 109 (2012) 46–56.

Microbiological concepts of MFCs

[89] G.V. Subhash, R. Chandra, S.V. Mohan, Microalgae mediated bio-electrocatalytic fuel cell facilitates bioelectricity generation through oxygenic photomixotrophic mechanism, Bioresour. Technol. 136 (2013) 644–653. [90] S.I. Ishii, K. Watanabe, S. Yabuki, B.E. Logan, Y. Sekiguchi, Comparison of electrode reduction activities of Geobacter sulfurreducens and an enriched consortium in an air-cathode microbial fuel cell, Appl. Environ. Microbiol. 74 (2008) 7348–7355. [91] N. Chabert, O.A. Ali, W. Achouak, All ecosystems potentially host electrogenic bacteria, Bioelectrochemistry 106 (2015) 88–96. [92] S. Mocali, C. Galeffi, E. Perrin, A. Florio, M. Migliore, F. Canganella, G. Bianconi, E. Di Mattia, M.T. Dell’Abate, R. Fani, Alteration of bacterial communities and organic matter in microbial fuel cells (MFCs) supplied with soil and organic fertilizer, Appl. Microbiol. Biotechnol. 97 (2013) 1299–1315. [93] L.M. Tender, S.A. Gray, E. Groveman, D.A. Lowy, P. Kauffman, J. Melhado, R.C. Tyce, D. Flynn, R. Petrecca, J. Dobarro, The first demonstration of a microbial fuel cell as a viable power supply: powering a meteorological buoy, J. Power Sources 179 (2008) 571–575. [94] L. De Schamphelaire, K. Rabaey, P. Boeckx, N. Boon, W. Verstraete, Outlook for benefits of sediment microbial fuel cells with two bio-electrodes, J. Microbial. Biotechnol. 1 (2008) 446–462. [95] M.J. Angelaalincy, R. Navanietha Krishnaraj, G. Shakambari, B. Ashokkumar, S. Kathiresan, P. Varalakshmi, Biofilm engineering approaches for improving the performance of microbial fuel cells and bioelectrochemical systems, Front. Energy Res. 6 (2018) 63. [96] L. Zhou, D. Deng, D. Zhang, Q. Chen, J. Kang, N. Fan, Y. Liu, Microbial electricity generation and isolation of exoelectrogenic bacteria based on petroleum hydrocarbon-contaminated soil, Electroanalysis 28 (2016) 1510–1516. [97] S.M. Iskander, B. Brazil, J.T. Novak, Z. He, Resource recovery from landfill leachate using bioelectrochemical systems: opportunities, challenges, and perspectives, Bioresour. Technol. 201 (2016) 347–354. [98] J.L. Varanasi, S. Roy, S. Pandit, D. Das, Improvement of energy recovery from cellobiose by thermophillic dark fermentative hydrogen production followed by microbial fuel cell, Int. J. Hydrogen Energy 40 (2015) 8311–8321. [99] S.T. Oh, J.R. Kim, G.C. Premier, T.H. Lee, C. Kim, W.T. Sloan, Sustainable wastewater treatment: how might microbial fuel cells contribute, Biotechnol. Adv. 28 (2010) 871–881. [100] W. Zhi, Z. Ge, Z. He, H. Zhang, Methods for understanding microbial community structures and functions in microbial fuel cells: a review, Bioresour. Technol. 171 (2014) 461–468. [101] D.R. Lovley, Powering microbes with electricity: direct electron transfer from electrodes to microbes, Environ. Microbiol. Rep. 3 (2011) 27–35. [102] L. Huang, J.M. Regan, X. Quan, Electron transfer mechanisms, new applications, and performance of biocathode microbial fuel cells, Bioresour. Technol. 102 (2011) 316–323. [103] L. Huang, H. Xue, Q. Zhou, P. Zhou, X. Quan, Imaging and distribution of Cd (II) ions in electrotrophs and its response to current and electron transfer inhibitor in microbial electrolysis cells, Sens. Actuators B 255 (2018) 244–254. [104] M. Rosenbaum, F. Aulenta, M. Villano, L.T. Angenent, Cathodes as electron donors for microbial metabolism: which extracellular electron transfer mechanisms are involved? Bioresour. Technol. 102 (2011) 324–333. [105] C. Wu, X.-W. Liu, W.-W. Li, G.-P. Sheng, G.-L. Zang, Y.-Y. Cheng, N. Shen, Y.-P. Yang, H.-Q. Yu, A white-rot fungus is used as a biocathode to improve electricity production of a microbial fuel cell, Appl. Energy 98 (2012) 594–596. [106] F. Caccavo, D.J. Lonergan, D.R. Lovley, M. Davis, J.F. Stolz, M.J. McInerney, Geobacter sulfurreducens sp. nov., a hydrogen-and acetate-oxidizing dissimilatory metal-reducing microorganism, Appl. Environ. Microbiol. 60 (1994) 3752–3759. [107] J.E. Champine, B. Underhill, J.M. Johnston, W.W. Lilly, S. Goodwin, Electron transfer in the dissimilatory iron-reducing bacterium Geobacter metallireducens, Anaerobe 6 (2000) 187–196. [108] J.B. Arends, W. Verstraete, 100 years of microbial electricity production: three concepts for the future, J. Microbial. Biotechnol. 5 (2012) 333–346.

59

60

Biological fuel cells

[109] B.E. Logan, J.M. Regan, Electricity-producing bacterial communities in microbial fuel cells, Trends Microbiol. 14 (2006) 512–518. [110] F. Aulenta, P. Reale, A. Catervi, S. Panero, M. Majone, Kinetics of trichloroethene dechlorination and methane formation by a mixed anaerobic culture in a bio-electrochemical system, Electrochim. Acta 53 (2008) 5300–5305. [111] T. Krieg, A. Sydow, U. Schr€ oder, J. Schrader, D. Holtmann, Reactor concepts for bioelectrochemical syntheses and energy conversion, Trends Biotechnol. 32 (2014) 645–655. [112] D.R. Lovley, K.P. Nevin, Electricity production with electricigens, in: Bioenergy, American Society of Microbiology, 2008, pp. 295–306. [113] D.R. Lovley, Live wires: direct extracellular electron exchange for bioenergy and the bioremediation of energy-related contamination, Energ. Environ. Sci. 4 (2011) 4896–4906. [114] M.D. Yates, M. Siegert, B.E. Logan, Hydrogen evolution catalyzed by viable and non-viable cells on biocathodes, Int. J. Hydrogen Energy 39 (2014) 16841–16851. [115] J.A. Smith, P.-L. Tremblay, P.M. Shrestha, O.L. Snoeyenbos-West, A.E. Franks, K.P. Nevin, D.R. Lovley, Going wireless: Fe (III) oxide reduction without pili by Geobacter sulfurreducens strain JS-1, Appl. Environ. Microbiol. 80 (2014) 4331–4340. [116] L. Shi, D.J. Richardson, Z. Wang, S.N. Kerisit, K.M. Rosso, J.M. Zachara, J.K. Fredrickson, The roles of outer membrane cytochromes of Shewanella and Geobacter in extracellular electron transfer, Environ. Microbiol. Rep. 1 (2009) 220–227. [117] M.Y. El-Naggar, G. Wanger, K.M. Leung, T.D. Yuzvinsky, G. Southam, J. Yang, W.M. Lau, K.H. Nealson, Y.A. Gorby, Electrical transport along bacterial nanowires from Shewanella oneidensis MR-1, Proc. Natl. Acad. Sci. 107 (2010) 18127–18131. [118] L. Shi, T.C. Squier, J.M. Zachara, J.K. Fredrickson, Respiration of metal (hydr) oxides by Shewanella and Geobacter: a key role for multihaem c-type cytochromes, Mol. Microbiol. 65 (2007) 12–20. [119] B. Methe, K.E. Nelson, J.A. Eisen, I.T. Paulsen, W. Nelson, J. Heidelberg, D. Wu, M. Wu, N. Ward, M. Beanan, Genome of Geobacter sulfurreducens: metal reduction in subsurface environments, Science 302 (2003) 1967–1969. [120] C. Levar, J. Rollefson, D. Bond, Energetic and molecular constraints on the mechanism of environmental Fe (III) reduction by Geobacter, in: Microbial Metal Respiration, Springer, 2013, pp. 29–48. [121] N.S. Malvankar, S.E. Yalcin, M.T. Tuominen, D.R. Lovley, Visualization of charge propagation along individual pili proteins using ambient electrostatic force microscopy, Nat. Nanotechnol. 9 (2014) 1012–1017. [122] D. Coursolle, D.B. Baron, D.R. Bond, J.A. Gralnick, The Mtr respiratory pathway is essential for reducing flavins and electrodes in Shewanella oneidensis, J. Bacteriol. 192 (2010) 467–474. [123] J.M. Myers, C.R. Myers, Role of the tetraheme cytochrome CymA in anaerobic electron transport in cells of Shewanella putrefaciens MR-1 with normal levels of menaquinone, J. Bacteriol. 182 (2000) 67–75. [124] N.S. Malvankar, D.R. Lovley, Microbial nanowires: a new paradigm for biological electron transfer and bioelectronics, ChemSusChem 5 (2012) 1039–1046. [125] N.S. Malvankar, M. Vargas, K.P. Nevin, A.E. Franks, C. Leang, B.-C. Kim, K. Inoue, T. Mester, S.F. Covalla, J.P. Johnson, Tunable metallic-like conductivity in microbial nanowire networks, Nat. Nanotechnol. 6 (2011) 573–579. [126] F. Qian, Y. Li, A natural source of nanowires, Nat. Nanotechnol. 6 (2011) 538–539. [127] R.Y. Adhikari, N.S. Malvankar, M.T. Tuominen, D.R. Lovley, Conductivity of individual Geobacter pili, RSC Adv. 6 (2016) 8354–8357. [128] N.S. Malvankar, M. Vargas, K. Nevin, P.-L. Tremblay, K. Evans-Lutterodt, D. Nykypanchuk, E. Martz, M.T. Tuominen, D.R. Lovley, Structural basis for metallic-like conductivity in microbial nanowires, MBio 6 (2015). [129] S. Pirbadian, S.E. Barchinger, K.M. Leung, H.S. Byun, Y. Jangir, R.A. Bouhenni, S.B. Reed, M.F. Romine, D.A. Saffarini, L. Shi, Shewanella oneidensis MR-1 nanowires are outer membrane and periplasmic extensions of the extracellular electron transport components, Proc. Natl. Acad. Sci. 111 (2014) 12883–12888.

Microbiological concepts of MFCs

[130] C. Pfeffer, S. Larsen, J. Song, M. Dong, F. Besenbacher, R.L. Meyer, K.U. Kjeldsen, L. Schreiber, Y.A. Gorby, M.Y. El-Naggar, Filamentous bacteria transport electrons over centimetre distances, Nature 491 (2012) 218–221. [131] D.R. Lovley, Happy together: microbial communities that hook up to swap electrons, ISME J. 11 (2017) 327–336. [132] A˚. Stenholm, M. Hedeland, T. Arvidsson, C.E. Pettersson, Removal of diclofenac from a non-sterile aqueous system using Trametes versicolor with an emphasis on adsorption and biodegradation mechanisms, Environ. Technol. 40 (2019) 2460–2472. [133] S. Sankaran, S.K. Khanal, N. Jasti, B. Jin, A.L. Pometto III, J.H. Van Leeuwen, Use of filamentous fungi for wastewater treatment and production of high value fungal byproducts: a review, Crit. Rev. Environ. Sci. Technol. 40 (2010) 400–449. [134] R. Guest, D. Smith, Isolation and screening of fungi to determine potential for ammonia nitrogen treatment in wastewater, J. Environ. Eng. Sci. 6 (2007) 209–217. [135] A. Silva, C. Delerue-Matos, S.A. Figueiredo, O.M. Freitas, The use of algae and fungi for removal of pharmaceuticals by bioremediation and biosorption processes: a review, Water 11 (2019) 1555. [136] J.A. Mir-Tutusaus, M. Sarra`, G. Caminal, Continuous treatment of non-sterile hospital wastewater by Trametes versicolor: how to increase fungal viability by means of operational strategies and pretreatments, J. Hazard. Mater. 318 (2016) 561–570. [137] S. Andersson, M. Nilsson, G. Dalhammar, G. Kuttuva Rajarao, Assessment of carrier materials for biofilm formation and denitrification, Vatten 64 (2008) 201–207. [138] A.P. Borole, G. Reguera, B. Ringeisen, Z.-W. Wang, Y. Feng, B.H. Kim, Electroactive biofilms: current status and future research needs, Energ. Environ. Sci. 4 (2011) 4813–4834. [139] U. Schr€ oder, Anodic electron transfer mechanisms in microbial fuel cells and their energy efficiency, Phys. Chem. Chem. Phys. 9 (2007) 2619–2629. [140] E. Marsili, D.B. Baron, I.D. Shikhare, D. Coursolle, J.A. Gralnick, D.R. Bond, Shewanella secretes flavins that mediate extracellular electron transfer, Proc. Natl. Acad. Sci. 105 (2008) 3968–3973. [141] H. Von Canstein, J. Ogawa, S. Shimizu, J.R. Lloyd, Secretion of flavins by Shewanella species and their role in extracellular electron transfer, Appl. Environ. Microbiol. 74 (2008) 615–623. [142] M. Hernandez, D. Newman, Extracellular electron transfer, Cell. Mol. Life Sci. 58 (2001) 1562–1571. [143] C.D. Cox, Role of pyocyanin in the acquisition of iron from transferrin, Infect. Immun. 52 (1986) 263–270. [144] F. Kracke, I. Vassilev, J.O. Kr€ omer, Microbial electron transport and energy conservation—the foundation for optimizing bioelectrochemical systems, Front. Microbiol. 6 (2015) 575. [145] E. Friedheim, L. Michaelis, Potentiometric study of pyocyanine, J. Biol. Chem. 91 (1931) 355–368. [146] N. Boon, K. De Maeyer, M. H€ ofte, K. Rabaey, W. Verstraete, Use of Pseudomonas species producing phenazine-based metabolites in the anodes of microbial fuel cells to improve electricity generation, Appl. Microbiol. Biotechnol. 80 (2008) 985–993. [147] K.P. Nevin, D.R. Lovley, Mechanisms for accessing insoluble Fe (III) oxide during dissimilatory Fe (III) reduction by Geothrix fermentans, Appl. Environ. Microbiol. 68 (2002) 2294–2299. [148] X.-Y. Yong, D.-Y. Shi, Y.-L. Chen, F. Jiao, X. Lin, J. Zhou, S.-Y. Wang, Y.-C. Yong, Y.-M. Sun, P.-K. OuYang, Enhancement of bioelectricity generation by manipulation of the electron shuttles synthesis pathway in microbial fuel cells, Bioresour. Technol. 152 (2014) 220–224. [149] S.J. Fuller, D.G. McMillan, M.B. Renz, M. Schmidt, I.T. Burke, D.I. Stewart, Extracellular electron transport-mediated Fe (III) reduction by a community of alkaliphilic bacteria that use flavins as electron shuttles, Appl. Environ. Microbiol. 80 (2014) 128–137. [150] S. Wu, Y. Xiao, L. Wang, Y. Zheng, K. Chang, Z. Zheng, Z. Yang, J.R. Varcoe, F. Zhao, Extracellular electron transfer mediated by flavins in Gram-positive Bacillus sp. WS-XY1 and yeast Pichia stipitis, Electrochim. Acta 146 (2014) 564–567. [151] D.R. Lovley, J.D. Coates, E.L. Blunt-Harris, E.J. Phillips, J.C. Woodward, Humic substances as electron acceptors for microbial respiration, Nature 382 (1996) 445–448. [152] D.R. Lovley, Bug juice: harvesting electricity with microorganisms, Nat. Rev. Microbiol. 4 (2006) 497–508.

61

62

Biological fuel cells

[153] E. Katz, A. Shipway, I. Willner, Handbook of Fuel Cells, Fundamentals, Technology and Applications, Wiley, Jerusalem, 2003, pp. 1–27. [154] J.K. Glenn, M.A. Morgan, M.B. Mayfield, M. Kuwahara, M.H. Gold, An extracellular H2O2requiring enzyme preparation involved in lignin biodegradation by the white rot basidiomycete Phanerochaete chrysosporium, Biochem. Biophys. Res. Commun. 114 (1983) 1077–1083. [155] M. Tien, T.K. Kirk, C. Bull, J.A. Fee, Steady-state and transient-state kinetic studies on the oxidation of 3,4-dimethoxybenzyl alcohol catalyzed by the ligninase of Phanerocheate chrysosporium Burds, J. Biol. Chem. 261 (1986) 1687–1693. [156] G. Henriksson, G. Johansson, G. Pettersson, A critical review of cellobiose dehydrogenases, J. Biotechnol. 78 (2000) 93–113. [157] R. Ludwig, R. Ortiz, C. Schulz, W. Harreither, C. Sygmund, L. Gorton, Cellobiose dehydrogenase modified electrodes: advances by materials science and biochemical engineering, Anal. Bioanal. Chem. 405 (2013) 3637–3658. [158] F. Tasca, L. Gorton, M. Kujawa, I. Patel, W. Harreither, C.K. Peterbauer, R. Ludwig, G. N€ oll, Increasing the coulombic efficiency of glucose biofuel cell anodes by combination of redox enzymes, Biosens. Bioelectron. 25 (2010) 1710–1716. [159] W. Harreither, C. Sygmund, M. Augustin, M. Narciso, M.L. Rabinovich, L. Gorton, D. Haltrich, R. Ludwig, Catalytic properties and classification of cellobiose dehydrogenases from ascomycetes, Appl. Environ. Microbiol. 77 (2011) 1804–1815. [160] G. Nie, N.S. Reading, S.D. Aust, Relative stability of recombinant versus native peroxidases from Phanerochaete chrysosporium, Arch. Biochem. Biophys. 365 (1999) 328–334. [161] I.-C. Kuan, M. Tien, Stimulation of Mn peroxidase activity: a possible role for oxalate in lignin biodegradation, Proc. Natl. Acad. Sci. 90 (1993) 1242–1246. [162] K.B. Gregory, D.R. Bond, D.R. Lovley, Graphite electrodes as electron donors for anaerobic respiration, Environ. Microbiol. 6 (2004) 596–604. [163] J. Liu, C.I. Pearce, C. Liu, Z. Wang, L. Shi, E. Arenholz, K.M. Rosso, Fe3–xTixO4 nanoparticles as tunable probes of microbial metal oxidation, J. Am. Chem. Soc. 135 (2013) 8896–8907. [164] C.R. Beckwith, M.J. Edwards, M. Lawes, L. Shi, J.N. Butt, D.J. Richardson, T.A. Clarke, Characterization of MtoD from Sideroxydans lithotrophicus: a cytochrome c electron shuttle used in lithoautotrophic growth, Front. Microbiol. 6 (2015) 332. [165] L. Shi, H. Dong, G. Reguera, H. Beyenal, A. Lu, J. Liu, H.-Q. Yu, J.K. Fredrickson, Extracellular electron transfer mechanisms between microorganisms and minerals, Nat. Rev. Microbiol. 14 (2016) 651–662. [166] S. Carbajosa, M. Malki, R. Caillard, M.F. Lopez, F.J. Palomares, J.A. Martı´n-Gago, N. Rodrı´guez, R. Amils, V.M. Ferna´ndez, A.L. De Lacey, Electrochemical growth of Acidithiobacillus ferrooxidans on a graphite electrode for obtaining a biocathode for direct electrocatalytic reduction of oxygen, Biosens. Bioelectron. 26 (2010) 877–880. [167] C. Jeans, S.W. Singer, C.S. Chan, N.C. VerBerkmoes, M. Shah, R.L. Hettich, J.F. Banfield, M.P. Thelen, Cytochrome 572 is a conspicuous membrane protein with iron oxidation activity purified directly from a natural acidophilic microbial community, ISME J. 2 (2008) 542–550. [168] Y.-Z. Wang, A.-J. Wang, A.-J. Zhou, W.-Z. Liu, L.-P. Huang, M.-Y. Xu, H.-C. Tao, Electrode as sole electrons donor for enhancing decolorization of azo dye by an isolated Pseudomonas sp. WYZ-2, Bioresour. Technol. 152 (2014) 530–533. [169] R.A. Rozendal, A.W. Jeremiasse, H.V. Hamelers, C.J. Buisman, Hydrogen production with a microbial biocathode, Environ. Sci. Technol. 42 (2008) 629–634. [170] P. Clauwaert, K. Rabaey, P. Aelterman, L. De Schamphelaire, T.H. Pham, P. Boeckx, N. Boon, W. Verstraete, Biological denitrification in microbial fuel cells, Environ. Sci. Technol. 41 (2007) 3354–3360. [171] C.-Y. Lai, S.-H. Liu, G.-P. Wu, C.-W. Lin, Enhanced bio-decolorization of acid orange 7 and electricity generation in microbial fuel cells with superabsorbent-containing membrane and laccase-based bio-cathode, J. Clean. Prod. 166 (2017) 381–386. [172] S. Kato, K. Hashimoto, K. Watanabe, Microbial interspecies electron transfer via electric currents through conductive minerals, Proc. Natl. Acad. Sci. 109 (2012) 10042–10046.

Microbiological concepts of MFCs

[173] Z. Zhao, Y. Zhang, L. Wang, X. Quan, Potential for direct interspecies electron transfer in an electric-anaerobic system to increase methane production from sludge digestion, Sci. Rep. 5 (2015) 11094. [174] Q. Cheng, D.F. Call, Hardwiring microbes via direct interspecies electron transfer: mechanisms and applications, Environ Sci Process Impacts 18 (2016) 968–980. [175] A. Kato Marcus, C.I. Torres, B.E. Rittmann, Conduction-based modeling of the biofilm anode of a microbial fuel cell, Biotechnol. Bioeng. 98 (2007) 1171–1182. [176] C.I. Torres, A.K. Marcus, H.-S. Lee, P. Parameswaran, R. Krajmalnik-Brown, B.E. Rittmann, A kinetic perspective on extracellular electron transfer by anode-respiring bacteria, FEMS Microbiol. Rev. 34 (2010) 3–17. [177] J.S. Seelam, D. Pant, S.A. Patil, B.P. Kapadnis, Biological electricity production from wastes and wastewaters, in: Microbial Factories, Springer, 2015, pp. 155–183. [178] C. Dumas, R. Basseguy, A. Bergel, DSA to grow electrochemically active biofilms of Geobacter sulfurreducens, Electrochim. Acta 53 (2008) 3200–3209. [179] V.S. Sarathi, K.S. Nahm, Recent advances and challenges in the anode architecture and their modifications for the applications of microbial fuel cells, Biosens. Bioelectron. 43 (2013) 461–475. [180] M. Rosenbaum, F. Zhao, M. Quaas, H. Wulff, U. Schr€ oder, F. Scholz, Evaluation of catalytic properties of tungsten carbide for the anode of microbial fuel cells, Appl. Catal. Environ. 74 (2007) 261–269. [181] P. Clauwaert, W. Verstraete, Methanogenesis in membraneless microbial electrolysis cells, Appl. Microbiol. Biotechnol. 82 (2009) 829–836. [182] H.-S. Lee, B.E. Rittmann, Significance of biological hydrogen oxidation in a continuous singlechamber microbial electrolysis cell, Environ. Sci. Technol. 44 (2010) 948–954. [183] K.K. Jefferson, What drives bacteria to produce a biofilm? FEMS Microbiol. Lett. 236 (2004) 163–173. [184] G. O’Toole, H.B. Kaplan, R. Kolter, Biofilm formation as microbial development, Annu. Rev. Microbiol. 54 (2000) 49–79. [185] G.D. Saratale, R.G. Saratale, M.K. Shahid, G. Zhen, G. Kumar, H.-S. Shin, Y.-G. Choi, S.-H. Kim, A comprehensive overview on electro-active biofilms, role of exo-electrogens and their microbial niches in microbial fuel cells (MFCs), Chemosphere 178 (2017) 534–547. [186] A.R. Rahmani, N. Navidjouy, M. Rahimnejad, D. Nematollahi, M. Leili, M.R. Samarghandi, S. Alizadeh, Application of the eco-friendly bio-anode for ammonium removal and power generation from wastewater in bio-electrochemical systems, J. Clean. Prod. 243 (2020), 118589. [187] A. Tofighi, M. Rahimnejad, M. Ghorbani, Ternary nanotube α-MnO2/GO/AC as an excellent alternative composite modifier for cathode electrode of microbial fuel cell, J. Therm. Anal. Calorim. 135 (2019) 1667–1675. [188] S.K. Hassaninejad-Darzi, M. Rahimnejad, F. Shajie, A.H.S. Kootenaei, Electrocatalytic oxidation of formaldehyde onto carbon paste electrode modified with hydrogen titanate nanotubes, including nickel hydroxide, Iran. J. Sci. Technol. Trans. A Sci. 42 (2018) 1259–1268. [189] K. Guo, The Effects of Electrode Surface Modifications on Biofilm Formation and Electron Transfer in Bioelectrochemical Systems, Ghent University, 2014. [190] H. Yuan, L. Deng, Y. Chen, Y. Yuan, MnO2/polypyrrole/MnO2 multi-walled-nanotube-modified anode for high-performance microbial fuel cells, Electrochim. Acta 196 (2016) 280–285. [191] M. Zhou, M. Chi, H. Wang, T. Jin, Anode modification by electrochemical oxidation: a new practical method to improve the performance of microbial fuel cells, Biochem. Eng. J. 60 (2012) 151–155. [192] J.L. Varanasi, A.K. Nayak, Y. Sohn, D. Pradhan, D. Das, Improvement of power generation of microbial fuel cell by integrating tungsten oxide electrocatalyst with pure or mixed culture biocatalysts, Electrochim. Acta 199 (2016) 154–163. [193] S. Rengaraj, Bioelectrochemical Films on Electrodes for Application to Biofuel Cells (Ph.D. thesis), 2012. http://hdl.handle.net/10379/3067. [194] S.D. Minteer, P. Atanassov, H.R. Luckarift, G.R. Johnson, New materials for biological fuel cells, Mater. Today 15 (2012) 166–173. [195] M. Shabani, H. Younesi, M. Ponti
e, A. Rahimpour, M. Rahimnejad, H. Guo, A. Szymczyk, Enhancement of microbial fuel cell efficiency by incorporation of graphene oxide and functionalized graphene oxide in sulfonated polyethersulfone membrane, Renew. Energy 179 (2021) 788–801.

63

64

Biological fuel cells

[196] M. Shabani, H. Younesi, A. Rahimpour, M. Rahimnejad, Power generation and wastewater treatment using Nafion and SPEEK/SGO membranes in microbial fuel cells, in: Linnaeus Eco-Tech, 2018, p. 85. [197] M. Rahimnejad, A. Adhami, S. Darvari, A. Zirepour, S.-E. Oh, Microbial fuel cell as new technology for bioelectricity generation: a review, Alex. Eng. J. 54 (2015) 745–756. [198] F. Qian, M. Baum, Q. Gu, D.E. Morse, A 1.5 μL microbial fuel cell for on-chip bioelectricity generation, Lab Chip 9 (2009) 3076–3081. [199] R. Veerubhotla, A. Bandopadhyay, D. Das, S. Chakraborty, Instant power generation from an airbreathing paper and pencil based bacterial bio-fuel cell, Lab Chip 15 (2015) 2580–2583. [200] H. Jiang, L.J. Halverson, L. Dong, A miniature microbial fuel cell with conducting nanofibers-based 3D porous biofilm, J. Micromech. Microeng. 25 (2015), 125017. [201] S.A. Patil, F. Harnisch, C. Koch, T. H€ ubschmann, I. Fetzer, A.A. Carmona-Martı´nez, S. M€ uller, U. Schr€ oder, Electroactive mixed culture derived biofilms in microbial bioelectrochemical systems: the role of pH on biofilm formation, performance and composition, Bioresour. Technol. 102 (2011) 9683–9690. [202] W. Miran, J. Jang, M. Nawaz, A. Shahzad, S.E. Jeong, C.O. Jeon, D.S. Lee, Mixed sulfate-reducing bacteria-enriched microbial fuel cells for the treatment of wastewater containing copper, Chemosphere 189 (2017) 134–142. [203] J.-Y. Nam, H.-W. Kim, K.-H. Lim, H.-S. Shin, B.E. Logan, Variation of power generation at different buffer types and conductivities in single chamber microbial fuel cells, Biosens. Bioelectron. 25 (2010) 1155–1159. [204] S. Pandit, S. Ghosh, M. Ghangrekar, D. Das, Performance of an anion exchange membrane in association with cathodic parameters in a dual chamber microbial fuel cell, Int. J. Hydrogen Energy 37 (2012) 9383–9392. [205] A. Larrosa-Guerrero, K. Scott, I. Head, F. Mateo, A. Ginesta, C. Godinez, Effect of temperature on the performance of microbial fuel cells, Fuel 89 (2010) 3985–3994. [206] A.G. del Campo, J. Lobato, P. Can˜izares, M. Rodrigo, F.F. Morales, Short-term effects of temperature and COD in a microbial fuel cell, Appl. Energy 101 (2013) 213–217. ´ .B. Roma´n, I. Angelidaki, Importance of temperature and anodic medium composition on [207] B. Min, O microbial fuel cell (MFC) performance, Biotechnol. Lett. 30 (2008) 1213–1218. [208] F. Hejazi, A. Ghoreyshi, M. Rahimnejad, Simultaneous phenol removal and electricity generation using a hybrid granular activated carbon adsorption-biodegradation process in a batch recycled tubular microbial fuel cell, Biomass Bioenergy 129 (2019), 105336. [209] D. Pant, G. Van Bogaert, L. Diels, K. Vanbroekhoven, A review of the substrates used in microbial fuel cells (MFCs) for sustainable energy production, Bioresour. Technol. 101 (2010) 1533–1543. [210] G.D. Saratale, S.-D. Chen, Y.-C. Lo, R.G. Saratale, J.-S. Chang, Outlook of biohydrogen production from lignocellulosic feedstock using dark fermentation—a review, J. Sci. Ind. Res. 67 (2008). http://nopr.niscpr.res.in/bitstream/123456789/2424/1/JSIR%2067%2811%29%20962-979.pdf. [211] D. Sun, D.F. Call, P.D. Kiely, A. Wang, B.E. Logan, Syntrophic interactions improve power production in formic acid fed MFCs operated with set anode potentials or fixed resistances, Biotechnol. Bioeng. 109 (2012) 405–414. [212] X.-W. Liu, W.-W. Li, H.-Q. Yu, Cathodic catalysts in bioelectrochemical systems for energy recovery from wastewater, Chem. Soc. Rev. 43 (2014) 7718–7745. [213] D. Juang, P. Yang, C. Lee, S. Hsueh, T. Kuo, Electrogenic capabilities of gram negative and gram positive bacteria in microbial fuel cell combined with biological wastewater treatment, Int. J. Environ. Sci. Technol. 8 (2011) 781–792. [214] R.M. Donlan, Biofilms: microbial life on surfaces, Emerg. Infect. Dis. 8 (2002) 881. [215] S. Srikanth, S.V. Mohan, P. Sarma, Positive anodic poised potential regulates microbial fuel cell performance with the function of open and closed circuitry, Bioresour. Technol. 101 (2010) 5337–5344. [216] Y. Lei, W. Chen, A. Mulchandani, Microbial biosensors, Anal. Chim. Acta 568 (2006) 200–210. [217] A.E. Franks, N. Malvankar, K.P. Nevin, Bacterial biofilms: the powerhouse of a microbial fuel cell, Biofuels 1 (2010) 589–604.

Microbiological concepts of MFCs

[218] P.D. Kiely, J.M. Regan, B.E. Logan, The electric picnic: synergistic requirements for exoelectrogenic microbial communities, Curr. Opin. Biotechnol. 22 (2011) 378–385. [219] S.V. Raghavulu, P.S. Babu, R.K. Goud, G.V. Subhash, S. Srikanth, S.V. Mohan, Bioaugmentation of an electrochemically active strain to enhance the electron discharge of mixed culture: process evaluation through electro-kinetic analysis, RSC Adv. 2 (2012) 677–688. [220] Y. Yang, Y. Ding, Y. Hu, B. Cao, S.A. Rice, S. Kjelleberg, H. Song, Enhancing bidirectional electron transfer of Shewanella oneidensis by a synthetic flavin pathway, ACS Synth. Biol. 4 (2015) 815–823. [221] G.J. Balzer, C. Thakker, G.N. Bennett, K.-Y. San, Metabolic engineering of Escherichia coli to minimize byproduct formate and improving succinate productivity through increasing NADH availability by heterologous expression of NAD+-dependent formate dehydrogenase, Metab. Eng. 20 (2013) 1–8. [222] K.-Y. San, G.N. Bennett, S.J. Berrı´os-Rivera, R.V. Vadali, Y.-T. Yang, E. Horton, F.B. Rudolph, B. Sariyar, K. Blackwood, Metabolic engineering through cofactor manipulation and its effects on metabolic flux redistribution in Escherichia coli, Metab. Eng. 4 (2002) 182–192. [223] A. Kouzuma, X.-Y. Meng, N. Kimura, K. Hashimoto, K. Watanabe, Disruption of the putative cell surface polysaccharide biosynthesis gene SO3177 in Shewanella oneidensis MR-1 enhances adhesion to electrodes and current generation in microbial fuel cells, Appl. Environ. Microbiol. 76 (2010) 4151–4157. [224] T. Proft, E. Baker, Pili in Gram-negative and Gram-positive bacteria—structure, assembly and their role in disease, Cell. Mol. Life Sci. 66 (2009) 613. [225] E.J. Van Schaik, C.L. Giltner, G.F. Audette, D.W. Keizer, D.L. Bautista, C.M. Slupsky, B.D. Sykes, R.T. Irvin, DNA binding: a novel function of Pseudomonas aeruginosa type IV pili, J. Bacteriol. 187 (2005) 1455–1464. [226] R.R. Isberg, Discrimination between intracellular uptake and surface adhesion of bacterial pathogens, Science 252 (1991) 934–938. [227] J.J. Martinez, M.A. Mulvey, J.D. Schilling, J.S. Pinkner, S.J. Hultgren, Type 1 pilus-mediated bacterial invasion of bladder epithelial cells, EMBO J. 19 (2000) 2803–2812. [228] R. Freudl, S. MacIntyre, M. Degen, U. Henning, Cell surface exposure of the outer membrane protein OmpA of Escherichia coli K-12, J. Mol. Biol. 188 (1986) 491–494.

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CHAPTER 3

Anode electrodes in MFCs Mostafa Rahimnejad

Biofuel and Renewable Energy Research Center, Chemical Engineering Department, Babol Noshirvani University of Technology, Babol, Mazandaran, Iran

3.1 Introduction Microbial fuel cell (MFC) systems have shown impressive developments and have found many applications, including wastewater treatment, bioremediation, biosensors, and power generation [1–3]. However, large-scale MFCs are still limited because of economic challenges [4]. To overcome the challenges, substantial optimization techniques are required. The optimizations exploit the unique power generation and performance of MFCs that, ideally, can be tuned by adjusting conductivity, biocompatibility, chemical stability, and mechanical strength of anode materials. The present chapter summarizes the recent advances in anode material design.

3.2 Necessities of anode materials An anode should possess the capability to form electroactive biofilms. For this purpose, anode materials should have superior characteristics such as excellent conductivity, good biocompatibility, and appropriate surface area for biofilm formation and attachment (Fig. 3.1). Anode materials also require chemical stability, resistance to corrosion, mechanical strength, and toughness to be able to get the perfect outcome.

3.2.1 Surface area and porosity The development of engineered anode electrodes with a rough surface has enabled the good adhesion of microorganisms. In many cases, a rough anode surface can facilitate higher power density compared to a smooth anode surface [5]. For microbial applications, such electrodes are often superior to smooth electrodes because the former ensures sufficient porosity and surface area necessary for providing actual surfaces accessible to microorganisms. Extended porosity enables a high surface area, facilitating microbial immobilization on the anode [6]. Furthermore, increment in the surface area of electrodes leads to minimum Ohmic losses, reduced internal resistance [7], and, consequently, higher current output. Hence, it will be necessary to evolve anode electrodes to further enhance surface area in order to increase MFC efficiency. Providing the required porosity and

Biological Fuel Cells https://doi.org/10.1016/B978-0-323-85711-6.00012-6

Copyright © 2023 Elsevier Inc. All rights reserved.

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Fig. 3.1 Necessities of anode materials.

surface area for biofilm formation, today, studies employ three-dimensional, open-porous anode structures such as carbon foam [3] or nickel foam [8].

3.2.2 Fouling and poisoning Biofilm formation is a necessity of power generation in MFCs. However, a high concentration of microorganisms in a confined region of the electrodes can lead to fouling or clogging. Moreover, during biofilm formation, microorganisms excrete an adhesive material, namely extracellular polymeric substances (EPSs) to support microbial growth and biofilm formation [9]. High concentration of microbes results in a thick biofilm layer and extra EPSs that can result in fouling on the electrode surface. To avoid such problems, an electrode texture with excellent porosity and surface area is required [10].

3.2.3 Electronic conductivity Electronic conductivity is an important factor to consider when designing a cost-effective MFC system with high power generation performance. The most serious problem in MFC performance is the loss of electronic conductivity caused by internal resistance (Rint), including charge transfer resistance (Rct) and Ohmic resistance (Rohm). When exposed to organic materials, microorganisms oxidize the materials and produce electron flows, which are transported to the cathodic chamber through an external circuit. However, anode conductivity can affect such electron flows and, consequently, consistency and efficiency of MFC systems. Low conductivity of anode electrodes means large Rct and Rohm associated with reduced level of power production [11]. What is well known is that anodes require good conductivity to enable the flow of electrons. The development of anode materials has been improved to seek a better quality of MFC performance with increased power generation capacity. Carbon-based materials, metal-based materials, and polymer-based materials are mainly involved in anode electrode textures, among which metal-based anodes are confirmed to have higher conductivity. However, a higher performance is reported for carbon-based electrodes due to their biocompatibility and excellent roughness that improve biofilm formation and alleviate internal resistance. In this way, electrode materials should have a combination of characteristics,

Anode electrodes in MFCs

including good conductivity, excellent corrosion resistance, high surface area, high porosity, and biocompatibility. Nowadays, new anode designs have been created, such as graphitic carbon nitride/ carbon brush composite [12], Nano-Fe3C@2D-N-doped carbon arrays [13], MnO2/ carbon nanotube (CNT) modified graphite anode [14], and S and N codoped graphene/iron carbide nanocomposites, which are being used to allow excellent electronic conductivity [15]. Maximum power of 772 mW m
2, 1606  52 mW m
2, 1044.21 mW m
2, and 3860 W m
2 were reported for the electrode designs. In order to achieve significant anode conductivity, we developed a bacterial cellulose-carbon nanotubes-electropolymerized polyaniline nanocomposite (BC-CNT-PANI) as a capacitive bioanode. Then, we used the novel anode design in a supercapacitive MFC inoculated with anaerobic sludge obtained from a biogas plant (Biotech. Sys. Srl, Bologna, Italy). The Rct (Ω) of the electrode was investigated through impedance spectroscopy analysis at 21 and 50 days after operation and was compared with the control group (BC-CNT). As seen in Fig. 3.2, low conductivity of PANI at neutral pH causes high Rct before biofilm formation. However, the composite anode displayed significant decreases in Rct after 21 and 50 days after operation. These results indicated that PANI has the capacity to promote the charge transfer activity of the biofilm. We observed that while BC-CNT was able to withstand low Rct at the beginning, surface fouling caused by biofilm formation can lead to significant enhancement of Rct during the operation. In another study, we examined graphite paint/stainless steel mesh anode with sinusoidal geometry in terms of electron conductivity within a single-chamber MFC. The system was fed with dairy wastewater and operated for 5 weeks. A combination of six

Fig. 3.2 Demonstrating Rct evaluation of BC-CNT and BC-CNT-PANI before colonization, after 21 days of colonization, and after 50 days of colonization.

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Fig. 3.3 Maximum power density and internal resistance of 6 anode electrodes measured by the galvanostatic method at pulse times of 1 and 2 s.

individual vertical/horizontal electrode was installed as the anode electrode. Maximum power density and internal resistances of MFC circuits measured by the galvanostatic method (at pulse times of 1 and 2 s) are shown in Fig. 3.3. Biofilm development decreased the Rct and the overall internal resistance, thereby improving microbial attachment, electron transfer process, and electronic conductivity of the anode composite.

3.2.4 Biocompatibility Microorganisms are the major participants responsible for power generation. Thus, anode biocompatibility plays a major role in MFC performance. Biocompatibility of the anode electrode is important for adhesion and spread of microbes over the electrode surface to form a biofilm [16,17]. Additionally, surface roughness is involved in biomass inoculation, improving the operation cycle of MFC systems [18]. The cytotoxicity of electrode materials could impede microbial growth and biofilm formation. This would result in weak microbial adhesion, higher contact resistance, and slower electron transfer rate [17,19]. Today, multiple fabrication methods have been developed to enhance the biocompatibility of anode electrodes. The strategies include increment in surface porosity and roughness, decrement in employed cytotoxic materials, and enhancement of surface hydrophobicity [20–22].

3.2.5 Stability and long durability Owing to being constantly immersed in aqueous systems, anode materials normally undergo swelling and corrosion. To overcome these aberrations, anode materials should possess satisfactory chemical and physical stability. Excellent physical and chemical

Anode electrodes in MFCs

stability are beneficial to design electrodes with desirable durability and minimum number of replacements. Increased efforts are hence being spent on designing electrodes with excellent stability and long-term durability. There are two major strategies that aim to achieve higher anode efficiency: the use of hydrophobic electrode materials and the optimization of surface roughness. The second strategy alters the stability of the electrodes through facilitating sufficient space for the microbes. High surface roughness can result in fouling that lead to decreased long-term output of MFCs.

3.2.6 Electrode cost and availability As the economic challenges of MFCs mostly depend on electrode materials, reducing the materials cost is essential for successful commercialization. Furthermore, the availability of electrode materials is particularly important for designing practical systems. Metal electrodes, for instance, pose distinct costs on the system design owing to their limited availability. Therefore, cost-effective nonmetallic materials have attracted substantial attention. Carbonaceous or stainless steel mesh electrodes are the most prevalent materials used for MFCs. Carbon materials are prone to alternate costly metal electrodes because of their abundant natural resources, cost efficiency, sufficient conductivity, and chemical inertness [23].

3.3 Anolytes Selection of electrolyte and pH of the anolyte are crucial factors of MFC performance [24,25]. Inappropriate selection of anolyte is associated with activation losses, concentration losses, and Ohmic losses [26,27]. Activation losses are often linked to lost available energy necessary for redox reactions and because of that electron transfer from the cell membrane to the anode surface requires the maximum amount of energy [26,28]. Moreover, concentration losses occur as a result of insufficient material flux (reactants or products) within the anodic chamber. Ohmic losses result from proton transfer resistance across the membrane [26]. Consequently, activation losses, concentration losses, and Ohmic losses negatively impact the power output of MFCs. The last few decades have hence seen multiple efforts toward overcoming such problems. One exciting approach has been to optimize the pH of anolytes. Optimizing the pH of anolytes offers advantages including increased microbial growth, maintaining a constant pH difference between the cathodic and the anodic compartments, and consequently favorable electron transfer between microorganisms and the electrodes [29,30]. Adjusting the pH of anolytes has the potential to mitigate the effect of concentration losses through improving proton transfer from the anode to the cathode [31]. Table 3.1 summarizes the studies in which the effect of anolyte pH has been investigated by researchers.

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Table 3.1 Review for impact of the anolyte pH on power density of MFCs. Anolyte pH

Anode solution/material

Power density

Ref.

7 5.5–7.5 6–10 5.5–7 10 6–9 7–9 6.5–7 4–9 6–9 6.0

Acetate + potassium phosphate/titanium plates Synthetic wastewater (glucose)/graphite rod Domestic wastewater/graphite rod Synthetic wastewater (glucose)/graphite rod Swine wastewater/graphite Synthetic wastewater (sucrose)/carbon paper Com dung and distilled water/graphite fiber brush Food wastewater /graphite sheet Food waste leachate/granular graphite Sucrose/carbon paper Synthetic wastewater (glucose)/graphite plates

144 W m
2 17.1 mW m
2 660 mW m
3 9.8 W m
3 226.3 mW m
2 181.48 mW m
3 0.46 W m
3 230 mW m
2 657.80 mW m
3 98.8 mW m
2 82.77 mW m
2

[32] [33] [34] [35] [36] [37] [38] [39] [40] [41] [42]

Satisfactory substrate distribution can be achieved through anolyte mixing. Owing to increased substrate distribution, concentration losses occur rarely, which suggests an optimized mass transfer of substrates and mediators. Optimized mass transfer should therefore significantly promote electricity generation [43]. Typical anolyte mixing can be mediated by magnetic stirring, electrode rotation, and anolyte recirculation. By employing a high recirculation rate, for instance, mass transfer can be enhanced, achieving thicker and denser electrochemically active biofilm and power density increment from 50 to 160 W m
3 [44]. Electrode rotation is employed in wastewater treatment technology [45]. Moreover, a rotating electrode was used in a sediment MFC and it increased the power density to 69% [46]. Finally, an anode capable of rotating at a speed of 3 rpm has recently been engineered and promoted power output by 1.4 times compared to the control MFC [47]. Another novel strategy for overcoming critical issues such as Ohmic losses and eliminating hydraulic pump energy consumption is the advent of solid anolyte MFC (saMFC) [48]. MFC autonomy is based on availability and density of the substrate: sufficient availability and higher density yield excellent power generation and lifetime of MFCs. Marine sediment [33,34] and urban solid wastes such as humus, cattle manure, peat moss, and sawdust [35,37] can be utilized as long-lasting sources of electricity for powering fully autonomous BESs [34,37,38]; however, they also require feeding pumps [49]. Aspects, such as sustainable microbial metabolism and the use of long-lasting retrieval substrate, will have to be weighed to confirm the feasibility of the developing saMFC [50]. Tommasi et al. [48] developed a portable, small-size MFC equipped with solid anolyte to trap the nutrients, to increase substrate density, and to sustain the release of nutrients. The saMFC demonstrated the fascinating autonomous operation of 4 months. Furthermore, in a study by Adekunle et al., humus and sawdust was combined and fed into a saMFC as a renewable solid anolyte [51]. The optimized saMFC system displayed sustainable

Anode electrodes in MFCs

long-term power generation for over 9 months. It was shown that the power production efficiency could be further increased through the use of electrical load, thereby optimizing the on/off times. These results confirmed the feasibility of solid anolyte for costeffective and sustainable MFC operation.

3.4 Anode-assisted electrochemical catalysis One of the most fascinating characteristics of anodes is their amenability to nature of the substrate metabolism, rate of the substrate metabolism, and also electron transfer mechanism adopted by microorganisms [52]. Gibbs free energy obtained from the oxidation of organic substrates supply required energy of heterotrophic organisms’ metabolism. Anaerobic respiration and fermentation are mainly used for microbial oxidation of organic substrates in MFCs. Facultative or obligate anaerobes are known as biocatalysts of anaerobe respiration. Anaerobic respiration mediates less energy production compared to that of aerobic respiration because of the less positive redox potential of the oxidizing agents involved. Lately, a wide range of prevalent respiratory pathways based on H2 and acetate, as electron donors, have been analyzed for their possible standard Gibbs free energy [53] (Table 3.2). Thus, oxic respiration is considered as the most energetic respiratory pathway, while methanogenesis is known as the least favorable. Recent studies have suggested that a key portion of Gibbs free energy obtained from metabolic conversions is consumed by microbes for their own growth and endurance. The energy available for cell growth and endurance can be determined theoretically through the difference between the free energy of the products (ΔG0 products) and substrates (ΔG0 substrates). The free energy available for microbial growth (ΔGrxn) can be estimated thermodynamically as follows [53]: ! П i am,i 00 i ΔGrxn ¼ ΔGrxn + R  T  ln (3.1) m,j П j aj

Table 3.2 Illustrating different Gibbs free energy obtained from various microbial reactions. Reaction

ΔG0 (H2) kJ per reaction

ΔG0 (acetate) kJ per reaction

Oxic respiration Denitrification Mn reduction Fe reduction Sulfate reduction Methanogenesis


456
460
440
296
98.8
74.8


402
359
385
241
43.8
19.9

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where R represents the gas constant, T is temperature, a and m elements imply the chemical activity and stoichiometric coefficient of the involved compounds, respectively, while i and j imply products and substrates, respectively. Furthermore, ΔG0rxn exhibits the variation of free energy under standard conditions. Although the real energy available is less than the calculated amount owing to consumption of energy for cell maintenance. The growth rate of microbial species is directly affected by the concentration of substrates and products and can be calculated through kinetic and thermodynamic factors associated with the dynamics of substrate uptake and the free energy of the metabolic conversions (Eq. 3.2) [53]. ν¼

ν max  ½S  ð1
exp ðΔGrxn ÞÞ K + ½S  ð1 + kr  exp ðΔGrxn ÞÞ

(3.2)

where ΔGrxn is the thermodynamic energy available from metabolic conversions, and K and kr imply the half-saturation constant of substrate turnover and the ratio of forward and reverse reaction rate, respectively. Within a mixed-culture biofilm, each species produces different end products from substrate consumption through chemically feasible catabolic reactions. Product generation constrains the availability of the free energy required for biomass growth and that is the balance of the substrate-product pair’s free energy that determines the dominance of microbial species within a mixed culture. It was found that for two species surviving on a single substrate, the species dominance is strongly correlated with the ΔG0rxn of their metabolic activities. Considering two microbial species (X1 and X2) in a chemostat (steady-state) mode that process the same substrate (S) and produce different end products (P1 and P2) we would have λ  ½X 1  ¼ Y 1  ½X 1  

ν max ,1  ½S  ð1
exp ðΔGrxn,1 ÞÞ K 1 + ½S  ð1 + kr,1  exp ðΔGrxn,1 ÞÞ

(3.3)

λ  ½X 2  ¼ Y 2  ½X 2  

ν max ,2  ½S  ð1
exp ðΔGrxn,2 ÞÞ K 1 + ½S  ð1 + kr,2  exp ðΔGrxn,2 ÞÞ

(3.4)

At equal forward and backward conversion rates, kr,1 and kr,2 are equal: kr1,2 ¼ 1. Moreover, it is assuming that K1 and K2 >>> S. Substituting these values into Eq. (3.3) gives A
1 ¼ A  exp ðΔGrxn,2 Þ
exp ðΔGrxn,1 Þ A ¼ Y 2  ν max ,2 

K1  ν max ,1  K 2 Y1

(3.5) (3.6)

Assuming the equal amount of maximal growth rate and uptake parameters of the two species results in A ¼ 1. Thus, the relation between the product concentration and

Anode electrodes in MFCs

standard free energy changes of the metabolic conversions can be found through the equation: ! ΔG0rxn,2
ΔG0rxn,1 P exp ¼ 1 (3.7) RT P2 All in all, both substrate dynamics and free energy of the metabolic conversions affect the dominance of microbial species within a mixed culture and product concentrations at steady state.

3.5 Anode materials Anode provides a support for biofilm formation and functions as an electron conductor in MFCs, making them critical components of the system. However, the anode electrode performance required for power production depends on various parameters such as architecture and composition. For example, graphite, graphite felt, graphite foil, activated graphite felt, carbon paper, carbon cloth, activated carbon cloth, Pt, Pt black, reticulated vitreous carbon (RVC), and tungsten carbide have been successfully applied as anodic materials. The materials possess good stability, conductivity, and economical benefits. Although, their hydrophobicity is associated with poor electron transfer potential and fouling challenges, especially in the case of robust biofilm adhesion. Therefore, high yield electricity production is still the major challenge of MFC operation [54]. In this regard, it is notable that the type and composition of anode material can impact MFC performance, by affecting polarization losses, microbial attachment, and electron flow [54]: using appropriate electrode materials leads to increased microbial attachment on the electrode surface and affects the overall power output.

3.5.1 Carbonaceous electrodes A variety of carbonaceous electrodes have been developed toward high-yield MFC operation. The application of CNT as an electrode substrate is based on its high surface area and conductivity. However, the small pore size of the two-dimensional nanostructures is associated with inaccessibility of the anode interior, fouling formation, and consequently reduced efficiency of MFCs [55,56]. To embrace a satisfactory MFC operation, threedimensionally structured anodes such as graphite fiber brush, RVC, and carbon fiber nonwovens have been designed to provide a suitable microenvironment for biofilm formation. The defined structure possesses a larger surface area and can influence biofilm behaviors and control electron transfer mechanisms [57]. However, the three-dimensional structures still suffer from small pore sizes for biofilm function and poor conductivity [58]. To overcome the challenges, carbon-based nanoparticles, such as graphene and CNTs, can be coated onto the three-dimensional anode materials. For instance, a maximum power density of 2142 mW m
2 has been reported for a graphene-modified anode [59]. Carbon brush is

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another modification technique, which offers high surface area for generating excellent MFC performance. However, the technique is still limited regarding its applicability. Carbon brush efficacy can be modified through heating, acid soaking, and a combination of these processes. For instance, power density of 1100, 1280, and 1370 mW m
2 have resulted from acidic oxidation treatment, heat treatment, and a combination of heat treatment and acidic oxidation, respectively [60]. To meet the anode requirements, the graphite rod is one of the most widely used substrates due to its excellent physiochemical characteristics. Although, there are some concerns about using the graphite rod as anode material, such as limited porosity and inadequate surface area for biofilm adhesion [61]. A maximum power density of 26 mW m
2 has been reported for graphite rod electrodes [62,63]. It could be inferred that graphite felt has a higher surface area and because of that better performance as an electrode substrate, compared with that of a graphite rod. The graphite fiber brush is another graphitic material, developing from graphite fiber surrounded by a conductive corrosion-resistant metal wire. Graphite fiber has recently shown promise for providing high surface area and decreasing electrode resistance [64]. Studies show that the graphite fiber brush-base anode resulted in a power density of 422 mW m
2 and has the potential to produce power density of up to 2400 mW m
2 in the presence of cobalt tetramethylphenylporphyrin carbon cloth as a cathode [65]. Carbon paper and carbon cloth are types of carbon materials, which increase MFC performance through decreasing the distance between the cathode and the anode. In carbon paper, the large surface area provides wiring for electron flows, so that the anode resistance decreases. One of the most challenges of using carbon paper is its fragility and rather high price [65].

3.5.2 Metal nanoparticles Carbon-based materials are commonly applied to fabricate anode electrodes with unique structures. The drawback of carbonaceous electrodes is less electric conductivity, compared with metal electrodes [66]. The application of metal-based bioanodes endows MFCs with improved performance. Some researchers have explored the possibility of using Au as a way to improve the bioactivity of electrogenic bacteria [67,68]. The enhanced extracellular electron transfer (EET) might be attributed to the increased active surface area and high conductivity via the metal nanoparticles. In another study, bioanodes modified with Cu and Ag generated current densities of 1.5 and 1.1 mA cm
2, respectively [66], which almost equals the current density produced by graphite bioanodes (1 mA cm
2). Owing to this similarity low-cost carbon-based materials are preferred over such expensive anode materials. The application of titanium (Ti) enhances biocompatibility, corrosion resistance, and dimensional stability [69]. However, Ti has some unappealing performances, such as

Anode electrodes in MFCs

poor electrical conductivity. Zhou et al. coated an oxide layer on the Ti anode through heat treatment and showed that the oxide layer retained good electrocatalytic activities for electron transfer [69]. Currently, stainless steel is receiving more and more attention in MFCs, as a favorable bioanode material, promoting electroconductivity within the anodic chamber. The use of stainless steel could increase the mechanical strength and stability of the electrode under harsh operating conditions. Pocaznoi et al. showed that the stainless steel bioanode increased the current density to 20.6 A m
2 [70]. The major drawback of stainless steel bioanodes is that they possess less active surface area, compared to the carbon-based materials. Ketep et al. fabricated a bioanode with stainless steel foam [71]. They found that the three-dimensional porous structure promotes biofilm formation and mass transport and results a maximum current density of 80 A m
2 [71]. The incorporation of metal ions assists in the induction of microbes to produce metal nanoparticles [72]. For example, Pd2+-ion incorporation could induce the formation of membrane-bound Pd-nanoassemblies by Desulfovibrio desulfuricans [73]. The function of the membrane-bound Pd-nanoassemblies is closely related to its higher electrical conductivity. Furthermore, doping of bacteria with nanomaterials is highly promising for accelerating EET. It was demonstrated that doping of Shewanella with iron oxide/sulfide and nickel nanoparticles enables enhancement in EET, thereby an increment in electrical conductivity [74]. In our experiments, the electrochemical behavior of the carbon-paste electrode modified with nickel-decorated nanoporous cobalt-nickel phosphate molecular sieve has been thoroughly investigated through cyclic voltammetry and chronoamperometry methods [75]. We found that the electrocatalytic properties of the modified electrode were strongly affected by metal ions. The electrode exhibited an improved electron transfer coefficient (0.66), the mean value of the catalytic rate constant (1.80  105 cm3 mol
1 s
1), and the diffusion coefficient (3.62  10
4 cm2 s
1).

3.5.3 Conducting polymers Conductive polymers are biocompatible, stable, and convenient electrode materials [76]. As the most studied polymer materials, polypyrrole (PPy) has excellent conductivity and good stability in aqueous environments. PPy has not only good surface properties but can also be easily altered for multiple applications. Zhao et al. prepared a PPy bioanode by a reactive self-degraded template method and analyzed the effect of PPy on power production [77]. The results showed that the PPy nanotubes modulated the charge transfer resistance of the electrode, which promoted the EET. Moreover, the PPy-containing electrode showed better biofilm adhesion. Compared with the carbon paper anode, the modified bioanode has shown better performance in terms of larger surface area and more functional groups. Similarly, a CNT-based bioanode was coated with PPy hydrogel and resulted in a satisfactory EET [78]. It was reported that the hydrophilic

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nature of the modified electrode is responsible for developing a thick biofilm and sufficient mass transport necessary for metabolic activity of the biofilm. Anthraquinone-2,6disulphonic (AQDS) is known as a mediator of EET [79]. Incorporation of PPy and AQDS promoted the current density by 13-fold using Shewanella decolorationis S12 as a bioactive agent [80]. It was reported that increased charge transfer rate and decreased mass transfer limitations account for improved current density. Another prevalent conductive polymer is PANI. Generally, the selection of PANI is based on its ease of synthesis, pseudo-capacitance, stability, low cost, and biocompatibility [81]. Ding et al. prepared nanowire arrays in order to control EET within the anodic chamber [82]. The results showed multiple oxidation levels for PANI at different applied potentials. Electron transfer between the biofilm and the electrode surface was enhanced at 0.2 V (vs Ag/AgCl) and inhibited by a thermodynamic barrier at 0.3 V. It was confirmed that the electron transfer process can be modulated by an external potential. Qiao et al. coated PANI on inorganic networks such as TiO2 and resulted in the maximum power output of 1495 mW m
2 in an Escherichia coli MFC [83]. The main disadvantage of the process is the use of mediator-dependent microorganisms as biocatalysts that can negatively affect MFC performance.

3.6 Surface modification of MFC anode materials Anode materials can alter Rint and costs of operation. Alternating anode materials can improve biofilm development/attachment, substrate metabolism, and electron transfer rate [54] (Fig. 3.4). This can develop better electrical conductivity, higher active surface area, anticorrosion and degradation resistance properties, and suitable mechanical strength [54]. Conducting polymers, CNTs, stainless steel, graphene, and metal oxides are among the commonly used anode electrode modifiers. Surface modification of electrodes results a higher power density, driven mainly by pretreatment under thermal or thermochemical conditions. The pretreatment methods are associated with the elimination of electrode impurities and porosity enhancement, which lead to enhanced microbial adhesion, improved electrical conductivity, and thus elevated power generation. Some pretreatment techniques include alkaline/acidic oxidation, heat treatment, electrochemical oxidation, and surface coating with metal or metal oxides, nanomaterials, polymeric materials, and composite materials. Using ammonia oxidation, promoted bacterial attachment concluded a higher electrical generation by 48% as well as a decrement in MFC activation time from 150 to 60 h [84]. Wang et al. further characterized the influence of pretreatment of a carbonaceous electrode with ammonia gas [62]. After electrode pretreatment, the power density was increased from 893 to 1015 mW m
2. Increased power production by 25% was also evident in MFCs equipped with simultaneous chemically and thermally pretreated electrodes [85]. Furthermore, the acidic oxidation of electrodes suggested the potential for

Anode electrodes in MFCs

Fig. 3.4 Different surface modification methods for the improvement of anode electrodes with their advantages and disadvantages.

electron collection efficiency [84]. Besides these, atmospheric pressure plasma jet treatment was found to significantly affect anodic biofilms and bacterial adhesion and therefore generation of maximum power density, resulting from an increment in the formation of carboxyl and ammonium functional groups, which influences electrode surface hydrophilicity [86]. Table 3.3 summarizes the application of different techniques used for anode modifications.

3.6.1 Alkaline/acidic surface oxidation A convenient and effective method used for enhancing the electrochemical properties of anodes is alkaline/acidic oxidation (Fig. 3.5A) [87,90,101]. Surface modification with

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Table 3.3 Modification of anode materials and improvement of MFC performance. Modification method

Heat treatment Ammonia treatment Ammonium peroxydisulphate treatment Ethylenediamine treatment Methylene blue treatment Acid treatment Acid and heat treatment Electrochemical oxidation NH3 gas treatment Heat treatment Heat treatment Acid (HNO3) treatment

Electrochemical oxidation Dip coating

Dip coating

Chemical reduction technique Electrochemical treatment Atmospheric pressure plasma jets

Anode material/biocatalyst

Improvement

Ref.

Carbon fiber brush/domestic wastewater Carbon mesh/anaerobic sludge

Power density increased by 25.5% Power density increased by 33% Power density increased by 25.4%

[85]

Graphite felt/sulfate reducing bacteria Graphite felt/sulfate reducing bacteria Graphite felt/Sulfate reducing bacteria Carbon mesh/anaerobic sludge Carbon fiber brush/domestic wastewater Carbon mesh/anaerobic sludge Carbon cloth/domestic wastewater Carbon mesh/preacclimated bacteria from an active MFC Carbon brush/domestic wastewater Graphite felt /brewery wastewater diluted with domestic wastewater (1:100 by volume) Graphite felt /preacclimated bacteria from an active MFC Carbon cloth-carbon nanotube/domestic wastewater

Power 92.6% Power 80.2% Power 43% Power 34.3% Power 43% Power 20% Power 3% Power 25% Power 2%

[87] [88]

density increased by

[88]

density increased by

[88]

density increased by

[87]

density increased by

[85]

density increased by

[87]

density increased by

[84]

density increased by

[62]

density increased by

[85]

density increased by

[89]

Power density increased by 39.5% Power density increased by 0.7–30.5-fold for different types of reactors Power density increased by 82-fold

[90] [91]

Glassy carbon-carbon nanotube/Shewanella oneidensis MR-1 Pt-multiwalled nanotube/ Escherichia coli

[92]

Power density increased by sixfold

[93]

Graphene-polyaniline/ anaerobic sludge Carbon cloth/Shewanella sp. WLP72

Power density increased by threefold Power density increased by 3.17-fold

[94] [95]

Anode electrodes in MFCs

Table 3.3 Modification of anode materials and improvement of MFC performance—cont’d Modification method

Electropolymerization Surface coating Surface coating

Dip coating Dip coating

Anode material/biocatalyst

Improvement

Ref.

Bacterial cellulose-carbon nanotube-polyaniline/ anaerobic sludge Graphite paint-stainless steel mesh/anaerobic sludge Gold nanoparticles-carbon nanotube-carbon paste electrode/domestic wastewater Bacterial cellulosepolypyrrole/anaerobic sludge Bacterial cellulose-Polyaniline/ anaerobic sludge

Power density improved by 20%

[96]

Power density increased by twofold Power density increased by 30-fold

[97]

Power density increased by 38-fold Maximum power density of 117.76 mW m
2 was achieved from 0.4 M of aniline

[99]

[98]

[100]

alkaline/acidic groups takes advantage of newly formed functional groups such as carboxyl [90] and amide groups [101] on the anode surface, and their capability of enhancing electron transfer between the microorganisms and the electrode. By the addition of such functional groups, electron transfer efficacies can be enhanced owing to the formation of peptide bonds. For example, electrochemical oxidation increased the active surface area of an anode electrode 2.9 times and, excitingly, improved the power output by 41% [101]. Zhou et al. developed an active carbon mesh anode through alkaline/acidic oxidation and reported an excellent improvement in power density by 43% [87]. Besides this, alkaline/acidic oxidation of graphite felt was demonstrated to improve the current density by approximately 39.5% [90]. Generally, the application of alkaline/acidic oxidation is relatively economical and feasible under moderate operating conditions, compared with other techniques. Successful doping of heteroatoms into carbonaceous materials would improve the efficacy of MFCs, thereby altering their electronic characteristics and modulating their biocompatibility [102–104]. For instance, introduction of N-containing functional groups into such materials offers advantages, including increased microbial adhesion and proliferation, improved biocatalytic activity, and therefore excellent EET [102,105,106]. NH4HCO3 pretreatment [101], ammonia and nitric acid treatment [107,108], and heterocycle-polymer modification [105] have the potential to improve the performance of MFCs. Owing to their increased surface charges, N-enriched materials promote electron transfer from the microorganism to the electrode surface, which applies mainly to better surface attachment of microbes. Moreover, under such surface modifications,

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Fig. 3.5 Schematic illustration of prevalent techniques applied for surface modification of MFC anode materials: alkaline/acidic oxidation (A), heat treatment (B), and surface coating with electroactive materials (C).

anode materials may face hydrophilic (N) defects created by N dopants that can accelerate electron transfer mediated by proteins located in cell membranes [109]. Yu et al. [106] reported a nitrogen-doped carbon nanoparticle (NDCN) anode exhibited an excellent catalytic current when inoculated with Shewanella oneidensis MR-1. As a matter of fact,

Anode electrodes in MFCs

the use of NDCN has some advantages such as improved absorption of flavins and enhancement of mediated electron transfer on the anode surface. Bi et al. [103] developed three-dimensional N-doped porous carbons through pyrolysis in order to improve the function of H-type dual-chamber MFCs. The as-prepared electrode was reported to exhibit good biocompatibility, facilitating microbial growth, and reducing the internal resistance of the electrode. The power output was increased by twofold. In another study, Yuan et al. [110] produced a porous N-doped anode. The acquired anode possessed a high N/C ratio of 3.9% with active surface area of 145.4 cm2. The experiments showed that the increased content of riboflavin on the anode surface enhanced bacterial attachment and prepared more active sites for EET.

3.6.2 Heat treatment Thermal treatment has a great potential in improving anode performance. This strategy has been commonly applied to modify anode electrodes due to its effectiveness and economic benefits. The thermal shock triggered by this method induces the formation of cracks on the electrode surface, which leads to enhancement in anode surface area (Fig. 3.5B). Importantly, the heat treatment resulted an increment in actual surface area by 6.94 times to 49.3 m2 g
1 as compared to the control [85]. Such enhancement enables the adhesion and proliferation of microbes on the anode surface. Thermal treatment of carbon mesh anodes, for instance, can promote the power density of MFCs by 3% [62]. In addition, a high temperature treatment has been employed to modify carbon fiber brush anodes in air (450°C for 30 min) [85]. The method resulted in power density enhancement up to 15%.

3.6.3 Surface coating with electroactive materials Some researchers have explored the possibility of surface coating with electroactive materials as a way to promote the surface area of the electrode as well as increase the EET (Fig. 3.5C). Conductive polymers are commonly used for anode modification in MFC systems [54,111]. Although, they are used in combination with nanomaterials in order to yield higher bioelectricity. PANI [112–114], poly (3,4-ethylenedioxythiophene) (PEDOT) [115,116], and PPy [113,117] are among the most frequently used polymers, each of which has unique characteristics that improve cell-electrode interactions. PANI is a positively charged polymer mainly utilized for providing electrostatic induction, thereby attracting negatively charged cells [111]. A porous PEDOT layer with sufficient redox active sites has potent conductivity, decreasing the interface resistance between the electrode and the microbes [118]. PPy possesses enhanced electrocatalytic properties, proper environmental stability, and facile synthesis, which consequently leads to satisfactory economic cost [119,120]. Pu et al. demonstrated that the PPy-stainless steel composite anode exhibited 29 times improved power production [120]. In addition, Kang et al. described

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anode configurations that were surface-modified with PEDOT [121]. Their investigation showed that the PEDOT coating had a synergetic effect, and that the increased surface area increased the power output of MFCs. Furthermore, an electrode coated with a PANI film on the surface of a stainless steel plate increased the power density up to 780 mW m
2 [112]. In a study, we developed a bacterial cellulose BC-PANI anode by an in situ chemical oxidative polymerization method [100]. The catalytic behavior of BC/PANI electrodes was systematically investigated. The combination of PANI increased the output power from 1 to 117 mW m
2, due to its significant conductivity throughout the process. In another study, a BC-CNT anode was coated with PANI through an electro-polymerization technique [96]. PANI showed promising results, the coating achieved a remarkable improvement in power density by 20%, compared with the control group (BC-CNT). Moreover, the electrode aimed to decrease the charge transfer resistance by 50%. Anode modification with carbon materials is another promising strategy to promote the performance of MFCs. Surface modification of anode with CNTs enhances the active surface area and promotes the conductivity and electrocatalytic properties of the electrode. Such enhancement in surface area provides more active sites for biofilm attachment and enables substrate and electron transfer pathways [111]. For instance, Delord et al. provided improved CNT-based fiber mats as MFC anode [122]. Specifically, they fabricated a modified electrode with excellent porosity and specific surface area through weaving fibers and reported a maximum current density of 75 A m
2. In our experiments, we found that electroconductive graphite paint could be a suitable candidate for enhancing the electrochemical properties of the stainless steel mesh [123]. Acrylic-based graphite paint was prepared and coated on a stainless steel mesh electrode. The surface-modified electrode showed a maximum power density of 463.88 mW m
3 at 1991 mA m
3. Graphene (Gr) is a honeycomb-like lattice nanomaterial with good biocompatibility and excellent EET [57,124]. The incorporation of Gr on an electrode surface has been shown to optimize electron transfer efficacy, thereby inducing microbes to secrete signaling molecules, which could serve as natural growth promoters and electron mediators [125,126]. Additionally, the function of Gr for power generation in MFCs is closely related to its ultrahigh specific surface area (2600 m2 g
1), decreasing the diffusion resistance and activation loss during the operation [127,128]. Cheng et al. incorporated graphene oxide and gold nanoparticles onto the carbon brush surface to improve the surface hydrophilicity of the electrode [129]. They found that the rGO/Au anode reduced the start-up time of the MFC system by 75% and resulted in a power output of 33.7 W m
3. This novel structure is promising for power generation, because its high biocompatibility and rough surface result in better bacterial attachment and biofilm formation. Furthermore, three-dimensional Gr anode electrodes are widely applied to improve MFC performance [130,131]. Yang et al. added a graphene oxide aerogel to a graphite fiber brush

Anode electrodes in MFCs

to form a composite electrode with a three-dimensional structure and showed that the system retained high reproducibility for 18 months of operation [132]. Interestingly, the power density was promoted from 714 to 2520 mW cm
2 over a long-term operation.

3.7 Conclusions The development of anode materials to promote MFC performance is now under extensive consideration. These results have focused on developing ideal anodes with a combination of satisfactory physiochemical and biological functions, inducing biofilm formation, enhancing electron transfer, and inhibiting electrode resistance. Regarding electrode materials, recent studies have concentrated on biocompatible materials such as carbon-based materials, metal nanoparticles, and conductive polymers. Carbon-based materials have convenient components with excellent surface properties. In comparison, metallic materials possess a relatively high electroconductivity. Therefore, the composite fabrication of an anode electrode can result in higher MFC performance. The modified electrodes possess many advantages and can enhance the catalytic activity of the biofilm for better electron transfer. Additionally, surface modification of the anode electrode should be considered as a promising technique for energy harvest due to developing satisfactory properties such as high electro-catalytic activity, thermochemical stability, biocompatibility, and excellent active surface area and porosity.

References [1] T.H. Han, M.M. Khan, S. Kalathil, J. Lee, M.H. Cho, Simultaneous enhancement of methylene blue degradation and power generation in a microbial fuel cell by gold nanoparticles, Ind. Eng. Chem. Res. 52 (2013) 8174–8181. [2] T.H. Han, M.H. Cho, J. Lee, Indole oxidation enhances electricity production in an E. coli-catalyzed microbial fuel cell, Biotechnol. Bioprocess Eng. 19 (2014) 126–131. [3] T.H. Han, S.Y. Sawant, S.-J. Hwang, M.H. Cho, Three-dimensional, highly porous N-doped carbon foam as microorganism propitious, efficient anode for high performance microbial fuel cell, RSC Adv. 6 (2016) 25799–25807. [4] J. Wei, P. Liang, X. Huang, Recent progress in electrodes for microbial fuel cells, Bioresour. Technol. 102 (2011) 9335–9344. [5] U. Michaelidou, A. Ter Heijne, G.J.W. Euverink, H.V. Hamelers, A.J. Stams, J.S. Geelhoed, Microbial communities and electrochemical performance of titanium-based anodic electrodes in a microbial fuel cell, Appl. Environ. Microbiol. 77 (2011) 1069–1075. [6] Y.P. Afsharian, M. Rahimnejad, Functional dynamics of microbial communities in bioelectrochemical systems: the importance of eco-electrogenic treatment of complex substrates, Curr. Opin. Electrochem. 31 (2022), 100816. [7] V.S. Sarathi, K.S. Nahm, Recent advances and challenges in the anode architecture and their modifications for the applications of microbial fuel cells, Biosens. Bioelectron. 43 (2013) 461–475. [8] H. Wang, G. Wang, Y. Ling, F. Qian, Y. Song, X. Lu, S. Chen, Y. Tong, Y. Li, High power density microbial fuel cell with flexible 3D graphene–nickel foam as anode, Nanoscale 5 (2013) 10283–10290. [9] S. Fatemi, A. Ghoreyshi, G. Najafpour, M. Rahimnejad, Bioelectricity generation in mediator-less microbial fuel cell: application of pure and mixed cultures, Iran. (Iranica) J. Energy Environ. 3 (2012).

85

86

Biological fuel cells

[10] H. Liu, S. Cheng, B.E. Logan, Power generation in fed-batch microbial fuel cells as a function of ionic strength, temperature, and reactor configuration, Environ. Sci. Technol. 39 (2005) 5488–5493. [11] B.E. Logan, Microbial Fuel Cells, John Wiley & Sons, 2008. [12] E.T. Sayed, M.A. Abdelkareem, H. Alawadhi, K. Elsaid, T. Wilberforce, A. Olabi, Graphitic carbon nitride/carbon brush composite as a novel anode for yeast-based microbial fuel cells, Energy 221 (2021), 119849. [13] M. Hu, Y. Lin, X. Li, W. Zhang, Z. Chen, Y. Yang, G. Li, Y. Lu, W. Li, Nano-Fe3C@ 2D-NC@ CC as anode for improving extracellular electron transfer and electricity generation of microbial fuel cells, Electrochim. Acta 404 (2022), 139618. [14] J. Zhou, H. Zhang, T. Zuo, Q. Jia, L. Wang, Y. Tian, L. Gong, Y. Zhou, J. Wang, Enhanced coppercontaining wastewater treatment with MnO2/CNTs modified anode microbial fuel cell, Process Saf. Environ. Prot. 159 (2022) 157–167. [15] J. Xia, Y. Geng, S. Huang, D. Chen, N. Li, Q. Xu, H. Li, J. He, J. Lu, High-performance anode material based on S and N co-doped graphene/iron carbide nanocomposite for microbial fuel cells, J. Power Sources 512 (2021), 230482. [16] J.Y. Chen, P. Xie, Z.P. Zhang, Reduced graphene oxide/polyacrylamide composite hydrogel scaffold as biocompatible anode for microbial fuel cell, Chem. Eng. J. 361 (2019) 615–624. [17] B.S. Thapa, T. Kim, S. Pandit, Y.E. Song, Y.P. Afsharian, M. Rahimnejad, J.R. Kim, S.-E. Oh, Overview of electroactive microorganisms and electron transfer mechanisms in microbial electrochemistry, Bioresour. Technol. 126579 (2021). [18] M. Rahimnejad, G.D. Najafpour, A.A. Ghoreyshi, F. Talebnia, G.C. Premier, G. Bakeri, J.R. Kim, S.-E. Oh, Thionine increases electricity generation from microbial fuel cell using Saccharomyces cerevisiae and exoelectrogenic mixed culture, J. Microbiol. 50 (2012) 575–580. [19] S. Fatemi, A. Ghoreyshi, G. Najafpour, M. Rahimnejad, Investigation of bioelectricity production in dual chamber microbial fuel cell by mixed culture as active biocatalyst, Cell. Mol. Res. (Iran. J. Biol.) 27 (2015) 546–554. [20] M. Rethinasabapathy, A.E. Vilian, S.K. Hwang, S.-M. Kang, Y. Cho, Y.-K. Han, J.-K. Rhee, Y.S. Huh, Cobalt ferrite microspheres as a biocompatible anode for higher power generation in microbial fuel cells, J. Power Sources 483 (2021), 229170. [21] K. Zhu, S. Wang, H. Liu, S. Liu, J. Zhang, J. Yuan, W. Fu, W. Dang, Y. Xu, X. Yang, Heteroatomdoped porous carbon nanoparticle-decorated carbon cloth (HPCN/CC) as efficient anode electrode for microbial fuel cells (MFCs), J. Clean. Prod. 130374 (2022). [22] T. Zhao, Z. Qiu, Y. Zhang, F. Hu, J. Zheng, C. Lin, Using a three-dimensional hydroxyapatite/graphene aerogel as a high-performance anode in microbial fuel cells, J. Environ. Chem. Eng. 9 (2021), 105441. [23] R.A. Rozendal, H.V. Hamelers, K. Rabaey, J. Keller, C.J. Buisman, Towards practical implementation of bioelectrochemical wastewater treatment, Trends Biotechnol. 26 (2008) 450–459. [24] G. Sun, A. Thygesen, M.T. Ale, M. Mensah, F.W. Poulsen, A.S. Meyer, The significance of the initiation process parameters and reactor design for maximizing the efficiency of microbial fuel cells, Appl. Microbiol. Biotechnol. 98 (2014) 2415–2427. [25] J.V. Boas, V. Oliveira, L. Marcon, D. Pinto, M. Simo˜es, A. Pinto, Effect of operating and design parameters on the performance of a microbial fuel cell with Lactobacillus pentosus, Biochem. Eng. J. 104 (2015) 34–40. [26] B.E. Logan, B. Hamelers, R. Rozendal, U. Schr€ oder, J. Keller, S. Freguia, P. Aelterman, W. Verstraete, K. Rabaey, Microbial fuel cells: methodology and technology, Environ. Sci. Technol. 40 (2006) 5181–5192. [27] N. Mokhtarian, M. Rahimnejad, G. Najafpour, W.R.W. Daud, A. Ghoreyshi, Effect of different substrate on performance of microbial fuel cell, Afr. J. Biotechnol. 11 (2012) 3363–3369. [28] M. Rahimnejad, G. Najafpour, A. Ghoreyshi, T. Jafari, F. Haghparast, Microbial fuel cell a reliable source for recovery of electrical power from synthetic wastewater, Linnaeus Eco-Tech (2010) 627–635. [29] A.R. Rahmani, N. Navidjouy, M. Rahimnejad, S. Alizadeh, M.R. Samarghandi, D. Nematollahi, Effect of different concentrations of substrate in microbial fuel cells toward bioenergy recovery and simultaneous wastewater treatment, Environ. Technol. 43 (2022) 1–9.

Anode electrodes in MFCs

[30] F. Aghili, A.A. Ghoreyshi, A. Rahimpour, M. Rahimnejad, Dynamic behavior of the adsorption, activated sludge and combined activated sludge-adsorption process for treatment of cheese whey wastewater, Desalin. Water Treat. 57 (2016) 16404–16414. [31] B.H. Kim, I.S. Chang, G.M. Gadd, Challenges in microbial fuel cell development and operation, Appl. Microbiol. Biotechnol. 76 (2007) 485. [32] A. Dekker, A.T. Heijne, M. Saakes, H.V. Hamelers, C.J. Buisman, Analysis and improvement of a scaled-up and stacked microbial fuel cell, Environ. Sci. Technol. 43 (2009) 9038–9042. [33] G. Jadhav, M. Ghangrekar, Performance of microbial fuel cell subjected to variation in pH, temperature, external load and substrate concentration, Bioresour. Technol. 100 (2009) 717–723. [34] S. Puig, M. Serra, M. Coma, M. Cabre, M.D. Balaguer, J. Colprim, Effect of pH on nutrient dynamics and electricity production using microbial fuel cells, Bioresour. Technol. 101 (2010) 9594–9599. [35] E. Martin, O. Savadogo, S. Guiot, B. Tartakovsky, The influence of operational conditions on the performance of a microbial fuel cell seeded with mesophilic anaerobic sludge, Biochem. Eng. J. 51 (2010) 132–139. [36] L. Zhuang, Y. Zheng, S. Zhou, Y. Yuan, H. Yuan, Y. Chen, Scalable microbial fuel cell (MFC) stack for continuous real wastewater treatment, Bioresour. Technol. 106 (2012) 82–88. [37] L. Wei, H. Han, J. Shen, Effects of cathodic electron acceptors and potassium ferricyanide concentrations on the performance of microbial fuel cell, Int. J. Hydrog. Energy 37 (2012) 12980–12986. [38] A. Kaushik, A. Chetal, Power generation in microbial fuel cell fed with post methanation distillery effluent as a function of pH microenvironment, Bioresour. Technol. 147 (2013) 77–83. [39] H.J. Mansoorian, A.H. Mahvi, A.J. Jafari, M.M. Amin, A. Rajabizadeh, N. Khanjani, Bioelectricity generation using two chamber microbial fuel cell treating wastewater from food processing, Enzym. Microb. Technol. 52 (2013) 352–357. [40] X.M. Li, K.Y. Cheng, J.W. Wong, Bioelectricity production from food waste leachate using microbial fuel cells: effect of NaCl and pH, Bioresour. Technol. 149 (2013) 452–458. [41] Q. Jia, L. Wei, H. Han, J. Shen, Factors that influence the performance of two-chamber microbial fuel cell, Int. J. Hydrog. Energy 39 (2014) 13687–13693. [42] S.V. Mohan, R. Saravanan, S.V. Raghavulu, G. Mohanakrishna, P. Sarma, Bioelectricity production from wastewater treatment in dual chambered microbial fuel cell (MFC) using selectively enriched mixed microflora: effect of catholyte, Bioresour. Technol. 99 (2008) 596–603. [43] P. Clauwaert, P. Aelterman, L. De Schamphelaire, M. Carballa, K. Rabaey, W. Verstraete, Minimizing losses in bio-electrochemical systems: the road to applications, Appl. Microbiol. Biotechnol. 79 (2008) 901–913. [44] H.T. Pham, N. Boon, P. Aelterman, P. Clauwaert, L. De Schamphelaire, P. Van Oostveldt, K. Verbeken, K. Rabaey, W. Verstraete, High shear enrichment improves the performance of the anodophilic microbial consortium in a microbial fuel cell, Microb. Biotechnol. 1 (2008) 487–496. [45] F. Hassard, J. Biddle, E. Cartmell, B. Jefferson, S. Tyrrel, T. Stephenson, Rotating biological contactors for wastewater treatment–a review, Process Saf. Environ. Prot. 94 (2015) 285–306. [46] Z. He, H. Shao, L.T. Angenent, Increased power production from a sediment microbial fuel cell with a rotating cathode, Biosens. Bioelectron. 22 (2007) 3252–3255. [47] Q. Liao, J. Zhang, J. Li, D. Ye, X. Zhu, B. Zhang, Increased performance of a tubular microbial fuel cell with a rotating carbon-brush anode, Biosens. Bioelectron. 63 (2015) 558–561. [48] T. Tommasi, G.P. Salvador, M. Quaglio, New insights in microbial fuel cells: novel solid phase anolyte, Sci. Rep. 6 (2016) 29091. € [49] A. Karluvalı, E.O. K€ oroglu, N. Manav, A.Y. C ¸ etinkaya, B. Ozkaya, Electricity generation from organic fraction of municipal solid wastes in tubular microbial fuel cell, Sep. Purif. Technol. 156 (2015) 502–511. [50] S.H. Hassan, S.M.G. El-Rab, M. Rahimnejad, M. Ghasemi, J.-H. Joo, Y. Sik-Ok, I.S. Kim, S.-E. Oh, Electricity generation from rice straw using a microbial fuel cell, Int. J. Hydr. Energy 39 (2014) 9490–9496. [51] A. Adekunle, V. Raghavan, B. Tartakovsky, Carbon source and energy harvesting optimization in solid anolyte microbial fuel cells, J. Power Sources 356 (2017) 324–330. [52] U. Schr€ oder, Anodic electron transfer mechanisms in microbial fuel cells and their energy efficiency, Phys. Chem. Chem. Phys. 9 (2007) 2619–2629.

87

88

Biological fuel cells

[53] T. Großkopf, O.S. Soyer, Microbial diversity arising from thermodynamic constraints, The ISME J. 10 (2016) 2725–2733. [54] Y. Hindatu, M. Annuar, A. Gumel, Mini-review: anode modification for improved performance of microbial fuel cell, Renew. Sust. Energ. Rev. 73 (2017) 236–248. [55] R. Kumar, L. Singh, A. Zularisam, F.I. Hai, Microbial fuel cell is emerging as a versatile technology: a review on its possible applications, challenges and strategies to improve the performances, Int. J. Energy Res. 42 (2018) 369–394. [56] Y. Liu, F. Harnisch, K. Fricke, U. Schr€ oder, V. Climent, J.M. Feliu, The study of electrochemically active microbial biofilms on different carbon-based anode materials in microbial fuel cells, Biosens. Bioelectron. 25 (2010) 2167–2171. [57] J. Liu, Y. Qiao, C.X. Guo, S. Lim, H. Song, C.M. Li, Graphene/carbon cloth anode for highperformance mediatorless microbial fuel cells, Bioresour. Technol. 114 (2012) 275–280. [58] Y.-C. Yong, X.-C. Dong, M.B. Chan-Park, H. Song, P. Chen, Macroporous and monolithic anode based on polyaniline hybridized three-dimensional graphene for high-performance microbial fuel cells, ACS Nano 6 (2012) 2394–2400. [59] J. Hou, Z. Liu, S. Yang, Y. Zhou, Three-dimensional macroporous anodes based on stainless steel fiber felt for high-performance microbial fuel cells, J. Power Sources 258 (2014) 204–209. [60] J. Li, C. Liu, Q. Liao, X. Zhu, D. Ye, Improved performance of a tubular microbial fuel cell with a composite anode of graphite fiber brush and graphite granules, Int. J. Hydrog. Energy 38 (2013) 15723–15729. [61] R. Shankar, N. Pathak, A.K. Chaurasia, P. Mondal, S. Chand, Energy Production through Microbial Fuel Cells, Sustainable Utilization of Natural Resources, CRC Press, 2017, pp. 353–380. [62] X. Wang, S. Cheng, Y. Feng, M.D. Merrill, T. Saito, B.E. Logan, Use of carbon mesh anodes and the effect of different pretreatment methods on power production in microbial fuel cells, Environ. Sci. Technol. 43 (2009) 6870–6874. [63] H. Yuan, Z. He, Graphene-modified electrodes for enhancing the performance of microbial fuel cells, Nanoscale 7 (2015) 7022–7029. [64] M. Zhou, M. Chi, J. Luo, H. He, T. Jin, An overview of electrode materials in microbial fuel cells, J. Power Sources 196 (2011) 4427–4435. [65] B. Logan, S. Cheng, V. Watson, G. Estadt, Graphite fiber brush anodes for increased power production in air-cathode microbial fuel cells, Environ. Sci. Technol. 41 (2007) 3341–3346. [66] A. Baudler, I. Schmidt, M. Langner, A. Greiner, U. Schr€ oder, Does it have to be carbon? Metal anodes in microbial fuel cells and related bioelectrochemical systems, Energy Environ. Sci. 8 (2015) 2048–2055. [67] M. Sun, F. Zhang, Z.-H. Tong, G.-P. Sheng, Y.-Z. Chen, Y. Zhao, Y.-P. Chen, S.-Y. Zhou, G. Liu, Y.-C. Tian, A gold-sputtered carbon paper as an anode for improved electricity generation from a microbial fuel cell inoculated with Shewanella oneidensis MR-1, Biosens. Bioelectron. 26 (2010) 338–343. [68] W. Guo, Y. Pi, H. Song, W. Tang, J. Sun, Layer-by-layer assembled gold nanoparticles modified anode and its application in microbial fuel cells, Colloids Surf. A Physicochem. Eng. Asp. 415 (2012) 105–111. [69] E.A. de Souza, M.J. Giz, G.A. Camara, E. Antolini, R.R. Passos, Ethanol electro-oxidation on partially alloyed Pt-Sn-rh/C catalysts, Electrochim. Acta 147 (2014) 483–489. [70] D. Pocaznoi, A. Calmet, L. Etcheverry, B. Erable, A. Bergel, Stainless steel is a promising electrode material for anodes of microbial fuel cells, Energy Environ. Sci. 5 (2012) 9645–9652. [71] S.F. Ketep, A. Bergel, A. Calmet, B. Erable, Stainless steel foam increases the current produced by microbial bioanodes in bioelectrochemical systems, Energy Environ. Sci. 7 (2014) 1633–1637. [72] S. Kalathil, J. Lee, M.H. Cho, Electrochemically active biofilm-mediated synthesis of silver nanoparticles in water, Green Chem. 13 (2011) 1482–1485. [73] X. Wu, F. Zhao, N. Rahunen, J.R. Varcoe, C. Avignone-Rossa, A.E. Thumser, R.C. Slade, A role for microbial palladium nanoparticles in extracellular electron transfer, Angew. Chem. Int. Ed. 50 (2011) 427–430. [74] X. Jiang, J. Hu, A.M. Lieber, C.S. Jackan, J.C. Biffinger, L.A. Fitzgerald, B.R. Ringeisen, C.M. Lieber, Nanoparticle facilitated extracellular electron transfer in microbial fuel cells, Nano Lett. 14 (2014) 6737–6742.

Anode electrodes in MFCs

[75] S. Hassaninejad-Darzi, M. Rahimnejad, M. Gholami-Esfidvajani, Electrocatalytic oxidation of formaldehyde onto carbon paste electrode modified with nickel decorated nanoporous cobalt-nickel phosphate molecular sieve for fuel cell, Fuel Cells 16 (2016) 89–99. [76] S. Kalathil, D. Pant, Nanotechnology to rescue bacterial bidirectional extracellular electron transfer in bioelectrochemical systems, RSC Adv. 6 (2016) 30582–30597. [77] C.E. Zhao, J. Wu, S. Kjelleberg, J.S.C. Loo, Q. Zhang, Employing a flexible and low-cost polypyrrole nanotube membrane as an anode to enhance current generation in microbial fuel cells, Small 11 (2015) 3440–3443. [78] X. Tang, H. Li, Z. Du, W. Wang, H.Y. Ng, Conductive polypyrrole hydrogels and carbon nanotubes composite as an anode for microbial fuel cells, RSC Adv. 5 (2015) 50968–50974. [79] M. Adachi, T. Shimomura, M. Komatsu, H. Yakuwa, A. Miya, A novel mediator-polymer-modified anode for microbial fuel cells, Chem. Commun. (2008) 2055–2057. [80] C. Feng, L. Ma, F. Li, H. Mai, X. Lang, S. Fan, A polypyrrole/anthraquinone-2, 6-disulphonic disodium salt (PPy/AQDS)-modified anode to improve performance of microbial fuel cells, Biosens. Bioelectron. 25 (2010) 1516–1520. [81] R. Balint, N.J. Cassidy, S.H. Cartmell, Conductive polymers: towards a smart biomaterial for tissue engineering, Acta Biomater. 10 (2014) 2341–2353. [82] C. Ding, H. Liu, Y. Zhu, M. Wan, L. Jiang, Control of bacterial extracellular electron transfer by a solid-state mediator of polyaniline nanowire arrays, Energy Environ. Sci. 5 (2012) 8517–8522. [83] Y. Qiao, S.-J. Bao, C.M. Li, X.-Q. Cui, Z.-S. Lu, J. Guo, Nanostructured polyaniline/titanium dioxide composite anode for microbial fuel cells, ACS Nano 2 (2008) 113–119. [84] S. Cheng, B.E. Logan, Ammonia treatment of carbon cloth anodes to enhance power generation of microbial fuel cells, Electrochem. Commun. 9 (2007) 492–496. [85] Y. Feng, Q. Yang, X. Wang, B.E. Logan, Treatment of carbon fiber brush anodes for improving power generation in air–cathode microbial fuel cells, J. Power Sources 195 (2010) 1841–1844. [86] S. Cheng, H. Liu, B.E. Logan, Power densities using different cathode catalysts (Pt and CoTMPP) and polymer binders (Nafion and PTFE) in single chamber microbial fuel cells, Environ. Sci. Technol. 40 (2006) 364–369. [87] M. Zhou, M. Chi, H. Wang, T. Jin, Anode modification by electrochemical oxidation: a new practical method to improve the performance of microbial fuel cells, Biochem. Eng. J. 60 (2012) 151–155. [88] H. Du, Y. Bu, Y. Shi, Q. Zhong, J. Wang, Effect of an anode modified with nitrogenous compounds on the performance of a microbial fuel cell, Energy Sour. Part A: Recov. Util. Environ. Effects 38 (2016) 527–533. [89] K. Scott, G. Rimbu, K. Katuri, K. Prasad, I. Head, Application of modified carbon anodes in microbial fuel cells, Process Saf. Environ. Prot. 85 (2007) 481–488. [90] X. Tang, K. Guo, H. Li, Z. Du, J. Tian, Electrochemical treatment of graphite to enhance electron transfer from bacteria to electrodes, Bioresour. Technol. 102 (2011) 3558–3560. [91] H.-Y. Tsai, C.-C. Wu, C.-Y. Lee, E.P. Shih, Microbial fuel cell performance of multiwall carbon nanotubes on carbon cloth as electrodes, J. Power Sources 194 (2009) 199–205. [92] L. Peng, S.-J. You, J.-Y. Wang, Carbon nanotubes as electrode modifier promoting direct electron transfer from Shewanella oneidensis, Biosens. Bioelectron. 25 (2010) 1248–1251. [93] T. Sharma, A.L.M. Reddy, T. Chandra, S. Ramaprabhu, Development of carbon nanotubes and nanofluids based microbial fuel cell, Int. J. Hydrog. Energy 33 (2008) 6749–6754. [94] J. Hou, Z. Liu, P. Zhang, A new method for fabrication of graphene/polyaniline nanocomplex modified microbial fuel cell anodes, J. Power Sources 224 (2013) 139–144. [95] S.-H. Chang, J.-S. Liou, J.-L. Liu, Y.-F. Chiu, C.-H. Xu, B.-Y. Chen, J.-Z. Chen, Feasibility study of surface-modified carbon cloth electrodes using atmospheric pressure plasma jets for microbial fuel cells, J. Power Sources 336 (2016) 99–106. [96] M. Mashkour, M. Rahimnejad, M. Mashkour, F. Soavi, Electro-polymerized polyaniline modified conductive bacterial cellulose anode for supercapacitive microbial fuel cells and studying the role of anodic biofilm in the capacitive behavior, J. Power Sources 478 (2020), 228822. [97] M. Masoudi, M. Rahimnejad, M. Mashkour, Enhancing operating capacity of microbial fuel cells by using low-cost electrodes and multi anode-cathode connections in a membrane-less configuration, Int. J. Hydrog. Energy 46 (2021) 8226–8238.

89

90

Biological fuel cells

[98] M. Asghary, J.B. Raoof, M. Rahimnejad, R. Ojani, Usage of gold nanoparticles/multi-walled carbon nanotubes-modified CPE as a nano-bioanode for enhanced power and current generation in microbial fuel cell, J. Iran. Chem. Soc. 16 (2019) 1677–1685. [99] M. Mashkour, M. Rahimnejad, M. Mashkour, G. Bakeri, R. Luque, S.E. Oh, Application of wet nanostructured bacterial cellulose as a novel hydrogel bioanode for microbial fuel cells, ChemElectroChem 4 (2017) 648–654. [100] M. Mashkour, M. Rahimnejad, M. Mashkour, Bacterial cellulose-polyaniline nano-biocomposite: a porous media hydrogel bioanode enhancing the performance of microbial fuel cell, J. Power Sources 325 (2016) 322–328. [101] J. Liu, J. Liu, W. He, Y. Qu, N. Ren, Y. Feng, Enhanced electricity generation for microbial fuel cell by using electrochemical oxidation to modify carbon cloth anode, J. Power Sources 265 (2014) 391–396. [102] M. Lu, Y. Qian, C. Yang, X. Huang, H. Li, X. Xie, L. Huang, W. Huang, Nitrogen-enriched pseudographitic anode derived from silk cocoon with tunable flexibility for microbial fuel cells, Nano Energy 32 (2017) 382–388. [103] L. Bi, S. Ci, P. Cai, H. Li, Z. Wen, One-step pyrolysis route to three dimensional nitrogen-doped porous carbon as anode materials for microbial fuel cells, Appl. Surf. Sci. 427 (2018) 10–16. [104] D. Li, L. Deng, H. Yuan, G. Dong, J. Chen, X. Zhang, Y. Chen, Y. Yuan, N, P-doped mesoporous carbon from onion as trifunctional metal-free electrode modifier for enhanced power performance and capacitive manner of microbial fuel cells, Electrochim. Acta 262 (2018) 297–305. [105] Y. Yuan, S. Zhou, Y. Liu, J. Tang, Nanostructured macroporous bioanode based on polyanilinemodified natural loofah sponge for high-performance microbial fuel cells, Environ. Sci. Technol. 47 (2013) 14525–14532. [106] Y.-Y. Yu, C.X. Guo, Y.-C. Yong, C.M. Li, H. Song, Nitrogen doped carbon nanoparticles enhanced extracellular electron transfer for high-performance microbial fuel cells anode, Chemosphere 140 (2015) 26–33. [107] N. Zhu, X. Chen, T. Zhang, P. Wu, P. Li, J. Wu, Improved performance of membrane free singlechamber air-cathode microbial fuel cells with nitric acid and ethylenediamine surface modified activated carbon fiber felt anodes, Bioresour. Technol. 102 (2011) 422–426. [108] H.O. Mohamed, E.T. Sayed, H. Cho, M. Park, M. Obaid, H.-Y. Kim, N.A. Barakat, Effective strategies for anode surface modification for power harvesting and industrial wastewater treatment using microbial fuel cells, J. Environ. Manag. 206 (2018) 228–235. [109] S. Ci, Z. Wen, J. Chen, Z. He, Decorating anode with bamboo-like nitrogen-doped carbon nanotubes for microbial fuel cells, Electrochem. Commun. 14 (2012) 71–74. [110] H.-R. Yuan, L.-F. Deng, X. Qian, L.-F. Wang, D.-N. Li, Y. Chen, Y. Yuan, Significant enhancement of electron transfer from Shewanella oneidensis using a porous N-doped carbon cloth in a bioelectrochemical system, Sci. Total Environ. 665 (2019) 882–889. [111] C.-E. Zhao, P. Gai, R. Song, Y. Chen, J. Zhang, J.-J. Zhu, Nanostructured material-based biofuel cells: recent advances and future prospects, Chem. Soc. Rev. 46 (2017) 1545–1564. [112] J.M. Sonawane, S. Al-Saadi, R.S. Raman, P.C. Ghosh, S.B. Adeloju, Exploring the use of polyaniline-modified stainless steel plates as low-cost, high-performance anodes for microbial fuel cells, Electrochim. Acta 268 (2018) 484–493. [113] J.M. Sonawane, S.A. Patil, P.C. Ghosh, S.B. Adeloju, Low-cost stainless-steel wool anodes modified with polyaniline and polypyrrole for high-performance microbial fuel cells, J. Power Sources 379 (2018) 103–114. [114] M. Yellappa, J.S. Sravan, O. Sarkar, Y.R. Reddy, S.V. Mohan, Modified conductive polyanilinecarbon nanotube composite electrodes for bioelectricity generation and waste remediation, Bioresour. Technol. 284 (2019) 148–154. [115] Y.L. Kang, S. Pichiah, S. Ibrahim, Facile reconstruction of microbial fuel cell (MFC) anode with enhanced exoelectrogens selection for intensified electricity generation, Int. J. Hydrog. Energy 42 (2017) 1661–1671. [116] J.J. Guzman, M.O.P. Kara, M.W. Frey, L.T. Angenent, Performance of electro-spun carbon nanofiber electrodes with conductive poly (3, 4-ethylenedioxythiophene) coatings in bioelectrochemical systems, J. Power Sources 356 (2017) 331–337.

Anode electrodes in MFCs

[117] A. Kisieliute, A. Popov, R.-M. Apetrei, G. C^ar^ac, I. Morkvenaite-Vilkonciene, A. Ramanaviciene, A. Ramanavicius, Towards microbial biofuel cells: improvement of charge transfer by self-modification of microoganisms with conducting polymer–Polypyrrole, Chem. Eng. J. 356 (2019) 1014–1021. [118] X. Liu, W. Wu, Z. Gu, Poly (3, 4-ethylenedioxythiophene) promotes direct electron transfer at the interface between Shewanella loihica and the anode in a microbial fuel cell, J. Power Sources 277 (2015) 110–115. [119] S. Phonsa, P. Sreearunothai, S. Charojrochkul, K. Sombatmankhong, Electrodeposition of MnO2 on polypyrrole-coated stainless steel to enhance electrochemical activities in microbial fuel cells, Solid State Ionics 316 (2018) 125–134. [120] K.-B. Pu, Q. Ma, W.-F. Cai, Q.-Y. Chen, Y.-H. Wang, F.-J. Li, Polypyrrole modified stainless steel as high performance anode of microbial fuel cell, Biochem. Eng. J. 132 (2018) 255–261. [121] Y.L. Kang, S. Ibrahim, S. Pichiah, Synergetic effect of conductive polymer poly (3, 4-ethylenedioxythiophene) with different structural configuration of anode for microbial fuel cell application, Bioresour. Technol. 189 (2015) 364–369. [122] B. Delord, W. Neri, K. Bertaux, A. Derre, I. Ly, N. Mano, P. Poulin, Carbon nanotube fiber mats for microbial fuel cell electrodes, Bioresour. Technol. 243 (2017) 1227–1231. [123] M. Masoudi, M. Rahimnejad, M. Mashkour, Fabrication of anode electrode by a novel acrylic based graphite paint on stainless steel mesh and investigating biofilm effect on electrochemical behavior of anode in a single chamber microbial fuel cell, Electrochim. Acta 344 (2020), 136168. [124] W. Lv, Z. Li, Y. Deng, Q.-H. Yang, F. Kang, Graphene-based materials for electrochemical energy storage devices: opportunities and challenges, Energy Storage Mater. 2 (2016) 107–138. [125] A. Jain, X. Zhang, G. Pastorella, J.O. Connolly, N. Barry, R. Woolley, S. Krishnamurthy, E. Marsili, Electron transfer mechanism in Shewanella loihica PV-4 biofilms formed at graphite electrode, Bioelectrochemistry 87 (2012) 28–32. [126] A. ElMekawy, H.M. Hegab, D. Losic, C.P. Saint, D. Pant, Applications of graphene in microbial fuel cells: the gap between promise and reality, Renew. Sust. Energ. Rev. 72 (2017) 1389–1403. [127] Y. Li, Z.Y. Fu, B.L. Su, Hierarchically structured porous materials for energy conversion and storage, Adv. Funct. Mater. 22 (2012) 4634–4667. [128] C. Liu, H. Zhang, Y. Tang, S. Luo, Controllable growth of graphene/Cu composite and its nanoarchitecture-dependent electrocatalytic activity to hydrazine oxidation, J. Mater. Chem. A 2 (2014) 4580–4587. [129] Y. Cheng, M. Mallavarapu, R. Naidu, Z. Chen, In situ fabrication of green reduced graphene-based biocompatible anode for efficient energy recycle, Chemosphere 193 (2018) 618–624. [130] F. Yu, C. Wang, J. Ma, Capacitance-enhanced 3D graphene anode for microbial fuel cell with longtime electricity generation stability, Electrochim. Acta 259 (2018) 1059–1067. [131] A. Yadav, N. Verma, Efficient hydrogen production using Ni-graphene oxide-dispersed laserengraved 3D carbon micropillars as electrodes for microbial electrolytic cell, Renew. Energy 138 (2019) 628–638. [132] X. Yang, X. Ma, K. Wang, D. Wu, Z. Lei, C. Feng, Eighteen-month assessment of 3D graphene oxide aerogel-modified 3D graphite fiber brush electrode as a high-performance microbial fuel cell anode, Electrochim. Acta 210 (2016) 846–853.

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CHAPTER 4

Cathode electrodes in MFCs Mostafa Rahimnejad

Biofuel and Renewable Energy Research Center, Chemical Engineering Department, Babol Noshirvani University of Technology, Babol, Mazandaran, Iran

4.1 Introduction Electrodes fulfill electrochemical functions of microbial fuel cells (MFCs). Additionally, microbes are indispensable for converting the chemical energy in substrates into electricity [1]. The potential difference between the cathode and the anode determines the MFC power output. The potential difference is made by the convergence of substrate oxidation at the anode and electrocatalytic oxygen reduction reaction (ORR) at the cathode [2]. Anodic oxidation significantly influences MFC performance, compared with cathodic reduction [3]. It is due to the unsustainable microbial metabolism in the anodic chamber, while the cathode is known to be more stable during the operation. An appropriate cathode design offers acceptable power production. The more efficient the cathode, the more the power production would be. Several researches have reported the recent advances of cathode manufacturing. However, there are still challenges and opportunities in developing high-yield cathode structures. This chapter investigates recent developments in cathode materials and designs toward enhanced MFC performance. In addition, cathodic treatment methods and catholyte characteristics are described in detail.

4.2 Cathode concepts Electrodes are the main components of MFCs. The starting point for power production is substrate oxidation at the anodic chamber through which the flow of electrons is generated. The electrons then travel from the anode surface to the cathode electrode via an external circuit [4] to reduce terminal electron acceptors, completing the electricity generation process. It is apparent that MFC performance is affected by cathode efficiency. Optimal cathode function is associated with the reduction kinetics of terminal electron acceptors [5,6]. Because cathodic electrochemical reactions occur at the electrode surface, the reduction kinetics depends strongly on the cathode surface characteristics. In carbon-based cathodes, the redox potential is shown to decrease. However, the development of electrocatalysts is shown to compensate for the problem. The effectiveness of Biological Fuel Cells https://doi.org/10.1016/B978-0-323-85711-6.00003-5

Copyright © 2023 Elsevier Inc. All rights reserved.

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such catalysts is relevant to factors such as excellent catalytic activity, stability, electrical conductivity, availability, scalability, and cost advantages [7,8]. A dual-chambered MFC and a single-chambered MFC are the most prevalent configurations of MFCs, of which dual-chambered MFC is the most extensively used configuration because a separate cathodic chamber offers the use of different final acceptors such as atmospheric oxygen (O2), ferricyanide, permanganate, dichromate, metal ion, and nitrate and prevents from electrode fouling (Fig. 4.1) [4,9,10], although it should be noted that non-O2 terminal electron acceptors have several drawbacks that lead to cathode failure. Since the regeneration of non-O2 terminal acceptors is rather impossible, they should be replaced at frequent intervals which could impose extra costs on the MFC operation. Furthermore, non-O2 terminal electron acceptors can produce insoluble end products. These problematic materials attenuate cathode performance and hinder the sustainability of the system.

Fig. 4.1 Schematic illustration of double-chamber MFC (A) and single-chamber MFC (B).

Cathode electrodes in MFCs

O2 is the sole element that can be utilized as a terminal electron acceptor in singlechambered MFCs [11]. O2 as an abundant and cost-effective terminal electron acceptor holds an empirically essential role in MFC systems. Because water is the sole end product of O2 reduction, O2 is an environmentally friendly electron acceptor that warrants attention [12]. Although electrochemical reduction of O2 requires high activation energy, it is clear that the uptake of O2 often involves the use of catalysts that are dedicated to the acquisition of low activation energy [13]. These catalysts facilitate cathodic ORR kinetics. The theoretical potential of various terminal electron acceptors is listed in Table 4.1. As is well known, the ORR pathways in acidic and alkaline-based electrolytic solutions involve a four-electron pathway from O2 to H2O and a two-electron pathway from O2 to H2O2 [14–16]: O2 + 4H+ + 4e
$ H2 O

(4.1)

O2 + 2H+ + 2e
$ H2 O2

(4.2)

H2 O2 + H+ + 2e
$ 2H2 O

(4.3)

In addition, the ORR mechanism for nonelectrolytic solutions can be described through the following equations. O2 + H2 O + 4e
$ 4OH


(4.4)

O2 + H2 O + 2e
$ HO2
+ OH


(4.5)

HO2
+ H2 O + 2e
$ 3OH


(4.6)

Table 4.1 Various alternative electron acceptors involved in MFCs. Electron acceptor

Cathodic reduction reaction

Fe(CN)3
6 MnO4


Fe (CN)6 +e !Fe(CN)6
+ MnO
4 +3e +2H !MnO2 + 2H2O
+ O2 + 4e +4H !2H2O O2 + 2e
+2H+!2H2O2
+ 2NO
3 +10e +12H !N2 + 6H2O
+
2NO3 +2e +2H !NO2 + H2O S2O82
+2e
!2SO2
4 ClO4
+8e
+8H+!Cl
+4H2O
+ 3+ Cr2O2
7 +6e +14H !2Cr +7H2O Cu2++2e
!Cu(s)
+ 2+ VO2+ 2 +2e +2H !VO +H2O

O2 O2 NO
3 NO
3 S2O2
8 ClO4
Cr2O2
7 Cu2+ VO2+ 2

3





4


E0

E

0.36 1.7 1.23 0.69 1.25 0.83 1.96 1.29 1.36 0.34 1.00

0.36 1.1 0.8 0.33 0.73 0.43 1.96 0.87 0.42 0.27 0.17

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It has long been confirmed that the four-electron pathway may have a pivotal role in excellent MFC performance. The two-electron pathway, on the other hand, is characterized as an incomplete ORR mechanism that can severely attenuate the energy conversion efficiency and induce the formation of toxic intermediates and free radicals. An example of this is the use of carbon cathodes where two consecutive twoelectron reactions dominate the formation of the H2O2 intermediate. Rate-limiting ORR steps can impede the overall MFC performance. Examples include oxygen adsorption to the cathode surface, cleavage of the OAO bond, and electron transfer [14]. There are also many parameters that directly affect the efficiency of ORR kinetics, including the nature of electrode material, temperature, pH, and the current density [17]. Mathematical methods are frequently used to optimize the ORR kinetics. For example, we can examine how oxygen solubility and the oxygen reduction potential are dependent upon temperature fluctuations within aqueous-air cathodes-based MFCs [18]. Assuming a homogenous concentration of dissolved oxygen (DO) within the bulk catholyte, DO concentration is characterized by Henry’s law [19]: C¼

P KH

(4.7)

where C represents the DO concentration (mM), p is the partial pressure of O2 in the atmosphere (atm), and KH is Henry’s law constant for O2 (atm mM
1). The KH for O2 at different temperatures is given by the van’t Hoff equation:   ΔH 0so ln  1 1 0 K H ¼ K H exp
(4.8) R T0 T where K0H exhibits Henry’s law constant for O2 in atm mM
1 at standard conditions, and ΔH0soln is known as the molar enthalpy change of solution for the dissolution of oxygen in water in J mol
1. Substituting Eq. (4.8) into Eq. (4.7) would give the relationship between the DO concentration and the catholyte temperature:   ΔH 0so ln  1 P 1 C ¼ 0 exp

(4.9) R KH T0 T We can also estimate the temperature dependence of the oxygen reduction potential through the van’t Hoff equation. In Eq. (4.10), it is clear that reduction potentials (E) are proportional to the Gibbs energy (ΔG) [20]: E¼


ΔG RT ¼ ln K r nF nF

(4.10)

Cathode electrodes in MFCs

where E represents the reduction potential in V, ΔG is the Gibbs energy in J mol
1, n is the number of electrons exchanged during oxidation-reduction reactions, F is the Faraday constant in s A mol
1, and Kr is the dimensionless equilibrium constant. Thus, we have   ΔH 0r  1 1 0
K r ¼ K r exp (4.11) R T0 T   nF 0 E (4.12) K 0r ¼ exp RT 0 where ΔH0r is the standard molar enthalpy of reduction for oxygen in J mol
1, and E0 is the standard reduction potential of oxygen in V. Combining Eqs. (4.11), (4.12), and (4.10) gives the general relationship between the reduction potential and the temperature:    T 0 RT ΔH 0r 1 1 E ¼ 0E +
(4.13) nF R T T0 T Eq. (4.13) applies to a single-step O2 reduction reaction (do not intermediate steps and possible formation of hydrogen peroxide):
O2 + 4H+ + 4e
$ 2H2 O E0 ¼ +815V SHE for pH ¼ 7 (4.14) It is likely that the electrochemical potential available at the cathode determines the ORR kinetics, and that is the DO concentration that regulates the current density magnitude in MFCs. In order to examine biologically catalyzed ORR, the electrode potential should be set below the standard reduction reaction where the contribution of the anodic reaction is ignored [21]. The biologically catalyzed ORR can be explored by the combined Michaelis-Menten-Butler-Volmer equation [22]: jc ¼
jOc, max


αnF ðє
E
E L +jc ½S  RT e K M,c + ½S

ARL Þ

(4.15)

The equation describes changes in cathodic current density (jc), changes as a function of the working electrode potential (ε), DO concentration (S), and temperature (T). Here joc, max and KM, c are Michaelis-Menten terms which characterize the maximum cathodic current density magnitude and the half-saturation constant, respectively. The term EL accounts for potential loss and the term RL accounts for Ohmic resistance [18]. n is the number of electrons transferred, F is Faraday’s constant, A is the electrode surface area, R is the universal gas constant, and α is the transfer coefficient obtained from the Tafel slope (b ¼αnFη/2.3RT).

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All in all, the combined Michaelis-Menten and Butler-Volmer model demonstrates that the distribution of dissolved oxygen concentration can greatly affect the oxygen reduction in cathodic biofilms regardless of the electrode surface area. However, the cathodic current density is controlled by the logarithm of the electrode surface area and Ohmic losses. Such sophisticated mathematical models will ultimately help to circumvent the cathodic scale-up challenges.

4.3 Cathodic structures in MFC 4.3.1 Plane cathodes Many reports have shown that carbon cloth, carbon paper, and graphite sheets or plates are the most prevalent carbon materials in MFCs, each of which has unique characteristics [23]. Carbon cloth has mechanical flexibility and a highly porous structure that can result in favorable electrode function [24]. The significant surface roughness of graphite electrodes leads to an increase in power output. However, poor specific areas and high-cost manufacturing have restricted the industrial-scale applications of graphite electrodes. Studies suggest that carbon felt and graphite felt are more susceptible to loose texture, inducing microbial growth. However, the microbial growth rate could be attenuated due to the mass transfer limitations of metabolites and substrates. Similar power densities have been reported for graphite felt and rod electrodes. It was shown that, depending on the excellent surface area, the use of graphite foam could lead to enhanced power generation and biofilm formation by 2.4- and 2.7-fold, respectively, compared to a graphite rod [25]. Work into cathode materials reveals that electrodes with high porosity increase power outputs owing to the higher surface area available for electrochemical reactions and that such porous biocathodes can induce microbial cell growth.

4.3.2 Packed cathodes Packed bed carbon cathodes play a vital role on the MFC outcome by providing the necessary surface area for biofilm formation and by modulating electrochemical reactions [26,27]. To date, extensive efforts have been devoted to developing packed bed cathodes using typical carbon materials such as graphite, activated carbon, and small cubes of carbon felt or graphite. Although these granular bed electrodes are packed together to prepare feasible electrical conductivity, defects or dead zones have been observed after a long-term operation [28]. Furthermore, the poor porosity of packed bed electrodes can lead to cathode fouling after a prolonged operation [29]. Zhang et al. fabricated a manganese dioxide/titanium dioxide/graphitic carbon nitridecoated granular-activated carbon cathode via in situ growth and the sol-gel method to treat organic acid wastewater [30].The removal capacity was reported to be 98% for

Cathode electrodes in MFCs

COD, 99% for NH+4 -N, and 99% for NO
3 -N. The maximum power density of 1176.47 mW m
3 was obtained from the system.

4.3.3 Tubular cathodes In recent years, there has been an increasing demand for the design of economical cathodes to accomplish scale-up requirements [31]. Tubular cathodic structures are conducted to increase the specific surface area of the electrodes. As a result, the specific surface area in electrodes exceeds 84 m2/m3. It was reported that the power density of tubular air-cathode MFCs can be improved through the use of cloth cathode assemblies (CCA) fabricated by coating the cloth with an electrocatalyst and conductive paint. For instance, the power densities of tubular air-cathode MFCs integrated with graphite-CCA and Ni-CCA has reached up to 24.67 and 86.03 mW m
2, respectively [31]. In another study, a tubular nitrogen-doped carbon cathode was prepared by thermally annealing green foxtail with melamine for mediating efficient cathode ORR [32]. The metal-free property and porous structure of the cathode resulted in high electricity generation efficiency and excellent cathode stability compared with commercial Pt/C.

4.3.4 Brush cathodes Graphite fiber brush cathodes (GFB) have a broad range of physiochemical properties such as high surface area and porosity that govern their reactivity in MFCs. Brush cathodes can be fabricated by attaching carbon fibers to a noncorrosive and conductive core such as titanium wires [33]. GFB are being evaluated as practical biocathode structures, which could be helpful in addressing Ohmic resistance and fouling challenges [34]. Nguyen et al. used a tubular photosynthetic MFC comprising a multiple carbon brush cathode to test how the cathode structure affects bioenergy generation and wastewater treatment efficiency [35]. Domestic wastewater supplemented with Bold’s basal medium was used as a cathode substrate, and successful generation of cell voltage (161 6 mV) and nutrients removal (phosphorous and nitrogen) was achieved. Furthermore, Lin et al. demonstrated that the presence of carbon-fiber-brush air cathode resulted in a power density of 40 mW cm
2 which was maintained for 45 days [36]. One approach to improve ORR kinetics involves utilizing a three-dimensional cathode that enables an enhanced ORR interface and oxygen mass transfer rate. In the case of Ramesh et al., this approach showed that GFB increased the power density of the system from 4.6 to 30 mW m
2 [37].

4.3.5 Rotating disk electrodes (RDE) RDE have a certain capability for enabling rapid homogeneous reactions under steadystate conditions. In recent years, there has been an increasing study on the use of RDE to study the electrocatalytic behavior of materials for ORR kinetics. In the RDE apparatus,

99

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a planar disk of the electrode material rotates at a constant speed around a central axis perpendicular to the disk. During the operation, the rotation of the disk draws toward the surface of the disk. As a result, laminar flow tends to occur, leading to a steady stream of material to the electrode surface. The bulk solution is stirred effectively due to the convection induced by rotation. An appropriate rotational velocity endows RDE with a certain mass transfer rate. Furthermore, it has been postulated that cathode rotation may play an important role in the improvement of dissolved oxygen concentration within the bulk catholyte. Such improvement will enable a higher cathode potential, which will ultimately lead to an enhanced overall cathode performance. Chen et al. provided a high-performance rotating graphite fiber brush air cathode for enhancing ORR electrocatalysis [38]. Results demonstrated an increment in power output from 486 11 to 879 16 mW m
2 for static air cathode obtained from slow speed rotation conditions. The rotating conditions promoted an oxygen diffusion rate and OH
transport at or within the air-cathode. Similar findings were also reported by He et al., who demonstrated that a rotating cathode could boost the dissolved oxygen concentration (from 0.4 to 1.6 mg L
1) and power production (from 29 to 49 mW m
2) [39]. Note that although excess oxygen in the bulk catholyte is beneficial, it nevertheless induces an anodic charge transfer resistance and causes an insufficient supply of protons/cations from the anode, leading to a high-pH anode. The problems can be solved through controlling the rotational speed of the cathode. Zhang et al. reported a higher total removal capacity through the coordination of a rotating bamboo charcoal cathode with the Fenton process because of enhanced O2 diffusivity into the catholyte, favoring O2 reduction to H2O2 and superoxide radical which induces a degradation rate of organic materials [40]. Compared with the traditional Fenton process, the integrated system exhibited 2.4 times higher removal efficiency of methyl orange.

4.4 Cathode requirements in MFCs Physicochemical properties of electrodes such as surface roughness, surface area, porosity, conductivity, and hydrophobicity are responsible for total biofilm mass formation and biocathode performance [41]. Efficient use of electrode materials leads to balanced microbial adhesion and electron transfer associated with the promoted electrochemical efficiency from anode to the cathode [42,43]. Moreover, it is important to select lowcost electrode materials capable of producing maximum power densities [42].

4.4.1 Biocompatibility and surface roughness In biocathode systems, microorganisms utilize the electrode surface as an electron source to catalyze redox reactions. Surface roughness determines the heterogeneity of biofilms on the electrode surface. This accounts for excellent electron exchange between the biofilm and the electrode surface. It was shown that the properties of microorganisms can

Cathode electrodes in MFCs

determine the structural heterogeneity of biofilm as well as mass transfer phenomena within the cathodic chamber [44]. Pons et al. reported the promising effect of the biofilm structure on current density mediated by isolated cells and small local colonies [45]. Biocompatibility could improve the adhesion of the biofilm. It was shown that a better biocompatible cathode has the potential to improve bacterial adhesion as well as the stability and performance of biocathode systems [42,46].

4.4.2 Surface area and porosity Electrodes with a high surface area support biofilm growth and electrocatalytic activity on the cathode surface [47]. The focus on increasing the effective surface area to overcome the current loss in MFCs can be attributed to decreasing the resistance of the electrodes, providing sufficient active area for reactions, and enhancing the involved kinetics [46,48]. The use of porous materials provides the surface area available for microbial colonization in biocathode systems [49], decreases the diffusional resistance to the mass transfer [50], and prevents the loss of current. As such, increasing the surface area while using a constant volume can be an effective strategy for preventing Ohmic losses in MFCs. The use of porous carbon with external cobalt nanoparticles as the catalytic cathode increased the specific surface area (335.08 m2 g
1) effectively and enhanced the power density by 44.5% [51]. In another study, the Fe/N-doped carbon (Fe/N/C) cathode catalyst was developed for the controlled ORR performance [52]. It was shown that the stability of the system was preserved due to the moderate porosity of the catalyst, facilitating the mass transfer of oxygen and protons, while inhibiting the water flooding of the triple-phase boundary during the operation.

4.4.3 Conductivity Power generation in MFCs involves the flow of electrons from the anode to the cathode through an external circuit. Power generation efficiency can be altered based on material resistance and interface impedance. Electrode materials possessing less resistance offer excellent electrical conductivity. This enables an effortless flow of electrons, which can form an effective power density. Higher resistance causes loss of electrical energy in the form of thermal energy. Highly conductive materials are reported to improve microbial electron uptake at the cathodic chamber [53]. Another notable factor of conductivity is interfacial resistance between the ion exchange membrane and the electrode. It was demonstrated that low interfacial resistance facilitates electron transfer in MFCs. It is worth noting that the use of cathode materials with higher ionic conductivity leads to better modulating triple-phase boundary reactions within the cathodic chamber [42,54].

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4.4.4 Hydrophobicity/hydrophilicity Hydrophobicity can affect the biofilm community, structure, and electrocatalytic efficiency of microbes on the electrode surface [55]. Studies show that biofilm attachment on the cathode surface is correlated with changes in the physiochemical characteristics of the electrode such as pH, hydrophobicity, and conductivity. The interface hydrophobicity and hydrophilicity are also critical in improving catalytic efficiency without altering the electrode morphology. For instance, by immobilizing the -NH2 and -NH-NH2 groups on the carbon cathode surface, Qui et al. found that the use of hydrophilic groups can improve the transformation efficiency of nitrobenzene to aniline [56]. Given the significant difference in biotransformation performance of -NH-NH2, -NH2, and -SH groups, it is of little surprise that a variety of functions have been attributed to the obvious microbial community structure difference. Excellent electro-selectivity for the electroactive nitroaromatic reducers was demonstrated. This interaction led to the domination of three dominant electroactive nitroaromatic reducers, including the Enterococcus, Desulfovibrio, and Klebsiella, by 72.20 1.87% and 74.868.71%, respectively. Therefore, the adherence of functional microbes within the cathodic biofilm might be strongly influenced by the hydrophilicity and surface charge of the electrodes. On the other hand, hydrophobicity promotes the coulombic efficiency of abiotic cathodes through the suppression of water intrusion and by allowing a more efficient water/air catalytic interface. The addition of hydrophobic polymer binders such as poly(dimethyl siloxane) [57], poly-vinylidene fluoride, and polytetrafluoroethylene [58,59] will allow higher power production. However, for successful improvement, we will need to use a limited amount of hydrophobic binders to circumvent a variety of issues such as increased electrical impedance and ion diffusion hindrance. In addition, another strategy is the use of hydrophobic cocatalysts such as phthalocyanine and the macrocyclic complex which improve the performance of ORR catalysts [60,61]. For instance, by using the Fe-N4/activated carbon composite catalyst, Yang et al. have recently shown that the hydrophobic catalyst can account for the simultaneous suppression of water electrolyte evaporation and oxygen intrusion, as well as the improvement of coulombic efficiency [62]. Therefore, tuning the catalyst hydrophobicity is one of the effective methods for advancement of MFCs.

4.4.5 Stability and durability Electrode materials should provide an electroactive environment for modulating electrochemical reactions in both biotic and abiotic cathode systems. New frontiers of studies should be conducted toward providing the highest DO concentration, which is provided by the relationship between the aeration rate and the electrode potential. Furthermore, recent scientific findings show the potential of excessive roughness to develop fouling that would inhibit the systemic function of biotic and abiotic cathodes in long-term

Cathode electrodes in MFCs

operation. To date, a variety of innovative strategies have been applied to overcome these difficulties and to extend cathode performance over time. For instance, it was shown that both external bio-fouling and internal salt fouling can be effectively mitigated through the use of a chemically bonded wipe separator [63]. Chemical bonding of the wipe separator to the cathode electrode decreased the bio-fouling formation and salt precipitation and allowed better MFC performance (maximum power density of 190  30 mW m
2) within 2 months of operation. Hence, the desired stability and durability of electrodes will play critical roles in the development of high-performance MFCs [12,46].

4.4.6 Cost and availability Following the large-scale application of MFC, the use of available materials as electrodes is a main factor. Material cost is another important factor that can influence the investment cost of the MFC to a large extent. The wide range of materials that are cheap, sustainable, and easily available might be appealing to MFC studies and give researchers flexibility in designing high-performance MFCs. For instance, platinum is known as a widely used electrode material, although it is expensive. Today, carbonaceous and nonprecious composites are used as alternatives to precious metals owing to their low cost, excellent electrochemical properties, and long sustainability [46,64]. However, ORR kinetics can be further promoted through the use of biocathode systems that utilize microorganisms instead of precious metals as biocatalysts [65]. Biocathodes can be inoculated either by wastewater or activated sludge. Moreover, the importance of costeffective bio-absorbance such as an eggshell in the improvement of reduction kinetics and removal efficiency of MFCs has been examined [66]. Perhaps the greatest advantage of introducing cost-effective biowaste into the catholyte is to bio-adsorb inorganic toxic materials (such as nitrate), leading to the enhancement of microbial growth and improvement of reduction kinetics at the cathode.

4.5 Cathodic surface treatment In recent decades, MFCs have been introduced as electrochemical devices having high potential in power production, wastewater treatment, biosensor design, and so forth. In an MFC device, exoelectrogenic microbes oxidize organic or inorganic substrates in the anodic chamber to generate electrons which then flow toward the cathode where ORR is carried out. The physiochemical characteristics of cathode electrodes determine the cost of the operation and ORR kinetics [67]. Cathode modification is an opportunity to enhance the kinetic rate of ORR and to achieve high-efficiency power generation. To date, several oxygen reduction catalysts such as platinum, carbon nanotubes, cobalt oxides, iron-nitrogen-carbon catalysts, and activated carbon [68–71] have been utilized to optimize cathode performance in MFCs. Two factors determine the choice of cathode treatments: the cost of available materials, good performance, and easy fabrication. Low-cost

103

104

Biological fuel cells

nonprecious metal and metal oxides, including MnO2 [72,73], Co3O4 [74], SnO2 [75], TiO2 [76], and Fe3O4 [77], displayed good performance, although the metal discharge phenomena and sensitivity of metal-based catalysts toward pH changes have limited their applications [78]. Composite materials can be attractive alternatives to conventional biocatalysts in that they have good electrical conductivity, great flexibility, and prominent catalytic activities. Cathodes are often modified using various ex situ and in situ techniques. For instance, in our recent work, we fabricated a binder-free Co3O4-polyaniline (PANI) through the in situ technique and compared the ORR activity and power generation capacity of the synthesized electrode with those of the coated Co3O4-PANI electrode and bare carbon cloth electrode [79]. We observed considerable variability both in the charge transfer resistance and power production capacity in all electrodes. As shown in Fig. 4.2, the in situ Co3O4-PANI electrode produced the maximum power density of 102.54mW m
2, which is 2.35-fold higher than that produced by the coated Co3O4-PANI electrode (43.6 mW m
2). Furthermore, the in situ Co3O4-PANI electrode exhibited a remarkable ORR activity and the lowest charge transfer resistance. It is obvious that PANI allows a conductive pathway within the composite structure, improving the electrocatalytic activity of the electrode [36]. Moreover, the presence of cobalt oxide allows a desirable active site on the electrode surface which improves the ORR activity [80]. Therefore, an intensive interaction between the Co3O4 and the PANI within the composite alleviates the charge transfer resistance and improves the ORR activity. We also found that the excellent electrochemical function of the in situ Co3O4-PANI electrode is due to the lack of a binder like polytetrafluoroethylene, mediating low internal resistance.

Fig. 4.2 Demonstrating power density, charge transfer resistance, and solution resistance evaluation of the in situ prepared Co3O4-PANI cathode, coated Co3O4-PANI cathode, and bare carbon cloth cathode.

Cathode electrodes in MFCs

In another study, we investigated the variability in maximum power density of graphite, carbon cloth, carbon paper, and carbon paper coated by the carbon nanotube/platine (CNT/Pt). As shown in Table 4.2, carbon cloth and carbon paper demonstrated an acceptable cathodic performance. Although the presence of the coated CNT/Pt electrode boosted the current density from 2.76 to 16.26 mW m
2, the observation suggests that CNT favors the high active surface area necessary for the desirable charge transfer rate and Pt increases the electrical conductivity of the electrode. Similar results have been reported in the literature, confirming the synergistic effect of composite cathode catalysts on the electron transfer rate and ORR activity of cathode electrodes. For instance, Wang et al. developed an in situ grown carbon nanotubes decorated electrocatalyst in order to increase the ORR performance in the alkaline electrolyte [81]. The CuCo@NCNTs nanocomposite was reported to exhibit good peer production (2757 mW m
3) and antibacterial activity. Karthick et al. fabricated a lowcost tungsten oxide/polypyrrole (WO3/Ppy) composite as a cathode catalyst by using coating methods, in which isopropanol and Nafion were used as a binder. The obtained structure possessed a high surface area, hence has high power production capacity (1.51 A m
2 at 100 Ω). In another study, the Ppy/molybdenum oxide composite was developed by the coating method, in which the addition of Polypyrrole improved the electroconductivity of the electrode, and increased the open-circuit potential of the system by 1.8-fold, compared with that of carbon cloth [82].

4.6 Catholytes MFC performance is correlated with catholyte quality, an electrolyte used in the cathodic chamber. It underpins the development of various catholyte materials, from landfill leachate and traditional aerobic sludge to phosphate buffer solution. It is often said that the chemical properties of the catholyte can affect the diffusivity and transport mechanism of electrons within the cathodic chamber [83]. Researchers have been attempting to upgrade catholyte materials for years in an effort to amplify the bio-electrochemical reactions of MFCs. Microbial degradation of agricultural waste in particular has been shown

Table 4.2 Illustrating the impact of cathode catalysts on potential current density in MFCs.

Power density (mW m
2) Current density (mA m
2)

Graphite

Carbon cloth

Carbon paper

Carbon paperCNT/Pt

0.937

3.35

2.76

16.26

13.92

33.07

23.09

82.38

105

106

Biological fuel cells

to enable significant advances in providing endogenous catalysts during the operation. For instance, continuous production of oxidoreductase enzymes (cellulase and laccase) in the catholyte can achieve greater high-harvesting energy than those of exogenous catalysts, and the ability of carbohydrate-rich liquid hydrolysate production can promote the growth of microorganisms involved (Paralepetopsis floridensis and Phlebia brevispora) [84]. Furthermore, the use of high concentration organic wastewater as a catholyte has been well appreciated. Feng et al. investigated the impacts of different volume ratios of aging landfill leachates and traditional aerobic sludge as a catholyte on the sustainable treatment of shale gas fracturing wastewater using an MFC. They observed a lower internal cathode resistance, a higher electrocatalytic redox performance, a good bacterial biofilm formation, and a maximum power density of 14.04 W m
3 [85]. If we look at MFC performance, we observe that precise control of pH is required to mitigate the loss of protons at high pHs [86]. To overcome this problem, studies use buffer solutions as catholytes, although they have some limitations in large-scale applications [87]. One of the best-known examples is the use of phosphate buffer solution (PBS), which can facilitate pH alteration, conductivity modulation, and internal resistance minimization [88], but the use of high concentration of PBS is costly and has an impact on environmental health. Researchers have introduced saline solutions as efficient alternatives to buffer solutions. Ebrahimi et al. investigated power generation and the desalination capacity of buffer saline solution, compared with those of PBS, nonbuffer saline solution, and bio-catholytes in a microbial desalination cell [89]. They found that the bio-catholyte and saline buffer catholyte resulted in maximum power density of 32.6 W m
3 and 29.4 W m
3, respectively. Moreover, desalination rates were in the range of 0.38 g NaCl L
1 h
1 for the bio-catholyte and 0.34 g NaCl L
1 h
1 for the saline buffer catholyte. Similarly, cathodic chambers containing potassium persulfate and hypochlorite can be designed to control the balance redox potential and MFC performance [90,91]. Hassan et al. demonstrated that the use of potassium persulfate as a catholyte enhanced the power density of Bacillus subtilis-catalyzed MFC (9.5 mW m
2) and promoted the degradation of 2,4-dichlorophenol by 60% [91]. Using a sustainable, green, and economical catholyte, Ghadge et al. further characterized the influence of hypochlorite on the performance of MFCs [90]. When hypochlorite was used as an actholyte, power production of 8.7 W m
3 was achieved, and total and volatile suspended solid reductions of 75.8% and 80.2%, respectively, were reported. All the findings were excellent compared with those reported from the use of oxygen as an electron acceptor. It was proposed that the decrement in polarization resistance (from 42.6 to 26.5 Ω) and supporting rapid sludge digestion might be the reason for this improvement.

4.7 Enzyme immobilization methods for biocathodes Enzyme activity plays a powerful role in MFC performance; controlling enzyme immobilization with precision could therefore be a fundamental aspect of MFC design.

Cathode electrodes in MFCs

In particular, enzyme immobilization is carried out by either a chemical or physical attachment. Physical methods such as adsorption and gel entrapment were emerged as a simple way which makes a poor physical association between the enzyme and the electrode surface. On the other hand, chemical methods enable a strong covalent binding between the enzyme and the cathode, although the strong connection can lead to exhaustion of enzyme activity [92]. Recent advances in biosensor enable unprecedented control over the detection of either coreactant or enzyme-catalyzed by-products, encompassing NADH or H2O2. Furthermore, a redox mediator enables electron transfer between the enzyme and the electrode. Direct electron transfer is preferred because of its high efficiency and economic benefits. Enzymes underpin analyte detection in complex matrices and are practical in biosensor design; however, enzyme stability on the electrode surface can be a major challenge of enzymatic commercial electrodes. Adsorption, copolymerization/entrapment, affinity, and covalent binding are the frequently used methods that make an enzyme-electrode connection (Table 4.3).

4.7.1 Physical adsorption The importance of this technique is so obvious that it is the simplest way to immobilize the enzyme protein on the solid electrode surface through nonspecific physical interaction without the need for any reagents. Therefore, the technique reserves the native enzyme characteristics. Activation steps are required before the immobilization process to create highly efficient enzymatic electrodes. Indeed, the enzymatic electrode can be configured on demand in response to ionic strength, pH, temperature, amount of substrate, and chemical agents. Cathode materials with a high specific surface area and adaptive surface properties are known as perfect platforms for the physical adsorption of enzyme. It was demonstrated that long-term storage can be a critical issue affecting the stability of an enzyme-electrode connection. The technique can be carried out via random physical absorption or molecular orientation-controlled adsorption. Controlled physical adsorption of enzyme based on molecular orientation can achieve a higher direct electron transfer rate than those made from random adsorption. The ability of various linking molecules such as anthracene-2diazonium [105], pyrene, and neocuproine [106] to act as electrode surface modifiers has been appreciated and exploited. For instance, Lalaoui et al. [107] explored whether the directional immobilization of laccase onto functionalized rGO by anthraquinone could influence the current density. The findings suggested that the hydrophobic interaction between anthraquinone and the hydrophobic enzyme pocket might be capable of directly regulating the electron transfer rate and high current density of 0.9 mA cm
2 correlated with high ORR efficiency.

4.7.2 Entrapment or copolymerization Enzyme immobilization through entrapment or copolymerization accounts for simpler final construction and retained enzyme bioactivity is associated with good confinement

107

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Table 4.3 Enzyme immobilization methods used for biocathode design. Cathode material

Gold-carbon threedimensional film electrode Carbon black XC72R in Nafion film Adsorbed enzyme on carbon material BM-4 and coated with Nafion Pressed hydrophobized carbon black with Teflon Micro/macrocellular foams from silica monolith PBSE-modified CNT Amine-modified CNT Graphene-Pt Multiwall carbon nanotube/ZnO Graphene/AuNPs Graphene oxide/Co (OH)2/chitosan Graphene Graphene oxide/singlewall carbon nanotubes

Enzyme

Immobilization method

Current density
2

Reference

BOD

–

0.05 mA cm

[93]

BOD from Myrothecium/ verrucaria Laccase from Trametes hirsuta BOD from Myrothecium verrucaria BOD

Physical

0.25 mA cm
2 1.5 mA cm
2

[94]

Physical

0.3 mA cm
2

[95]

–

0.3 mA cm
2

[94]

–

2 mA cm
2

[96]

Laccase or BOD Laccase – Laccase

Covalent binding – Entrapment Physical absorption Covalent binding Covalent binding Physical adsorption Entrapment

0.4 mA cm
2

[97]

0.5 mA cm
2 46 μW cm
2 0.054 μW cm
2

[98] [99] [100]

1960 μW cm
2

[101]

517 μW cm
2

[102]

34.3 μW cm
2

[103]

1900 μW cm
2

[104]

Laccase Laccase Bilirubin oxidase Bilirubin oxidase

of both the enzyme and the redox mediator during the process. The general role of supporting materials is to provide an appropriate environment for operation and to preserve enzyme stability against harsh conditions. It was shown that a polymer layer is formed during the polymerization process which can restrict substrate diffusion. Moreover, formation of free radicals, leakage of enzyme/mediator, and providing sufficient solution pH for polymerization are the additional disadvantages of the entrapment technique. Polymer-graphene composites are the frequently used materials employed for enzyme entrapment. It is observed that some specific polymer composites are capable of mediating electron transfer between the enzymes and the electrodes. Another best-known example is the encapsulation of enzymes through the sol-gel method. Liu et al. developed a silica

Cathode electrodes in MFCs

sol-gel matrix for coimmobilization of graphene sheets and bilirubin oxidase [108]. The graphene/bilirubin oxidase-based cathode showed good potency in current generation. The large surface area of graphene allows a larger number of dislocations and electroactive functional groups that can covalently bind with more bilirubin oxidase. This endows the enzymatic electrode with efficient redox reactions.

4.7.3 Affinity The development of an avidin-biotin bridge and avidin-conjugated biomolecules allows enzymes to appear with a high degree of affinity toward the cathode surface [109]. Biotinylated polymer films can be achieved via electro-polymerization of biotin derivatives. Such electro-polymerization is carried out by functionalized phenol groups and linked pyrrole groups. For instance, the formation of an avidin-biotin bridge enabled researchers to immobilize biotinylated glucose oxide onto a copolymer electrode. This method allows to accurately retain enzyme properties, although providing appropriate biotin derivatives has remained a challenge. Furthermore, another strategy is used whereby enzymes are immobilized on a metal electrode surface in order to increase the ORR kinetics based on direct electron transfer (DET). To this aim, the electrode surface could be functionalized in a controlled way through the electrochemical reduction of diazonium salts. This embellishes the electrode surface with multiple aromatic rings containing different functional groups [110,111]. Subsequently, a propitious orientation of the enzyme T1 site to the electrode surface is achieved through specific covalent bonds. However, the diazonium salt method can lead to a multilayered film formation on the cathode surface due to aryl radical attack on the aromatic rings [110]. This problem has been tackled through altering the electro-reduction time. It was demonstrated that further incubation of the enzymatic cathode within the thiol solution allows a self-assembled monolayer formation on naked regions. The self-assembled monolayer can be beneficial in avoiding physical adsorption of the enzyme on the electrode surface and withdrawing any organic residues physically adsorbed on the cathode surface [112]. Furthermore, its rigid anchoring groups induce hydrogen bond formation, resulting in the stable immobilization of protein molecules. The maximum ORR on enzyme-modified cathodes can be determined by DET efficiency (Eq. 4.16), catalytic activity of the enzyme (Eq. 4.17), and oxygen diffusion to the cathode surface (Eq. 4.18) [113]. iDET ¼ nFAΓkDET

(4.16)

nFAΓkcat C o2 ðC o2 + K M Þ

(4.17)

icat ¼

2


1

1

idiff ¼ 0:62 nF D3 A  N o2 ν 6 ω2

(4.18)

109

110

Biological fuel cells

where i exhibits the steady-state current,  N o2 demonstrates the bulk concentration of the substrate, Γ demonstrates the surface concentration of the adsorbed enzyme, A is the cathode surface area, ν is the kinetic viscosity of the solution, and w is the angular frequency.

4.7.4 Covalent binding Steady covalent binding between the support matrix and the enzyme is challenging. For example, it has been observed for some time that active reagents can affect the enzymeactive site and therefore cause enzymatic activity loss. Apart from the enzyme immobilization technique, the type of electrode material can affect the biocathode performance. Carbon materials such as CNT or graphene can be designed to make an excellent connection with enzymes due to their good conductivity and biocompatibility [114,115]. Sufficient electron transfer from enzyme electrode can be induced by careful control of carbon materials. For instance, systematic control of the CNT electrode has been achieved through attaching 2,20 -azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) to the CNT on the end tube or the side wall [116]. Similarly, glutaraldehyde, 1-pyrene butanoic acid succinimidyl ester, and an aminophenyl layer have been utilized for covalent attachment of enzyme to the electrode [97,98]. The interaction between the aromatic-like structures in CNT and the aromatic pyrenyl moiety can be induced by irreversible π-π stacking. Furthermore, glutaraldehyde can be utilized as an effective conjugate. Studies show that modification with amine groups is required for the development of a successful glutaraldehyde—CNT connection [115].

4.8 Cathode catalysts: Conventional, photo, and biocatalysts Electrochemical O2 reduction is the most established reaction at the cathode surface for power generation in MFCs [11], although they are suppressed by carbon-based cathodes [117,118]. Electrocatalysts are utilized to revert cathode performance. Noble metals and Pt are frequently used cathode catalysts [119]. High cost and toxicity have restricted their applications in MFCs [117]. Multiple techniques have been applied to develop alternate efficient catalysts, including altering the size, shape, and architecture of conventional Pt nanostructures, designing novel Pt-based nanostructures, and generating more practical ORR catalysts using earth-abundant elements. To date, various Pt and Pt-based composites are well established for ORR catalysis [120]. According to the researches, it is theoretically possible to alter ORR activity as a function of the surface structure, electronic property, geometry, and lattice strain of cathode materials [121]. Therefore, studies have focused on designing durable non-Pt nanomaterials to upgrade ORR activity. Furthermore, the application of earth-abundant active elements to develop composite materials with a high surface area, more active sites, and special structure has been demonstrated to promote ORR function [122,123].

Cathode electrodes in MFCs

Non-Pt catalysts exhibit weak catalytic activity compared with Pt-containing ones [122]. Their loss of action can be compensated for through higher catalyst loading, leading to an intense reduction in mass transfer onto the cathode surface. For this reason, it is pivotal to impose intrinsic catalytic sites on the cathode surface using doping and/or forming micropore/mesopore to inhibit mass transfer exhaustion. Several scientific studies have been carried out to design more practical cathodes fabricated from nonprecious metals, oxides, and sulfides using microorganisms as biocatalysts. Table 4.4 summarizes the different types of cathode catalysts used in MFCs.

Table 4.4 A summary of different cathode catalysts used in MFCs. Cathode

Carbon cloth Carbon cloth Carbon cloth Carbon paper Stainless steel net Carbon cloth Carbon cloth Carbon cloth Carbon paper Carbon felt Graphite felt Graphite rod – Carbon fiber brush cathode Carbon paper Noncatalyzed graphite plate Carbon fiber cloth Carbon Cloth Carbon cloth Activated carbon Graphite paste Graphite plate Carbon paper/Pt Carbone black

Cathode catalyst

Crumpled graphene particles GNS/biofilm composite NGNS NGNS N-carbon nanosheet/GNS NGNS Pt-Co/GNS Ag NPs/rGO FeTsPc/GNS Fe3O4/rGO PANI/GNS PB/GNS Chlorella vulgaris Chlorella/phormidium Chlorella vulgaris Cyanobacteria (Anabaena strain) Chlorella vulgaris PANI/QDs Co3O4/PANI α-MnO2/GO TiO2 Seaweed PANI/V2O5 Copper-phthalocyanine

Maximum power density

3.3 W m


3

Reference

[124]

323.272 mW m
2 4.06 W m
3 776  12 mW m
2 1159.34 mW m
2 1618.75 mW m
2 1378 mW m
2 474.5 mW m
2 817 mW m
2 0.283 W m
2 99 mW m
2 16.26 W m
3 0.6 mW m
2 0.8 mW m
2

[125] [7] [126] [127] [128] [129] [130] [125] [131] [132] [133] [134] [135]

69 mW m
2 52.81 mW m
2 76.05 mW m
2 100.1 mW m
2 2485.35 mW m
3 166.93 mW m
2 102.54 mW m
2 148.4 mW m
2 220 mW m
2 42.156 mW m
2 79.26 mW m
2 118.2 mW m
2

[136] [137]

[138] [64] [79] [72] [139] [140] [141] [142]

NGNs, nitrogen-doped graphene nanosheets; GNs, graphene nanosheets; Pt, platinum; Co, cobalt; Rgo, reduced graphene oxide; FeTsPc, iron tetrasulfophthalocyanine; PANI, polyaniline; PB, poly(1-butene); QDs, cadmium sulfide quantum dots; GO, graphene oxide.

111

112

Biological fuel cells

4.8.1 Cathodic photocatalysts Toxicity and economic issues are the major challenges of air-cathodes equipped with a platinum catalyst. Additionally, it was shown that the use of such chemicals is impractical for large-scale applications. To overcome these problems, the use of biocathodes could be an alternative (Fig. 4.3). The method of using biocathodes is often referred to as a sustainable, environmentally friendly, and cost-effective route. The use of algae has furnished a remarkable array of biocatalysts by mimicking a natural syntrophic relationship between photosynthetic bacteria and algae. Algae mediate the conversion of carbon dioxide into organics when exposed to sunlight. The organics are reverted to carbon dioxide and water by benthic heterotrophs and reused by algae to regenerate organic matter and oxygen. Hence, it is revealed that such natural cycles can be utilized for energy production and water treatment within MFCs [143,144] . One reason for this is that there are substantial benefits to how the anode effluent saturated with carbonate materials, nitrate, ammonia nitrogen, and phosphorus can trigger cell growth and function. A second and more fundamental reason is that oxygen production of algae can supply the electron acceptor material in the cathodic chamber [145,146]. Furthermore, a continuous flow can regulate pH fluctuations of both the cathodic and anodic chambers. It was demonstrated that the algal biomass is valuable for the production of bioproducts and fuel [147]. In a study, Chlorella vulgaris has been utilized in cathodic half-cells in MFCs [134,148]. The growth of Chlorella vulgaris led to an optimum value of dissolved CO2 concentration [148]. In this study, Saccharomyces cerevisiae was used as the biocatalyst of the anodic chamber. Chlorella vulgaris is often selected due to its excellent tolerance for high levels of CO2, as well as high efficiency in taking up CO2 during photosynthesis. Bioelectricity and bioethanol production can be resulted, thereby utilizing a combination of Chlorella vulgaris photosynthesis and Saccharomyces cerevisiae fermentation. However, the higher growth rate of Saccharomyces cerevisiae can affect the yield of the operation. A continuous flow MFC system has been developed to address the problem, in which the growth rate of algae can be tuned perfectly [134].

4.8.2 Biocatalysts 4.8.2.1 Biology Microorganisms used for accepting electron from the cathode surface are called electrotrophs [149]. The process has been demonstrated for a large variety of electron acceptors, including oxygen, nitrate, sulfate, iron, manganese, arsenate, fumarate, or carbon dioxide [150,151]. It is an advanced technology that allows the use of bewildering variety of bacteria and fungi. Mixed-community aerobe biofilms are preferred as suitable biocatalysts rather than those of chemicals because of their cost, robustness, and sustainability. Alphaproteobacteria [152,153], Betaproteobacteria [154], Gammaproteobacteria [155],

Cathode electrodes in MFCs

Fig. 4.3 Schematic illustration of a double-chamber MFC equipped with a cathodic biocatalyst (A) and a cathodic photocatalyst (B).

Bacteroidetes [156], and other less well-known species [152,157,158] have been utilized as dominant mixed-community aerobic biocathodes. Carbajosa et al. reported that acidophilic Acidithiobacillus ferrooxidans can be involved in ORR [159]. Under anoxic conditions, nitrate and sulfate can serve as electron acceptors [160]. This means that it is straightforward for some microbes to catalyze denitrification, sulfate reduction, and autotrophic mechanisms in contrast to ORR by changing the concentration of oxygen.

113

114

Biological fuel cells

A majority of studies have detected autotrophic hydrogen, sulfate, and nitrogen consumer microbial consortia, including Desulfovibrio, Nitrosomonas sp., Nitrospira sp., Nitrobacter sp., Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, and Flavobacteria [152,160,161]. 4.8.2.2 Advantages of biocathode Lower cost, improved sustainability, and easy improvement have been introduced as the major advantages of biocathodes [162]. Precious metals such as Pt and cobalt are ideal abiotic cathode catalysts due to their high performance. Pt-containing electrodes are the most common types of cathodes which can promote the electrochemical performance of MFCs by fourfold. However, its maintenance costs can increase the total cost of constructing an MFC. Cobalt tetramethylphenylporphyrin (CoTMPP) can be an alternative to Pt-containing cathodes, as its power density is just 12% lower than that of Pt. The same problem is faced with CoTMPP. Biocathode MFCs possess moderate construction and operation costs, compared with abiotic MFCs. Biological cathode is preferred because microbes act as catalysts, and the addition of metal catalysts or chemicals as artificial electron mediators is not required. Furthermore, biocathodes enhance MFC sustainability through eliminating the possibility of metal poisoning and consumption replenishment of chemical mediators. It was found that MFC performance is correlated with many factors such as cathode material, electrode surface, electrode spacing, configuration, buffer solution properties, and concentration of substrate. When using microorganisms as biocatalysts, the abovementioned electrode properties are more adaptable, leading to an increment in production efficiency. 4.8.2.3 Disadvantages of biocathodes In some cases, the proton transport rate through the membrane is reported to be slower than that of proton production in the anodic chamber and proton consumption in the cathodic chamber. This has made it possible to develop high pHs in the anode chamber, and low pHs at cathode chamber. As microorganisms’ function is highly related to the pH of the environment, this can cause a reduction in the biocathode performance and consequently causes fluctuation in voltage output [163,164]. The trouble can be solved using a nonmembrane biocathode MFC. Cathode materials represent another type of problem. Cathode materials are required to provide an appropriate environment for biofilm growth and function. However, the search for a suitable cathode material remains largely empirical [140]. As an alternative, materials can be rationally tuned by simple alteration methods. Today, it is possible to design biocathode materials for achieving more sustainable energy recovery from organics. Moreover, in a large commercial application, the total power output is required to be improved in biocathode MFCs. It is because of the fact that in biocathode MFCs the biofilm activity is more restricted in contrast to that in abiotic cathode MFCs. One way to overcome this problem is to alter the operating

Cathode electrodes in MFCs

conditions such as temperature and pH. Furthermore, a fresh culture of microorganisms which possess a high metabolism rate can be used to address the problem.

4.8.3 Conventional catalysts 4.8.3.1 Pt and Pt-based ORR catalysts ORR is a kinetically controllable process requiring a significant amount of energy. Possessing a high reduction potential is considered as the main characteristic of ORR catalysts. Instability of materials at high potentials restricts their applications as metal-based ORR catalysts [165]. Among the noble metals like Hg, Au, Ag, Cu, Pd, Pt, etc., Pt has a well-suited reduction potential. Pt supported on activated carbon has been designed successfully and is available as a unique standard cathode catalyst of MFCs, although high cost and scarcity of Pt have restricted its large-scale production. Furthermore, Pt-containing electrodes are susceptible to agglomeration and dissolution in the long term [117]. The key to control is that Pt alloying with other earth-abundant metals can reduce the costs and promote the catalytic activity of Pt as well. Indeed, the extension of alloying to fabricating a Pt-based catalyst could provide a route to rational engineering of cathode electrodes, in which an alteration in the atomic structure leads to the creation of more active sites on the electrode surface. Toward this end, several studies have recently reported a tunable binding affinity with a composition change of alloy catalysts [117]. For instance, a high power density of 1724 mW m
2 has been achieved using Pt2-Ni/C as the catalyst [119]. Similarly, the Pt-Co/graphene composite allowed an excellent power production capacity (1378 mW m
2) even in low Pt content (15%) [129]. Fe contribution resulted in a significant improvement in power production from 1422 mW m
2 reported for the Pt/C catalyst to 1680 mW m
2 reported for the Pt3-Fe/C catalyst [166]. The studies demonstrated a strong connection between the catalytic efficacy and chemical composition of the alloys. 4.8.3.2 PMG-free catalyst The high cost and toxicity of Pt has led to the advent of Pt-free alternate catalysts. As electrode design specifies most of the MFC operation, researchers are attempting to fabricate suitable Pt-free electrode structures which can facilitate sufficient O2 adsorption and mass transfer rate in low costs [78]. Controlled mass transfer can only be provided with three-dimensional photo architectures. For instance, 3D nano-Pd-Cu and activated carbon-Ni foam have exhibited excellent ORR catalytic activity [167,168]. Fabrication of highly active ORR catalysts are also reported through encapsulation of bamboo-like CNT within CoNi alloy nanoparticles [169]. The ORR rate of 3.63 and average current density of 6.7 A m
2 are comparable with those of Pt-containing electrodes. In this case, nitrogenous functional groups in support material and the bimetallic catalysts electrode surface are used to improve the electrocatalytic activity.

115

116

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One way to increase ORR catalytic activity is by the contribution of low-cost metal oxide (MO) catalysts. Simple MOs, spinel-type MOs, and hybrids are the common types of transition MOs. Multiple researchers have utilized spinel type MOs such as MnCo2O4, Fe3O4, MnFe2O4, Co3O4, and NiCo2O4 as high-performance ORR catalysts [170–172]. In principle, valent metal centers in spinel-type MOs provide active sites for ORR function. Important electrocatalytic properties can be achieved through altering the chemical composition of MO [173], although poor electrical conductivity remains a major challenge of the MO-based cathode which increases the internal resistance. Contributions of electrically conductive supports such as active carbon, graphitized carbon, CNTs, graphene, and conducting polymer are proposed to increase the power generation capacity [79,174]. The high electronic conductivity and environmental stability of polymers such as PANI, Ppy, poly (3-methyl)thiophene, and poly(3,4-ethylenedioxythiophene) have made them potential ORR catalysts. As long-term electrochemical stability of such polymers is poor, they are utilized in combination with other catalyst materials, including active carbon, CNTs, graphene, metal complexes, and MOs. For instance, multiple uses of MO/PANI or Ppy composite catalysts such as MnCo2O4/PPy [11], V2O5/PANI [141], MnO2/PANI [175], and MnFe2O4/PANI [170] have been reported as a convenient route of increasing ORR activity within the cathode chamber of MFCs. .

4.9 Conclusions The current approaches for improving cathode performance involve the use of cost-effective, composite catalysts in MFCs. Nanotopography could directly modulate the electrochemical efficiency of cathode materials and produce a favorable power density. The structural pattern of electrodes could provide sufficient active sites for mass transfer and O2 activity and eventual water production. It is clear that the adaptation of cathode properties can facilitate high power generation by increasing the ORR catalytic activity. There is a growing emphasis on the development of superior functional cathode catalysts for use as tools to stimulate the use of waste for bioelectricity generation in MFCs. Despite the extensive research reported to date, the study of scale-up of MFCs is still limited, and appropriate synchronization of engineering, scientific experience, and design of effective catalyst materials is required to meet the scale-up requirements.

References [1] B.S. Thapa, T. Kim, S. Pandit, Y.E. Song, Y.P. Afsharian, M. Rahimnejad, J.R. Kim, S.-E. Oh, Overview of electroactive microorganisms and electron transfer mechanisms in microbial electrochemistry, Bioresour. Technol. 126579 (2021).

Cathode electrodes in MFCs

[2] A.R. Rahmani, N. Navidjouy, M. Rahimnejad, S. Alizadeh, M.R. Samarghandi, D. Nematollahi, Effect of different concentrations of substrate in microbial fuel cells toward bioenergy recovery and simultaneous wastewater treatment, Environ. Technol. 43 (2022) 1–9. [3] D. Pant, A. Singh, G. Van Bogaert, S.I. Olsen, P.S. Nigam, L. Diels, K. Vanbroekhoven, Bioelectrochemical systems (BES) for sustainable energy production and product recovery from organic wastes and industrial wastewaters, RSC Adv. 2 (2012) 1248–1263. [4] M. Lu, S.F.Y. Li, Cathode reactions and applications in microbial fuel cells: a review, Crit. Rev. Environ. Sci. Technol. 42 (2012) 2504–2525. [5] R. Alipanahi, M. Rahimnejad, Effect of different ecosystems on generated power in sediment microbial fuel cell, Int. J. Energy Res. 42 (2018) 4891–4897. [6] M. Omidi, M. Mashkour, J.K. Biswas, V.K. Garlapati, L. Singh, M. Rahimnejad, D. Pant, From electricity to products: recent updates on microbial electrosynthesis (MES), Top. Catal. (2021) 1–18. [7] M. Kannan, Current status, key challenges and its solutions in the design and development of graphene based ORR catalysts for the microbial fuel cell applications, Biosens. Bioelectron. 77 (2016) 1208–1220. [8] K.B. Liew, W.R.W. Daud, M. Ghasemi, J.X. Leong, S.S. Lim, M. Ismail, Non-Pt catalyst as oxygen reduction reaction in microbial fuel cells: a review, Int. J. Hydrog. Energy 39 (2014) 4870–4883. [9] L. Wei, H. Han, J. Shen, Effects of cathodic electron acceptors and potassium ferricyanide concentrations on the performance of microbial fuel cell, Int. J. Hydrog. Energy 37 (2012) 12980–12986. [10] M. Masoudi, M. Rahimnejad, M. Mashkour, Enhancing operating capacity of microbial fuel cells by using low-cost electrodes and multi anode-cathode connections in a membrane-less configuration, Int. J. Hydrog. Energy 46 (2021) 8226–8238. [11] S. Khilari, S. Pandit, D. Das, D. Pradhan, Manganese cobaltite/polypyrrole nanocomposite-based aircathode for sustainable power generation in the single-chambered microbial fuel cells, Biosens. Bioelectron. 54 (2014) 534–540. [12] A. Tardast, G. Najafpour, M. Rahimnejad, A.A. Ghoreyshi, H. Zare, K. Pirzadeh, Bioelectricity production by air cathode microbial fuel cell, in: 2012 Second Iranian Conference on Renewable Energy and Distributed Generation, IEEE, 2012, pp. 162–166. [13] M. Rahimnejad, A. Adhami, S. Darvari, A. Zirepour, S.-E. Oh, Microbial fuel cell as new technology for bioelectricity generation: a review, Alexandria Eng. J. 54 (2015) 745–756. [14] S. Bajracharya, A. ElMekawy, S. Srikanth, D. Pant, Cathodes for microbial fuel cells, in: Microbial Electrochemical and Fuel Cells, Elsevier, 2016, pp. 179–213. [15] E. Yeager, Dioxygen electrocatalysis: mechanisms in relation to catalyst structure, J. Mol. Catal. (Switzerland) 38 (1986). [16] K. Kinoshita, Electrochemical Oxygen Technology, John Wiley & Sons, 1992. [17] R.A. Rozendal, F. Harnisch, A. Jeremiasse, U. Schroder, Chemically Catalyzed Cathodes in Bioelectrochemical Systems, IWA Publishing, 2010. [18] R. Renslow, C. Donovan, M. Shim, J. Babauta, S. Nannapaneni, J. Schenk, H. Beyenal, Oxygen reduction kinetics on graphite cathodes in sediment microbial fuel cells, Phys. Chem. Chem. Phys. 13 (2011) 21573–21584. [19] R. Battino, H.L. Clever, The solubility of gases in liquids, Chem. Rev. 66 (1966) 395–463. [20] L. Allen, J. Bard, Electrochemical Methods Fundamental and Applications, John Wiley&Sons, Inc, The United State of America, 2001. [21] L.R. Faulkner, A.J. Bard, Electrochemical Methods: Fundamentals and Applications, John Wiley and Sons, 2002. [22] A. Mohamed, P.T. Ha, H. Beyenal, Kinetics and scale up of oxygen reducing cathodic biofilms, Biofilms 3 (2021), 100053. [23] J.-J. Sun, H.-Z. Zhao, Q.-Z. Yang, J. Song, A. Xue, A novel layer-by-layer self-assembled carbon nanotube-based anode: preparation, characterization, and application in microbial fuel cell, Electrochim. Acta 55 (2010) 3041–3047. [24] Y.H.P. Zhang, Production of biocommodities and bioelectricity by cell-free synthetic enzymatic pathway biotransformations: challenges and opportunities, Biotechnol. Bioeng. 105 (2010) 663–677.

117

118

Biological fuel cells

[25] S.K. Chaudhuri, D.R. Lovley, Electricity generation by direct oxidation of glucose in mediatorless microbial fuel cells, Nat. Biotechnol. 21 (2003) 1229–1232. [26] M. Di Lorenzo, K. Scott, T.P. Curtis, I.M. Head, Effect of increasing anode surface area on the performance of a single chamber microbial fuel cell, Chem. Eng. J. 156 (2010) 40–48. [27] F. Li, Y. Sharma, Y. Lei, B. Li, Q. Zhou, Microbial fuel cells: the effects of configurations, electrolyte solutions, and electrode materials on power generation, Appl. Biochem. Biotechnol. 160 (2010) 168. [28] B.E. Logan, M.J. Wallack, K.-Y. Kim, W. He, Y. Feng, P.E. Saikaly, Assessment of microbial fuel cell configurations and power densities, Environ. Sci. Technol. Lett. 2 (2015) 206–214. [29] K. Rabaey, L. Angenent, U. Schroder, J. Keller, Bioelectrochemical Systems: From Extracellular Electron Transfer to Biotechnological Applicaton, IWA Publishing, 2010. [30] Q. Zhang, L. Liu, A microbial fuel cell system with manganese dioxide/titanium dioxide/graphitic carbon nitride coated granular activated carbon cathode successfully treated organic acids industrial wastewater with residual nitric acid, Bioresour. Technol. 304 (2020), 122992. [31] L. Zhuang, S. Zhou, Y. Wang, C. Liu, S. Geng, Membrane-less cloth cathode assembly (CCA) for scalable microbial fuel cells, Biosens. Bioelectron. 24 (2009) 3652–3656. [32] X. Wang, X. Gong, L. Peng, Z. Yang, Y. Liu, Tubular nitrogen-doped carbon materials derived from green foxtail as a metal-free electrocatalyst in microbial fuel cells for efficient electron generation, Bioelectrochemistry 127 (2019) 104–112. [33] J. Wei, P. Liang, X. Cao, X. Huang, Use of inexpensive semicoke and activated carbon as biocathode in microbial fuel cells, Bioresour. Technol. 102 (2011) 10431–10435. [34] S.J. You, N.Q. Ren, Q.L. Zhao, J.Y. Wang, F.L. Yang, Power generation and electrochemical analysis of biocathode microbial fuel cell using graphite fibre brush as cathode material, Fuel Cells 9 (2009) 588–596. [35] Z. Zhang, I.M. O’Hara, W.O. Doherty, Pretreatment of sugarcane bagasse by acid-catalysed process in aqueous ionic liquid solutions, Bioresour. Technol. 120 (2012) 149–156. [36] C.-W. Lin, C.-H. Wu, Y.-Y. Lin, S.-H. Liu, S.-H. Chang, Enhancing the performance of microbial fuel cell using a carbon-fiber-brush air cathode with low-cost mushroom Ganoderma laccase enzyme, J. Taiwan Inst. Chem. Eng. 85 (2018) 115–120. [37] R. Kakarla, B. Min, Evaluation of microbial fuel cell operation using algae as an oxygen supplier: carbon paper cathode vs. carbon brush cathode, Bioprocess Biosyst. Eng. 37 (2014) 2453–2461. [38] S. Chen, S.A. Patil, U. Schr€ oder, A high-performance rotating graphite fiber brush air-cathode for microbial fuel cells, Appl. Energy 211 (2018) 1089–1094. [39] Z. He, H. Shao, L.T. Angenent, Increased power production from a sediment microbial fuel cell with a rotating cathode, Biosens. Bioelectron. 22 (2007) 3252–3255. [40] J. Zhang, L. Li, J. Zheng, P. Yang, X. Wu, C. Cheng, J. Li, Y. Tian, F. Wang, Improved organic pollutants removal and simultaneous electricity production via integrating Fenton process and dual rotating disk photocatalytic fuel cell system using bamboo charcoal cathode, Chem. Eng. J. 361 (2019) 1198–1206. [41] M. Rahimnejad, N. Mokhtarian, G. Najafpour, A.A. Ghoreyshi, W.R.W. Dahud, Effective parameters on performance of microbial fuel cell, in: 2009 Second International Conference on Environmental and Computer Science, IEEE, 2009, pp. 411–415. [42] M. Mustakeem, Electrode materials for microbial fuel cells: nanomaterial approach, Mater. Renew. Sustain. Energy 4 (2015). [43] Y.P. Afsharian, M. Rahimnejad, Functional dynamics of microbial communities in bioelectrochemical systems: the importance of eco-electrogenic treatment of complex substrates, Curr. Opin. Electrochem. 31 (2022), 100816. [44] N. Jayasinghe, A. Franks, K.P. Nevin, R. Mahadevan, Metabolic modeling of spatial heterogeneity of biofilms in microbial fuel cells reveals substrate limitations in electrical current generation, Biotechnol. J. 9 (2014) 1350–1361. [45] L. Pons, M.-L. Delia, A. Bergel, Effect of surface roughness, biofilm coverage and biofilm structure on the electrochemical efficiency of microbial cathodes, Bioresour. Technol. 102 (2011) 2678–2683. [46] N.J. Vickers, Animal communication: when i’m calling you, will you answer too? Curr. Biol. 27 (2017) R713–R715.

Cathode electrodes in MFCs

[47] M. Rahimnejad, M. Asghary, M. Fallah, Microbial fuel cell (MFC): an innovative technology for wastewater treatment and power generation, in: Bioremediation of Industrial Waste for Environmental Safety, Springer, 2020, pp. 215–235. [48] H. Ren, H.-S. Lee, J. Chae, Miniaturizing microbial fuel cells for potential portable power sources: promises and challenges, Microfluid. Nanofluid. 13 (2012) 353–381. [49] C. Santoro, M. Guilizzoni, J.C. Baena, U. Pasaogullari, A. Casalegno, B. Li, S. Babanova, K. Artyushkova, P. Atanassov, The effects of carbon electrode surface properties on bacteria attachment and start up time of microbial fuel cells, Carbon 67 (2014) 128–139. [50] H. Tursun, R. Liu, J. Li, R. Abro, X. Wang, Y. Gao, Y. Li, Carbon material optimized biocathode for improving microbial fuel cell performance, Front. Microbiol. 7 (2016) 6. [51] B. Liang, Y. Zhao, K. Li, C. Lv, Porous carbon codoped with inherent nitrogen and externally embedded cobalt nanoparticles as a high-performance cathode catalyst for microbial fuel cells, Appl. Surf. Sci. 505 (2020), 144547. [52] D. Wang, J. Hu, J. Yang, K. Xiao, S. Liang, J. Xu, B. Liu, H. Hou, Fe and N co-doped carbon derived from melamine resin capsuled biomass as efficient oxygen reduction catalyst for air-cathode microbial fuel cells, Int. J. Hydrog. Energy 45 (2020) 3163–3175. [53] L. Jourdin, S. Freguia, B.C. Donose, J. Chen, G.G. Wallace, J. Keller, V. Flexer, A novel carbon nanotube modified scaffold as an efficient biocathode material for improved microbial electrosynthesis, J. Mater. Chem. A 2 (2014) 13093–13102. [54] D. Natarajan, T. Van Nguyen, Effect of electrode configuration and electronic conductivity on current density distribution measurements in PEM fuel cells, J. Power Sources 135 (2004) 95–109. [55] V. Eerten-Jansen, C. Mieke, A.B. Veldhoen, C.M. Plugge, A.J. Stams, C.J. Buisman, A. Ter Heijne, Microbial community analysis of a methane-producing biocathode in a bioelectrochemical system, Archaea 2013 (2013). [56] M. Qi, B. Liang, R. Chen, X. Sun, Z. Li, X. Ma, Y. Zhao, D. Kong, J. Wang, A. Wang, Effects of surface charge, hydrophilicity and hydrophobicity on functional biocathode catalytic efficiency and community structure, Chemosphere 202 (2018) 105–110. [57] F. Zhang, G. Chen, M.A. Hickner, B.E. Logan, Novel anti-flooding poly (dimethylsiloxane)(PDMS) catalyst binder for microbial fuel cell cathodes, J. Power Sources 218 (2012) 100–105. [58] H. Dong, H. Yu, X. Wang, Q. Zhou, J. Feng, A novel structure of scalable air-cathode without Nafion and Pt by rolling activated carbon and PTFE as catalyst layer in microbial fuel cells, Water Res. 46 (2012) 5777–5787. [59] H. Dong, H. Yu, X. Wang, Catalysis kinetics and porous analysis of rolling activated carbon-PTFE air-cathode in microbial fuel cells, Environ. Sci. Technol. 46 (2012) 13009–13015. [60] C. Santoro, R. Gokhale, B. Mecheri, A. D’Epifanio, S. Licoccia, A. Serov, K. Artyushkova, P. Atanassov, Design of Iron (II) phthalocyanine-derived oxygen reduction electrocatalysts for high-powerdensity microbial fuel cells, ChemSusChem 10 (2017) 3243–3251. [61] B. Mecheri, V.C. Ficca, M.A.C. de Oliveira, A. D’Epifanio, E. Placidi, F. Arciprete, S. Licoccia, Facile synthesis of graphene-phthalocyanine composites as oxygen reduction electrocatalysts in microbial fuel cells, Appl. Catal. B Environ. 237 (2018) 699–707. [62] W. Yang, X. Wang, M. Son, B.E. Logan, Simultaneously enhancing power density and coulombic efficiency with a hydrophobic Fe-N4/activated carbon air cathode for microbial fuel cells, J. Power Sources 465 (2020), 228264. [63] W. Yang, R. Rossi, Y. Tian, K.-Y. Kim, B.E. Logan, Mitigating external and internal cathode fouling using a polymer bonded separator in microbial fuel cells, Bioresour. Technol. 249 (2018) 1080–1084. [64] E.F. Talooki, M. Ghorbani, M. Rahimnejad, M.S. Lashkenari, Evaluation of a visible light-responsive polyaniline nanofiber˗ cadmium sulfide quantum dots photocathode for simultaneous hexavalent chromium reduction and electricity generation in photo-microbial fuel cell, J. Electroanal. Chem. 873 (2020), 114469. [65] C. Liao, J. Wu, L. Zhou, T. Li, J. An, Z. Huang, N. Li, X. Wang, Repeated transfer enriches highly active electrotrophic microbial consortia on biocathodes in microbial fuel cells, Biosens. Bioelectron. 121 (2018) 118–124.

119

120

Biological fuel cells

[66] V. Kugarajah, J. Solomon, K. Rajendran, S. Dharmalingam, Enhancement of nitrate removal and electricity generation in microbial fuel cell using eggshell supported biocathode, Process Biochem. 113 (2022) 1–10. [67] Y. Qiao, S.-J. Bao, C.M. Li, Electrocatalysis in microbial fuel cells—from electrode material to direct electrochemistry, Energy Environ. Sci. 3 (2010) 544–553. [68] C. Santoro, B. Li, P. Cristiani, G. Squadrito, Power generation of microbial fuel cells (MFCs) with low cathodic platinum loading, Int. J. Hydrog. Energy 38 (2013) 692–700. [69] M. Ghasemi, M. Ismail, S.K. Kamarudin, K. Saeedfar, W.R.W. Daud, S.H. Hassan, L.Y. Heng, J. Alam, S.-E. Oh, Carbon nanotube as an alternative cathode support and catalyst for microbial fuel cells, Appl. Energy 102 (2013) 1050–1056. [70] F. Jaouen, V. Goellner, M. Lefvre, J. Herranz, E. Proietti, J.P. Dodelet, Oxygen reduction activities compared in rotating-disk electrode and proton exchange membrane fuel cells for highly active FeNC catalysts, Electrochim. Acta 87 (2013) 619–628. [71] F. Zhang, S. Cheng, D. Pant, G. Van Bogaert, B.E. Logan, Power generation using an activated carbon and metal mesh cathode in a microbial fuel cell, Electrochem. Commun. 11 (2009) 2177–2179. [72] A. Tofighi, M. Rahimnejad, M. Ghorbani, Ternary nanotube α-MnO2/GO/AC as an excellent alternative composite modifier for cathode electrode of microbial fuel cell, J. Therm. Anal. Calorim. 135 (2019) 1667–1675. [73] Z. Zeng, W. Zhang, Y. Liu, P. Lu, J. Wei, Uniformly electrodeposited α-MnO2 film on superaligned electrospun carbon nanofibers for a bifunctional catalyst design in oxygen reduction reaction, Electrochim. Acta 256 (2017) 232–240. [74] L. Tan, Y.-D. Yang, N. Li, S. Chen, Z.-Q. Liu, Enhanced activity and stability of Co 3 O 4-decorated nitrogen-doped carbon hollow sphere catalysts for microbial fuel cells, Catalysis, Sci. Technol. 7 (2017) 1315–1323. [75] N. Garino, A. Sacco, M. Castellino, J.A. Mun˜oz-Tabares, A. Chiodoni, V. Agostino, V. Margaria, M. Gerosa, G. Massaglia, M. Quaglio, Microwave-assisted synthesis of reduced graphene oxide/SnO2 nanocomposite for oxygen reduction reaction in microbial fuel cells, ACS Appl. Mater. Interfaces 8 (2016) 4633–4643. [76] M.-C. Tsai, T.-T. Nguyen, N.G. Akalework, C.-J. Pan, J. Rick, Y.-F. Liao, W.-N. Su, B.-J. Hwang, Interplay between molybdenum dopant and oxygen vacancies in a TiO2 support enhances the oxygen reduction reaction, ACS Catal. 6 (2016) 6551–6559. [77] C.J. Kirubaharan, D.J. Yoo, A.R. Kim, Graphene/poly (3, 4-ethylenedioxythiophene)/Fe3O4 nanocomposite—an efficient oxygen reduction catalyst for the continuous electricity production from wastewater treatment microbial fuel cells, Int. J. Hydrog. Energy 41 (2016) 13208–13219. [78] H. Rismani-Yazdi, S.M. Carver, A.D. Christy, O.H. Tuovinen, Cathodic limitations in microbial fuel cells: an overview, J. Power Sources 180 (2008) 683–694. [79] E.F. Talooki, M. Ghorbani, M. Rahimnejad, M.S. Lashkenari, Investigating the effects of in-situ fabrication of a binder-free Co3O4-polyaniline cathode towards enhanced oxygen reduction reaction and power generation of microbial fuel cells, Synth. Met. 258 (2019), 116225. [80] R. Kumar, L. Singh, A. Zularisam, Enhanced oxygen reduction reaction in air-cathode microbial fuel cells using flower-like Co3O4 as an efficient cathode catalyst, Int. J. Hydrog. Energy 42 (2017) 19287–19295. [81] Y. Wang, K. Zhong, H. Li, Y. Dai, H. Zhang, J. Zuo, J. Yan, T. Xiao, X. Liu, Y. Lu, Bimetallic hybrids modified with carbon nanotubes as cathode catalysts for microbial fuel cell: effective oxygen reduction catalysis and inhibition of biofilm formation, J. Power Sources 485 (2021), 229273. [82] S. Karthick, K. Haribabu, Bioelectricity generation in a microbial fuel cell using polypyrrolemolybdenum oxide composite as an effective cathode catalyst, Fuel 275 (2020), 117994. [83] M. Mashkour, M. Rahimnejad, Effect of various carbon-based cathode electrodes on the performance of microbial fuel cell, Biofuel Res. J. 2 (2015) 296–300. [84] M. Pal, R.K. Sharma, Development of wheat straw based catholyte for power generation in microbial fuel cell, Biomass Bioenergy 138 (2020), 105591. [85] Q. Feng, L. Xu, C. Liu, H. Wang, Z. Jiang, Z. Xie, Y. Liu, Z. Yang, Y. Qin, Treatment of shale gas fracturing wastewater using microbial fuel cells: mixture of aging landfill leachate and traditional aerobic sludge as catholyte, J. Clean. Prod. 269 (2020), 121776.

Cathode electrodes in MFCs

[86] S. Pandit, A. Sengupta, S. Kale, D. Das, Performance of electron acceptors in catholyte of a twochambered microbial fuel cell using anion exchange membrane, Bioresour. Technol. 102 (2011) 2736–2744. [87] H. Luo, P. Xu, T.M. Roane, P.E. Jenkins, Z. Ren, Microbial desalination cells for improved performance in wastewater treatment, electricity production, and desalination, Bioresour. Technol. 105 (2012) 60–66. [88] L. Qiang, L. Yuan, Q. Ding, Influence of buffer solutions on the performance of microbial fuel cell electricity generation, Huan Jing Ke Xue 32 (2011) 1524–1528. [89] A. Ebrahimi, G.D. Najafpour, D.Y. Kebria, Performance of microbial desalination cell for salt removal and energy generation using different catholyte solutions, Desalination 432 (2018) 1–9. [90] A.N. Ghadge, D.A. Jadhav, H. Pradhan, M.M. Ghangrekar, Enhancing waste activated sludge digestion and power production using hypochlorite as catholyte in clayware microbial fuel cell, Bioresour. Technol. 182 (2015) 225–231. [91] H. Hassan, B. Jin, S. Dai, T. Ma, C. Saint, Chemical impact of catholytes on Bacillus subtilis-catalysed microbial fuel cell performance for degrading 2, 4-dichlorophenol, Chem. Eng. J. 301 (2016) 103–114. [92] J.H. Yang, H.R. Kim, J.H. Lee, J.-H. Jin, H.U. Lee, S.W. Kim, Electrochemical properties of enzyme electrode covalently immobilized on a graphite oxide/cobalt hydroxide/chitosan composite mediator for biofuel cells, Int. J. Hydrog. Energy (2020). [93] A. Lesniewski, M. Paszewski, M. Opallo, Gold-carbon three dimensional film electrode prepared from oppositely charged conductive nanoparticles by layer-by-layer approach, Electrochem. Commun. 12 (2010) 435–437. [94] A. Habrioux, T. Napporn, K. Servat, S. Tingry, K. Kokoh, Electrochemical characterization of adsorbed bilirubin oxidase on Vulcan XC 72R for the biocathode preparation in a glucose/O2 biofuel cell, Electrochim. Acta 55 (2010) 7701–7705. [95] S. Shleev, G. Shumakovich, O. Morozova, A. Yaropolov, Stable ‘Floating’ air diffusion biocathode based on direct electron transfer reactions between carbon particles and high redox potential laccase, Fuel Cells 10 (2010) 726–733. [96] V. Flexer, N. Brun, O. Courjean, R. Backov, N. Mano, Porous mediator-free enzyme carbonaceous electrodes obtained through integrative chemistry for biofuel cells, Energy Environ. Sci. 4 (2011) 2097–2106. [97] R.P. Ramasamy, H.R. Luckarift, D.M. Ivnitski, P.B. Atanassov, G.R. Johnson, High electrocatalytic activity of tethered multicopper oxidase-carbon nanotube conjugates, Chem. Commun. 46 (2010) 6045–6047. [98] E. Nazaruk, M. Karaskiewicz, K. Z˙elechowska, J.F. Biernat, J. Rogalski, R. Bilewicz, Powerful connection of laccase and carbon nanotubes: material for mediator-free electron transport on the enzymatic cathode of the biobattery, Electrochem. Commun. 14 (2012) 67–70. [99] B. Devadas, V. Mani, S.-M. Chen, A glucose/O2 biofuel cell based on graphene and multiwalled carbon nanotube composite modified electrode, Int. J. Electrochem. Sci. 7 (2012) 8064–8075. [100] S. Palanisamy, S. Cheemalapati, S.-M. Chen, An enzymatic biofuel cell based on electrochemically reduced graphene oxide and multiwalled carbon nanotubes/zinc oxide modified electrode, Int. J. Electrochem. Sci. 7 (2012) 11477–11487. [101] Y. Chen, P. Gai, J. Zhang, J.-J. Zhu, Design of an enzymatic biofuel cell with large power output, J. Mater. Chem. A 3 (2015) 11511–11516. [102] H.U. Lee, H.Y. Yoo, T. Lkhagvasuren, Y.S. Song, C. Park, J. Kim, S.W. Kim, Enzymatic fuel cells based on electrodeposited graphite oxide/cobalt hydroxide/chitosan composite-enzymeelectrode, Biosens. Bioelectron. 42 (2013) 342–348. [103] K. Hoshi, K. Muramatsu, H. Sumi, Y. Nishioka, Graphene-coated carbon fiber cloth for flexible electrodes of glucose fuel cells, Jpn. J. Appl. Phys. 55 (2016) 02BE05. [104] A.S. Campbell, Y.J. Jeong, S.M. Geier, R.R. Koepsel, A.J. Russell, M.F. Islam, Membrane/mediator-free rechargeable enzymatic biofuel cell utilizing graphene/single-wall carbon nanotube cogel electrodes, ACS Appl. Mater. Interfaces 7 (2015) 4056–4065.

121

122

Biological fuel cells

[105] C.F. Blanford, R.S. Heath, F.A. Armstrong, A stable electrode for high-potential, electrocatalytic O2 reduction based on rational attachment of a blue copper oxidase to a graphite surface, Chem. Commun. (2007) 1710–1712. [106] S. L€ orcher, P. Lopes, A. Kartashov, E.E. Ferapontova, Direct bio-electrocatalysis of O2 reduction by streptomyces coelicolor laccase orientated at promoter-modified graphite electrodes, ChemPhysChem 14 (2013) 2112–2124. [107] N. Lalaoui, A. Le Goff, M. Holzinger, M. Mermoux, S. Cosnier, Wiring laccase on covalently modified graphene: carbon nanotube assemblies for the direct bio-electrocatalytic reduction of oxygen, Chem Eur J 21 (2015) 3198–3201. [108] C. Liu, S. Alwarappan, Z. Chen, X. Kong, C.-Z. Li, Membraneless enzymatic biofuel cells based on graphene nanosheets, Biosens. Bioelectron. 25 (2010) 1829–1833. [109] G. Merle, L. Brunel, S. Tingry, M. Cretin, M. Rolland, K. Servat, C. Jolivalt, C. Innocent, P. Seta, Electrode biomaterials based on immobilized laccase. Application for enzymatic reduction of dioxygen, Mater. Sci. Eng. C 28 (2008) 932–938. [110] J. Lyskawa, D. Belanger, Direct modification of a gold electrode with aminophenyl groups by electrochemical reduction of in situ generated aminophenyl monodiazonium cations, Chem. Mater. 18 (2006) 4755–4763. [111] G. Liu, T. B€ ocking, J.J. Gooding, Diazonium salts: stable monolayers on gold electrodes for sensing applications, J. Electroanal. Chem. 600 (2007) 335–344. [112] D.M. Shewchuk, M.T. McDermott, Comparison of diazonium salt derived and thiol derived nitrobenzene layers on gold, Langmuir 25 (2009) 4556–4563. [113] M. Pita, C. Gutierrez-Sanchez, D. Olea, M. Velez, C. Garcia-Diego, S. Shleev, V.M. Fernandez, A.L. De Lacey, High redox potential cathode based on laccase covalently attached to gold electrode, J. Phys. Chem. C 115 (2011) 13420–13428. [114] J.-F. Wu, M.-Q. Xu, G.-C. Zhao, Graphene-based modified electrode for the direct electron transfer of cytochrome c and biosensing, Electrochem. Commun. 12 (2010) 175–177. [115] X. Wang, P. Sj€ oberg-Eerola, K. Immonen, J. Bobacka, M. Bergelin, Immobilization of Trametes hirsuta laccase into poly (3, 4-ethylenedioxythiophene) and polyaniline polymer-matrices, J. Power Sources 196 (2011) 4957–4964. [116] K. Sadowska, K. Stolarczyk, J.F. Biernat, K. Roberts, J. Rogalski, R. Bilewicz, Derivatization of single-walled carbon nanotubes with redox mediator for biocatalytic oxygen electrodes, Bioelectrochemistry 80 (2010) 73–80. [117] W. Xia, A. Mahmood, Z. Liang, R. Zou, S. Guo, Earth-abundant nanomaterials for oxygen reduction, Angew. Chem. Int. Ed. 55 (2016) 2650–2676. [118] M. Ghasemi, W.R.W. Daud, S.H. Hassan, S.-E. Oh, M. Ismail, M. Rahimnejad, J.M. Jahim, Nanostructured carbon as electrode material in microbial fuel cells: a comprehensive review, J. Alloys Compd. 580 (2013) 245–255. [119] Z. Wang, Z. Yan, M. Wang, J. Zhao, Glycerol stabilized NaBH4 reduction for preparation carbon supported Pt-Ni alloy nanoparticles used as oxygen-reduction electrocatalysts for microbial fuel cells, Int. J. Electrochem. Sci. 10 (2015) 1953–1965. [120] I.E. Stephens, A.S. Bondarenko, U. Grønbjerg, J. Rossmeisl, I. Chorkendorff, Understanding the electrocatalysis of oxygen reduction on platinum and its alloys, Energy Environ. Sci. 5 (2012) 6744–6762. [121] M. RahimNeghad, R. Alipanahi, Investigation of the performance of sediment microbial fuel cells, in the presence of brush cathodes of various metal, Nashrieh Shimi va Mohandesi Shimi Iran 38 (2020) 271–278. [122] Y. Nie, L. Li, Z. Wei, Recent advancements in Pt and Pt-free catalysts for oxygen reduction reaction, Chem. Soc. Rev. 44 (2015) 2168–2201. [123] Z. Chen, D. Higgins, A. Yu, L. Zhang, J. Zhang, A review on non-precious metal electrocatalysts for PEM fuel cells, Energy Environ. Sci. 4 (2011) 3167–3192. [124] L. Xiao, J. Damien, J. Luo, H.D. Jang, J. Huang, Z. He, Crumpled graphene particles for microbial fuel cell electrodes, J. Power Sources 208 (2012) 187–192.

Cathode electrodes in MFCs

[125] Y. Zhang, G. Mo, X. Li, J. Ye, Iron tetrasulfophthalocyanine functionalized graphene as a platinumfree cathodic catalyst for efficient oxygen reduction in microbial fuel cells, J. Power Sources 197 (2012) 93–96. [126] Y. Liu, H. Liu, C. Wang, S.-X. Hou, N. Yang, Sustainable energy recovery in wastewater treatment by microbial fuel cells: stable power generation with nitrogen-doped graphene cathode, Environ. Sci. Technol. 47 (2013) 13889–13895. [127] Q. Wen, S. Wang, J. Yan, L. Cong, Y. Chen, H. Xi, Porous nitrogen-doped carbon nanosheet on graphene as metal-free catalyst for oxygen reduction reaction in air-cathode microbial fuel cells, Bioelectrochemistry 95 (2014) 23–28. [128] H. Xia, D. Zhu, Z. Luo, Y. Yu, X. Shi, G. Yuan, J. Xie, Hierarchically structured Co3O4@ Pt@ MnO2 nanowire arrays for high-performance supercapacitors, Sci. Rep. 3 (2013) 1–8. [129] Z. Yan, M. Wang, B. Huang, R. Liu, J. Zhao, Graphene supported Pt-Co alloy nanoparticles as cathode catalyst for microbial fuel cells, Int. J. Electrochem. Sci. 8 (2013) 149–158. [130] H. Sun, K. Xu, G. Lu, H. Lv, Z. Liu, Graphene-supported silver nanoparticles for pH-neutral electrocatalytic oxygen reduction, IEEE Trans. Nanotechnol. 13 (2014) 789–794. [131] G.H. Qi, X.Q. Li, J. Cao, Research on the phenol degradation in microbial fuel cells with Fe3O4reduced graphene oxide cathodic catalyst, in: Advanced Materials Research, Trans Tech Publications, 2014, pp. 310–314. [132] Y. Ren, D. Pan, X. Li, F. Fu, Y. Zhao, X. Wang, Effect of polyaniline-graphene nanosheets modified cathode on the performance of sediment microbial fuel cell, J. Chem. Technol. Biotechnol. 88 (2013) 1946–1950. [133] L. Xu, G. Zhang, J. Chen, L. Fu, F. Yang, Prussian blue/graphene-modified electrode used as a novel oxygen reduction cathode in microbial fuel cell, J. Taiwan Inst. Chem. Eng. 58 (2016) 374–380. [134] P. Mitra, G.A. Hill, Continuous microbial fuel cell using a photoautotrophic cathode and a fermentative anode, Can. J. Chem. Eng. 90 (2012) 1006–1010. [135] H. Jiang, S. Luo, X. Shi, M. Dai, R.-B. Guo, A novel microbial fuel cell and photobioreactor system for continuous domestic wastewater treatment and bioelectricity generation, Biotechnol. Lett. 34 (2012) 1269–1274. [136] Y. Zhang, J.S. Noori, I. Angelidaki, Simultaneous organic carbon, nutrients removal and energy production in a photomicrobial fuel cell (PFC), Energy Environ. Sci. 4 (2011) 4340–4346. [137] S. Pandit, B.K. Nayak, D. Das, Microbial carbon capture cell using cyanobacteria for simultaneous power generation, carbon dioxide sequestration and wastewater treatment, Bioresour. Technol. 107 (2012) 97–102. [138] M. Zhou, H. He, T. Jin, H. Wang, Power generation enhancement in novel microbial carbon capture cells with immobilized Chlorella vulgaris, J. Power Sources 214 (2012) 216–219. [139] M. Mashkour, M. Rahimnejad, S. Pourali, H. Ezoji, A. ElMekawy, D. Pant, Catalytic performance of nano-hybrid graphene and titanium dioxide modified cathodes fabricated with facile and green technique in microbial fuel cell, Prog. Nat. Sci.: Mater. Int. 27 (2017) 647–651. [140] Z. Najafgholi, M. Rahimnejad, Improvement of sediment microbial fuel cell performance by application of sun light and biocathode, Korean J. Chem. Eng. 33 (2016) 154–158. [141] K.B. Ghoreishi, M. Ghasemi, M. Rahimnejad, M.A. Yarmo, W.R.W. Daud, N. Asim, M. Ismail, Development and application of vanadium oxide/polyaniline composite as a novel cathode catalyst in microbial fuel cell, Int. J. Energy Res. 38 (2014) 70–77. [142] M. Ghasemi, W.R.W. Daud, M. Rahimnejad, M. Rezayi, A. Fatemi, Y. Jafari, M. Somalu, A. Manzour, Copper-phthalocyanine and nickel nanoparticles as novel cathode catalysts in microbial fuel cells, Int. J. Hydrog. Energy 38 (2013) 9533–9540. [143] L. Xiao, E.B. Young, J.J. Grothjan, S. Lyon, H. Zhang, Z. He, Wastewater treatment and microbial communities in an integrated photo-bioelectrochemical system affected by different wastewater algal inocula, Algal Res. 12 (2015) 446–454. [144] L. Xiao, Z. He, Applications and perspectives of phototrophic microorganisms for electricity generation from organic compounds in microbial fuel cells, Renew. Sust. Energ. Rev. 37 (2014) 550–559. [145] A.G. del Campo, P. Can˜izares, M.A. Rodrigo, F.J. Ferna´ndez, J. Lobato, Microbial fuel cell with an algae-assisted cathode: a preliminary assessment, J. Power Sources 242 (2013) 638–645.

123

124

Biological fuel cells

[146] I. Gajda, J. Greenman, C. Melhuish, I. Ieropoulos, Photosynthetic cathodes for microbial fuel cells, Int. J. Hydrog. Energy 38 (2013) 11559–11564. [147] B. Kokabian, V.G. Gude, Photosynthetic microbial desalination cells (PMDCs) for clean energy, water and biomass production, Environ Sci Process Impacts 15 (2013) 2178–2185. [148] E. Powell, R. Evitts, G. Hill, J. Bolster, A microbial fuel cell with a photosynthetic microalgae cathodic half cell coupled to a yeast anodic half cell, Energ. Sources Part A 33 (2011) 440–448. [149] D.R. Lovley, Powering microbes with electricity: direct electron transfer from electrodes to microbes, Environ. Microbiol. Rep. 3 (2011) 27–35. [150] B. Virdis, K. Rabaey, R.A. Rozendal, Z. Yuan, J. Keller, Simultaneous nitrification, denitrification and carbon removal in microbial fuel cells, Water Res. 44 (2010) 2970–2980. [151] S. Freguia, S. Tsujimura, K. Kano, Electron transfer pathways in microbial oxygen biocathodes, Electrochim. Acta 55 (2010) 813–818. [152] Y. Du, Y. Feng, Y. Dong, Y. Qu, J. Liu, X. Zhou, N. Ren, Coupling interaction of cathodic reduction and microbial metabolism in aerobic biocathode of microbial fuel cell, RSC Adv. 4 (2014) 34350–34355. [153] Z. Wang, Y. Zheng, Y. Xiao, S. Wu, Y. Wu, Z. Yang, F. Zhao, Analysis of oxygen reduction and microbial community of air-diffusion biocathode in microbial fuel cells, Bioresour. Technol. 144 (2013) 74–79. [154] H. Wang, S.C. Jiang, Y. Wang, B. Xiao, Substrate removal and electricity generation in a membraneless microbial fuel cell for biological treatment of wastewater, Bioresour. Technol. 138 (2013) 109–116. [155] Z. Wang, D.H. Leary, A.P. Malanoski, R.W. Li, W.J. Hervey, B.J. Eddie, G.S. Tender, S.G. Yanosky, G.J. Vora, L.M. Tender, A previously uncharacterized, nonphotosynthetic member of the Chromatiaceae is the primary CO2-fixing constituent in a self-regenerating biocathode, Appl. Environ. Microbiol. 81 (2015) 699–712. [156] Y. Sun, J. Wei, P. Liang, X. Huang, Microbial community analysis in biocathode microbial fuel cells packed with different materials, AMB Express 2 (2012) 1–8. [157] M. Rimboud, E. Desmond-Le Quemener, B. Erable, T. Bouchez, A. Bergel, The current provided by oxygen-reducing microbial cathodes is related to the composition of their bacterial community, Bioelectrochemistry 102 (2015) 42–49. [158] E. Blanchet, S. Pecastaings, B. Erable, C. Roques, A. Bergel, Protons accumulation during anodic phase turned to advantage for oxygen reduction during cathodic phase in reversible bioelectrodes, Bioresour. Technol. 173 (2014) 224–230. [159] S. Carbajosa, M. Malki, R. Caillard, M.F. Lopez, F.J. Palomares, J.A. Martı´n-Gago, N. Rodrı´guez, R. Amils, V.M. Ferna´ndez, A.L. De Lacey, Electrochemical growth of Acidithiobacillus ferrooxidans on a graphite electrode for obtaining a biocathode for direct electrocatalytic reduction of oxygen, Biosens. Bioelectron. 26 (2010) 877–880. [160] S. Hong, Y. Park, K. Jo, T. Lee, Autotrophic denitrification performance and bacterial community at biocathodes of bioelectrochemical systems with either abiotic or biotic anodes, J. Biosci. Bioeng. 119 (2015) 180–187. [161] G. Pozo, L. Jourdin, Y. Lu, P. Ledezma, J. Keller, S. Freguia, Methanobacterium enables high rate electricity-driven autotrophic sulfate reduction, RSC Adv. 5 (2015) 89368–89374. [162] H.-L. Song, Y. Zhu, J. Li, Electron transfer mechanisms, characteristics and applications of biological cathode microbial fuel cells—a mini review, Arab. J. Chem. 12 (2019) 2236–2243. [163] T. Jafary, W.R.W. Daud, M. Ghasemi, B.H. Kim, J.M. Jahim, M. Ismail, S.S. Lim, Biocathode in microbial electrolysis cell; present status and future prospects, Renew. Sust. Energ. Rev. 47 (2015) 23–33. [164] Y. Cui, N. Rashid, N. Hu, M.S.U. Rehman, J.-I. Han, Electricity generation and microalgae cultivation in microbial fuel cell using microalgae-enriched anode and bio-cathode, Energy Convers. Manag. 79 (2014) 674–680. [165] K.P. Singh, M.Y. Song, J.-S. Yu, Iodine-treated heteroatom-doped carbon: conductivity driven electrocatalytic activity, J. Mater. Chem. A 2 (2014) 18115–18124.

Cathode electrodes in MFCs

[166] Z. Yan, M. Wang, J. Liu, R. Liu, J. Zhao, Glycerol-stabilized NaBH4 reduction at room-temperature for the synthesis of a carbon-supported PtxFe alloy with superior oxygen reduction activity for a microbial fuel cell, Electrochim. Acta 141 (2014) 331–339. [167] L. Xiong, Y.-X. Huang, X.-W. Liu, G.-P. Sheng, W.-W. Li, H.-Q. Yu, Three-dimensional bimetallic Pd-Cu nanodendrites with superior electrochemical performance for oxygen reduction reaction, Electrochim. Acta 89 (2013) 24–28. [168] S. Cheng, J. Wu, Air-cathode preparation with activated carbon as catalyst, PTFE as binder and nickel foam as current collector for microbial fuel cells, Bioelectrochemistry 92 (2013) 22–26. [169] Y. Hou, H. Yuan, Z. Wen, S. Cui, X. Guo, Z. He, J. Chen, Nitrogen-doped graphene/CoNi alloy encased within bamboo-like carbon nanotube hybrids as cathode catalysts in microbial fuel cells, J. Power Sources 307 (2016) 561–568. [170] S. Khilari, S. Pandit, J.L. Varanasi, D. Das, D. Pradhan, Bifunctional manganese ferrite/polyaniline hybrid as electrode material for enhanced energy recovery in microbial fuel cell, ACS Appl. Mater. Interfaces 7 (2015) 20657–20666. [171] M. Ma, Y. Dai, J.-L. Zou, L. Wang, K. Pan, H.-G. Fu, Synthesis of iron oxide/partly graphitized carbon composites as a high-efficiency and low-cost cathode catalyst for microbial fuel cells, ACS Appl. Mater. Interfaces 6 (2014) 13438–13447. [172] B. Ge, K. Li, Z. Fu, L. Pu, X. Zhang, Z. Liu, K. Huang, The performance of nano urchin-like NiCo2O4 modified activated carbon as air cathode for microbial fuel cell, J. Power Sources 303 (2016) 325–332. [173] F. Cheng, J. Shen, B. Peng, Y. Pan, Z. Tao, J. Chen, Rapid room-temperature synthesis of nanocrystalline spinels as oxygen reduction and evolution electrocatalysts, Nat. Chem. 3 (2011) 79–84. [174] A. Tofighi, M. Rahimnejad, M. Ghorbani, Ternary nanotube α-MnO 2/GO/AC as an excellent alternative composite modifier for cathode electrode of microbial fuel cell, J. Therm. Anal. Calorim. 135 (2019) 1667–1675. [175] S.A. Ansari, N. Parveen, T.H. Han, M.O. Ansari, M.H. Cho, Fibrous polyaniline@ manganese oxide nanocomposites as supercapacitor electrode materials and cathode catalysts for improved power production in microbial fuel cells, Phys. Chem. Chem. Phys. 18 (2016) 9053–9060.

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CHAPTER 5

Energy and power measurement methods in MFCs Mostafa Rahimnejad

Biofuel and Renewable Energy Research Center, Chemical Engineering Department, Babol Noshirvani University of Technology, Babol, Mazandaran, Iran

5.1 Introduction Microbial fuel cell (MFC) is an electrochemical device with excellent potential for power generation. It exploits microbial metabolism for power production, wastewater treatment, biosensing, and desalination. The excellent performance of MFCs is closely correlated with electroactive microorganisms and involved biological factors. Moreover, it was found that power generation in MFCs is strongly affected by temperature and hydraulic retention [1] as well as substrate composition, type of separator , electrode catalysts, and aeration rate [2]. Normally, the catalytic activity of microorganisms is significant in a certain temperature range, which directly influence intracellular and extracellular biological processes [3]. Therefore, temperature evaluation is crucial to achieve optimal MFC performance. Furthermore, studies show that appropriate separators and electrode catalysts represent 90% of the MFC cost, determining the possibility of MFC commercialization. Control over biological environment is pivotal for understanding the behavior of electroactive biofilm and for engineering MFC performance [4]. The properties of the MFC apparatus are often largely or entirely determined by anaerobic microbial substrate oxidation at anode and dissolved oxygen reduction rate at cathode [5]: Anodic reaction : ðCH2 OÞn + nH2 O ! nCO2 + 4ne + 4nH+ 



Cathodic reaction : O2 + 4e + 2H2 O ! 4OH

(5.1) (5.2)

Since anode is operated under anoxic conditions, Monod-type equation can be used to evaluate the microbial degradation/oxidation rate of substrate. In the case of bioelectrochemical reactions Butler-Volmer expression is adopted to describe the correlation between the biodegradation kinetics and the electrical potential [6]:
 F Cs r 1 ¼ k01 exp α: :X (5.3) :ŋa1 K s + Cs R:T

Biological Fuel Cells https://doi.org/10.1016/B978-0-323-85711-6.00011-4

Copyright © 2023 Elsevier Inc. All rights reserved.

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where Cs and X denote substrate and biomass concentrations, respectively. ŋa1 denotes the anodic overpotential, k01 indicates the maximum specific growth rate, Ks is the halfvelocity rate constant for substrate, α is the charge transfer coefficient, F is the Faraday constant, R is the gas constant, and T is the MFC operating temperature. Similar calculation can be made for estimating the reaction rate of dissolved oxygen (r2) at the cathode chamber [6]:
 C O2 F r 2 ¼ k02 exp ðβ  1Þ: :ŋa2 K O2 + C O2 R:T

(5.4)

where k02, β, and KO2 are positive constants which represent the rate constant of the cathode reaction, cathodic charge-transfer coefficient, and half-velocity rate of dissolved oxygen, respectively. CO2denotes the concentration of dissolved oxygen within the cathode chamber and ŋa2 is the cathode overpotential. If both anode and cathode chambers are treated as continuous stirred tank electrochemical reactors, all mass-transfer processes are likely to be faster than those of biochemical and redox reactions, so the concentrations of all active species present within the balk and on the surface of the electrodes are equal. Assuming negligible substrate and gas diffusivity throughout the membrane, Eqs. (5.5), (5.6), (5.7), and (5.8) can be applied, respectively, to the mass balances of the substrate, biomass, H+, and dissolved CO2 in the anode compartment [6]:   dC V a s ¼ Qa C ins  C s  Am  r 1 (5.5) dt  in  dX X X Va + Am Y ac r 1  V a K d X (5.6) ¼ Qa dt fx   dC H ¼ Qa C inH  C H + 4nAm r 1 dt
 dC V a CO2 ¼ Qa C inCO2  C CO2 + nAm r 1 dt Va

(5.7) (5.8)

It is also possible to apply equations of the mass transfer to the dissolved O2, hydroxyl, and cation M+ at cathode chamber [6]:
 dC V c CO2 ¼ Qc C inCO2  C CO2 + Am r 2 (5.9) dt   dC (5.10) V c OH ¼ Qc C inOH  C OH  4Am r 2 dt   dC V c M ¼ Qc C inM  C M + N M Am (5.11) dt

Energy and power measurement methods in MFCs

Here, V denotes the volume of the chambers, Q is the feed flow rate, Am is the crosssectional area of membrane, fx is the reciprocal of the wash-out fraction, Yac demonstrates the microbial yield, and Kd displays the decay constant of substrate utilizers. The subscripts “a,” “in,” and “c” represent the anode, the feed flow, and the cathode, respectively. These show the relevance of the various parameters that are being examined when practicing high-yield MFC power output. Both cathodic mass transfer and anodic mass transfer can control MFC performance. Moreover, suppression in fuel feed flow rate can result in remarkable power output, and thereafter limited power density is reported [7]. However, increment in fuel concentration can achieve high levels of power output and attainable current density [8]. All in all, regulating the MFC performance is a vital issue necessary to evaluate the efficiency of the bioelectrochemical reactions. This chapter deals with a range of electroanalytical techniques used in study of MFC performance in order to achieve optimal operating conditions. We summarize the techniques used to control the MFC performance and solve issues in fundamentals of bioelectrochemical systems. The methods described here are the techniques described in the literature.

5.2 Power indicators 5.2.1 Coulombic efficiency Coulombic efficiency (CE) can be used to investigate MFC performance. CE is defined as the ratio of coulombs transported to the anode, to the total coulombs available from bioelectro-oxidation of the substrate [9]. High CE is the aim of the MFC operation, ensuring sufficient electrogenesis. Suppression of methanogenesis, improvement of catalysis, and application of appropriate current collector provide an opportunity to promote CE in an MFC system. Two mode of operation make the net columbic efficiency truly unique though. They include batch or fed-batch mode of operation and continuous mode of operation. In the former, CE is a function of output current and is calculated as follows:  Z  M I dt CE ¼ (5.12) Fb V and ΔCOD where F denotes the Faraday’s constant, b is the number of electrons per mole of substrate, M is molar mass of substrate, and COD demonstrates the organic content, within which four electrons are required for oxygen reduction. The following equation is used to determine the value of CE in a continuous mode of operation organized under a steady-state current:

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ðM I Þ (5.13) Fbk ΔCOD where k is the influent flow rate of substrate and I is the current intensity. Furthermore, CE can be calculated based on the charge transfer in relation to molar mass of O2 using the following equation:   Z MO2 Idt (5.14) CE ¼ ne F V and ΔCOD CE ¼

where Vand denotes the volume of the anode chamber, ΔCOD is the difference between initial and final COD (g/L) of the substrate during MFC operation, MO2 indicates the molecular mass of O2, and ne shows the number of electrons required to reduce oxygen to water. Indeed, CE demonstrates the fraction of substrate that may be utilized for power generation.

5.2.2 Open circuit voltage (OCV) OCV is defined as the maximum voltage produced in MFC at infinite resistance and is calculated when the electric current flow between the anodes and the cathodes is disconnected [9]. Theoretically, since voltage losses do not affect OCV value, it is expected to be equal to electromotive force (emf ), although in experimental investigations, the voltage losses lead to significant reduction in OCV value. Open circuit potential refers to the potential of the electrode, whereas OCV apparently relates to voltage of the entire electrochemical cell. OCV is used in cell analysis when no current flows through the cell and no potential difference is applied to the cell. Indeed, techniques such as OCV have been successfully used for evaluation of biofilm formation on the electrode surface in the absence of an external electrical stimulus. Furthermore, studies show that OCV can be used to determine temporal stability of the electrochemical systems.

5.2.3 Current density Current density is utilized to analyze electron transfer rate and overall performance of MFC. Current density is defined as the amount of charge per surface area of the electrode: Id ¼

I Aele

(5.15)

where Id denotes the current density, I is the resultant current (amperes), and Aele indicates the surface area of the electrodes (A cm2). Additionally, current density can be calculated as current per unit volume of anodic chamber (A cm3) [10]:

Energy and power measurement methods in MFCs

I Vol where Vol indicates the volume of the anodic chamber. Id ¼

(5.16)

5.2.4 Power density An important parameter of MFC optimization is the power density for stable and consistent power output measurements. Thus, besides providing data to support practical application of MFCs, it also provides an opportunity to compare various fluctuations in different MFC configurations that can occur due to changes in metabolic activity of the microbes, disruption in catalytic activities, and membrane fouling [10]. Power density can be obtained as a function of electrode surface or the volume of specific chamber: V I Aele V I Id ¼ Vol

Pd ¼

(5.17) (5.18)

5.3 Electrochemical methods 5.3.1 Polarization study Polarization study serves as a basis for the analysis and description of MFC operational variables, including temperature, relative humidity, pressure, current, and flow rate. A polarization curve is a graphical representation of changes in current density (I) as a function of electrode potential (E). With balanced internal and external resistances maximum power and current densities within an MFC system can be achieved. Using polarization analysis MFC components can be formulated. In fact, this paradigm can determine the I-V characteristics of either MFC cell or independent anodes and cathodes, regarding as reference electrode. Potentiostat and resistance box are utilized to carry out the analysis [9]. The resistance is changed manually in both increasing and decreasing orders to record the stable operating voltage, where Ohm’s law is used to calculate the current density. Subsequently, a polarization curve is plotted as a function of current density. Studies show that the total resistance of MFC is related with several parameters such as MFC volume as well as internal resistance of the cell. There would be three distinct zones in polarization graph. Firstly, activation losses lead to a sharp decline in the operating voltage. These losses are correlated with activation energy needed to modulate redox reactions. Secondly, a steady decline in voltage occurs due to Ohmic losses. These losses are mainly caused by resistance of electrodes, membranes, electrolyte used, interconnects, and the current collectors. Finally, concentration polarization drops the voltage drastically at high currents. Moreover, a power plot

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obtained from the polarization graph demonstrates the point of maximum attainable power (Rint). The power graph displays power density changes as a function of current density. The graph is also utilized to estimate the internal resistance of the cell. One of the simplest techniques to evaluate anode and cathode potentials is singlecycle polarization method, which is originally used to study MFC performance. Anode potential (EAn,m) can be calculated based on the potential difference between the anode and the reference electrode. Subsequently, anode and cathode potentials (EAn and ECat) are adjusted through alteration in solution conductivity and electrode distances from the reference electrode. The following coupled equations can be used to predict EAn and ECat within an MFC system [11]: RΩ 103 ¼ l σA  3  10 RΩ dAnRE EAn ¼ E An,m  i l  3  10 RΩ dCatRE i E Cat ¼ ðE An + U Þ + l

(5.19) (5.20) (5.21)

where RΩ/l (Ω cm1) indicates the solution Ohmic resistance per distance, dAn-Cat (cm) is the distance between the anode and the cathode, σ (mS cm1) is the conductivity of the solution, U is the voltage drop, A (cm2) demonstrates the electrode surface area (cm2), dAn-RE (cm) is the distance between the anode and the reference electrode, and dCat-RE (cm) indicates the distance between the cathode and the reference electrode.

5.3.2 Current interruption Current interruption (CI) represents the internal resistance of MFCs. In this technique, MFC operation under a fixed external resistance can be made to detect a stable current, where the circuit is disconnected to record the voltage transient. The internal resistance is calculated using the following equation: ðV 2  V 1Þ Re xt (5.22) I where Rint and Rext are internal resistance (Ω) and external resistance (Ω), respectively. V1 denotes closed circuit voltage (V), V2 indicates steep-fronted high voltage (V), and I is closed-circuit current. CI obtained resistance is related to Ohmic overpotential, an instantaneous potential loss possessing longer relaxation times [12]. CI technique provides a single data point which is easy to interpret. It is reported that short-duration perturbations can cause interruption in data collection and lead to confusing results. Rint ¼

Energy and power measurement methods in MFCs

5.3.3 Voltammetry techniques Voltammetry techniques play powerful roles in determining analyte reactivity in an electrochemical half-reaction [13,14]. In this method, a voltammogram, a plot of the resulting current (I) as a function of applied potential (Eapp), is depicted to examine sensitive characteristics of anolyte and electrode materials. Controlling these aspects with precision is thus the fundamental aim of these electroanalytical techniques. In MFCs, voltammetry techniques are utilized as a potent techniques to deduce electron transfer mechanisms within anodic chamber, enabling biofilm characterization as well as evaluation of bioelectrochemical reactions [15]. A potentiostat, encompassing a working electrode, a counter electrode, and a reference electrode, is utilized for conducting voltammetry experiments. The working electrode is assembled into the network to make a direct contact with anolyte solution, facilitating electron transfer within anodic chamber under a constant desired potential. Reference electrodes, such as saturated calomel electrode (SCE; +0.25 V vs SHE) and silver/silver chloride electrodes (Ag/AgCl; +0.210 V vs SHE) can be configured to maintain a constant working electrode potential. The counter electrode completes the circuit through passing the current to the working electrode. Linear sweep voltammetry (LSV), cyclic voltammetry (CV), differential pulse voltammetry (DPV), and chronoamperometry (CA) are voltammetry techniques used for MFC performance analysis. 5.3.3.1 Linear sweep voltammetry technique LSV technique has received much attention as an alternative polarization technique. It is commonly used to detect unknown species, to determine anolyte concentration, and to deduce electron transfer mechanisms involved in electrochemically irreversible reactions. The general process of LSV technique is the change of potential in working electrode as a function of time and record the current response. To do so, voltage is changed within a certain range and at a constant scan rate (v ¼dE/dt). Oxidation/reduction peaks are observed during the potential scan due to the presence of oxidized/reduced species [16] (Fig. 5.1). It was shown that electrode transfer rate and reactivity of mediator species can alter LSV characteristics [17]. The main drawback of the technique is significant decrement in capacitive currents at high scan rates which is difficult to be compensated. 5.3.3.2 Cyclic voltammetry technique CV is one of the most widely used techniques for evaluating the nature of the electron transfer mechanisms, the value of the formal potential, the reversibility of the electroactive species, the kinetic behavior of the microbe-electrode interactions, and the impact of the material mass transfer [18,19]. In principle, potential is scanned from a lower limit to an upper limit; through which the scan is ramped reversibly at upper limit and the voltage is swept back to the lower limit. CV plot can elucidate the mechanism of the involved

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Fig. 5.1 Illustrating linear sweep voltammetry (A) and effect of scan rate on current density (B).

redox reactions, in which the presence of both anodic and cathodic peaks accounts for a reversible redox reaction and a single peak displays an irreversible redox system [20] (Fig. 5.2). Furthermore, more than one peak is observed during the CV experiment of biological reactions [21,22]. Additionally, the absence of the reversible peak is reported when the bioelectrochemical reaction is followed by a chemical reaction, which restricts the detection of the overall rate-limiting step of the reaction [23]. Therefore, CV should be carefully scrutinized during MFC investigation. The formal potential of the redox species is estimated by CV technique as follows: Ef ¼

E pa + Epc 2

Fig. 5.2 Illustrating cyclic voltammetry (A) and current versus potential response (B).

(5.23)

Energy and power measurement methods in MFCs

where Epa and Epc are anodic and cathodic peak potentials, respectively. Obtained formal potentials are compared to standard redox potentials (E0) to determine the redox entity involved in bioelectrochemical reactions. For instance, we used CV to investigate the relationship between biofilm behavior and type of mediator in a double-chamber MFC inoculated with Escherichia coli ATCC 8739 [23]. Methylene blue, thionine, potassium ferricyanide, and neutral red at different concentrations (50–500 μmo1) were utilized as electron shuttles at anode compartment. In a cyclic voltammogram, the upper peak demonstrates the process of electron transfer from electrode to biofilm, while the lower peak displays the process of electron transfer from biofilm to the electrode surface. Maximum oxidation peak of 6 mA was achieved for natural red at 350 μmo1 concentration and 220 mV imposed potential. The impact of substrate concentration, incubation time, and cell concentration were also tested by comparing the oxidation and reduction peaks and the position of the maximum current. Results show that oxidation and reduction peaks associated with the incubation time are changed. However, the position of peaks remained unchanged after 46 h of incubation. We demonstrated that alteration in substrate and biocatalyst concentration contributes to the changeable profile of oxidation and reduction peaks. 5.3.3.3 Differential pulse voltammetry Literally, DPV is based on potential scanning with a series of pulses, within which each pulse possesses a fixed small amplitude (Fig. 5.3) [24]. This technique is based on the difference in the rate of the decay between the charging current and the Faradic current after applying the potential pulses. The Faradic current is a function of time and, therefore, its rate of decay is much slower than that of charging current. A peak-shaped voltammogram is obtained through differential reading of current, at the beginning and the end of each pulse. The monitored current rarely includes Faradic current due to its limited rate of decay.

Fig. 5.3 Differential pulse voltammetry (A) and effect of scan rate on current response (B).

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DPV is a practical strategy to estimate quality and quantity of redox active species involved in electron transfer mechanisms within MFCs [25,26]. Today, DPV is combined with spectrophotometric or chromatographic techniques for obtaining more details about the nature of the electroactive species. In a study, DPV technique was used to determination of the Flutamide. We used glassy carbon electrode modified with gold nanoparticles for determination of the Flutamide in our fabricated sensor [26]. DPV was performed in potential range of 0.55 to 0.85. Linear peak currents were reported for Flutamide within the concentration range of 1–600 μM. Furthermore, gradual increment in peak currents was observed with the increment in Flutamide concentration. Detection limit of 1.5 nM was achieved for Flutamide using DPV technique. Table 5.1 shows examples of using DPV technique to examine sensitive characteristics of analyte and electrode materials. 5.3.3.4 Chronoamperometry technique CA technique is a process of applying a step potential followed by monitoring the current-time profile. Cottrell equation describes the type of current-time dependency at a constant potential: nFAC 0 D0 1=2 (5.24) n1=2 t 1=2 where n is stoichiometric number of the involved electrons, F displays Faraday’s constant (96,485 C/equivalent), A is electrode area (cm2), C0 demonstrates concentration of electroactive species (mol/cm3), and D0 denotes diffusion constant for electroactive species (cm2/s). In CA technique, determined electrode area makes a convenience measurement of n and D0 for electroactive species. CA technique is ubiquitous in MFC analysis and regarded as the foundation for evaluating electrogenic species in the natural environment [35], biofilm formation on electrode surfaces [36], as well as comparing capacitive and Faradaic currents [37]. One of the most challenging aspects of CA is discovery of current-consuming electrotrophs that has widened CA applications in the evaluation of conversion of current to useful products such as alcohols. CA technique is a technique to develop a constant potential for the working electrode against the reference electrode. The chronoamperogram gives an overview of the electrical current response as a function of time (Fig. 5.4). Current-overpotential equation introduces the factors that can affect the electrical response [38]:  C ox αfn C red ð1αÞf ŋ i ¼ i0 (5.25) e  ∗ e C ∗ox C red it ¼

where C represents the concentration of the oxidized and reduced active species, and asterisk displays the bulk concentration. Chronoamperometry can be utilized to study

Table 5.1 PDV application in analyze detection. Electrode

Voltammetry method

ZrO2NPs/GACh/CNTPE AuNPs/GCE CPE/NiFe2O4

DPV DPV DPV

GRNP/CPE CPE

DPV DPV

Gr/αFe2O3/ CPE Au

DPV DPV

CPE/CNT

DPV

GC/AuNPs CPE NiCl2/GCE CS-MPAAuNPs

DPV DPV DPV DPV

linear range

Analyte

Limit of detection

Reference

0.01–0.1 0.3–6 μM 1–600 μM 1–90 μM

Bisphenol A

15 nM

[24]

Flutamide Rizatriptan benzoate, Acetaminophen Gabapentin Buserelin

1.5 nM Acetaminophen: 0.49 μM, Rizatriptan benzoate,0.44 μM 7.04 nM 0.73 μM

[26] [27] [20] [22]

Rizatriptan, Benzoate

0.42 μM

[28]

Flutamide

1.8 μM

[29]

Diazinon

4.5  1010

[30]

Gabapentin Curcumin Curcumin Nitric oxide

3.25 μM 5.03 μM 0.109 μM 0.199 μM

[31] [32] [33] [34]

0.01–1 μM 1.0 104– 6.0 106 μM 2 and 50 μM 6–60 μM and 100–600 μM 1 1010– 6 108 M – 3–300 μM 10–600 μM 1  107– 21.5  107 M

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Fig. 5.4 Illustrating chronoamperogram (A) and response waveform (B).

direct substrate biodegradation and biofilm formation on electrode surface at constant substrate concentration. Furthermore, CA technique provides clearance of substrate cycles, where the overall charge density can be calculated through the integration of chronoamperogram in the determined period of time.

5.3.4 Butler-Volmer analysis and Tafel Plots Researchers have been attempting to evaluate electron transfer kinetics and overpotentials found in MFCs in an effort to optimize charge transfer between the anolyte and the electrode. Butler-Volmer equation in particular has shown significant advances in examination of electron transfer kinetics and the associated overpotentials in MFCs. Electrode kinetics can be evaluated by estimating the charge transfer value between the anolyte and the electrode in less Ohmic and concentration overpotentials: n o j ¼ A i0 eanFŋ=RT  eð1aÞnFŋ=RT (5.26) where j represents the current density, A corresponds to the surface of the electrode, io indicates exchange current density, α is barrier of the charge transfer (symmetry coefficient), n is number of electrons involved in the redox reaction, and ŋ demonstrates the charge transfer overpotential. It has been known that exchange current density is the maximum current obtained when overpotential is negligible. The higher the exchange current density the faster the electrochemical reaction would be. Two limiting conditions make the Butler-Volmer equation truly unique though. First, when overpotential is high enough to yield Tafel equation (Eq. 5.27). Second, when low overpotential region yields polarization resistance (Eq. 5.28).

Energy and power measurement methods in MFCs

 i ¼ i0

 anF ðŋÞ exp RT

(5.27)

nF ðŋÞ (5.28) RT where i indicates current (A), ŋ is overpotential (V), (anF/RT) demonstrates the Tafel slope, and E shows the equilibrium potential. Tafel slopes can be used to evaluate charge transfer capabilities of electrogenic biofilm; low Tafel slopes demonstrate high transfer of electrons to the electrode surface (Fig. 5.5). Furthermore, electron transfer coefficient (α) can be deduced by careful estimation of Tafel slopes. Electron transfer coefficient (α) is a challenging parameter, describing the symmetry between the forward and reverse redox reactions. Therefore, Butler-Volmer analysis and Tafel Plots provide precise control over bacterial-electrode electron transfer mechanisms in MFCs. It was demonstrated that overpotential is major trigger for the initiation of redox reactions and suppression of concentration gradients. The Ohmic drop accounts for the energy losses occurred in various MFC components such as electrolyte, electrode structure, and external connections. Overall, both overpotentials and Ohmic drop change as a function of current density. It was shown that increment in current density induces the overpotential and the Ohmic drop. Tafels law illustrates the correlation between the electrode overpotential and the current density (Eq. 5.29), while the connection between the Ohmic drop and the current density can be examined by Ohms’s law (Eq. 5.30):     j j ŋ ¼ ba ln + bc ln (5.29) j0,a j0,c i ¼ i0

U Ω ¼ IR

Fig. 5.5 Illustrating Butler-Volmer analysis (A) and Tafel Plot (B).

(5.30)

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5.3.5 Electrochemical impedance spectroscopy (EIS) analysis The general performance of EIS in the calculation of the internal resistance of MFCs is well appreciated. Compared with other techniques, EIS is more informative about polarization losses in MFCs and have greater potential for estimating the value of these losses and individual contribution of each loss [28]. Moreover, EIS enables excellent comparison of MFC components, as well as electrode and biofilm characterization. One reason for its uniqueness is the use of known AC current as an alternative to DC [30]. The most established instrument for performing the analysis is potentiostat. Twoelectrode mode and three-electrode mode are simple configurations of a potentiostat that are selected depending on the aim of the analysis. In the former, the anode/cathode is utilized as the working electrode while the other makes the counter electrode. The same connection is used in the three-electrode mode along with the addition of a reference electrode. Small, well-defined AC perturbance is first given to the system and then the impedance and resulting phase shift are monitored in the second step. This technique results in two distinct plots, namely Bode plot and Nyquist plot. A small AC sinusoidal signal in a definite frequency range is used to form Nyquist and Bode plots. Nyquist plot report the real part of the impedance on the X-axis and the complex part on the Y-axis. The graph can be either a semicircle or a straight line followed by a semicircle (Fig. 5.6). Semicircle diameter represents the charge transfer resistance (Rp) or the polarization resistance of the MFC, whereas the straight line demonstrates MFC capacitance. Bode plot affords valuable information on frequency, phase angles, and impedance. Nevertheless, the plots are considerably complex, consisting of capacitances and resistances, and also differ from system to system.

Fig. 5.6 Randles circuit (A) and typical Nyquist plot (B).

Energy and power measurement methods in MFCs

5.4 Biofilm characterization methods Certain biological, microscopic, and chemical methods fulfill biofilm community characterization in MFCs. Each method possesses a distinct taxonomic resolution and a unique application purpose. Today, genomic/metagenomic, transcriptomic/metatranscriptomic, proteomic/meta-proteomic, metabolomics/meta-metabomoics, and microscopic coupled with flow cytometry have a multitude of applications to understand microbial interactions and microbial metabolic cross-communication. Furthermore, understanding of electron transfer pathways involved in electrode-grown biofilms were made possible following the combination of metagenomic and metaproteomic analyses.

5.4.1 Detection of biofilm forming microorganisms Culture-dependent and independent approaches are pertinent determinants of biofilm communities. A broad range of culture-dependent methods such as serial dilution are used to isolate specific populations. Serial dilution is followed by solid plate culture where a pure culture is obtained from single colonies. Furthermore, culture-independent techniques provide complete detection of biofilm populations. Moreover, fluorescence in situ hybridization (FISH) can be used to detect and quantify biofilm-forming microorganisms [39]. In FISH, fluorescent oligonucleotide probes are designed to discriminate genus specific sequences. The level of discrimination is varied, depending on signal generated from the sample that is useful when low microbial population densities are predicted [40]. Quantitative real-time polymerase chain reaction (q-PCR) is another technique that is central to detect specific microbes within biofilm structure [41].

5.4.2 Characterization of microbial communities In addition to the biofilm detection, complete characterization of the microbial population is a pivotal requirement for improving MFC performance. Genetic fingerprinting techniques can help to characterize biofilm composition. Gel electrophoresis, for example, functions as an effective technique, providing visual identification of separate amplicons. Denaturing gradient gel electrophoresis (DGGE) has been explored to separate polymerase chain reaction (PCR)-generated DNA products so DGGE enables detection of dominant microbial organisms. Studies show that similar size distribution of PCR products are obtained from a given reaction, leading to separation of a single DNA band that is largely nondescriptive using conventional agarose gel electrophoresis. To overcome this, DGGE has been used to separate PCR products based on sequence differences to mediate differential denaturing characteristics of the DNA. DGGE offers a pattern of bands, resulting from denaturation of DNA sequences (from different bacteria) at different denaturant concentrations. Each band demonstrates different microbial population of the biofilm. The fingerprints can be utilized to evaluate microbial structural differences. DGGE allows separation of amplicons through increasing gradient of denaturants

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(formamide and urea), whereas secondary structure of the fragments is maintained using nondenaturing electrophoresis. Furthermore, temperature gradient gel electrophoresis (TGGE) can make temperature gradient for amplicon separation. Terminal restriction fragment length polymorphism (T-RFLP) amplifies target genes, specifically the hypervariable region of 16S rRNA genes, from microbial population [42]. Moreover, as an alternative version of RFLP, amplified ribosomal DNA restriction analysis (ARDRA) amplifies the conserved regions at the end of the 16S gene [43]. The amplification is followed by digestion using tetracutter restriction enzymes. Having amplified the cultured isolates and 16S genes, ARDRA can be utilized for phylogenetical evaluation of species. Biofilm genetic variation is determined through single-strand conformation polymorphism (SSCP) analysis [44] that compares altered conformations with defined conformations. In this instance, a single base substitution is consistent with alteration in mobility of the single-stranded DNA, most likely throughout nondenaturing electrophoresis. Metagenomics is a genomic approach devoted to the characterization of biofilm community through nucleic acid extraction followed by data analysis. It was shown that further phenotypic or chemotaxonomic characterization is an essential requirement to complete the classification. For instance, cellular fatty acid methyl ester (FAME) analysis, a chemotaxonomy, is employed while combining with gas chromatography (GC) or liquid chromatography (LC) coupled with mass spectrometry (MS) [45]. Polyphasic approach allows detection of phylogenetic relationships between microbes and contributes to characterization of new species. The approach takes advantage of multiple techniques such as complete gene sequencing and comparative analysis using phylogenetic trees, DNA-DNA hybridization, analysis of molecular markers, biochemical assays, and microscopic characterization [45]. Researchers have noted that additional genotypic, phenotypic, and phylogenetic data can accommodate polyphasic taxonomy. Microbial communities are also determined using flow cytometry, through which the stained samples are evaluated by a series of lasers. Detectors are utilized either for quantifying the abundance of microbes [46] or determining the composition of samples [47,48]. A combination of flow cytometry with fluorescent in situ hybridization techniques can be used to detect specific microbial species [49]. In this technique, fluorescently labeled probes directed to 16S ribosomal RNA (rRNA) sequences are used to identify microbial species within biofilm.

5.4.3 Analysis of biofilm activity Researchers can use techniques based on metatranscriptome and metaproteome to analyze biofilm activity. For instance, metatranscriptomics evaluates gene expression levels of

Energy and power measurement methods in MFCs

biofilm. The technique involves RNA isolation followed by real-time PCR (RT-PCR) or microarray analysis [50]. RT-PCR is central to quantifying the altered gene expression of functional genes in response to different environmental conditions [51]. Similarly, microarray-based metatranscriptomic analysis provides a rapid, high-throughput consideration of functional gene expression. Metatranscriptomics and metaproteomics provide similar information about functional attributes of microbial communities in MFCs [52]. However, another important characteristic of metaproteomics is a high capacity to provide information at the level of protein expression [53]. Since protein expression in cells determines specific microbial activities, functional activity of biofilm can be characterized using metaproteomics. Stable isotope probing (SIP) is a method through which active populations of biofilm is determined [54]. Density gradient centrifugation is utilized for the detection of stable isotope substrate (13C or 15N) as a probe of substrate content. Nuclear magnetic resonance imaging (NMRI) allows evaluation of water movement within microbial communities. As mass transfer within biofilm is affected by intrabiofilm flow [55], the application of NMRI technique can be practical for perception of molecular diffusion and, also, biofilm process modeling [56].

5.5 Conclusions Although bioelectrochemical systems hold great promise, some critical factors such as material characteristics and microbial factors affect electron transfer rate and limit their current use. In many instances, the mechanisms remain uncertain, and identifying the specific challenges associated with power loss is a key issue confronting MFC performance. Multiple biological and chemical tools have been used to evaluate power loss challenges as well as electron transfer rate limitations within MFCs. Several studies have considered technical fundamentals and confirmed their applications, although, innovative electrochemical analysis are also required for further improvements in MFC science.

References [1] L. Wei, Z. Yuan, M. Cui, H. Han, J. Shen, Study on electricity-generation characteristic of twochambered microbial fuel cell in continuous flow mode, Int. J. Hydrog. Energy 37 (2012) 1067–1073. [2] M. Ghasemi, M. Ismail, S.K. Kamarudin, K. Saeedfar, W.R.W. Daud, S.H. Hassan, L.Y. Heng, J. Alam, S.-E. Oh, Carbon nanotube as an alternative cathode support and catalyst for microbial fuel cells, Appl. Energy 102 (2013) 1050–1056. [3] B.S. Thapa, T. Kim, S. Pandit, Y.E. Song, Y.P. Afsharian, M. Rahimnejad, J.R. Kim, S.-E. Oh, Overview of electroactive microorganisms and electron transfer mechanisms in microbial electrochemistry, Bioresour. Technol. (2021), 126579. [4] Y.P. Afsharian, M. Rahimnejad, Functional dynamics of microbial communities in bioelectrochemical systems: the importance of eco-electrogenic treatment of complex substrates, Curr. Opin. Electrochem. 31 (2022), 100816.

143

144

Biological fuel cells

[5] A.Y. Radeef, Z.Z. Ismail, Polarization model of microbial fuel cell for treatment of actual potato chips processing wastewater associated with power generation, J. Electroanal. Chem. 836 (2019) 176–181. [6] Y. Zeng, Y.F. Choo, B.-H. Kim, P. Wu, Modelling and simulation of two-chamber microbial fuel cell, J. Power Sources 195 (2010) 79–89. [7] M. Rahimnejad, G. Najafpour, A.A. Ghoreyshi, Effect of mass transfer on performance of microbial fuel cell, INTECH 5 (2011) 233–250. [8] N. Mokhtarian, M. Rahimnejad, G. Najafpour, W.R.W. Daud, A. Ghoreyshi, Effect of different substrate on performance of microbial fuel cell, Afr. J. Biotechnol. 11 (2012) 3363–3369. [9] B.E. Logan, B. Hamelers, R. Rozendal, U. Schr€ oder, J. Keller, S. Freguia, P. Aelterman, W. Verstraete, K. Rabaey, Microbial fuel cells: methodology and technology, Environ. Sci. Technol. 40 (2006) 5181–5192. [10] M. Sun, L.-F. Zhai, W.-W. Li, H.-Q. Yu, Harvest and utilization of chemical energy in wastes by microbial fuel cells, Chem. Soc. Rev. 45 (2016) 2847–2870. [11] B.E. Logan, E. Zikmund, W. Yang, R. Rossi, K.-Y. Kim, P.E. Saikaly, F. Zhang, Impact of ohmic resistance on measured electrode potentials and maximum power production in microbial fuel cells, Environ. Sci. Technol. 52 (2018) 8977–8985. [12] F. Zhao, R.C. Slade, J.R. Varcoe, Techniques for the study and development of microbial fuel cells: an electrochemical perspective, Chem. Soc. Rev. 38 (2009) 1926–1939. [13] H. Zare, G.D. Najafpour, M. Jahanshahi, M. Rahimnejad, M. Rezvani, Highly stable biosensor based on glucose oxidase immobilized in chitosan film for diagnosis of diabetes, Roman. Biotechnol. Lett. 22 (2017) 12611–12619. [14] M. Asghary, J.B. Raoof, M. Rahimnejad, R. Ojani, A novel self-powered and sensitive label-free DNA biosensor in microbial fuel cell, Biosens. Bioelectron. 82 (2016) 173–176. [15] H. Ezoji, M. Rahimnejad, G. Najafpour-Darzi, Advanced sensing platform for electrochemical monitoring of the environmental toxin; bisphenol A, Ecotoxicol. Environ. Saf. 190 (2020), 110088. [16] R. Zokhtareh, M. Rahimnejad, An investigation of new electrochemical sensors for curcumin detection: a mini review, Anal. Methods 11 (2019) 4401–4409. [17] M. Asghary, J.B. Raoof, M. Rahimnejad, R. Ojani, Microbial fuel cell-based self-powered biosensing platform for determination of ketamine as an anesthesia drug in clinical serum samples, J. Iran. Chem. Soc. 15 (2018) 445–453. [18] F. Harnisch, S. Freguia, A basic tutorial on cyclic voltammetry for the investigation of electroactive microbial biofilms, Chem. Asian J. 7 (2012) 466–475. [19] A. Zabihollahpoor, M. Rahimnejad, G. Najafpour-Darzi, Recent advances in electroanalytical methods for the therapeutic monitoring of antiepileptic drugs: a comprehensive review, J. Pharm. Biomed. Anal. 188 (2020), 113394. [20] A. Zabihollahpoor, M. Rahimnejad, G. Najafpour-Darzi, A.A. Moghadamnia, Biomedical application of a novel nanostructured-based electrochemical platform for therapeutic monitoring of an antiepileptic drug; Gabapentin, Analyt. Bioanalyt. Electrochem. 12 (2020) 536–552. [21] E. Marsili, J.B. Rollefson, D.B. Baron, R.M. Hozalski, D.R. Bond, Microbial biofilm voltammetry: direct electrochemical characterization of catalytic electrode-attached biofilms, Appl. Environ. Microbiol. 74 (2008) 7329–7337. [22] M. Fallah, M. Rahimnejad, M. Asghary, M. Mashkour, An electrochemical sensor based on a carbon paste electrode for the determination of buserelin, Anal. Methods 12 (2020) 33–38. [23] M. Rahimnejad, G.D. Najafpour, A. Ghoreyshi, G. Bakeri, F. Talebnia, S.-E. Oh, B. Noshirvani, Investigation of different mediators in microbial fuel cell with cyclic voltammeter, Pak. J. Biotechnol. 10 (2013) 37–51. [24] H. Ezoji, M. Rahimnejad, G. Najafpour-Darzi, Development of the electrochemical and molecular dynamics approaches toward the monitoring of biomolecular interaction between DNA and the intercalative endocrine disruptor; Bisphenol A, Measurement 185 (2021), 109977. [25] M. Sharma, P. Jain, J.L. Varanasi, B. Lal, J. Rodrı´guez, J.M. Lema, P.M. Sarma, Enhanced performance of sulfate reducing bacteria based biocathode using stainless steel mesh on activated carbon fabric electrode, Bioresour. Technol. 150 (2013) 172–180.

Energy and power measurement methods in MFCs

[26] A. Mehrabi, M. Rahimnejad, M. Mohammadi, M. Pourali, Electrochemical detection of Flutamide as an anticancer drug with gold nanoparticles modified glassy carbon electrode in the presence of prostate cancer cells, J. Appl. Electrochem. 51 (2021) 597–606. [27] M. Nouri, M. Rahimnejad, G. Najafpour, A.A. Moghadamnia, Simultaneous voltammetric determination of rizatriptan and acetaminophen using a carbon paste electrode modified with NiFe2O4 nanoparticles, Microchim. Acta 187 (2020) 1–9. [28] M. Nouri, M. Rahimnejad, G. Najafpour, A. Akbar Moghadamnia, A gr/αFe2O3/carbon paste electrode developed as an electrochemical sensor for determination of rizatriptan benzoate: an antimigraine drug, ChemistrySelect 4 (2019) 13421–13426. [29] A. Mehrabi, M. Rahimnejad, M. Mohammadi, M. Pourali, Electrochemical detection of flutamide with gold electrode as an anticancer drug, Biocatal. Agric. Biotechnol. 22 (2019), 101375. [30] M. Rahimnejad, R.A. Abdulkareem, G. Najafpour, Determination of Diazinon in fruit samples using electrochemical sensor based on carbon nanotubes modified carbon paste electrode, Biocatal. Agric. Biotechnol. 20 (2019), 101245. [31] A. Zabihollahpoor, M. Rahimnejad, G. Najafpour, A.A. Moghadamnia, Gold nanoparticle prepared by electrochemical deposition for electrochemical determination of gabapentin as an antiepileptic drug, J. Electroanal. Chem. 835 (2019) 281–286. [32] M. Rahimnejad, R. Zokhtare, A.A. Moghadamnia, M. Asghary, Fabrication of electrochemical curcumin sensor based on carbon paste electrode, Appl. Chem. 13 (2018) 91–104. [33] R. Zokhtareh, M. Rahimnejad, A novel sensitive electrochemical sensor based on nickel chloride solution modified glassy carbon electrode for curcumin determination, Electroanalysis 30 (2018) 921–927. [34] E. Pashai, G.N. Darzi, M. Jahanshahi, F. Yazdian, M. Rahimnejad, An electrochemical nitric oxide biosensor based on immobilized cytochrome c on a chitosan-gold nanocomposite modified gold electrode, Int. J. Biol. Macromol. 108 (2018) 250–258. [35] S. Parot, M.-L. Delia, A. Bergel, Forming electrochemically active biofilms from garden compost under chronoamperometry, Bioresour. Technol. 99 (2008) 4809–4816. [36] B. Cercado-Quezada, M.-L. Delia, A. Bergel, Testing various food-industry wastes for electricity production in microbial fuel cell, Bioresour. Technol. 101 (2010) 2748–2754. [37] S. Khilari, S. Pandit, J.L. Varanasi, D. Das, D. Pradhan, Bifunctional manganese ferrite/polyaniline hybrid as electrode material for enhanced energy recovery in microbial fuel cell, ACS Appl. Mater. Interfaces 7 (2015) 20657–20666. [38] R. Carden˜a, B. Cercado, G. Buitro´n, Microbial electrolysis cell for biohydrogen production, in: Biohydrogen, Elsevier, 2019, pp. 159–185. [39] Y. Liu, Y.-H. Bi, Z.-G. Zhou, Dual-color fluorescence in situ hybridization with combinatorial labeling probes enables a detailed karyotype analysis of Saccharina japonica, Algal Res. 62 (2022), 102636. [40] J.M. Brown, S. De Ornellas, E. Parisi, L. Schermelleh, V.J. Buckle, RASER-FISH: non-denaturing fluorescence in situ hybridization for preservation of three-dimensional interphase chromatin structure, Nat. Protoc. (2022) 1–26. [41] A. Şahiner, S. C ¸ alıs¸kan, E. Halat, Development of a new multiplex quantitative real-time polymerase chain reaction method for Clostridium butyricum, Clostridium sporogenes and Clostridium tyrobutyricum detection in cheese, LWT 155 (2022), 112914. [42] Z. Syed, M. Sogani, J. Rajvanshi, K. Sonu, Electroactive biofilm and electron transfer in microbial electrochemical systems, in: Scaling Up of Microbial Electrochemical Systems, 2022, pp. 29–48. € [43] D.K. Ozdo gan, N. Akc¸elik, M. Akc¸elik, Genetic diversity and characterization of plant growthpromoting effects of bacteria isolated from rhizospheric soils, Curr. Microbiol. 79 (2022) 1–11. [44] T.G. Ambaye, A. Chebbi, F. Formicola, S. Prasad, F.H. Gomez, A. Franzetti, M. Vaccari, Remediation of soil polluted with petroleum hydrocarbons, and their reuse for agriculture: recent progress, challenges, and perspectives, Chemosphere 133572 (2022). [45] P.B. Gannibal, Polyphasic approach to fungal taxonomy, Biol. Bull. Rev. 12 (2022) 18–28. [46] A. James, Ceramic-microbial fuel cell (C-MFC) for waste water treatment: a mini review, Environ. Res. (2022), 112963. [47] M. Bouix, S. Ghorbal, D. Picque, B. Perret, C. Saulou-Berion, A rapid method for the assessment of the vitality of microorganisms using flow cytometry, Cytometry A (2022).

145

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[48] A.C. Pereira, A. Tenreiro, M.V. Cunha, When FLOW-FISH met FACS: combining multiparametric, dynamic approaches for microbial single-cell research in the total environment, Sci. Total Environ. 806 (2022), 150682. [49] H. Maan, T.L. Povolotsky, Z. Porat, M. Itkin, S. Malitsky, I. Kolodkin-Gal, Imaging flow cytometry reveals a dual role for exopolysaccharides in biofilms: to promote self-adhesion while repelling non-selfcommunity members, Comput. Struct. Biotechnol. J. 20 (2022) 15–25. [50] K. Zhang, T. Wang, J. Chen, J. Guo, H. Luo, W. Chen, Y. Mo, Z. Wei, X. Huang, The reduction and fate of antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs) in microbial fuel cell (MFC) during treatment of livestock wastewater, J. Contam. Hydrol. 247 (2022), 103981. [51] H. Wang, X. Qi, S. Chen, X. Wang, The efficient treatment of breeding wastewater by an electroactive microbial community in microbial fuel cell, J. Environ. Chem. Eng. (2022), 107187. [52] P. Sharma, S.P. Singh, H.M. Iqbal, Y.W. Tong, Omics approaches in bioremediation of environmental contaminants: an integrated approach for environmental safety and sustainability, Environ. Res. (2022), 113102. [53] V.K. Gaur, K. Gautam, P. Sharma, P. Gupta, S. Dwivedi, J.K. Srivastava, S. Varjani, H.H. Ngo, S.-H. Kim, J.-S. Chang, Sustainable strategies for combating hydrocarbon pollution: special emphasis on mobil oil bioremediation, Sci. Total Environ. (2022), 155083. [54] M. Arslan, J.A. M€ uller, M.G. El-Din, Aerobic naphthenic acid-degrading bacteria in petroleum-coke improve oil sands process water remediation in biofilters: DNA-stable isotope probing reveals methylotrophy in Schmutzdecke, Sci. Total Environ. 815 (2022), 151961. [55] M. Gupta, N. Savla, C. Pandit, S. Pandit, P.K. Gupta, M. Pant, S. Khilari, Y. Kumar, D. Agarwal, R.R. Nair, Use of biomass-derived biochar in wastewater treatment and power production: a promising solution for a sustainable environment, Sci. Total Environ. (2022), 153892. [56] J. Huang, Y. Zhang, X. Deng, J. Li, S. Huang, X. Jin, X. Zhu, Self-encapsulated enzyme through in-situ growth of polypyrrole for high-performance enzymatic biofuel cell, Chem. Eng. J. 429 (2022), 132148.

CHAPTER 6

MFC designing and performance Mostafa Rahimnejad

Biofuel and Renewable Energy Research Center, Chemical Engineering Department, Babol Noshirvani University of Technology, Babol, Mazandaran, Iran

6.1 Introduction Microbial fuel cells (MFCs) play a vital role in producing electricity from microbial degradation of organic molecules [1]. Similar to other novel energy technologies, scaling up MFCs is associated with several practical challenges. To overcome such challenges, more efforts should be devoted toward eliminating the gaps between laboratory-scale setups and those in industrial applications. Generally, smaller electrodes and more concentrated substrates endow MFCs with better performance [2]. In recent years, many studies have focused on evaluating different configurations and modes of operation in MFCs for obtaining ideal operation factors on a large scale. Moreover, a successful MFC scaleup can be achieved through the investigation of some key design and operational parameters such as size of the electrodes and the flow mode over them. Electrode costs and diminished power at larger scales are known as critical factors that restrict the translation of laboratory-scale processes to larger scales. Although MFC has a certain capability for power production, the intrinsic loss of power at larger scales caused by reactor geometry is undeniable [3,4]. The design of reactor geometry relative to electrode configurations can handle the loss of power within larger reactors [5,6]. This chapter discusses the MFC design kinetics and thermodynamics and introduces different configurations and modes of operation for their potential to investigate how MFCs can progress from laboratory-scale setups to industrial applications.

6.2 MFC configurations The application of MFCs have been applied for electricity generation, wastewater treatment, bioremediation, degradation or removal of pollutants, production of by-products, acting as biosensors, and recovery of valuable chemicals and metals. To date, various types of reactor configurations have been designed to support all of the different MFC applications and to improve MFC performance.

Biological Fuel Cells https://doi.org/10.1016/B978-0-323-85711-6.00005-9

Copyright © 2023 Elsevier Inc. All rights reserved.

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6.2.1 Dual-chambered MFCs Double-chambered MFCs (DC-MFCs) consist of microorganisms in the anodic chamber separated from the cathodic chamber via a salt bridge or a membrane, conducting ionic transfer between the chambers. It also includes an external circuit mediating electron transport from the anode to the cathode. It has been postulated that continuous oxidation at the cathodic chamber as well as maintaining anaerobic microbial metabolic reactions is pivotal for the production of higher power densities [7]. Chemicals, air, or oxygen can be used as terminal electron acceptors within a DC-MFC. This configuration is generally operated in a batch mode. However, the requirement of continuous oxygen flow makes DC-MFC a high-cost and energy-intensive configuration. Several evidence show that DC-MFC conversion into a larger scale attenuates the power production density [8]. It is associated with a decrement in the ratio of surface area to volume and, therefore, reduced surface reactions of electrodes. Simple H-shaped, cuboid-shaped, dual-chambered upflow and concentric tubular type are regarded as important DC-MFC configurations (Fig. 6.1). Table 6.1 presents a list of DC-MFCs used for power generation and COD removal. 6.2.1.1 H-shaped DC-MFCs This configuration is an engineered apparatus that recapitulates the functional aspects of DC-MFCs. They are established from a cation-exchange salt bridge located in a glass tube. The device offers novel tools for basic research and the study of MFC components such as electrode materials, microbial communities, and membranes. All platforms of such structures have two critical drawbacks: it is difficult to scale up the salt bridge, and the increment in the reactor size decreases the power output. This is because of intensive suppression in the active surface area and increment in internal resistance. Das et al. constructed an H-shaped double-chambered MFC with glass chambers and poly(vinyl alcohol) cross-linked with glutaraldehyde used as a catalyst-free membrane to harvest energy from wastewater [24]. Similarly, Reyes et al. developed an MFC through connecting the glass chambers with a glass tube for biodegradation of anthraquinone dyes [25]. Min et al. produced 45 mW m
2 of power density using swine wastewater as the substrate [26]. Fatemi et al. developed a mediator-less DC-MFC to convert the chemical energy embedded within organic and inorganic materials into bioelectricity and reported a maximum power generation of 186 mW m
2 and current density of 1078 mA m
2 [27]. In another study, Meignanalakshmi and Kumar fabricated an H-shaped DC-MFC and introduced goat rumen fluid from the slaughterhouse wastewater to improve electricity generation [28]. Min et al. demonstrated that the use of the cation-exchange membrane enhances the power output and Coulombic efficiency of DC-MFC, compared to the use of the salt bridge [29]. Studies show that the length of the salt bridge and pretreatment and biofouling of a proton exchange membrane can also affect the MFC power generation

MFC designing and performance

Fig. 6.1 Schematic illustration of H-shaped DC-MFC (A), cuboid-shaped DC-MFC (B), double-chamber up-flow MFC (C), dual-chambered up-flow U-shaped MFC (D), and dual-chambered concentric tubular MFC (E).

[30,31]. Ghasemi et al. confirmed that the treatment of bio-fouled cation-exchange membranes enhanced the power density of DC H-shaped MFCs [31]. They demonstrated that the highest power density can be obtained from an H-shaped DC-MFC using a high substrate load [32]. 6.2.1.2 Cuboid-shaped DC-MFCs When creating cuboid-shaped DC-MFCs, researchers make rectangular Plexiglass cathode and anode chambers and connect the chambers with a separator membrane. This configuration allows a lesser separation distance between the chambers, offers a minimum internal resistance, and thus promotes ionic transfer rates. Currently, cubic chambers can operate stacked modules in the continuous mode. The modules can be designed either in

149

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Biological fuel cells

Table 6.1 An overview of DC-MFCs apparatus reported in literature. MFC design

DC-MFC DC photosynthetic MFC DC-MFC DC-MFC DC-MFC DC-MFC DC-MFC DC-MFC DC photosynthetic MFC DC-MFC DC-MFC DC-MFC DC-MFC DC-MFC DC-MFC

Substrate

Power output
2

COD removal (%)

Reference

Municipal wastewater Fruit juice

7.7 mW m 42.98 mW m
2

94.8 75

[9] [10]

Organic acid fermentation Yeast Industrial acid mine + municipal Distillery wastewater Rice mill wastewater Landfill leachate Kitchen wastewater

543.75 mW m
2

75.59

[11]

6.1 mW 1188 mW m
2

90 15

[12] [13]

63.8 mW m
2 656.1 mW m
3 300 mV 41.5 mW m
2

63.5 85.22 97 73.5

[14] [15] [16] [17]

5839 mV 82.1 mV 102.54 mW m
2

80 98 –

[18] [19] [20]

60.43 mW m
2

78.05

[21]

490 mW m
2 22 mW m
2

– 69

[22] [23]

Vegetable oil Spent caustic Anaerobic wastewater sludge Medicinal herbs wastewater Rice straw Acetone 3 g L
1

series or parallel. In the former, fluid flows sequentially throughout the system, while in the latter, all cubic chambers receive the fluid simultaneously. Generally, a cuboid-shaped double-chamber configuration is preferred owing to compactness and convenience and is frequently used for evaluation of MFC parameters. Delaney et al. led a pioneering work to study the importance of microorganism, mediator, and substrate combinations using cuboid-shaped DC-MFCs [33]. In this study, various phenoxazine, phenothiazine, phenazine, indophenol, or bipyridylium derivatives have been used as redox mediators; Alcaligenes eutrophus, Bacillus subtilis, Escherichia coli, or Proteus vulgaris employed as microbial communities; and glucose or succinate utilized as substrates. Proteus vulgaris, thionine, and glucose were reported as an effective biological agent, mediator, and substrate, respectively. Ieropoulos et al. used two 25 mL Perspex chambers to realize the influence of various microbial communities on MFC performance [34]. Lai et al. developed cubic chambers linked with an Ultrex anion-exchange membrane to study the effect of electrode material on power generation [35]. The power density of 140 mW m
2 was obtained using Fe/Zn wires with three-carbon fibers as electrode material. Izadi et al.

MFC designing and performance

have also demonstrated that the DC-MFC can be used for simultaneous electricity generation and sulfide removal [36]. They have shown that the maximum power generation of 48.68 mW m
2 and current density of 231.47 mA m
2 could be obtained from the operation. 6.2.1.3 Double-chamber up-flow MFCs Cylindrical chambers could contribute to the development of up-flow MFCs within which the cathodic chamber is placed on top of the anodic compartment connected through the separator. The configuration is prevalently used to work in the continuous mode. The inclination of the chamber joints enables an enhancement in the separator’s surface contact and prevents accumulation of gas bubbles. Openings for the entry and exit of the substrate established at the bottom and top of the anodic chambers enabled the continuous mode of operation. Studies show that this type of MFC configuration is effective for sustainable power generation during a particular period of time. He et al. prepared an upflow MFC with cylindrical Plexiglas chambers and reported a maximum power generation of 170 mW m
2 from treatment of artificial wastewater [37]. Angelov et al. engineered a unique design of Dc continuous MFC for electricity generation and simultaneous sulfate reduction [38]. They studied the effect of bacterial sulfate-reduction rate on MFC performance. The electroactive sulfate reducing biofilm provided a maximum power density of 680 mW m
2 as well as sufficient sulfate purification. In the same way, Ismail and Habeeb successfully fabricated a similar MFC structure for treatment of pharmaceutical wastewater [39]. The structure concluded a power density of 204.9 mW m
2. Ye et al. fabricated an upflow DC-MFC with a continuous flow mode for recovering nutrients from municipal wastewater and simultaneous power generation [40]. They found that the lab-scale configuration enables efficient removal of organic materials, excellent nutrient recovery, and acceptable electricity output at a specific hydraulic retention time (HRT). Taken together, the power output resulting from upflow DC-MFCs is analogous to those of other DC configurations. 6.2.1.4 Dual-chambered upflow U-shaped MFCs The cathodic chamber can be designed in U shape and implemented to establish up-flow U-shaped MFCs. Javed et al. fabricated an up-flow U-shaped MFC using polypropylene random tubes [41]. CMI 7000 sheets were used as cation-exchange membrane. They introduced graphite rods as potential electrodes to improve the resulting power density. The configuration provided a maximum power density of 88,990 mW m
2. It was found that the U-shaped configuration possesses a higher power generation capacity compared with H-shaped structures. This study highlights the ongoing engineering developments that are offering a better performance of MFCs.

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6.2.1.5 Dual-chambered concentric tubular MFCs A double-chambered concentric tubular MFC includes cylindrical concentric anode and cathode chambers made of two concentric polyvinylchloride (PVC) pipes and connected with a cation-exchange membrane. For instance, Adelaja et al. incorporated two PVC pipes in a DC concentric tubular MFC [42]. They found that the use of carbon felt as electrode material and CMI 7000 as the cation-exchange membrane enhanced MFC performance. This novel construction was highly promising for in situ COD removal and hydrocarbon degradation. However, a very low power output of 6.75 mW m
2 was obtained from the apparatus. 6.2.1.6 Decoupled MFCs A decoupled MFC comprises distinct electrodes. One example of such a configuration is the decoupled microbial desalination cell (MDC), within which cathode and anode electrode units are independently inserted into a tank containing saline water [43] (Fig. 6.2). The configuration is associated with convenience in MDC construction and operation. Furthermore, the MDC performance can be induced through adjusting the electrode ratio. However, changing the electrode position exhibits a minor influence on MDC performance. Recent studies have shown the efficiency of MDCs to eliminate salts from water using microorganisms as biocatalysts. This technology can greatly improve potable water production from the abundant ocean and also significantly promote environmental sanitation through wastewater treatment. Based on the published case report, commercialized MDC designs may be capable of providing bioelectricity for remote rural areas. It was confirmed that decoupled MDCs are potential configurations for scaling up purposes owing to their flexibility in adjusting the liquid volume ratios. For instance, Ping and He developed a new configuration with a decoupled anode and cathode and reported excellent current generation while conducting desalination [44].

Fig. 6.2 Schematic illustration of decoupled MDC.

MFC designing and performance

6.2.2 Single-chamber MFCs Single-chamber design as replacements for DC configurations is a rapidly advancing pursuit in the field of MFC (Table 6.2). Single-chamber MFCs require an anode chamber and a cathode electrode exposed to air directly modulating oxygen reduction reactions (ORR) while maintaining the anaerobic condition within the chamber. The configuration is less effective in power production, compared to the DC design, although it is much easier to implement the scaling up process in terms of design simplicity and economic challenges. Furthermore, the design has enabled the conversion of anaerobic digesters into MFCs. Single-chamber MFCs avoid the requirement of aeration and provide oxygen, thereby exposing the cathode surface to the air. Although this reduces operating expenses, air-cathode configurations should be engineered to withstand the hydraulic pressure and control the leakage of the electrolyte. Such configurations include cubicair-cathode MFCs and cylindrical-air-cathode MFCs. For instance, Chang et al. Table 6.2 Examples of practical single-chamber MFCs for power generation. MFC design

Substrate

Power output

COD removal (%)

Reference

Single-chamber MFC Single-chamber MFC Single-chamber MFC Single-chamber MFC Single-chamber MFC Single-chamber MFC Single-chamber MFC Single-chamber MFC Single-chamber MFC Single-chamber MFC Single-chamber MFC Single-chamber MFC

Swine wastewater

175.7 W m
2

77.1

[45]

Distillery wastewater

124.35 mW m
2

72.84

[46]

Swine wastewater

2.3 mW m
2

91

[47]

Paper recycling wastewater Domestic wastewater

144 mW m
2

73

[48]

3.2 W m
3

80

[49]

Tannery

7 mW m
2

88

[50]

Petroleum refinery

132 mW m
2

47

[51]

Dairy wastewater

3.5 W m
3

94

[52]

Yogurt

1043 mW m
2

87

[53]

Wood hydrothermal

178 mW m
2

94

[54]

Seafood

570 mW m
2

90

[55]

Chocolate industry wastewater

4.8 W m
3

91.2

[56]

153

154

Biological fuel cells

developed a novel biochar air-cathode cylindrical internally and cuboid externally inoculated with a supernatant from a local lake sediment for electricity generation [57]. The acquired design exhibited a high catalytic activity toward ORR and achieved a maximum power density of 200 mW m
2. Although air cathodes have the potential for applications in commercial set ups, in neutral media, the slow kinetics of ORR are generally regarded as the main causes of potential loss at cathodes [58]. Some studies have suggested that the use of catalysts can be effective for increasing the cathode power density. He et al. synthesized novel catalysts composed of Fe-N-C complexes by sacrificial support method [59]. The catalysts with organic contents improved the toxicity tolerance of the cathode and resulted in a higher power density, compared to those of control MFCs. Chen et al. developed an energy-efficient air cathode of graphene, MnO2, and stainless steel fiber felt (SSFF) through electro-reducing followed by in situ deposition [60]. The three-dimensional framework was reported to exhibit a high performance of electricity output. In the same way, Chen et al. produced a Pd-SSFF cathode and achieved a high output voltage and power density (492.65 mV, 390.79 mW m
2) [61]. 6.2.2.1 Up-flow single-chamber MFCs It became apparent that the importance of up-flow single-chamber configuration is functionally associated with the operation in the continuous mode, allowing a packed-bed anode, and offering more aerial surface for biofilm formation (Fig. 6.3A). Mohanakrishna et al. reported that a single-chambered up-flow configuration with a batch-mode operation designed for distillery wastewater treatment exhibited a good COD removal and power density of 124.35 mW m
2 [46]. Rabaey’s team developed a single-chambered, continuous, upflow MFC by using Ultrex CMI7000, graphite granules, and a graphite mat as a cation-exchange membrane, anode electrode, and cathode electrode, respectively [62]. The engineered configuration was utilized for degradation of acetate, glucose, and wastewater and concluded an optimal power density of 52 W m
3 from acetate biodegradation. 6.2.2.2 Single-chambered concentric tubular MFCs It could be stipulated that a single-chambered concentric tubular configuration would be suitable for direct integration with a single-flow wastewater treatment process, which is associated with its continuous mode of operation (Fig. 6.3B). The configuration is beneficial for two reasons. First, HRT can be adjusted. Second, a large surface area is provided for biofilm growth and function. Liu et al. developed a single-chambered concentric tubular MFC consisting of eight anodes, a three-layered cathode, and a portion-exchange membrane for COD removal and simultaneous power production [63]. The configuration was reported to generate a power density of 26 mW m
2 and excellent COD removal from wastewater. Kim et al. demonstrated that a maximum power of 1.75 Wh g
1 COD can be achieved from

MFC designing and performance

Fig. 6.3 Schematic illustration of an up-flow single-chamber MFC (A) and a single-chambered concentric tubular MFC (B).

an organic loading rate of 0.24g L
1 d
1 using a single-chambered concentric tubular MFC [64]. Adelaja et al. developed a similar design of MFC, in which a peak power density of 6.75 mW m
2 was obtained from petroleum hydrocarbon wastewater [42].

6.2.3 Multichambered MFCs A multichambered MFC is the typical configuration of bio-electrochemical systems, which provides an ideal MFC performance. Current configurations are designed to improve wastewater treatment as well as inducing power generation. Therefore, such configurations can be the most promising. The defined structure can influence the Ohmic resistance and control energy consumption during the treatment process. Various studies have been applied to investigate multichambered MFCs. Kim et al. introduced a three-chambered system consisting of dual-anode chambers and an air-cathode configuration to improve power generation [65]. The materials used in anode chambers included carbon felt, graphite rods, exoelectrogen Shewanella oneidensis, and a lactate medium which was continuously recirculated in an upflow manner. The setup was useful to achieve a maximum volumetric power density of 23.6 W m
3 and a maximum current of 3.66 mA. Zhang and He used a dual-cathode configuration with two different types of electron acceptors to enable simultaneous nitrification and denitrification [66]. The cathode chambers were connected to a common anode through a cation-exchange

155

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Biological fuel cells

membrane and an anion-exchange membrane. The anaerobic cathode was reported as a power producing compartment, while the anoxic cathode was developed to reduce nitrate to nitrogen gas (N2). Additionally, some multichambered MDC configurations such as three-chamber and four-chamber MDC are applied to generate a high potential gradient and reduce energy consumption during the treatment process. Morel et al. coupled MDC with ion-exchange resin and showed that resins packed in the desalination chamber retained lower Ohmic resistances but a remarkably higher desalination rate [67]. Similarly, Kim et al. developed a four-chamber MDC to stimulate the desalination rate and overall performance [68]. In this study, they demonstrated that the MDC architecture influenced the practical application of MDC in energy production and desalination.

6.2.4 Other innovative MFC configurations Innovative MFC configurations endow them with cost reduction and improvement in the overall performance. Some researchers have investigated the possibility of using flatplate MFC architecture as a way to improve the ultimate power output. The enhanced power production is attributed to the reduction of internal resistance. The researchers reduced the distance between the electrodes by locating a cation-exchange membrane between them. They intriguingly found that this type of configuration provides a serpentine flow of wastewater, while the closer distance between the electrodes restricted the growth of electrogenic bacteria. Similarly, Liu et al. demonstrated that the miniaturization of MFC exhibited a short start-up time, a controllable environment, and small internal resistance [69]. In addition, some studies described tubular packed-bed MFCs that were equipped with packing materials [37,63,70]. Their investigation showed that innovative electrode orientation had a significant effect on reducing the internal resistance and, therefore, improvement in MFC performance. Furthermore, membrane-less MFCs displayed a high maximum power density. It is unequivocal that such configuration facilitates the transfer of electrons through reactions of NAD, FAD, cytochrome c, and cytochrome a3 [71,72]. Stacked and recirculation MFCs have been shown to optimize energy harvesting during the operation, in terms of improvement in substrate availability, microbial growth conditions, and preventing from voltage reversal. For example, a recirculation MDC could increase the recirculation of solutions between the electrode cells and maintain microbial metabolism [73]. The function of recirculation mode is closely related with preventing from pH variation that could constrain biofilm function. Bagchi et al. studied the effect of anolyte recirculation on MFC performance [74]. They found that the recirculation process enhanced proton exchange across the membrane as well as improved substrate availability to the microorganisms. This construct is highly promising for organic removal and power generation. Additionally, some stacked MFC designs are widely applied to stimulate voltage output which is impossible by using individual

MFC designing and performance

MFC units. In a study, we developed a stack MFC containing three individual units [75]. In order to investigate the power production performance, the design was fed with 20 g L
1 of glucose-fructose-sucrose and operated in parallel or series connection mode. As shown in Fig. 6.4, maximum power and current density have been achieved using a parallel unit connection mode. However, a high-voltage value of 2.042 V was obtained for serial connection. Therefore, it can be concluded that an alteration in the mode of connection is effective in promoting the stack power production performance. Furthermore, Tremouli et al. developed two ceramic stacks, namely terracotta (t-stack) and mullite (m-stack), each of which consisted of twelve identical MFC units arranged in cascades [76]. They reported a maximum power of 800 μW for m-stack and 520 μW for t-stack after 62.6 h of operation. Interestingly, there are reports showing that the use of innovative designs such as origami star-inspired fuel cell [77], 3D-paper-based MFC [78], and microfluidic MFCs [79] has a significant effect on the sustainability of the apparatus and eliminates the requirement of external power. Such structures are considered as promising devices capable of practical applications as a biosensor. Table 6.3 presents examples of MFC stacks reported in the literature.

Fig. 6.4 Demonstrating the impact of connection mode (series vs parallel) on the power generation capacity of MFCs.

157

Table 6.3 Power generation efficiency of different MFC stack modes. Stack design

Number of cells

Total volume (L)

Internal resistance (Ω)

Maximum power density (W m23)

Maximum current density (A m23)

DC-MFC stack

6

0.936

Series: 6.5

4

20

DC-MFC stack

3

1.8

Series: 0.11 W m
2 Parallel: 0.13 W m
2

Series: 0.098 A m
2 Parallel: 0.381 A m
2

[75]

DC-MFC stack

4

–

Series: 1.2 mΩ m
3 Series: 11.5 Ω m
2 Parallel: 1 Ω m
2 –

Series: 0.085 A Parallel: 0.425 A 2.8 A m
2

[80]

DC-MFC stack

Series: 308 Parallel: 263 Series:144

Series:16.9 A m
2 Parallel: 4.45 A m
2

[82]

Single-chamber MFC stack Single-chamber MFC stack

10

0.063

–

Series: 2.22 W m
2 Parallel: 1.98 W m
2 Parallel:0.97

Parallel:  7.1

[83]

5

1.475

Parallel: 10–15

40

10

Single-chamber MFC stack

3

0.35

Series: 800 Seriesparallel: 15 634

Series: 0.128 A m
2 Parallel: 0.675 A m
2 Series: 2.1 Series-parallel: 13.8

[45]

Single-chamber MFC stack

Series: 67.5 W m
2 Parallel: 175.7 W m
2 Series: 4.1 Series-parallel: 6.0 Series:0.023 W m
2

0.037 A m
2

Reference

[81]

[84]

[85]

MFC designing and performance

Our group at the Babol Noshirvani University of Technology (Babol, Iran) has recently developed an innovative membrane-less single-chamber air-cathode-type MFC design with a cubic structure facilitating a drastic promotion of power production [6]. Six stainless steel mesh were coated with graphite paint and used as anode electrodes. The anode electrodes were installed either vertically or horizontally within the MFC configuration. Similarly, six activated carbon-carbon black-coated stainless steel mesh structures used as air-cathode electrodes. The MFC was inoculated with dairy wastewater with a dilution ratio of 50:50. Six separate circuits were formed through connection of anodes and air cathodes via a copper wire: anode 1-cathode 5, anode2-cathode4, anode 3-cathode1, anode4-cathode3, anode5-cathode2, and anode 6-cathode6. The galvanostatic method at 1 and 2 s pulse times was utilized to evaluate the power production capacity of each circuit. As shown in Fig. 6.5, the best power production performance was achieved for the anode2-cathode4 circuit. This could be attributed to the excellent electrochemical properties of its anode and cathode electrodes, as well as lower internal resistance. In another study, we designed a cubic single-chamber MFC containing one anode and four air cathodes [4]. A carbon brush was placed at the center and used as the anode electrode, while monolithic membrane electrode assemblies (fabricated from bacterial cellulose, conductive multiwalled carbon nanotube, and snano-zycosil) were settled at the cubic sides and utilized as air cathodes. The apparatus was inoculated with anaerobic sludge at a dilution ratio of 50/50. A pulse power density of 1790 mW m
2, internal resistance of 0.8 KΩ, Coulombic efficiency of 11.7%, and the capacitance of 65 mF were achieved for the design.

6.2.5 MFC hybrid systems Recently, hybridization is getting more and more attention in MFC science, as a favorable conjugation with other technologies plays a vital role in developing better system sustainability and reducing the overall costs. MFC-microbial electrolysis coupled systems,

Fig. 6.5 Illustrating the synergistic effect of different anode-cathode connections on the energy efficiency of the membrane-less single-chamber air-cathode-type MFC design.

159

160

Biological fuel cells

for example, could orchestrate a self-sustained process by supplying the external potential required for wastewater treatment. MFC could provide the power required for the high rate removal system [86]. Koffi et al. reported that the hybridization of a single-chamber MEC with a double-chamber MFC could increase anoxic NH4+-N oxidation and promote the total nitrogen removal rates [87]. The applied voltage of 0.8 V (the anode potential Eanode ¼ +0.633  0.218 V vs SHE) concluded an NH4+-N oxidation rate of 151  42 g NH4+-N m
3 d
1 and a total nitrogen removal rate of 95 42 g-TN m
3 d
1 without aeration. MFCs assisted with photosynthesis are shown to induce solar energy conversion into chemical energy stored in the organic carbon products which are subsequently oxidized by electrogenic biofilm to supply anode electrons. Yang et al. showed that the incorporation of algae biofilm into a Plexiglas cylinder enhances nutrient removal and bioenergy generation from wastewater [88]. Zhang et al. also demonstrated that constructed wetland (CW)-MFC systems improved electricity production and controlled CH4 emissions from CWs [89]. Furthermore, excellent energy production and a high rate of nutrient and heavy metal removal are achieved by plant-MFC systems [90,91]. Besides, MFC hybridization with chemical processes such as electro-Fenton and physical processes such as electrosorption increases the removal of contaminants and power output [92,93].

6.3 Different modes of operation in MFCs Apart from setup configuration and electrode design, MFC properties appear to be affected by operating conditions, regulating the substrate concentration. This factor is crucial in promoting biofilm survival and function. In general, MFC studies are carried out through three common operating modes: batch, semibatch, and continuous modes (Fig. 6.6). As reported in the literature, MFC operating modes are strongly affected by anode, cathode, and separator kinetics which we will discuss in the next section.

Fig. 6.6 Schematic illustration of different operation modes in MFCs.

MFC designing and performance

Batch-mode operation has been conducted in most MFC studies [94] due to the simplicity of the setup. The typical deficiencies of the batch-mode process included substrate depletion in terms of available nutrients and toxicity of its by-products [95]. Furthermore, it was suggested that the batch mode could inhibit the volumetric maximization of the MFC apparatus. Studies have also been put forward to indicate the potential for fed-batch operation to favor enrichment of electroactive organisms in the anode chamber and depletion of methanogens and other nonelectrogens. These differing results may be attributed to the capability of the batch-mode operation in providing sufficient substrate concentration at a rate proportional to the bioanode’s current generation. Recent studies have developed the continuous mode to improve the electricity output within MFCs. The continuous mode not only provides a much higher removal efficiency but also offers more stable and higher current densities, compared to those of batch and fed-batch modes. This is correlated with the linear relationship between the electrons harvested from substrates and the electrons accepted on the electrodes. To date, a series of experiments were carried out to provide insight into the MFC operation mode. For instance, in our experiments, we investigated the power production capacity of a DC air-cathode MFC operated in either the batch mode or continuous mode [95]. The MFC was inoculated with Saccharomyces cerevisiae PTCC 5269 and fed with 30 g L
1 glucose as the substrate. The maximum power density of 133 mW m
2 and current density of 410 mA m
2 were achieved from batch processing. In an attempt to examine the practicality of the continuous mode, the effect of HRT on produced power and current were investigated. As shown in Fig. 6.7, 6.66 h was achieved as

Fig. 6.7 Maximum power density of DC air-cathode MFC operated in the continuous mode at different HRT.

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Table 6.4 Illustrating the impact of operating mode on potential current density in MFCs. Operation mode

Current density (mA m22)

Power density (mW m22)

Batch Continuous

930 6447

241 2003

the optimum HRT. We concluded that the maximum power generation would be more practically achieved in the continuous mode due to the constant cell density, as well as stable substrate and product concentrations during the operation. In another study, we developed a novel stack of MFCs containing four individual anodes and three cathodes [96]. The setup was operated either in the batch mode or continuous mode. As presented in Table 6.4, the continuous mode exhibited a boost of power production performance compared to the batch mode. Besides, the Coulombic efficiency of 22% was achieved from the system. Moreover, Cai et al. investigated the effect of continuous and batch operating modes on the simultaneous treatment of sulfide and nitrate [97]. The results showed that the continuous mode improved the treatment of sulfide and nitrate.

6.4 Kinetic analysis and modeling of MFCs An understanding of the MFC fundamentals could provide insights into discerning the limiting factors of the operation, as well as improvement in the MFC design. In the past decade, the MFC field has seen dramatic advances in system performance evaluation prior to experimentation in order to save time and money. These advances have also revealed new opportunities to provide valuable information that will be needed to monitor the dynamics of the MFC process and reactor design.

6.4.1 Bioanode kinetics In addition to understanding anode composition, engineering a bioanode chamber requires an understanding of the functional interplay of the microbial species and the anode. Today, MFC science uses kinetic models to investigate the effect of the anode, as a limiting factor, on the function of MFCs. First of all, the choice of the electron transfer mechanism must be considered. Recent advances in modeling allow the investigation of electron transfer between the microbes and the anode through the shuttling mechanism and the direct electron transfer mechanism mediated by suspended microbes and adhered biofilms, respectively. The models propose a sequential reaction scheme surveying the incorporation of mediator molecules in electron shuttling from the cells to the electrode. For example, Zhang and Halme introduced a diffusion-based model to predict the effect of the mediator concentration on MFC power generation [98].

MFC designing and performance

d ½S ½S½X  ¼ k1 dt ½S + ks

(6.1)

where d[S]/dt demonstrates the substrate degradation rate, [X] is the bacterial concentration, Kl is the reaction rate constant, and Ks is the substrate limiting constant. Assuming that the mediator is neither used nor dissociated, mediator kinetics can be considered in a same way as enzyme kinetics: d ½M int  ½S½X 
k2 ½M ½M int 
kd ½M int  + k
2 ½M red  ¼m dt ½S + ks

(6.2)

d½M (6.3) ¼
k2 ½M  ½M int 
k3 ½M red  + k
2 ½M red  dt where [M] and [Mred] are concentrations of the mediator and its reducing ones, respectively. [Mint] demonstrates the reducing intermediates. k1 (mmol g
1 h
1), k2 (mM
1 h
1), m (mmol g
1 h
1), k3 (h
1), and k
2 (h
1) display the reaction rate constants, and kd (h
1) and ks (mM) are the dissociation and substrate limiting constants. The resulting current density and final electromotive force of the system can be mathematically calculated as follows: I ¼ n F k3 ½M red 
 ½M  RT red 0 E¼E + ln 2F ½M

(6.4) (6.5)

where I (mA) is the current density, n is the electron number, F is Faraday’s constant, E0 is a constant for certain MFC apparatus, and T (K) is the temperature. Additionally, Picioreanu et al. proposed a model to investigate the mass balances of the biomass and added mediator [99]. They demonstrated that a higher mass transfer rate of the mediator and higher biomass concentrations can promote the power output, both of which facilitate the availability of the reduced mediator for the following oxidation. They also noted that an effectual mixing of the anode compartment makes a thinner boundary layer and results in a higher current density. The model can be utilized for evaluation of other bio-electrochemical systems. Y s S + M oxd ! M red + products

(6.6)

M red $ M oxd + nH + + ne
    ½S  ½M oxd  r 1 ¼ k1 ½X ½S + ks ½M oxd  + kM oxd

(6.7) (6.8)

where Ys is the Stoichiometric coefficient which depends on the substrate electron content, e is the electron, r is the biological reaction rate, and [Mred] and [Moxd] are

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the reducing and oxidizing intermediates, respectively. Linking current generation with biofilm conductivity through microbial nanowire and shuttling requires a consideration of endogenous microbial metabolism [99]. For example, the following equations can be utilized for the evaluation of the amount of biomass consumed for electricity production in the presence of mediators. The mechanism demonstrates how the rate of biomass utilization and the further addition of substrate can influence the resulting current density and peak currents. Y endo X + M oxd ! M red + products   ½M oxd  r 2 ¼ k2 ½X ½M oxd  + kM oxd

(6.9) (6.10)

The second mechanism describes the substrate storage in the form of complex polymeric compounds and their slower degradation rates: Y s S ¼ M oxd ! M red + products + Y p polyS

(6.11)

Y p polyS ¼ M oxd ! M red + products

(6.12)

The oxidation of such polymeric substances is considered as follows:     ½polyS ½M oxd  r 2 ¼ k2 ½X ½M oxd  + kM oxd ½polyS + ks

(6.13)

Studies show that electricity production occurs even in the absence of the shuttling process. This makes sense in the possibility of electron conduction from the cell surface toward the electrode. Marcus et al. utilized the one-dimensional Nernst Monod equation to describe such a mechanism [100]. The model demonstrates the connection between electricity generation and biofilm conductivity. They suggested that a high-shear environment is the main factor that can develop a high active biomass, leading to a higher power output. The model which involves the rate of substrate utilization and respiration, steady-state electron mass balance, and biomass balance are given by Eqs. (6.14), (6.15), and (6.16), respectively. d ½S ½S ¼ k1 dt ½S + ks

½Sa  ½Sa + ksa

(6.14)

where ksa ¼ half-max-rate EA concentration, k1 ¼qmaxφa, and Sa displays the electron acceptor (EA) concentration and is calculated using the Nernst Equation as follows:
 S0  RT a Eanode ¼ E0A
(6.15) ln nF ½Sa

MFC designing and performance

where S0a is the standard anodic, EA concentration, and E0A corresponds to the standard reduction potential for anodic EA.  2 ∂ 0 ¼ Ds,f
X f ,a q (6.16) ∂z2 1 ¼ φa + φi

(6.17)

where φa and φi indicate the active and inert mass, respectively. φa involves in electricity generation, while φi contributes to extracellular conductive materials such as nanowires.

6.4.2 Cathode kinetics ORR are being evaluated because they rate the limiting steps of the MFC process in terms of reaction activation energy. Cathode size, dissolved oxygen concentration, and temperature are the most commonly studied factors which affect the oxygen reduction kinetics. Renslow et al. showed that temperature and dissolved oxygen concentration determine the effectiveness of the cathode compartment and, therefore, the overall MFC performance [101]. They introduced a kinetic model for considering the performance of a nonisothermal sediment MFC device. In this model, the equilibrium constant of solubility [Keq] is defined as 0 1 P O2 A C O2 ¼ @ (6.18) ΔH 0 1
T10 Þ ð 0 R T K e eqO2

where CO2 is the dissolved oxygen concentration, PO2 corresponds to the partial pressure of oxygen, and Keq0 O2 exhibits Henry’s constant at standard conditions. ΔH0 and T0 are the standard enthalpy change and reference temperature, respectively. Furthermore, the electron potential of the ORR as a function of temperature is calculated as follows:  0    E ΔH 0ORR  EORR ¼ T ORR + T
T0 (6.19) 0 0 T nFT
nf a

K f ORR ¼ K 0ORR e RT

ðe
E+Eloss Þ

(6.20)

where Eloss demonstrates both the Ohmic loss and potential loss, KfORR is the rate constant, and K0ORR exhibits the standard rate constant. The overall power output is calculated by the following equation: j ¼
nF CO2 K f ORR

(6.21)

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Biological fuel cells

6.4.3 Membrane/separator kinetics Charge transport and flux density are used to determine the impact of membranes’ ionexchange capacities on the performance of the bio-electrochemical systems. Several studies have modeled the effect of ion transfer capacity and membrane fouling on the energy production of electrochemical systems. For instance, Harnisch et al. used a simplified one-dimensional model for such an investigation [102]. They designed a doublechambered MFC consisting of platinum mesh electrodes and Nafion 117. The model divides the entire system into three distinct components (electrode chambers, membrane diffusion layers, and the ion-exchange membrane) allowing the evaluation of charge transport and flux density given by Eqs. (6.22) and (6.23), respectively. δC i ðX Þ δ ¼
ð f i ðxÞ + SÞ (6.22) δt δx δC ðX Þ z F (6.23) Di,m C i ðX Þ ϕðX Þ + i f i ðxÞ ¼
Di,m i RT δx where Ci is the concentration of the charged species which cross the membrane, s represents the source term, Di,m corresponds to the diffusion coefficient of the charged species (i) in the cell structure (m), and ϕ(x) is the electric field. The model helps the evaluation of how ion distribution can affect the potential drop across the membrane and offers highly concentrated electrolyte solutions as a promising prospect to overcome membrane resistance and pH splitting problems. Concerning biofilm prevention, another need in the evaluation of membrane kinetics is the development of models to determine the effects of membrane fouling on the overall MFC performance. Xu et al. modeled the current profiles resulting from raw and fouled membrane systems by using the following equation [103]: dQ Σ Na2+ ,K+ ,NH4+ , Ca+ ,Mg2+ V 2 FZ c dC 2,t (6.24) ¼ dt dt where Q is the net of cation species, V2 is the volume of the cathode chamber, Zc corresponds to the valence of the cation species, and C2,t is the positive charge concentration in the cathode chamber. Moreover, investigations of the oxygen transfer coefficient, ion conductivity, membrane permeability and diffusion coefficients provide a way to compare membrane performances, opening prospective for designing an effectual MFC membrane [104,105]. i¼

6.5 MFCs at a larger laboratory scale Multiple MFC operation in larger volumes is processed, depending on the prevention from long cycles or continuous pumping of medium volumes [106]. As undersigned configurations, MFC cells are evaluated in terms of electrode spacing and surface area.

MFC designing and performance

A similar power density was reported for both large and small fed-batch systems, corresponding to the preserved electrode size and electrode spacing [107]. However, a low power density is concluded from continuous-flow systems with simple designs [108]. Beyond the type of operation, longer operation periods are required for confirming the data. For instance, a stack configuration was designed in a separate cathode chamber to enhance biofilm performance [80], although studies report an increment in MFC performance as a function of time [109]. Studies show that voltage reversal could be the main problem of such operations that is directly linked to the substrate starvation reported, especially in fed-batch cycles [110]. They proved that the issue can be conquered through matching of the internal resistances of large-scale MFCs such as stack cells. They also confirmed that cathode biofouling is correlated with the reactor’s performance during shorter operation periods of laboratory systems [111].

6.6 Pilot-scale MFC designs Design of the reactor, separator, and low-cost electrode materials conserve are critical quantitative criteria for successful progress from laboratory level to pilot-scale MFC plants. Design of electrodes with a large surface area to volume ratio, adaptation of scalable reactor configurations, and optimization of operating conditions are some examples of strategies used in the construction of pilot-scale MFCs. Modularization and replication of the fundamental MFC structures may offer insights for developing efficient pilot-scale MFC designs with a suitable volume and energy output. Substrate composition, bioreactor configuration, membrane and electrode design, biocatalysts and mediators, and oxygen availability impact the overall MFC performance [112]. Actually, multiple types of MFC configurations have been proposed for broad applications in pilot scale, including single-chamber, double-chamber, up-flow cylindrical-/tubular-type, flat bed-type, stacked-type [113,114], benthic or sediment [115,116], submersible, multielectrode, photosynthetic, and MFC hybrid designs. The design of bio-electrochemical systems mediated by sediments, acting as potential biocatalyst, substrates and nutrients, provides a sustainable benthic power supply. Pilot-scale benthic MFCs have been utilized for several purposes: as power suppliers of meteorological buoy [117] and oceanographic sensor [118] or enhancing sediment organic removal [119]. Submersible systems are other pilot-scale designs which allow MFC integration with other treatment processes such as an anaerobic bioreactor. The technology is especially beneficial in promoting long-term operation, stability, complete utilization of substrate, enhanced product generation and recovery. Photosynthetic MFCs are developed in biocontrol (plants) and bioprocess (microbial population) structures for bioelectricity generation. Sunlight largely contributes to power production in biocontrol structures, whereas in bioprocess systems the voltage output is related to the availability of material resources [120,121]. Studies show that bioelectricity generation of plant MFCs is

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sufficient for operating small-scale electrical devices. However, the system possesses some inherent restrictions in plant growth and food security, such as competition for productive land and requirement of chemicals like pesticides. The use of photosynthetic microorganisms circumvents such limitations and promotes food security, aqueous media growth, CO2 fixation, solar power conversion, uptake of nutrients, and O2 generation [122]. When dealing with pilot-scale MFCs, the potential of stacked systems should not be overlooked. A stacked MFC consists of a number of individual cells designed in either parallel or series connections. For obtaining a higher power generation, this type of configuration is preferable to increasing the volume of individual MFCs due to its capacity of controlling Ohmic resistance [83] and scalable costs. The four main types of stacked configuration include series flow mode in parallel electrode connections; (2) parallel flow mode in parallel electrode connections, (3) parallel flow mode in series electrode connections, and (4) series flow mode in series electrode connections [123]. Under similar conditions, the parallel connected stack MFCs exhibit a higher COD removal and bioelectrogenesis [124]. Other pilot-scale configurations are single-chamber, two-chamber, up-flow chamber, and flat-plate MFCs which have been designed to overcome economic issues, internal resistance challenges, and challenges for the implementation of continuous processing. For example, a single-chamber hexagonal-shaped MFC was designed on a large scale for treatment of activated sludge [125] and demonstrated that the power density is greatly linked to the reactor size, affecting the internal resistance. Moreover, the excellent COD removal and coulombic efficiencies of dual-chamber structures infer a particular capacity of the designs at the pilot scale [126]. It was also proved that the efficiency of large-scale up-flow chamber MFCs is significant for treatment of industry wastewater [127,128]. The internal resistance is a significant factor in the pilot-scale operation of the MFCs. Actually, flat-plate structures can influence the ease of the pilot-scale, continuous mode of operation [129,130]. Additionally, innovative modes of hybrid MFCs have been studied so far. Such hybrid configurations are effectual in reducing operating costs and enhancing capacity of integration with other processes. A ferric-based MFC, for instance, was combined with a ferrous-based fuel cell, mediating catholyte regeneration and bioelectricity production [131]. In another study, an air-biocathode microbial fuel cell-membrane bioreactor system was designed for direct water reclamation and maximum power density production [132]. As the large-scale implementations have been discussed in more detail in Chapter 10, here we will limit the content.

6.7 Conclusions This chapter has discussed MFC designs optimized and engineered to overcome material, geometrics, and configuration barriers. These barriers to achieve maximum electrical output are conquered by feedstock pretreatment, control of pH, lowering of

MFC designing and performance

the internal resistance, integration of biocathode and bio-augmentation. This diverse array of necessities can be met by using simple reactor design, economic electrode materials, and wastewater as a potential substrate. Furthermore, MFC platforms offer an assortment of bioprocesses such as fermentation, desalination, and wastewater treatment that can be integrated with MFC. This customization can also be used with methane production to improve the future of MFC technology when organizing selfsufficient treatment, widen the envision of their usage in recovery of nutrients from wastewater by allowing their remarkable implementation in rural areas to meet the energy demand.

References [1] M. Rahimnejad, M. Asghary, M. Fallah, Microbial fuel cell (MFC): an innovative technology for wastewater treatment and power generation, in: Bioremediation of Industrial Waste for Environmental Safety, Springer, 2020, pp. 215–235. [2] M. Mashkour, M. Rahimnejad, F. Raouf, N. Navidjouy, A review on the application of nanomaterials in improving microbial fuel cells, Biofuel Res. J. 8 (2021) 1400–1416. [3] M. Masoudi, M. Rahimnejad, M. Mashkour, Enhancing operating capacity of microbial fuel cells by using low-cost electrodes and multi anode-cathode connections in a membrane-less configuration, Int. J. Hydrog. Energy 46 (2021) 8226–8238. [4] M. Mashkour, M. Rahimnejad, M. Mashkour, F. Soavi, Increasing bioelectricity generation in microbial fuel cells by a high-performance cellulose-based membrane electrode assembly, Appl. Energy 282 (2021) 116150. [5] M. Mashkour, M. Rahimnejad, M. Mashkour, F. Soavi, Electro-polymerized polyaniline modified conductive bacterial cellulose anode for supercapacitive microbial fuel cells and studying the role of anodic biofilm in the capacitive behavior, J. Power Sources 478 (2020) 228822. [6] M. Masoudi, M. Rahimnejad, M. Mashkour, Fabrication of anode electrode by a novel acrylic based graphite paint on stainless steel mesh and investigating biofilm effect on electrochemical behavior of anode in a single chamber microbial fuel cell, Electrochim. Acta 344 (2020) 136168. [7] M. Rahimnejad, A. Adhami, S. Darvari, A. Zirepour, S.-E. Oh, Microbial fuel cell as new technology for bioelectricity generation: a review, Alexandria Eng. J. 54 (2015) 745–756. [8] F. Hejazi, A. Ghoreyshi, M. Rahimnejad, Simultaneous phenol removal and electricity generation using a hybrid granular activated carbon adsorption-biodegradation process in a batch recycled tubular microbial fuel cell, Biomass Bioenergy 129 (2019) 105336. [9] L. Koo´k, T. Ro´zsenberszki, N. Nemesto´thy, K. B
elafi-Bako´, P. Bakonyi, Bioelectrochemical treatment of municipal waste liquor in microbial fuel cells for energy valorization, J. Clean. Prod. 112 (2016) 4406–4412. [10] A.G. Del Campo, J.F. Perez, P. Canizares, M.A. Rodrigo, F.J. Fernandez, J. Lobato, Study of a photosynthetic MFC for energy recovery from synthetic industrial fruit juice wastewater, Int. J. Hydrog. Energy 39 (2014) 21828–21836. [11] T. Xia, X. Zhang, H. Wang, Y. Zhang, Y. Gao, C. Bian, X. Wang, P. Xu, Power generation and microbial community analysis in microbial fuel cells: a promising system to treat organic acid fermentation wastewater, Bioresour. Technol. 284 (2019) 72–79. [12] P.P. Włodarczyk, B. Włodarczyk, Microbial fuel cell with Ni-Co cathode powered with yeast wastewater, Energies 11 (2018) 3194. [13] L. V
elez-P
erez, J. Ramirez-Nava, G. Herna´ndez-Flores, O. Talavera-Mendoza, C. EscamillaAlvarado, H. Poggi-Varaldo, O. Solorza-Feria, J. Lo´pez-Dı´az, Industrial acid mine drainage and municipal wastewater co-treatment by dual-chamber microbial fuel cells, Int. J. Hydrog. Energy 45 (2020) 13757–13766.

169

170

Biological fuel cells

[14] N. Samsudeen, T. Radhakrishnan, M. Matheswaran, Bioelectricity production from microbial fuel cell using mixed bacterial culture isolated from distillery wastewater, Bioresour. Technol. 195 (2015) 242–247. [15] A. Raychaudhuri, M. Behera, Comparative evaluation of methanogenesis suppression methods in microbial fuel cell during rice mill wastewater treatment, Environ. Technol. Innov. 17 (2020) 100509. [16] H.T. Nguyen, R. Kakarla, B. Min, Algae cathode microbial fuel cells for electricity generation and nutrient removal from landfill leachate wastewater, Int. J. Hydrog. Energy 42 (2017) 29433–29442. [17] S.N. Mohamed, P.A. Hiraman, K. Muthukumar, T. Jayabalan, Bioelectricity production from kitchen wastewater using microbial fuel cell with photosynthetic algal cathode, Bioresour. Technol. 295 (2020) 122226. [18] S. Firdous, W. Jin, N. Shahid, Z. Bhatti, A. Iqbal, U. Abbasi, Q. Mahmood, A. Ali, The performance of microbial fuel cells treating vegetable oil industrial wastewater, Environ. Technol. Innov. 10 (2018) 143–151. [19] N. Fazli, N.S.A. Mutamim, N.M.A. Jafri, N.A.M. Ramli, Microbial fuel cell (MFC) in treating spent caustic wastewater: varies in hydraulic retention time (HRT) and mixed liquor suspended solid (MLSS), J. Environ. Chem. Eng. 6 (2018) 4339–4346. [20] E.F. Talooki, M. Ghorbani, M. Rahimnejad, M.S. Lashkenari, Investigating the effects of in-situ fabrication of a binder-free Co3O4-polyaniline cathode towards enhanced oxygen reduction reaction and power generation of microbial fuel cells, Synth. Met. 258 (2019) 116225. [21] N. Birjandi, H. Younesi, A.A. Ghoreyshi, M. Rahimnejad, Electricity generation through degradation of organic matters in medicinal herbs wastewater using bio-electro-Fenton system, J. Environ. Manag. 180 (2016) 390–400. [22] S.H. Hassan, S.M.G. El-Rab, M. Rahimnejad, M. Ghasemi, J.-H. Joo, Y. Sik-Ok, I.S. Kim, S.-E. Oh, Electricity generation from rice straw using a microbial fuel cell, Int. J. Hydrog. Energy 39 (2014) 9490–9496. [23] M. Rahimnejad, G. Mostafa, N. Ghasem, A. Ghoreyshi, G. Bakeri, S.H. Nejad, F. Talebnia, Acetone removal and bioelectricity generation in dual chamber microbial fuel cell, Am. J. Biochem. Biotechnol. 8 (2012) 304–310. [24] B. Das, S.S. Gaur, A.R. Katha, C.-T. Wang, V. Katiyar, Crosslinked poly (vinyl alcohol) membrane as separator for domestic wastewater fed dual chambered microbial fuel cells, Int. J. Hydrog. Energy 46 (2021) 7073–7086. [25] K.R.E. Reyes, P.-W. Tsai, L.L. Tayo, C.-C. Hsueh, B.-Y. Chen, Biodegradation of anthraquinone dyes: interactive assessment upon biodecolorization, biosorption and biotoxicity using dual-chamber microbial fuel cells (MFCs), Process Biochem. 101 (2021) 111–127. [26] B. Min, J. Kim, S. Oh, J.M. Regan, B.E. Logan, Electricity generation from swine wastewater using microbial fuel cells, Water Res. 39 (2005) 4961–4968. [27] S. Fatemi, A. Ghoreyshi, G. Najafpour, M. Rahimnejad, Investigation of bioelectricity production in dual chamber microbial fuel cell by mixed culture as active biocatalyst, J. Cell. Mol. Res. 27 (2015) 546–554. [28] S. Meignanalakshmi, S.V. Kumar, Bioelectricity production by using goat (Capra hircus) rumen fluid from slaughterhouse waste in mediator-less microbial fuel cells, Energy Sourc. Part A 38 (2016) 1364–1369. [29] B. Min, S. Cheng, B.E. Logan, Electricity generation using membrane and salt bridge microbial fuel cells, Water Res. 39 (2005) 1675–1686. [30] J.M. Morris, S. Jin, Feasibility of using microbial fuel cell technology for bioremediation of hydrocarbons in groundwater, J. Environ. Sci. Health A 43 (2007) 18–23. [31] M. Ghasemi, W.R.W. Daud, M. Ismail, M. Rahimnejad, A.F. Ismail, J.X. Leong, M. Miskan, K.B. Liew, Effect of pre-treatment and biofouling of proton exchange membrane on microbial fuel cell performance, Int. J. Hydrog. Energy 38 (2013) 5480–5484. [32] S.V. Mohan, S.V. Raghavulu, D. Peri, P. Sarma, Integrated function of microbial fuel cell (MFC) as bio-electrochemical treatment system associated with bioelectricity generation under higher substrate load, Biosens. Bioelectron. 24 (2009) 2021–2027. [33] S.V. Mohan, A. Pandey, S. Varjani, Biomass, Biofuels, Biochemicals: Microbial Electrochemical Technology: Sustainable Platform for Fuels, Chemicals and Remediation, Elsevier, 2018.

MFC designing and performance

[34] I.A. Ieropoulos, J. Greenman, C. Melhuish, J. Hart, Comparative study of three types of microbial fuel cell, Enzym. Microb. Technol. 37 (2005) 238–245. [35] M.F. Lai, C.W. Lou, J.H. Lin, Using 3D composite electrode materials for electricity generation from swine wastewater in a dual-chamber microbial fuel cells, J. Chin. Chem. Soc. 64 (2017) 618–626. [36] P. Izadi, M. Rahimnejad, A. Ghoreyshi, Power production and wastewater treatment simultaneously by dual-chamber microbial fuel cell technique, Biotechnol. Appl. Biochem. 62 (2015) 483–488. [37] Z. He, S.D. Minteer, L.T. Angenent, Electricity generation from artificial wastewater using an upflow microbial fuel cell, Environ. Sci. Technol. 39 (2005) 5262–5267. [38] A. Angelov, S. Bratkova, A. Loukanov, Microbial fuel cell based on electroactive sulfate-reducing biofilm, Energy Convers. Manag. 67 (2013) 283–286. [39] Z.Z. Ismail, A.A. Habeeb, Experimental and modeling study of simultaneous power generation and pharmaceutical wastewater treatment in microbial fuel cell based on mobilized biofilm bearers, Renew. Energy 101 (2017) 1256–1265. [40] Y. Ye, H.H. Ngo, W. Guo, S.W. Chang, D.D. Nguyen, X. Zhang, S. Zhang, G. Luo, Y. Liu, Impacts of hydraulic retention time on a continuous flow mode dual-chamber microbial fuel cell for recovering nutrients from municipal wastewater, Sci. Total Environ. 734 (2020) 139220. [41] M.M. Javed, M.A. Nisar, B. Muneer, M.U. Ahmad, Production of bioelectricity from vegetable waste extract by designing a U-shaped microbial fuel cell, Pakistan J. Zool. 49 (2017). [42] O. Adelaja, T. Keshavarz, G. Kyazze, Treatment of phenanthrene and benzene using microbial fuel cells operated continuously for possible in situ and ex situ applications, Int. Biodeterior. Biodegradation 116 (2017) 91–103. [43] Q. Ping, Z. He, Effects of inter-membrane distance and hydraulic retention time on the desalination performance of microbial desalination cells, Desalin. Water Treat. 52 (2014) 1324–1331. [44] Q. Ping, Z. He, Improving the flexibility of microbial desalination cells through spatially decoupling anode and cathode, Bioresour. Technol. 144 (2013) 304–310. [45] L. Zhuang, Y. Zheng, S. Zhou, Y. Yuan, H. Yuan, Y. Chen, Scalable microbial fuel cell (MFC) stack for continuous real wastewater treatment, Bioresour. Technol. 106 (2012) 82–88. [46] G. Mohanakrishna, S.V. Mohan, P. Sarma, Bio-electrochemical treatment of distillery wastewater in microbial fuel cell facilitating decolorization and desalination along with power generation, J. Hazard. Mater. 177 (2010) 487–494. [47] O. Ichihashi, K. Hirooka, Removal and recovery of phosphorus as struvite from swine wastewater using microbial fuel cell, Bioresour. Technol. 114 (2012) 303–307. [48] L. Huang, B.E. Logan, Electricity generation and treatment of paper recycling wastewater using a microbial fuel cell, Appl. Microbiol. Biotechnol. 80 (2008) 349–355. [49] S. Ayyaru, S. Dharmalingam, Development of MFC using sulphonated polyether ether ketone (SPEEK) membrane for electricity generation from waste water, Bioresour. Technol. 102 (2011) 11167–11171. [50] V. Sawasdee, N. Pisutpaisal, Simultaneous pollution treatment and electricity generation of tannery wastewater in air-cathode single chamber MFC, Int. J. Hydrog. Energy 41 (2016) 15632–15637. [51] G. Mohanakrishna, I.M. Abu-Reesh, S. Kondaveeti, R.I. Al-Raoush, Z. He, Enhanced treatment of petroleum refinery wastewater by short-term applied voltage in single chamber microbial fuel cell, Bioresour. Technol. 253 (2018) 16–21. [52] R.J. Marassi, L.G. Queiroz, D.C.V. Silva, F.T. da Silva, G.C. Silva, T.C.B. de Paiva, Performance and toxicity assessment of an up-flow tubular microbial fuel cell during long-term operation with highstrength dairy wastewater, J. Clean. Prod. 259 (2020) 120882. [53] H. Luo, G. Xu, Y. Lu, G. Liu, R. Zhang, X. Li, X. Zheng, M. Yu, Electricity generation in a microbial fuel cell using yogurt wastewater under alkaline conditions, RSC Adv. 7 (2017) 32826–32832. [54] M. Kloch, R. Toczyłowska-Mami
nska, Toward optimization of wood industry wastewater treatment in microbial fuel cells—mixed wastewaters approach, Energies 13 (2020) 263. [55] M.T. Jamal, A. Pugazhendi, R.B. Jeyakumar, Application of halophiles in air cathode MFC for seafood industrial wastewater treatment and energy production under high saline condition, Environ. Technol. Innov. 20 (2020) 101119. [56] G. Najafpour, P. Nouri, M. Rahimnejad, Bioelectricity Generation in Annulus Structure of Single Chamber Membrane-Less Microbial Fuel Cell Using Wastewater From Chocolate Industry, Linnaeus Eco-Tech, 2014.

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172

Biological fuel cells

[57] H.-C. Chang, W. Gustave, Z.-F. Yuan, Y. Xiao, Z. Chen, One-step fabrication of binder-free air cathode for microbial fuel cells by using balsa wood biochar, Environ. Technol. Innov. 18 (2020) 100615. [58] I. Das, M.T. Noori, G.D. Bhowmick, M. Ghangrekar, Synthesis of bimetallic iron ferrite Co0. 5Zn0. 5Fe2O4 as a superior catalyst for oxygen reduction reaction to replace noble metal catalysts in microbial fuel cell, Int. J. Hydrog. Energy 43 (2018) 19196–19205. [59] W. He, J. Wei, T. Huang, E. Zhang, Enhanced electricity production in single-chamber MFCs with air cathodes decorated by Fe-N-C catalysts derived from 5H-dibenz [b, f] azepine-5-carboxamide (Carbamazepine), Int. J. Hydrog. Energy 45 (2020) 17525–17532. [60] W. Chen, Z. Liu, Y. Li, Q. Liao, X. Zhu, High electricity generation achieved by depositing rGO@ MnO2 composite catalysts on three-dimensional stainless steel fiber felt for preparing the energyefficient air cathode in microbial fuel cells, Energy 222 (2021) 119971. [61] W. Chen, Z. Liu, Y. Li, K. Jiang, J. Hou, X. Lou, X. Xing, Q. Liao, X. Zhu, A novel stainless steel fiber felt/Pd nanocatalysts electrode for efficient ORR in air-cathode microbial fuel cells, Electrochim. Acta 324 (2019) 134862. [62] K. Rabaey, P. Clauwaert, P. Aelterman, W. Verstraete, Tubular microbial fuel cells for efficient electricity generation, Environ. Sci. Technol. 39 (2005) 8077–8082. [63] H. Liu, R. Ramnarayanan, B.E. Logan, Production of electricity during wastewater treatment using a single chamber microbial fuel cell, Environ. Sci. Technol. 38 (2004) 2281–2285. [64] J.R. Kim, G.C. Premier, F.R. Hawkes, J. Rodrı´guez, R.M. Dinsdale, A.J. Guwy, Modular tubular microbial fuel cells for energy recovery during sucrose wastewater treatment at low organic loading rate, Bioresour. Technol. 101 (2010) 1190–1198. [65] M.H. Kim, I.J. Iwuchukwu, Y. Wang, D. Shin, J. Sanseverino, P. Frymier, An analysis of the performance of an anaerobic dual anode-chambered microbial fuel cell, J. Power Sources 196 (2011) 1909–1914. [66] F. Zhang, Z. He, Simultaneous nitrification and denitrification with electricity generation in dualcathode microbial fuel cells, J. Chem. Technol. Biotechnol. 87 (2012) 153–159. [67] A. Morel, K. Zuo, X. Xia, J. Wei, X. Luo, P. Liang, X. Huang, Microbial desalination cells packed with ion-exchange resin to enhance water desalination rate, Bioresour. Technol. 118 (2012) 43–48. [68] Y. Kim, B.E. Logan, Microbial desalination cells for energy production and desalination, Desalination 308 (2013) 122–130. [69] L. Liu, S. Choi, Self-sustaining, solar-driven bioelectricity generation in micro-sized microbial fuel cell using co-culture of heterotrophic and photosynthetic bacteria, J. Power Sources 348 (2017) 138–144. [70] Z. He, N. Wagner, S.D. Minteer, L.T. Angenent, An upflow microbial fuel cell with an interior cathode: assessment of the internal resistance by impedance spectroscopy, Environ. Sci. Technol. 40 (2006) 5212–5217. [71] M. Christwardana, Y. Kwon, Yeast and carbon nanotube based biocatalyst developed by synergetic effects of covalent bonding and hydrophobic interaction for performance enhancement of membraneless microbial fuel cell, Bioresour. Technol. 225 (2017) 175–182. [72] A. Tardast, M. Rahimnejad, G. Najafpour, A. Ghoreyshi, G.C. Premier, G. Bakeri, S.-E. Oh, Use of artificial neural network for the prediction of bioelectricity production in a membrane less microbial fuel cell, Fuel 117 (2014) 697–703. [73] Y. Qu, Y. Feng, X. Wang, J. Liu, J. Lv, W. He, B.E. Logan, Simultaneous water desalination and electricity generation in a microbial desalination cell with electrolyte recirculation for pH control, Bioresour. Technol. 106 (2012) 89–94. [74] S. Bagchi, M. Behera, Evaluation of the effect of anolyte recirculation and anolyte pH on the performance of a microbial fuel cell employing ceramic separator, Process Biochem. 102 (2021) 207–212. [75] T. Jafary, M. Rahimnejad, A.A. Ghoreyshi, G. Najafpour, F. Hghparast, W.R.W. Daud, Assessment of bioelectricity production in microbial fuel cells through series and parallel connections, Energy Convers. Manag. 75 (2013) 256–262. [76] A. Tremouli, J. Greenman, I. Ieropoulos, Investigation of ceramic MFC stacks for urine energy extraction, Bioelectrochemistry 123 (2018) 19–25.

MFC designing and performance

[77] A. Fraiwan, L. Kwan, S. Choi, A disposable power source in resource-limited environments: a paperbased biobattery generating electricity from wastewater, Biosens. Bioelectron. 85 (2016) 190–197. [78] N. Hashemi, J.M. Lackore, F. Sharifi, P.J. Goodrich, M.L. Winchell, N. Hashemi, A paper-based microbial fuel cell operating under continuous flow condition, Technology 4 (2016) 98–103. [79] D. Panjiara, H. Pramanik, Optimization of process parameters using response surface methodology (RSM) for power generation via electrooxidation of glycerol in T-Shaped air breathing microfluidic fuel cell (MFC), Int. J. Hydrog. Energy 45 (2020) 33968–33979. [80] P. Aelterman, K. Rabaey, H.T. Pham, N. Boon, W. Verstraete, Continuous electricity generation at high voltages and currents using stacked microbial fuel cells, Environ. Sci. Technol. 40 (2006) 3388–3394. [81] A. Dekker, A.T. Heijne, M. Saakes, H.V. Hamelers, C.J. Buisman, Analysis and improvement of a scaled-up and stacked microbial fuel cell, Environ. Sci. Technol. 43 (2009) 9038–9042. [82] L. Zhang, J. Li, X. Zhu, D.-d. Ye, Q. Fu, Q. Liao, Response of stacked microbial fuel cells with serpentine flow fields to variable operating conditions, Int. J. Hydrog. Energy 42 (2017) 27641–27648. [83] I. Ieropoulos, J. Greenman, C. Melhuish, Microbial fuel cells based on carbon veil electrodes: stack configuration and scalability, Int. J. Energy Res. 32 (2008) 1228–1240. [84] L. Zhuang, Y. Yuan, Y. Wang, S. Zhou, Long-term evaluation of a 10-liter serpentine-type microbial fuel cell stack treating brewery wastewater, Bioresour. Technol. 123 (2012) 406–412. [85] J. An, B. Kim, J.K. Jang, H.-S. Lee, I.S. Chang, New architecture for modulization of membraneless and single-chambered microbial fuel cell using a bipolar plate-electrode assembly (BEA), Biosens. Bioelectron. 59 (2014) 28–34. [86] Y. Li, H.-Y. Yang, J.-Y. Shen, Y. Mu, H.-Q. Yu, Enhancement of azo dye decolourization in a MFC-MEC coupled system, Bioresour. Technol. 202 (2016) 93–100. [87] S. Okabe, Bioelectrochemical anoxic ammonium nitrogen removal by an MFC driven single chamber microbial electrolysis cell, Chemosphere 274 (2021) 129715. [88] Z. Yang, H. Pei, Q. Hou, L. Jiang, L. Zhang, C. Nie, Algal biofilm-assisted microbial fuel cell to enhance domestic wastewater treatment: nutrient, organics removal and bioenergy production, Chem. Eng. J. 332 (2018) 277–285. [89] K. Zhang, X. Wu, H. Luo, X. Li, W. Chen, J. Chen, Y. Mo, W. Wang, CH4 control and associated microbial process from constructed wetland (CW) by microbial fuel cells (MFC), J. Environ. Manag. 260 (2020) 110071. [90] D.P. Strik, H. Hamelers, J.F. Snel, C.J. Buisman, Green electricity production with living plants and bacteria in a fuel cell, Int. J. Energy Res. 32 (2008) 870–876. [91] L.D. Schamphelaire, L.V.D. Bossche, H.S. Dang, M. H€ ofte, N. Boon, K. Rabaey, W. Verstraete, Microbial fuel cells generating electricity from rhizodeposits of rice plants, Environ. Sci. Technol. 42 (2008) 3053–3058. [92] D. Wang, J. Hu, B. Liu, H. Hou, J. Yang, Y. Li, Y. Zhu, K. Xiao, Degradation of refractory organics in dual-cathode electro-Fenton using air-cathode for H2O2 electrogeneration and microbial fuel cell cathode for Fe2+ regeneration, J. Hazard. Mater. 412 (2021) 125269. [93] W. Zhao, J. Qu, Y. Zhou, J. Zhao, Y. Feng, C. Guo, Y. Lu, Y. Zhao, W.J. Peijnenburg, Y.-n. Zhang, Continuous flow electrosorption-microbial fuel cell system for efficient removal of oxytetracycline without external electrical supply, Bioresour. Technol. 290 (2019) 121751. [94] B. Logan, B. Hamelers, R. Rozendal, U. Schr€ oder, J. Keller, S. Freguia, P. Aelterman, W. Verstraete, K. Rabaey, Microbial fuel cells: methodology and technology, Environ. Sci. Technol. 40 (2006) 5181–5192. [95] M. Rahimnejad, A.A. Ghoreyshi, G. Najafpour, T. Jafary, Power generation from organic substrate in batch and continuous flow microbial fuel cell operations, Appl. Energy 88 (2011) 3999–4004. [96] M. Rahimnejad, A. Ghoreyshi, G. Najafpour, H. Younesi, M. Shakeri, A novel microbial fuel cell stack for continuous production of clean energy, Int. J. Hydrog. Energy 37 (2012) 5992–6000. [97] J. Cai, P. Zheng, M. Qaisar, Y. Xing, Effect of operating modes on simultaneous anaerobic sulfide and nitrate removal in microbial fuel cell, J. Ind. Microbiol. Biotechnol. 41 (2014) 795–802.

173

174

Biological fuel cells

[98] X.-C. Zhang, A. Halme, Modelling of a microbial fuel cell process, Biotechnol. Lett. 17 (1995) 809–814. [99] C. Picioreanu, K.P. Katuri, M.C. Van Loosdrecht, I.M. Head, K. Scott, Modelling microbial fuel cells with suspended cells and added electron transfer mediator, J. Appl. Electrochem. 40 (2010) 151–162. [100] A. Kato Marcus, C.I. Torres, B.E. Rittmann, Conduction-based modeling of the biofilm anode of a microbial fuel cell, Biotechnol. Bioeng. 98 (2007) 1171–1182. [101] R. Renslow, C. Donovan, M. Shim, J. Babauta, S. Nannapaneni, J. Schenk, H. Beyenal, Oxygen reduction kinetics on graphite cathodes in sediment microbial fuel cells, Phys. Chem. Chem. Phys. 13 (2011) 21573–21584. [102] F. Harnisch, R. Warmbier, R. Schneider, U. Schr€ oder, Modeling the ion transfer and polarization of ion exchange membranes in bioelectrochemical systems, Bioelectrochemistry 75 (2009) 136–141. [103] J. Xu, G.-P. Sheng, H.-W. Luo, W.-W. Li, L.-F. Wang, H.-Q. Yu, Fouling of proton exchange membrane (PEM) deteriorates the performance of microbial fuel cell, Water Res. 46 (2012) 1817–1824. [104] B. Christgen, K. Scott, J. Dolfing, I.M. Head, T.P. Curtis, An evaluation of the performance and economics of membranes and separators in single chamber microbial fuel cells treating domestic wastewater, PLoS One 10 (2015), e0136108. [105] K.J. Chae, M. Choi, F.F. Ajayi, W. Park, I.S. Chang, I.S. Kim, Mass transport through a proton exchange membrane (Nafion) in microbial fuel cells, Energy Fuel 22 (2008) 169–176. [106] S. Cheng, B.E. Logan, Increasing power generation for scaling up single-chamber air cathode microbial fuel cells, Bioresour. Technol. 102 (2011) 4468–4473. [107] Z. Li, L. Yao, L. Kong, H. Liu, Electricity generation using a baffled microbial fuel cell convenient for stacking, Bioresour. Technol. 99 (2008) 1650–1655. [108] F. Li, Y. Sharma, Y. Lei, B. Li, Q. Zhou, Microbial fuel cells: the effects of configurations, electrolyte solutions, and electrode materials on power generation, Appl. Biochem. Biotechnol. 160 (2010) 168. [109] P.-Y. Zhang, Z.-L. Liu, Experimental study of the microbial fuel cell internal resistance, J. Power Sources 195 (2010) 8013–8018. [110] S.-E. Oh, B.E. Logan, Proton exchange membrane and electrode surface areas as factors that affect power generation in microbial fuel cells, Appl. Microbiol. Biotechnol. 70 (2006) 162–169. [111] S. Cheng, H. Liu, B.E. Logan, Increased power generation in a continuous flow MFC with advective flow through the porous anode and reduced electrode spacing, Environ. Sci. Technol. 40 (2006) 2426–2432. [112] S. Kondaveeti, J.M. Moon, B. Min, Optimum spacing between electrodes in an air-cathode single chamber microbial fuel cell with a low-cost polypropylene separator, Bioprocess Biosyst. Eng. 40 (2017) 1851–1858. [113] V. Oliveira, M. Simo˜es, L. Melo, A. Pinto, Overview on the developments of microbial fuel cells, Biochem. Eng. J. 73 (2013) 53–64. [114] P. Pandey, V.N. Shinde, R.L. Deopurkar, S.P. Kale, S.A. Patil, D. Pant, Recent advances in the use of different substrates in microbial fuel cells toward wastewater treatment and simultaneous energy recovery, Appl. Energy 168 (2016) 706–723. [115] A. Zabihallahpoor, M. Rahimnejad, F. Talebnia, Sediment microbial fuel cells as a new source of renewable and sustainable energy: present status and future prospects, RSC Adv. 5 (2015) 94171–94183. [116] V. Agostino, D. Ahmed, A. Sacco, V. Margaria, C. Armato, M. Quaglio, Electrochemical analysis of microbial fuel cells based on enriched biofilm communities from freshwater sediment, Electrochim. Acta 237 (2017) 133–143. [117] L.M. Tender, S.A. Gray, E. Groveman, D.A. Lowy, P. Kauffman, J. Melhado, R.C. Tyce, D. Flynn, R. Petrecca, J. Dobarro, The first demonstration of a microbial fuel cell as a viable power supply: powering a meteorological buoy, J. Power Sources 179 (2008) 571–575. [118] Y. Gong, S.E. Radachowsky, M. Wolf, M.E. Nielsen, P.R. Girguis, C.E. Reimers, Benthic microbial fuel cell as direct power source for an acoustic modem and seawater oxygen/temperature sensor system, Environ. Sci. Technol. 45 (2011) 5047–5053.

MFC designing and performance

[119] H. Li, Y. Tian, Y. Qu, Y. Qiu, J. Liu, Y. Feng, A pilot-scale benthic microbial electrochemical system (BMES) for enhanced organic removal in sediment restoration, Sci. Rep. 7 (2017) 1–9. [120] D.P. Strik, R.A. Timmers, M. Helder, K.J. Steinbusch, H.V. Hamelers, C.J. Buisman, Microbial solar cells: applying photosynthetic and electrochemically active organisms, Trends Biotechnol. 29 (2011) 41–49. [121] M. Rosenbaum, Z. He, L.T. Angenent, Light energy to bioelectricity: photosynthetic microbial fuel cells, Curr. Opin. Biotechnol. 21 (2010) 259–264. [122] X. Hu, J. Zhou, B. Liu, Effect of algal species and light intensity on the performance of an air-lift-type microbial carbon capture cell with an algae-assisted cathode, RSC Adv. 6 (2016) 25094–25100. [123] J. Choi, Y. Ahn, Continuous electricity generation in stacked air cathode microbial fuel cell treating domestic wastewater, J. Environ. Manag. 130 (2013) 146–152. [124] T.H. Sleutels, A. Ter Heijne, C.J. Buisman, H.V. Hamelers, Bioelectrochemical systems: an outlook for practical applications, ChemSusChem 5 (2012) 1012–1019. [125] Y. Jeon, K. Koo, H.J. Kim, S. Kim, Construction and operation of a scaled-up microbial fuel cell, Bull. Korean Chem. Soc. 34 (2013) 317–320. [126] D. Cecconet, D. Molognoni, A. Callegari, A.G. Capodaglio, Agro-food industry wastewater treatment with microbial fuel cells: energetic recovery issues, Int. J. Hydrog. Energy 43 (2018) 500–511. [127] J.R. Kim, J. Rodrı´guez, F.R. Hawkes, R.M. Dinsdale, A.J. Guwy, G.C. Premier, Increasing power recovery and organic removal efficiency using extended longitudinal tubular microbial fuel cell (MFC) reactors, Energy Environ. Sci. 4 (2011) 459–465. [128] F. Haugen, R. Bakke, B. Lie, J. Hovland, K. Vasdal, Optimal design and operation of a UASB reactor for dairy cattle manure, Comput. Electron. Agric. 111 (2015) 203–213. [129] M. Helder, D.P. Strik, H.V. Hamelers, C.J. Buisman, The flat-plate plant-microbial fuel cell: the effect of a new design on internal resistances, Biotechnol. Biofuels 5 (2012) 1–11. [130] S. Kazemi, M. Mohseni, K. Fatih, A systematic study of separators in air-breathing flat-plate microbial fuel cells—part 1: structure, properties, and performance correlations, Energies 9 (2016) 78. [131] H. Eom, K. Chung, I. Kim, J.-I. Han, Development of a hybrid microbial fuel cell (MFC) and fuel cell (FC) system for improved cathodic efficiency and sustainability: the M2FC reactor, Chemosphere 85 (2011) 672–676. [132] L. Malaeb, K.P. Katuri, B.E. Logan, H. Maab, S.P. Nunes, P.E. Saikaly, A hybrid microbial fuel cell membrane bioreactor with a conductive ultrafiltration membrane biocathode for wastewater treatment, Environ. Sci. Technol. 47 (2013) 11821–11828.

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CHAPTER 7

Separators and membranes Mostafa Rahimnejad

Biofuel and Renewable Energy Research Center, Chemical Engineering Department, Babol Noshirvani University of Technology, Babol, Mazandaran, Iran

7.1 Introduction Separators play powerful roles in determining the performance of MFCs; controlling their characteristics with precision is hence a vital, fundamental aim of the MFC sciences. Separators divide the anodic and cathodic chambers physically while conjugating the chambers both ionically and electronically [1]. When using a dual-chambered MFC, the separator enables distinctive cathodic and anodic half-cell potentials through splitting anolytes and catholytes. During the operation of electrochemical cells, electrons produced from microbial metabolic activity flow toward the cathode via an external circuit, while the separators allow proton transport between the anolyte and the catholyte [2]. Although the use of a separator is a potent way to access better energy generation and sensing capability, compared with membraneless devices [3], there are some reports on their contribution in cathode contamination and mixed potential generation, which lead to poor MFC performance [4]. As an additional configuration, membraneless singlechambered MFCs have been designed in order to enhance the mass transfer rate and to decrease operating costs [5,6], although an increase in oxygen and substrate diffusivity has been reported for such MFC configuration, leading to a reduction in coulombic efficiency [7]. It is worth noting that recent advances in material design are now enabling unprecedented control over separator efficiency and fabricating a variety of membrane configurations. This chapter introduces different types of separators and investigates the benefits and challenges associated with their applications.

7.2 Membrane types for MFCs MFCs are bioelectrical devices with a complex microbial metabolic activity for which the redox reactions can be highly controlled [8,9]. Separators present in dual or multichambered MFCs enable a physical separation of the cathodic and anodic chambers while supporting the ionic-based conjugation between the chambers. Ion-exchange membranes (IEMs), porous membranes, ceramic membranes, polymer electrolyte membranes (PEMs), and salt bridges are the different types of membranes used to alter the performance, cost and multilevel applications of MFCs. These membranes are precisely Biological Fuel Cells https://doi.org/10.1016/B978-0-323-85711-6.00018-7

Copyright © 2023 Elsevier Inc. All rights reserved.

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formulated and can be engineered to have a variety of structures, material choices, and arrangements. We discuss below the role of IEMs in modulating MFC performance and cite some examples of MFC operation.

7.2.1 Ion-exchange membranes IEMs are categorized into three main classes, based on the type of matrix material: cationexchange membranes (CEMs), anion-exchange membranes (AEMs), and bipolar membranes (BPMs) (Fig. 7.1). The CEMs possess a negative charge at their surface and selectively pass positive ions, while AEMs possess a positive charge at their surface and selectively let negative ions pass through. As a further improvement, Chlanda et al. [10] compiled anion and cation- exchange layers to create BPMs. High selectivity, low electrical resistance, and good thermomechanical properties make IEMs useful in food, drug, and chemical process industries, as well as wastewater treatment. Inorganic materials such as zeolites, bentonite, and phosphate salts have unique properties that make them potential IEM materials. Because of their excellent ionic conductivity, multiple polymer-based IEMs have also been introduced. Today, a wide variety of IEMs, including inorganicorganic IEM, mosaic IEM, and bipolar IEM, are available for scientific investigations and commercial applications [11]. 7.2.1.1 Cationexchange membranes Sulfonation and bromination are the commonly used processes for CEM production. It was demonstrated that the content of bromo methylation and aryl sulfonation determines the overall membrane properties [12,13]. Nafion is a well-known copolymer with high proton conductivity prevalently used for fabricating a majority of CEMs. Nafion is a well-known sulfonated tetrafluoroethylene copolymer with high proton conductivity prevalently used for fabricating a majority of CEMs. Multiple Nafion membranes capable of selective transfer of protons through hydrophilic sulfonate groups (SO
3 ) attached to the hydrophobic fluorocarbon backbone (dCF2dCF2d) have been fabricated. For instance, we have investigated the effects on the power generation capacity of 9 cm2 Nafion 117 and Nafion 112 as nanomembranes. The membranes were operated within a dual-chambered MFC under the same conditions. As shown in Table 7.1, Nafion 112 is an excellent nanomembrane which shows an improved voltage, current, and power density compared to Nafion 117. Today, nylon, cellulose, J-cloths, polycarbonates, and teflon-coated layers have shown good efficiency to replace Nafion [1]. Other common CEMs include Hyflon, Zifron, Ultrex, and CMI-7000, which have been used successfully as commercial membranes. Venkatesan and Sangeetha [14] produced a sulfonated polyether ether ketone (SPEEK) membrane for operating in a single-chamber MFC using sulfuric acid as the sulfonating agent. Thickness of 120 mm, IEC of 0.9 mmol/g, and water uptake capacity of 20% water were reported as the dominant properties of SPEEK. In a study, we have

Separators and membranes

Fig. 7.1 Schematic illustration of ion-exchange membranes. Cation-exchange membrane (A), anionexchange membrane (B), and bipolar membrane (C).

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Table 7.1 Illustrating the impact of separator on potential MFC performance.

Nafion 117 Nafion 112

Voltage

Current density

Power density

668 mV 670 mV

60.28 mA m
2 150.6 mA m
2

9.95 mW m
2 31.32 mW m
2

examined the power generation and chemical oxygen demand (COD) removal performance of Nafion 117 and SPEEK as proton exchange membranes [15]. SPEEK was synthesized through in situ precipitation. We found that negatively charged SO3
ions endow SPEEK with excellent proton conductivity and hydrophilic features. Therefore, SPEEK can be recommended as a viable alternative for Nafion 117. We used Eq. (7.1) to estimate the degree of sulfonation: DS A ¼ 1 S
2DS A2

ð0  DS  1Þ

(7.1)

where S exhibits the total number of hydrogen atoms before sulfonation, A1 and A2 are the peak area of the distinct signal (H13) and the integrated peak area of the signals (aromatic hydrogen), respectively. Furthermore, we calculated the coulombic efficiency by the following equation: ðt M I dt 0 CE ¼ (7.2) F b V an ΔCOD where M exhibits the molecular weight of oxygen, F is Faraday’s constant, b demonstrates the number of electrons transferred per mole of oxygen, and Van is the anolyte volume. The results showed a higher power production capacity for the MFC system operated with Nafion 117 by 27.5% (Fig. 7.2). This could be attributed to the higher conductivity and lower internal resistance of Nafion 117. Moreover, higher COD removal efficiency (88%) was achieved for SPEEK. In terms of cost-efficiency, we suggest the SPEEK is the better choice, since the use of SPEEK could surpass the operating costs by 50%. Advancement in CEM design can be further achieved through the development of composite membranes. Importantly, we found that the use of polymer/inorganic nanoparticle membranes can overcome some of the critical limitations of conventional CEMs such as Nafion and thereby improve their power generation capacity. The incorporation of inorganic nanoparticles could be used to alter the surface morphology of the membrane, which is reported to bias the fouling tendency of membranes. For example, we synthesized polyethersulfone (PES) membranes with four different Fe3O4 contents (5%, 10%, 15%, and 20%) [16]. The variation in pore size and surface roughness of the synthesized Fe3O4/PES membranes is shown in Fig. 7.3. Propitious membrane morphology and power generation capacity was achieved for the PES membrane containing

Separators and membranes

Fig. 7.2 Demonstrating power density, internal resistance, and current density evaluation of Nafion 117 and SPEEK.

Fig. 7.3 Average pore size, surface roughness, and maximum power density of PES membranes containing four different Fe3O4 content (5%, 10%, 15%, and 20%).

15% Fe3O4 nanoparticles. In contrast to Nafion 117, the addition of 15% Fe3O4 nanoparticles increased the maximum power generation by 29%. Similarly, various nanocomposite membranes have been recently developed that would accelerate the advancement of MFC devices [17]. For instance, ion-exchange resin (IER) was utilized to develop the SPEEK composite membrane [18]. Excellent

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cation conductivity was reported for IER-based composite membranes, compared with the conventional Nafion membrane. Mokhtarian et al. [19] developed composite membranes of Nafion 112 and PANI through dipping Nafion 112 into aniline solutions for different immersion periods in order to increase the proton conductivity and antifouling characteristics. The Nafion 112/PANI membranes were reported to exhibit a ninefold increment in power density, compared with the control. Shahgaldi et al. [20] fabricated the PVDF/Nafion composite membrane, in which the addition of 0.4 g of Nafion improved the power density and coulombic efficiency of the MFC. Kugarajah et al. fabricated a cation-exchange membrane comprising SPEEK and sulfonated titanium nanotubes (S-TNT), in which SO3H groups of S-TNT formed effective ionic channels that were even better than OH
groups [21]. The obtained structure forms electrochemically stable biofilm, which exhibits a high power density of 121 mW m
2, a good ion exchange capacity of 3.2 meq g
1, and a low internal resistance of 30 Ω. Chakraborty et al. conducted a systemic research on how sulfonated biochar derived from pyrolysis of food waste influence the power density and costs of MFC operation [21]. The results showed that the Sayong ball clay (SBC)-600 membrane improved the proton conductivity, ion transport number, and oxygen diffusion coefficient (0.07 S cm
1, 0.891, and 6.46  10
9 m2 s
1, respectively). Furthermore, the contribution of the SBC-600 membrane resulted in 26 times higher power production per unit cost, compared with that of Nafion. Table 7.2 introduces examples of recently developed CEM membranes for application in MFCs. 7.2.1.2 Anion-exchange membranes Possessing positively charged cation groups such as NH4+, NHR2+, NR2 H+, NR3+, PR3+, and SR2+ within the polymer matrix, AEMs are qualified to pass negatively charged ions [30,31] (Table 7.3). AEMs have analogous working principles to alkaline fuel cells containing potassium hydroxide as the electrolyte [38]. The disadvantages of AEMs include low anionic conductivity and lesser hydration behavior of the cation head group. Hence, AEMs are pushed for better water retention, physicochemical stability, and ionic conductivity to overcome the limitations. The chemical reactions involved in an anionic exchange membrane fuel cell (AEMFC) are as follows: Anodic reaction : H2 + 2OH
! 2H2 O + 2e


E 0 ¼ 0:83 V

1 Cathodic reaction : O2 + H2 O + 2e
! 2OH
E 0 ¼ 0:40 V 2 1 Net reaction : O2 + H2 ! H2 O E 0 ¼ 1:23 V 2

(7.3) (7.4) (7.5)

In AEMFC, hydroxide ions transfer from the cathode to the anode and to be combined with hydrogen which is the normal reaction of water formation. It is synchronized

Separators and membranes

Table 7.2 Reports on CEM developed for application in MFCs. Membrane material

Membrane properties

Power density

Ref.

Chitosan carbon nanotubes

Thickness ¼ 0.024 cm Water absorption ¼ 0.7% Mean pore size ¼ 45 nm Average roughness ¼ 25.45 nm Porosity ¼ 47.6 Thickness ¼ 0.15 mm Oxygen mass transfer coefficient (K0) ¼12.96  10
4 cm s
1 Dissolved oxygen (DO) ¼ 19.44  10
6 cm s
1 σ ¼ 3.5  10
2 S cm
1 K0 ¼ 6.1  106 cm s
1 Ώ ¼ 112 coulombic efficiency (CE) % ¼ 3.14 K0 ¼ 2.4  106 cm s
1 IEC ¼ 1.87 meq g
1 σ ¼ 0.148  10
3 S cm
1 Water swelling ¼ 15.87 Thickness ¼ 0.020 cm Thickness ¼ 120 mm IEC ¼ 1.05 meq g
1 WU (%) ¼ 39 K0 ¼ 0.8  10
6 cm s
1 IEC ¼ 3.35 meq g
1 WU (%) ¼ 220 σ ¼ 3.574  10
2 S cm
1 Thickness ¼ 180 mm IEC ¼1.98 meq g
1 WU (%) ¼ 21.83 σ ¼ 0.167  10
2 S cm
1 Thickness ¼ 0.018 mm K0 ¼ 2.2  10
6 cm s
1 IEC ¼ 1.88 meq g
1 WU (%) ¼ 20.63 σ ¼ 0.165  10
2 S cm
1 Thickness ¼ 0.018 mm IEC ¼ 1.98 meq g
1 WU (%) ¼ 21.28 σ ¼ 0.154  10
2 S cm
1 Thickness ¼ 0.019 cm

46.94 mW m
2

[14]

57.64 mW m
2

[22]

140 mW m
2

[23]

1.9 W m
3

[24]

5.7 W m
3

[14]

1202.5 mW m
2

[25]

1345 mW m
2

[26]

98.1 mW m
2

[18]

104 mW m
2

[27]

207 mW m
2

[28]

Activated carbon/Nafion 117

Sulfonated polyether ether ketone(SPEEK)/poly ether sulfone

Polyvinyl alcohol/silicotungstic acid (STA)/graphene oxide

SPEEEK

SPEEK/sulfonated TiO2

SPSEBS/sulfonated TiO2

SPEEK/Rutile TiO2

SPEEK/Fe3O4

SPEEK/STA

Continued

183

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Table 7.2 Reports on CEM developed for application in MFCs—cont’d Membrane material

SPEEK/GO

sPSf/sMILFe

Membrane properties

Power density


1

IEC ¼ 2.21 meq g WU(%) ¼ 67.85 σ ¼ 2.88 mS cm
1 K0 ¼ 0.00048 cm s
1 D0 ¼ 8.67  10
6 IEC ¼ 3.03 meq g
1 WU(%) ¼ 54.05 σ ¼ 3.82 mS cm
1 K0 ¼ 0.000492 cm s
1 D0 ¼ 9.35  10
6

53.12 mW m


2

64.2 mW m
2

Ref.

[29]

[13]

Table 7.3 Reports on recently developed AEMs for application in MFCs. Membrane material

QPEEK

QPEI

QPSU/GO

RALEX QA-AEM AFN

Membrane properties
1

IEC ¼ 1.39 meq g WU (%) ¼ 24% Thickness ¼ 0.0002 mm IEC ¼ 0.968 meq g
1 WU (%) ¼ 42 Thickness ¼ 30 mm IEC ¼ 1.45 meq g
1 WU (%) ¼ 43.34 Thickness ¼ 30 mm Area ¼ 64 cm2 IEC ¼ 2.46  0.25 meq g
1 WU (%) ¼ 92.8  2.8 IEC ¼ 2.0–3.5 meq g
1 Thickness ¼ 0.15–0.18 mm

Power density

58 W m


3

Ref.

[32]

612 m/m
2

[33]

1036.15 mW m
2

[34]

57.8  5.509 mW m
2 16 mW m
2

[35] [36]

0.38 mA cm
2

[37]

with electron transfer to the cathode through an external circuit, where they reduce oxygen to produce OH
. AEMFCs are required to be improved in terms of materials and processing schemes. Such improvements include durability and conductivity of the membrane, appropriate detection of suitable OH
ion conductive polymers, and good identification/optimization of membrane electrode assembly preparation methods. An improvement in the thermomechanical and physicochemical properties of the membranes has been reported by using organic-inorganic hybrid materials. For instance, SiO2, TiO2, bentonite, ZrO2, graphene are the commonly used inorganic fillers. The contribution of such fillers has been essential in the development of several membranes with good water uptake and ion conductivity characteristics. Moreover, the ionic groups of these inorganic fillers are currently conducted to improve ion exchange [39].

Separators and membranes

Mahendiravarman et al. [40] used polyetherimide as an AEM in a dual-chamber MFC and obtained better kinetic and static characteristics, compared with the commercial one. By partially cross-linking the macromolecular structure, Mohanty et al. produced comb-shaped AEMs functionalized with dimethyl hexadecyl ammonium groups, which could be used to improve flexibility, water uptake, and swelling properties better than those of conventional uncross-linked or fully cross-linked ones [41]. Rossi et al. led a pioneering work to reveal the importance of AEM in the decrement of internal resistance and consequently the increment in the power density of MFCs [42]. In this study, a combination of carbon felt anode and an air cathode was used to fabricate small electrode spacing and to promote hydroxide ions transport between electrodes. The operation showed a maximum power density of 7.1  0.4 W m
2 in 100 mM PBS. Koo´k et al. used metagenomics, electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV) techniques to compare the performance of a Nafion-based PEM with an AEM, 1,4diazabicyclo [2.2.2] octane (DABCO)-functionalized PSEBS [43]. Regardless of the membrane type, the anodic biofilms were dominated by Geobacter sulfurreducens. Moreover, the internal resistance in AEM-MFC was much lower. The maximum power density and energy yield of 360 vs 320 mA m
2 was reported for the contribution of 10 mM acetate. As mentioned before, MFCs could orchestrate sustainable organic waste management through organic removal capabilities and simultaneous conversion of the chemical energy stored in the substrate(s) into electrical energy. However, insufficient power production and limited removal efficiencies are still critical issues of MFC devices. Herna´ndez-Flores et al. have reported that a single- chamber MFC equipped with a Zirfon membrane (ZF) could facilitate the volumetric power (PV) and chemical oxygen removal efficiency, as ZF plays an important role in promoting organic substrate-inoculum correlation, in which a maximum PV value of 10,380 mW m
3 was achieved from 50% leachate as the substrate and 50% sulfate-reducing inocula as the biocatalyst [44]. In addition, Changkhamchom et al. have also demonstrated that the use of quaternized graphene oxide-quaternized polybenzimidazole (Q-GO/Q-PBI) composites as AEM can stimulate hydroxide conductivity, ion exchange capacity, water uptake, and substrate permeability [45]. They have shown that a 0.5%v/vQ-GO/Q-PBI composite AEM can result in the hydroxide conductivity of 1.12  0.01 mS cm
1, the ion exchange capacity of 1.70  0.03 mmolg
1, the water uptake of 66.61  0.57%, and the glucose permeability of (1.79  0.83)  10
8 cm2 s
1. Taken together, the AEM design could directly modulate removal efficiency and produce a favorable power density. It is therefore regarded as a powerful strategy for enhancing MFC performance. 7.2.1.3 Bipolar membranes A BPM is a combination of two monopolar membranes allowing the transfer of both cations and anions. Generally, BPMs are designed using a variety of techniques, among

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which fabricating a single sheet of BPM through casting of cation-selective resin on the anion-exchange resin has attracted great interest, due to its high ion-selectivity, low internal resistance, excellent current density, and good water splitting rate even at low drops of potential. pH gradient and interfacial resistance between the cation-selective and anion-selective layers are the main challenges faced by using such membranes [46]. For overcome this, the cation-selective and anion-selective layers must be designed with an optimal thickness. Furthermore, a high ion concentration and a sufficient rate of ion transfer are required to attenuate the interfacial resistance. Wang et al. compared the remediation performance of mixed heavy metal contaminated soil with that of single heavy metal contaminated soil using air-cathode two-chamber MFCs [47]. They found that more sustainable pH and high metal removal efficiencies can be concluded during bioremediation of Cr (VI)-, Cd (II)-, Cr (VI)/Cd (II)-contaminated soils than in those of soils contaminated with single heavy metal. Migration of heavy metal ions toward the cathode accounts for making concentration gradient under a weak electric field. Similarly, Kim et al. have shown that PEM-MFC can mediate excellent removal of hexavalent chromium (from electroplating wastewater) and better bioelectricity generation, compared with those of PEM-MFC [48]. The maximum power densities of 47.2 and 150.5 mW m
2 were reported for PEM-MFCs and BPM-MFC, respectively, using 50% of chromium wastewater. Besides, more sustainable pH in both the cathodic and anodic chambers confirmed sufficient proton generation through water dissociation in BPM-MFC, maintaining the balance of bioelectrochemical reactions during the operation.

7.2.1.4 Capacity of ion-exchange membranes Ion-exchange capacity (IEC) is a promising assessment utilized for investigating the quantity of membrane ions that have been replaced with opposite ions from the surrounding solution. IEC measurement is correlated with the number of functional groups incorporated within the membrane matrix. In case of CEM, IEC is carried out through immersion of membranes into a saturated potassium chloride solution overnight, allowing proton replacement with potassium ions. Subsequently, the released protons are measured and titrated with sodium carbonate solutions using phenolphthalein as indicator. The IEC is calculated as follows [10]:   Titer value ðmLÞ  Normality of Na2 CO3 mmol g IEC ¼ (7.6) Weight of dry polymer membrane ðgÞ For IEC measurement, AEMs undergo alkalization and immersion in HCl aqueous solution (0.01 M) overnight. Then the released ions are investigated through titration. IEC of AEM would be [10]

Separators and membranes

IEC ¼

M0
Mt Md

(7.7)

where M0 and Mt represent the number of HCl moles added and consumed, respectively, in the system. Wd exhibits the weight of the dry membrane. Furthermore, the degree of functionalization (DF) of membranes can be determined using the nuclear magnetic resonance (NMR) [49]. The intensity and downshift of the HE signal confirms the presence of functional groups. n AHE ¼ ’ 12
2n σ AHA ; B; B’ ; C; D

(7.8)

where AHE is called the peak area of the HE signal, and AHA’; B; B’; C; D displays the total peak of other aromatic hydrogen. Therefore, the value of DF would be DF ¼ n  100%

(7.9)

It is worth noting that temperature is a factor that can alter DF and IEC. An increment in the temperature enhances the IEC, water uptake, and swelling features of membranes.

7.2.2 Porous membranes Porous membranes such as glass wools, ultrafiltration membranes (UFMs), and microfiltration membranes (MFMs) are known as promising low-cost separators in MFCs. It is increasingly appreciated that, in order to utilize expensive CEM, the use of cheap glass wool offers more economical wastewater treatment and power generation. The porous structure of membranes enables rapid biofouling formation. This decreases membrane internal resistance and enhances long-term membrane performance; however, it increases the probability of bigger molecules such as substrates crossover. Studies show that the use of such membranes as IEM has a vast untapped potential [11,22,50]. 7.2.2.1 Ultrafiltration membranes UFMs with different molecular weights (in Daltons) have been utilized for wastewater treatment. Today, UFMs contribute to MFC configuration as effective separators because they are permeable to anions and cations. Hou et al. compared different types of membranes: microfiltration membrane (MFM), CEM, and UFM with different molecular cutoff weights (1, 5, and 10 K) [51]. The membranes were investigated in terms of simultaneous azo dye decolorization and electricity generation within aircathode single-chamber MFCs. They found that MFC with a UFM-1K produced a higher power density (324 mW m
2) and exhibited coulombic efficiency higher than those obtained with MFM. Furthermore, decolorization rates of 4.77, 3.61, 2.38, 2.02, and 1.72 mg L
1 h
1 were obtained from UMF-10K, MFM, UFM-5K,

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Biological fuel cells

UFM-1K, and CEM, respectively. They showed that UFM-1K was the best choice for optimizing MFC cost and performance. Although UFM has been proven to have excellent performance, substrate loss and low coulombic efficiency prompt researchers to focus on the optimization of pore size and thickness of UFMs [52]. Kim et al. used polydopamine (PD) coating to engineer UFM surfaces [53]. They studied the effect of membrane surface characteristics on the power generation capacity of MFCs and found that PD coating can increase membrane hydrophilicity and negative surface charge. Less biofouling formation resulted in a remarkable decrement in charge transfer resistance from 283.4 to 162.0 Ω. 7.2.2.2 Microfiltration membranes Recent advances in MFCs have addressed the use of MFMs that enable excellent filtration efficiencies and high durability [54,55]. Several polymer MFMs are accessible as cost-effective MFC separators, including nylon mesh, cellulose filters, and polycarbonate filters [56]. Compared with other membranes, MFMs offer much more flexibility in terms of isolating the anodic and cathodic solutions because they possess a broader range of pore size, allowing various charged and neutral species to pass over. Tang et al. successfully fabricated cellulose acetate MFMs that enabled an internal resistance of 263 Ω, a maximum power density of 0.831  0.016 W m
2, and a coulombic efficiency of 38.5  3.5% [57]. The results were in correspondence with values obtained from CEM-MFC. Besides the aforementioned advantages, systemic control of mass transport and Ohmic resistance using MFMs are considerably challenging [58,59]. The high permeation rate of substrate and oxygen increased internal resistance and consequently reduced power production. This limitation can be overcome using large electrode spacing [52]. For instance, Lai et al. developed a bilayer MFM as a separator to promote MFC performance [60]. In this study, they demonstrated that MFM induced the proton transfer, sustainability, and antipollution capability of dual-chamber MFC. A maximum power density of 6.24 mW m
2, pollutant degradation rate of 48.34%, and COD removal efficiency of 56% were reported when p-nitroaniline and acetate were employed as the substrate. In another study, Zuo et al. prepared a hollow fiber microfiltration membrane (HFM) coupled with a bio-cathode microbial desalination cell (MDC) [61] that realized remarkable purification of real domestic wastewater during 105 days of operation.

7.2.3 Ceramic membranes Ceramic membranes were introduced to electrochemical devices due to the fact that the porosity, permeability, and tolerance to higher temperature have been shown to have a substantial influence on their applications in MFCs (Table 7.4). The use of ceramic membranes, in particular, leads to a whole host of economic and power output benefits inaccessible to conventional Nafion membranes, as has been demonstrated in several recent

Separators and membranes

Table 7.4 An overview of ceramic membrane performance. Ceramic-based separator

COD removal (%)

CE (%)

Current (mA)

Ref.

clayware Earthen pot Earthen pot Terracotta Terracotta Red soil clayware Black soil clayware

90  3.2 92–95.5 96.5 – 92 78.9  3 89.6  3.2

25.6  29 612 mW m
2 21.2 21  5 – 7.69  6.39 6.39  1.40

10.714 (A m
3) 12.25 3.04 22 5.9  1.3 –

[62] [63] [64] [65] [66] [67]

studies. The majority of researches in this area have focused on comparing the cost of fabrication and the power output achieved from naturally occurring clay with those obtained from conventional CEM [64,68]. Behera et al. demonstrated that the use of ceramic separator as CEM exhibited an improved power density of 16.8 W m
3 using synthetic wastewater as the substrate [68]. The same group described clayware ceramic pots as ceramic separators [64]. Their investigation showed that the MFCs made with ceramic separators had a power density of 2.3 W m
3 and that the power output is comparable to that of Nafion-based CEM. The use of a terracotta flower pot as a ceramic separator prepared by Ajayi et al. provided a peak power density of 33.13 mW m
2 in an air-cathode MFC [69]. Similarly, Chatterjee and Ghangrekar reported the power density of 4.38 W m
3 from clayware ceramic pots in an air-cathode MFC [70]. In this study, deposition of salts on the cathode and the loss of electrolytes by evaporation were introduced as the main challenges faced with the use of such membranes. Jana et al. incorporated ceramic cylinders into a continuous flow operation [64]. They found that the ceramic cylinder enhanced the power density of MFC by 46%, compared with the use of Nafion-based CEM in the same operating condition. Additionally, Ghadge and Ghangrekar added a clayware separator to an air-cathode MFC of 26 L capacity, which resulted in a maximum power density of 7.5 W m
3 and a coulombic efficiency of 30% [71]. 7.2.3.1 Cation exchange mechanism in clay-based separators The crystalline structure of the ceramics and chemical composition of the ionic solution are critical factors which affect the ion exchange capability of the clay matrix. Ionic activity within the mineral matrices leads to unbalanced electrical charges which are responsible for modulating reversible reactions throughout the ionic solution. This mediates the migration of charge species from the solution to the clay structure [72]. These negative species collected on the matrix edges contribute to the neutralization of the positive species within the ionic solution, thereby electrostatic-attraction forces and mass action. For instance, the increasing ratio of the negative charge on the octahedral sites, interlayer of the montmorillonite ((Mg0.4Al1.6)Si4O10(OH)2) crystal must be saturated with water to

189

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Biological fuel cells

neutralize the unbalanced negative charge [73]. Note that the number of ion-exchange sites and electrostatic forces between the cations present in the ionic solution and the anions of the minerals determine the total performance of the ion-exchange chemical reactions. Ca2+, Mg2+, Na+, and K+ are examples of prevalently used cations. These metallic ions are replaced with H+ ions at low pHs as follows [74]: X ðclayÞ + H+ ! H+ ðclayÞ + X

(7.10)

7.2.3.2 Modification of clay-based separators Clay-based separators have enabled important advances in MFC performance to generate maximum power density. However, it remains challenging to control the mechanical and thermal stability of the separators during the operation. Ceramic separators are susceptible to vibration, affecting their long-term applications. Heating or baking of clay provides one round around this problem [73], but other methods are required. Polymer reinforcing of ceramic membranes are used to enhance the mechanical strength of the membranes [75]. Reinforcing technology is utilized to exert precise control over the shapes and sizes of batteries, such as the synthesis of a thin and flexible magnesium aluminate-based porous ceramic separator using poly(vinylidene fluoride-hexafluoropropylene) (PVdF-HFP) for application in a lithium iron phosphate battery [76]. The membrane demonstrated good mechanical stability and excellent thermal stability at 350°C. Studies have shown how structural irregularities and large pores can cause physical degradation of membrane layers under stress [77]. Beyond this, various fillers can be utilized to control the structural integrity of the membranes. For instance, TiO2 and alumina (Al2O3), as filler materials, are capable of developing good thermal and mechanical stability in ceramic membranes, a process that can be developed at low cost [78,79]. Salar-Garcı´a et al. synthesized ceramic membranes containing different amounts of iron oxide (1.06, 2.76, and 5.75 vol%) at different temperatures (1100°C, 1200°C, and 1300°C) and found that the membranes containing 5.75 vol% of iron oxide developed at 1100°C possess increased structural porosity and suppressed matrix pore size, mediating the maximum power density of 1.045 mW
2 during 26 days operation of a urine-fed MFC [80]. Cheraghipoor demonstrated that the incorporation of 30% SiO2 into nonleached soil exhibited improved porous structure, resulting in the enhancement of power density by approximately 15-fold, and excellent improvement in coulombic efficiency from 27% to 79% [81]. Additionally, the use of a natural cation exchanger allows an incredible increase in cation exchange capacity and stability of the separators. Such enhancement was carried out with the contribution of montmorillonite into the polarized polyvinylidene fluoride/trifluoroethylene (P(VdF-TrFE)) host polymer at the rate of 4% (w/w) [82]. Another challenge is to enhance the cation conductivity of the ceramic membranes, which is significantly low compared to that of Nafion [83,84]. For instance, cation

Separators and membranes

conductivity of glauconite (K,Na)(Fe3+,Al,Mg)2(Si,Al)4O10(OH)2 clay is affected by NaOH or heat treatment. NaOH activity breaks the bonds at the edge of the surface, leading to partial decomposition of the clay into halloysite ((Si,Al)2O5(OH)4) and consequently an increment in cation exchange [85]. Thermal treatment could be another way to control the stability and cation conductivity of ceramic separators. This technique improves the mechanical strength of grains and makes sufficient distances between adjacent ions. A combination of hydrothermal and alkaline treatment enables an enhancement in exchange of cesium and strontium ions carried out with neoline [86]. Enhancement in water uptake capacity may also be a promising avenue to alter the cation conductivity of the clay-based separators. Water uptake can be used to hydrate the protons, weakening the binding between the anionic matrix and the protons, while increasing proton mobility within lattice matrices [87,88]. Alternatively, the use of microporous filler materials, such as Zeolite, may be fruitful, as they can support proton mobility through channeling them into water-saturated porous structures. Furthermore, it was demonstrated that cations present in the solution can create bridge groups to replace the negative charges of the clay matrix resulting in the remarkable enhancement of proton conductivity [89]. Ultimately, the goal must be to increase the interlayer space of the membrane structure for the uptake of large volumes of water. The development of composite ceramic membranes, through which organic sulfonic acid functionalized montmorillonite (HSO3RSR-MMT) was doped into the Nafion skeleton, increased the water uptake capacity from 20.1% to 13.5% [90]. Similarly, Ghadge and Ghangrekar have shown that the addition of montmorillonite and kaolinite as cation exchangers into natural clay could provide sufficient cation transport and specific conductivity and resemblance to those of Nafion 117 [91]. Frattini et al. synthesized barium-cerium-gadolinium oxide (BCGO) ceramics codoped with lithium (Li) or cobalt (Co) to attenuate biofouling resistance [92]. They demonstrated that BCGO doped with 5 mol% Co exhibits good surface morphology, porosity, and permeability correlated with lower absolute biofouling, as compared to Nafion 117. Yousefi et al. assembled chitosan/montmorillonite nanocomposite films over the surface of commercial unglazed wall ceramics and reported the maximum power and current densities of 119.58  19.16mW m
2 and 869.44  27.49 mA m
2 for seven bilayers of nanocomposite [93]. Furthermore, Raychaudhuri and Behera blended rice husk ash (RHA) with soil to develop a ceramic membrane with excellent proton mass transfer, Ohmic resistance, power density, and antifouling properties [94]. Ohmic resistance of 47.1 Ω, maximum power density of 2.14 Wm
3, high proton mobility, and good antifouling characteristics were reported for ceramic membrane with 10% RHA.

7.2.4 Polymer electrolyte membranes (PEMs) Electrochemical science seeks to increase the performance of alternative energy devices, often using PEM with favorable properties such as thinness, permeability, light weight,

191

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Biological fuel cells

and excellent efficiency at low temperatures [95–97]. Many of the PEMs such as sulfonated polymers like SPEEK and polystyrene-ethylene-butylene-polystyrene (SPSEBS) membranes were developed as economic materials [98,99]. The target of using such materials is the increment in membrane durability associated with the presence of the aromatic backbone in the macromolecules as well as enhancement in proton conductivity. Moreover, the addition of sulfonated nanoparticles into the polymer matrix can lead to a higher power density [100]. The technique results in very low oxygen diffusivity within MFCs [26]. Polymeric membranes with low conductivity require organic conductive nanofillers to generate the desired power [101]. Alternatively, as is the case for enhancing proton conductivity, conducting polymers such as PANI, polypyrrole, or polythiophene can often be required [102]. A summary of the recently developed polymeric separators has been presented in Table 7.5, based on the power generation capacity. Metal-organic frameworks (MOFs) are another important class of materials that are utilized in PEM systems. MOF-based PEMs have been shown to possess better properties than ordinary MFC separators such as Nafion. Their unique characteristics include high porosity, excellent thermal stability, good crystalline features, and remarkable proton conductivity. In our recent study, we established a precise design criteria to develop a novel composite polymer-electrolyte membrane consisting of a metal–organic framework and sulfonated polysulfone (SPSU/MIL-100(Fe)) [107]. Polysulfone (PSU) was decorated by sulfonated aromatic rings using a chlorosulfonic acid (ClSO3H) reagent. Subsequently, the composite SPSU/MOF membranes containing different amounts of MIL-100(Fe) (1, 3, 5, and 7 wt%) were synthesized through the dry phase inversion technique and investigated in terms of power production and COD removal capacity. As seen in Fig. 7.4, SPSU/MIL 7% displayed better physiochemical properties and excellent MFC performance. This could be attributed to the multiple functional groups established

Table 7.5 Power generation study of various PEM in MFCs.

Membrane materials

Semi-IPN of cross-linked sulfonated polystyrene (SS)/ sulfonated PVDFco-HFP Sulfonated PVDF-co-HFP S-PVDF coated Nafion-117 S-PVDF laminated Nafion-117 Py-PBI/SBA15 SPSU/MIL-100(Fe)

MFC performance (mW m22)

Ref.

0.54

2.47  10


2

447.42  22

[103]

0.42 0.57 0.46 – 1.2

3.63  10
3 5.91  10
3 5.11  10
3 0.05 2.55  10
3

290.17  15 446.45  21 413.79  20 21.3 27.60

[104] [105] [105] [106] [107]

IEC (meq g21)

Proton Conductivity (S cm21)

Separators and membranes

Fig. 7.4 Maximum power density, COD removal, and coulombic efficiency of composite SPSU/MOF membranes containing different amounts of MIL-100(Fe) (1, 3, 5, and 7 wt%).

on composite membranes, as well as the existing proton transition patterns at the sulfonated polymer and MOF edges. 7.2.4.1 PEM functions in MFCs PEM-MFC technology has attracted scientific attention for its potential to protect the global environment [108]. PEM function in an MFC device is correlated with allowing the produced protons (resulted from microbial oxidation of substrates) to cross over from anode to cathode chamber [109,110]. Hence, PEMs determine the rate of proton conductivity within the MFCs. Furthermore, they separate the cathodic and anodic chambers, allowing limited ions to pass through and preventing from fuel-oxidant blending during the operation. The poor function of PEMs causes free electron or substrate transfer through the membrane, disturbing the feasibility of the electrochemical device [111]. 7.2.4.2 PEM materials Synthetic polymer-based membranes Nafion117-based membranes were actively involved in MFCs as potential synthetic polymer-based membranes. However, their high cost, poor oxygen diffusivity, and uncontrolled biofouling have limited their application [11,12,112,113]. Afterward, numerous innovative polymeric materials such as polystyrene, poly(ether ether ketone) PEEK, poly(arylene ether sulfone), polyethylene, polyvinyl alcohol, polybenzimidazole (PBI), poly(vinylidene fluoride) (PVDF), as well as chemically modified Nafions, have been introduced as promising alternatives to Nafion-based membranes

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[99,106,114,115]. Kugarajah et al. produced sulfonated polyhedral oligomeric silsesquioxane (S-POSS) incorporated SPEEK nanocomposite membranes for upgrading the performance and sustainability in a Tubular MFC [116]. The acquired membrane with 5 wt% S-POSS stimulated MFC performance in terms of power production (162  1.4 mW m
2) and proton conductivity (1.8  0.05 meq g
1). Sen et al. developed a Nafion/polymer blend membrane using the film casting method, where poly(1vinyl-1,2,4-triazole) (PVTri) was used as the polymer [117]. The addition of PVTri improved the morphology of the membranes and increased the water uptake capacity of the structures. Yisi Guan et al. conducted a systemic research on how a cross-linker (N-vinylimidazole) influence the PBI-Nafion212 composite membrane in terms of thermal stability, mechanical properties, and proton conductivity [118]. The results showed that the cross-linking process resulted in excellent thermal stability, high-dimensional stability, improved mechanical properties, and better proton conductivity compared to the control. Additionally, studies show that the contribution of composite fillers such as Al2O3, zeolites, carbon nanofibers, graphene oxide (GO), corundum, zircon, montmorillonite (MMT), and silicates within polymer matrices can effectively increase the electrical, thermal, chemical, and conductive characteristics of PEM membranes [119–121]. Shabani et al. demonstrated that the presence of 3% GO in a SPEEK membrane enhanced the chemical and morphological properties of the membranes and promoted MFC performance, compared to that of Nafion-117 [29]. Moreover, Altaf et al. synthesized novel poly(dopamine)-modified carbon nanotube-based polymer electrolyte membranes for the direct methanol fuel cell [122]. The PCSPS 0.5% composite membrane provided efficient methanol permeability (5.68  10
7 cm2 s
1) and higher proton conductivity of 0.1216 S cm
1 at 80°C, compared to Nafion117. Sudipta et al. fabricated sulfonated graphene oxide (SGO) incorporated sulfonated polybenzimidazole (SPBI) polymer electrolyte membranes for application in MFCs [123]. The obtained 3% SGO/SPBI composite membrane mediated power density of 472.46 mW m
2 at the potential value of 0.234 V closely resembles those of Nafion membranes (481.3 mW m
2). Ben Liew et al. developed a silver graphene oxide/graphene oxide/sulfonated polyether ether ketone (AgGO-GO-SPEEK) composite membrane, in which the addition of AgGO improved the antibiofouling property, proton conductivity, and oxygen diffusion coefficient of the membrane and tailored higher power generation [124]. Natural polymer-based membranes The high production costs and inconvenience associated with the isolation of synthetic polymers underscore the need for new substances as membrane materials. In addition, the synthetic polymers used in MFC membranes can cause environmental risk owing to the long degradation time. There is a growing interest in the application of natural polymers such as chitosan, cellulose, alginate, starch, pectin, agar, and gelatin as promising MFC

Separators and membranes

membrane materials. As they are parts of the natural carbon cycle, they can be degraded easily in nature. Natural polymers are known to be insoluble or less soluble in water, affecting the stable biofilm formation. To overcome this, one promising approach could be the modification of polysaccharide and protein biopolymers. The modification can be carried out by either chemical or physical methods. Chemical methods include etherification, esterification, grafting, and cross-linking, while plasticization, composite formation, and mixing are classified as physical methods [125]. Modification reactions account for the replacement or addition of functional groups within the polymer chain, promoting the gelatinization or retrogradation of the biomaterials, and make more stable films with more convenient applications. Chitosan. Chitosan is typically a hydrophilic material with a favorable stability at high temperature. Research in the field were focused on the cationic nature of the chitosan at low pHs owing to the presence of amino groups on the polymer backbone, making cationic polyelectrolytes when dissolving in acidic solvents [126]. Studies established that the polyelectrolyte gel-forming capacity of chitosan can be utilized to fabricate electrodes of polymer electrolyte-based fuel cells and ion-solvating polymer composite membranes as well. However, pure chitosan has some disadvantages, including less solubility in organic solvents, a rigid crystalline structure, low electrical conductivity, sharp swelling changes, and poor mechanical properties [127]. Subsequently, research over the recent years demonstrated that the chemical modification of chitosan exhibits a promising solution for developing new derivatives which possess excellent physiochemical properties [128,129]. Sulfonation, phosphorylation, quaternization, and chemical cross-linking processes have yet to be introduced for the chemical modification of chitosan [130–134]. Such modification reactions are associated with the development of water-soluble sulfonated, sulfated, sulfamated, phosphorylated, or phosphonated chitosan derivatives. More recent approaches include targeting the chitosan-based membrane electrolytes. Opportunities to fabricate chitosan-based membrane electrolytes, including chitosan-based membranes, self-cross-linked and salt-complexed chitosan, chitosan-based polymer blends, chitosan/inorganic filler composites, and chitosan/polymer composites, can promote MFC performance. Cellulose. Another established natural material used for preparing selective solid electrolyte membranes is cellulose. Cellulose is a stable, nontoxic, renewable, biodegradable, hydrophilic material with good mechanical strength and poor solubility in water and common organic solvents. An intra- and intermolecular hydrogen bonding network organized by hydroxyl groups located at equatorial positions of a chair-like conformation illustrates such material characteristics. Higher plants are the main source of cellulose [135]; however, some bacterial species such as Gluconacetobacter xylinus and Gluconacetobacter hansenii can produce the biopolymer as an alternative source [136]. Bacterial cellulose has unique characteristics which enable their potential applications in full cell technology. These include high crystallinity [137], a unique nanostructure [138], a high degree of

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polymerization [139], high water holding capacity [140], excellent thermomechanical stability, and low hydrogen permeation [141,142]. With respect to mechanical processing methods, laboratory studies show that crystalline and amorphous cellulose phases can result in low density, high aspect ratio, high mechanical strength, high optical transparency and low optical haze, low porosity, and low expansion coefficient in cellulose nanofibers (CNFs) [143–145]. Acid treatment of CNFs provides an important approach to hydrolyze the amorphous part of CNFs and develop innovative configurations of cellulose such as nanocrystal cellulose (NCC) or cellulose nanocrystals (CNCs). Esterification, etherification, oxidation, salt formation, cross-linking with small organic compounds, and grafting using reactive secondary and primary hydroxyl groups at carbons C-2, C-3, and C-6 of dehydroglucose units have been developed and used for developing new materials appropriate for application as MFC membranes. Furthermore, physical modification strategies, including doping with acidic or amphoteric components, and plasticizing with lowmolecular weight substances have provided excellent material structures within cellulose-based membranes. Alginate. Recently, alginate-based membranes have been introduced as an alternative for fuel cell applications. Alginate possesses good biocompatibility, high biodegradability, low cost, and an excellent degree of gelatinization when cross-linked with divalent cations such as Ca2+ [137,146], although its high solubility in water weakens the permeability and selectivity of membranes to water or gas [147], and its six-membered ring structure causes low mechanical strength associated with large void volumes enabling a high level of water absorption [148]. Covalent cross-linking, ionic cross-linking, and nonbond interactions promote stability, mechanical strength, and proton conductivity, while maintaining a good level of hydrophilicity [149]. Starch. Pure starch, analogous to synthetic polymers, is resistant to passage of oxygen and semipermeable to carbon dioxide. However, pure stretch is also considered as a water-sensitive material with poor mechanical and ion-conducting properties [150]. Being comparable in physiochemical characteristics to synthetic polymers, starch can be engineered as a novel membrane material in MFCs. Several physical and chemical approaches have been developed to improve the physiochemical characteristics of pure starch. Chemical methods include etherifications and esterifications with inorganic and organic compounds, oxidations, and cross-linking and grafting with bifunctional species. Moreover, starch characteristics can be altered using physical modification methods such as plasticization with low-molecular weight compounds and blending with other polymers or hydrophobic substances. Other materials. Electrolyte membranes can also be of pectin, agar, and gelatin derivatives. Such polymers are biodegradable, cost-effective, and hydrophilic. As a matter of fact, pectins are anionic biopolymers that possess some advantages such as good gelling and stabilizing properties as well as low methanol permeability. In addition, stable natural polymers like agar have cation coordinating oxygen sites and are structurally ideal

Separators and membranes

candidates as biomaterials for allowing ion migration [151]. Another important type of biopolymers is represented by gelatin, which has high conductivity, excellent electrochemical reversibility, and very good transparency [152]. Specifically, gelatin-based membranes, whose monomers are cross-linked with formaldehyde and plasticized with glycerol, are fabricated using inorganic acids such as hydrochloric and acetic acid [153,154]. The use of inorganic acids leads to the development of amorphous electrolytes with good thermal and chemical stability, as well as excellent ionic conductivity.

7.2.5 Salt bridge A salt bridge (SB) offers unique capabilities as an MFC separator. SB is a glass tube containing conductive electrolytes such as saturated KCl [155], NaCl [156], and phosphate buffer [157]. It was shown that 10% agar contribution resulted in the maximum power density due to its unique physicochemical properties which promote proton conductivity within SB. The use of an SB-MFC can be an appropriate alternative to other MFC configurations mainly due to its low-cost operation (Fig. 7.5). However, many challenges

Fig. 7.5 Schematic illustration of SB-MFC.

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still hamper SB application, including poor power density and high internal resistance [121]. A decrement in electrode spacing and increment in the SB surface area are emerging approaches to overcome such limitations. Sevda et al. reported that the use of agar salt bridges as proton exchangers in MFC increases power generation from wastewater [158]. A 5% salt concentration with 10% agar was shown to induce a maximum power density of 84.99 mW m
3 and 88.41% COD removal. Min et al. compared the power output obtained from a salt bridge system with that from a membrane system [159]. They showed that the SB-MFC resulted in a low power output, compared to the MFC equipped with a membrane system. The result is consistent with the higher internal resistance of the salt bridge system. Additionally, Uddin et al. investigated the performance of an SB-double compartment MFC using sucrose, glucose, and starch as substrate [159]. They found that the use of sucrose as a substrate increases the power output of SB-MFC owing to its higher solubility in water.

7.3 Membrane requirements in MFCs 7.3.1 Water uptake Water uptake (WU) is defined as water content that attaches to the surface or interstitial sites of membranes through hydrogen bonding [160]. WU is an essential parameter that can directly affect membrane function [161]. It was found that a high amount of WU accounts for the decreased mechanical strength in membrane [162]. Hence, there is an optimal amount of WU which is obtained from the following equation: W
W Water uptake ðwt%Þ ¼ 0  100 (7.11) W where W0 and W are the wet and dry mass of the hydrated membranes (g), respectively [163]. To measure WU, membranes are immersed in deionized water for 12 h (W0), followed by drying in a vacuum oven at 60°C for 12 h (W). the functional network of polymer content and three-dimensional structure of the membrane are considered potentially valuable in controlling WU% [164]. Similarly, the swelling ratio of the samples can be calculated using the following equation: L
Ld Swelling ratio ð%Þ ¼ w  100 (7.12) Ld Ld and Lw are lengths of the membrane at dry and soaked status. To measure the swelling ratio, membranes are soaked in deionized water for 24 h at 30°C followed by wiping off using blotting paper.

Separators and membranes

7.3.2 Proton conductivity The membrane matrix provides an ideal channel for proton flows from the cathodic chamber toward the anode. The proton conductivity of the membrane is measured via EIS. The method measures membrane resistivity against the flow of current using a signal amplitude of 10 mV and a frequency range of 1 MHz–100 Hz. To measure proton conductivity, membranes are soaked in demonized water at ambient temperature (30°C) for 24 h and sealed between the two inner electrodes. The following equation is used to determine the value of membrane conductivity: σ¼

L RA

(7.13)

where sigma is the proton conductivity of the samples (S cm
1), L displays the membrane thickness (cm), R is the membrane resistance (U), and A exhibits the surface area of the electrode (cm2) [165]. The proton transfer number (t+) can be examined based on the current carried in an electrolyte by a given ion. For this aim, different doses of a univalent cation such as Na+ are added to the cathodic and anodic chambers. Subsequently, reference electrodes are used to record the potential difference at certain time intervals. t+ is calculated as follows [166]: Eν ¼


RT C ð2t+
1Þ ln 1 C2 F

(7.14)

where Eν exhibits the cell voltage (mV), T displays the temperature (°K), F is the Faraday constant (C mol
1), and R displays the molar gas constant. C1 and C2 demonstrate the concentrations of univalent cation ions within the cathode and anode chambers.

7.3.3 Ion exchange capacity Functional groups of the polymer matrix have been clearly recognized as a virulence factor that determines the IEC of the membranes. Indeed, the availability of charged species throughout the membrane conducts the rate of ion exchange and modulates the MFC power output [164]. IEC estimates the total membrane charge [167] that can be measured by the back-titration technique: IEC ðmeq=gÞ ¼

V titrant
C titrant Md

(7.15)

where Vtitrant is the required volume of titrant used to restore the solution to its initial pH, Ctitrant is defined as the molar concentration of titrant, and Md exhibits the dry mass of the sample (g).

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7.3.4 pH splitting pH splitting is defined as the pH imbalance between the cathodic and anodic chambers mediated by membrane separators which upsets the MFC performance. After a period of power generation, anolytes and catholytes become more acidic and basic, respectively. The pH splitting degree is associated with type of the membrane involved. For instance, CEMs mediate higher pH splitting compared to AEMs [35]. Because of the increased concentration of alternative cations such as Na+, K+, Ca2+, Mg2+, NH4, and also proton accumulation in the anolyte, the pH of the anodic chamber decreases over time. This disrupts the microbial metabolism and reduces proton generation [168]. Therefore, proton flow cannot be maintained at an effective balance, which causes ORR inhibition and consequently pH enhancement within the cathodic chamber [169]. It was shown that the optimum anaerobic bacteria activity depends on the pH of the anode [170]. Acidic anolytes disrupt the current and power generation of MFCs [56]. The use of buffer solutions can result in persistent anodic pH condition, optimizing the catalytic activity of anaerobes [169,170].

7.3.5 Membrane permeability Oxygen mass transfer coefficient (K0) is a critical membrane performance factor which demonstrates the oxygen permeability of the membrane. Oxygen diffusion from the cathode to the anode has been shown to disturb MFC performance. K0 of the electrolyte membrane can be measured using a portable DO probe. In this strategy, an uninoculated MFC is used to evaluate DO crossover. The DO probe is placed within the nitrogensaturated anode chamber, while the cathode chamber is continuously aerated to make saturated DO conditions. K0 is calculated using the following equation: K0 ¼


V At ln ðC 0
CjC 0 Þ

(7.16)

where V exhibits the anolyte volume, A is the membrane cross-sectional area, C0 demonstrates the saturated oxygen concentration within the cathodic chamber, and C displays the DO concentration within the anodic chamber at time t. The diffusion coefficient (DO, cm2 S
1) can be calculated as follows [171]: DO ¼ K 0 Lt

(7.17)

Lt is the membrane thickness in cm. Apart from K0, researchers also investigate the substrate crossover from the anaerobic anode chamber to the aerobic cathode chamber, where the substrates are oxidized on the cathode surface by aerobic bacteria and induce biofouling [63,172]. Initially, biofouling enhances the power density of MFCs, but it drops significantly followed by biofilm thickening and decrement of the cathode active surface area necessary for ORR. The substrate

Separators and membranes

crossover of both the CEM and PEM is negligible, compared to those of porous membranes with a large pore size [35,173]. Anaerobic fermentative and planktonic aerobic or facultative bacteria exhibit a higher substrate loss through diffusion in short-term operations [174], although this result is also indicated followed by membrane damage owing to either the low pH or chemical precipitation throughout the long-term operations [170]. A dual-chambered MFC is utilized to measure the substrate crossover, in which sodium acetate is used as the anolyte and distilled water is the choice of catholyte. The mass transfer coefficient of the anolyte is calculated using the following formula [175]: KA ¼


V 2At ln ðC 0
2C 2 =C 0 Þ

(7.18)

where V is the anolyte volume (cm3), A displays the cross-sectional area of the membrane (cm2), C0 is the initial concentration of oxygen within the anodic chamber (mol cm
3), C demonstrates the oxygen concentration of the cathodic chamber (mol cm
3), and C2 is the acetate concentration within the anodic chamber at time t (s).

7.3.6 Membrane biofouling Biofilm formation usually occurs on the membrane surface facing the anodic chamber, depending on the types of organic substrates and microbial community. Additionally, oxygen crossover through the membrane can create a negative oxygen gradient within the anodic chamber, inducing the oxygen diffusion process [2]. The biofilm acts as a physical barrier which prevents proton crossover. This increases the pH gradient and electrical resistance of the MFC and attenuates power density [50]. Replacing the biofouled membrane, chemically modifying the surface of the membrane, and using antimicrobial/heavy metal biocides could be feasible techniques to circumvent the exhaustion [176]. Replacement of the bio-fouled membrane with a new one increases the operating costs. Membrane surface modification attenuates the substrate adsorption and cellular adhesion, thereby altering the membrane hydrophilicity or even electrical property, through which positive/negative bacteria would be prevented by electrostatic repulsion forces. Studies show that biocides such as copper, silver [177], and titanium dioxide particles can be used as fouling preventers [178], although the contribution can be toxic for microbial communities in the anode. In a study, we modified the PVDF/SPES blend with TiO2 nanoparticles to improve the antifouling properties of the membranes. The addition of 4 wt% TiO2 improved the hydrophilicity and the pure water flux of the membranes from 616 to 670 kg m
2, leading to the promoted fouling mitigation effect. In addition, membranes containing 4 wt% TiO2 exhibited excellent antibacterial activity against Escherichia coli. Moreover, it was demonstrated that embracing grafting with long-chain polymers such as quaternized 2-(dimethylamino) ethyl methacrylate can damage the microbial cell walls and prevent biofilm formation. The combination of antiadhesion and biocides can be adopted to suppress membrane

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biofouling during the long MFC operations [40]. Membrane biofouling can be measured through the investigation of membrane surface morphology, IEC, electrical resistance, proton conductivity, OCV, and total power density.

7.3.7 Membrane resistance Membrane internal resistance blocks proton flows toward the cathode [37]. Porous structures such as microfiltration membranes possess low resistance, although there are major issues related to the use of such membranes, which suppress MFC performance. The low coulombic efficiency and power density in such systems is critically dependent on the oxygen and substrate crossover through the membrane pores [179]. The nature of the electrolyte, pH, and electrolyte concentration determine the overall membrane resistance [180]. It is noted that electroconductive membranes show less internal resistance and the maximum amount of power densities [19]. Polarization curve methods, the power density curve method, EIS, the current interruption method, and the computer simulation method are used to investigate the internal resistance of MFC membranes.

7.4 Conclusions The past decade has witnessed the development of innovative membrane structures to promote MFC performance. MFC membranes are physical barriers which physically separate the anodic and cathodic chambers. Furthermore, membrane structures enable balanced MFC performance through improving the ion conductivity and preventing from the oxygen/substrate crossover. Recent progress in MFC science has led to precise control over membrane characteristics such as IEC, water uptake, swelling ratio, ionic conductivity, pH splitting, substrate crossover, oxygen permeation, membrane resistance, and biofouling. Generally, MFC membranes are classified as porous/nonporous structures. Nonporous membranes include CEM, AEM, BPM, whereas UFM, MFM, and CMs are known as porous membranes. Some membranes such as Nafion 117 possess high ion conductivity, mediating high power density in MFCs, although most such materials are costly and show toxicity, poor proton conductivity, and high substrate and oxygen crossover. Hydrocarbon-based polymers exhibit excellent ionic conductivity, low substrate crossover, and low oxygen permeation as alternative membrane materials. Such materials are also economical and, more importantly, environmentally friendly. Despite the recent developments in MFC science, many challenges associated with MFC commercialization need to be overcome. Appropriately designed and well-fictionalized membranes are critically required to further the enhancement of MFC application in electricity generation from biowastes, desalination, sensors, hydrogen production, heavy metal removal, bioremediation, and so forth.

Separators and membranes

References [1] M. Shabani, H. Younesi, M. Pontie, A. Rahimpour, M. Rahimnejad, A.A. Zinatizadeh, A critical review on recent proton exchange membranes applied in microbial fuel cells for renewable energy recovery, J. Clean. Prod. 264 (2020), 121446. [2] J.X. Leong, W.R.W. Daud, M. Ghasemi, K.B. Liew, M. Ismail, Ion exchange membranes as separators in microbial fuel cells for bioenergy conversion: a comprehensive review, Renew. Sust. Energ. Rev. 28 (2013) 575–587. [3] J. Chouler, I. Bentley, F. Vaz, A. O’Fee, P.J. Cameron, M. Di Lorenzo, Exploring the use of costeffective membrane materials for microbial fuel cell based sensors, Electrochim. Acta 231 (2017) 319–326. [4] M. Rahimnejad, N. Mokhtarian, G. Najafpour, A.A. Ghoreyshi, W.R.W. Dahud, Effective parameters on performance of microbial fuel cell, in: 2009 Second International Conference on Environmental and Computer Science, IEEE, 2009, pp. 411–415. [5] M. Masoudi, M. Rahimnejad, M. Mashkour, Enhancing operating capacity of microbial fuel cells by using low-cost electrodes and multi anode-cathode connections in a membrane-less configuration, Int. J. Hydrog. Energy 46 (2021) 8226–8238. [6] A. Tardast, M. Rahimnejad, G.D. Najafpour, A. Asghar Ghoreyshi, H. Zare, Fabrication and operation of a novel membrane-less microbial fuel cell as a bioelectricity generator, Iranian (Iranica), J. Energy Environ. 3 (2012). [7] A. Tardast, G.D. Najafpour, M. Rahimnejad, A. Amiri, Bioelectrical power generation in a membrane less microbial fuel cell, World Appl. Sci. J. 16 (2012) 179–182. [8] M. Rahimnejad, M. Asghary, M. Fallah, Microbial Fuel Cell (MFC): An Innovative Technology for Wastewater Treatment and Power Generation, Springer, Bioremediation of Industrial Waste for Environmental Safety, 2020, pp. 215–235. [9] M. Rahimnejad, G. Najafpour, A. Ghoreyshi, T. Jafari, F. Haghparast, Microbial fuel cell a reliable source for recovery of electrical power from synthetic wastewater, Linnaeus Eco-Tech. (2010) 627–635. [10] S. Dharmalingam, V. Kugarajah, M. Sugumar, Membranes for Microbial Fuel Cells, Microbial Electrochemical Technology, Elsevier, 2019, pp. 143–194. [11] M. Rahimnejad, G. Bakeri, G. Najafpour, M. Ghasemi, S.-E. Oh, A review on the effect of proton exchange membranes in microbial fuel cells, Biofuel Res. J. 1 (2014) 7–15. [12] M. Rahimnejad, G. Bakeri, M. Ghasemi, A. Zirepour, A review on the role of proton exchange membrane on the performance of microbial fuel cell, Polym. Adv. Technol. 25 (2014) 1426–1432. [13] B. Roshanravan, H. Younesi, M. Abdollahi, M. Rahimnejad, S.-H. Pyo, Incorporating sulfonated MIL-100 (Fe) in sulfonated polysulfone for enhancing microbial fuel cell performance, Fuel 312 (2022), 122962. [14] P.N. Venkatesan, S. Dharmalingam, Effect of cation transport of SPEEK–rutile TiO2 electrolyte on microbial fuel cell performance, J. Membr. Sci. 492 (2015) 518–527. [15] M. Ghasemi, M. Rahimnejad, D.W.R. Wan, I.A. Fauzi, Y. Jafari, A. Mayahi, J. Othman, Economical comparison of power generation in microbial fuel cell by Nafion 117 and SPEEK as proton exchange membranes, 6th Iranian Fuel Cell Seminar, Tehran, Iran, March 2013. [16] M. Rahimnejad, M. Ghasemi, G. Najafpour, M. Ismail, A. Mohammad, A. Ghoreyshi, S.H. Hassan, Synthesis, characterization and application studies of self-made Fe3O4/PES nanocomposite membranes in microbial fuel cell, Electrochim. Acta 85 (2012) 700–706. [17] M. Ghasemi, M. Rahimnejad, C. Esmaeili, Polysulfone composed of polyaniline nanoparticles as nanocomposite proton exchange membrane in microbial fuel cell, Fuel 1 (2013) 3. [18] P.N. Venkatesan, S. Dharmalingam, Development of cation exchange resin-polymer electrolyte membranes for microbial fuel cell application, J. Mater. Sci. 50 (2015) 6302–6312. [19] N. Mokhtarian, M. Ghasemi, W.R. Wan Daud, M. Ismail, G. Najafpour, J. Alam, Improvement of microbial fuel cell performance by using nafion polyaniline composite membranes as a separator, J. Fuel Cell Sci. Technol. 10 (2013). [20] S. Shahgaldi, M. Ghasemi, W.R.W. Daud, Z. Yaakob, M. Sedighi, J. Alam, A.F. Ismail, Performance enhancement of microbial fuel cell by PVDF/Nafion nanofibre composite proton exchange membrane, Fuel Process. Technol. 124 (2014) 290–295.

203

204

Biological fuel cells

[21] V. Kugarajah, S. Dharmalingam, Investigation of a cation exchange membrane comprising sulphonated poly ether ether ketone and sulphonated titanium nanotubes in microbial fuel cell and preliminary insights on microbial adhesion, Chem. Eng. J. 125558 (2020). [22] M. Ghasemi, W.R.W. Daud, A.F. Ismail, Y. Jafari, M. Ismail, A. Mayahi, J. Othman, Simultaneous wastewater treatment and electricity generation by microbial fuel cell: performance comparison and cost investigation of using Nafion 117 and SPEEK as separators, Desalination 325 (2013) 1–6. [23] W.R.W. Daud, M. Ghasemi, P.S. Chong, J.M. Jahim, S.S. Lim, M. Ismail, SPEEK/PES composite membranes as an alternative for proton exchange membrane in microbial fuel cell (MFC), in: 2011 IEEE Conference on Clean Energy and Technology (CET), IEEE, 2011, pp. 400–403. [24] S. Khilari, S. Pandit, M.M. Ghangrekar, D. Pradhan, D. Das, Graphene oxide-impregnated PVA– STA composite polymer electrolyte membrane separator for power generation in a single-chambered microbial fuel cell, Ind. Eng. Chem. Res. 52 (2013) 11597–11606. [25] S. Ayyaru, S. Dharmalingam, Development of MFC using sulphonated polyether ether ketone (SPEEK) membrane for electricity generation from waste water, Bioresour. Technol. 102 (2011) 11167–11171. [26] S. Ayyaru, S. Dharmalingam, A study of influence on nanocomposite membrane of sulfonated TiO2 and sulfonated polystyrene-ethylene-butylene-polystyrene for microbial fuel cell application, Energy 88 (2015) 202–208. [27] N.V. Prabhu, D. Sangeetha, Characterization and performance study of sulfonated poly ether ether ketone/Fe3O4 nano composite membrane as electrolyte for microbial fuel cell, Chem. Eng. J. 243 (2014) 564–571. [28] P.N. Venkatesan, S. Dharmalingam, Characterization and performance study of phase inversed sulfonated poly ether ether ketone–silico tungstic composite membrane as an electrolyte for microbial fuel cell applications, Renew. Energy 102 (2017) 77–86. [29] M. Shabani, H. Younesi, A. Rahimpour, M. Rahimnejad, Upgrading the electrochemical performance of graphene oxide-blended sulfonated polyetheretherketone composite polymer electrolyte membrane for microbial fuel cell application, Biocatal. Agric. Biotechnol. 22 (2019), 101369. [30] S.J. Peighambardoust, S. Rowshanzamir, M. Amjadi, Review of the proton exchange membranes for fuel cell applications, Int. J. Hydrog. Energy 35 (2010) 9349–9384. [31] D. Jadhav, A. Ghadge, D. Mondal, M. Ghangrekar, Comparison of oxygen and hypochlorite as cathodic electron acceptor in microbial fuel cells, Bioresour. Technol. 154 (2014) 330–335. [32] E. Mahendiravarman, D. Sangeetha, Increased microbial fuel cell performance using quaternized poly ether ether ketone anionic membrane electrolyte for electricity generation, Int. J. Hydrog. Energy 38 (2013) 2471–2479. [33] A. Alaswad, A. Baroutaji, H. Achour, J. Carton, A. Al Makky, A.-G. Olabi, Developments in fuel cell technologies in the transport sector, Int. J. Hydrog. Energy 41 (2016) 16499–16508. [34] M. Elangovan, S. Dharmalingam, A facile modification of a polysulphone based anti biofouling anion exchange membrane for microbial fuel cell application, RSC Adv. 6 (2016) 20571–20581. [35] S. Pandit, A. Sengupta, S. Kale, D. Das, Performance of electron acceptors in catholyte of a twochambered microbial fuel cell using anion exchange membrane, Bioresour. Technol. 102 (2011) 2736–2744. [36] C. Zhang, Y.C. Wang, B. An, R. Huang, C. Wang, Z. Zhou, W. Lin, Networking pyrolyzed zeolitic imidazolate frameworks by carbon nanotubes improves conductivity and enhances oxygen-reduction performance in polymer-electrolyte-membrane fuel cells, Adv. Mater. 29 (2017) 1604556. [37] E. Ji, H. Moon, J. Piao, P.T. Ha, J. An, D. Kim, J.-J. Woo, Y. Lee, S.-H. Moon, B.E. Rittmann, Interface resistances of anion exchange membranes in microbial fuel cells with low ionic strength, Biosens. Bioelectron. 26 (2011) 3266–3271. [38] V. Elumalai, S. Dharmalingam, Synthesis characterization and performance evaluation of ionic liquid immobilized SBA-15/quaternised polysulfone composite membrane for alkaline fuel cell, Microporous Mesoporous Mater. 236 (2016) 260–268. [39] C.-C. Yang, Synthesis and characterization of the cross-linked PVA/TiO2 composite polymer membrane for alkaline DMFC, J. Membr. Sci. 288 (2007) 51–60.

Separators and membranes

[40] M. Elangovan, S. Dharmalingam, Preparation and performance evaluation of poly (ether-imide) based anion exchange polymer membrane electrolyte for microbial fuel cell, Int. J. Hydrog. Energy 41 (2016) 8595–8605. [41] A.K. Mohanty, Y.E. Song, B. Jung, J.R. Kim, N. Kim, H.-J. Paik, Partially crosslinked comb-shaped PPO-based anion exchange membrane grafted with long alkyl chains: synthesis, characterization and microbial fuel cell performance, Int. J. Hydrog. Energy 45 (2020) 27346–27358. [42] R. Rossi, X. Wang, B.E. Logan, High performance flow through microbial fuel cells with anion exchange membrane, J. Power Sources 475 (2020), 228633. [43] L. Koo´k, J. Zˇitka, P. Bakonyi, P. Taka´cs, L. Pavlovec, M. Otmar, R. Kurdi, K. Belafi-Bako´, N. Nemesto´thy, Electrochemical and microbiological insights into the use of 1, 4-diazabicyclo [2.2.2] octane-functionalized anion exchange membrane in microbial fuel cell: a benchmarking study with Nafion, Sep. Purif. Technol. 237 (2020), 116478. [44] G. Herna´ndez-Flores, H. Poggi-Varaldo, T. Romero-Castan˜o´n, O. Solorza-Feria, N. RinderknechtSeijas, Harvesting energy from leachates in microbial fuel cells using an anion exchange membrane, Int. J. Hydrog. Energy 42 (2017) 30374–30382. [45] S. Changkhamchom, P. Kunanupatham, K. Phasuksom, A. Sirivat, Anion exchange membranes composed of quaternized polybenzimidazole and quaternized graphene oxide for glucose fuel cell, Int. J. Hydrog. Energy (2020). [46] M. Rahimnejad, A. Adhami, S. Darvari, A. Zirepour, S.-E. Oh, Microbial fuel cell as new technology for bioelectricity generation: a review, Alexandria Eng. J. 54 (2015) 745–756. [47] H. Wang, H. Zhang, X. Zhang, Q. Li, C. Cheng, H. Shen, Z. Zhang, Bioelectrochemical remediation of Cr (VI)/Cd (II)-contaminated soil in bipolar membrane microbial fuel cells, Environ. Res. 109582 (2020). [48] C. Kim, C.R. Lee, Y.E. Song, J. Heo, S.M. Choi, D.-H. Lim, J. Cho, C. Park, M. Jang, J.R. Kim, Hexavalent chromium as a cathodic electron acceptor in a bipolar membrane microbial fuel cell with the simultaneous treatment of electroplating wastewater, Chem. Eng. J. 328 (2017) 703–707. [49] R.S. Yee, K. Zhang, B.P. Ladewig, The effects of sulfonated poly (ether ether ketone) ion exchange preparation conditions on membrane properties, Membranes 3 (2013) 182–195. [50] W.-W. Li, G.-P. Sheng, X.-W. Liu, H.-Q. Yu, Recent advances in the separators for microbial fuel cells, Bioresour. Technol. 102 (2011) 244–252. [51] B. Hou, J. Sun, Y.-Y. Hu, Simultaneous Congo red decolorization and electricity generation in aircathode single-chamber microbial fuel cell with different microfiltration, ultrafiltration and proton exchange membranes, Bioresour. Technol. 102 (2011) 4433–4438. [52] J.R. Kim, G.C. Premier, F.R. Hawkes, R.M. Dinsdale, A.J. Guwy, Development of a tubular microbial fuel cell (MFC) employing a membrane electrode assembly cathode, J. Power Sources 187 (2009) 393–399. [53] K.-Y. Kim, E. Yang, M.-Y. Lee, K.-J. Chae, C.-M. Kim, I.S. Kim, Polydopamine coating effects on ultrafiltration membrane to enhance power density and mitigate biofouling of ultrafiltration microbial fuel cells (UF-MFCs), Water Res. 54 (2014) 62–68. [54] Z. Du, H. Li, T. Gu, A state of the art review on microbial fuel cells: a promising technology for wastewater treatment and bioenergy, Biotechnol. Adv. 25 (2007) 464–482. [55] J. Sun, Y. Hu, Z. Bi, Y. Cao, Improved performance of air-cathode single-chamber microbial fuel cell for wastewater treatment using microfiltration membranes and multiple sludge inoculation, J. Power Sources 187 (2009) 471–479. [56] J.C. Biffinger, R. Ray, B. Little, B.R. Ringeisen, Diversifying biological fuel cell designs by use of nanoporous filters, Environ. Sci. Technol. 41 (2007) 1444–1449. [57] Y. Furuhashi, R. Honda, M. Noguchi, H. Hara-Yamamura, S. Kobayashi, K. Higashimine, H. Hasegawa, Optimum conditions of pH, temperature and preculture for biosorption of europium by microalgae Acutodesmus acuminatus, Biochem. Eng. J. 143 (2019) 58–64. [58] Z. Fallahnejad, G. Bakeri, M. Rahimnejad, Study on the application of membrane technology and performance of nanostructured polyethersulfone (PES) hollow fiber membrane in treatment of oily wastewaters, J. Environ. Sci. Technol. 19 (2017) 261–273.

205

206

Biological fuel cells

[59] Z. Fallahnejad, G. Bakeri, M. Rahimnejad, Treatment of oily wastewater by polyethersulfone (PES) hollow fiber nanostructure membranes, Nashrieh Shimi va Mohandesi Shimi, Iran 34 (2015) 73–85. [60] C. Lai, B. Li, M. Chen, G. Zeng, D. Huang, L. Qin, X. Liu, M. Cheng, J. Wan, C. Du, Simultaneous degradation of P-nitroaniline and electricity generation by using a microfiltration membrane dualchamber microbial fuel cell, Int. J. Hydrog. Energy 43 (2018) 1749–1757. [61] K. Zuo, M. Chen, F. Liu, K. Xiao, J. Zuo, X. Cao, X. Zhang, P. Liang, X. Huang, Coupling microfiltration membrane with biocathode microbial desalination cell enhances advanced purification and long-term stability for treatment of domestic wastewater, J. Membr. Sci. 547 (2018) 34–42. [62] D.A. Jadhav, A.N. Ghadge, M.M. Ghangrekar, Simultaneous organic matter removal and disinfection of wastewater with enhanced power generation in microbial fuel cell, Bioresour. Technol. 163 (2014) 328–334. [63] P.S. Jana, M. Behera, M. Ghangrekar, Performance comparison of up-flow microbial fuel cells fabricated using proton exchange membrane and earthen cylinder, Int. J. Hydrog. Energy 35 (2010) 5681–5686. [64] M. Behera, P.S. Jana, T.T. More, M. Ghangrekar, Rice mill wastewater treatment in microbial fuel cells fabricated using proton exchange membrane and earthen pot at different pH, Bioelectrochemistry 79 (2010) 228–233. [65] J. Winfield, J. Greenman, D. Huson, I. Ieropoulos, Comparing terracotta and earthenware for multiple functionalities in microbial fuel cells, Bioprocess Biosyst. Eng. 36 (2013) 1913–1921. [66] I. Gajda, J. Greenman, C. Melhuish, I. Ieropoulos, Simultaneous electricity generation and microbially-assisted electrosynthesis in ceramic MFCs, Bioelectrochemistry 104 (2015) 58–64. [67] A.N. Ghadge, M. Sreemannarayana, N. Duteanu, M.M. Ghangrekar, Influence of ceramic separator’s characteristics on microbial fuel cell performance, J. Electrochem. Sci. Eng. 4 (2014) 315–326. [68] M. Behera, P.S. Jana, M. Ghangrekar, Performance evaluation of low cost microbial fuel cell fabricated using earthen pot with biotic and abiotic cathode, Bioresour. Technol. 101 (2010) 1183–1189. [69] F.F. Ajayi, P.R. Weigele, A terracotta bio-battery, Bioresour. Technol. 116 (2012) 86–91. [70] P. Chatterjee, M. Ghangrekar, Design of clayware separator-electrode assembly for treatment of wastewater in microbial fuel cells, Appl. Biochem. Biotechnol. 173 (2014) 378–390. [71] A.N. Ghadge, M.M. Ghangrekar, Performance of low cost scalable air–cathode microbial fuel cell made from clayware separator using multiple electrodes, Bioresour. Technol. 182 (2015) 373–377. [72] S. Kumar, S. Jain, History, introduction, and kinetics of ion exchange materials, J. Chem. 2013 (2013). [73] S. Guggenheim, J. Brady, D. Mogk, D. Perkins, Introduction to the properties of clay minerals, in: J. Brady, D. Mogk, D. Perkins (Eds.), Teaching Mineralogy, Mineralogical Society of America, Washington, DC, 1977, pp. 371–388. [74] D. Carroll, Ion exchange in clays and other minerals, Geol. Soc. Am. Bull. 70 (1959) 749–779. [75] J. Syzdek, M. Armand, M. Gizowska, M. Marcinek, E. Sasim, M. Szafran, W. Wieczorek, Ceramicin-polymer versus polymer-in-ceramic polymeric electrolytes—a novel approach, J. Power Sources 194 (2009) 66–72. [76] M. Raja, N. Angulakshmi, S. Thomas, T.P. Kumar, A.M. Stephan, Thin, flexible and thermally stable ceramic membranes as separator for lithium-ion batteries, J. Membr. Sci. 471 (2014) 103–109. [77] Y. Cao, H. Yang, X. Ai, L. Xiao, The mechanism of oxygen reduction on MnO2-catalyzed air cathode in alkaline solution, J. Electroanal. Chem. 557 (2003) 127–134. [78] H. Qi, Y. Fan, W. Xing, L. Winnubst, Effect of TiO2 doping on the characteristics of macroporous Al2O3/TiO2 membrane supports, J. Eur. Ceram. Soc. 30 (2010) 1317–1325. [79] F. Xu, S. Mu, Nanoceramic oxide hybrid electrolyte membranes for proton exchange membrane fuel cells, J. Nanosci. Nanotechnol. 14 (2014) 1169–1180. [80] M. Salar-Garcı´a, X. Walter, J. Gurauskis, A. de Ramo´n Ferna´ndez, I. Ieropoulos, Effect of iron oxide content and microstructural porosity on the performance of ceramic membranes as microbial fuel cell separators, Electrochim. Acta (2020), 137385. [81] M. Cheraghipoor, D. Mohebbi-Kalhori, M. Noroozifar, M.T. Maghsoodlou, Production of greener energy in microbial fuel cell with ceramic separator fabricated using native soils: Effect of lattice and porous SiO2, Fuel 284 (2021) 118938.

Separators and membranes

[82] J. Nunes-Pereira, A. Lopes, C. Costa, R. Leones, M. Silva, S. Lanceros-Mendez, Porous membranes of montmorillonite/poly (vinylidene fluoride-trifluorethylene) for Li-Ion battery separators, Electroanalysis 24 (2012) 2147–2156. [83] M. Yoon, K. Suh, S. Natarajan, K. Kim, Proton conduction in metal–organic frameworks and related modularly built porous solids, Angew. Chem. Int. Ed. 52 (2013) 2688–2700. [84] Y. Sone, P. Ekdunge, D. Simonsson, Proton conductivity of Nafion 117 as measured by a fourelectrode AC impedance method, J. Electrochem. Soc. 143 (1996) 1254. [85] D. Lewis, Ion exchange reactions of clays, Clay Clay Miner. 1 (1952) 54–69. [86] N. Yamasaki, S. Kanahara, K. Yanagisawa, Adsorptions of strontium and cesium ions on hydrothermally altered minerals of feldspar, lithia-mica and bauxite, Nippon Kagaku Kaishi 12 (1984) 2015–2018. [87] M.E. Franke, U. Simon, Solvate-supported proton transport in zeolites, ChemPhysChem 5 (2004) 465–472. [88] K. Schwarz, E. Nusterer, P.E. Bl€ ochl, First-principles molecular dynamics study of small molecules in zeolites, Catal. Today 50 (1999) 501–509. [89] W.J. Mortier, R.A. Schoonheydt, Surface and solid state chemistry of zeolites, Prog. Solid State Chem. 16 (1985) 1–125. [90] Y. Kim, Y. Choi, H.K. Kim, J.S. Lee, New sulfonic acid moiety grafted on montmorillonite as filler of organic–inorganic composite membrane for non-humidified proton-exchange membrane fuel cells, J. Power Sources 195 (2010) 4653–4659. [91] A.N. Ghadge, M. Ghangrekar, Development of low cost ceramic separator using mineral cation exchanger to enhance performance of microbial fuel cells, Electrochim. Acta 166 (2015) 320–328. [92] D. Frattini, G. Accardo, Y. Kwon, Perovskite ceramic membrane separator with improved biofouling resistance for yeast-based microbial fuel cells, J. Membr. Sci. 599 (2020), 117843. [93] V. Yousefi, D. Mohebbi-Kalhori, A. Samimi, Application of layer-by-layer assembled chitosan/ montmorillonite nanocomposite as oxygen barrier film over the ceramic separator of the microbial fuel cell, Electrochim. Acta 283 (2018) 234–247. [94] A. Raychaudhuri, M. Behera, Ceramic membrane modified with rice husk ash for application in microbial fuel cells, Electrochim. Acta 363 (2020), 137261. [95] P. Kumar, K. Dutta, S. Das, P.P. Kundu, Membrane prepared by incorporation of crosslinked sulfonated polystyrene in the blend of PVdF-co-HFP/Nafion: a preliminary evaluation for application in DMFC, Appl. Energy 123 (2014) 66–74. [96] P. Kumar, P.P. Kundu, Coating and lamination of Nafion117 with partially sulfonated PVdF for low methanol crossover in DMFC applications, Electrochim. Acta 173 (2015) 124–130. [97] P. Kumar, A. Singh, V. Kumar, P.P. Kundu, Incorporation of nano-Al2O3 within the blend of sulfonated-PVdF-co-HFP and Nafion for high temperature application in DMFCs, RSC Adv. 5 (2015) 63465–63472. [98] S.S. Lim, W.R.W. Daud, J.M. Jahim, M. Ghasemi, P.S. Chong, M. Ismail, Sulfonated poly (ether ether ketone)/poly (ether sulfone) composite membranes as an alternative proton exchange membrane in microbial fuel cells, Int. J. Hydr. Energy 37 (2012) 11409–11424. [99] S. Ayyaru, P. Letchoumanane, S. Dharmalingam, A.R. Stanislaus, Performance of sulfonated polystyrene–ethylene–butylene–polystyrene membrane in microbial fuel cell for bioelectricity production, J. Power Sources 217 (2012) 204–208. [100] A. Sivasankaran, D. Sangeetha, Influence of sulfonated SiO2 in sulfonated polyether ether ketone nanocomposite membrane in microbial fuel cell, Fuel 159 (2015) 689–696. [101] J.X. Leong, W.R.W. Daud, M. Ghasemi, A. Ahmad, M. Ismail, K.B. Liew, Composite membrane containing graphene oxide in sulfonated polyether ether ketone in microbial fuel cell applications, Int. J. Hydr. Energy 40 (2015) 11604–11614. [102] K. Dutta, P.P. Kundu, A review on aromatic conducting polymers-based catalyst supporting matrices for application in microbial fuel cells, Polym. Rev. 54 (2014) 401–435. [103] V. Kumar, P. Kumar, A. Nandy, P.P. Kundu, Crosslinked inter penetrating network of sulfonated styrene and sulfonated PVdF-co-HFP as electrolytic membrane in a single chamber microbial fuel cell, RSC Adv. 5 (2015) 30758–30767.

207

208

Biological fuel cells

[104] V. Kumar, A. Nandy, S. Das, M. Salahuddin, P.P. Kundu, Performance assessment of partially sulfonated PVdF-co-HFP as polymer electrolyte membranes in single chambered microbial fuel cells, Appl. Energy 137 (2015) 310–321. [105] V. Kumar, P. Kumar, A. Nandy, P.P. Kundu, Fabrication of laminated and coated Nafion 117 membranes for reduced mass transfer in microbial fuel cells, RSC Adv. 6 (2016) 21526–21534. [106] S. Angioni, L. Millia, G. Bruni, D. Ravelli, P. Mustarelli, E. Quartarone, Novel composite polybenzimidazole-based proton exchange membranes as efficient and sustainable separators for microbial fuel cells, J. Power Sources 348 (2017) 57–65. [107] B. Roshanravan, H. Younesi, M. Abdollahi, M. Rahimnejad, S.-H. Pyo, Application of protonconducting sulfonated polysulfone incorporated MIL-100 (Fe) composite materials for polymerelectrolyte membrane microbial fuel cells, J. Clean. Prod. 300 (2021), 126963. [108] A.S. Mathuriya, J. Yakhmi, Microbial fuel cells—applications for generation of electrical power and beyond, Crit. Rev. Microbiol. 42 (2016) 127–143. [109] D.L. Hoskins, X. Zhang, M.A. Hickner, B.E. Logan, Spray-on polyvinyl alcohol separators and impact on power production in air-cathode microbial fuel cells with different solution conductivities, Bioresour. Technol. 172 (2014) 156–161. [110] Y. Hou, K. Li, H. Luo, G. Liu, R. Zhang, B. Qin, S. Chen, Using crosslinked polyvinyl alcohol polymer membrane as a separator in the microbial fuel cell, Front. Environ. Sci. Eng. 8 (2014) 137–143. [111] M. Shabani, H. Younesi, A. Rahimpour, M. Rahimnejad, Power generation and wastewater treatment using Nafion and SPEEK/SGO membranes in microbial fuel cells, Linnaeus Eco-Tech (2018) 85. [112] V. Kumar, P. Kumar, A. Nandy, P.P. Kundu, A nanocomposite membrane composed of incorporated nano-alumina within sulfonated PVDF-co-HFP/Nafion blend as separating barrier in a single chambered microbial fuel cell, RSC Adv. 6 (2016) 23571–23580. [113] M. Rahimnejad, T. Jafary, F. Haghparast, G. Najafpour, A.A. Ghoreyshi, Nafion as a nanoproton conductor in microbial fuel cells, Turk. J. Eng. Environ. Sci. 34 (2011) 289–292. [114] V. Kumar, R. Rudra, A. Nandy, S. Hait, P.P. Kundu, Analysis of partially sulfonated low density polyethylene (LDPE) membranes as separators in microbial fuel cells, RSC Adv. 7 (2017) 21890–21900. [115] C.V. Rohatgi, N.K. Dutta, N.R. Choudhury, Separator membrane from crosslinked poly (vinyl alcohol) and poly (methyl vinyl ether-alt-maleic anhydride), Nano 5 (2015) 398–414. [116] V. Kugarajah, S. Dharmalingam, Sulphonated polyhedral oligomeric silsesquioxane/sulphonated poly ether ether ketone nanocomposite membranes for microbial fuel cell: insights to the miniatures involved, Chemosphere 260 (2020), 127593. [117] U. Sen, A. Bozkurt, A. Ata, Nafion/poly (1-vinyl-1, 2, 4-triazole) blends as proton conducting membranes for polymer electrolyte membrane fuel cells, J. Power Sources 195 (2010) 7720–7726. [118] Y. Guan, H. Pu, H. Pan, Z. Chang, M. Jin, Proton conducting membranes based on semiinterpenetrating polymer network of Nafion® and polybenzimidazole, Polymer 51 (2010) 5473–5481. [119] Z. Ghezelbash, D. Ashouri, S. Mousavian, A.H. Ghandi, Y. Rahnama, Surface modified Al2O3 in fluorinated polyimide/Al2O3 nanocomposites: synthesis and characterization, Bull. Mater. Sci. 35 (2012) 925–931. [120] M. Johnsi, S.A. Suthanthiraraj, Synthesis and characterization of a new composite polymer electrolyte based on Al2O3 nanofiller, Int. J. Chem. Environ. Technol. 1 (2013) 12–21. [121] A. Tofighi, M. Rahimnejad, Synthetic polymer-based membranes for microbial fuel cells, synthetic polymeric membranes for advanced water treatment, Gas Separ. Energy Sustain. (2020) 309–335. [122] F. Altaf, R. Gill, R. Batool, H. Majeed, G. Abbas, K. Jacob, Synthesis and applicability study of novel of poly (dopamine)-modified carbon nanotubes based polymer electrolyte membranes for direct methanol fuel cell, J. Environ. Chem. Eng. (2020), 104118. [123] S. Mondal, F. Papiya, S.N. Ash, P.P. Kundu, Composite membrane of sulfonated polybenzimidazole and sulfonated graphene oxide for potential application in microbial fuel cell, J. Environ. Chem. Eng. (2020), 104945.

Separators and membranes

[124] K.B. Liew, J.X. Leong, W.R.W. Daud, A. Ahmad, J.J. Hwang, W. Wu, Incorporation of silver graphene oxide and graphene oxide nanoparticles in sulfonated polyether ether ketone membrane for power generation in microbial fuel cell, J. Power Sources 449 (2020), 227490. [125] A. Dufresne, Nanocellulose: From Nature to High Performance Tailored Materials, Walter de Gruyter GmbH & Co KG, 2017. [126] A. Kakoria, S. Sinha-Ray, A review on biopolymer-based fibers via electrospinning and solution blowing and their applications, Fibers 6 (2018) 45. [127] Y. Xiang, M. Yang, Z. Guo, Z. Cui, Alternatively chitosan sulfate blending membrane as methanolblocking polymer electrolyte membrane for direct methanol fuel cell, J. Membr. Sci. 337 (2009) 318–323. [128] E. Bedini, A. Laezza, M. Parrilli, A. Iadonisi, A review of chemical methods for the selective sulfation and desulfation of polysaccharides, Carbohydr. Polym. 174 (2017) 1224–1239. [129] T.R. Sobahi, M.Y. Abdelaal, M.S. Makki, Chemical modification of chitosan for metal ion removal, Arab. J. Chem. 7 (2014) 741–746. [130] J. Yang, Q. Xie, J. Zhu, C. Zou, L. Chen, Y. Du, D. Li, Preparation and in vitro antioxidant activities of 6-amino-6-deoxychitosan and its sulfonated derivatives, Biopolymers 103 (2015) 539–549. [131] P.H. Lima, S.V. Pereira, R.B. Rabello, E. Rodriguez-Castello´n, M.M. Beppu, P. Chevallier, D. Mantovani, R.S. Vieira, Blood protein adsorption on sulfonated chitosan and κ-carrageenan films, Colloids Surf. B: Biointerfaces 111 (2013) 719–725. [132] S. Ouerghemmi, S. Dimassi, N. Tabary, L. Leclercq, S. Degoutin, F. Chai, C. Pierlot, F. Cazaux, A. Ung, J.-N. Staelens, Synthesis and characterization of polyampholytic aryl-sulfonated chitosans and their in vitro anticoagulant activity, Carbohydr. Polym. 196 (2018) 8–17. [133] G. Qu, X. Wu, L. Yin, C. Zhang, N-octyl-O-sulfate chitosan-modified liposomes for delivery of docetaxel: preparation, characterization, and pharmacokinetics, Biomed. Pharmacother. 66 (2012) 46–51. [134] S. Dimassi, N. Tabary, F. Chai, N. Blanchemain, B. Martel, Sulfonated and sulfated chitosan derivatives for biomedical applications: a review, Carbohydr. Polym. 202 (2018) 382–396. [135] F. Esa, S. Tasirin, N. Rahman, Overview of bacterial cellulose production and application, Agric. Agric. Sci. Proc. 2 (2014) 113–119. [136] B.R. Evans, H.M. O’Neill, V.P. Malyvanh, I. Lee, J. Woodward, Palladium-bacterial cellulose membranes for fuel cells, Biosens. Bioelectron. 18 (2003) 917–923. [137] S. Keshk, Bacterial cellulose production and its industrial applications, J. Bioproc. Biotechn. 4 (2014) 1–10. [138] P. Chen, S.Y. Cho, H.-J. Jin, Modification and applications of bacterial celluloses in polymer science, Macromol. Res. 18 (2010) 309–320. [139] Y. Dahman, K.E. Jayasuriya, M. Kalis, Potential of biocellulose nanofibers production from agricultural renewable resources: preliminary study, Appl. Biochem. Biotechnol. 162 (2010) 1647–1659. [140] O.-A. Saibuatong, M. Phisalaphong, Novo aloe vera–bacterial cellulose composite film from biosynthesis, Carbohydr. Polym. 79 (2010) 455–460. [141] D. Klemm, F. Kramer, S. Moritz, T. Lindstr€ om, M. Ankerfors, D. Gray, A. Dorris, New materials from nature, Angew. Chem. Int. Ed. 50 (2011) 5438–5466. [142] T.D. Gadim, F.J. Loureiro, C. Vilela, N. Rosero-Navarro, A.J. Silvestre, C.S. Freire, F.M. Figueiredo, Protonic conductivity and fuel cell tests of nanocomposite membranes based on bacterial cellulose, Electrochim. Acta 233 (2017) 52–61. [143] M. Nogi, C. Kim, T. Sugahara, T. Inui, T. Takahashi, K. Suganuma, High thermal stability of optical transparency in cellulose nanofiber paper, Appl. Phys. Lett. 102 (2013), 181911. [144] S.S. Nair, J. Zhu, Y. Deng, A.J. Ragauskas, High performance green barriers based on nanocellulose, Sustain. Chem. Proc. 2 (2014) 23. [145] Z. Fang, H. Zhu, Y. Yuan, D. Ha, S. Zhu, C. Preston, Q. Chen, Y. Li, X. Han, S. Lee, Novel nanostructured paper with ultrahigh transparency and ultrahigh haze for solar cells, Nano Lett. 14 (2014) 765–773.

209

210

Biological fuel cells

[146] M.A. de Moraes, D.S. Cocenza, F. da Cruz Vasconcellos, L.F. Fraceto, M.M. Beppu, Chitosan and alginate biopolymer membranes for remediation of contaminated water with herbicides, J. Environ. Manag. 131 (2013) 222–227. [147] K. Listiarini, W. Chun, D.D. Sun, J.O. Leckie, Fouling mechanism and resistance analyses of systems containing sodium alginate, calcium, alum and their combination in dead-end fouling of nanofiltration membranes, J. Membr. Sci. 344 (2009) 244–251. [148] A. Buekenhoudt, F. Bisignano, G. De Luca, P. Vandezande, M. Wouters, K. Verhulst, Unravelling the solvent flux behaviour of ceramic nanofiltration and ultrafiltration membranes, J. Membr. Sci. 439 (2013) 36–47. [149] Y. Li, H. Jia, F. Pan, Z. Jiang, Q. Cheng, Enhanced anti-swelling property and dehumidification performance by sodium alginate–poly (vinyl alcohol)/polysulfone composite hollow fiber membranes, J. Membr. Sci. 407 (2012) 211–220. [150] E. Bertoft, Understanding starch structure: recent progress, Agronomy 7 (2017) 56. [151] S.C. Nunes, R.F. Pereira, N. Sousa, M.M. Silva, P. Almeida, F.M. Figueiredo, V. de Zea Bermudez, Eco-friendly red seaweed-derived electrolytes for electrochemical devices, Adv. Sustain. Syst. 1 (2017) 1700070. [152] D. Perahia, D. Goldfarb, Z. Luz, Sodium-23 NMR in the lyomesophases of disodiumcromoglycate, Mol. Cryst. Liq. Cryst. 108 (1984) 107–123. [153] A. Pawlicka, R. Mattos, J. Lima, C. Tambelli, C. Magon, J. Donoso, Magnetic resonance and conductivity study of a gelatin-based polymer gel electrolyte, Electrochim. Acta 57 (2011) 187–191. [154] R. Mattos, A. Pawlicka, J. Lima, C. Tambelli, C. Magon, J. Donoso, Magnetic resonance and conductivity study of gelatin-based proton conductor polymer electrolytes, Electrochim. Acta 55 (2010) 1396–1400. [155] J. Sudarsan, K. Prasana, S. Nithiyanantham, K. Renganathan, Comparative study of electricity production and treatment of different wastewater using microbial fuel cell (MFC), Environ. Earth Sci. 73 (2015) 2409–2413. [156] A. Muralidharan, O.A. Babu, K. Nirmalraman, M. Ramya, Impact of salt concentration on electricity production in microbial hydrogen based salt bridge fuel cells, Indian J. Fundam. Appl. Life Sci. 1 (2011) 178–184. [157] B. Min, S. Cheng, B.E. Logan, Electricity generation using membrane and salt bridge microbial fuel cells, Water Res. 39 (2005) 1675–1686. [158] X.-Y. Zeng, S.-X. Cao, D.-L. Zhang, S.-T. Gao, Z.-Q. Yu, H.-R. Li, G.-Y. Sheng, J.-M. Fu, Levels and distribution of synthetic musks and polycyclic aromatic hydrocarbons in sludge collected from Guangdong Province, J. Environ. Sci. Health A 47 (2012) 389–397. [159] B. Min, S. Cheng, B. Logan, Thermodynamic analysis of a single chamber microbial fuel cell, Water Res. 39 (2005) 1675–1686. [160] S.-J. Seo, B.-C. Kim, K.-W. Sung, J. Shim, J.-D. Jeon, K.-H. Shin, S.-H. Shin, S.-H. Yun, J.-Y. Lee, S.-H. Moon, Electrochemical properties of pore-filled anion exchange membranes and their ionic transport phenomena for vanadium redox flow battery applications, J. Membr. Sci. 428 (2013) 17–23. [161] K. Gaurav, R. Singh, B.K. Tiwari, R. Srivastava, Novel proton exchange membranes based on PVC for microbial fuel cells (MFCs), J. Polym. Eng. 39 (2019) 360–367. [162] V. Pupkevich, V. Glibin, D. Karamanev, The effect of ferric ions on the conductivity of various types of polymer cation exchange membranes, J. Solid State Electrochem. 11 (2007) 1429–1434. [163] T. Watari, J. Fang, K. Tanaka, H. Kita, K.-I. Okamoto, T. Hirano, Synthesis, water stability and proton conductivity of novel sulfonated polyimides from 4, 40 -bis (4-aminophenoxy) biphenyl-3, 30 -disulfonic acid, J. Membr. Sci. 230 (2004) 111–120. [164] J. Gohil, D. Karamanev, Novel pore-filled polyelectrolyte composite membranes for cathodic microbial fuel cell application, J. Power Sources 243 (2013) 603–610. [165] K.A. Weber, L.A. Achenbach, J.D. Coates, Microorganisms pumping iron: anaerobic microbial iron oxidation and reduction, Nat. Rev. Microbiol. 4 (2006) 752–764. [166] S. Bagchi, M. Behera, Performance evaluation of microbial fuel cells employing ceramic separator of different surface area modified with mineral cation exchanger, SN Appl. Sci. 2 (2020) 1–8.

Separators and membranes

[167] J. Xu, G.-P. Sheng, H.-W. Luo, W.-W. Li, L.-F. Wang, H.-Q. Yu, Fouling of proton exchange membrane (PEM) deteriorates the performance of microbial fuel cell, Water Res. 46 (2012) 1817–1824. [168] G. Jadhav, M. Ghangrekar, Performance of microbial fuel cell subjected to variation in pH, temperature, external load and substrate concentration, Bioresour. Technol. 100 (2009) 717–723. [169] G. Kim, G. Webster, J. Wimpenny, B.H. Kim, H. Kim, A.J. Weightman, Bacterial community structure, compartmentalization and activity in a microbial fuel cell, J. Appl. Microbiol. 101 (2006) 698–710. [170] A. Ter Heijne, H.V. Hamelers, V. De Wilde, R.A. Rozendal, C.J. Buisman, A bipolar membrane combined with ferric iron reduction as an efficient cathode system in microbial fuel cells, Environ. Sci. Technol. 40 (2006) 5200–5205. [171] O. Lefebvre, Y. Shen, Z. Tan, A. Uzabiaga, I.S. Chang, H.Y. Ng, A comparison of membranes and enrichment strategies for microbial fuel cells, Bioresour. Technol. 102 (2011) 6291–6294. [172] H. Liu, S. Cheng, B.E. Logan, Production of electricity from acetate or butyrate using a singlechamber microbial fuel cell, Environ. Sci. Technol. 39 (2005) 658–662. [173] X. Tang, K. Guo, H. Li, Z. Du, J. Tian, Microfiltration membrane performance in two-chamber microbial fuel cells, Biochem. Eng. J. 52 (2010) 194–198. [174] K.-Y. Kim, W. Yang, B.E. Logan, Impact of electrode configurations on retention time and domestic wastewater treatment efficiency using microbial fuel cells, Water Res. 80 (2015) 41–46. [175] L. Fan, J. Li, Overviews on internal resistance and its detection of microbial fuel cells, Int. J. Circuits Syst. Signal Process 10 (2016) 316–320. [176] M. Ghasemi, W.R.W. Daud, M. Ismail, M. Rahimnejad, A.F. Ismail, J.X. Leong, M. Miskan, K.B. Liew, Effect of pre-treatment and biofouling of proton exchange membrane on microbial fuel cell performance, Int. J. Hydrog. Energy 38 (2013) 5480–5484. [177] M.T. Noori, S.C. Jain, M. Ghangrekar, C. Mukherjee, Biofouling inhibition and enhancing performance of microbial fuel cell using silver nano-particles as fungicide and cathode catalyst, Bioresour. Technol. 220 (2016) 183–189. [178] A. Rahimpour, M. Jahanshahi, B. Rajaeian, M. Rahimnejad, TiO2 entrapped nano-composite PVDF/SPES membranes: preparation, characterization, antifouling and antibacterial properties, Desalination 278 (2011) 343–353. [179] Y.-H. Huang, G. Liang, M. Croft, M. Lehtimaki, M. Karppinen, J.B. Goodenough, Doubleperovskite anode materials Sr2MMoO6 (M ¼ Co, Ni) for solid oxide fuel cells, Chem. Mater. 21 (2009) 2319–2326. [180] F. Harnisch, U. Schr€ oder, Selectivity versus mobility: separation of anode and cathode in microbial bioelectrochemical systems, ChemSusChem: Chem. Sustain. Energy Mater. 2 (2009) 921–926.

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CHAPTER 8

Supercapacitive microbial fuel cells Federico Polia, Francesca Soavia, and Carlo Santorob a

Department of Chemistry “Giacomo Ciamician” Alma Mater Studiorum, Universita` di Bologna, Bologna, Italy Department of Material Science, Universita` degli Studi di Milano-Bicocca, Milan, Italy

b

8.1 Introduction Microbial fuel cells (MFCs) represent a key (bio)technology for water treatment and electric energy generation, but their promise is kept unleashed by poor power performance. MFCs’ theoretical cell voltage can be as high as 1.1 V when acetate is used as the electron donor and O2 as the electron acceptor. In this case, the expected bio-anode and cathode potentials are expected to be
0.3 V (vs NHE) and 0.8 V (vs NHE), respectively [1]. However, a practical open circuit potential of roughly 0.7–0.8 V is often reported due to activation overpotentials and mixed potentials that occur mainly on the cathode electrode. Moreover, cell voltage during operations decreases to values of c. 0.6 V, and low currents are generated, leading to poor power performance. This hinders their practical application as standalone systems [2]. A strategy to circumvent this issue demonstrated through the powering of small electronic devices [3,4], remote sensors [5,6], the development of autonomous robots [6,7], and mobile phones [8] is the coupling of MFCs with external electrochemical energy storage systems (EEESS). The EEESS stores the energy produced by the MFC, releasing it at the higher power pulses needed for the selected application. It is worth mentioning that, to maintain the overall system power balance, usually, the stored energy is consumed in a pulsed mode empowering external power management units composed of a voltage multiplier and the selected EEESS [9]. A further option that has been exploited in recent years is the integration with an external supercapacitor. Indeed, supercapacitors are high specific power devices (>10 kWkg
1) that store energy electrostatically by the formation of the electrical double layer (EDL) at the interfaces of high specific surface area carbonaceous electrodes with the electrolyte [10]. Electric double-layer capacitors (EDLCs) are characterized by robust performance due to the absence of a faradaic process, simple design, impressive cycle life, and rapid response times. This unique combination of features enables the use of EDLCs in a great number of applications such as stabilization of fluctuating loads both in consumer electronics and at the grid level, low-power equipment buffer, voltage stabilizer in photovoltaic and wind systems, motor start-up, and special application in electric mobility (kinetic energy recovery system and acceleration boost) [11,12]. The direct integration of MFCs with external supercapacitors connected in parallel to the cell is a simple approach in improving the power output of MFCs [13]. Indeed, Biological Fuel Cells https://doi.org/10.1016/B978-0-323-85711-6.00001-1

Copyright © 2023 Elsevier Inc. All rights reserved.

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supercapacitors feature an extremely small equivalent series resistance for the MFC cell. Indeed, 1, 3, and 6 F commercial EDLC cells feature equivalent series resistance (ESR) values of 0.2, 0.08, and 0.035 Ω [13]. The small values of ESR allow for minimizing the ohmic drop of the system when discharged at high rates, enabling high power pulses, also at low cell voltages typical of the MFCs. Moreover, this parallel connection results in a synergic interaction between MFC and EDLC with improved power (at high current regimes) and energy (at low currents) performance with respect to those of the separate units. Specifically, at high current pulses, the use of EDLCs enabled output power not feasible with single MFCs. At the low current pulses, the MFC contributed to the overall system capacitance, probably owing to its faradaic component. The MFC faradic response contributed to an apparent increase of the system capacitance, a feature that was defined as “apparent capacitance.” Overall, this study highlighted that basic electrochemical characterization of MFC and SC, singularly and combined, is necessary for right system sizing and application [13]. Nevertheless, this approach enables practical application in which the MFCs are the main powers source, but as stated previously, is a circumvention of the main problem, that is the low specific power of MFCs. To directly face this problem, a strategy that has been recently demonstrated is the direct integration of supercapacitive/capacitive features in MFC electrodes [14–16]. This can be achieved mainly following three main directions: (i) improving the double layer capacitance, exploiting high specific surface area electrodes, (ii) exploiting the capacitance of MFC’s electrodes through pulsed discharges, and (iii) exploiting fast surface redox reactions, with the decoration of MFC’s electrodes with pseudocapacitive materials. This last approach requires a few words to discuss the different effects related to the improved electron transfer among the biofilm and the electrode and improved pseudocapacitive features. The first electrocatalytic effect could improve the power performance, while the latter is the fast redox reaction of the external species on the electrode that is responsible for the improved power response. In this chapter, these strategies that have been pursued to improve the supercapacitive features of microbial fuel cells and they are reported and discussed.

8.2 High surface area capacitive electrodes in MFCs The exploitation of capacitive features in MFC anode has been reported in 2012 by Deeke et al. [17]. Here, the authors investigated the effect of supercapacitor-like MFC anodes. High specific Brunauer-Emmett-Teller (BET) surface area (1081 m2 g
1) activated carbon-based electrodes, realized by means of N-methyl pyrrolidone (NMP) casting knife processing with a polyvinyl difluoride (pVdF) binder, have been prepared to coat graphitebased current collectors (20 cm2). The authors compared the response of the capacitive electrode to a control one, featuring bare graphite, finding that the capacitive electrode was able to improve the response of the MFC in terms of current density. In this work, the authors

Supercapacitive microbial fuel cells

proposed the utilization of MFCs both as energy conversion and as electrochemical energy storage systems. Indeed, the authors investigated the current output of the cell by alternating open-circuit steps with pulsed discharges, by means of voltage step polarization. They highlighted the presence of two distinct responses, a capacitive one during the transitory response of the cell and a stationary one related to the faradaic activity of the anode. The capacitive electrodes featured a higher transitory discharge current with respect to the noncapacitive electrodes and higher power densities. The higher power achieved by the MFC featuring capacitive electrodes was related by the authors to a reduction of the instantaneous ohmic drop of the capacitive electrode, with respect to the bare graphite control one, 0.07 vs 0.110 V, which in turn can be related to the higher electrode area exposed to the electrolyte [17,18]. In a successive work, the authors investigated the effect of the thickness of the capacitive electrode on the power performance of MFCs featuring graphite anodes coated with different loadings of activated carbon (AC) (2.5, 0.5, and 0.2 mm thick) [19]. It is worth highlighting that the thickness of the electrodes plays an important role in electrical double-layer supercapacitors. Indeed, several authors demonstrated that, according to the electrode formulation, an optimal thickness exists in terms of energy density and electrode capacitance [20]. The optimal thickness was the thinner one, with a current density normalized to the anode surface area of 2.53 A m
2 vs 1.96 A m
2, and 1.86 A m
2, for the 0.2, 0.5, and 2.5 mm thicknesses, respectively. BET specific surface area of the realized electrodes was measured too, finding that, increasing the thickness of the electrode led to a constant decrease of the BET specific surface area and surface roughness (measured by atomic force microscopy), from 942 to 742 m2 g
1 and from 67.2 to 52.9 m2 g
1, respectively. The higher the surface area of the electrodes, the more energy can be stored, because the carbon surface provides an interface for the formation of the double layer [21]. The application of high BET surface area in MFC electrodes seems, therefore, a promising solution to improve the MFC performance. However, in EDLC application, high gain of both the BET specific surface area and electrode specific capacitance has been related to a well-developed microporosity. On the contrary, in MFCs, anode macropores (larger than 50 nm), usually, achieve better performance than micropores (194.8 mW/m2

[47]

COD:83%

102.08 mW/m2

[48]

COD: 93 and 78%

20.5 and 6.5 W/m3

[42]

COD: 80.55%

[43]

COD: 55  1.0 and 48  0.5% 91.9%

330 mV 168 mA/m 32.5  0.5 28.5  0.3 mW/m2 26.4 kWh

COD: 74% NH4-N: generate 62% COD: 92.5%

2500 mW/m2 500 mA/m2 0.0197 kWh/m3

[51]

SS: >90% COD: 5.11  0.94 kg COD/ m3/d)

3.96  3.01 W/m3

[35]

[49] [50]

[52]

Fig. 12.9 Schematic description of MFC integrated wastewater treatment systems.

Application of biological fuel cell in wastewater treatment

Fig. 12.10 Schematic description of MFC-based electron Fenton (MFC-EF) process.

In BEF systems, during the biological decomposition of organic carbon in the anode chamber by electroactive microorganisms that produce electricity, the oxidation of environmental organic pollutants in the cathode chamber is done by Fenton-based reactions. The BEF systems could have significant benefits because of their unique features (Fig. 12.10). In recent years, the feasibility of the BEF system to treat a wide range of synthetic wastewaters, which contains a variety of environmental organic compounds, such as dyes, industrial pollutants, and pharmaceutical compounds has been demonstrated. The aims of the present review are to introduce the BEF system as an efficient technology for wastewater treatment and clean energy production, as well as to provide a reference for researchers in developing more efficient BEF systems [57,58]. The electrogenic bacteria oxidize the substrate (e.g., glucose) as an electron donor to produce electrons and H+ ions [Eq. (12.5)], thereby the electrons transfer to the electrode surface and H+ ions also diffuse through the membrane into the cathode. At the same time, electrons are also transferred from the anode to the cathode through an external resistor, to be used to generate electricity and reduce the dissolved oxygen. H2O2 is continuously produced in the site [Eq. (12.6)] due to the reduction of two oxygen electrons in the cathode chamber. Moreover, Cathodic Fenton-based reactions take place. H2O2 reacts with Fe2+ ions under acidic conditions and produces •OH [Eqs. (12.7) and (12.8)]. • OH with high oxidation potential can result in the nonselective degradation of environmental organic pollutants [Eq. (12.9)] (Fig. 12.10). Meanwhile, in this process, Fe2+ is continuously produced by reducing Fe3+ (Eq. 12.10) [57].

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Anodic reaction: C6 H12 O6 + 6H2 O ! 6CO2 + 24H+ + 24e


(12.5)

Cathodic reactions: O2 + 2H+ + 2e
! H2 O2 2+

Fe

3+

Fe

+ H2 O2 ! Fe

3+

+ H2 O2 ! Fe

2+



(12.6)

+ OH + OH 

+ HO2 + H






+

Environmental organic pollutants + OH ! Oxidation products Fe3+ + e
! Fe2+

(12.7) (12.8) (12.9) (12.10)

It has been proven that the BEF process can simultaneously produce bioenergy and decompose the environmental persistent organic pollutants in effluent without the need for external energy. This process has attracted many researchers’ attention as a costeffective and efficient treatment process that produces in situ H2O2 electrochemically instead of its commercial application in the cathode chamber [57,59].

12.10 Future perspective In general, the important advantage of MFC in wastewater treatment compared to other methods is energy production from biomass, less sludge production, and self-sufficiency. Numerous studies have examined the treatment capacity of various wastewater [60]. The results show that MFC can be used on a large scale and is practical to remove pollutants from industrial, domestic, and agricultural wastewater. MFC systems are an important option for wastewater treatment with resistant organic compounds. By combining and hybridizing MFC with conventional biological and chemical methods, the efficiency and performance of the systems will be improved. The results show that MFCs are capable of removing organic matter, nutrients, dyes, petroleum products, heavy metals, phenol and phenolic compounds, and pharmaceutical compounds. However, for MFCs to be used on a large scale their performance must be investigated with real wastewater and operational-scale studies must be performed. The main disadvantages of MFCs are membrane clogging, high membrane cost, high cost of electrode supply, lower power generation, and higher cost of MFC materials, which poses challenges in replacing this method with conventional large-scale wastewater treatment methods. Future studies should focus on addressing these issues.

12.11 Conclusions MFCs are a sustainable energy technology and green approach to meeting growing energy needs. Wastewater treatment and environmental protection by the native

Application of biological fuel cell in wastewater treatment

electrogenic outer microbial layer in MFCs are capable of degrading various wastewater contaminants. While producing bioelectricity and effluents without the presence of pollutants. However, advances in science and knowledge and the use of nanotechnology have led to an increase in power density and current in MFCs and good results have been achieved in increasing the removal efficiency of organic matter, nutrients, and emerging pollutants. However, more research efforts and advances are needed to upgrade these systems to large-scale practical applications. In the future, significant improvements in MFCs will require research with costeffective electrode surface type and size approaches, low-cost building materials for low-cost power generation, and integration with other existing process settings to increase wastewater treatment potential. Experience with real wastewater should be the focus of future research development. In addition, the benefits of MFCs can be maximized by creating new configurations in the anode-cathode architecture, and improving the biocathode performance of alkalizing and other nitrifying/nitrifying bacterial biofilms. Finally, the separation of wastewater compounds from the source may be an efficient method that should be demonstrated for MFCs.

References [1] C.P. Gerba, I.L. Pepper, Municipal wastewater treatment, third ed., Elsevier Inc, Environmental Microbiology, 2015, pp. 583–606. [2] M. Aghababaie, M. Farhadian, A. Jeihanipour, D. Biria, Effective factors on the performance of microbial fuel cells in wastewater treatment—a review, Environ. Technol. Rev. 4 (1) (2015) 71–89. [3] K.R. Sukrampal, S.A. Patil, Removal of heavy metals using bioelectrochemical systems, in: Integrated Microbial Fuel Cells for Wastewater Treatment, INC, 2020, pp. 49–71. [4] M. Rahimnejad, M. Asghary, M. Fallah, Microbial fuel cell (MFC): an innovative technology for wastewater treatment and power generation, in: Bioremediation of Industrial Waste for Environmental Safety, 2020, pp. 215–235. [5] M. Mashkour, M. Rahimnejad, F. Raouf, N. Navidjouy, A review on the application of nanomaterials in improving microbial fuel cells, Biofuel Res. J. 8 (2) (2021) 1400–1416. [6] Application of the eco-friendly bio-anode for ammonium removal and power generation from wastewater in bio-electrochemical systems. [7] M. Rahimnejad, G. Bakeri, G. Najafpour, M. Ghasemi, S. Oh, A review on the effect of proton exchange membranes in microbial fuel cells, Biofuel Res. J. 1 (2014) 7–15. [8] M. Rahimnejad, A. Adhami, S. Darvari, A. Zirepour, S.-E. Oh, Microbial fuel cell as new technology for bioelectricity generation: a review, Alex. Eng. J. 54 (3) (2015) 745–756. [9] M. Mashkour, M. Rahimnejad, M. Mashkour, Bacterial cellulose-polyaniline nano-biocomposite: a porous media hydrogel bioanode enhancing the performance of microbial fuel cell, J. Power Sources 325 (2016) 322–328. [10] L. He, P. Du, Y. Chen, H. Lu, X. Cheng, B. Chang, et al., Advances in microbial fuel cells for wastewater treatment, Renew. Sust. Energ. Rev. 71 (December) (2017) 388–403. [11] C. Abourached, M.J. English, H. Liu, Wastewater treatment by microbial fuel cell prior irrigation water reuse, J. Clean. Prod. 137 (2016) 144–149. [12] H. Wang, Z.J. Ren, A comprehensive review of microbial electrochemical systems as a platform technology, Biotechnol. Adv. 31 (8) (2013) 1796–1807. [13] V.G. Gude, Microbial fuel cells for wastewater treatment and energy generation, in: Microbial Electrochemical and Fuel Cells: Fundamentals and Applications, Elsevier Ltd, 2016, pp. 247–285.

317

318

Biological fuel cells

[14] F. Soltani, N. Navidjouy, H. Khorsandi, M. Rahimnejad, S. Alizadeh, A novel bio-electro-Fenton system with dual application for the catalytic degradation of tetracycline antibiotic in wastewater and bioelectricity generation, RSC Adv. 11 (44) (2021) 27160–27173. [15] N. Navidjouy, Tetracycline Removal from Wastewater and Electricity Generation, 2021. [16] Y. Ye, H.H. Ngo, W. Guo, Y. Liu, S.W. Chang, D.D. Nguyen, et al., Feasibility study on a double chamber microbial fuel cell for nutrient recovery from municipal wastewater, Chem. Eng. J. 358 (September 2018) (2019) 236–242. [17] E.D. Penteado, C.M. Fernandez-Marchante, M. Zaiat, P. Can˜izares, E.R. Gonzalez, M.A. Rodrigo, Influence of sludge age on the performance of MFC treating winery wastewater, Chemosphere 151 (2016) 163–170. [18] Y. Zhang, M. Liu, M. Zhou, H. Yang, L. Liang, T. Gu, Microbial fuel cell hybrid systems for wastewater treatment and bioenergy production: synergistic effects, mechanisms and challenges, Renew. Sust. Energ. Rev. 103 (December 2018) (2019) 13–29. [19] M. Rahimnejad, A.A. Ghoreyshi, G. Najafpour, T. Jafary, Power generation from organic substrate in batch and continuous flow microbial fuel cell operations, Appl. Energy 88 (11) (2011) 3999–4004. [20] I. Gajda, J. Greenman, I.A. Ieropoulos, Recent advancements in real-world microbial fuel cell applications, Curr. Opin. Electrochem. (2018). [21] C. Santoro, C. Arbizzani, B. Erable, I. Ieropoulos, Microbial fuel cells: from fundamentals to applications. A review, J. Power Sources 356 (2017) 225–244. [22] V.G. Gude, Wastewater treatment in microbial fuel cells - an overview, J. Clean. Prod. 122 (287–307) (2016) 2. [23] S. Bagchi, M. Behera, Pharmaceutical wastewater treatment in microbial fuel cell, in: Integrated Microbial Fuel Cells for Wastewater Treatment, vol. 2, 2020, pp. 135–155 (1911). [24] D. Journal, C.E. Ubdtce, D. Manjunath, C.E. Ubdtce, Treatment of dairy wastewater using MFC employing zinc electrode, Glob. Res. Dev. J. Eng. 3 (7) (2018) 34–38. [25] T. Sangeetha, C.P. Rajneesh, W.M. Yan, Integration of microbial electrolysis cells with anaerobic digestion to treat beer industry wastewater, in: Integrated Microbial Fuel Cells for Wastewater Treatment, INC, 2020, pp. 313–346. [26] K.A. Dwivedi, S.J. Huang, C.T. Wang, Integration of various technology-based approaches for enhancing the performance of microbial fuel cell technology: a review, Chemosphere 287 (P3) (2022), 132248. [27] A.R. Rahmani, N. Navidjouy, M. Rahimnejad, S. Alizadeh, M.R. Samarghandi, D. Nematollahi, Effect of different concentrations of substrate in microbial fuel cells toward bioenergy recovery and simultaneous wastewater treatment, Environ. Technol. 43 (1) (2022) 1–9. [28] L. Zhang, H. Tao, Bioelectro-Fenton System for Environmental Pollutant Degradation, 2019. [29] A. ElMekawy, S. Srikanth, S. Bajracharya, H.M. Hegab, P.S. Nigam, A. Singh, et al., Food and agricultural wastes as substrates for bioelectrochemical system (BES): the synchronized recovery of sustainable energy and waste treatment, Food Res. Int. 73 (2015) 213–225. [30] S.R. Mise, S. Saware, Electricity generation using textile wastewater by single chambered microbial fuel cell, Int. Res. J. Eng. Technol. 3 (2) (2016) 710–716. [31] M. Malakootian, B. Hatami, Dairy wastewater treatment and simultaneous electricity generation using microbial fuel cell technology, J. Environ. Stud. 39 (2) (2013) 83–92. [32] A.J.O. Al-saned, B.A. Kitafa, A.S. Badday, Microbial fuel cells (MFC) in the treatment of dairy wastewater, IOP Conf. Ser.: Mater. Sci. Eng. 1067 (1) (2021), 012073. [33] E. Elakkiya, M. Matheswaran, Comparison of anodic metabolisms in bioelectricity production during treatment of dairy wastewater in microbial fuel cell, Bioresour. Technol. 136 (2013) 407–412. [34] A.D. Sekar, T. Jayabalan, H. Muthukumar, N.I. Chandrasekaran, S.N. Mohamed, M. Matheswaran, Enhancing power generation and treatment of dairy waste water in microbial fuel cell using cu-doped iron oxide nanoparticles decorated anode, Energy 172 (2019) 173–180. [35] M.T. Jamal, A. Pugazhendi, R.B. Jeyakumar, Application of halophiles in air cathode MFC for seafood industrial wastewater treatment and energy production under high saline condition, Environ. Technol. Innov. 20 (2020), 101119.

Application of biological fuel cell in wastewater treatment

[36] S.P. Tan, H.F. Kong, M.J.K. Bashir, P.K. Lo, C.D. Ho, C.A. Ng, Treatment of palm oil mill effluent using combination system of microbial fuel cell and anaerobic membrane bioreactor, Bioresour. Technol. 245 (July) (2017) 916–924. [37] E. Baranitharan, M.R. Khan, D.M.R. Prasad, S.J. Bin, Bioelectricity generation from palm oil mill effluent in microbial fuel cell using polacrylonitrile carbon felt as electrode, Water Air Soil Pollut. 224 (5) (2013). [38] L.C. Wu, C.Y. Chen, T.K. Lin, Y.Y. Su, Y.C. Chung, Highly efficient removal of victoria blue R and bioelectricity generation from textile wastewater using a novel combined dual microbial fuel cell system, Chemosphere 258 (2020), 127326. [39] N. Selim, H.H. Maghrawy, R. Fathy, M. Gamal, H. Abd El Kareem, K. Bowman, et al., Modification of bacterial cell membrane to accelerate decolorization of textile wastewater effluent using microbial fuel cells: role of gamma radiation, J. Radiat. Res. Appl. Sci. 13 (1) (2020) 373–382. [40] C.R. Holkar, A.J. Jadhav, D.V. Pinjari, N.M. Mahamuni, A.B. Pandit, A critical review on textile wastewater treatments: possible approaches, J. Environ. Manag. 182 (2016) 351–366. [41] K. Sonu, Z. Syed, M. Sogani, Up-scaling microbial fuel cell systems for the treatment of real textile dye wastewater and bioelectricity recovery, Int. J. Environ. Stud. 77 (4) (2020) 692–702. [42] S. Amari, G.M. Boshrouyeh, Non-steroidal anti-inflammatory pharmaceutical wastewater treatment using a two-chambered microbial fuel cell, Water Environ. J. 34 (3) (2020) 413–419. [43] T. Rashid, F. Sher, A. Hazafa, R.Q. Hashmi, A. Zafar, T. Rasheed, et al., Design and feasibility study of novel paraboloid graphite based microbial fuel cell for bioelectrogenesis and pharmaceutical wastewater treatment, J. Environ. Chem. Eng. 9 (1) (2021), 104502. [44] M. Mahdi Mardanpour, M. Nasr Esfahany, T. Behzad, R. Sedaqatvand, Single chamber microbial fuel cell with spiral anode for dairy wastewater treatment, Biosens. Bioelectron. 38 (1) (2012) 264–269. [45] B. Tharan, M.R. Khan, D. Prasad, Treatment of palm oil mill effluent in microbial fuel cell using Polyacrylonitrile carbon felt as electrode, J. Med. Bioeng. 2 (4) (2013) 252–256. [46] B.C. Jong, P.W.Y. Liew, M.L. Juri, B.H. Kim, A.Z. Mohd Dzomir, K.W. Leo, et al., Performance and microbial diversity of palm oil mill effluent microbial fuel cell, Lett. Appl. Microbiol. 53 (6) (2011) 660–667. [47] S. Kalathil, J. Lee, M.H. Cho, Granular activated carbon based microbial fuel cell for simultaneous decolorization of real dye wastewater and electricity generation, New Biotechnol. 29 (1) (2011) 32–37. [48] K. Sonu, M. Sogani, Z. Syed, Integrated constructed wetland-microbial fuel cell using biochar as wetland matrix: influence on power generation and textile wastewater treatment, ChemistrySelect 6 (32) (2021) 8323–8328. [49] S. Naina Mohamed, T. Jayabalan, K. Muthukumar, Simultaneous bioenergy generation and carbon dioxide sequestration from food wastewater using algae microbial fuel cell, Energy Sources, Part A 00 (00) (2019) 1–9. [50] E. Dannys, T. Green, A. Wettlaufer, C.M.R. Madhurnathakam, A. Elkamel, Wastewater treatment with microbial fuel cells: a design and feasibility study for scale-up in microbreweries, J. Bioprocess. Biotech. 6 (1) (2016) 1–6. [51] E.B. Estrada-Arriaga, J. Herna´ndez-Romano, L. Garcı´a-Sa´nchez, R.A. Guillen Garces, E.O. BahenaBahena, O. Guadarrama-Perez, et al., Domestic wastewater treatment and power generation in continuous flow air-cathode stacked microbial fuel cell: effect of series and parallel configuration, J. Environ. Manag. 214 (2018) 232–241. [52] L. Ren, Y. Ahn, B.E. Logan, A two-stage microbial fuel cell and anaerobic fluidized bed membrane bioreactor (MFC-AFMBR) system for effective domestic wastewater treatment, Environ. Sci. Technol. 48 (7) (2014) 4199–4206. [53] S. Bajracharya, Microbial fuel cell coupled with anaerobic treatment processes for wastewater treatment. Integrated microbial fuel cells for wastewater treatment, Inc (2020) 295–311. [54] C. Hong, Z. Zainon, N. Sabrina, A. Mutamim, C. Kim, Green technology in wastewater treatment technologies : integration of membrane bioreactor with various wastewater treatment systems, Chem. Eng. J. 283 (2016) 582–594. [55] X. Zhu, J. Ni, Simultaneous processes of electricity generation and p-nitrophenol degradation in a microbial fuel cell, Electrochem. Commun. 11 (2) (2009) 274–277.

319

320

Biological fuel cells

[56] X.Y. Yong, D.Y. Gu, Y.D. Wu, Z.Y. Yan, J. Zhou, X.Y. Wu, et al., Bio-Electron-Fenton (BEF) process driven by microbial fuel cells for triphenyltin chloride (TPTC) degradation, J. Hazard. Mater. 324 (2017) 178–183. [57] F. Soltani, N. Navidjouy, M. Rahimnejad, A review on bio-electro-Fenton systems as environmentally friendly methods for degradation of environmental organic pollutants in wastewater, RSC Adv. 12 (9) (2022) 5184–5213. [58] N. Xu, Y. Zhang, H. Tao, S. Zhou, Y. Zeng, Bio-electro-Fenton system for enhanced estrogens degradation, Bioresour. Technol. 138 (2013) 136–140. [59] M. Hassan, H. Olvera-vargas, X. Zhu, B. Zhang, Y. He, Microbial electro-Fenton : an emerging and energy-efficient platform for environmental remediation, vol. 424, 2019, pp. 220–244 (March). [60] G. Palanisamy, H.-Y. Jung, T. Sadhasivam, M.D. Kurkuri, S.C. Kim, S.-H. Roh, A comprehensive review on microbial fuel cell technologies: processes, utilization, and advanced developments in electrodes and membranes, J. Clean. Prod. 221 (2019) 598–621.

CHAPTER 13

Biohydrogen generation and MECs Mostafa Rahimnejad

Biofuel and Renewable Energy Research Center, Chemical Engineering Department, Babol Noshirvani University of Technology, Babol, Mazandaran, Iran

13.1 Introduction Unlike other alternative energy sources such as CH4 and ethanol, hydrogen offers higher calorific value (120–142 MJ kg
1) [1]. In addition, compared with the most alternatives, higher energy (3432 kJ/mol-glucose) can be obtained for H2: C6 H12 O6 + 6H2 O ! 6CO2 + 12H+ + 3432 kJ

(13.1)

C6 H12 O6 ! 2CO2 + 2C2 H5 OH + 2465:6 kJ

(13.2)

C6 H12 O6 ! 3CO2 + 3CH4 + 2670 kJ

(13.3)

Recently, hydrogen has been considered as a clean, sustainable, and storable energy carrier [2], and it is perceived that two electrons and protons are the only participants of hydrogen production [3]. To date, many varied technologies, including water electrolysis, dark/photo-fermentation, gasification, microalgae-based methods, and MECs have been utilized for biohydrogen production, among which MECs are paramount because of high yield of biohydrogen production, substrate versatility, and the feasibility of significantly low energy demand (external energy input of >0.14 V) [4,5]. MECs are known as cost-effective and efficient hydrogen production methods. Over the past decade, biotechnology has been receiving an increasing attention in biohydrogen generation from wastewater, and the eminence of MECs is now recognized [1]. In terms of structure, MEC and MFC are similar. Nonetheless, MEC requires a sealed cathode and an external voltage. Electroactive biofilm is located at anode to convert the low-cost carbon compounds into electrons, protons, and CO2 [6]. Electron flows then shuttle toward the hydrogen evolution cathode through an external circuit. Anion exchange membranes/cation exchange membranes are settled to avoid the chemical reaction between hydrogen and oxygen. MEC technology can achieve high hydrogen production yield, however, large-scale efficacy of biocathodes, lack of propitious MEC design, spectrum of substrates, inherent thermodynamic limitation, and membrane biofouling [7] are some of the appealing issues regarding MEC design. Many varied strategies are available to overcome these challenges, including the use of high-performance electrode materials and cathode Biological Fuel Cells https://doi.org/10.1016/B978-0-323-85711-6.00015-1

Copyright © 2023 Elsevier Inc. All rights reserved.

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catalysts [8,9], highly selective membrane [10], methanogen inhibitors [11], external power sources [12,13], and MEC coupled systems [14]. Nowadays, the research community aims at integrating anaerobic digestion (AD) and MEC to facilitate organic decomposition and promote hydrogen production [15]. As the AD produces a methane-rich biogas, strategies such as exposure to oxygen [16], alamethicin, or a chemical inhibitor (2-bromoethanesulfonate) [17] are required to alleviate methanogenesis. Besides integration strategy, the rate of hydrogen evolution reaction (HER) on cathode surface needs to be thought out in depth. Overall, the rate of HER is slow on plain cathode materials. A common solution is the use of cathode catalysts that decrease the cathode overpotential and promote the hydrogen generation. However, high cost and poor hydrophilicity of these catalysts are still problematic [18]. One promising prospect is to use biocathodes that help catalyze the HER through combining protons and electrons to form hydrogen [19]. Moreover, the use of microorganisms as cathode catalysts benefits the hydrogen production yield, start-up time, and cathodic hydrogen recovery. In addition to the HER on cathode surface, there is a need for an external power supply to allow thermodynamically nonspontaneous hydrogen generation. In the literature, 0.25 V was reported as the minimum requirement to achieve sustained hydrogen production in MECs [20]. Studies have confirmed that integration of MEC systems with carbon-neutral sources, such as solar, osmotic, thermoelectric, and microbe powers, can obviate the necessity of external input [21]. Furthermore, membraneless single-chambered MEC design reduces the capital cost. Thus, it is feasible to maintain self-sustainability and economic viability of the system. The main purpose of this chapter is to introduce the principles and discuss the advantages, difficulties, and research progresses of MEC.

13.2 MEC fundamentals Basically, MEC consists of two electrode chambers, connecting with anion exchange membranes/cation exchange membranes. Anodic reactions produce CO2, electron (e
), and proton (H+) from wastewater’s organic substrates. At cathode, electrons and protons are combined to form hydrogen gas. Anodic oxidation: CH3 COO
+ 2H2 O ! 2CO2 + 7H+ + 8 e
ðE ¼
0:291 V vs SHE at pH 7Þ (13.4) Cathodic hydrogen evolution: 8H+ + 8 e
! 4H2 ðe ¼
0:414 V vs SHE at pH 7Þ

(13.5)

Overall reaction of MEC: CH3 COO
+ 2H2 O + H+ ! 2CO2 + 4H2

(13.6)

Biohydrogen generation and MECs

The yield of anodic electroactive mechanisms depends on the type of organic substrate. In other words, the rate of exoelectrogenic oxidization of simple carbon sources (acetate and glucose) is much higher than those of complex carbon sources (wastewater, sludge, and cellulosic compounds) [4]. It was shown that MEC can achieve maximum hydrogen yield of 4 mol/mol and 12 mol/mol from acetate and glucose, respectively [22]. Moreover, H2 production rate could increase threefold, compared to other conventional methods such as dark fermentation (Eqs. 13.7 and 13.8) [23]. MEC reaction: C6 H12 O6 + 12H2 O ! 6CO2 + 12H2

(13.7)

Dark fermentation reaction: C6 H12 O6 + 4H2 O ! 2CH3 COO
+ 2HCO3
+ 4H2 + 4H+

(13.8)

The endothermic barrier is another important factor in determining the rate of HER. Endothermic barrier of MEC can be calculated based on the Nernst equation. E cathode ¼ E 0cathode
¼0


P RT ln H+2 8 2F ½H 

(13.9)

8:314  298:15 1 ln 8 ¼
0:414 V 2  96,485 ½10
7 

where E0cathode corresponds to the standard electrode potential of hydrogen (0 V), R demonstrates the universal gas constant (8.314 J K
1 mol
1), T is the absolute temperature in kelvin, and F represents the Faraday’s constant (96,485 C mol
1). For the anode electrode, the theoretical reduction potential can be calculated by Eq. (13.2): ½CH3 COO
 RT Eanode ¼ E 0anode
(13.10) ln 2 8F ½HCO3
 ½H+ 9 ¼ 0:187


8:314  298:15 0:0169 ln 9 ¼
0:3000 V 8  96,485 ½0:0052 ½10
7 

where E0anode is set equal to 0.187 V, and CO2 and CH3COO
concentrations are equal to 0.005 and 0.0169 M, respectively, at pH ¼ 7 [24]. Therefore, the overall cell voltage (Ecell) is Ecell ¼ Ecathode
E anode ¼ ð
0:414 VÞ
ð
0:3000 VÞ ¼
0:123 V

(13.11)

The negative value of Ecell is linked to impossibility of spontaneous HER. Thus, an external voltage higher than 0.114 V is required to overcome the endothermic barrier. The applied voltage deals with Ohmic loss, activation loss, and the mass transport

323

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Biological fuel cells

limitation within MEC system. MEC potential loss is highly dependent on overpotentials of the electrodes and Ohmic loss of the system. The required external voltage for H2 production is calculated as follows: Eap ¼ E thermo
ðηanode + ηcathode + ηohm Þ

(13.12)

where Ethermo exhibits the theoretical voltage, ηcathode, ηanode, and ηohm are cathodic overpotential, anodic overpotential, and the general Ohmic loss, respectively [25]. MEC configuration, exoelectrogenic activity, electrode characteristics, membrane selectivity, and concentration of organics would directly affect the required external energy input. Integration of MEC with carbon-neutral technologies could be a management approach toward sustainable hydrogen production.

13.3 Theoretical yields of MEC systems In MEC, electroactive microorganisms serve as biocatalysts and oxidize the organic compounds to provide electrons and protons for hydrogen production. Thanks to biofilm function, microbial electrolysis requires considerably less energy than that required by abiotic water electrolysis. Microbial species are accordingly ubiquitous in organic electrolyte and will develop a microbial anode spontaneously without the need for electrode pretreatment as for abiotic conventional catalytic layers. Evidence has gradually accrued demonstrating that microbial biofilms possess a high survival rate and allow a sustained MEC operation using low-cost carbon-based materials [26]. Furthermore, concomitant production of hydrogen and oxygen has remained a potential cause of persistent safety issues in water electrolysis especially in the production of pressurized hydrogen [27,28]. Particularly, MEC obliterates the possibility of oxygen production under propitious control procedure, enhancing process safety. Moreover, biofilms are developed around neutrality [29] which is identified as additional term of safety due to the fact that there is no need for drastic precautions.

13.4 MEC Challenges and promising solutions 13.4.1 Self-sustainability of MECs Biohydrogen production through MEC technology possesses a variety of advantages over other conventional methods, including dark fermentation, water electrolysis, and steam reforming. However, an important problem in MEC operation is providing an external energy input for sustainable hydrogen production. As a promising solution, the use of a renewable energy such as solar energy would definitely provide the required extra electrons for hydrogen production. The operation of solar-assisted MECs has been explored through combining MEC with photosynthetic bacteria, semiconductor photoelectrodes, solar cells, or photoelectrochemical cells (PECs) [30,31]. Photovoltaic devices such as PEC and dye-sensitized solar cells (DSSCs) can convert sunlight into electrical energy and to make significant progress in hydrogen production [32,33] (Fig. 13.1A).

Biohydrogen generation and MECs

Fig. 13.1 Schematic illustration of MEC devices coupled with DSSC (A), photocathode (B), and photobioanode (C).

325

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Biological fuel cells

The DSSC is a pathway of electron flow, through which the electrons are energized by sunlight and shuttled toward the cathode to produce hydrogen [34]. For instance, a DSSC can result in an open-circuit voltage of >0.6 V, favoring 400 mmol hydrogen production within 5 h [35]. Using microbial PECs (MPECs) is another approach to provide the required power input (Table 13.1). In MPEC-MEC couples, semiconductors can be utilized for clean energy conversion in either cathode or anode. Thus, MPECs are classified as photo-bioanode MPECs and photocathode MPECs (Fig. 13.1B and C). In photocathode MPECs, sunlight photons are absorbed and used for producing electrons at the conduction band (CB) and holes at the valence band (VB) [36]. CB electrons are utilized for conducting hydrogen reduction reaction and the VB holes are filled with bioanode electrons [37,38]. To date, an array of semiconductors has been served as photocathode in MPECs to promote HER, including titanium dioxide (TiO2) [39,40], TiO2-coated nickel foam [41], cuprous oxide (Cu2O) [42], Cu2O/NiOx composite [43], MoS3 modified p-type Si nanowire [44], MoS2/PDA/TiO2 composite [45], polyaniline nanofibers [46], g-C3N4/BiOBr heterojunction [47], and g-C3N4/CdS heterojunction [48]. Table 13.1 Practical examples of MEC-MPEC device utilized for bio-hydrogen production. Solar-assisted system

Substrate

H2 production rate (m3 m23 d21)

Reference

MPEC with CeO2-rGO/ carbon film photo-anode MPEC with hematite nanowire-arrayed photo-anode MPEC with polydopamine-coated TiO2 nanotube photocathode MPEC with MoS2/Cu2O photo cathode MPEC with TiO2 photo-cathode MPEC with g-C3N4/BiOBr photo-cathode MPEC with Cu2O/NiOx photo-cathode MPEC with polyaniline nanofiber MPEC with MoS3
silicon nanowire photocathode MPEC with TiO2 photo-cathode

Wastewater

5

[49]

Lactate

Photocurrent: 95 μA cm
2

[52]

Acetate

4.32

[45]

Acetate

2.72

[53]

Methyl orange+acetate

113 mL

[41]

Acetate

0.148

[47]

Acetate

5.09 μL h
1 cm
2

[43]

Acetate

1.70

[46]

Acetate

7.5 μmol h
1 cm
2

[44]

Acetate

3.5 μmol h
1

[37]

Biohydrogen generation and MECs

Knowledge on photo-bioanode is of particular interest for effective combining of bio-energy and solar energy in the same electrode, within which a high hydrogen evolution rate can be achieved [49]. The semiconductor side of the photo-bioanode contributes to sunlight absorption and electron-hole production, while bio-electricity generation occurs at the backside of the photo-bioanode, assisting cathode reduction reaction [50]. For instance, a photo-bioanode fabricated from a photocatalyst (∝-Fe2O3) and biocarbon material was utilized for promoting exoelectrogenic function and enhancing extracellular electron transfer [51]. In addition, for HER management, a metal-free CeO2-rGO-based carbon film was utilized as a photo-bioanode, which resulted in HER of 5 m
3 m
3 day
1 under visible light irradiation [49]. Besides solar-assisted technologies, coupling with other carbon-neutral technologies such as dark fermentation (DF), AD, thermo-electric generator (TEG), MFC, reverse electrodialysis (RED), and pressure retarded osmosis (PRO) can also maintain the self-sustainability of MECs. The biogas obtained from DF and AD act as energy source to produce electricity for the MEC [54,55] (Fig. 13.2A). Furthermore, integration of DF/AD and MECs has the added advantage of providing simple carbon sources supporting sustainability of the MECs. Volatile fatty acid (VFA)-rich effluent of DF and AD exhibited much higher hydrogen production efficiencies [56]. Another promising prospect to power MECs is to settle a RED stack between the cathode and anode chambers of MECs to achieve salinity gradient power (Fig. 13.2B). RED stack captures power from the high concentration gradient across the ion exchange membranes [57]. Salinity-driven energy is exploited for self-sustainable hydrogen production in MECs. Kim and Logan fabricated a RED stack from combining five pairs of freshwater and seawater cells and found that the hydrogen production rate can be improved by providing 0.5–0.6 V of potential [58]. In addition, many studies have confirmed that salinity-gradient power from ammonium bicarbonate salts can also improve the MEC function. PRO is another membrane-based technology to capture power from the salinity gradient. Unlike the RED, PRO supports a self-sustainable hydrogen production through exploiting the osmotic pressure along a semipermeable membrane [59]. In a PRO-MEC coupled system, the anode chamber of MEC is fueled with feed solution of PRO and, conversely, the cathode chamber of MEC is hydraulically connected with draw side of the PRO (Fig. 13.3A). It is estimated that the hydrogen production rate of 0.016 m3 m
3 d
1 can be achieved under electrical power of 578 J provided by the PRO compartment [60]. Moreover, external power input of MECs can be provided through conversion of AD waste heat into electrical power using TEG [61]. TEG deals with the utilization of waste heat in the form of electricity. TEG-generated electricity favors high yield of hydrogen production in TEG-MEC coupling systems [12] (Fig. 13.3B). It has been reported that electrical power produced from four serially connected TEG fuels with

327

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Biological fuel cells

Fig. 13.2 MEC integration with AD/FD (A) and RED stack (B) in order to provide self-sustainability.

Biohydrogen generation and MECs

Fig. 13.3 Schematic representation of PRO-MEC (A) and TEG-MEC (B).

hot flue gas can enhance hydrogen production performance of MECs [61]. However, TEG modules still have issues considering the possibility of unstable heat transfer when using flue gas as a heat source. In addition, some studies have shown that the integration of MEC anode chamber with the cold side of a TEG can provide a stable cold source for electricity generation and simultaneous warm wastewater for electron harvesting of anode exoelectrogens [62].

329

330

Biological fuel cells

MFC can also be an important power source for MEC operation because it can support stable electricity generation through spontaneous redox reactions. It was demonstrated that a stack of in series connected MFC systems can supply a high power input for hydrogen production [13]. However, MFC-MEC hybrid systems still face challenges considering the choice of feedstock and voltage reversal. In the first case, the poor oxidation rate of complex organics such as cellulose restricts the yield of hydrogen production. In the second case, the inefficiency of MFC-MEC hybrid systems is linked with voltage reversal resulting from using a stack of MFCs for power generation. One strategy is to combine DF process with an MFC-MEC hybrid system [63]. For instance, a stack of serially connected two DF-effluent-fed MFCs generated a maximum voltage of 0.43 V, obtaining hydrogen production yield of 0.48 m3 m
3 d
1 [63]. Furthermore, MFC-capacitor-MEC hybrid systems alleviate the possibility of voltage reversal of MFC stacks and provide a stable external output for MEC [64].

13.4.2 Methanogenesis The activity of methanogens such as Methanobacteriales, Methanomicrobiales, Methanosarcinaceae, and Methanosaetaceae has been shown to induce the opposite effect and suppress the hydrogen yield in MECs [16]. In fully anaerobic MEC operation, the function of acetoclastic methanogens and hydrogenotrophic methanogens has been exclusively studied to improve cathodic hydrogen recovery [14,65]. Acetoclastic methanogenesis: CH3 COOH ! CH4 + CO2

(13.13)

Hydrogenotrophic methanogenesis: 4H2 + CO2 ! CH4 + 2H2 O

(13.14)

Methanogenesis management involves lowering the electrolyte pH, lowering the operating temperature, and optimization of the applied voltage [66]. The aim of acidic shock is to temporarily inhibit methanogenesis [67]. Furthermore, Kim et al. and Chae et al. demonstrated that the acidification weakens the exoelectrogenic function of the cathode and thus alleviates H2 production efficiency. Significant inhibition was reported in 15°C and 4–9°C [68]. However, it is now well known that most methanogens can tolerate a broad range of temperatures, and that the strategy is not efficient in case of long-term operations [69]. The optimization of applied voltage can increase H2 production and concentration and also suppress methane production [70]. However, the strategy can be problematic in terms of energy consumption. Particularly interesting is the study of the combination of short operation cycles and higher applied voltages and its influence on elimination of methanogenesis [70]. Another problem is that the improved

Biohydrogen generation and MECs

hydrogen yield under optimized anode potential is transient and the biogas would be enriched with methane after long hours of operation [71]. The use of specific chemical inhibitors such as halogenated hydrocarbons is another management approach in order to hamper acetate-utilizing sulfate reducers, acetoclastic methanogens, hydrogen-utilizing sulfate reducers, hydrogenotrophic methanogens, and homoacetogens by interrupting biochemical pathways involved in methane formation [17]. For instance, 2-bromomethane sulfonate and Lumazine are specific methanogenesis inhibitors that inhibit methyl-coenzyme M reductase in hydrogenotrophic and acetoclastic methanogens [72]. Moreover, it is well known that sodium molybdate can impede sulfate-reducing bacteria [73] and halogenated aliphatic hydrocarbon compounds can hamper methanogenic archaea, homoacetogenic bacteria, and acetate
/ hydrogen-utilizing sulfate-reducing bacteria [72,73]. Furthermore, chloroform can be used as a methanogen inhibitor to achieve more hydrogen yield and high energy efficiency [74]. The addition of chloroform is a possible way to reduce methanogenesis through interrupting the activity of corrinoid enzymes, as well as methyl-coenzyme M reductase which is efficacious on methanogenic archaea. Alamethicin can also serve as methanogen suppressor and acetogen inducer [75]. Similar finding were also reported for Neomycin sulfate, 8-aza-hypoxanthine, 2-bromoethanesulfonate, and 2-chloroethane sulfonate [76].

13.4.3 Economic issues Investigation of cost and efficiency is of particular importance for upscaling H2 production in MECs. Although MEC upscaling from laboratory scale to pilot scale has been successfully reported in the literature, more studies are required for optimization of H2 production and coulombic efficiency on a large scale [77,78]. In addition, lack of technical requirements and high equipment costs are the main restrictions of MEC scale-up for pollutant removal, chemical synthesis, and metal recovery purposes. Anode electrode contributes to electron uptake from electroactive bacteria and the anode failure is related to overpotential and internal resistance in MEC systems. Anode electrode can be made of many components, among which carbon-based materials are most commonly used because of economic benefits. However, anode catalysts are required to alleviate the overpotential and the internal resistance [79]. When dealing with large-scale operation, the use of noble metals as anode catalysts could be a promise. However, there are some shortcomings owing to their high cost and some environmental impacts [80]. Moreover, the use of biocathode has been reported to induce hydrogen production yield. However, its effectiveness on pilot scale and large scale is still unknown. Another scale-up challenge is reactor design. It was shown that the cost of reactor construction can be remarkably suppressed in pilot scale (1000L), membrane-less, singlechambered MEC systems [81].

331

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Biological fuel cells

13.5 MEC operation 13.5.1 MEC architecture The practitioner wanting to construct an MEC has encountered a bewildering array of smart and sophisticated reactor designs (Table 13.2). It is worth noting that a key aspect of MEC architecture is membrane, which maintains the purity of the produced hydrogen gas, hinders microbial consumption of biohydrogen, and impedes any short circuit. Common MEC membranes include proton exchange membranes, anion-exchange membranes, bipolar membranes, and charge-mosaic membranes [6,82–84]. Another key element is economic and financial feasibility of MEC architectures. For industrial electrolyzers, plate-and-frame (sandwich) design are largely used [26]. It is tempting to transpose to the simplest possible configuration to achieve suitable benches in commercial hydrogen production. The fabrication of two coaxial cylindrical electrodes with the cathode as the inner electrode is a way to achieve larger anode surface area, overcoming rate-limiting bioanode reactions [26]. The electrolyte resistance between the two cylindrical electrodes can be calculated as follows: Table 13.2 Examples of different MEC designs and comparison of their performance. MEC design

Substrate

Applied potential (V)

H2 production rate (m3 m23 d21)

Reference

Single chamber Single chamber Two chamber Two chamber Two chamber Continuous flow Continuous flow DF-MEC DF-MEC AD-MEC TEG-MEC MFC-MEC MFC-MEC MREC PRO-MEC

Sludge wastewater

0.9

0.038

[85]

Dairy wastewater

0.7

0.200

[86]

Glycerol

1.2

0.46

[87]

Vegetable wastewater

0.8

0.025

[88]

Industrial wastewater

1.0

0.03

[89]

Cellulose fermentation wastewaters Fermentation wastewater Molasses wastewater Corn stock Food waste Acetate Acetate Glucose Wastewater Acetate

0.6–1.2

0.49  0.05

[90]

0.44–1

0.9  0.1

[91]

0.6 0.8 0.8 0.5 – 1.97 0.44–0.52 0.8

1.41 3.43 4.86 0.75 0.014 0.09 0.9 0.016

[14] [92] [93] [61] [13] [94] [91] [60]

Biohydrogen generation and MECs

Rs:cylindrical ¼

ρ 2  π  h  ln

  r2 r1

(13.15)

where r1 and r2 are the radius of cathode and anode, respectively, and p exhibits the resistivity of the electrolyte. Decoupled electrolysis cell is another possible design for high rate of hydrogen production through overcoming cathode deposition issues and better controlling the pH gradients within two separated reactors. The design offers the advantage of using two different electrochemical reactors as cathode and anode chambers, connected by a hydraulic loop. The loop contains a redox mediator, conducting oxidation-reduction reactions within electrode chambers [26]. This section provides a conceptual overview of MEC reactor designs and configurations. 13.5.1.1 Two-chamber MECs Lack of standardization impedes hydrogen production and results in the fermentation of end products. The practitioner wanting to design a two-chamber MEC is faced with an array of problems. Two-chamber MECs consist of independent anode and cathode chambers separated by an ion exchange membrane (Fig. 13.4A). Despite sparging the cathode chamber with air, the cathode chamber can be sealed and characterized for hydrogen production. One of the limitations of hydrogen gas production is microbial conversion of substrate into fermentation end products such as acetate (2 mol/mol glucose). The best-known strategy for overcoming this biochemical barrier is the use of acetate as substrate. Indeed, additional voltage is utilized for the augmentation of electrochemical potential at cathode leading to high yield of hydrogen production (more than 90%) from oxidized organic substrates. For instance, Cheng and Logan reported a high-performance MEC constructed from graphite granules as anode, carbon cloth as cathode, and AMI-7001 as anion exchange membrane [18,95]. Hydrogen production yields of 2.01–3.95 mol was obtained under applied voltages of 0.2–0.8 V using acetic acid. Another strategy could be the use of innovative MEC architectures. Kyazze et al. designed a concentric tubular MEC with two concentric tubular chambers. The anode electrode was placed within the inner tube, wrapping with a cation exchange membrane. Hydrogen yield of 1.1 mol/1 mol of acetate and 30.5% chemical oxygen demand (COD) reduction was achieved under applied voltage of 0.85 V. In another study, An and Lee developed a two-chamber MEC in which the large anode surface area increased the hydrogen recovery and hydrogen production rate up to 93  25% and 137.2  14.4 L-H2 m
3 d
1, respectively, under applied voltage of 0–1.2 V [96]. 13.5.1.2 Single-chambered MECs It is possible to operate microbial hydrogen production within a single-chambered membraneless MECs (Fig. 13.4B). The design allows to reduce membrane associated potential losses and increase the overall energy recovery [97,98]. Moreover, single-chambered

333

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Biological fuel cells

Fig. 13.4 Schematic representation of (A) double-chambered and (B) single-chambered MECs.

MEC is a simplified architecture, which requires lower capital costs [99]. However, one of the limitations of this design is the microbial hydrogen losses to methanogens. It was shown that methanogens compete with exoelectrogens for both substrate and biohydrogen [100]. Call and Logan developed a single-chambered MEC with an ammonia-treated graphite brush anode and a wet-proofed (30%) carbon cloth cathode [101]. The design was shown to result in cathodic hydrogen recovery up to 96  1% and hydrogen

Biohydrogen generation and MECs

production rate of 3.12  0.02 m3 H2 m
3 reactor per day under applied voltage of 0.8 V. Hu et al. designed a bottle-type single-chambered MEC and studied the effect of microbial community on hydrogen production efficiency [67]. In this study, type A carbon cloth and type B carbon cloth containing 0.5 mg cm
2 Pt catalyst were used as anode and cathode. Additionally, the possibility of short circuit was diminished through separating the electrodes with a layer of J-Cloth. The MEC system operated with a mixed culture achieved the maximum hydrogen production rate of 0.69 m3 m
3d
1 and current density of 14 A m
2 at pH 5.8 under the applied voltage of 0.6 V. Guo et al. led a pioneering work to reveal the importance of the cathode on top design in hydrogen recovery [102]. In this study, anode (graphite granules) was placed in the bottom and the cathode (titanium tube coated with platinum) placed on the top of the MEC chamber. After 24 h operation, the MEC showed an increase in overall hydrogen recovery from 26.03% to 87.73% and hydrogen production rate from 0.03 to 1.58 L L
1 d
1. Similarly, Lee et al. have shown that up-flow singlechambered MECs could increase the H2 yield up to 59  2% in 32 h in batch-evaluation experiments by inhibiting methanogenesis [103]. 13.5.1.3 Continuous flow MECs The system consists of two cells, each of which was equipped with influent, effluent, recirculation, and gas exits lines. The absence of membrane and the distance between the electrodes are important factors that determine the yield of hydrogen production. Tartakovsky et al. developed a membraneless continuous flow MEC equipped with a gas-phase cathode and a carbon felt anode [104]. The design achieved hydrogen production rate of 6.3 L L
1 d
1 at 0.3 mm distance between the electrodes. Organic loading rate and type of configuration are important aspects of net energy consumption and wastewater treatment performance of continuous-flow single-chambered MECs. Gil-Carrera et al. prepared a semipilot tubular MEC consisting of a series of two tubular modules for domestic wastewater treatment [105]. They found that the design can induce COD removal of domestic wastewater up to 85% and optimize the overall energy consumption. Interestingly, Cusicka et al. constructed a pilot-scale (1000 L) continuous flow MEC for simultaneous hydrogen production and winery wastewater treatment [81]. The system fabricated from 24 electrode modules, each of which contain six heat-treated graphite fiber brush anodes and 6 SS 304 cathodes. Current generation of 7.4 A m
3 and gas production rate of 0.19  0.04 L L
1 d
1 were achieved at an applied voltage of 0.9 V. 13.5.1.4 MEC integration with other carbon-neutral technologies Numerous studies and trials have demonstrated the promise of integrating MEC with AD [106]. The process benefits from overcoming AD obstacles such as long start-up times and low biogas production. It was shown that engineered AD-MEC systems aim to

335

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Biological fuel cells

provide control over microbial metabolism and wastewater recycling [107]. Gao et al. reported that a novel anaerobic osmotic membrane bioreactor-MEC system exhibited excellent soluble COD and phosphorus removal and 1.6-fold increment in methane yield when an SnO2 nanoparticle electrocatalytic cathode is used [108]. Integration of MEC with MFC systems is critical to provide the extra power required for hydrogen production. Sun et al. demonstrated that using an MEC-MFC-coupled system supplied with acetate hydrogen production rate of 2.2  0.2 mL L
1 day
1 can be achieved [109]. As a matter of fact, additional MFC cells can be connected in series to boost hydrogen production [13]. In a study, a DF reactor was connected with an MEC, integrated with two MFCs for hydrogen production [63]. The system resulted in hydrogen production rate of 0.48 m3-H2 m
3 d
1 (based on the MEC volume) and an yield of 33.2 mmol H2 per g COD removed. DSSC can also be adjusted to provide an external power for MEC operation. For instance, H-shaped two-chamber glass bottle MECs were coupled with DSSCs for hydrogen production [35]. The DSSC-powered MEC achieved 400 mmol H2 within 5 h as well as recovery efficiency of 78%. Microbial reverse-electrodialysis electrolysis cells (MRECs) is another integrated system in which a small reverse electrodialysis stack (five-membrane pairs) is combined with an MEC. In such a system anodic microbial oxidation and salinity gradient obviate the need for external power resources [58]. Hydrogen production rate of 1.6 m3-H2/m3-anolyte/day was obtained from an MREC constructed from five pairs of seawater and river water cells sandwiched between the anode and cathode electrodes. The reverse electrodialysis stack provided 0.5–0.6 V at a salinity ratio of 50, and the presence of exoelectrogens suppressed anode overpotential through providing an additional electrical power from acetate oxidation. Microbial electrodialysis cell (MEDC) constructed from an MEC integrated with microbial desalination cell (MDC) has great potential in desalination performance and energy recovery. It was found that integration of MEC with MDC can result in maximum hydrogen production rates of 0.16  0.05 m3-H2 m
3 d
1 at an applied voltage of 0.55 V [110].

13.5.2 MEC electrode design MEC anode could be made of various components, among which metals are paramount [111,112]. Metals, such as stainless steel, are electro-conductive and therefore can enhance the MEC performance [113–115]. Under high power potential and chloride ions, the anode undergoes severe corrosion. For instance, the relation between the high power potential and the release of Cu2+ ions into analyte solution has been studied [116]. The release of Cu2+ ions results from accidental drift of the power potential toward high values. Since the ions possess significant cytotoxicity, it is vital to accurately control the potential when using copper anodes. Moreover, the use of copper-polymer hybrid compounds can yield high productivity, which should be investigated. Furthermore, poorly

Biohydrogen generation and MECs

conductive metals such as titanium can be coated with metal oxides (ruthenium and tantalum oxides) to be certified as dimensionally stable anodes [117]. However, the strategy has economic obstacles when dealing with chemical surface modification of large sized electrodes [118]. Three-dimensional porous anodes allow better performance of MEC either using multispecies communities [119] or with pure cultures [120] as microbial catalyst. It was showed that a three-dimensional electrode can boost the current density up to 390 A m
2 [121]. Pore clogging makes the application of three-dimensional anode challenging, and exploiting all the porosity especially difficult. Surface topography of anode can also affect the efficacy of abiotic electrodes [122–124]. Electrode surface modification contributes to increase in current density in pure cultures, while it is ineffectual in case of multispecies biofilms [125]. It is known that using pure cultures of Geobacter sulfurreducens, random microroughness and microstructuring of the electrode increase the current density by 7- and 10-fold, respectively [126]. Furthermore, the impact of surface topography is directly related to the age of the biofilm. It is likely that the surface topography significantly affect immature biofilm, while is useless in case of fully developed biofilms [125–127]. The most frequently used anode materials and their performance are summarized in Table 13.3. Hydrogen evolution rate depends strongly on the surface area and porosity of the cathode. However, at high current density, the adhering bubbles would weld together within the porous structure and impede the electrode [132]. Hence, the use of porous cathode may pose challenges to hydrogen evolution and the conductivity of the

Table 13.3 Examples of anode materials used in MEC systems. Anode material

Cathode potential (V)

Graphite granules Porous graphite felt GAC/FeS

0.6

GAC/Fe3O4

1

GAC/CaS

1

316 L SS fiber felt Carbon aerogel

1

1 1

0.3

MEC design

Double chamber Double chamber Double chamber Double chamber Double chamber Single chamber Double chamber

Hydrogen production rate (m3 m23 d21)

Reference

1.23

[83]

5.6

[128]

0.46

[129]

0.36

[129]

0.55

[129]

7.10 L L
1 d
1

[130]

0.37 mol cm
2 h
1

[131]

337

338

Biological fuel cells

Table 13.4 Hydrogen production rate of various cathode materials used in MECs.

Cathode material

Pt Pt on stainless steel mesh Polyaniline/graphene on stainless steel mesh MoS2 Ni-P Ni mesh Ni 210 NiMo Stainless steel PtCu/C Nickel foam/Co3O4. rGo Nickel foam/NiO. rGO Mg(OH)2/Gr

Cathode potential (V)

MEC design

Hydrogen production rate (m3 m23 d21)
2

Reference
1

0.6 0.9

Double chamber Single chamber

2.1  0.3 L m 0.85

0.9

Single chamber

0.65

[138]

0.8 0.7 1.1 0.6 0.6 0.9 0.4 1

Single chamber Single chamber Single chamber Single chamber Single chamber Single chamber Double chamber Double chamber

2.72  0.31 1.42 L L
1 d
1 4.18  1 1.3  0.3 2.1 1.50  0.04 0.044 3.66 mmol L
1 d
1

[53] [139] [140] [141] [142] [82] [8] [143]

1

Double chamber

4.38 mmol L
1 d
1

[143]

0.7

Single chamber

0.63  0.11

[144]

d

[137] [138]

interstitial electrolyte. As an alternative, carbonates and weak acids favor the catalysis of hydrogen evolution through cathodic deprotonation reaction [26,133–135]. Electrochemical deprotonation is a reaction pathway through which the weak acid or carbonate molecules transfer electron on some metallic surfaces such as mild steel [136] and stainless steel [134,135]. A summary of cathode materials previously reported in literature is presented in Table 13.4.

13.5.3 Operating conditions Biofilm is a fragile living structure whose survival and performance are closely influenced by pH, electrode material, temperature, substrate concentration, and solution conductivity [145,146]. Since the main part of the MEC system is anaerobic, changes in temperature may impact the enzyme-catalyzed reactions in the microbial catalysis which in turn is linked to establishing further overpotential into the kinetics [147,148]. Di Lorenzo et al. optimized MEC temperature in order to obtain the best performance [149]. They achieved the best performance of MEC at 30°C. To date, a wide array of electroactive microorganisms has been used in MECs, among which thermophilic species has been started to be grown. For the application of thermophilic species rector needs to be heated,

Biohydrogen generation and MECs

which can impose extra costs. It was shown that the energy loss due to Ohmic drop increases the operating temperature of industrial electrolyzers, therefore the strategy can be utilized for maintaining the optimum temperature suitable for growth and function of thermophilic biofilms. Substrate concentration could also affect the MEC performance. In this case, the relation between the substrate concentration and the resulting current density can be expressed by Michaelis-Menten type law: j ¼ j max

½acetate K S + ½acetate

(13.16)

Accordingly, substrate inhibition is liable to occurred at high concentrations [150,151]. This is why, the substrate concentration would not affect current generation in a certain range [152]. It is worth noting that substrate concentration is a critical factor that determines the mass transport rate of MECs [153]. Furthermore, at large scale, there is a correlation between the MEC performance and the ionic conductivity of the electrolytes. Call and Logan demonstrated that the use electrolyte with conductivity of 20 mS can increase the overall H2 production [101]. Similarly, Logan et al. reported a remarkable reduction in Ohmic losses through using solutions with high conductivity [154]. Hypersaline electrolytes have been reported as ideal solutions in MEC systems. However, high concentrations of salts alleviate buffering capacity of the electrolyte, leading to local acidification of the anodic biofilm. Besides adaptation of anode biofilm, high buffer concentration infers MEC improvement [155]. Studies show that hypersaline chloride electrolytes cause electrode corrosion, especially during maintenance phases or under hindered polarization. Studies also proved that the choice of electrode materials as well as optimization of the electrolyte composition are significant factors of biofilm acclimatization [156]. More recently, change in electrode spacing has been implemented for reduction of internal resistance using electrolyte solutions with low conductivities [84,154]. For instance, Hutchinson et al. used solution conductivity of 1.8 mS cm
1 and electrode spacing of 1.4 cm to manage MEC internal resistance [157]. Moreover, thermodynamics and kinetics of the MEC reactions rely on pH of the electrolyte [145]. The choice of the optimum pH depends on the Ecell, and the type of MEC performance [28]. The literature specifies the optimum pH of 9 for hydrogen production and COD removal [28]. It was found that pH increment offers intensive suppression of anodic potential and subsequently increase overall potential difference. Additionally, bacterial biofilms grow under alkaline pH, while acidic pH is propitious for fungi grow. Nimje et al. reported high electrochemical activities of exoelectrogenic population at pH 9 [158]. As a matter of fact, electron transfer from exoelectrogens to anode surface increases at high pH [159].

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The electrode catalysts is another pivotal factor that makes MEC systems achieve rapid H2 production [160]. Cathode catalysts can attenuate the overpotential and increase MEC reactions. For instance, Liu et al. used catalyst loading rate of 0.2 mg cm2 to optimize MEC power and energy efficiency [161]. However, one of the limitations of the strategy is the possibility of poisoning that impact biofilm survival [162]. Another drawback of this strategy is high cost of metal catalysts, which imposes additional costs. To overcome these problems, cathode biofilm can be used as it is a nontoxic, inexpensive, and renewable cathode catalyst [145].

13.6 MEC Performance The development of techniques such as intermittent and continuous gas release methods [163] has allowed tracking of produced gases in MEC systems. For instance, in Owen method, known as intermittent gas release method, produced gases can be measured using durable gas-tight vessel [164]. The volumetric fraction of H2 (VH2) taken from the glass syringe is recorded. Intermittent and continuous gas release methods determine produced H2, while the gas composition is sampled and analyzed during the process. Alternatively, the gas sample can be provided and analyzed after a complete cycle [83]. This approach eliminates the errors caused by variation in gas composition during the experiment. Calculation of H2 yield is another strategy to estimate MEC performance. H2 yield is calculated as follows [164]: n Y H2 ¼ H2 (13.17) Ys V H 2 P ðdensityÞ (13.18) RT where nH2 and nS denote moles of H2 produced and moles of substrate consumed, respectively, and VH2 is the volume of H2 produced. Generally, the following equation is utilized for molar-based calculation of the H2 yield: nH 2 ¼

Y H2 ¼

mol H 2 V H 2 PMs ¼ RT Δc S mol S

(13.19)

where MS (g.mol
1) and ΔcS (g) are molecular weight and consumption rate of substrate, respectively. YH2 ¼ mH2/ms is used in case of complex substrates such as wastewater, where ms demonstrates the mass of substrate consumed and mH2 denotes the overall mass of gas produced. In addition, the H2 yield is calculated as follows: n (13.20) Y H 2 ¼ H 2  100 nth where nth is theoretical maximal hydrogen production.

Biohydrogen generation and MECs

Energy yield of MEC systems is one of the most widely used factors for estimating the performance of energy recovery. The energy yield is defined as the energy content of H2 recovered in comparison to the amount of substrate and electrical power consumed. In principle, energy content of a material is equal to energy released upon combustion. Thermodynamically, the energy content depends on the heat of combustion and the Gibbs free energy: W H 2 ¼ nH 2 ΔH H 2 ðnH 2 ¼ the moles of produced H2 Þ

(13.21)

W H 2 ¼ nH 2 ΔGH 2 ðnH 2 ¼ the moles of produced H2 Þ

(13.22)

The Gibbs free energy is equivalent to the electric voltage input [164] and its calculation is based on real reactor operating conditions such as temperature, concentrations, and partial pressures. It was found that the most of the energy content is derived from the power input compared to the substrate.

13.7 Conclusions Significant progress has been made in improvement of H2 as an alternative clean fuel. MEC system can serve as a novel platform for H2 production. Although MEC system can be utilized for simultaneous wastewater treatment and hydrogen gas production at low power input, energy losses due to overpotential and internal resistance and methanogens are driving the research toward the development of optimal MEC designs that allow higher H2 recovery rates. A variety of techniques has been addressed in this chapter, including optimization of electrode materials, operating conditions, and MEC reactor. In addition, substrate concentration and solution conductivity have shown beneficial potential, but further studies are needed to investigate how to manage sustainable and high yield hydrogen gas production.

References [1] A. Kadier, M.S. Kalil, P. Abdeshahian, K. Chandrasekhar, A. Mohamed, N.F. Azman, W. Logron˜o, Y. Simayi, A.A. Hamid, Recent advances and emerging challenges in microbial electrolysis cells (MECs) for microbial production of hydrogen and value-added chemicals, Renew. Sust. Energ. Rev. 61 (2016) 501–525. [2] D.C. Aiken, T.P. Curtis, E.S. Heidrich, Avenues to the financial viability of microbial electrolysis cells [MEC] for domestic wastewater treatment and hydrogen production, Int. J. Hydrog. Energy 44 (2019) 2426–2434. [3] D. Liang, L. Zhang, W. He, C. Li, J. Liu, S. Liu, H.-S. Lee, Y. Feng, Efficient hydrogen recovery with CoP-NF as cathode in microbial electrolysis cells, Appl. Energy 264 (2020), 114700. [4] I.S. Kim, E. Yang, M.-J. Choi, K.-J. Chae, Bioelectrochemical production of hydrogen from organic waste, in: Production of Hydrogen from Renewable Resources, Springer, 2015, pp. 249–281. [5] R. Rousseau, L. Etcheverry, E. Roubaud, R. Bass
eguy, M.-L. D
elia, A. Bergel, Microbial electrolysis cell (MEC): strengths, weaknesses and research needs from electrochemical engineering standpoint, Appl. Energy 257 (2020), 113938.

341

342

Biological fuel cells

[6] R.A. Rozendal, H.V. Hamelers, G.J. Euverink, S.J. Metz, C.J. Buisman, Principle and perspectives of hydrogen production through biocatalyzed electrolysis, Int. J. Hydrog. Energy 31 (2006) 1632–1640. [7] L. Koo´k, P. Bakonyi, F. Harnisch, J. Kretzschmar, K.-J. Chae, G. Zhen, G. Kumar, T. Ro´zsenberszki, G. To´th, N. Nemesto´thy, Biofouling of membranes in microbial electrochemical technologies: causes, characterization methods and mitigation strategies, Bioresour. Technol. 279 (2019) 327–338. [8] M.-J. Choi, E. Yang, H.-W. Yu, I.S. Kim, S.-E. Oh, K.-J. Chae, Transition metal/carbon nanoparticle composite catalysts as platinum substitutes for bioelectrochemical hydrogen production using microbial electrolysis cells, Int. J. Hydrog. Energy 44 (2019) 2258–2265. [9] K.-R. Kim, J. Kang, K.-J. Chae, Improvement in methanogenesis by incorporating transition metal nanoparticles and granular activated carbon composites in microbial electrolysis cells, Int. J. Hydrog. Energy 42 (2017) 27623–27629. [10] K.-J. Chae, K.-Y. Kim, M.-J. Choi, E. Yang, I.S. Kim, X. Ren, M. Lee, Sulfonated polyether ether ketone (SPEEK)-based composite proton exchange membrane reinforced with nanofibers for microbial electrolysis cells, Chem. Eng. J. 254 (2014) 393–398. [11] S.-G. Park, C. Rhee, S.G. Shin, J. Shin, H.O. Mohamed, Y.-J. Choi, K.-J. Chae, Methanogenesis stimulation and inhibition for the production of different target electrobiofuels in microbial electrolysis cells through an on-demand control strategy using the coenzyme M and 2-bromoethanesulfonate, Environ. Int. 131 (2019), 105006. [12] Y. Chen, M. Chen, N. Shen, R.J. Zeng, H2 production by the thermoelectric microconverter coupled with microbial electrolysis cell, Int. J. Hydrog. Energy 41 (2016) 22760–22768. [13] M. Sun, G.-P. Sheng, Z.-X. Mu, X.-W. Liu, Y.-Z. Chen, H.-L. Wang, H.-Q. Yu, Manipulating the hydrogen production from acetate in a microbial electrolysis cell-microbial fuel cell-coupled system, J. Power Sources 191 (2009) 338–343. [14] L. Lu, N. Ren, D. Xing, B.E. Logan, Hydrogen production with effluent from an ethanol-H2-coproducing fermentation reactor using a single-chamber microbial electrolysis cell, Biosens. Bioelectron. 24 (2009) 3055–3060. [15] Z. Yu, X. Leng, S. Zhao, J. Ji, T. Zhou, A. Khan, A. Kakde, P. Liu, X. Li, A review on the applications of microbial electrolysis cells in anaerobic digestion, Bioresour. Technol. 255 (2018) 340–348. [16] R.C. Tice, Y. Kim, Methanogenesis control by electrolytic oxygen production in microbial electrolysis cells, Int. J. Hydrog. Energy 39 (2014) 3079–3086. [17] T. Catal, K.L. Lesnik, H. Liu, Suppression of methanogenesis for hydrogen production in singlechamber microbial electrolysis cells using various antibiotics, Bioresour. Technol. 187 (2015) 77–83. [18] R.A. Rozendal, H.V. Hamelers, K. Rabaey, J. Keller, C.J. Buisman, Towards practical implementation of bioelectrochemical wastewater treatment, Trends Biotechnol. 26 (2008) 450–459. [19] T. Jafary, W.R.W. Daud, M. Ghasemi, B.H. Kim, J.M. Jahim, M. Ismail, S.S. Lim, Biocathode in microbial electrolysis cell; present status and future prospects, Renew. Sust. Energ. Rev. 47 (2015) 23–33. [20] I. Ivanov, Y. Ahn, T. Poirson, M.A. Hickner, B.E. Logan, Comparison of cathode catalyst binders for the hydrogen evolution reaction in microbial electrolysis cells, Int. J. Hydrog. Energy 42 (2017) 15739–15744. [21] E. Yang, H.O. Mohamed, S.-G. Park, M. Obaid, S.Y. Al-Qaradawi, P. Castan˜o, K. Chon, K.-J. Chae, A review on self-sustainable microbial electrolysis cells for electro-biohydrogen production via coupling with carbon-neutral renewable energy technologies, Bioresour. Technol. 320 (2021), 124363. [22] P.A. Selembo, J.M. Perez, W.A. Lloyd, B.E. Logan, High hydrogen production from glycerol or glucose by electrohydrogenesis using microbial electrolysis cells, Int. J. Hydrog. Energy 34 (2009) 5373–5381. [23] R. Łukajtis, I. Hołowacz, K. Kucharska, M. Glinka, P. Rybarczyk, A. Przyjazny, M. Kami
nski, Hydrogen production from biomass using dark fermentation, Renew. Sust. Energ. Rev. 91 (2018) 665–694. [24] B.E. Logan, Microbial fuel cells, John Wiley & Sons, 2008. [25] G. Reguera, K.D. McCarthy, T. Mehta, J.S. Nicoll, M.T. Tuominen, D.R. Lovley, Extracellular electron transfer via microbial nanowires, Nature 435 (2005) 1098–1101.

Biohydrogen generation and MECs

[26] N.J. Vickers, Animal communication: when i’m calling you, will you answer too? Curr. Biol. 27 (2017) R713–R715. [27] M. Symes, L. Cronin, Decoupling hydrogen and oxygen evolution during electrolytic water splitting using an electron-coupled-proton buffer, Nat. Chem. 5 (5) (2013) 403. [28] L. Chen, X. Dong, Y. Wang, Y. Xia, Separating hydrogen and oxygen evolution in alkaline water electrolysis using nickel hydroxide, Nat. Commun. 7 (2016) 1–8. [29] M. Dopson, G. Ni, T.H. Sleutels, Possibilities for extremophilic microorganisms in microbial electrochemical systems, FEMS Microbiol. Rev. 40 (2016) 164–181. [30] F. Fischer, Photoelectrode, photovoltaic and photosynthetic microbial fuel cells, Renew. Sust. Energ. Rev. 90 (2018) 16–27. [31] H. Wang, F. Qian, Y. Li, Solar-assisted microbial fuel cells for bioelectricity and chemical fuel generation, Nano Energy 8 (2014) 264–273. [32] H. Zhang, Y. Yu, L. Zhang, S. Dong, Fuel-free bio-photoelectrochemical cells based on a water/oxygen circulation system with a Ni: FeOOH/BiVO4 photoanode, Angew. Chem. 130 (2018) 1563–1567. [33] J.M. Cole, G. Pepe, O.K. Al Bahri, C.B. Cooper, Cosensitization in dye-sensitized solar cells, Chem. Rev. 119 (2019) 7279–7327. [34] F.F. Ajayi, K.-Y. Kim, K.-J. Chae, M.-J. Choi, I.S. Chang, I.S. Kim, Optimization studies of biohydrogen production in a coupled microbial electrolysis-dye sensitized solar cell system, Photochem. Photobiol. Sci. 9 (2010) 349–356. [35] F.F. Ajayi, K.-Y. Kim, K.-J. Chae, M.-J. Choi, S.-Y. Kim, I.-S. Chang, I.S. Kim, Study of hydrogen production in light assisted microbial electrolysis cell operated with dye sensitized solar cell, Int. J. Hydrog. Energy 34 (2009) 9297–9304. [36] L. Zheng, F. Teng, X. Ye, H. Zheng, X. Fang, Photo/electrochemical applications of metal sulfide/ TiO2 heterostructures, Adv. Energy Mater. 10 (2020) 1902355. [37] Y.-R. He, F.-F. Yan, H.-Q. Yu, S.-J. Yuan, Z.-H. Tong, G.-P. Sheng, Hydrogen production in a light-driven photoelectrochemical cell, Appl. Energy 113 (2014) 164–168. [38] E.F. Talooki, M. Ghorbani, M. Rahimnejad, M.S. Lashkenari, Evaluation of a visible light-responsive polyaniline nanofiber˗ cadmium sulfide quantum dots photocathode for simultaneous hexavalent chromium reduction and electricity generation in photo-microbial fuel cell, J. Electroanal. Chem. 873 (2020), 114469. [39] M. Sabeeh, R. Liaquat, A. Maryam, Effect of alkaline and alkaline-photocatalytic pretreatment on characteristics and biogas production of rice straw, Bioresour. Technol. 309 (2020), 123449. [40] L. Wang, L. Liu, F. Yang, Efficient gas phase VOC removal and electricity generation in an integrated bio-photo-electro-catalytic reactor with bio-anode and TiO2 photo-electro-catalytic air cathode, Bioresour. Technol. 270 (2018) 554–561. [41] Y. Hou, R. Zhang, Z. Yu, L. Huang, Y. Liu, Z. Zhou, Accelerated azo dye degradation and concurrent hydrogen production in the single-chamber photocatalytic microbial electrolysis cell, Bioresour. Technol. 224 (2017) 63–68. [42] Y.J. Jang, J.S. Lee, Photoelectrochemical water splitting with p-type metal oxide semiconductor photocathodes, ChemSusChem 12 (2019) 1835–1845. [43] D. Liang, G. Han, Y. Zhang, S. Rao, S. Lu, H. Wang, Y. Xiang, Efficient H2 production in a microbial photoelectrochemical cell with a composite Cu2O/NiOx photocathode under visible light, Appl. Energy 168 (2016) 544–549. [44] G.-L. Zang, G.-P. Sheng, C. Shi, Y.-K. Wang, W.-W. Li, H.-Q. Yu, A bio-photoelectrochemical cell with a MoS 3-modified silicon nanowire photocathode for hydrogen and electricity production, Energy Environ. Sci. 7 (2014) 3033–3039. [45] L. Zeng, X. Li, S. Fan, M. Zhang, Z. Yin, M. Tad
e, S. Liu, Photo-driven bioelectrochemical photocathode with polydopamine-coated TiO2 nanotubes for self-sustaining MoS2 synthesis to facilitate hydrogen evolution, J. Power Sources 413 (2019) 310–317. [46] Y. Jeon, S. Kim, Persistent hydrogen production by the photo-assisted microbial electrolysis cell using ap-type polyaniline nanofiber cathode, ChemSusChem 9 (2016) 3276–3279.

343

344

Biological fuel cells

[47] Y. Hou, Y. Gan, Z. Yu, X. Chen, L. Qian, B. Zhang, L. Huang, J. Huang, Solar promoted azo dye degradation and energy production in the bio-photoelectrochemical system with a g-C3N4/BiOBr heterojunction photocathode, J. Power Sources 371 (2017) 26–34. [48] Y. Hou, G. Yuan, S. Qin, L. Tu, Y. Yan, Z. Yu, H. Lin, Y. Chen, H. Zhu, H. Song, Photocathode optimization and microbial community in the solar-illuminated bio-photoelectrochemical system for nitrofurazone degradation, Bioresour. Technol. 302 (2020), 122761. [49] A. Pophali, S. Singh, N. Verma, Simultaneous hydrogen generation and COD reduction in a photoanode-based microbial electrolysis cell, Int. J. Hydrog. Energy 45 (2020) 25985–25995. [50] F. Qian, H. Wang, Y. Ling, G. Wang, M.P. Thelen, Y. Li, Photoenhanced electrochemical interaction between Shewanella and a hematite nanowire photoanode, Nano Lett. 14 (2014) 3688–3693. [51] H. Feng, Y. Liang, K. Guo, N. Li, D. Shen, Y. Cong, Y. Zhou, Y. Wang, M. Wang, Y. Long, Hybridization of photoanode and bioanode to enhance the current production of bioelectrochemical systems, Water Res. 102 (2016) 428–435. [52] G. Zhu, Y. Yang, J. Liu, F. Liu, A. Lu, W. He, Enhanced photocurrent production by the synergy of hematite nanowire-arrayed photoanode and bioengineered Shewanella oneidensis MR-1, Biosens. Bioelectron. 94 (2017) 227–234. [53] Y. Jeon, J.H. Kim, K. Koo, S. Kim, A photo-assisted microbial electrolysis cell for the exclusive biohydrogen production using a MoS2-coated p-type copper oxide, J. Power Sources 373 (2018) 79–84. [54] J.R. Beegle, A.P. Borole, Energy production from waste: evaluation of anaerobic digestion and bioelectrochemical systems based on energy efficiency and economic factors, Renew. Sust. Energ. Rev. 96 (2018) 343–351. [55] K. Chandrasekhar, S. Kumar, B.-D. Lee, S.-H. Kim, Waste based hydrogen production for circular bioeconomy: current status and future directions, Bioresour. Technol. 302 (2020), 122920. [56] S. Zou, Z. He, Efficiently “pumping out” value-added resources from wastewater by bioelectrochemical systems: a review from energy perspectives, Water Res. 131 (2018) 62–73. [57] Y. Mei, C.Y. Tang, Recent developments and future perspectives of reverse electrodialysis technology: a review, Desalination 425 (2018) 156–174. [58] Y. Kim, B.E. Logan, Hydrogen production from inexhaustible supplies of fresh and salt water using microbial reverse-electrodialysis electrolysis cells, Proc. Natl. Acad. Sci. 108 (2011) 16176–16181. [59] B.E. Logan, M. Elimelech, Membrane-based processes for sustainable power generation using water, Nature 488 (2012) 313–319. [60] H. Yuan, Y. Lu, I.M. Abu-Reesh, Z. He, Bioelectrochemical production of hydrogen in an innovative pressure-retarded osmosis/microbial electrolysis cell system: experiments and modeling, Biotechnol. Biofuels 8 (2015) 1–12. [61] A. Jain, Z. He, Powering microbial electrolysis cells by electricity generation from simulated waste heat of anaerobic digesters using thermoelectric generators, Int. J. Hydrog. Energy 45 (2020) 4065–4072. [62] A. Jain, Z. He, Improving hydrogen production in microbial electrolysis cells through hydraulic connection with thermoelectric generators, Process Biochem. 94 (2020) 51–57. [63] A. Wang, D. Sun, G. Cao, H. Wang, N. Ren, W.-M. Wu, B.E. Logan, Integrated hydrogen production process from cellulose by combining dark fermentation, microbial fuel cells, and a microbial electrolysis cell, Bioresour. Technol. 102 (2011) 4137–4143. [64] M.C. Hatzell, Y. Kim, B.E. Logan, Powering microbial electrolysis cells by capacitor circuits charged using microbial fuel cell, J. Power Sources 229 (2013) 198–202. [65] K.-J. Chae, M.-J. Choi, K.-Y. Kim, F. Ajayi, I.-S. Chang, I.S. Kim, Selective inhibition of methanogens for the improvement of biohydrogen production in microbial electrolysis cells, Int. J. Hydrog. Energy 35 (2010) 13379–13386. [66] N.S. Tehrani, G.D. Najafpour, M. Rahimnejad, H. Attar, Performance of up flow anaerobic sludge fixed film bioreactor for the treatment of high organic load and biogas production of cheese whey wastewater, Chem. Ind. Chem. Eng. Q. 21 (2015) 229–237. [67] H. Hu, Y. Fan, H. Liu, Hydrogen production using single-chamber membrane-free microbial electrolysis cells, Water Res. 42 (2008) 4172–4178.

Biohydrogen generation and MECs

[68] L. Lu, N. Ren, X. Zhao, H. Wang, D. Wu, D. Xing, Hydrogen production, methanogen inhibition and microbial community structures in psychrophilic single-chamber microbial electrolysis cells, Energy Environ. Sci. 4 (2011) 1329–1336. [69] G.K. Rader, B.E. Logan, Multi-electrode continuous flow microbial electrolysis cell for biogas production from acetate, Int. J. Hydrog. Energy 35 (2010) 8848–8854. [70] A. Wang, W. Liu, S. Cheng, D. Xing, J. Zhou, B.E. Logan, Source of methane and methods to control its formation in single chamber microbial electrolysis cells, Int. J. Hydrog. Energy 34 (2009) 3653–3658. [71] J.-Y. Nam, B.E. Logan, Enhanced hydrogen generation using a saline catholyte in a two chamber microbial electrolysis cell, Int. J. Hydrog. Energy 36 (2011) 15105–15110. [72] H. Liu, J. Wang, A. Wang, J. Chen, Chemical inhibitors of methanogenesis and putative applications, Appl. Microbiol. Biotechnol. 89 (2011) 1333–1340. [73] J.C. Scholten, R. Conrad, A.J. Stams, Effect of 2-bromo-ethane sulfonate, molybdate and chloroform on acetate consumption by methanogenic and sulfate-reducing populations in freshwater sediment, FEMS Microbiol. Ecol. 32 (2000) 35–42. [74] J. Zhang, Y. Bai, Y. Fan, H. Hou, Improved bio-hydrogen production from glucose by adding a specific methane inhibitor to microbial electrolysis cells with a double anode arrangement, J. Biosci. Bioeng. 122 (2016) 488–493. [75] X. Zhu, M. Siegert, M.D. Yates, B.E. Logan, Alamethicin suppresses methanogenesis and promotes acetogenesis in bioelectrochemical systems, Appl. Environ. Microbiol. 81 (2015) 3863–3868. [76] R. Karthikeyan, K.Y. Cheng, A. Selvam, A. Bose, J.W. Wong, Bioelectrohydrogenesis and inhibition of methanogenic activity in microbial electrolysis cells-a review, Biotechnol. Adv. 35 (2017) 758–771. [77] L. Gil-Carrera, A. Escapa, P. Mehta, G. Santoyo, S. Guiot, A. Mora´n, B. Tartakovsky, Microbial electrolysis cell scale-up for combined wastewater treatment and hydrogen production, Bioresour. Technol. 130 (2013) 584–591. [78] E. Heidrich, J. Dolfing, K. Scott, S. Edwards, C. Jones, T. Curtis, Production of hydrogen from domestic wastewater in a pilot-scale microbial electrolysis cell, Appl. Microbiol. Biotechnol. 97 (2013) 6979–6989. [79] M. Mashkour, M. Rahimnejad, F. Raouf, N. Navidjouy, A review on the application of nanomaterials in improving microbial fuel cells, Biofuel Res. J. 8 (2021) 1400–1416. [80] A. Kundu, J.N. Sahu, G. Redzwan, M. Hashim, An overview of cathode material and catalysts suitable for generating hydrogen in microbial electrolysis cell, Int. J. Hydrog. Energy 38 (2013) 1745–1757. [81] R.D. Cusick, B. Bryan, D.S. Parker, M.D. Merrill, M. Mehanna, P.D. Kiely, G. Liu, B.E. Logan, Performance of a pilot-scale continuous flow microbial electrolysis cell fed winery wastewater, Appl. Microbiol. Biotechnol. 89 (2011) 2053–2063. [82] P.A. Selembo, M.D. Merrill, B.E. Logan, The use of stainless steel and nickel alloys as low-cost cathodes in microbial electrolysis cells, J. Power Sources 190 (2009) 271–278. [83] S. Cheng, B.E. Logan, Sustainable and efficient biohydrogen production via electrohydrogenesis, Proc. Natl. Acad. Sci. 104 (2007) 18871–18873. [84] R.A. Rozendal, T.H.J.A. Sleutels, H.V. Hamelers, C.J. Buisman, Effect of the type of ion exchange membrane on performance, ion transport, and pH in biocatalyzed electrolysis of wastewater, Water Sci. Technol. 57 (2008) 1757–1762. [85] K. Hu, L. Xu, W. Chen, S.-q. Jia, W. Wang, F. Han, Degradation of organics extracted from dewatered sludge by alkaline pretreatment in microbial electrolysis cell, Environ. Sci. Pollut. Res. 25 (2018) 8715–8724. [86] M. Hasany, S. Yaghmaei, M.M. Mardanpour, Z.G. Naraghi, Simultaneously energy production and dairy wastewater treatment using bioelectrochemical cells: in different environmental and hydrodynamic modes, Chin. J. Chem. Eng. 25 (2017) 1847–1855. [87] M. Badia-Fabregat, L. Rago, J.A. Baeza, A. Guisasola, Hydrogen production from crude glycerol in an alkaline microbial electrolysis cell, Int. J. Hydrog. Energy 44 (2019) 17204–17213.

345

346

Biological fuel cells

[88] L. Zhang, Y.-Z. Wang, T. Zhao, T. Xu, Hydrogen production from simultaneous saccharification and fermentation of lignocellulosic materials in a dual-chamber microbial electrolysis cell, Int. J. Hydrog. Energy 44 (2019) 30024–30030. [89] N. Samsudeen, J. Spurgeon, M. Matheswaran, J. Satyavolu, Simultaneous biohydrogen production with distillery wastewater treatment using modified microbial electrolysis cell, Int. J. Hydrog. Energy 45 (2020) 18266–18274. [90] J.-Y. Nam, M.D. Yates, Z. Zaybak, B.E. Logan, Examination of protein degradation in continuous flow, microbial electrolysis cells treating fermentation wastewater, Bioresour. Technol. 171 (2014) 182–186. [91] V.J. Watson, M. Hatzell, B.E. Logan, Hydrogen production from continuous flow, microbial reverseelectrodialysis electrolysis cells treating fermentation wastewater, Bioresour. Technol. 195 (2015) 51–56. [92] X.-H. Li, D.-W. Liang, Y.-X. Bai, Y.-T. Fan, H.-W. Hou, Enhanced H2 production from corn stalk by integrating dark fermentation and single chamber microbial electrolysis cells with double anode arrangement, Int. J. Hydrog. Energy 39 (2014) 8977–8982. [93] J. Huang, H. Feng, L. Huang, X. Ying, D. Shen, T. Chen, X. Shen, Y. Zhou, Y. Xu, Continuous hydrogen production from food waste by anaerobic digestion (AD) coupled single-chamber microbial electrolysis cell (MEC) under negative pressure, Waste Manag. 103 (2020) 61–66. [94] A. Fadakar, M.M. Mardanpour, S. Yaghmaei, The coupled microfluidic microbial electrochemical cell as a self-powered biohydrogen generator, J. Power Sources 451 (2020), 227817. [95] A. Kadier, Y. Simayi, M.S. Kalil, P. Abdeshahian, A.A. Hamid, A review of the substrates used in microbial electrolysis cells (MECs) for producing sustainable and clean hydrogen gas, Renew. Energy 71 (2014) 466–472. [96] J. An, H.-S. Lee, Implication of endogenous decay current and quantification of soluble microbial products (SMP) in microbial electrolysis cells, RSC Adv. 3 (2013) 14021–14028. [97] A. Tardast, M. Rahimnejad, G.D. Najafpour, A. Asghar Ghoreyshi, H. Zare, Fabrication and operation of a novel membrane-less microbial fuel cell as a bioelectricity generator, Iran. J. Energy Environ. 3 (2012). [98] M. Masoudi, M. Rahimnejad, M. Mashkour, Enhancing operating capacity of microbial fuel cells by using low-cost electrodes and multi anode-cathode connections in a membrane-less configuration, Int. J. Hydrog. Energy 46 (2021) 8226–8238. [99] G. Najafpour, P. Nouri, M. Rahimnejad, Bioelectricity generation in annulus structure of single chamber membrane-less microbial fuel cell using wastewater from chocolate industry, Linnaeus Eco-Tech (2014). [100] Y. Zhang, I. Angelidaki, Microbial electrolysis cells turning to be versatile technology: recent advances and future challenges, Water Res. 56 (2014) 11–25. [101] D. Call, B.E. Logan, Hydrogen production in a single chamber microbial electrolysis cell lacking a membrane, Environ. Sci. Technol. 42 (2008) 3401–3406. [102] K. Guo, X. Tang, Z. Du, H. Li, Hydrogen production from acetate in a cathode-on-top singlechamber microbial electrolysis cell with a mipor cathode, Biochem. Eng. J. 51 (2010) 48–52. [103] H.-S. Lee, C.I. Torres, P. Parameswaran, B.E. Rittmann, Fate of H2 in an upflow single-chamber microbial electrolysis cell using a metal-catalyst-free cathode, Environ. Sci. Technol. 43 (2009) 7971–7976. [104] B. Tartakovsky, M.-F. Manuel, H. Wang, S. Guiot, High rate membrane-less microbial electrolysis cell for continuous hydrogen production, Int. J. Hydrog. Energy 34 (2009) 672–677. [105] L. Gil-Carrera, A. Escapa, R. Moreno, A. Mora´n, Reduced energy consumption during low strength domestic wastewater treatment in a semi-pilot tubular microbial electrolysis cell, J. Environ. Manag. 122 (2013) 1–7. [106] W. Wang, D.-J. Lee, Z. Lei, Integrating anaerobic digestion with microbial electrolysis cell for performance enhancement: a review, Bioresour. Technol. 344 (2022), 126321. [107] T. Sangeetha, C.P. Rajneesh, W.-M. Yan, Integration of microbial electrolysis cells with anaerobic digestion to treat beer industry wastewater, in: Integrated Microbial Fuel Cells for Wastewater Treatment, Elsevier, 2020, pp. 313–346.

Biohydrogen generation and MECs

[108] T. Gao, H. Zhang, X. Xu, J. Teng, Integrating microbial electrolysis cell based on electrochemical carbon dioxide reduction into anaerobic osmosis membrane reactor for biogas upgrading, Water Res. 190 (2021), 116679. [109] M. Sun, G.-P. Sheng, L. Zhang, C.-R. Xia, Z.-X. Mu, X.-W. Liu, H.-L. Wang, H.-Q. Yu, R. Qi, T. Yu, An MEC-MFC-coupled system for biohydrogen production from acetate, Environ. Sci. Technol. 42 (2008) 8095–8100. [110] M. Mehanna, P.D. Kiely, D.F. Call, B.E. Logan, Microbial electrodialysis cell for simultaneous water desalination and hydrogen gas production, Environ. Sci. Technol. 44 (2010) 9578–9583. [111] B.J. Sanghavi, S.M. Mobin, P. Mathur, G.K. Lahiri, A.K. Srivastava, Biomimetic sensor for certain catecholamines employing copper (II) complex and silver nanoparticle modified glassy carbon paste electrode, Biosens. Bioelectron. 39 (2013) 124–132. [112] A. Baudler, I. Schmidt, M. Langner, A. Greiner, U. Schr€ oder, Does it have to be carbon? Metal anodes in microbial fuel cells and related bioelectrochemical systems, Energy Environ. Sci. 8 (2015) 2048–2055. [113] D. Pocaznoi, A. Calmet, L. Etcheverry, B. Erable, A. Bergel, Stainless steel is a promising electrode material for anodes of microbial fuel cells, Energy Environ. Sci. 5 (2012) 9645–9652. [114] W. Li, P. Zheng, J. Guo, J. Ji, M. Zhang, Z. Zhang, E. Zhan, G. Abbas, Characteristics of selfalkalization in high-rate denitrifying automatic circulation (DAC) reactor fed with methanol and sodium acetate, Bioresour. Technol. 154 (2014) 44–50. [115] C. Berrı´os, M. Ureta-Zan˜artu, C. Guti
errez, Impedance study of electropolymerized films of polyNi (II)-macrocycles, Electrochim. Acta 53 (2007) 792–802. [116] A. Baudler, M. Langner, C. Rohr, A. Greiner, U. Schr€ oder, Metal-polymer hybrid architectures as novel anode platform for microbial electrochemical technologies, ChemSusChem 10 (2017) 253–257. [117] S. Trasitti, Electrocatalysis: understanding the success of DSA (R), Electrochim. Acta 45 (2000) 2377–2385. [118] M. Asghary, J.B. Raoof, M. Rahimnejad, R. Ojani, Usage of gold nanoparticles/multi-walled carbon nanotubes-modified CPE as a nano-bioanode for enhanced power and current generation in microbial fuel cell, J. Iran. Chem. Soc. 16 (2019) 1677–1685. [119] K. Zhao, H. Song, S. Zhuang, L. Dai, P. He, Y. Fang, Determination of nitrite with the electrocatalytic property to the oxidation of nitrite on thionine modified aligned carbon nanotubes, Electrochem. Commun. 9 (2007) 65–70. [120] E. Kipf, R. Zengerle, J. Gescher, S. Kerzenmacher, How does the choice of anode material influence electrical performance? A comparison of two microbial fuel cell model organisms, ChemElectroChem 1 (2014) 1849–1853. [121] S. Chen, G. He, Q. Liu, F. Harnisch, Y. Zhou, Y. Chen, M. Hanif, S. Wang, X. Peng, H. Hou, Layered corrugated electrode macrostructures boost microbial bioelectrocatalysis, Energy Environ. Sci. 5 (2012) 9769–9772. [122] L. Peng, S.-J. You, J.-Y. Wang, Carbon nanotubes as electrode modifier promoting direct electron transfer from Shewanella oneidensis, Biosens. Bioelectron. 25 (2010) 1248–1251. [123] M. Sun, F. Zhang, Z.-H. Tong, G.-P. Sheng, Y.-Z. Chen, Y. Zhao, Y.-P. Chen, S.-Y. Zhou, G. Liu, Y.-C. Tian, A gold-sputtered carbon paper as an anode for improved electricity generation from a microbial fuel cell inoculated with Shewanella oneidensis MR-1, Biosens. Bioelectron. 26 (2010) 338–343. [124] Y. Fan, S. Xu, R. Schaller, J. Jiao, F. Chaplen, H. Liu, Nanoparticle decorated anodes for enhanced current generation in microbial electrochemical cells, Biosens. Bioelectron. 26 (2011) 1908–1912. [125] C. Moß, S.A. Patil, U. Schr€ oder, Scratching the surface—how decisive are microscopic surface structures on growth and performance of electrochemically active bacteria? Fronti. Energy Res. 7 (2019) 18. [126] P. Champigneux, C. Renault-Sentenac, D. Bourrier, C. Rossi, M.-L. Delia, A. Bergel, Effect of surface nano/micro-structuring on the early formation of microbial anodes with Geobacter sulfurreducens: experimental and theoretical approaches, Bioelectrochemistry 121 (2018) 191–200.

347

348

Biological fuel cells

[127] P. Champigneux, C. Renault-Sentenac, D. Bourrier, C. Rossi, M.-L. Delia, A. Bergel, Effect of surface roughness, porosity and roughened micro-pillar structures on the early formation of microbial anodes, Bioelectrochemistry 128 (2019) 17–29. [128] T.H. Sleutels, R. Lodder, H.V. Hamelers, C.J. Buisman, Improved performance of porous bioanodes in microbial electrolysis cells by enhancing mass and charge transport, Int. J. Hydrog. Energy 34 (2009) 9655–9661. [129] N.G. Yasri, G. Nakhla, The performance of 3-D graphite doped anodes in microbial electrolysis cells, J. Power Sources 342 (2017) 579–588. [130] K. Guo, S. Freguia, P.G. Dennis, X. Chen, B.C. Donose, J. Keller, J.J. Gooding, K. Rabaey, Effects of surface charge and hydrophobicity on anodic biofilm formation, community composition, and current generation in bioelectrochemical systems, Environ. Sci. Technol. 47 (2013) 7563–7570. [131] W.-K. Wang, B. Tang, J. Liu, H. Shi, Q. Xu, G. Zhao, Self-supported microbial carbon aerogel bioelectrocatalytic anode promoting extracellular electron transfer for efficient hydrogen evolution, Electrochim. Acta 303 (2019) 268–274. [132] A. Tardast, G. Najafpour, M. Rahimnejad, A.A. Ghoreyshi, H. Zare, K. Pirzadeh, Bioelectricity production by air cathode microbial fuel cell, in: 2012 Second Iranian Conference on Renewable Energy and Distributed Generation, IEEE, 2012, pp. 162–166. [133] T. Hurlen, S. Gunvaldsen, F. Blaker, Effects of buffers on hydrogen evolution at iron electrodes, Electrochim. Acta 29 (1984) 1163–1164. [134] S. Da Silva, R. Bass
eguy, A. Bergel, Electrochemical deprotonation of phosphate on stainless steel, Electrochim. Acta 49 (2004) 4553–4561. [135] E. Roubaud, R. Lacroix, S. Da Silva, A. Bergel, R. Bass
eguy, B. Erable, Catalysis of the hydrogen evolution reaction by hydrogen carbonate to decrease the voltage of microbial electrolysis cell fed with domestic wastewater, Electrochim. Acta 275 (2018) 32–39. [136] L.D.S. Munoz, A. Bergel, R. Bass
eguy, Role of the reversible electrochemical deprotonation of phosphate species in anaerobic biocorrosion of steels, Corros. Sci. 49 (2007) 3988–4004. [137] Y.-X. Huang, X.-W. Liu, X.-F. Sun, G.-P. Sheng, Y.-Y. Zhang, G.-M. Yan, S.-G. Wang, A.-W. Xu, H.-Q. Yu, A new cathodic electrode deposit with palladium nanoparticles for cost-effective hydrogen production in a microbial electrolysis cell, Int. J. Hydrog. Energy 36 (2011) 2773–2776. [138] B. Ghasemi, S. Yaghmaei, K. Abdi, M.M. Mardanpour, S.A. Haddadi, Introducing an affordable catalyst for biohydrogen production in microbial electrolysis cells, J. Biosci. Bioeng. 129 (2020) 67–76. [139] F. Li, W. Liu, Y. Sun, W. Ding, S. Cheng, Enhancing hydrogen production with Ni-P coated nickel foam as cathode catalyst in single chamber microbial electrolysis cells, Int. J. Hydrog. Energy 42 (2017) 3641–3646. [140] A. Kadier, Y. Simayi, K. Chandrasekhar, M. Ismail, M.S. Kalil, Hydrogen gas production with an electroformed Ni mesh cathode catalysts in a single-chamber microbial electrolysis cell (MEC), Int. J. Hydrog. Energy 40 (2015) 14095–14103. [141] P.A. Selembo, M.D. Merrill, B.E. Logan, Hydrogen production with nickel powder cathode catalysts in microbial electrolysis cells, Int. J. Hydrog. Energy 35 (2010) 428–437. [142] H. Hu, Y. Fan, H. Liu, Hydrogen production in single-chamber tubular microbial electrolysis cells using non-precious-metal catalysts, Int. J. Hydrog. Energy 34 (2009) 8535–8542. [143] T. Jayabalan, M. Matheswaran, V. Preethi, S.N. Mohamed, Enhancing biohydrogen production from sugar industry wastewater using metal oxide/graphene nanocomposite catalysts in microbial electrolysis cell, Int. J. Hydrog. Energy 45 (2020) 7647–7655. [144] H. Dai, H. Yang, X. Liu, X. Jian, Z. Liang, Electrochemical evaluation of nano-mg (OH) 2/graphene as a catalyst for hydrogen evolution in microbial electrolysis cell, Fuel 174 (2016) 251–256. [145] M. Khan, A. Nizami, M. Rehan, O. Ouda, S. Sultana, I. Ismail, K. Shahzad, Microbial electrolysis cells for hydrogen production and urban wastewater treatment: a case study of Saudi Arabia, Appl. Energy 185 (2017) 410–420. [146] B.S. Thapa, T. Kim, S. Pandit, Y.E. Song, Y.P. Afsharian, M. Rahimnejad, J.R. Kim, S.-E. Oh, Overview of electroactive microorganisms and electron transfer mechanisms in microbial electrochemistry, Bioresour. Technol. (2021) 126579.

Biohydrogen generation and MECs

[147] M.Z. Khan, S. Singh, T. Sreekrishnan, S. Ahammad, Feasibility study on anaerobic biodegradation of azo dye reactive orange 16, RSC Adv. 4 (2014) 46851–46859. [148] Y.P. Afsharian, M. Rahimnejad, Functional dynamics of microbial communities in bioelectrochemical systems: the importance of eco-electrogenic treatment of complex substrates, Curr. Opin. Electrochem. 31 (2022), 100816. [149] M. Di Lorenzo, K. Scott, T.P. Curtis, K.P. Katuri, I.M. Head, Continuous feed microbial fuel cell using an air cathode and a disc anode stack for wastewater treatment, Energy Fuel 23 (2009) 5707–5716. [150] D. Pocaznoi, B. Erable, L. Etcheverry, M.-L. Delia, A. Bergel, Towards an engineering-oriented strategy for building microbial anodes for microbial fuel cells, Phys. Chem. Chem. Phys. 14 (2012) 13332–13343. [151] A.R. Rahmani, N. Navidjouy, M. Rahimnejad, S. Alizadeh, M.R. Samarghandi, D. Nematollahi, Effect of different concentrations of substrate in microbial fuel cells toward bioenergy recovery and simultaneous wastewater treatment, Environ. Technol. 43 (2022) 1–9. [152] T. Jafary, A.A. Ghoreyshi, G.D. Najafpour, S. Fatemi, M. Rahimnejad, Investigation on performance of microbial fuel cells based on carbon sources and kinetic models, Int. J. Energy Res. 37 (2013) 1539–1549. [153] M. Rahimnejad, G. Najafpour, A.A. Ghoreyshi, Effect of mass transfer on performance of microbial fuel cell, INTECH 5 (2011) 233–250. [154] B.E. Logan, B. Hamelers, R. Rozendal, U. Schr€ oder, J. Keller, S. Freguia, P. Aelterman, W. Verstraete, K. Rabaey, Microbial fuel cells: methodology and technology, Environ. Sci. Technol. 40 (2006) 5181–5192. [155] Y. Li, W.-K. Yu, L. Chen, D. Liu, C.-C. Fong, T. Xu, G. Zhu, D. Sun, M. Yang, Electrotaxis of tumor-initiating cells of H1975 lung adenocarcinoma cells is associated with both activation of stretchactivated cation channels (SACCs) and internal calcium release, Bioelectrochemistry 124 (2018) 80–92. [156] E.M. Ryan, P.P. Mukherjee, Mesoscale modeling in electrochemical devices—a critical perspective, Prog. Energy Combust. Sci. 71 (2019) 118–142. [157] A.J. Hutchinson, J.C. Tokash, B.E. Logan, Analysis of carbon fiber brush loading in anodes on startup and performance of microbial fuel cells, J. Power Sources 196 (2011) 9213–9219. [158] V.R. Nimje, C.-Y. Chen, C.-C. Chen, H.-R. Chen, M.-J. Tseng, J.-S. Jean, Y.-F. Chang, Glycerol degradation in single-chamber microbial fuel cells, Bioresour. Technol. 102 (2011) 2629–2634. [159] M.Z. Khan, Y.L. Sim, Y.J. Lin, K.M. Lai, Testing biological effects of hand-washing grey water for reuse in irrigation on an urban farm: a case study, Environ. Technol. 34 (2013) 545–551. [160] Y. Chen, Y. Xu, L. Chen, P. Li, S. Zhu, S. Shen, Microbial electrolysis cells with polyaniline/multiwalled carbon nanotube-modified biocathodes, Energy 88 (2015) 377–384. [161] Y.-P. Liu, Y.-H. Wang, B.-S. Wang, Q.-Y. Chen, Effect of anolyte pH and cathode Pt loading on electricity and hydrogen co-production performance of the bio-electrochemical system, Int. J. Hydrog. Energy 39 (2014) 14191–14195. [162] S. Fatemi, A. Ghoreyshi, G. Najafpour, M. Rahimnejad, Investigation of bioelectricity production in dual chamber microbial fuel cell by mixed culture as active biocatalyst, Cell. Mol. Res. (Iran. J. Biol.) 27 (2015) 546–554. [163] W. Owen, D. Stuckey, J. Healy Jr., L. Young, P. McCarty, Bioassay for monitoring biochemical methane potential and anaerobic toxicity, Water Res. 13 (1979) 485–492. [164] B.E. Logan, D. Call, S. Cheng, H.V. Hamelers, T.H. Sleutels, A.W. Jeremiasse, R.A. Rozendal, Microbial electrolysis cells for high yield hydrogen gas production from organic matter, Environ. Sci. Technol. 42 (2008) 8630–8640.

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CHAPTER 14

CO2 reduction and MES Mostafa Rahimnejad

Biofuel and Renewable Energy Research Center, Chemical Engineering Department, Babol Noshirvani University of Technology, Babol, Mazandaran, Iran

14.1 Introduction In the context of microbial electrosynthesis (MES), the importance of microbial CO2 capture and conversion into higher-value products is well characterized. Our understanding of the contribution of CO2 emissions to climate change is revealing the necessity of CO2 capture and storage and CO2 capture and utilization [1–3]. In fact, many CO2 storage techniques such as underground storage, marine storage, and forest storage often result in geological instability [4], destruction of the marine ecological environment, and shrinking of forest areas [5]. As a result, CO2 capture through chemical, physical, or biological processes need to be developed and incorporated into energy efficiency programs [6]. The consequences of chemical and physical processes—including absorption [7], adsorption [8], photochemical [9], and electrochemical processes [10]—are high capital cost, production of leaching toxicities, and short life cycles [11]. In fact, the indication for changes in the valence of CO2 or mediating value-added compound production is high activation energy, to the extent that chemically stable CO2 requires energy to undergo state changes [12]. Accordingly, the central role of MES in nonspontaneous CO2 reduction into multicarbon chemicals under little energy input, as well as the function of microbial communities as biocatalysts are highlighted in this chapter. Indeed, MES application in utilizing CO2 as a substrate to carry out biosynthesis of organics with the assistance of an external power is largely underrepresented at resent and are specifically focused in this chapter, which links bioelectrochemical systems (BESs) with bio-based CO2 capture and conversion.

14.2 Basic principles of MECs utilized for CO2 capture Physiological activities among biological organisms are responsible for MES function. These activities include degradation of organic pollutants, CO2 capture, electricity production, and generation of high-grade chemicals. MES is a subclass of MECs that focuses on cathodic CO2 conversion. The dynamic of MES is a consequence of the constant electron and proton generation through microbial metabolism at the anode, followed by electrosynthesis reactions at the cathode that produce biochemical compounds [13]. Moreover, MES can constantly Biological Fuel Cells https://doi.org/10.1016/B978-0-323-85711-6.00017-5

Copyright © 2023 Elsevier Inc. All rights reserved.

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undergo CO2 emission reduction through cathodic CO2 capture and the recycling of CO2 into a variety of high-value chemicals [1,14]. An external power supply provides electrons through which the possibility of a thermodynamic barrier is alleviated. Microbial carbon capture cell (MCC) is another subclass of microbial electro-synthesis cell that allows CO2 capture, biochemical production, and wastewater treatment (Fig. 14.1). Both MCC and MES are associated with CO2 conversion through dehydrogenase catalysis. Interestingly, dehydrogenase catalysis has been implicated in the enhancement of CO2 solubility, which is a critical factor for the efficiency of its further conversion [15]. The sole difference between

Fig. 14.1 Schematic illustration of an MCC (A) and a typical MES system (B).

CO2 reduction and MES

the MES and MCC is that the MES process is nonspontaneous, requiring external power input, while the MCC system works spontaneously with the addition of photosynthesis. However, it was shown that CO2 fixation efficiency is limited in MCC owing mainly to nutrient availability [16]. Microbial metabolisms orchestrate electron generation, while solid electrodes are responsible for electron uptake from the exoelectrogenic biofilm. Via extracellular electron transfer (EET) rate, MES can produce efficient bioelectricity, as well as mediate excellent CO2 capture and conversion. Importantly, EET is done either through a direct electron transfer (DET) pathway or mediated electron transfer (MET) pathway. DET pathway is expanded via direct electron exchange between the electrode surface and electroactive microorganism [17,18] using intracellular materials (NADH delivering enzyme, coenzyme Q, ubiquinone) and extracellular proteins or appendages (cytochromes, nanowires, and membrane vesicles) [19–21]. In contrast, electroactive biofilm can interact indirectly with electrode surface by redox mediators and electron shuttles such as flavins, phenazines, neutral red, methylene blue, anthraquinone, thionin, methyl viologen, and anthraquinones [22,23]. Furthermore, both DET and MET can be utilized by a microorganism [24]. The emergence of redox mediators is now recognized to be associated with slight toxic effects on microorganisms. Thus, the DET pathway is likely to be more efficient for EET due to preventing from cellular cytotoxicity and, more importantly, conversion of intermediates and loss of electrons. It was demonstrated that electrode specific surface area, biocompatibility, and conductivity can also influence the efficiency of EET. Table 14.1 provides some examples of EET conducted on cathode Table 14.1 An overview about possible EET on cathode surface of MEC devices. Electron donor/ acceptor

Product

EET mechanism

Ref.

Sulfurreducens Sporomusa ovata, Moorella thermoacetica Sporomusa ovata

Fumarate CO2

Succinate Acetate

DET DET

[25] [26]

CO2

Acetate, ethanol

[27]

Sporomusa silvacetica, Clostridium ljungdahlii, Clostridium aceticum Clostridium carboxidivorans, Clostridium ragsdalei, etc. Acetoanaerobium

CO2

Acetate, formate, 2-oxobutyrate Butyrate, thanol, butanol Acetate

Indirect EET DET

[28]

Ralstonia eutropha

CO2

Indirect EET Indirect EET Indirect EET

Moorella thermoacetica, Clostridium formicoaceticum

CO2

MET

[31]

Cathodic microorganism

CO2 CO2

Isobutanol, 3-methyl-1butanol Formate

[26]

[29] [30]

353

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surface during CO2 bioconversion within MEC devices. For further reading about electron transfer concepts within electroactive biofilm we refer to Chapter 2.

14.3 MES microbial community Electroactive microbes are the main compartments of BESs [17]. During MES operation, microorganisms undergo CO2 capture and recycling that determine the sustainability, productivity, and energy conversion efficiency of the system. Several studies have highlighted the high contribution of chemoautotrophic bacteria in electron uptake from electrode surfaces without the need for electrochemically active redox mediators [32,33]. Moreover, multiple studies have identified the role of microorganisms with the capability of CO2 recycling such as methanogens and acetogens in methane and acetate production [34,35]. Collectively, it seems that pure cultures or mixed cultures have evolved as functional microbial communities [36]. Pure cultures can be achieved through separation and purification of mixed cultures and are believed to orchestrate highly selective generation of specific simple products such as methane, acetate, etc., from CO2 recycling [12] without negatively affecting Coulombic efficiency [37]. Genetic and metabolic engineering play a pivotal role in the production of genetically tractable modified strains to synthesize more valuable long-chain organics. On the other hand, mixed cultures are easy to obtain and require lower operating costs [38–40]. The hypothetical major role of collaboration among biofilm cells has gained attention with the advent of mixed communities that have proved very effective in directing MES due to possessing more intricate microbial communities and more various metabolic pathways, which lead to substrate versatility [41]. Moreover, mixed cultures possess a high tolerance to fluctuant environmental conditions and can be adopted for investigation of MES performance under parameters and conditions such as temperature, pH, reactor configurations, electrode materials, or hydraulic residence time. However, in mixed cultures, many bioproducts are produced through multiple active microbial synthesis pathways that interrupt the electron flux to the target product [42]. All in all, both pure cultures and mixed cultures represent high potential in CO2 capture and conversion and the main difference lies in the yield of bioproducts and the power density of MES (Table 14.2).

14.4 MES products Current evidence highlights that MES is a remarkable system that contains functional microbial communities. The microbial communities have the capacity for bioelectrochemical transformation of CO2 into typical value-added bio-based products (Fig. 14.2). Such products can be classified as C1, C2, C3, and C4 biochemicals based on the number of carbon atoms they contain.

CO2 reduction and MES

Table 14.2 Examples of pure and mixed-cultures used in MES systems for biochemical production. Cathode potential (V vs SHE)

Inoculum

Products

Cathode material

Ref.

[13]

Graphite felt Graphite felt Graphite granules 3 Carbon felts stacked together

[3] [43] [44] [45]


1.02 V

Mixed culture

3 Carbon felts stacked together

[45]


0.95 V
0.4 V

Mixed culture Sporomusa ovata Sporomusa ovata Sporomusa ovata

Methane 8.81  0.51 mmol m
2 day
1 Isobutyrate 0.63 mM
1 day
1 Caprylate 36 mg
1 L
1 Acetate 1.03 g m
2 day
1 Acetate 371  5 g m
2 day
1, butyrate 160  29 g m
2 day
1, caproate 46  1 g m
2 day
1 Acetate 234  57.7 g
2 day
1, butyrate 125  45 g
2 day
1, caproate 42  10 g
2 day
1 Caproate 2.1  0.01 g
2 day
1 Acetate 13.5  3.3 g
2 day
1

Graphite rods


0.7 V
0.9 V
0.59 V
0.85 V

Methanococcus maripaludis Mixed culture Mixed culture Mixed culture Mixed culture

Carbon felt Chitosan on carbon cloth Graphene paper

[46] [47]

Porous Ni-hollow fiber with multiwall carbone nanotube NiMo deposition on doped Si wafer NiMo deposition on doped Si wafer 3D Graphene Ni-foam Graphite sticks

[49]


700 mV


0.69 V
0.4 V
0.7 V
0.7 V
0.85 V
0.74 V

Sporomusa ovata Acetobacterium woodii Mixed culture Sporomusa ovata

Acetate 39.8 g
2 day
1 Acetate 1.85 g
2 day
1 Acetate 6.7 g L
1 day
1 Acetate 6 g L
1 day
1 Acetate  0.15 g L
1 day
1, butyrate, isobutyrate, caproate Acetate and oxybutyrate, 4.68 mM day
1, 9.68 g m
2 day
1

[48]

[50] [50] [51] [52]

14.4.1 C1 biochemicals Methane (CH4), formic acid (HCOOH), and methanol (CH3OH) are C1 compounds that can be produced either by pure cultures or mixed cultures. Methane refers to the simplest microbial organic. In MES, methane is resulted from cathode methanogenesis under an external power supply and can serve the need of substrate for microbial production of hydrogen (H2), acetylene (C2H4), and formaldehyde (HCHO) [53]. Cathodic and anodic reactions that modulate methane production from CO2 conversion have been summarized as follows:

355

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Biological fuel cells

Fig. 14.2 Demonstrating synthesis mechanisms of value-added bioproducts on MEC cathode surface.

Anode : H2 O ! H+ + OH



(14.1)

Cathode : CO2 + 8H + 8e ! 2H2 O + CH4 ðDET pathwayÞ

(14.2)

Cathode : CO2 + 4H+ + 4e
! 2H2 O + CH4 ðIET pathwayÞ

(14.3)

+

The presence of CO2 and electrode is essential as the final electron acceptor and the electron donor, respectively. Methanococcus vannielii, Methanococcus maripaludis, Methanolacinia petrolearia, Methanobacterium congolense, Methanoculleus submarinus, and Methanococcus maripaludis are considered prevalent methanogen species that have biocatalytic function upon methane production. Mixed-culture biocathodes have the unique capacity to give rise to methane production, although the use of electron shuttles such as neutral red and anthraquinone-2, 6-disulfonate is suggested to promote the EET rate and alleviate the internal resistance [54]. However, methane leakage into the atmosphere should be restricted due to its global warming potential [55,56]. Thus, During MES operation, multiple techniques should be applied to prevent bioelectromethanogenesis. Importantly, formic acid has also emerged as C1 MES bioproduct. Thermophilic microbes that contain formate dehydrogenase can effectively capture CO2 and mediate formidable

CO2 reduction and MES

electron transfer [57]. It was demonstrated that formic acid production is enhanced at high temperatures owing to pyruvate dehydrogenase activities conducted by thermophilic microbes. In addition, Shewanella oneidensis MR-1 is known as a biocatalyst of formic acid electrosynthesis [58]. Moreover, methanol dehydrogenase, formaldehyde dehydrogenase, and formate dehydrogenase have been used as tools to mediate CO2 reduction into methanol [59]. Enhanced methanol production has been directly linked to the sequential immobilization of enzymes. For instance, the balance between formate dehydrogenase and methanol dehydrogenase is an important dynamic and is modulated by oxidizing bacteria. Hence, the critical points are the concept of multienzymatic bioconversion and interdependent relationship of oxidizing bacteria.

14.4.2 C2 biochemicals Acetate (CH3COOH), ethanol (C2H5OH), dimethyl ether (CH3OCH3), and ethylene (C2H4) are the main MES C2 bioproducts. In MES, autotrophic bacteria such as Sporomusa ovata, Sporomusa silvacetica, Sporomusa sphaeroides, Clostridium ljungdahlii, Clostridium aceticum, and Moorella thermoacetica can produce acetate from CO2 within acidic, alkaline, saline or hot environments [26,56]. However, it is pivotal to impede methanogenesis in order to obtain higher acetate production rates [60]. For instance, 2-bromoethanosulfonate and magnetite nanoparticles have been utilized for suppression of methanogenic activity and increment of microbial electrosynthesis of acetate from CO2 [61,62]. Furthermore, acetate within a microbial niche can be used as a precursor for the synthesis of valuable compounds such as alcohols or long-chain fatty acids. A summary of the involved acetate electrosynthesis has been represented as follows: CO2 + 7H+ + 8e
! 2H2 O + CHCOO



CO2 + 4H2 ! 2H2 O + CH3 COO + H

+

(14.4) (14.5)

Ethanol is also an MES product that can be produced by CO2 fixation through the Wood-Ljungdahl pathway conducted by anaerobic, acetogenic bacteria [63]. The future trend would be the genetic and metabolic engineering of microorganisms toward the integration of electroactive recipient strains with BESs. For instance, bioelectrochemical conversion of CO2 to ethylene can be viable through the use of microbes that can use syngas as feedstock [64].

14.4.3 C3 biochemicals In MES, propionate (CH3CH2COOH), propanol (C3H8O), isopropanol (CH3CHOHCH3), 1,3-propanediol (C3H8O2), lactate (C3H6O3), and glycerol (C3H8O3) are known as the most common C3 bioproducts. Currently, it is known that microbial reduction of propionic acid under the catalysis of dehydrogenase produces propanol on the cathode surface. Nowadays, microbial strains have been engineered and are

357

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being utilized for better bioconversion with higher purification and selectivity [65]. For instance, the yield of propionate bioproduction from adequate CO2 has been promoted to seek high purity associated with engineering of a sophisticated strain through the deletion of branch pathways and chromosomal incorporation of heterologous L-threonine deaminase, permease, and acyl-CoA thioesterase. Moreover, the introduction of a synthetic metabolic pathway can lead to the creation of sophisticated cyanobacteria capable of producing 1,3-propanediol from CO2 [66,67]. The use of Geobacter sulfurreducens as the biocatalyst of CO2 conversion into glycerol would be another example of MES widening [25].

14.4.4 C4 biochemicals The success of bioelectrochemical catalysis depends on the elongation of the product carbon chain [12]. There is a general agreement that medium-chain bioproducts are easy to catalyze and demands sophisticated microorganisms [68]. Butyrate (CH3(CH2)2COOH), butanol (CH3 (CH2)3OH), isobutyrate ((CH3)2CHCOOH), and succinate ([CH2COOH]2) are examples of bioelectrochemical products obtained from CO2 conversion. WoodLjungdahl pathway is susceptible to being used to direct production of butyrate from CO2 integrated with acetyl-CoA reduction [69]. Integration of butyrate production genes into the host chromosome can favor its production from CO2 [70]. Furthermore, the variables of feeding type and retention time should be designed to achieve high selectivity of butyrate over other by-products such as acetate [71]. It is also known that providing large surface areas of the electrode materials is another crucial factor to increase the production rate of biochemicals [72]. Its function is to induce direct electron transfer pathway within the adjacent enriched biofilm.

14.5 Requirements for MES operation It is important to develop less expensive CO2 capture, storage, and transportation techniques that can be implemented in the MES industry. The development of these techniques would circumvent the problems of operational costs and reduce carbon footprints [73]. The extensive amount of CO2 emission from power plants fueled by coal, peat, or crude oil combustion makes it necessary to create integrated MES systems at industrial sites. Furthermore, great progress could be the design of flexible MES plants that promise advantages in adaptability to gas volume and gas composition. Another advantage of this technique is the possibility of excess heat recovery in power plants that can be further utilized for warming up the MES reactors. Another goal is to alleviate microbial contamination and induce production kinetics under thermophilic conditions. However, this reduces the gas solubility and, therefore, restricts available carbon and energy sources.

CO2 reduction and MES

Moreover, waste gas often contains impurities and toxic components such as CO, O2, SOx, NOx, HCl, and particulate ash that necessitate the pretreatment process prior to fueling MES reactors [74,75]. Such contaminants cause suppression of Coulombic efficiency through either hindering MES microbial communities or diverging electrons toward electrochemical side reactions [76,77]. It is worth noting that flue gas released from natural gas processing and alcohol fermentation has the characteristic of significant CO2 purity (96%–99%) and prevents the pretreatment step. Reduction of gas waste impurities below the tolerance limit of the microorganisms has been preferred as a more economic strategy compared with the production of pure CO2 stream. The use of lime or limestone mediated desulfurization, catalytic NOx reduction, and CO2/O2 separation via adsorption or membrane separation help to mitigate flue gas impurity [78,79]. The need for renewable, low-cost energy source is another pivotal factor in sustainable MES operation. MES can be supplied by either renewable electric energy obtained from solar, wind, geothermal, hydro, and biomasses or the power resulting from solar-toproduct conversion using photoactive electrodes. The former provides low-cost excess power [80]. However, fluctuating electric supply can impact the robust MES operation [81]. The use of energy storage systems such as batteries and dedicated electronic circuits can circumvent the problem through the efficient recovery of excessive energy and providing a constant flow. However, there have been various problems with the use of these storage technologies. One of these problems is the charging of energy storage devices. In order to overcoming the problem, MFC systems can be incorporated for charging energy storage devices [82]. On the other hand, photoelectrochemical cells have high potential in providing sufficient currents (up to 5.8 mA cm
2) which are necessary to conduct electro-chemical CO2 reduction [83]. These biological networks consist of a photoanode connected to an enzymatic/microbial biocathode [84]. However, in contrast to microbial biocathodes, the application of enzymatic electrodes is limited owing to high production and operation costs. It was found that the addition of adsorbing sensitizers or bio- and photocatalysts such as TiO2 nanowires into photoanode has a significant effect on the rate of biochemical production [85]. Another level of action could be the development of integrated MES systems for simultaneous carbon recycling and wastewater treatment, which in turn result in the decrement of MES energy demand and elimination of current environmental challenges. A bio-cathode is connected to a bio-anode that is fed with synthetic wastewater. The development of these integrations allows the possibility of capturing CO2 produced from wastewater treatment at bio-cathode with maximum effectiveness to prevent carbon footprint [86]. Additionally, the capacity of photo-catalytic oxidation can be utilized for selective degradation of target pollutants such as alkenes [87]. Further research is required to investigate the viability of the integrated wastewater treatment system.

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Any imbalance in MES charge distribution can eventuate in the shift of microbial communities and subsequently the involved metabolic pathways [88]. Therefore, the uniformity of charge distribution is also very important within MES electrodes, and it could be controlled by using smart electronic designs such as power management systems (PMS). The application of PMS is based on the detection of overvoltage and overloading states and subsequent switching off the connection [89]. This reduces contact stress in battery units, regulates voltage or current delivery, and results in a sustained chemical output. Bio-electrodes provide a conducive solid surface that is going to be colonized by electroactive microorganisms and thereby allow CO2 reduction to different kinds of bio-products [90]. In order to solve the issue that comes from the MES productivity, electrodes should possess a biocompatible surface, good stability, high hydrophilicity, excellent electron transfer, and low CO2 mass transfer resistance [91,92]. Some of the interesting types of bio-electrodes recently designed are carbonaceous structures, metallic materials, and carbon-metallic designs. Carbonaceous materials are highly porous structures used for enhancing MES productivity. The application of this type of bio-electrode shows the excellent microbial attachment and good chemical stability. It was shown that carbon-based materials are cost-effective and commercially available and favor higher current output [93,94]. Furthermore, surface-modified carbonaceous materials are the next generation of carbon-based electrodes; they are distinguished depending on the nature of the substances that are used to treat. Having more conductivity not only promotes the electron transfer rate but also allows to induce electrosynthesis rate of by-products from CO2 [95]. Metallic electrodes are prevalently fabricated from stainless steel [96,97], iron [98], platinum [99], palladium, gold [100], molybdenum [101], rubidium [102], and nickel [103], and possess higher mechanical roughness and conductivity compared with those of carbonaceous electrodes. These types of electrodes have poor corrosion resistance since electrochemical electrolyte solution can mediate metal leaching, this is why metallic electrodes are toxic to microorganism growth. In addition, metal-based electrodes have a low level of specific surface area and impose higher costs. Previous studies demonstrate that by adding carbon materials to pure metals the physiochemical characteristics of bio-electrodes would be optimized. Carbon electrodes are modified with metal or metal oxide nanoparticles in order to maximise the specific surface area and electro-chemical function of the electrodes which enhance bioelectrochemical CO2 capture microbial electrosynthesis of by-products such as volatile fatty acids [62]. Alternatively, metallic structures can be coated with carbonaceous materials to promote conductivity, biocompatibility, and mechanical strength of the bio-electrode [96].

CO2 reduction and MES

14.6 MES scale-up Nowadays, researchers study many functionalities to promote lab-scale MES cells into large-scale configurations [104,105]. Some of these improvements made to the electrode surface/volume, membrane surface, and the distance between the anode and the cathode are based on Ohmic losses and overpotential. The principle strategies to alleviate Ohmic losses on large scale are increment of electrode surface/volume capacity, enhancement of membrane surface, development of efficient hydrodynamics, decrement of the distance between the anode and the cathode, and use of stackable reactor design. Design of compact and stackable reactor avoids system overpotential and facilitates MES maintenance [106,107]. For instance, multichamber reactors with flat [108,109] or tubular [110,111] configurations can achieve optimized electrode surface/volume ratio [109]. However, the microbial function can somehow hamper the yield of MES cells on a large scale [112,113]. Parallel connected MES stacks have superior performance than those of series connections [114]. Series connections suffer toxic effect on contaminates that can be attenuated in parallel connected stacks. In addition, polarity reversal and substrate cross-conduction effect are frequently reported issues of series stacks [114,115]. Studies indicate that by developing hybrid configurations of both parallel and series connections MES characteristics improve. The number of parallel lines is a function of reaction rates, while the length of the series connections is determined through required CO2 removal efficiency. The feasibility of flue gas delivery to the MES reactor can be done either indirectly through feeding dissolved bicarbonate or directly through gas feeding (Figs. 14.3 and 14.4; Table 14.3). Gas spargers and gas diffusion electrodes are prevalently used to fulfill the direct flu gas delivery. Feeding the MES reactor with a bicarbonate-containing stream promotes carbon conversion efficiency, however, requires additional costs and larger space dedicated to the CO2 solubilization procedure [135]. On the other hand, electrode design and gas control (composition and pressure) are critical factors in using the direct gas feeding method. In this way, electrodes with a high specific active surface or gas diffusion electrodes (GDEs) can be used for inducing contact between the CO2 and the biocatalysts, resulting in a high CO2 conversion rate [51,136]. GDEs are fabricated by hydrophobic polymeric gas diffusion layers integrated with catalytic films [137]. Development of a three-phase (gas-liquid-solid) interphase is important for maximizing CO2 availability necessary for biofilm function [135]. Having a low growth rate of autotrophic microorganisms and operating with pure catholyte are the key factors that minimize the possibility of GDEs’ fouling in MES. Hence, GDEs can be potential candidates for largescale MES designs.

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Fig. 14.3 Flue gas delivery to the MES reactor through directing diffusing (A) and pressurized diffusing (B).

Moreover, the propitious separator is needed in order to eliminate Ohmic drops that may be caused by limited proton transfer or O2 diffusion toward the cathodic chamber [138]. Using membrane-less MES systems also prevents Ohmic drops. However, oxygen diffusion toward the cathode chamber should be controlled [139]. Gas sparking from the bottom of MES reactor is a technique that can omit the oxygen diffusion problem in membrane-less designs [52]. All in all, a higher CO2 conversion rate is reported for membrane-containing reactors [47,140] and further studies are required for scaling up MES setups with membranes [141].

CO2 reduction and MES

Fig. 14.4 Flue gas delivery to the MES reactor through diffusing electrode.

Table 14.3 Different strategies of flue gas delivery to MES reactor previously reported in literature. CO2 source

CO2 (2.5%, 0.4 vvm) CO2 5% Syngas NaHCO3 50 mM CO2 (1%, 10 vvm) NaHCO3 50 mM NaHCO3 50 mM NaHCO3 50 mM NaHCO3 100 mM CO2 1% CO2 (5%, 4.8 L h
1), NaHCO3 0.5 M

Cathodic microorganism

Scenedesmus obliquus Synechocystis sp. PCC6803 Clostridium ljungdahlii Synechococcus elongates PCC7942 Synechococcus elongates PCC7942 Synechococcus PCC7942 Synechocystis sp. PCC6803 Synechococcus elongates PCC7942 Synechococcus elongates Synechocystis sp. PC6803 Synechococcus elongates

Product

Production rate

Ref.

Ethanol

8.55 g L
1

[116]

Ethanol

212 mg L
1 h
1

[117]

Ethanol

0.301 g L
1 h
1

[118]

1,3-Propanediol

150 mg L
1

[119]

1,3-Propanediol

1.22 g L
1

[66]

1-Butanol

29.9 mg L
1

[120]

Isobutanol

298 mg L
1

[121]

2-Methyl butanol

20 g L
1 day
1

[122]

2,3-Butanediol

3000 mg L
1

[123]

1-Octanol

905 mg L
1

[124]

Isoprene

4.26 mg L
1 h
1

[125] Continued

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Table 14.3 Different strategies of flue gas delivery to MES reactor previously reported in literature—cont’d CO2 source

CO2 1% CO2 1% CO2 5% CO2 5% NaHCO3 (1–4 g L
1) CO2 NaHCO3 50 mM CO2 CO2 (1%, 30–50 mL min
1) CO2 1%

Cathodic microorganism

Product

Production rate
1

Ref.

Synechococcus sp. PCC7002 Synechococcus sp. PCC7002 Synechocystis sp. PCC6803 Synechocystis sp. PCC6803 Mixed culture

α-Bisabolene

0.6 mg L

Limonene

4 mg L
1

[126]

Ethylene

9739 μL L
1 h
1

[127]

Heptadecane

26 mg L
1

[128]

Acetate

685 g
1 m
2 day
1

[129]

Acetobacterium woodi Synechococcus elongates PCC7942 Citrobacter amalonaticus Synechocystis sp. PCC6803 Synechococcus elongates PCC7942

Acetate

50 g L
1

[130]

Succinate

430 mg L
1

[131]

Succinate

0.36 g L
1 h
1

[132]

Succinate, lactate Lactate

141 mg L
1

[133]

13.7 mmol L
1

[134]

[126]

14.7 Conclusions This chapter represents a review of the art of MES technology, specifically in the converting of CO2-containing gas into various value-added bioproducts. MES stacks were described in terms of their applications with an increased focus on avoiding overpotential and facilitating MES maintenance. The main limitations of MES application are the choice of electrode materials, microbial communities, and the development of less expensive CO2 capture, storage, and transportation techniques that can be implemented in the MES industry. The use of GDEs is a more convenient strategy to fulfill the direct flu gas delivery into MES designs. These structures are designed by hydrophobic polymeric gas diffusion layers integrated with catalytic films. The ideal CO2 GDE will incorporate a three-phase (gas-liquid-solid) interphase to enhance CO2 availability. Overall, future study is ongoing to advance MES technology further to close the gap between CO2 bioelectrochemical conversion technology and industrial application of MES systems.

CO2 reduction and MES

References [1] M. Omidi, M. Mashkour, J.K. Biswas, V.K. Garlapati, L. Singh, M. Rahimnejad, D. Pant, From electricity to products: recent updates on microbial electrosynthesis (MES), Top. Catal. (2021) 1–18. [2] J. Qiao, Y. Liu, F. Hong, J. Zhang, A review of catalysts for the electroreduction of carbon dioxide to produce low-carbon fuels, Chem. Soc. Rev. 43 (2) (2014) 631–675. [3] S. Das, P. Chatterjee, M. Ghangrekar, Increasing methane content in biogas and simultaneous value added product recovery using microbial electrosynthesis, Water Sci. Technol. 77 (5) (2018) 1293–1302. [4] N. Chu, Q. Liang, Y. Jiang, R.J. Zeng, Microbial electrochemical platform for the production of renewable fuels and chemicals, Biosens. Bioelectron. 150 (2020), 111922. [5] J.M. Lainez-Aguirre, M. Perez-Fortes, L. Puigjaner, Economic evaluation of bio-based supply chains with CO2 capture and utilisation, Comput. Chem. Eng. 102 (2017) 213–225. [6] M. Anwar, A. Fayyaz, N. Sohail, M. Khokhar, M. Baqar, A. Yasar, K. Rasool, A. Nazir, M. Raja, M. Rehan, CO2 utilization: turning greenhouse gas into fuels and valuable products, J. Environ. Manage. 260 (2020), 110059. [7] B. Zhao, W. Tao, M. Zhong, Y. Su, G. Cui, Process, performance and modeling of CO2 capture by chemical absorption using high gravity: a review, Renew. Sustain. Energy Rev. 65 (2016) 44–56. [8] P.A. Webley, Adsorption technology for CO2 separation and capture: a perspective, Adsorption 20 (2) (2014) 225–231. [9] Z. Fang, J. Zhou, X. Zhou, M.A. Koffas, Abiotic-biotic hybrid for CO2 biomethanation: from electrochemical to photochemical process, Sci. Total Environ. 791 (2021), 148288. [10] A.S.R. Machado, M.N. da Ponte, CO2 capture and electrochemical conversion, current opinion in green and sustainable, Chemistry 11 (2018) 86–90. [11] R.A. Tufa, D. Chanda, M. Ma, D. Aili, T.B. Demissie, J. Vaes, Q. Li, S. Liu, D. Pant, Towards highly efficient electrochemical CO2 reduction: cell designs, membranes and electrocatalysts, Appl. Energy 277 (2020), 115557. [12] X. Christodoulou, T. Okoroafor, S. Parry, S.B. Velasquez-Orta, The use of carbon dioxide in microbial electrosynthesis: advancements, sustainability and economic feasibility, J. CO₂ Util. 18 (2017) 390–399. [13] F. Mayer, F. Enzmann, A.M. Lopez, D. Holtmann, Performance of different methanogenic species for the microbial electrosynthesis of methane from carbon dioxide, Bioresour. Technol. 289 (2019), 121706. [14] J. Sadhukhan, J.R. Lloyd, K. Scott, G.C. Premier, H.Y. Eileen, T. Curtis, I.M. Head, A critical review of integration analysis of microbial electrosynthesis (MES) systems with waste biorefineries for the production of biofuel and chemical from reuse of CO2, Renew. Sustain. Energy Rev. 56 (2016) 116–132. [15] S. Srikanth, Y. Alvarez-Gallego, K. Vanbroekhoven, D. Pant, Enzymatic electrosynthesis of formic acid through carbon dioxide reduction in a bioelectrochemical system: effect of immobilization and carbonic anhydrase addition, ChemPhysChem 18 (22) (2017) 3174–3181. [16] G. Dragone, B.D. Fernandes, A.P. Abreu, A.A. Vicente, J.A. Teixeira, Nutrient limitation as a strategy for increasing starch accumulation in microalgae, Appl. Energy 88 (10) (2011) 3331–3335. [17] B.S. Thapa, T. Kim, S. Pandit, Y.E. Song, Y.P. Afsharian, M. Rahimnejad, J.R. Kim, S.-E. Oh, Overview of electroactive microorganisms and electron transfer mechanisms in microbial electrochemistry, Bioresour. Technol. (2021), 126579. [18] A.R. Rahmani, N. Navidjouy, M. Rahimnejad, D. Nematollahi, M. Leili, M.R. Samarghandi, S. Alizadeh, Application of the eco-friendly bio-anode for ammonium removal and power generation from wastewater in bio-electrochemical systems, J. Clean. Prod. 243 (2020), 118589. [19] J.M. Myers, C.R. Myers, Role for outer membrane cytochromes OmcA and OmcB of Shewanella putrefaciens MR-1 in reduction of manganese dioxide, Appl. Environ. Microbiol. 67 (1) (2001) 260–269. [20] G. Reguera, K.D. McCarthy, T. Mehta, J.S. Nicoll, M.T. Tuominen, D.R. Lovley, Extracellular electron transfer via microbial nanowires, Nature 435 (7045) (2005) 1098–1101. [21] J. Zhao, F. Li, Y. Cao, X. Zhang, T. Chen, H. Song, Z. Wang, Microbial extracellular electron transfer and strategies for engineering electroactive microorganisms, Biotechnol. Adv. 53 (2021), 107682.

365

366

Biological fuel cells

[22] H. Von Canstein, J. Ogawa, S. Shimizu, J.R. Lloyd, Secretion of flavins by Shewanella species and their role in extracellular electron transfer, Appl. Environ. Microbiol. 74 (3) (2008) 615–623. [23] N. Boon, P. Aelterman, P. Clauwaert, L. De Schamphelaire, L. Vanhaecke, K. De Maeyer, M. H€ ofte, W. Verstraete, K. Rabaey, Metabolites produced by Pseudomonas sp. enable a Gram-positive bacterium to achieve extracellular electron transfer, Appl. Microbiol. Biotechnol. 77 (5) (2008) 1119–1129. [24] U. Schr€ oder, A basic introduction into microbial fuel cells and microbial electrocatalysis, ChemTexts 4 (4) (2018) 1–6. [25] K.B. Gregory, D.R. Bond, D.R. Lovley, Graphite electrodes as electron donors for anaerobic respiration, Environ. Microbiol. 6 (6) (2004) 596–604. [26] K.P. Nevin, S.A. Hensley, A.E. Franks, Z.M. Summers, J. Ou, T.L. Woodard, O.L. SnoeyenbosWest, D.R. Lovley, Electrosynthesis of organic compounds from carbon dioxide is catalyzed by a diversity of acetogenic microorganisms, Appl. Environ. Microbiol. 77 (9) (2011) 2882–2886. [27] E. Blanchet, F. Duquenne, Y. Rafrafi, L. Etcheverry, B. Erable, A. Bergel, Importance of the hydrogen route in up-scaling electrosynthesis for microbial CO 2 reduction, Energ. Environ. Sci. 8 (12) (2015) 3731–3744. [28] R. Ganigue, S. Puig, P. Batlle-Vilanova, M.D. Balaguer, J. Colprim, Microbial electrosynthesis of butyrate from carbon dioxide, Chem. Commun. 51 (15) (2015) 3235–3238. [29] L. Jourdin, Y. Lu, V. Flexer, J. Keller, S. Freguia, Biologically induced hydrogen production drives high rate/high efficiency microbial electrosynthesis of acetate from carbon dioxide, ChemElectroChem 3 (4) (2016) 581–591. [30] H. Li, P.H. Opgenorth, D.G. Wernick, S. Rogers, T.-Y. Wu, W. Higashide, P. Malati, Y.-X. Huo, K.M. Cho, J.C. Liao, Integrated electromicrobial conversion of CO2 to higher alcohols, Science 335 (6076) (2012) 1596. [31] J. Song, Y. Kim, M. Lim, H. Lee, J.I. Lee, W. Shin, Microbes as electrochemical CO2 conversion catalysts, ChemSusChem 4 (5) (2011) 587–590. [32] S. Li, Y.E. Song, J. Baek, H.S. Im, M. Sakuntala, M. Kim, C. Park, B. Min, J.R. Kim, Bioelectrosynthetic conversion of CO2 using different redox mediators: electron and carbon balances in a bioelectrochemical system, Energies 13 (10) (2020) 2572. [33] M. Rahimnejad, G. Najafpour, Microbial fuel cells: a new source of power, Biochem. Eng. Biotechnol. (2011) 1–31. [34] M. Irfan, Y. Bai, L. Zhou, M. Kazmi, S. Yuan, S.M. Mbadinga, S.-Z. Yang, J.F. Liu, W. Sand, J.-D. Gu, Direct microbial transformation of carbon dioxide to value-added chemicals: a comprehensive analysis and application potentials, Bioresour. Technol. 288 (2019), 121401. [35] Y. Jiang, M. Su, Y. Zhang, G. Zhan, Y. Tao, D. Li, Bioelectrochemical systems for simultaneously production of methane and acetate from carbon dioxide at relatively high rate, Int. J. Hydrogen Energy 38 (8) (2013) 3497–3502. [36] Y.P. Afsharian, M. Rahimnejad, Functional dynamics of microbial communities in bioelectrochemical systems: the importance of eco-electrogenic treatment of complex substrates, Curr. Opin. Electrochem. 31 (2022), 100816. [37] S. Fatemi, A. Ghoreyshi, G. Najafpour, M. Rahimnejad, Bioelectricity generation in mediator-less microbial fuel cell: application of pure and mixed cultures, Iran. J. Energy Environ. 3 (2) (2012). [38] A. AlSayed, A. Fergala, S. Khattab, A. ElSharkawy, A. Eldyasti, Optimization of methane biohydroxylation using waste activated sludge mixed culture of type I methanotrophs as biocatalyst, Appl. Energy 211 (2018) 755–763. [39] S.A. Patil, F. Harnisch, C. Koch, T. H€ ubschmann, I. Fetzer, A.A. Carmona-Martı´nez, S. M€ uller, U. Schr€ oder, Electroactive mixed culture derived biofilms in microbial bioelectrochemical systems: the role of pH on biofilm formation, performance and composition, Bioresour. Technol. 102 (20) (2011) 9683–9690. [40] H. Song, O. Choi, A. Pandey, Y.G. Kim, J.S. Joo, B.-I. Sang, Simultaneous production of methane and acetate by thermophilic mixed culture from carbon dioxide in bioelectrochemical system, Bioresour. Technol. 281 (2019) 474–479. [41] B. Bian, S. Bajracharya, J. Xu, D. Pant, P.E. Saikaly, Microbial electrosynthesis from CO2: challenges, opportunities and perspectives in the context of circular bioeconomy, Bioresour. Technol. 302 (2020), 122863.

CO2 reduction and MES

[42] F. Enzmann, D. Holtmann, Rational scale-up of a methane producing bioelectrochemical reactor to 50 L pilot scale, Chem. Eng. Sci. 207 (2019) 1148–1158. [43] M.C. Van Eerten-Jansen, A. Ter Heijne, T.I. Grootscholten, K.J. Steinbusch, T.H. Sleutels, H.V. Hamelers, C.J. Buisman, Bioelectrochemical production of caproate and caprylate from acetate by mixed cultures, ACS Sustain. Chem. Eng. 1 (5) (2013) 513–518. [44] C.W. Marshall, D.E. Ross, E.B. Fichot, R.S. Norman, H.D. May, Long-term operation of microbial electrosynthesis systems improves acetate production by autotrophic microbiomes, Environ. Sci. Technol. 47 (11) (2013) 6023–6029. [45] L. Jourdin, S.M. Raes, C.J. Buisman, D.P. Strik, Critical biofilm growth throughout unmodified carbon felts allows continuous bioelectrochemical chain elongation from CO2 up to caproate at high current density, Front. Energy Res. 6 (2018) 7. [46] Y. Jiang, N. Chu, D.-K. Qian, R.J. Zeng, Microbial electrochemical stimulation of caproate production from ethanol and carbon dioxide, Bioresour. Technol. 295 (2020), 122266. [47] T. Zhang, H. Nie, T.S. Bain, H. Lu, M. Cui, O.L. Snoeyenbos-West, A.E. Franks, K.P. Nevin, T.P. Russell, D.R. Lovley, Improved cathode materials for microbial electrosynthesis, Energ. Environ. Sci. 6 (1) (2013) 217–224. [48] N. Aryal, A. Halder, M. Zhang, P.R. Whelan, P.-L. Tremblay, Q. Chi, T. Zhang, Freestanding and flexible graphene papers as bioelectrochemical cathode for selective and efficient CO2 conversion, Sci. Rep. 7 (1) (2017) 1–8. [49] B. Bian, D. Shi, X. Cai, M. Hu, Q. Guo, C. Zhang, Q. Wang, A.X. Sun, J. Yang, 3D printed porous carbon anode for enhanced power generation in microbial fuel cell, Nano Energy 44 (2018) 174–180. [50] F. Kracke, A.B. Wong, K. Maegaard, J.S. Deutzmann, M.A. Hubert, C. Hahn, T.F. Jaramillo, A.M. Spormann, Robust and biocompatible catalysts for efficient hydrogen-driven microbial electrosynthesis, Commun. Chem. 2 (1) (2019) 1–9. [51] I. Vassilev, P.A. Hernandez, P. Batlle-Vilanova, S. Freguia, J.O. Kr€ omer, J.R. Keller, P. Ledezma, B. Virdis, Microbial electrosynthesis of isobutyric, butyric, caproic acids, and corresponding alcohols from carbon dioxide, ACS Sustain. Chem. Eng. 6 (7) (2018) 8485–8493. [52] C.G. Giddings, K.P. Nevin, T. Woodward, D.R. Lovley, C.S. Butler, Simplifying microbial electrosynthesis reactor design, Front. Microbiol. 6 (2015) 468. [53] Y. Nakasugi, M. Himeno, H. Kobayashi, M. Ikarashi, H. Maeda, K. Sato, Experimental and mathematical analyses of bio-electrochemical conversion of carbon dioxide to methane, Energy Procedia 114 (2017) 7133–7140. [54] H.-Y. Yang, Y.-X. Wang, C.-S. He, Y. Qin, W.-Q. Li, W.-H. Li, Y. Mu, Redox mediatormodified biocathode enables highly efficient microbial electro-synthesis of methane from carbon dioxide, Appl. Energy 274 (2020), 115292. [55] A. Van Amstel, Methane. A review, J. Integr. Environ. Sci. 9 (sup1) (2012) 5–30. [56] M. Zeppilli, H. Chouchane, L. Scardigno, M. Mahjoubi, M. Gacitua, R. Askri, A. Cherif, M. Majone, Bioelectrochemical vs hydrogenophilic approach for CO2 reduction into methane and acetate, Chem. Eng. J. 396 (2020), 125243. [57] L. Yu, Y. Yuan, J. Tang, S. Zhou, Thermophilic Moorella thermoautotrophica-immobilized cathode enhanced microbial electrosynthesis of acetate and formate from CO2, Bioelectrochemistry 117 (2017) 23–28. [58] Q.A.T. Le, H.G. Kim, Y.H. Kim, Electrochemical synthesis of formic acid from CO2 catalyzed by Shewanella oneidensis MR-1 whole-cell biocatalyst, Enzyme Microb. Technol. 116 (2018) 1–5. [59] J. Luo, A.S. Meyer, R.V. Mateiu, M. Pinelo, Cascade catalysis in membranes with enzyme immobilization for multi-enzymatic conversion of CO2 to methanol, N. Biotechnol. 32 (3) (2015) 319–327. [60] Y. Jiang, R.J. Zeng, Expanding the product spectrum of value added chemicals in microbial electrosynthesis through integrated process design—a review, Bioresour. Technol. 269 (2018) 503–512. [61] P. Batlle-Vilanova, S. Puig, R. Gonzalez-Olmos, M.D. Balaguer, J. Colprim, Continuous acetate production through microbial electrosynthesis from CO2 with microbial mixed culture, J. Chem. Technol. Biotechnol. 91 (4) (2016) 921–927. [62] C.C. Viggi, S. Colantoni, F. Falzetti, A. Bacaloni, D. Montecchio, F. Aulenta, Conductive magnetite nanoparticles enhance the microbial electrosynthesis of acetate from CO2 while diverting electrons away from methanogenesis, Fuel Cells 20 (1) (2020) 98–106.

367

368

Biological fuel cells

[63] H. Liu, T. Song, K. Fei, H. Wang, J. Xie, Microbial electrosynthesis of organic chemicals from CO2 by Clostridium scatologenes ATCC 25775T, Bioresour. Bioprocess. 5 (1) (2018) 1–10. [64] K. Verbeeck, S. Gildemyn, K. Rabaey, Membrane electrolysis assisted gas fermentation for enhanced acetic acid production, Front. Energy Res. (2018) 88. [65] M. Ghasemi, G. Najafpour, M. Rahimnejad, P.A. Beigi, M. Sedighi, B. Hashemiyeh, Effect of different media on production of lactic acid from whey by Lactobacillus bulgaricus, Afr. J. Biotechnol. 8 (1) (2009). [66] Y. Hirokawa, Y. Maki, T. Hanai, Improvement of 1, 3-propanediol production using an engineered cyanobacterium, Synechococcus elongatus by optimization of the gene expression level of a synthetic metabolic pathway and production conditions, Metab. Eng. 39 (2017) 192–199. [67] M. Mohammadi, G. Najafpour, M. Asadi, M. Rahimnejad, S. Najafpour, M. Pazouki, Production of organic acids in an immobilized cell reactor using Propionibacterium acidi-propionici, Afr. J. Biotechnol. 7 (18) (2008). [68] M. Mohammadi, G. Najafpour, M. Asadi, M. Rahimnejad, S. Najafpour, M. Pazouki, A study of acetic and propionic acids from the hydrolyzed sugars obtained from lignocellulosic wastes, Int. J. Histol. Cytol. 5 (3) (2018) 396–402. [69] X. Zhu, X. Tan, Metalloproteins/metalloenzymes for the synthesis of acetyl-CoA in the WoodLjungdahl pathway, Sci. China Ser. B: Chem. 52 (12) (2009) 2071–2082. [70] T. Ueki, K.P. Nevin, T.L. Woodard, D.R. Lovley, Converting carbon dioxide to butyrate with an engineered strain of Clostridium ljungdahlii, MBio 5 (5) (2014), e01636–14. [71] L. Jourdin, M. Winkelhorst, B. Rawls, C.J. Buisman, D.P. Strik, Enhanced selectivity to butyrate and caproate above acetate in continuous bioelectrochemical chain elongation from CO2: steering with CO2 loading rate and hydraulic retention time, Bioresour. Technol. Rep. 7 (2019), 100284. [72] D. Thatikayala, B. Min, Copper ferrite supported reduced graphene oxide as cathode materials to enhance microbial electrosynthesis of volatile fatty acids from CO2, Sci. Total Environ. 768 (2021), 144477. [73] D. Leeson, N. Mac Dowell, N. Shah, C. Petit, P. Fennell, A techno-economic analysis and systematic review of carbon capture and storage (CCS) applied to the iron and steel, cement, oil refining and pulp and paper industries, as well as other high purity sources, Int. J. Greenh. Gas Control 61 (2017) 71–84. [74] I. Aouini, A. Ledoux, L. Estel, S. Mary, Pilot plant studies for CO2 capture from waste incinerator flue gas using MEA based solvent, Oil Gas Sci. Technol. 69 (6) (2014) 1091–1104. [75] T. Pihu, A. Konist, D. Neshumayev, L. Loo, A. Molodtsov, A. Valtsev, Full-scale tests on the co-firing of peat and oil shale in an oil shale fired circulating fluidized bed boiler, Oil Shale 34 (3) (2017) 250–263. [76] F.M. McRobb, V. Sahagu´n, I. Kufareva, R. Abagyan, In silico analysis of the conservation of human toxicity and endocrine disruption targets in aquatic species, Environ. Sci. Technol. 48 (3) (2014) 1964–1972. [77] M. Rahimnejad, N. Mokhtarian, G. Najafpour, A.A. Ghoreyshi, W.R.W. Dahud, Effective parameters on performance of microbial fuel cell, in: 2009 Second International Conference on Environmental and Computer Science, IEEE, 2009, pp. 411–415. [78] Y. Sun, E. Zwoli nska, A.G. Chmielewski, Abatement technologies for high concentrations of NOx and SO2 removal from exhaust gases: a review, Crit. Rev. Environ. Sci. Technol. 46 (2) (2016) 119–142. [79] T. Wilberforce, A. Baroutaji, B. Soudan, A.H. Al-Alami, A.G. Olabi, Outlook of carbon capture technology and challenges, Sci. Total Environ. 657 (2019) 56–72. [80] S.A. Patil, J.B. Arends, I. Vanwonterghem, J. Van Meerbergen, K. Guo, G.W. Tyson, K. Rabaey, Selective enrichment establishes a stable performing community for microbial electrosynthesis of acetate from CO2, Environ. Sci. Technol. 49 (14) (2015) 8833–8843. [81] R. Mateos, A. Escapa, M.I. San-Martı´n, H. De Wever, A. Sotres, D. Pant, Long-term open circuit microbial electrosynthesis system promotes methanogenesis, J. Energy Chem. 41 (2020) 3–6. [82] M.C. Hatzell, Y. Kim, B.E. Logan, Powering microbial electrolysis cells by capacitor circuits charged using microbial fuel cell, J. Power Sources 229 (2013) 198–202. [83] J.T. Kirner, R.G. Finke, Water-oxidation photoanodes using organic light-harvesting materials: a review, J. Mater. Chem. A 5 (37) (2017) 19560–19592.

CO2 reduction and MES

[84] S.Y. Lee, S.Y. Lim, D. Seo, J.Y. Lee, T.D. Chung, Light-driven highly selective conversion of CO2 to formate by electrosynthesized enzyme/cofactor thin film electrode, Adv. Energy Mater. 6 (11) (2016) 1502207. [85] A. Prevoteau, J.M. Carvajal-Arroyo, R. Ganigue, K. Rabaey, Microbial electrosynthesis from CO2: forever a promise? Curr. Opin. Biotechnol. 62 (2020) 48–57. [86] N.J. Vickers, Animal communication: when i’m calling you, will you answer too? Curr. Biol. 27 (14) (2017) R713–R715. [87] P. Farra`s, C. Di Giovanni, J.N. Clifford, P. Garrido-Barros, E. Palomares, A. Llobet, Light driven styrene epoxidation and hydrogen generation using H2O as an oxygen source in a photoelectrosynthesis cell, Green Chem. 18 (1) (2016) 255–260. [88] C. Sa´nchez, P. Dessı`, M. Duffy, P.N. Lens, Microbial electrochemical technologies: electronic circuitry and characterization tools, Biosens. Bioelectron. 150 (2020), 111884. [89] D.-I. Stroe, A. Zaharof, F. Iov, Power and energy management with battery storage for a hybrid residential PV-wind system–a case study for Denmark, Energy Procedia 155 (2018) 464–477. [90] T.R. Garrett, M. Bhakoo, Z. Zhang, Bacterial adhesion and biofilms on surfaces, Prog. Nat. Sci. 18 (9) (2008) 1049–1056. [91] M.T. Noori, M.T. Vu, R.B. Ali, B. Min, Recent advances in cathode materials and configurations for upgrading methane in bioelectrochemical systems integrated with anaerobic digestion, Chem. Eng. J. 392 (2020), 123689. [92] B.E. Logan, B. Hamelers, R. Rozendal, U. Schr€ oder, J. Keller, S. Freguia, P. Aelterman, W. Verstraete, K. Rabaey, Microbial fuel cells: methodology and technology, Environ. Sci. Technol. 40 (17) (2006) 5181–5192. [93] J. Hui, X. Jiang, H. Xie, D. Chen, J. Shen, X. Sun, W. Han, J. Li, L. Wang, Laccase-catalyzed electrochemical fabrication of polyaniline/graphene oxide composite onto graphite felt electrode and its application in bioelectrochemical system, Electrochim. Acta 190 (2016) 16–24. [94] X. Jiang, S. Lou, D. Chen, J. Shen, W. Han, X. Sun, J. Li, L. Wang, Fabrication of polyaniline/graphene oxide composite for graphite felt electrode modification and its performance in the bioelectrochemical system, J. Electroanal. Chem. 744 (2015) 95–100. [95] N. Aryal, A. Halder, P.-L. Tremblay, Q. Chi, T. Zhang, Enhanced microbial electrosynthesis with three-dimensional graphene functionalized cathodes fabricated via solvothermal synthesis, Electrochim. Acta 217 (2016) 117–122. [96] D.-C. Xu, S.-Y. Zhai, H.-Y. Cheng, A. Guadie, H.-C. Wang, J.-L. Han, C.-Y. Liu, A.-J. Wang, Wire-drawing process with graphite lubricant as an industrializable approach to prepare graphite coated stainless-steel anode for bioelectrochemical systems, Environ. Res. 191 (2020), 110093. [97] S. Bajracharya, A. ter Heijne, X.D. Benetton, K. Vanbroekhoven, C.J. Buisman, D.P. Strik, D. Pant, Carbon dioxide reduction by mixed and pure cultures in microbial electrosynthesis using an assembly of graphite felt and stainless steel as a cathode, Bioresour. Technol. 195 (2015) 14–24. [98] C.M. Dykstra, S.G. Pavlostathis, Zero-valent iron enhances biocathodic carbon dioxide reduction to methane, Environ. Sci. Technol. 51 (21) (2017) 12956–12964. [99] A. Nandy, M. Sharma, S.V. Venkatesan, N. Taylor, L. Gieg, V. Thangadurai, Comparative evaluation of coated and non-coated carbon electrodes in a microbial fuel cell for treatment of municipal sludge, Energies 12 (6) (2019) 1034. [100] M. Sun, F. Zhang, Z.-H. Tong, G.-P. Sheng, Y.-Z. Chen, Y. Zhao, Y.-P. Chen, S.-Y. Zhou, G. Liu, Y.-C. Tian, A gold-sputtered carbon paper as an anode for improved electricity generation from a microbial fuel cell inoculated with Shewanella oneidensis MR-1, Biosens. Bioelectron. 26 (2) (2010) 338–343. [101] M. Siegert, M.D. Yates, D.F. Call, X. Zhu, A. Spormann, B.E. Logan, Comparison of nonprecious metal cathode materials for methane production by electromethanogenesis, ACS Sustain. Chem. Eng. 2 (4) (2014) 910–917. [102] S. Das, S. Das, M. Ghangrekar, Application of TiO2 and Rh as cathode catalyst to boost the microbial electrosynthesis of organic compounds through CO2 sequestration, Process Biochem. 101 (2021) 237–246. [103] M.F. Alqahtani, K.P. Katuri, S. Bajracharya, Y. Yu, Z. Lai, P.E. Saikaly, Porous hollow fiber nickel electrodes for effective supply and reduction of carbon dioxide to methane through microbial electrosynthesis, Adv. Funct. Mater. 28 (43) (2018) 1804860.

369

370

Biological fuel cells

[104] J. Gavilanes, C.N. Reddy, B. Min, Microbial electrosynthesis of bioalcohols through reduction of high concentrations of volatile fatty acids, Energy Fuel 33 (5) (2019) 4264–4271. [105] G. Mohanakrishna, I.M.A. Reesh, K. Vanbroekhoven, D. Pant, Microbial electrosynthesis feasibility evaluation at high bicarbonate concentrations with enriched homoacetogenic biocathode, Sci. Total Environ. 715 (2020), 137003. [106] R. Rossi, D. Jones, J. Myung, E. Zikmund, W. Yang, Y.A. Gallego, D. Pant, P.J. Evans, M.A. Page, D.M. Cropek, Evaluating a multi-panel air cathode through electrochemical and biotic tests, Water Res. 148 (2019) 51–59. [107] J. Greenman, I.A. Ieropoulos, Allometric scaling of microbial fuel cells and stacks: the lifeform case for scale-up, J. Power Sources 356 (2017) 365–370. [108] S. Bajracharya, R. Yuliasni, K. Vanbroekhoven, C.J. Buisman, D.P. Strik, D. Pant, Long-term operation of microbial electrosynthesis cell reducing CO2 to multi-carbon chemicals with a mixed culture avoiding methanogenesis, Bioelectrochemistry 113 (2017) 26–34. [109] S. Srikanth, D. Singh, K. Vanbroekhoven, D. Pant, M. Kumar, S. Puri, S. Ramakumar, Electrobiocatalytic conversion of carbon dioxide to alcohols using gas diffusion electrode, Bioresour. Technol. 265 (2018) 45–51. [110] R. Blasco-Go´mez, S. Ramio´-Pujol, L. Ban˜eras, J. Colprim, M.D. Balaguer, S. Puig, Unravelling the factors that influence the bio-electrorecycling of carbon dioxide towards biofuels, Green Chem. 21 (3) (2019) 684–691. [111] T.P. Sciarria, P. Batlle-Vilanova, B. Colombo, B. Scaglia, M.D. Balaguer, J. Colprim, S. Puig, F. Adani, Bio-electrorecycling of carbon dioxide into bioplastics, Green Chem. 20 (17) (2018) 4058–4066. [112] T. Haas, R. Krause, R. Weber, M. Demler, G. Schmid, Technical photosynthesis involving CO2 electrolysis and fermentation, Nat. Catal. 1 (1) (2018) 32–39. [113] Z. Yin, H. Peng, X. Wei, H. Zhou, J. Gong, M. Huai, L. Xiao, G. Wang, J. Lu, L. Zhuang, An alkaline polymer electrolyte CO2 electrolyzer operated with pure water, Energ. Environ. Sci. 12 (8) (2019) 2455–2462. [114] A. Gurung, S.-E. Oh, The performance of serially and parallelly connected microbial fuel cells, Energy Sources, Part A 34 (17) (2012) 1591–1598. [115] L. Zhuang, Y. Zheng, S. Zhou, Y. Yuan, H. Yuan, Y. Chen, Scalable microbial fuel cell (MFC) stack for continuous real wastewater treatment, Bioresour. Technol. 106 (2012) 82–88. [116] S.-H. Ho, P.-J. Li, C.-C. Liu, J.-S. Chang, Bioprocess development on microalgae-based CO2 fixation and bioethanol production using Scenedesmus obliquus CNW-N, Bioresour. Technol. 145 (2013) 142–149. [117] Z. Gao, H. Zhao, Z. Li, X. Tan, X. Lu, Photosynthetic production of ethanol from carbon dioxide in genetically engineered cyanobacteria, Energ. Environ. Sci. 5 (12) (2012) 9857–9865. [118] M.E. Martin, H. Richter, S. Saha, L.T. Angenent, Traits of selected Clostridium strains for syngas fermentation to ethanol, Biotechnol. Bioeng. 113 (3) (2016) 531–539. [119] H. Li, J.C. Liao, Engineering a cyanobacterium as the catalyst for the photosynthetic conversion of CO 2 to 1, 2-propanediol, Microb. Cell Fact. 12 (1) (2013) 1–9. [120] E.I. Lan, J.C. Liao, ATP drives direct photosynthetic production of 1-butanol in cyanobacteria, Proc. Natl. Acad. Sci. 109 (16) (2012) 6018–6023. [121] A.M. Varman, Y. Xiao, H.B. Pakrasi, Y.J. Tang, Metabolic engineering of Synechocystis sp. strain PCC 6803 for isobutanol production, Appl. Environ. Microbiol. 79 (3) (2013) 908–914. [122] C.R. Shen, J.C. Liao, Photosynthetic production of 2-methyl-1-butanol from CO2 in cyanobacterium Synechococcus elongatus PCC7942 and characterization of the native acetohydroxyacid synthase, Energ. Environ. Sci. 5 (11) (2012) 9574–9583. [123] J.T. McEwen, M. Kanno, S. Atsumi, 2, 3 Butanediol production in an obligate photoautotrophic cyanobacterium in dark conditions via diverse sugar consumption, Metab. Eng. 36 (2016) 28–36. [124] I.S. Yunus, P.R. Jones, Photosynthesis-dependent biosynthesis of medium chain-length fatty acids and alcohols, Metab. Eng. 49 (2018) 59–68.

CO2 reduction and MES

[125] X. Gao, F. Gao, D. Liu, H. Zhang, X. Nie, C. Yang, Engineering the methylerythritol phosphate pathway in cyanobacteria for photosynthetic isoprene production from CO 2, Energ. Environ. Sci. 9 (4) (2016) 1400–1411. [126] F.K. Davies, V.H. Work, A.S. Beliaev, M.C. Posewitz, Engineering limonene and bisabolene production in wild type and a glycogen-deficient mutant of Synechococcus sp. PCC 7002, Front. Bioeng. Biotechnol. 2 (2014) 21. [127] T. Zhu, X. Xie, Z. Li, X. Tan, X. Lu, Enhancing photosynthetic production of ethylene in genetically engineered Synechocystis sp. PCC 6803, Green Chem. 17 (1) (2015) 421–434. [128] W. Wang, X. Liu, X. Lu, Engineering cyanobacteria to improve photosynthetic production of alka (e) nes, Biotechnol. Biofuels 6 (1) (2013) 1–9. [129] L. Jourdin, T. Grieger, J. Monetti, V. Flexer, S. Freguia, Y. Lu, J. Chen, M. Romano, G.G. Wallace, J. Keller, High acetic acid production rate obtained by microbial electrosynthesis from carbon dioxide, Environ. Sci. Technol. 49 (22) (2015) 13566–13574. [130] M. Straub, M. Demler, D. Weuster-Botz, P. D€ urre, Selective enhancement of autotrophic acetate production with genetically modified Acetobacterium woodii, J. Biotechnol. 178 (2014) 67–72. [131] E.I. Lan, C.T. Wei, Metabolic engineering of cyanobacteria for the photosynthetic production of succinate, Metab. Eng. 38 (2016) 483–493. [132] K. Amulya, S.V. Mohan, Fixation of CO2, electron donor and redox microenvironment regulate succinic acid production in Citrobacter amalonaticus, Sci. Total Environ. 695 (2019), 133838. [133] S. Ueda, Y. Kawamura, H. Iijima, M. Nakajima, T. Shirai, M. Okamoto, A. Kondo, M.Y. Hirai, T. Osanai, Anionic metabolite biosynthesis enhanced by potassium under dark, anaerobic conditions in cyanobacteria, Sci. Rep. 6 (1) (2016) 1–9. [134] Y. Hirokawa, R. Goto, Y. Umetani, T. Hanai, Construction of a novel d-lactate producing pathway from dihydroxyacetone phosphate of the Calvin cycle in cyanobacterium, Synechococcus elongatus PCC 7942, J. Biosci. Bioeng. 124 (1) (2017) 54–61. [135] S. Srikanth, M. Kumar, D. Singh, M. Singh, S. Puri, S. Ramakumar, Long-term operation of electrobiocatalytic reactor for carbon dioxide transformation into organic molecules, Bioresour. Technol. 265 (2018) 66–74. [136] K.P. Katuri, S. Kalathil, A.A. Ragab, B. Bian, M.F. Alqahtani, D. Pant, P.E. Saikaly, Dual-function electrocatalytic and macroporous hollow-fiber cathode for converting waste streams to valuable resources using microbial electrochemical systems, Adv. Mater. 30 (26) (2018) 1707072. [137] S. Bajracharya, K. Vanbroekhoven, C.J. Buisman, D. Pant, D.P. Strik, Application of gas diffusion biocathode in microbial electrosynthesis from carbon dioxide, Environ. Sci. Pollut. Res. 23 (22) (2016) 22292–22308. [138] D.M. Weekes, D.A. Salvatore, A. Reyes, A. Huang, C.P. Berlinguette, Electrolytic CO2 reduction in a flow cell, Acc. Chem. Res. 51 (4) (2018) 910–918. [139] C.S. Butler, D.R. Lovley, How to sustainably feed a microbe: strategies for biological production of carbon-based commodities with renewable electricity, Front. Microbiol. 7 (2016) 1879. [140] H. Nie, T. Zhang, M. Cui, H. Lu, D.R. Lovley, T.P. Russell, Improved cathode for high efficient microbial-catalyzed reduction in microbial electrosynthesis cells, Phys. Chem. Chem. Phys. 15 (34) (2013) 14290–14294. [141] O.G. Sa´nchez, Y.Y. Birdja, M. Bulut, J. Vaes, T. Breugelmans, D. Pant, Recent advances in industrial CO2 electroreduction, current opinion in green and sustainable, Chemistry 16 (2019) 47–56.

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CHAPTER 15

Bioremediation by MFC technology
b, Mehri Shabania,b, Bita Roshanravanc, Habibollah Younesic,d, Maxime Pontie e f Sang-Hyun Pyo , and Mostafa Rahimnejad a

ESAIP La Salle, CERADE, Graduate School of Engineering, Saint-Barth
elemy d’Anjou, France Group of Analysis & Processes (GA&P), Faculty of Science, University of Angers, Angers, France c Department of Environmental Science, Faculty of Natural Resources, Tarbiat Modares University, Tehran, Iran d Department of Renewable Energy, Faculty of Interdisciplinary Science and Technology, Tarbiat Modares University, Tehran, Iran e Division of Biotechnology, Department of Chemistry, Center for Chemistry and Chemical Engineering, Lund University, Lund, Sweden f Biofuel and Renewable Energy Research Center, Chemical Engineering Department, Babol Noshirvani University of Technology, Babol, Mazandaran, Iran b

15.1 Types of microbial fuel cells for bioremediation of pollutants Microbial fuel cells (MFCs) are bioelectrochemical systems that convert chemical energy from organic compounds into electrical energy during microbial catalysis. Fig. 15.1 shows the removal or recovery of heavy metals in an MFC assembled with a proton exchange membrane and MFC assembled with a bipolar membrane as a pH separator. Fig. 15.1A shows an MFC comprising an anode and a cathode, often separated by a proton exchange membrane (PEM). A bipolar membrane can be applied to separate the anode and cathode chambers. The bipolar membrane can be employed in the MFC with the anion exchange membrane (hydroxide ions migrate through the AEM) facing the anodic chamber and the cation exchange membrane (protons migrate through the PEM) facing the cathodic chamber (Fig. 15.1B). The bipolar membrane maintains a pH difference between both chambers, indicating that sustaining microbial growth and current production require neutral pH at the anode and acidic pH in the range 2–5 at the cathode to remain stable for metal plating. A metallurgical MFC system is an attractive alternative for the removal or recovery of metal from metal ions containing wastewater streams, as a layer of metal is deposited on the metal electrode which acts as the cathode during electrolysis. However, the energy for metal reduction can be achieved from the oxidation of organic materials at the anode with the potential for generating surplus electricity. Conversely, fermentation or anaerobic oxidation of organic matters takes place using the anode bacteria (either by direct electron transfer (DET) or by mediated electron transfer (MET) classes) via several mechanisms such as enzyme electron carriers (cytochromes), extracellular mediators (enzymes), conductive biopolymers, and microconductive pili (nanowire), as demonstrated by the following typical electrode reactions: +  Acetate + 4H2 O ! 2HCO 3 + 9H + 8e

Biological Fuel Cells https://doi.org/10.1016/B978-0-323-85711-6.00006-0

ðE o ¼ 0:279 VÞ

(15.1)

Copyright © 2023 Elsevier Inc. All rights reserved.

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Fig. 15.1 Concept of removal or recovery of heavy metals in a microbial fuel cell (MFC) assembled with (A) a proton exchange membrane and (B) bipolar membrane as a pH separator. Bacteria generate electrons and protons from the oxidization of the substrate at the anode chamber of the MFCs. The electrons are transferred to the cathode chamber through an external circuit, while the protons diffuse through a conductive separator to the cathode compartment, where metallic cations are being reduced (Mn+ ! Metal ion). +  Glucose + 12H2 O ! 6HCO 3 + 30H + 24e

ðE o ¼ 0:412 VÞ

(15.2)

+  Fructose + 12H2 O ! 6HCO 3 + 30H + 24e

ðEo ¼ 0:413 VÞ

(15.3)

+  Sucrose + 25H2 O ! 12HCO 3 + 60H + 48e

ðEo ¼ 0:422 VÞ

(15.4)

+  C5 H7 O2 N + 13H2 O ! 5HCO 3 + NH3 + 25H + 20e

ðE o ¼ 1:284 VÞ (15.5)

Bioremediation by MFC technology

Protons generated at the anode site pass through the proton exchange membrane toward the cathode compartment and the electrons produced at the anode compartment pass through the external circuit from the anode to the cathode side to complete the cathode reaction. H2 ! 2H+ + 2e

ðEo ¼ 0:414 VÞ

O2 + 4H+ + 4e ! 2H2 O ðE o ¼ 0:815 VÞ

(15.6) (15.7)

The MFCs can be applied (1) for anaerobic wastewater purification with simultaneous generation of bioelectricity, (2) in sediment microbial fuel cells (SMFCs) as a power source for wireless sensors, and (3) for providing power in rural remote regions and removal of contaminants such as heavy metals from wastewater.

15.1.1 Anaerobic microbial fuel cells (ANMFCs) Conversion of biomass to bioenergy can be achieved through various pathways including anaerobic digestion [1,2]. MFCs are among those methods that harness energy by applying anaerobic digestion. Generally, it is configured with two compartments of an anaerobic anode and an aerobic cathode. In the anode, degradation of the substrate takes place under anoxic conditions [3] by microbes. The movement of microbes in the direction of the electrodes causes microcolonization and then results in strong development of biofilm. The formed biofilm plays the role of biocatalysts for the degradation and production of electrons and protons [4]. Aerobic MFC requires a constant oxygen supply and can lead to an increase in energy needed to carry out the process. On the contrary, ANMFCs are more environment friendly as their energy demand is lower than aerobic MFC [5]. In 2016, ANMFCs training combined with industrial wastewater resulted in the treatment efficiency of COD ranging between 85% and 90% [5]. Later, a study focused on the treatment of chocolaterie wastewater by applying it to up-flow anaerobic microbial fuel cells and reported 70% organic removal [4]. However, varieties of reduction reactions are possible at the MFC cathode, for example, oxygen reduction reaction (ORR), hydrogen gas and hydrogen peroxide production, caustic solutions, and metal plating. Furthermore, an ANMFC anode can be constructed with organic matters (the fuel) as the electron donor, and heavy metals (arsenic (As), nickel (Ni), cadmium (Cd); mercury (He), vanadium (V), cobalt (Co), silver (Ag), chromium (Cr), zinc (Zn), selenium (Se), platinum (Pt), copper (Cu), gold (Au), and manganese (Mn)) as the electron acceptors on the cathode. Fig. 15.2 shows the possibility to remove heavy metals from wastewater in combination with electricity generation.

15.1.2 Sediment microbial fuel cells Sediment microbial fuel cells (SMFCs) provide the opportunity for the application of MFCs in water bodies taking advantage of the naturally occurring redox gradients in

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Fig. 15.2 Diagram of anaerobic MFC and configuration for metal recovery using organic matters as an electron donor.

organic-rich sediments [6]. In such a configuration, an electrode is placed in layers of sediments (anaerobic anode) and connected to a cathode exposed to ambient oxygen at the air/water interface [7]. Dissolved oxygen is essential for the cathodic reaction. Therefore, sediment MFCs are typically installed in shallow waters with the cathode close to the water surface, or they are installed in deep ocean locations, while the cathode electrode is fixed in the water phase with reasonably high oxygen concentration [8]. The common structure of SMFCs usually does not consider a membrane, as the necessary potential difference is being created by decreasing the oxygen gradient over the depth of water and sediment columns [9]. SMFCs are capable of converting a wide range of organic materials in aquatic ecosystems to electricity [10], by being installed directly in marine environments or as well rivers [11,12]. River water has lower electrical conductivity (500 vs  50,000 μS/cm at 20oC) and higher electrolyte resistance than seawater, which hence results in greater production of electrical energy by seawater sediments [8]. There are studies on the application of SMFCs to provide energy to low-power oceanographic sensors in remote settings [13–15] and for bioremediation [16–18]. The more recent application of SMFCs as bioremediation is because of their ability to provide sustainable and flexible electron donors or acceptors, at the same time less aggressiveness toward water bodies and easier monitoring features [19]. Recently, Kubota et al. [20] have succeeded in reducing porewater sulfide concentrations by deploying a set of five SMFCs in the organic-rich sediment

Bioremediation by MFC technology

(12% w/w organic carbon) of Tokyo Bay. Also, the bioremediation of toxic metals [21] such as Cu [22], mercury (Hg), zinc (Zn), and silver (Ag) [23] has been successfully achieved with the high efficiency of remediation. Wang et al. applied SMFCs to remove the antibiotics and the results proved the 95% degradation of sulfamethoxazole with a power density production of 368.52 mW/m2 [24]. However, a three-chamber MFC was studied with citric acid, HCl, and acetic acid as auxiliary reagents to remove heavy metals from soil [25]. A total copper removal (94.78%) after 74 days, the highest soil electrical conductivity (15.29 ms/cm), and electricity generation performance (363.04 mW h) were obtained when HCl was used as an auxiliary reagent in three-chamber MFC. A schematic diagram of the SMFC is demonstrated in Fig. 15.3. As expected, this configuration is accompanied by limitations related to high internal electrical resistance due to sediment in the anode chamber and slow oxygen reduction reaction (ORR) in the cathode chamber; these could be reasons for obtaining results on low power density [26,27].

15.1.3 Benthic microbial fuel cells (BMFC) This type also follows the basic principles of MFCs with aim of energy production and wastewater treatment. Herein, we can observe that BMFCs produce electrical energy from the natural redox gradient that happens in the water-sediment interface. In the BMFC, the anode is buried in the nonaerated benthic waste while the cathode will be placed in the wastewater/groundwater [28,29]. An external connection for both electrodes is provided to complete the external circuit. In BMFCs, the redox potential difference between the sediment and water is responsible for electrons’ movement [30].

Fig. 15.3 A schematic prototype of a typical double-chamber sediment MFC.

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Over the last 20 years, more DMFC-related research has focused on the function and power limits of these technologies [31,32]. These efforts led to the creation of large arrays of anode and cathode material and design structure [33,34], incorporation of power management for ocean sensors [35], and a few cases of acoustic communication [36,37]. The studies are being conducted continuously and have resulted in development and improvement in topics of scaling up, electrode configuration, power production, energy storage, and data transfer [38]. In 2022, the application of BMFCs as a persistent underwater power source has been evaluated and it has been reported that one of the experiments was run for 1045 days at an ocean depth of 580 m demonstrating that these systems can be sustained [38]. The graphical representation of benthic microbial fuel cells (BMFCs) is shown in Fig. 15.4.

15.1.4 Enzyme-based microbial fuel cells (EBC) Enzyme-based microbial fuel cells (EBC) or enzymatic biofuel cells are a type of bioelectrochemical system, which employs isolated enzymes (instead of conventional noble metal catalysts) as catalysts at the anode to catalyze the oxidation process [39]. The rest of the structure is almost the same as conventional fuel cells, where the fuel is oxidized in an anode and provides the electron movement and results in current production [40]. The two compartments of an EBC are separated by a membrane. The advantages of biocatalysts over conventional types include their cost efficiency, longer life usage, and availability. They are quite efficient and selective under mild conditions (neutral pH and near-body temperature), and also they allow the utilization of

Fig. 15.4 Schematic diagram of electron transfer in benthic microbial fuel cells (BMFCs).

Bioremediation by MFC technology

more complex fuels (as their natural substrates are abundant in nature) [41]. The last 10 years have followed the great trend of research in translating EBCs from the lab bench to implantable systems. In 2003, the first enzymatic-based biofuel cell was implemented by Mano et al. [42], later in 2010 [43], the first glucose EBC and after them in 2012, a trehalose EBS was studied [44,45]. The research continues on these types of fuel cells; for the moment, we could observe that the two main application areas considered for EBCs are in vivo, implantable power supplies for sensors and pacemakers, and ex vivo power supplies for small portable power devices (wireless sensor networks, portable electronics, etc.) [40,41]. Fig. 15.5 exhibits the working principle of mediated electron transfer in EBCs. In this device, multicopper oxidases (MCOs) catalyze the oxidation of glucose and metal ions and transfer the liberated electrons to a copper cluster causing the associated four-electron reduction of dioxygen to water. A multicopper oxidase can be projected to contribute to copper detoxification by changing Cu+ to less toxic Cu2+. Recently, the application of fungi has been studied in the anodic compartment of MFC (fungal MFC) because of its enzymatic ability to break the phenolic compounds [46]. As reported by Shabani et al. [47], Trichoderma harzianum has been used to biodegrade the paracetamol and its CMR (carcinogenic, mutagenic, or toxic to reproduction) by-products resulting from oxidation of paracetamol in pharmaceutical wastewater.

15.1.5 Air-breathing cathode-based microbial fuel cells (ABC-MFC) As mentioned earlier, one of the limiting parameters of MFCs is the cathodic reaction [48] due to its poor kinetics of oxygen reduction reaction (ORR), which has raised the interest

Fig. 15.5 Schematic diagram of enzymatic biofuel cells.

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in air-breathing cathode structures for MFCs. In this configuration, the cathode is generally comprised of an electrode substrate, oxygen reduction catalyst layer, and air-diffusion layer (a polymer coating) [49]. Each of these parts plays an individual role in cathode efficiency, as for an air-diffusion layer, recently porous materials are also being in use [50]. Commercially, platinum is one of the most commonly utilized catalysts in MFCs for ORR [51]. Xu et al. [52], studied a single chamber MFC equipped with carbon nanotube-hybridized molybdenum disulfide nanocomposites (CNT/MoS2) cathode, which resulted in a maximum power density of 53.0 mW/m2, which is much higher than those MFCs with normal CNTs. Recently, a platinum-free catalyst was synthesized as an iron-nitrogen-carbon electrocatalyst (Fe-N-C). The results over 6 months displayed stable voltage generation cycles, indicating high durability in an operating condition, which was coupled with a maximum power density value of 126  8 μW/cm2 [53].

15.1.6 Constructed wetland-microbial fuel cells (CW-MFC) However, constructed wetlands and microbial fuel cells have been separately studied but their combination (CW-MFC) is an emergent field of research. CWs are being applied in wastewater treatments because of their high performance and comparatively low cost in terms of installation, operation, and maintenance in the last two decades [54,55]. CW-MFCs are electrochemical devices that change solar energy into bioelectricity with the help of microorganisms present in the roots of the rhizosphere (see Fig. 15.6) [56]. There are many advantages of coupling a CW to an MFC including: simultaneous bioelectricity production and wastewater treatment, production of energy without the contribution of an exogenous organic substrate, reduction of methane release, extraction of bioelectricity from natural water bodies, and they are reactors of landscape integration [57]. In many studies, CW-MFC has been reported with a buried anode and cathode at the surface and/or in the plant rhizosphere. This type of arrangement helps to reduce the dissolved oxygen (DO) at the anode while ensuring maximum availability in the cathode region [58]. Just like an SMFCs, the use of a separator is not necessary if there is an up-flow regime in CW-MFCs, as it can create a sufficient redox profile for the efficiency of the MFC [59]. The problem with such a design is the large distance between electrodes, which results in high ohmic resistance [60]. To overcome this challenge, in 2015, the use of a glass wool separator has been proposed with simultaneous upflow into the anode and downflow into the cathode [61], which resulted in a 70% boost of the maximum power density in this study. The literature review revealed that CW-MFCs have been applied in producing bioenergy [62], aromatic compound degradation [63], and microbial community analysis [64], removal of chemical oxygen demand (COD) [65] and electrode studies [66,67] and design [62].

Bioremediation by MFC technology

Fig. 15.6 The basic construction of constructed wetland-microbial fuel cell for heavy metal removal with wastewater treatment and simultaneous electricity generation.

15.1.7 Thermophilic microbial fuel cells (TMFC) The common microbial fuel cells work in a mesophilic condition, while the thermophilic condition has been seldomly studied and reported. Considering the advantages of the anaerobic thermophilic degradation as higher substrate degradation rate, lower risk of contamination from ubiquitous mesophilic microorganisms, easier maintenance of anaerobic reducing conditions because of the lower solubility of O2 [68], and efficient heat utilization of high-temperature wastewater, make us focus more on the integration of this methodology in MFCs as TMFCs [69]. The first report of TMFCs was given in 2004 when the thermophilic Bacillus licheniformis and Bacillus thermoglucosidasius were applied in an anode chamber with redox mediators and achieved an open circuit voltage reaching 700 mV [70]. A few years later, many thermophilic bacteria such as Thermincola ferriacetica, Thermincola potens, and Calditerrivibrio nitroreducens have been used individually or in a mixed culture for the objective, and they were named thermophilic exoelectrogenic microorganisms [68,71–73]. Like a traditional MFC, here also we can have two anodic and cathodic compartments separated by a membrane. In 2011, a thermophilic MFC design has been tested at 57°C with an anaerobic, thermophilic consortium that achieved a power density of 375 mW/m2 after 590 h by reporting minimal activation losses from the polarization curve [74]. Earlier in 2008, another research by Wrighton et al. [68] operated an MFC at 55°C, where over a 100-day operation, these MFCs were stable and achieved a power density of 37 mW/m2 with a coulombic efficiency of 89%.

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15.1.8 Algae MFCs Integrating microalgae as biocatalysts in MFCs has provided opportunities in terms of pollutant removal, including organic matter, nitrogen, and phosphate, from wastewaters in algal bioelectrochemical systems. The photocathode simply aims to provide (1) the required level of oxygen for the ORR and reduction of air provider cost [75], and (2) the biomass that can be subsequently used directly as the fuel for the MFC anode. This half-cell photo-compartment could also be part of a carbon-capture system by the mineralization of CO2 for algal growth [76]. The photocathodes are the most promising method of integrating photosynthesis in MFCs. Other than minimizing process costs, microalgae-based MFCs can be used for the production of value-added chemicals such as lipids and pigments from low-cost harvesting techniques (biofilm formation) [77]. There are different designs of algal-based MFCs including single, dual, or three-chambered built-in tubular, plate shapes and frames, rectangular, circular, or H-type configurations made of plexiglass or acrylic material to allow light transfer [78]. It has been reported that under the optimal condition, this type of MFCs can produce power densities up to 153 mW/m2 (32% higher than mechanical aeration) compared to 116 mW/m2 with mechanical aeration (Fig. 15.7) [79].

15.2 Applications of MFC for sludge remediation Wastewater treatment processes generate huge quantities of excess sludge that need to be disposed of. Sludge disposal is expensive and incurs a major cost in wastewater

Fig. 15.7 Schematic diagram of the algae-microbial fuel cell in biocathode with heavy metal removal and simultaneous electricity generation.

Bioremediation by MFC technology

management. Microbial fuel cell technology sometimes is being applied to treat the sludge, as one of the advantages of the MFCs is its ability to overcome the challenge of excess sludge compared to other treatment methods. In 2009, a study focused on degrading excess sewage sludge and generating electricity. The results showed a 46% reduction in the total chemical oxygen demand (COD) of sludge [80]. In 2016, Fabiano Passos et al. [81], utilized an anaerobic consortium to treat the secondary sludge obtained from a sewage treatment plant. The system investigated herein employed excess sludge as a biocatalyst in an MFC. Later in 2018, a single-chamber aircathode MFC was operated with dewatered sludge from a municipal wastewater treatment plant as the substrate. Herein, the bacteria present in the sludge played the role of catalysts and the voltage of average of 900 mV and good efficiency of COD removal was achieved and reported [82].

15.3 Bioremediation of chromium released from industrial wastewater using MFC Among the different heavy metals, chromium is being intensively used for industrial aims like pigment manufacturing, electroplating, mining, leather tanning, and welding [83]. Cr(VI) and Cr(III) (hexavalent and trivalent Cr, respectively) are the two valence states of Cr present in the natural environment [84]. The application of MFC to treat Cr is an advanced and sustainable process coupled with electric energy through the reduction of toxic Cr(VI) to less toxic Cr(III) [85] and it has attracted the attention of many scientists [86–88]. It can be applied in the cathode of MFC as an electron acceptor and play the reaction of reduction to complete the cycle. Interestingly, it has been reported that chromium could be a better oxidant than O2 and K3Fe(CN)6 [89] because the oxidation potential of Cr(VI) is 1.33V, which is higher than that of O2 (1.23 V). In 2017 [90], 100% removal efficiency of Cr(VI) with a maximum power density of 1540 mW/m2 has been reported. The same efficiency was also confirmed in 2018 by Li et al. [91], with a maximum power density of 1220 mW/m2. Therefore, this waste has the potential to become an important energy resource in the near future.

15.4 Bioremediation of landfill leachates and municipal wastewater via MFC The application of MFCs in municipal wastewater treatment plants is getting noticed more and more in terms of attaining energy self-sufficiency. Despite all the studies, this topic faces challenges including insufficient power generation and high capital cost [92]; so, breakthroughs are still required to make this technology cost-efficient and energy-efficient. Liter-scale MFCs with a volume of more than 1 L have been intensively studied for the degradation of wastewater [93–97]. Another function of municipal

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Biological fuel cells

wastewater is that it could be applied as a substrate in MFCs, but it has been reported that this is associated with a notable decline in power densities [98]. One of the suitable proposed methods is to integrate the MFCs with the existing treatment system to avoid the high cost and ensure its efficiency. Hence, it also faces challenges like cathode fouling, tenuous COD removal, and, accordingly, limited electricity [99,100].

15.5 MFC-assisted biodegradation of azo dyes The textile industry applies more than 10,000 dyes [101], among which, 60%–70% contain azo molecules [102]. These azo molecules transform into highly toxic by-products when achieving the environment caused by the emerging methods related to their treatment [103]. MFCs are one of the biotreatment methods that have been understudied due to their ability to anaerobically degrade of tough molecules as dyes. Studies are focusing on efficient power generation and decolorization during recent years; [104–106] all these configurations not only vary in cost, but these designs also show a trade-off between power output and dye decolorization. However, the mineralization of dyes still needs attention, as the resulting molecules after degradation are aromatic amines, which can cause environmental toxicity and unacceptably high COD levels [107]. Successful dye removal from real textile wastewater has been reported by the application of a single-chamber MFC (cathodic microalgal biofilm) reactor with an up-flow approach. In this system, 42% dye removal from real effluent after 30 days of operation was obtained [108]. In 2016, an MFC-MEC (microbial electrolysis cell) coupled system was established in order to enhance azo dye decolorization. The results indicate that the decolorization rate in the coupled system had a 36.52%–75.28% improvement compared to the single MFC [109]. In general, we can estimate that the application of MFCs for dye removal could have advantages of dual duty of degrading dye effluents and power generation, reduction in the sludge generation and CO2 emission, the lower operating cost compared to the conventional process, and ability to complete mineralization of aromatic amines when combining with other technologies. It should be noted that like other approaches, limitations related to low coulombic efficiency and power generation are still in the way of scaling up this method [110].

15.6 Bioremediation of hydrocarbons and their derivatives Industrial wastewater contains many aromatic hydrocarbons, which could cause high toxicity as well as challenges in treatment. Among various methods, MFCs are a promising technology for anaerobic bioremediation of these compounds in wastewater or sediments [111]. Polycyclic aromatic hydrocarbons (PAHs), especially high molecularweight PAHs, are carcinogenic and mutagenic organic compounds that are difficult to

Bioremediation by MFC technology

degrade. To the best of our knowledge, among all 16 PAHs, only 6 of them have been reported to be treated by using MFCs [112–114] and nonstop research is being carried out to improve and identify the potential [115]. In 2012, sediments MFC has been applied for hydrocarbon degradation, and results showed effective remediation for cleaning the contaminated sediments [116]. Until now, most of the projects have been limited to the laboratory scale and there are gaps in this topic. For example, the respective role of electrochemical degradation and microbial degradation has not been distinguished clearly. PAHs in contaminated sites can be removed by adsorption and/or degradation, albeit through distinct mechanisms. How to exert the synergistic effect of these three is still elusive. In future research design, more corresponding control groups need to be set up.

15.7 Removal of heavy metals 15.7.1 Concept and principle The term “heavy metals” refers to a class of metals and metalloids that have a relatively high density and are dangerous or poisonous in trace amounts [117]. Both natural and man-made sources discharge a wide range of heavy metals into the environment, some of the more well-known ones being mercury, cadmium, arsenic, chromium, thallium, and lead. Pollution caused by the improper disposal of heavy metals is considered to be one of the most serious water-quality problems facing the globe today. Rapid population growth and urbanization have accelerated industrialization, damaging both surface and groundwater. In the case of highly polluted wastewater generated by industries (such as mining and fertilizer manufacturing; steel processing; metal refining; electroplating; leather tanning; dye manufacturing; battery manufacturing; glass making, etc.) as well as small businesses (such as households; hospitals; and research and testing laboratories), the environment cannot easily degrade it [118]. Thus, heavy metals ingested through the food chain, drinking water, and air represent a significant risk to human health. Bio-particles react with the metals, creating poisonous chemicals, which impair immune defenses, stunt growth, reduce cerebral and nerve function, raise blood pressure, damage the kidneys and other organs including the liver and spleen, and disrupt psychological functioning [119]. Due to the fact that they cannot be broken down and are not biodegradable, they also tend to bioaccumulate, and appropriate procedures for their efficient removal from the environment must be created. Bio-electrochemical systems (BESs) or microbial electrochemical systems are the most cost-effective and sustainable approach to generating energy by converting chemical to electrical energy from the decomposition of organic matter at the anode of microbial fuel cells (MFC) [120]. MFC has wide applications in controlling pollution and it consists of anode and cathode connected by an ion-exchange membrane (IEM) or separator that avoids the migration of electrolytes from one chamber to another. Microorganisms incubated in the anode

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chamber act as catalysts for the breakdown of organic matter producing electrons and protons. The electrons produced are transferred to the cathode chamber via an external circuit, while the protons are transported through an ion exchange separator. Some heavy metals such as Cr(VI), Cu(II), Ag(I), Mn(II), and Cd(II) that are good electronic acceptors have strong reducibility for MFC, which produces electricity. Hence, metals can be electrochemically reduced and are obtained from the cathode surface. Studies on removal or degradation of heavy metals by MFCs are also conducted separately in two types including single- and double-chambered microbial fuel cells [121].

15.7.2 Electrode materials used for heavy metal removal in bio-electrochemical systems Electrochemical system performance in terms of bacterial adhesion, electron transport, and electrochemical efficiency are all dependent on the electrode material selected. Different materials used for anode should be biocompatible, conductive, and chemically stable when they are placed in a solution of the reactor. These materials include carbon rods, carbon cloth, carbon fiber, stainless steel mesh, and other similar materials. High-porosity materials are required for proper biofilm formation, and anodes would not get clogged up. For improving the performance of the anode, different chemical and physical methods are used. Incorporated metals such as Mn(IV) and Fe(III) and neutral red were covalently linked in order to mediate the electron transfer. Further, the current generation can be enhanced by using electrocatalytic materials such as polyanilines [122]. While the majority of materials used as anodes can also be used as cathodes, a robust MFC cathode should have certain features, including high mechanical strength, catalytic activity, and high electronic and ionic conductivity. The cathode’s ability to remove heavy metals from wastewater is highly dependent on the material it is made of, and there are two types: nonbiological and biological [123]. 15.7.2.1 BES for metal recovery with abiotic cathode In the presence of a catalyst, wastewater containing heavy metal pollutants is employed as an electron acceptor, and abiotic cathodes typically decrease oxygen to generate water. Carbon-activated, platinum transition metals, and others such as nickel foam and carbon mesh are frequently employed as oxygen-reducing cathodes in MFCs. However, practical uses of Pt-based cathodes are limited due to their high cost and toxicity of the catalyst. Nowadays, scientists are making use of other nonprecious electrodes like Mn2O3, Fe2O3, and heteroatom-doped carbon due to their low cost. If a ferricyanide catholyte is employed as a common electron donor, the cathode catalyst is unnecessary. However, the use of ferricyanide is not currently viable for the long-term functioning of MFCs in a sustainable manner [122,124].

Bioremediation by MFC technology

15.7.2.2 Metal recovery with bio electrodes Higher cost of traditional catalysts, lack of environmental friendliness, and complexity in production led to the creation of biocathodes, which use aerobic and anaerobic microbes to act as a catalyst. The biofilm formed over the cathode catalyzes the reduction reaction and, on the other hand, the microbes use oxygen, inorganic salts, or oxidized metal as terminal electron acceptors [125]. Biocathodes are classified as aerobic or anaerobic. While oxygen serves as the terminal electron acceptor (TEA) and hydrogen peroxide serves as an intermediary in aerobic biocathodes, anaerobic microorganisms utilize carbon dioxide, fumarate, nitrate, and sulfate as electron acceptors. Discoveries are made in which firstly exoelectrogenic microorganism biofilm is used in the MFC anode and then acts as a biocathode after switching the polarity. Among the different transition metals, iron and manganese act as electron mediators between the electrode and oxygen. Fe(III) was reduced to ferrous iron [Fe(II)] via electrons created by the biofilm, which is then oxidized by oxygen. The cathode electrode sends electrons to the terminal electron acceptor (oxygen) [126]. Under anaerobic conditions, where oxygen is not present, nitrates and sulfates are the most important terminal electron acceptors. The most frequently used metals such as oxidized chromium can be reduced using biocathodes [127].

15.7.3 Conventional technologies vs bioelectrochemical systems-based technology Many treatment techniques have been extensively used for the expulsion of heavy metals from wastewater. Physical and chemical methods have high efficiency but have a disadvantage as they are highly polluting, very costly, and not economical, whereas biological and organic methods are environmentally friendly and comparatively less expensive [128]. These strategies incorporate chemical precipitation, coagulation/flocculation, reverse osmosis, adsorption, membrane filtration, and electro-treatments such as electrochemical precipitation and electro-dialysis [129]. One method for removing heavy metals is coagulation/flocculation, which involves adding simple or complicated flocculants or precipitating insoluble metal carbonates, sulfides, or hydroxides. However, this method involves increased sludge volume generation and large chemical consumption [130]. Another method that has been proven to be effective is ion exchange, in which heavy metal ions are replaced with less toxic cations in the effluent. Arsenic metals are removed from water using this technique, which is most commonly used for this purpose. Researchers have employed cation-exchange resins to selectively extract metal ions such as Ce2+, Fe2+, and Pb2+ from the solution. Zeolite resins have a better performance to remove chromium, nickel, copper, cadmium, lead, zinc, and barium. However, the primary disadvantages of ion-exchange technologies are bio- and chemical fouling, organic and inorganic contamination of resin, and high recovery costs. Regeneration of ionexchange resins is possible using strong acidic or saline reagent solutions, which require

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extra treatment [131,132]. Chemical precipitation is a reasonably inexpensive technique that utilizes precipitate-forming compounds, which get separated through sedimentation. Chemical precipitation is mostly applied to eliminate Cu2+, Cd2+, Mn2+, and Zn2+ ions. Numerous disadvantages of chemical precipitation include incompatibility with low metal concentrations, the demand for sedimentation, filtration, and massive amounts of chemicals, as well as the formation of a considerable amount of sludge [119,133]. Another method of removing heavy metals from wastewater is using a membrane-based filtration process. It is not a highly recommended procedure due to its primary shortcomings, which include fouling issues, membrane replacement on a periodic basis, and high maintenance expenses [134]. Although reverse osmosis (RO) is a water-purification technology that utilizes a partially permeable membrane to remove heavy metals, it has certain drawbacks, including wastewater pretreatment and a high energy input [119]. Adsorption is a highly efficient mass transfer process in which waste is transported to the active sites of the adsorbent by means of physical or chemical transport processes. Adsorption has been described as a treatment approach that is simple, adaptable, and free of hazardous contaminants. Activated carbon, carbon nanotubes, and biomass are among the most recently produced adsorbents used to remove heavy metals from wastewater. However, the primary disadvantage of adsorbents is their high cost of recovery [135,136]. Electro-treatments for the removal of heavy metals are one of the most efficient and impact methods such as electrochemical precipitation and electrodialysis [137,138]. These procedures consume a large amount of energy, and the focus is raised on developing clean and novel approaches in order to make these strategies economical and eco-friendly. When compared to traditional methods, bioelectrochemical systems (BESs) are now preferred as alternative technologies for pollutant treatment because they have proven to be a sustainable method that simultaneously produces energy and treats wastewater from industrial sources, thereby reducing pollution. BESs also provide opportunities for producing clean and efficient fuels along with high-value compounds using microorganisms. Employing electrodes as inexhaustible electron donors and acceptors significantly improves the efficiency of BES over other conventional technologies, which require little external energy and generate only a limited quantity of energy for on-site consumption. Thus, BES enables enhanced energy management and the removal of chemical expenditures [139,140]. Recent studies have concentrated on this field because it is capable of extracting economically useful heavy metals from wastewater containing heavy metals and other harmful contaminants [128,141,142].

15.7.4 Bioelectrochemical metal removal and recovery For heavy metal removal and recovery from wastewater, bio-electrochemical research is promising because of its ability to provide a two-chamber cell for anode and cathode

Bioremediation by MFC technology

oxidation and reduction [143,144]. Heavy metals with a positive reduction potential are reduced in an MFC’s cathode chamber, while those with a negative reduction potential are removed and recovered in a MEC’s cathode, which require additional voltage input [145]. While the application of MFC in metal recovery has been extensively investigated, little work has been done on MEC technology due to its energy input need. Similarly, MDC is a newly established technology, with little study being conducted in this area. Because of their high redox potentials, metals are classified as electron acceptors in chemistry. Thus, metals are reduced and deposited on the cathode, which is known as the most effective and extensively used method to recover heavy metals from wastewater. Oxidized versions of some metals, such as arsenic and vanadium, are less poisonous; therefore, they can be handled in the anode chambers of BESs [146]. The pH of the wastewater, the metal content, the electrode surface material, and the presence of mediators are some of the most important criteria for such metals. Numerous researchers have also changed the anode and prepared and coated it with catalysts in order to enhance bacterial adherence and electron transfer [147,148]. The electrode surface is critical for metal deposition on the cathode. Electrodes with a large specific surface area, such as stainless steel mesh or graphite felt, have been found to significantly increase bacterial adherence during metal anode oxidation or biocathode reduction, as well as metal deposition. Using a cathode coated with catalysts improves performance by enhancing power generation, electrical conductivity, and metal reduction [149]. By modifying numerous operating conditions, such as pH and temperature, influent metal concentration, and other variables, metal recovery from BESs can be enhanced even further. Precipitated or deposited metals that require an acidic environment for recovery can be used in an anode chamber, whereas alkaline metals require a cathode chamber [150]. The recovery process in MFCs, MECs, and MDCs has been shown to be affected by the pH of metal-containing effluent. The MDC’s ability to generate alkalinity is an additional benefit because it aids in the precipitation of metal hydroxides [151]. The pH of the wastewater has a considerable impact on the sort of microorganisms that flourish in the reactor, where they are crucial for metal reduction and precipitation. Both microbial population and recovery rate are affected by the initial metal concentration in wastewater. Voltage drops significantly when the influent has a high proportion of metals. MFCs can be combined with other technologies, such as constructed wetland or advanced oxidation processes or supported liquid membrane technology, to recover metals and generate electricity [152,153]. Electric stimulation is required to recover and remove metals having a negative reduction potential from an MEC. It was discovered that increasing the applied voltage increased the metal removal efficiency. It is also possible to utilize voltage control to selectively recover metals (see Table 15.1) [154]. One of the extremely interesting uses of the MFC-MEC combined systems is the provision of the requisite electric stimulation from MFC [155]. The heavy metals can be recovered

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Table 15.1 MFC comparison between different studies and cathode configuration. Metal ions

Open cell voltage (V)

Ipeak (mA/m2)

Pmax (mW/m2)

Specific surface area (cm2)

Recovery (%)

Cr (VI) Cu (II) V (V) Cu (II) Ni (II) Cd (II) Au (II) Ag (I) Pd (II) Pt (IV) Rh (III)

1.330 0.286 0.900 0.361 0.570 0.590 1.002 0.880 0.596 0.341 0.389

1300 1250 1200 1700 1400 1900 2000 150 4520 7750 5890

138.72 108.00 94.08 430.00 392 722 606.25 109.00 2960 2640 2290

12.0 12.0 12.0 22.0 9.0 9.0 8.0 13.5 2.2 2.2 2.2

80.00 74.00 70.00 84.00 92.00 87.00 95.00 95.00 99.20 99.50 98.70

Ref.

[156]

[157] [158] [159] [160] [161]

from wastewater streams in an MFC device via the cathodic reduction from their ionic species to their elemental nature, adsorption, and precipitation. In a possible reaction for an MFC removing metal ions at the cathode chamber, a standard reduction potential of the metal ions should be more positive than the potential oxidation of organic material. This means that an MFC receives a positive cell potential with the spontaneous reaction and then electricity can be generated. Choosing acetate as a carbon source, metal ions such as chromium [Cr (VI)], nickel [Ni (II)], lead [Pb (II)], copper [Cu (II)], silver [Ag (I)], and mercury [Hg (II)] can theoretically be reduced with power generation in an MFC device. Table 15.1 shows studies reporting the current and power densities, the specific surface of the anode cell, and the recovery percentage of heavy metal ions by using a bioelectrochemical system (BES) as MFC using acetate as oxidizing organic material in a bioanode chamber. This is to be noticed that power density and removal efficiency are important for the feasibility of the MFC technology because it demonstrates how fast and how effectively these metals are recovered from the wastewater. Aiyer [156] reported that the two-chambered MFCs technology in which mixtures of three metal ions such as chromium [Cr (VI)], copper [Cu (II)], and vanadium [V (V)], in domestic wastewaters were reduced to a less toxic aqueous species. They reported that Cr (VI) achieved the highest cathodic efficiency (80%) followed by Cu (II) (74%) and V (V) (70%), which indicated that more electrons were recorded for current generation than for reduction of the metal. Theofilos et al. [157] reported a synthetic silver (Ag) containing wastewater in a dual MFC chamber observed Ag recovery of 93% and a power output of 202 mW/m2 at pH 7. However, Singh and Kaushik [158] investigated the potential of using a biocathode for energy recovery from wastewater and removal of Cd (II) and Ni (II) metal ions from aqueous solutions in a double chamber MFC (Table 15.1). As seen in Table 15.1, Ag (I) and Cu (II) showed

Bioremediation by MFC technology

the maximum recoveries, while Cr (VI) exhibits higher power generation. Results obtained that the specific surface area and the choice of materials are important parameters for the design of the MFC. According to Table 15.1, open-circuit voltage (VOC) is related to energy that the biofilm can deliver electrons to the anode and transfer them to the cathode. If the VOC is high enough, the cell potential is much closer to the equilibrium potential (Eocell  VOC), then theoretically the better the rate of catalysis of the reaction increases. 15.7.4.1 Arsenic In wastewater, arsenic can come through soil erosion and leaching as well as mining activities and the use of arsenic insecticides and herbicides, among other things. Long-term arsenic exposure causes conjunctivitis, hyperkeratosis, hyperpigmentation, cardiovascular disease, skin cancer, and other health problems. Arsenic exists in a variety of oxidation states, the most common of which are arsenite [As(III)] and arsenate [As(V)]. Acids like As(III), which are hard acids, and interact with nitrogen and oxides to form compounds that are difficult to break down. Sulfides with As(V) form a sulfide complex. When it comes to toxicity and mobility, As(III) is more hazardous and mobile than As(V), and removing As(V) is significantly easier than removing As(III). The principal method for removing arsenic is the oxidation of As(III) to As(V), as seen in AsðIIIÞ ! AsðVÞ + 2e ðE° ¼ 0:56 VÞ

(15.8)

Chemical or biological oxidants can be utilized since they function at a wide range of temperatures and pH levels [162]. In a single-chambered MFC with an anode chamber seeded with synthetic wastewater containing arsenic and achieving a maximum power density of 752.6 mW/m2, it was found that arsenic did not affect the microbial population [146]. Pous et al. [163] demonstrated the anaerobic oxidation of As(III) to As(V) using a polarized graphite electrode as an anode. At the electrode, gammaproteobacteria predominated. Bioelectricity is considered to be generated by the interaction of arsenic-resistant bacteria such as Actinobacteria, Comamonas, and Pseudomonas with the arsenic-oxidizing bacteria Enterobacter and Lactococcus [146,164]. While biological oxidation has taken place in the anode chamber, extremely reactive oxidants have also been used to remove arsenic via iron precipitation or oxidation. For instance, Leiva et al. [152] evaluated the removal of arsenic in a single-chambered MFC and found that pH neutralization and iron mineralization increased removal efficacy, obtaining 80% removal of arsenic and Fe while maintaining a pH of 3.2–7. The reaction is followed by the elimination process + FeðOHÞ + AsO3 4 + 3H ! FeH2 AsO4 + H2 O

(15.9)

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As previously reported by Katsoyiannis and Zouboulis [165], arsenic was removed from groundwater via the sorptive properties of iron oxides produced during biological iron oxidation. Additionally, the bio-electron-Fenton and zerovalent iron (ZVI) technologies were combined with an MFC to recover arsenic from wastewater. The bio-electrons generated by microbial metabolism reduce oxygen at the cathode, forming H2O2, which then reacts with an Fe2+ source (FeOOH on the cathode) to form hydroxyl radicals for pollutant oxidative destruction [166]. O2 + 2H+ + 2e ! H2 O2

(15.10)

Fe3+ + e ! Fe2+

(15.11)

Fe2+ + H2 O2 ! Fe3+ + OH + HO

(15.12)

In the cathode chamber of an MFC during a bio-electro-Fenton process, the hydroxyl radicals created by the process oxidize As(III) to As(V). The oxidation current efficiency of As(III) to As(V) oxidation was 73.1%, with a maximum power density of 135.3 mW/m2 observed at the highest FeOOH dosage. But, As(V) removal efficiency from solution was not attained [167]. The most often used approach for removing arsenic from ZVI is coprecipitation and adsorption using hydrous ferrous oxides (HFOs), which are formed when Fe2+ is oxidized in water. In addition, O2-producing oxidants such as H2O2 and OH further oxidize the Fe2+ released to Fe3+, which oxidizes As(III) to As(V) [168]. In an experiment involving an MFC-ZVI combination system, an MFC provided the electrical energy required to drive the ZVI corrosion process. A singlechamber air cathode MFC with a beaker containing two electrodes was used for ZVI corrosion and arsenic removal. 15.7.4.2 Cadmium (Cd) Water used for electroplating, mining, and making rechargeable batteries contains cadmium. Cadmium is carcinogenic and toxic; so, its presence in wastewater should be limited [169]. It is possible to extract cadmium from wastewater using one of the following methods: electrodeposition Cd2+ + 2e ! Cd ðE° ¼ 0:40 VÞ

(15.13)

Cadmium hydroxide precipitation


 Cd2+ + 2OH ! CdðOHÞ2 Ksp ¼ 1014:3

As well as precipitation of cadmium carbonate
 13:7 Cd2+ + CO2 3 ! CdCO3 Ksp ¼ 10

(15.14)

(15.15)

In a study, laboratory-scale MECs were utilized to remove cadmium from wastewater at varied voltage values of 0.4, 0.6, and 1.0 V. (volts). The efficiency of removal

Bioremediation by MFC technology

was 50%–67% in 24 h, regardless of the electric settings used [154]. In another investigation, a biocathode MEC removed cadmium while producing hydrogen. There were two carbon sources employed in this experiment: acetate and NaHCO3. Acetate removed Cd(II) at a rate of 7.33  0.37 mg/L/h, whereas NaHCO3 removed Cd(II) at a rate of 6.56  0.38 mg/L/h, while hydrogen generation was 0.301  0.005 and 0.127  0.024 m3/day for acetate and NaHCO3, respectively [169]. 15.7.4.3 Chromium (Cr) Numerous industries, including electroplating, leather tanning, metallurgy, and dye manufacture, release chromium. Hexavalent Cr(VI) and trivalent Cr(III) are the two most stable forms of chromium in the environment, while Cr(VI) is more soluble in water and thus more hazardous. The microbial reduction of Cr(VI) to Cr(III) results in the purification of water and wastewater [170]. Cr6+ + 3e ! Cr3+ ðE° ¼ 1:09 VÞ

(15.16)

Cr(VI) can accumulate in both prokaryotic and eukaryotic cells, reducing the viability of the cells. Hexavalent chromium may cause nasal, throat, and skin irritations, as well as cancer of the lungs. In an MFC, genuine electroplating wastewater was used as a catholyte, removing 99.5% hexavalent chromium and 66.2% total chromium [171,172]. However, reducing pH boosted hexavalent chromium removal effectiveness. By digesting heavy metals and human urine, the urine/Cr(VI) fuel cell provides electrochemical energy. With chromium solution as the catholyte and human urine as the anolyte, a maximum power density of 3.4 W/m2 and a 90% reduction in Cr(VI) were attained: + 3+ COðNH2 Þ2 + Cr2 O2 + 6H2 O ðE° ¼ 2:076 VÞ 7 + 8H ! N2 + CO2 + 2Cr (15.17)

It was also discovered that carbon and nitrogen could be extracted from urine with an efficiency of 78% [173]. The removal of chromium from MFCs using acidic catholyte has been found to be more effective [174]. +  3+ Cr2 O2 + 7 H2 O ðE° ¼ 1:33 VÞ 7 + 14 H + 6e ! 2Cr

(15.18)

Few studies on biocathode MFC for Cr(VI) removal have been conducted. The biocathode is created by inserting the cathode electrode into the anode chamber of a dual-chamber MFC and using it as an anode. The electrode is removed once the biofilm has formed and is then placed in the cathodic chamber to act as a biocathode. After 24 h, the biocathode microbial fuel cell removed 80% of Cr(VI). Such a material can be used to further increase the removal effectiveness, as revealed by Song et al. [147], who discovered that a graphene biocathode reduced Cr(VI) by 40% when compared to graphite felt biocathodes [148]. Singhvi and Chhabra [175] found that algae utilized as a biomass

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source and electron provider in a cathode removed 98% of chromium in 96 h. For abiotic cathodes as well, cathode material has a significant impact on MFC efficiency [176]. Due to its high surface area, graphite fiber was found to be a superior cathode for biocatalytic reduction and power generation in a tubular MFC when compared to graphite felt and graphite granules [149]. For both power generation and the removal of chromium, an MFC with a cathode covered with pyrrhotite, a natural iron sulfide mineral, outperformed a graphite-coated cathode. The MFC’s performance can be improved by covering the cathode with a catalyst [174]. Li et al. [177] used a titanium oxide mineral to coat the cathode and found that it improved the effectiveness of removing Cr(VI). However, efficiency varied with visible light. Light irradiation increased chromium reduction compared to darkness. Because of the photoexcited electrons, a greater amount of Cr(VI) was reduced. To remove Cr(VI) completely, researchers employed carbon nanofiber electrodes to scatter alumina nickel nanoparticles in an aqueous solution. Alumina nanoparticles were thought to improve electrode conductivity, while nickel nanoparticles aided in Cr(VI) reduction at the cathode [90]. Additionally, it was claimed that an MFC operating at neutral pH was capable of reducing Cr(VI) by shuttling electrons from the cathode to the Cr(VI) via a conductive polymer. AQS (9,10-anthraquinone-2-sulfonic acid sodium salt) was a good dopant due to its high surface area and electrochemically active interaction with Cr(VI) [178]. Hexavalent chromium was eliminated from wastewater using MFC in an experimental inquiry employing a liquid crystal polaroid glass electrode made from e-waste. LCDs contain functional groups such as NH2 and C^N, CdO, and/or CdOdC that are believed to aid bacterial adhesion. A maximum power density of 10 mW/m2 was achieved, as well as total removal of Cr(VI) [179]. As the surface features of the electrode influence bacterial growth adhesion and the flow of electrons between them, anode modification can also boost peak power density. NaX zeolite graphite felts were utilized as the anode in one of these experiments. NaX zeolite is a crystalline aluminosilicate mineral with a large pore volume and appropriate ionexchange capacity. NaX zeolite boosted bacterial adhesion and decreased resistance to mass transport when used as an anode. After treatment with HNO3, NaX zeolitemodified graphite felt anodes generated a power density of around 200 mW/m2, which was found to be larger than that of normal anodes [180]. Cr(VI) was also reduced in situ in an air cathode MFC powered by iron-reducing bacteria via electrogenerated hydrogen peroxide at the cathode [181]. Serratia marcescens was demonstrated to have an 84% Cr(VI) reduction potential using a Cr(III) fluorescence probe in an electrochemically active bacteria test [182]. The cathode chamber of an MDC was used to decrease chromium while simultaneously desalinating brine solution. The reduction efficiency of hexavalent chromium was 75% at 760 mA/m2 current density and 2.1 mg/h desalination rate with an initial Cr(VI) concentration of 100 mg/L. The rate of desalination and current output increase with an initial Cr(VI) concentration [183].

Bioremediation by MFC technology

15.7.4.4 Cobalt (Co) In MFCs, cobalt recovery from a LiCoO2 cathode of used lithium-ion batteries has piqued the curiosity of many researchers. Inflammatory and other immunological reactions can occur in humans when cobalt is inhaled [184]. Co(III) in lithium cobalt oxide was discovered to have been transformed to Co(II) Co3+ + e ! Co2+ ðE° ¼ 1:80 VÞ

(15.19)

which disintegrated rapidly in an MFC. In contrast, LiCoO2 + 4H+ + e ! Li2+ + CO2+ + 2H2 O

(15.20)

Due to parameters such as pH, temperature, external resistance, and solution conductivity, the procedure was found to be highly sensitive [185]. Oxygen-reducing biocathode microbial fuel cells can also be used to recover cobalt dihydroxide [186]. Bioleaching can be used to recover cobalt from wasted lithium-ion batteries in MECs. The simultaneous recovery of acetate and methane generation with the recovery of cobalt can be done in a biocathode microbial electrolysis cell. A 0.2 V applied voltage resulted in an 88% cobalt recovery rate and simultaneous generation of methane and acetate in the biocathode [187]. Co2+ + 2e ! Co 

CO2 + 8H + 8e ! CH4 + H2 O +

HCO 3



+ 5H + 4e ! ðCH2 OÞ2 + 2H2 O +

(15.21) (15.22) (15.23)

Jiang and colleagues have reported a 0.81-mol Co/mol COD recovery efficiency at an applied voltage of 0.3–0.5 V for the recovery of cobalt in the form of flakes. The recovery process is dependent on temperature in both investigations, although Jiang et al. [188] found that pH and solution conductivity also play a role. 15.7.4.5 Copper (Cu) Copper is a relatively uncommon metal that is mostly produced as a by-product of copper and nickel refining. Copper poisoning can result in a variety of health problems, including cramping, convulsions, and even death [189]. Copper ion (Cu2+/Cu) has a strong redox potential and, upon reduction, is deposited on cathodes, as seen in Cu2+ + 2e ! Cu ðE° ¼ 0:34 VÞ

(15.24)

As a result, an MFC that treats copper ions produces more electricity. Deposits of Cu or Cu2O precipitates on the cathode are used to extract copper from it. 2Cu2+ + H2 O + 2e ! Cu2 O + 2H+ ðE° ¼ 0:207 VÞ

(15.25)

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2Cu2 O + 2H+ + 2e ! 2Cu + 2H2 O ðE° ¼ 0:059 VÞ

(15.26)

The elimination of more than 80% of COD and copper in an MFC resulted in a maximum power density of up to 2 W/m2 [190]. With no membrane, a low-cost MFC with the highest power density (314 mW/m3) and the highest Cu2+ removal efficiency (70%) was achieved. However, it has been observed that the amount of power generated is dependent on the initial copper concentration as well as the external resistance that is used [191,192]. There was an inverse relationship between electrode distance and internal resistance and voltage output in a membrane-free reactor with several cathodes [191]. Proper metal deposition necessitates consideration of the cathode material as well. Researchers discovered that a stainless steel woven mesh (SSM) cathode outperformed carbon rod (CR), titanium sheet (TS), and carbon sheet (CS) cathodes due to the fact that it had the least amount of copper deposition when it was first tested, resulting in the highest power density and copper removal efficiency. The copper removal rate is greatly influenced by the ratio of copper to the bonded chemical, which is typical of real industrial effluent, as Zhang et al. demonstrate. First, Cu (NH4)4+2 was reduced to Cu (NH4)+3, and then Cu or Cu2O was deposited on the cathode as a result of this process [180,193]. Acid washing can be used as a pretreatment step prior to introducing the sample into the cathode chamber, as demonstrated by Fedje et al. [194], who recovered copper with a purity of 99.9% from polluted areas using BESs. Ntagia et al. [195] demonstrated that when anodic hydrogen oxidation and cathodic copper reduction are coupled, a maximum power density of 0.25 W/m2 and a maximum current density of 0.48 A/m2 may be achieved. Copper was also removed in an MEC that concurrently produced hydrogen for denitrification and copper ion removal. When the cathode of this reactor was coated with denitrifying microorganisms, the reactor worked properly. During the passage of an electric current through the cathode, copper ions were removed from the solution, resulting in the formation of hydrogen. Denitrification was then carried out using the hydrogen gas and acetate generated [196]. By combining hydrogen oxidation and copper reduction, Ntagia et al. [195] achieved a maximum power density of 0.25 W/m2. Initially, the reactor was run with acetate as the electron donor: +  CH3 COO + 4H2 O + 4Cu2+ ! 2HCO 3 + 9H + 8e + 4Cu ðE° ¼ 0:578 VÞ (15.27)

and subsequently, hydrogen was used in its substitute H2 + Cu2+ ! 2H+ + Cu ðE° ¼ 0:636 VÞ

(15.28)

Copper was removed concurrently with seawater desalination and energy generation in an FMDC. As a result of using a batch-fed cycle for testing, the removal rates of copper, salt, and the total desalination rate were found to be 94.1  1.2%,

Bioremediation by MFC technology

43.9  0.9%, and 5.1  0.6 mg/h, respectively. It was possible to obtain a current density of 2 A/m2 by using this method [183]. Copper can also be extracted utilizing the hydroxide precipitation method in conjunction with the desalination cell’s alkalinity. A breakthrough five-chambered MDC has been developed that removes almost 100% copper at a maximum removal rate of 5.07 kg/m3/day at a comparatively low cost [151]. 15.7.4.6 Mercury (Hg) Mercury is used in a broad variety of applications, including paint, pulp, and paper production, oil refining, battery manufacturing, pharmaceutical processing, amalgams, mirror coating, insecticides, and fungicides. Methyl mercury is a highly toxic type of mercury that has the potential to accumulate in aquatic food chains. Mercury, while functioning as an electron acceptor, behaves as seen in Hg2+ + 2e ! Hg ðE° ¼ 0:7986 VÞ

(15.29)

When Cl is present, precipitation can take place by chemical reaction  Hg2+ 2 + 2Cl ! Hg2 Cl2

(15.30)

It is possible to further decrease it as follows: Hg2 Cl2 + 2e ! 2Hg + 2Cl ðE° ¼ 0:268 VÞ

(15.31)

Mercury was recovered in the form of cathode Hg deposits and Hg2Cl2 precipitates. However, it was discovered that higher pH had an effect on mercury removal efficiency, where H+ had an effect on the removal of Hg2+ via chemical mechanisms and power generation had an effect on the internal resistance of the MFC, respectively [197]. 15.7.4.7 Gold (Au) Jewelry, dentistry, electronics, and aerospace are just a few of the many industries that rely heavily on gold. A variety of liquids, including leach solution, activated carbon, wasted liquors, electroplating waste, and electroplating solutions, can be used to extract gold. Cyanide-thiosulfate gold compounds can be hazardous to humans [198]. An MFC can be used to extract pure gold from tetrachloroaurate effluent. Maximum power density (6.58 W/m2) and gold recovery efficiency (99.89%) were achieved at gold concentrations of 2000 and 200 ppm, respectively, when employing catholyte as a tetrachloroaurate wastewater and anolyte as acetate wastewater. Tetrachloroaurate itself acted as an electron acceptor in this circumstance, as proved by [199]

397

398

Biological fuel cells  AuCl 4 + 3e ! Au + 4Cl ðE° ¼ 0:93 VÞ

(15.32)

15.7.4.8 Nickel (Ni) The primary sources of nickel pollution are domestic wastewater discharges and nonferrous metal smelting output. Skin allergies in humans are the most common symptoms. The reduction reaction of Ni at the cathode can be described by the following equation: Ni2+ + 2e ! Ni ðE° ¼ 0:25 VÞ

(15.33)

Experiments were conducted to determine the effect of the initial Ni concentration in the catholyte and applied voltages on MEC performance. When the initial Ni concentration was increased from 50 to 1000 mg/L, the effectiveness of Ni removal decreased from 99% to 33%, but increased to 67% when the voltage was increased from 0.5 to 1.1 V. Thus, the removal efficiency is negatively affected by the initial nickel concentration, but voltage stimulation has a beneficial effect [200]. 15.7.4.9 Selenium (Se) There are many different sources of selenium found in the aquatic environment, including agricultural drainage and sewage sludge, fly ash from a coal-fired power plant, oil refineries, phosphate, metal ore mining, and wastewater from the glass manufacturing and electronic sectors, among others. In trace amounts, selenium is a necessary nutrient for animals. When the concentration is high enough, toxic effects can be both chronic and acute, particularly in aquatic species. Compared to selenate, the poisonous form of selenium is selenite [201]. Catal et al. [202] reported that a single-chamber MFC fed with glucose was able to remove 99% of the selenite. The reaction that takes place is depicted in H2 SeO3 + 4H+ + 4e ! Se + 3H2 O ðE° ¼ 0:74 VÞ

(15.34)

Selenite acted as an electron acceptor in this circumstance, receiving electrons and converting them to selenate in the process. It is expected that selenite, when used as an electron acceptor, will reduce the coulombic efficiency of the MFC. However, adding selenite at a low to moderate concentration boosted the cell’s coulombic efficiency due to its inhibitory effect on nonelectrogenic bacteria, whereas cathode deposition reduced oxygen transmission into the anode chamber. When selenite was treated with acetate instead of glucose as an electron donor, the recovery efficiency was reduced. Electron availability following the oxidation of acetate is lower than that of glucose, which explains why this occurred. 15.7.4.10 Silver (Ag) Silver is used extensively in photography, mirrors, jewelry, and flatware. Silver oxide is used in trace levels as a disinfectant for drinking water. Silver can induce argyria, a

Bioremediation by MFC technology

permanent blue-gray coloring of the skin and eyes. Concentrations of 0.4–1 mg/L had an effect on the kidneys, spleen, and liver of test rats [203]. Silver, like mercury and gold, has the ability to serve as an electron acceptor in electronic devices. A cathode chamber that is kept anaerobic in order to prevent the loss of electrons to oxygen throughout the recovery process has therefore been attempted. Silver is typically found in the form of silver halide, for example, AgBr, which dissolves when exposed to thiosulfate   S2 O2 3 + AgBr ! AgS2 O3 + Br

(15.35)

The following electrochemical processes occur in an MFC cathode chamber when treated in this manner: Ag+ + e ! Ag ðE° ¼ 0:799 VÞ  2 AgS2 O2 3 + e ! Ag + S2 O3

ðE° ¼ 0:250 VÞ

(15.36) (15.37)

When organic wastewater was employed as the anolyte and wastewater containing silver ions as the catholyte, it was possible to achieve removal efficiency of 99% while maintaining metallic purity of 95% [203]. Choi and Cui observed a decrease in silver removal effectiveness when the starting AgNO3 concentration was increased from 50 to 200 ppm. They were able to recover 69.9 kg of silver for each kilowatt-hour of power produced [204]. 15.7.4.11 Vanadium (V) In the Earth’s crust, vanadium is a metal that is widely used in the refinement of petroleum and metallurgy because of its abundance. Animal cells become poisonous at concentrations of 1–10 g/L when it comes into contact with them [205]. Among the most hazardous forms of vanadium, vanadium pentoxide is the most lethal compound, as it can cause gastrointestinal and respiratory disorders. In addition, because of its high redox potential, vanadium can be employed as an alternate electron acceptor, as demonstrated in V2+ + 2e ! VðsÞ ðE° ¼ 1:13 VÞ

(15.38)

V(V) is reduced to V(IV) at the cathode, which is less poisonous and can be recovered by changing the solution’s pH, as depicted in the following equation: VO+2 + 2H+ + 2e ! VO2+ + H2 O

(15.39)

When tested in water, it was discovered that vanadium was more soluble than oxygen, which preferred the electron acceptance by vanadium more. When this happened, the electron acceptors in the catholyte became more readily available because the mass transfer barrier was reduced. The vanadium solution was employed as both a catholyte

399

400

Biological fuel cells

and anolyte in an MFC-treating vanadium, with various starting concentrations. The concentration in the catholyte was reduced to the anolyte’s starting concentration. Furthermore, it was virtually eliminated in the anolyte. The reduction product V(IV) has an efficiency of 76.8  2.9% in the elimination process [206].

15.8 Mechanism and thermodynamic of metal bioelectrodeposition Microbial electrocatalysis considers microbes as catalysts for electrode reactions in order to facilitate novel bioremediation and bioproduction processes. Then, it is essential to understand the bio-electrochemical thermodynamics performance of the electrode reactions associated with the bioremediation of metal ions. In bio-electrochemical systems (BESs), two half-reactions (reduction-oxidation reactions) happen simultaneously, one for the oxidation of an electron donor and the other one for a reduction of the electron acceptor. On the other hand, the electron donor (organic matter) is oxidized liberating electrons to the electrode, and these electrons transfer to the second electrode, where they reduce another reactant (reducing agent). In the overall reaction, species A and B are oxidized and reduced to species C and D, respectively, in each of the following reactions: aA + bB $ cC + dD

(15.40)

Using the equilibrium constant expression for the Eq. (15.39), we can calculate Keq: K eq ¼

anCC  anBB anAA  anDD

(15.41)

where Keq is the equilibrium constant, a is the activity of the different species, and nA, nB, nC, and nD are the stoichiometric coefficients for the species in the reaction. The energy input or output could be measured by the change in Gibbs free energy (ΔG) of the reaction according to the following equation: ΔGr ¼ ΔGor + RT lnQ

(15.42)

where ΔG is the Gibbs free energy change of the overall reaction (kJ/mol), ΔGor is the standard Gibbs free energy of reaction (kJ/mol, at 1 atm, 273 K, and 1 M), R is the gas constant (8.31 J/K.mol), and T is the temperature (K). For a system at equilibrium (K ¼ Q), and ΔG ¼ 0, Eq. (15.40) can be described between ΔG° and K as follows: ΔGo ¼ RT ln K eq

(15.43)

If we combine Eqs. (15.41), (15.42), we get the following equation: ΔGo ¼ RT ln

anCC  anBB anAA  anDD

(15.44)

Bioremediation by MFC technology

In a diluted system, like in BES, the Gibbs free energy change can be written by the expression ΔGo ¼ RT ln

½C nC  ½DnD ½AnA  ½BnB

(15.45)

where [A]nA, [B]nB, [C]nC, and [D]nD, are the molar concentration of the species A, B, C, and D in solution, respectively (mol/L). However, a generic thermodynamic equation for the Gibbs free energy change for multicomponent systems can be written by the expression ΔGr ¼

ΔGor

+

NX REAC j¼1



nj nj RT ln nT

 

N PD X



nj 0 n RT ln nT j0

j0 ¼1

 (15.46)

where nj is the stoichiometric number of moles of reactant j in the overall reaction of the cell, nT is the total number of moles of reactants and products in the overall reaction of the cell, nj0 is the stoichiometric number of moles of product j0 in the overall reaction of the cell, NREAC is the total number of moles of reactants in the overall reaction of the cell, and NPD is the total number of moles of products in the overall reaction of the cell. The maximum amount of work performed in a chemical process, that is related between the change in the Gibbs free energy of the overall reaction (ΔG) and the potential of an electrochemical cell (Ecell) in volts, can be measured as the cell voltage by the following equation: E cell ¼ 

ΔG nF

(15.47)

When both reactants and products are under standard conditions, the relationship between the standard cell potential (Eocell) in volts, the change in Gibbs free energy (ΔG°) is as follows: E ocell ¼ 

ΔGo nF

(15.48)

The Nernst equation describes the relationship between the cell potential at any moment in time and the standard-state cell potential: RT (15.49) ln K eq nF where E is the potential in volts, Eocell is the standard potential in volts, R is the gas constant (8.314 J/mol/K), T is the temperature in kelvin (K), n is the number of moles of electrons shifted during the reaction process, and F is the Faraday constant (96,485 mol/C). At standard temperature (T ¼ 298 K), Eq. (15.45) can be simplified as follows: E cell ¼ E ocell 

401

402

Biological fuel cells

Eo ¼ 

0:0592 V ln K eq n

(15.50)

At the anode, the potential of the oxidation of acetate (oxidation half-reaction) can be determined according to the Nernst equation (Eq. 15.45):  + CH3 COO + 4H2 O ! 2HCO 3 + 8e + 8H

(15.51)

½CH 3 COO  0:0592 ln  2 + 9 n HCO 3 ½H 

(15.52)

E Anode ¼ E oHCO =AC  3

where EAnode is the anode potential in volts, EoHCO3/AC is the standard potential for bicarbonate/acetate (in volts) that can be achieved from Eq. (15.45), [CH3COO] is the acetate concentration in solution in mol/L, [HCO 3 ] is the bicarbonate concentration in solution in mol/L, and [H+] is the proton concentration in mol/L. However, the anode side oxidation of substrate can be expressed as follows: +  Cx Hy Oz + ð3x  zÞH2 O ! xHCO 3 + wH + we +

y + 5x  w  2z H2 2 (15.53)

8ð3x  zÞ > 0, ðy + 5x  w  2zÞ  0, and w, x, y, z > 0

(15.54)

Nevertheless, a Gibbs free energy change value (ΔGoe ) per electron for each specific compound can be calculated; for the case of acetate:  +  2HCO 3 + 8e + 8H ! CH3 COO + 4H2 O

(15.55)

At the Gibbs energy change ΔGo under standard conditions [207] (temperature 25°C and pressure 1 atm), reactants are converted to products as follows: X X Δf Gref ¼ ϑΔf Go ðproductsÞ  ϑΔf Go ðreactantsÞ (15.56) The ΔGoe for acetate can be computed as follows: ΔGoref ¼ 1 Δf GoCH3 COO + 4 Δf GoH2 O  2 Δf GoHCO  9 Δf GoH+ 3

(15.57)

From thermodynamic data, the ΔGoe values can be substituted into Eq. (15.54). ΔGoref ¼ 1 ð369:41Þ + 4 ð237:18Þ  2 ð586:85Þ  9 ð39:87Þ (15.58) ΔGoref ¼ 214:4 kJ mol1

(15.59)

ΔGoe is positive, indicating that the reaction is nonspontaneous. The Gibbs free energy change value (ΔGoe ) per electron is obtained as follows:

Bioremediation by MFC technology

ΔGoe ¼

214:4 ¼ 26:80 kJ e  mol1 8

(15.60)

Using Eq. (15.60), the standard-state cell potential yields Eo ¼ 

ΔGor 26:80 ¼ ¼ 0:274 V nF 96:485

(15.61)

Using Eq. (15.48), the standard-state cell potential yields Eo ¼ 

ΔGor 214:4 ¼ ¼ 0:274 V nF 8 96:485

(15.62)

The Gibbs free energy change of reaction an MFC operated on acetate can also be computed from thermodynamic data: + CH3 COO + 2O2 ! 2HCO 3 +H

(15.63)

Besides, by applying the degree of reduction (γ) and Gibbs energy per electron ΔGoe of specific compounds as defined in the growth reference system (biochemical standard conditions: pressure 1 atm, temperature 25°C (298 K), the concentration of 1 M at pH 7) [208]: ΔGor ¼ 2 γ HCO3 Δe GoHCO + 1 γ H+  1 γ CH3 COO Δe ΔGoCH3 COO 3

2 γ O2

Δe GoO2

(15.64)

Substituting thermodynamic data gives: ΔGor ¼ 0 + 0  1 8 26:801  2 4 78:719 ¼ 844:16 kJ=mol (15.65) ΔGo is negative, indicating that the reaction is spontaneous at room temperature. Using Eq. (15.48), the standard-state cell potential yields Eo ¼ 

ΔGor 844:16 ¼ ¼ 1:09 V nF 8 96:485

(15.66)

The half-reaction for oxygen reduction to water is O2 + 4H+ + 4e ! 2H2 O

(15.67)

The corresponding standard-state cell potential yields Eo ¼ 

Δe GoO2 78:719 ¼ ¼ 0:815 V F 96:485

(15.68)

An MFC cell voltage-operated on acetate can be obtained by subtracting the equilibrium potential of the anode reaction from that of the cathode reaction

403

404

Biological fuel cells

E ocell ¼ Eocathode  Eoanode

(15.69)

and substituting values from Eqs. (15.62), (15.68) into Eq. (15.69) E ocell ¼ 0:815  ð0:278Þ ¼ 1:09 V

(15.70)

This gives the same result as Eq. (15.66). At the cathode, the metal ions are obtained electrons to form atoms of the element. The BES reduction-deposition of the cathode potential depends on the free metal ion concentration and the species in the solution that are involved in the reduction half-reaction: M n+ ðn  mÞe ! M m+

(15.71)

Fig. 15.8 illustrates a schematic representation of the BES deposition mechanism of metal on the surface cathode electrode. Under acidic conditions (pH ¼ 3), the dominating aqueous metal species in the bulk water solutions is expected aqua-complexes of Mn+ ions. As presented in Fig. 15.8, the metal bio-electrodeposition reaction for recovering metals consists of four possible rate-controlling steps: (i) in the bulk solutions, the possible induced metal cations transport from the electrolyte to the cathode, and the metal ions get hydrated to give an aqua-complex type of [M(H2O)x]n+ and [M(H2O)x1]n+; equilibrium is recognized as shown below  n+  n+ M ðH2 OÞx ! M ðH2 OÞx1 + H2 O (15.72) (ii) near the surface of the electrode, an electric double layer of the ion hydration layer at the cathode-solution interface is formed. The hydrated metal cation complexes are rapidly adsorbed and desorbed; (iii) in the electric double layer, the metal aqua complexes can react by the electron transfer from the cathode to the adsorbed metal ions via

Fig. 15.8 Schematic representation of BES deposition mechanism of metal on the surface cathode electrode.

Bioremediation by MFC technology



 ðn1Þ+ + e ! M ðH2 OÞx4 + 4H2 O  n+   ðn1Þ+ + e ! M ðH2 OÞx4 + 3H2 O M ðH2 OÞx1 M ðH2 OÞx

n+

(15.73) (15.74)

(iv) in the Helmholtz double layer, the adsorbed metal aqua complexes are discharged at the cathode electrode surface:  ðn1Þ+ M ðH2 OÞx1 + ðn  1Þe ! M 0 + ðx  1ÞH2 O (15.75) (v) subsequently, the final stage of the reaction is the growth of metallic formation films and transformation into bulk aggregation. Surface diffusion can be a rate-controlling step when the metallic coating bio-electrodeposition is carried out at low current densities. The BES reduction-deposition of cathode potential for the general case of most of the metals can be written as follows: ECathode ¼ EoM m+ =M n+ 

ðaM n+ Þox RT ln ðn  mÞF ðaM m+ Þred

(15.76)

n+ is the standard reduction potential of the target metal to recover in where EMm+ /M n+ volts and (aM )ox and (aMm+)red are the chemical activities of the reduced and oxidized metal ions in solution, respectively, in mol/L. The overall oxidation-reduction reaction, when acetate oxidation is combined with mercury (II) reduction is

+ CH3 COO + 4H2 O + 4Hg2+ ! 2HCO 3 + 4Hg + 9H

(15.77)

In AC/Hg2+ BESs, the potential difference between cathode and anode defines the theoretical cell voltage of the BES (Eq. 15.55), and the energetics of the overall reaction   +9  2 HCO ½H  RT 3 E BES ¼ ECathode  E Anode ¼ EoHg2+  Eo AC  (15.78) ln 4  HCO nF Hg ½CH3 COO ½Hg2+  3 Furthermore, the conversion of CO2 as a reactant in photoelectrochemical reactions can be supposed a photosynthesis method that produces fuels and value-added products such as methane, acetic acid, methanol, formaldehyde, and formate [209]. It is believed that CO2 participates in the cathodic reduction reactions via HCO3 or higher chain carboxylic acids. In terms of the thermodynamics, spontaneous processes with the following electron acceptors, molecular hydrogen (H2) via hydrogenation reaction, and carbon dioxide (CO2) in the form of bicarbonate (HCO3) via catalytic carboxylation at the cathode as follows:

405

406

Biological fuel cells + o HCO 3 + H + 4H2 ! CH4 + 3H2 O E r,cathode ¼ 0:266 V + 2HCO 3 + 2H + 4H2 ! CH3 COOH + 4H2 O

Eor,cathode ¼ 0:227 V

(15.79) (15.80)

+ o HCO 3 + H + 3H2 ! CH3 OH + 2H2 O E r,cathode ¼ 0:133 V

(15.81)

+ o HCO 3 + H + 2H2 ! HCHO + 2H2 O E r,cathode ¼ 0:366 V

(15.82)

+ HCO 3 + H + H2 ! HCOOH + H2 O

(15.83)

Eor,cathode ¼ 0:429 V

where the standard reduction potential (Eor, cathode) is determined at the cathode side reaction under standard conditions at the temperature of 298 K (25°C), pressure 1 atm, and pH 7.

15.9 Removal of other pollutants Denitrification at the cathode of bioelectrochemical systems is used to remove biological nitrogen. H2 can be produced in the cathode compartment and ingested by denitrifying autotrophs, or denitrifiers can absorb electrons directly from the cathode surface and carry out denitrification there. Clauwaert et al. demonstrated an MFC with acetate as the anode electron donor and nitrate as the cathode electron acceptor [210,211]. Continuous stirred tank reactors (CSTRs) have been shown to promote denitrification when the cathode potential remains constant around the typical potential value of the nitrate/ nitrite redox pair. Applicable potential and current affect the denitrification rate. When the oxygen saturation level is low, the beneficial effect of current on nitrate removal is increased [212,213]. Bio-electrochemical systems can easily be linked with other techniques or may be utilized for the posttreatment of effluents of other techniques. Denitrification happens at the cathode while anodic oxidation of organic materials provides power. Additionally, an external nitrification reactor allows for ammonium removal from effluent. Optimizing the oxygen supply in the aerated cathode chamber of an MFC can even result in the simultaneous nitrification and denitrification of nitrogen and oxygen [214,215]. A further development was the construction of a tubular dualcathode MFC with an anoxic inner cathode for denitrification and an aerobic outer cathode for the nitrification process, which used both anion and cation exchange membranes for the nitrification process [216]. An algae biofilm microbial fuel cell (ABMFC) was created by integrating an MFC with an algal biofilm (AB) (ABMFC). It has been demonstrated to be significantly more effective at nitrogen and phosphorus removal than an AB and MFC alone. ABMFC generated 18% more power density in bioenergy generation than the MFC alone [217]. Cheese industry wastewater treatment is another example of mixing MFCs with other technologies. MFC removes pollutants including COD, suspended particles, and nitrite from this sort of wastewater using a membrane

Bioremediation by MFC technology

bio-electrochemical reactor. Consequently, energy is recovered since the ratio of energy recovery to consumption is greater than one. Furthermore, posttreatment in numerous bio-electrochemical reactors results in the production of high-quality effluent [218].

References [1] A. Schievano, A. Tenca, S. Lonati, E. Manzini, F. Adani, Can two-stage instead of one-stage anaerobic digestion really increase energy recovery from biomass? Appl. Energy 124 (2014) 335–342, https://doi.org/10.1016/J.APENERGY.2014.03.024. [2] F. Monlau, C. Sambusiti, N. Antoniou, A. Barakat, A. Zabaniotou, A new concept for enhancing energy recovery from agricultural residues by coupling anaerobic digestion and pyrolysis process, Appl. Energy 148 (2015) 32–38, https://doi.org/10.1016/J.APENERGY.2015.03.024. [3] G.D. Saratale, R.G. Saratale, M.K. Shahid, G. Zhen, G. Kumar, H.S. Shin, Y.G. Choi, S.H. Kim, A comprehensive overview on electro-active biofilms, role of exo-electrogens and their microbial niches in microbial fuel cells (MFCs), Chemosphere 178 (2017) 534–547, https://doi.org/ 10.1016/J.CHEMOSPHERE.2017.03.066. [4] C. Subha, S. Kavitha, S. Abisheka, K. Tamilarasan, P. Arulazhagan, J. Rajesh Banu, Bioelectricity generation and effect studies from organic rich chocolaterie wastewater using continuous upflow anaerobic microbial fuel cell, Fuel 251 (2019) 224–232, https://doi.org/10.1016/J.FUEL.2019.04.052. [5] U. Abbasi, W. Jin, A. Pervez, Z.A. Bhatti, M. Tariq, S. Shaheen, A. Iqbal, Q. Mahmood, Anaerobic microbial fuel cell treating combined industrial wastewater: correlation of electricity generation with pollutants, Bioresour. Technol. 200 (2016) 1–7, https://doi.org/10.1016/j.biortech.2015.09.088. [6] D.R. Lovley, Microbial fuel cells: novel microbial physiologies and engineering approaches, Curr. Opin. Biotechnol. 17 (3) (2006) 327–332, https://doi.org/10.1016/j.copbio.2006.04.006. [7] C.K. Algar, A. Howard, C. Ward, G. Wanger, Sediment microbial fuel cells as a barrier to sulfide accumulation and their potential for sediment remediation beneath aquaculture pens, Sci. Rep. 10 (1) (2020) 1–12, https://doi.org/10.1038/s41598-020-70002-4. [8] C.E. Reimers, P. Girguis, H.A. Stecher, L.M. Tender, N. Ryckelynck, P. Whaling, Microbial fuel cell energy from an ocean cold seep, Geobiology 4 (2) (2006) 123–136, https://doi.org/10.1111/ j.1472-4669.2006.00071.x. [9] Z. He, H. Shao, L.T. Angenent, Increased power production from a sediment microbial fuel cell with a rotating cathode, Biosens. Bioelectron. 22 (12) (2007) 3252–3255, https://doi.org/10.1016/j. bios.2007.01.010. [10] R. Alipanahi, M. Rahimnejad, G. Najafpour, Improvement of sediment microbial fuel cell performances by design and application of power management systems, Int. J. Hydrogen Energy 44 (31) (2019) 16965–16975, https://doi.org/10.1016/j.ijhydene.2019.04.162. [11] A. Shantaram, H. Beyenal, R.R.A. Veluchamy, Z. Lewandowski, Wireless sensors powered by microbial fuel cells, Environ. Sci. Technol. 39 (13) (2005) 5037–5042, https://doi.org/10.1021/es0480668. [12] D.R. Lovley, Bug juice: harvesting electricity with microorganisms, Nat. Rev. Microbiol. 4 (7) (2006) 497–508, https://doi.org/10.1038/nrmicro1442. [13] J.R. Trapero, L. Horcajada, J.J. Linares, J. Lobato, Is microbial fuel cell technology ready? An economic answer towards industrial commercialization, Appl. Energy 185 (2017) 698–707, https://doi. org/10.1016/j.apenergy.2016.10.109. [14] L.M. Tender, C.E. Reimers, H.A. Stecher, D.E. Holmes, D.R. Bond, D.A. Lowy, K. Pilobello, S.J. Fertig, D.R. Lovley, Harnessing microbially generated power on the seafloor, Nat. Biotechnol. 20 (8) (2002) 821–825, https://doi.org/10.1038/nbt716. [15] D.R. Bond, D.E. Holmes, L.M. Tender, D.R. Lovley, Electrode-reducing microorganisms that harvest energy from marine sediments, Science 295 (5554) (2002) 483–485, https://doi.org/10.1126/ science.1066771. [16] C.L. Chun, R.B. Payne, K.R. Sowers, H.D. May, Electrical stimulation of microbial PCB degradation in sediment, Water Res. 47 (1) (2013) 141–152, https://doi.org/10.1016/j.watres.2012.09.038.

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408

Biological fuel cells

[17] H. Li, W. He, Y. Qu, C. Li, Y. Tian, Y. Feng, Pilot-scale benthic microbial electrochemical system (BMES) for the bioremediation of polluted river sediment, J. Power Sources 356 (2017) 430–437, https://doi.org/10.1016/j.jpowsour.2017.03.066. [18] M. Sherafatmand, H.Y. Ng, Using sediment microbial fuel cells (SMFCs) for bioremediation of polycyclic aromatic hydrocarbons (PAHs), Bioresour. Technol. 195 (2015) 122–130, https://doi.org/ 10.1016/j.biortech.2015.06.002. [19] X. Yang, S. Chen, Microorganisms in sediment microbial fuel cells: ecological niche, microbial response, and environmental function, Sci. Total Environ. 756 (2021), 144145, https://doi.org/ 10.1016/j.scitotenv.2020.144145. [20] K. Kubota, T. Watanabe, H. Maki, G. Kanaya, H. Higashi, K. Syutsubo, Operation of sediment microbial fuel cells in Tokyo Bay, an extremely eutrophicated coastal sea, Bioresour. Technol. Rep. 6 (2019) 39–45, https://doi.org/10.1016/j.biteb.2019.02.001. [21] L. Hsu, A. Mohamed, P.T. Ha, J. Bloom, T. Ewing, M. Arias-Thode, B. Chadwick, H. Beyenal, The Influence of energy harvesting strategies on performance and microbial community for sediment microbial fuel cells, J. Electrochem. Soc. 164 (3) (2017) H3109–H3114, https://doi.org/ 10.1149/2.0171703jes. [22] X. Li, S. Mu, Y. Ren, X. Wang, Behavior of copper in membrane-less sediment microbial fuel cell, J. Renew. Sustain. Energy 9 (2) (2017), 023103, https://doi.org/10.1063/1.4979569. [23] S.Z. Abbas, M. Rafatullah, M.A. Khan, M.R. Siddiqui, Bioremediation and electricity generation by using open and closed sediment microbial fuel cells, Front. Microbiol. 10 (2019) 3348, https://doi. org/10.3389/fmicb.2018.03348. [24] Y. Wang, H. Zhang, Y. Feng, B. Li, M. Yu, X. Xu, L. Cai, Bio-electron-fenton (BEF) process driven by sediment microbial fuel cells (SMFCs) for antibiotics desorption and degradation, Biosens. Bioelectron. 136 (2019) 8–15, https://doi.org/10.1016/j.bios.2019.04.009. [25] J. Zhang, X. Cao, H. Wang, X. Long, X. Li, Simultaneous enhancement of heavy metal removal and electricity generation in soil microbial fuel cell, Ecotoxicol. Environ. Saf. 192 (2020), 110314, https:// doi.org/10.1016/j.ecoenv.2020.110314. [26] J. Lawan, S. Wichai, C. Chuaypen, A. Nuiyen, T. Phenrat, Constructed sediment microbial fuel cell for treatment of fat, oil, grease (FOG) trap effluent: role of anode and cathode chamber amendment, electrode selection, and scalability, Chemosphere 286 (2022), 131619, https://doi.org/10.1016/j. chemosphere.2021.131619. [27] A. Zabihallahpoor, M. Rahimnejad, F. Talebnia, Sediment microbial fuel cells as a new source of renewable and sustainable energy: present status and future prospects, RSC Adv. 5 (114) (2015) 94171–94183, https://doi.org/10.1039/c5ra15279h. [28] M.F. Umar, M. Rafatullah, S.Z. Abbas, M.N. Mohamad Ibrahim, N. Ismail, Advancement in benthic microbial fuel cells toward sustainable bioremediation and renewable energy production, Int. J. Environ. Res. Public Health 18 (7) (2021) 3811, https://doi.org/10.3390/ijerph18073811. [29] F.S. Fadzli, M. Rashid, A.A. Yaqoob, M.N. Mohamad Ibrahim, Electricity generation and heavy metal remediation by utilizing yam (Dioscorea alata) waste in benthic microbial fuel cells (BMFCs), Biochem. Eng. J. 172 (2021), 108067, https://doi.org/10.1016/j.bej.2021.108067. [30] P. Girguis, M. Nielsen, C. Reimers, Fundamentals of benthic microbial fuel cells: theory, development and application, Biotechnol. Appl. (2010) 1–30. [31] K.L. Joiner, G.L. Tukeman, A.Y. Obraztsova, Y.M. Arias-Thode, Impact of sediment parameters in the prediction of benthic microbial fuel cell performance, RSC Adv. 10 (44) (2020) 26220–26228, https://doi.org/10.1039/d0ra03459b. [32] M.E. Nielsen, D.M. Wu, P.R. Girguis, C.E. Reimers, Influence of substrate on electron transfer mechanisms in chambered benthic microbial fuel cells, Environ. Sci. Technol. 43 (22) (2009) 8671–8677, https://doi.org/10.1021/es9013773. [33] R.A. Rozendal, H.V.M. Hamelers, K. Rabaey, J. Keller, C.J.N. Buisman, Towards practical implementation of bioelectrochemical wastewater treatment, Trends Biotechnol. 26 (8) (2008) 450–459, https://doi.org/10.1016/j.tibtech.2008.04.008. [34] Y.M. Arias-Thode, L. Hsu, G. Anderson, J. Babauta, R. Fransham, A. Obraztsova, G. Tukeman, D.B. Chadwick, Demonstration of the septi strand benthic microbial fuel cell powering a magnetometer for ship detection, J. Power Sources 356 (2017) 419–429, https://doi.org/10.1016/j. jpowsour.2017.03.045.

Bioremediation by MFC technology

[35] L.M. Tender, S.A. Gray, E. Groveman, D.A. Lowy, P. Kauffman, J. Melhado, R.C. Tyce, D. Flynn, R. Petrecca, J. Dobarro, The First demonstration of a microbial fuel cell as a viable power supply: powering a meteorological buoy, J. Power Sources 179 (2) (2008) 571–575, https://doi. org/10.1016/j.jpowsour.2007.12.123. [36] P.S. Schrader, C.E. Reimers, P. Girguis, J. Delaney, C. Doolan, M. Wolf, D. Green, Independent benthic microbial fuel cells powering sensors and acoustic communications with the MARS underwater observatory, J. Atmos. Oceanic Tech. 33 (3) (2016) 607–617, https://doi.org/10.1175/ JTECH-D-15-0102.1. [37] Y. Gong, S.E. Radachowsky, M. Wolf, M.E. Nielsen, P.R. Girguis, C.E. Reimers, Benthic microbial fuel cell as direct power source for an acoustic modem and seawater oxygen/temperature sensor system, Environ. Sci. Technol. 45 (11) (2011) 5047–5053, https://doi.org/10.1021/es104383q. [38] C.E. Reimers, M. Wolf, Y. Alleau, C. Li, Benthic microbial fuel cell systems for marine applications, J. Power Sources 522 (2022), 231033, https://doi.org/10.1016/j.jpowsour.2022.231033. [39] I. Jeerapan, J.R. Sempionatto, J.M. You, J. Wang, Enzymatic glucose/oxygen biofuel cells: use of oxygen-rich cathodes for operation under severe oxygen-deficit conditions, Biosens. Bioelectron. 122 (2018) 284–289, https://doi.org/10.1016/j.bios.2018.09.063. [40] S.A. Neto, J.C. Forti, A.R. de Andrade, An overview of enzymatic biofuel cells, Electrocatalysis 1 (1) (2010) 87–94, https://doi.org/10.1007/s12678-010-0013-2. [41] I. Ivanov, T. Vidakovi
c-Koch, K. Sundmacher, Recent advances in enzymatic fuel cells: experiments and modeling, Energies 3 (4) (2010) 803–846, https://doi.org/10.3390/en3040803. [42] N. Mano, F. Mao, A. Heller, A miniature membrane-less biofuel cell operating at +0.60 V under physiological conditions, ChemBioChem 50 (12) (2004) 1703–1705, https://doi.org/10.1002/ cbic.200400275. [43] P. Cinquin, C. Gondran, F. Giroud, S. Mazabrard, A. Pellissier, F. Boucher, J.P. Alcaraz, K. Gorgy, F. Lenouvel, S. Math
e, P. Porcu, S. Cosnier, A glucose biofuel cell implanted in rats, PLoS One 5 (5) (2010), e10476, https://doi.org/10.1371/journal.pone.0010476. [44] M. Rasmussen, R.E. Ritzmann, I. Lee, A.J. Pollack, D. Scherson, An implantable biofuel cell for a live insect, J. Am. Chem. Soc. 134 (3) (2012) 1458–1460, https://doi.org/10.1021/ja210794c. [45] E. Katz, Biofuel cells with switchable power output, Electroanalysis 22 (7–8) (2010) 744–756, https:// doi.org/10.1002/elan.200904648. [46] M. Pontie, E. Jaspard, D. Chery, S. Mbokou, P. Pontalier, B. Cagnon, A sustainable fungal microbial fuel cell (FMFC) for the bioremediation of acetaminophen (APAP) and its main by-product (PAP) and energy production from biomass, Biocatal. Agric. Biotechnol. 22 (2019), https://doi.org/ 10.1016/j.bcab.2019.101376. [47] M. Shabani, M. Ponti
e, H. Younesi, M. Nacef, A. Rahimpour, M. Rahimnejad, R.M. Bouchenak Khelladi, Biodegradation of acetaminophen and its main by-product 4-aminophenol by Trichoderma harzianum versus mixed biofilm of Trichoderma harzianum/Pseudomonas fluorescens in a fungal microbial fuel cell, J. Appl. Electrochem. 51 (4) (2021), https://doi.org/10.1007/s10800-020-01518-w. [48] H. Rismani-Yazdi, S.M. Carver, A.D. Christy, O.H. Tuovinen, Cathodic limitations in microbial fuel cells: an overview, J. Power Sources 180 (2) (2008) 683–694, https://doi.org/10.1016/j. jpowsour.2008.02.074. [49] J.M. Sonawane, S.B. Adeloju, P.C. Ghosh, Landfill leachate: a promising substrate for microbial fuel cells, Int. J. Hydrogen Energy 42 (37) (2017) 23794–23798, https://doi.org/10.1016/j.ijhydene.2017.03.137. [50] Y. Luo, F. Zhang, B. Wei, G. Liu, R. Zhang, B.E. Logan, The use of cloth fabric diffusion layers for scalable microbial fuel cells, Biochem. Eng. J. 73 (2013) 49–52, https://doi.org/10.1016/j. bej.2013.01.011. [51] Z. Wang, C. Cao, Y. Zheng, S. Chen, F. Zhao, Abiotic oxygen reduction reaction catalysts used in microbial fuel cells, ChemElectroChem 1 (11) (2014) 1813–1821, https://doi.org/10.1002/ celc.201402093. [52] Y. Xu, S. Zhou, M. Li, Enhanced bioelectricity generation and cathodic oxygen reduction of air breathing microbial fuel cells based on MoS2 decorated carbon nanotube, Int. J. Hydrogen Energy 44 (26) (2019) 13875–13884, https://doi.org/10.1016/j.ijhydene.2019.04.040. [53] W. da Silva Freitas, D. Gemma, B. Mecheri, A. D’Epifanio, Air-breathing cathodes for microbial fuel cells based on iron-nitrogen-carbon electrocatalysts, Bioelectrochemistry 146 (2022), 108103, https://doi.org/10.1016/j.bioelechem.2022.108103.

409

410

Biological fuel cells

[54] A. Ghrabi, L. Bousselmi, F. Masi, M. Regelsberger, Constructed wetland as a low cost and sustainable solution for wastewater treatment adapted to rural settlements: the chorfech wastewater treatment pilot plant, Water Sci. Technol. 63 (12) (2011) 3006–3012, https://doi.org/10.2166/wst.2011.563. [55] R. Harrington, G. O’Donovan, G. McGrath, Integrated constructed wetlands (ICW) working at the landscape scale: the anne valley project, Ireland, Eco. Inform. 14 (2013) 104–107, https://doi.org/ 10.1016/j.ecoinf.2012.12.004. [56] R. Nitisoravut, R. Regmi, Plant microbial fuel cells: a promising biosystems engineering, Renew. Sustain. Energy Rev. 76 (2017) 81–89, https://doi.org/10.1016/j.rser.2017.03.064. [57] O. Guadarrama-P
erez, T. Guti
errez-Macı´as, L. Garcı´a-Sa´nchez, V.H. Guadarrama-P
erez, E.B. Estrada-Arriaga, Recent advances in constructed wetland-microbial fuel cells for simultaneous bioelectricity production and wastewater treatment: a review, Int. J. Energy Res. 43 (10) (2019) 5106–5127, https://doi.org/10.1002/er.4496. [58] L. Doherty, Y. Zhao, X. Zhao, Y. Hu, X. Hao, L. Xu, R. Liu, A review of a recently emerged technology: constructed wetland–microbial fuel cells, Water Res. 85 (2015) 38–45, https://doi.org/ 10.1016/j.watres.2015.08.016. [59] C. Corbella, M. Garfı´, J. Puigagut, Vertical redox profiles in treatment wetlands as function of hydraulic regime and macrophytes presence: surveying the optimal scenario for microbial fuel cell implementation, Sci. Total Environ. 470–471 (2014) 754–758, https://doi.org/10.1016/j.scitotenv.2013.09.068. [60] S. Srikanth, S. Venkata Mohan, Influence of terminal electron acceptor availability to the anodic oxidation on the electrogenic activity of microbial fuel cell (MFC), Bioresour. Technol. 123 (2012) 480–487, https://doi.org/10.1016/j.biortech.2012.07.049. [61] L. Doherty, Y. Zhao, X. Zhao, W. Wang, Nutrient and organics removal from swine slurry with simultaneous electricity generation in an alum sludge-based constructed wetland incorporating microbial fuel cell technology, Chem. Eng. J. 266 (2015) 74–81, https://doi.org/10.1016/j.cej.2014.12.063. [62] M. Helder, D.P. Strik, H.V. Hamelers, C.J. Buisman, The flat-plate plant-microbial fuel cell: the effect of a new design on internal resistances, Biotechnol. Biofuels 5 (1) (2012) 1–11, https://doi. org/10.1186/1754-6834-5-70. [63] Z. Yan, H. Jiang, H. Cai, Y. Zhou, L.R. Krumholz, Complex interactions between the macrophyte Acorus calamus and microbial fuel cells during pyrene and benzo[a]pyrene degradation in sediments, Sci. Rep. 5 (1) (2015) 1–11, https://doi.org/10.1038/srep10709. [64] R.A. Timmers, M. Rothballer, D.P.B.T.B. Strik, M. Engel, S. Schulz, M. Schloter, A. Hartmann, B. Hamelers, C. Buisman, Microbial community structure elucidates performance of Glyceria maxima plant microbial fuel cell, Appl. Microbiol. Biotechnol. 94 (2) (2012) 537–548, https://doi.org/ 10.1007/s00253-012-3894-6. [65] N. Klaisongkram, K. Holasut, Electricity generation of plant microbial fuel cell (PMFC) using Cyperus involucratus R, Eng. Appl. Sci. Res. 42 (1) (2015) 117–124, https://doi.org/10.14456/kkuenj.2015.2. [66] K. Wetser, E. Sudirjo, C.J.N. Buisman, D.P.B.T.B. Strik, Electricity generation by a plant microbial fuel cell with an integrated oxygen reducing biocathode, Appl. Energy 137 (2015) 151–157, https:// doi.org/10.1016/j.apenergy.2014.10.006. [67] K. Takanezawa, K. Nishio, S. Kato, K. Hashimoto, K. Watanabe, Factors affecting electric output from rice-paddy microbial fuel cells, Biosci. Biotechnol. Biochem. 74 (6) (2010) 1271–1273, https://doi.org/10.1271/bbb.90852. [68] K.C. Wrighton, P. Agbo, F. Warnecke, K.A. Weber, E.L. Brodie, T.Z. DeSantis, P. Hugenholtz, G.L. Andersen, J.D. Coates, A novel ecological role of the firmicutes identified in thermophilic microbial fuel cells, ISME J. 2 (11) (2008) 1146–1156, https://doi.org/10.1038/ismej.2008.48. [69] F. Zhang, J.H. Yang, K. Dai, Y. Chen, Q.R. Li, F.M. Gao, R.J. Zeng, Characterization of microbial compositions in a thermophilic chemostat of mixed culture fermentation, Appl. Microbiol. Biotechnol. 100 (3) (2016) 1511–1521, https://doi.org/10.1007/s00253-015-7130-z. [70] Y. Choi, E. Jung, H. Park, S.R. Paik, S. Jung, S. Kim, Construction of microbial fuel cells using thermophilic microorganisms, Bacillus licheniformis and Bacillus thermoglucosidasius, Bull. Korean Chem. Soc. 25 (6) (2004) 813–818, https://doi.org/10.5012/bkcs.2004.25.6.813. [71] Q. Fu, H. Kobayashi, H. Kawaguchi, T. Wakayama, H. Maeda, K. Sato, A thermophilic gramnegative nitrate-reducing bacterium, Calditerrivibrio nitroreducens, exhibiting electricity generation capability, Environ. Sci. Technol. 47 (21) (2013) 12583–12590, https://doi.org/10.1021/es402749f.

Bioremediation by MFC technology

[72] C.W. Marshall, H.D. May, Electrochemical evidence of direct electrode reduction by a thermophilic gram-positive bacterium, Thermincola Ferriacetica, Energ. Environ. Sci. 2 (6) (2009) 699–705, https:// doi.org/10.1039/b823237g. [73] F. Zhang, Y. Zhang, J. Ding, K. Dai, M.C.M. Van Loosdrecht, R.J. Zeng, Stable acetate production in extreme-thermophilic (70°C) mixed culture fermentation by selective enrichment of hydrogenotrophic methanogens, Sci. Rep. 4 (1) (2014) 1–9, https://doi.org/10.1038/ srep05268. [74] S.M. Carver, P. Vuoriranta, O.H. Tuovinen, A thermophilic microbial fuel cell design, J. Power Sources 196 (8) (2011) 3757–3760, https://doi.org/10.1016/j.jpowsour.2010.12.088. [75] R.S. Berk, J.H. Canfield, Bioelectrochemical Energy Conversion, Appl. Microbiol. 12 (1) (1964) 10–12, https://doi.org/10.1128/aem.12.1.10-12.1964. [76] X. Wang, Y. Feng, J. Liu, H. Lee, C. Li, N. Li, N. Ren, Sequestration of CO2 discharged from anode by algal cathode in microbial carbon capture cells (MCCs), Biosens. Bioelectron. 25 (12) (2010) 2639–2643, https://doi.org/10.1016/j.bios.2010.04.036. [77] E. Bazdar, R. Roshandel, S. Yaghmaei, M.M. Mardanpour, The effect of different light intensities and light/dark regimes on the performance of photosynthetic microalgae microbial fuel cell, Bioresour. Technol. 261 (2018) 350–360, https://doi.org/10.1016/j.biortech.2018.04.026. [78] Y. Zhang, J.S. Noori, I. Angelidaki, Simultaneous organic carbon, nutrients removal and energy production in a photomicrobial fuel cell (PFC), Energ. Environ. Sci. 4 (10) (2011) 4340–4346, https:// doi.org/10.1039/c1ee02089g. [79] R. Kakarla, B. Min, Photoautotrophic microalgae Scenedesmus obliquus attached on a cathode as oxygen producers for microbial fuel cell (MFC) operation, Int. J. Hydrogen Energy 39 (19) (2014) 10275–10283, https://doi.org/10.1016/j.ijhydene.2014.04.158. [80] J. Jiang, Q. Zhao, J. Zhang, G. Zhang, D.J. Lee, Electricity generation from bio-treatment of sewage sludge with microbial fuel cell, Bioresour. Technol. 100 (23) (2009) 5808–5812, https://doi.org/ 10.1016/j.biortech.2009.06.076. [81] V.F. Passos, S. Aquino Neto, A.R. de Andrade, V. Reginatto, Energy generation in a microbial fuel cell using anaerobic sludge from a wastewater treatment plant, Sci. Agric. 73 (5) (2016) 424–428, https://doi.org/10.1590/0103-9016-2015-0194. [82] M.Z.M. Muaz, R. Abdul, V.M. Vadivelu, Recovery of energy and simultaneous treatment of dewatered sludge using membrane-less microbial fuel cell, Environ. Prog. Sustain. Energy 38 (1) (2019) 208–219, https://doi.org/10.1002/ep.12919. [83] Z. Peng, C. Xiong, W. Wang, F. Tan, Y. Xu, X. Wang, X. Qiao, Facile modification of nanoscale zero-valent iron with high stability for Cr(VI) remediation, Sci. Total Environ. 596–597 (2017) 266–273, https://doi.org/10.1016/j.scitotenv.2017.04.121. [84] C.Y. Chen, C.Y. Cheng, C.K. Chen, M.C. Hsieh, S.T. Lin, K.Y. Ho, J.W. Li, C.P. Lin, Y.C. Chung, Hexavalent chromium removal and bioelectricity generation by Oachrobactrum Sp. YC211 under different oxygen conditions, J. Environ. Sci. Health A Tox. Hazard. Subst. Environ. Eng. 51 (6) (2016) 502–508, https://doi.org/10.1080/10934529.2015.1128731. [85] M.J. Uddin, Y.K. Jeong, W. Lee, Microbial fuel cells for bioelectricity generation through reduction of hexavalent chromium in wastewater: a review, Int. J. Hydrogen Energy 46 (20) (2021) 11458–11481, https://doi.org/10.1016/j.ijhydene.2020.06.134. [86] D. Pradhan, L.B. Sukla, M. Sawyer, P.K.S.M. Rahman, Recent bioreduction of hexavalent chromium in wastewater treatment: a review, J. Ind. Eng. Chem. 55 (2017) 1–20, https://doi.org/ 10.1016/j.jiec.2017.06.040. [87] K. Fei, T.S. Song, H. Wang, D. Zhang, R. Tao, J. Xie, Electrophoretic deposition of carbon nanotube on reticulated vitreous carbon for hexavalent chromium removal in a biocathode microbial fuel cell, R. Soc. Open Sci. 4 (10) (2017), https://doi.org/10.1098/rsos.170798. [88] P. Gangadharan, I.M. Nambi, Hexavalent chromium reduction and energy recovery by using dualchambered microbial fuel cell, Water Sci. Technol. 71 (3) (2015) 353–358, https://doi.org/10.2166/ wst.2014.524. [89] S. Pandit, A. Sengupta, S. Kale, D. Das, Performance of electron acceptors in catholyte of a twochambered microbial fuel cell using anion exchange membrane, Bioresour. Technol. 102 (3) (2011) 2736–2744, https://doi.org/10.1016/j.biortech.2010.11.038.

411

412

Biological fuel cells

[90] S. Gupta, A. Yadav, N. Verma, Simultaneous Cr(VI) reduction and bioelectricity generation using microbial fuel cell based on alumina-nickel nanoparticles-dispersed carbon nanofiber electrode, Chem. Eng. J. 307 (2017) 729–738, https://doi.org/10.1016/j.cej.2016.08.130. [91] M. Li, S. Zhou, Y. Xu, Z. Liu, F. Ma, L. Zhi, X. Zhou, Simultaneous Cr(VI) reduction and bioelectricity generation in a dual chamber microbial fuel cell, Chem. Eng. J. 334 (2018) 1621–1629, https:// doi.org/10.1016/j.cej.2017.11.144. [92] P. Sivasankar, S. Poongodi, P. Seedevi, M. Sivakumar, T. Murugan, S. Loganathan, Bioremediation of wastewater through a quorum sensing triggered MFC: a sustainable measure for waste to energy concept, J. Environ. Manage. 237 (2019) 84–93, https://doi.org/10.1016/j.jenvman.2019.01.075. [93] J.H. Ryu, H.L. Lee, Y.P. Lee, T.S. Kim, M.K. Kim, D.T.N. Anh, H.T. Tran, D.H. Ahn, Simultaneous carbon and nitrogen removal from piggery wastewater using loop configuration microbial fuel cell, Process Biochem. 48 (7) (2013) 1080–1085, https://doi.org/10.1016/j.procbio.2013.05.016. [94] R. Rossi, P.J. Evans, B.E. Logan, Impact of flow recirculation and anode dimensions on performance of a large scale microbial fuel cell, J. Power Sources 412 (2019) 294–300, https://doi.org/10.1016/j. jpowsour.2018.11.054. [95] Y. Dong, Y. Qu, W. He, Y. Du, J. Liu, X. Han, Y. Feng, A 90-liter stackable baffled microbial fuel cell for brewery wastewater treatment based on energy self-sufficient mode, Bioresour. Technol. 195 (2015) 66–72, https://doi.org/10.1016/j.biortech.2015.06.026. [96] J.M. Sonawane, A. Gupta, P.C. Ghosh, Multi-electrode microbial fuel cell (MEMFC): a close analysis towards large scale system architecture, Int. J. Hydrogen Energy 38 (12) (2013) 5106–5114, https:// doi.org/10.1016/j.ijhydene.2013.02.030. [97] F. Zhang, Z. Ge, J. Grimaud, J. Hurst, Z. He, Long-term performance of liter-scale microbial fuel cells treating primary effluent installed in a municipal wastewater treatment facility, Environ. Sci. Technol. 47 (9) (2013) 4941–4948, https://doi.org/10.1021/es400631r. [98] D. Pant, G. Van Bogaert, L. Diels, K. Vanbroekhoven, A review of the substrates used in microbial fuel cells (MFCs) for sustainable energy production, Bioresour. Technol. 101 (6) (2010) 1533–1543, https://doi.org/10.1016/j.biortech.2009.10.017. [99] F. Zhang, Z. Ge, J. Grimaud, J. Hurst, Z. He, In situ investigation of tubular microbial fuel cells deployed in an aeration tank at a municipal wastewater treatment plant, Bioresour. Technol. 136 (2013) 316–321, https://doi.org/10.1016/j.biortech.2013.02.107. [100] A. AlSayed, M. Soliman, A. Eldyasti, Microbial fuel cells for municipal wastewater treatment: from technology fundamentals to full-scale development, Renew. Sustain. Energy Rev. 134 (2020), 110367, https://doi.org/10.1016/j.rser.2020.110367. [101] S. Velusamy, A. Roy, S. Sundaram, T. Kumar Mallick, A review on heavy metal ions and containing dyes removal through graphene oxide-based adsorption strategies for textile wastewater treatment, Chem. Rec. 21 (7) (2021) 1570–1610, https://doi.org/10.1002/TCR.202000153. € C [102] A. Yurtsever, O. ¸ inar, E. Sahinkaya, Treatment of textile wastewater using sequential sulfatereducing anaerobic and sulfide-oxidizing aerobic membrane bioreactors, J. Membr. Sci. 511 (2016) 228–237, https://doi.org/10.1016/J.MEMSCI.2016.03.044. [103] V. Mishra, U. Sharma, D. Rawat, D. Benson, M. Singh, R.S. Sharma, Fast-changing life-styles and ecotoxicity of hair dyes drive the emergence of hidden toxicants threatening environmental sustainability in Asia, Environ. Res. 184 (2020), 109253, https://doi.org/10.1016/J. ENVRES.2020.109253. [104] B. Saba, B.V. Kjellerup, A.D. Christy, Eco-friendly bio-electro-degradation of textile dyes wastewater, Bioresour. Technol. Rep. 15 (2021), 100734, https://doi.org/10.1016/J.BITEB.2021.100734. [105] R. Ilamathi, J. Jayapriya, Microbial fuel cells for dye decolorization, Environ. Chem. Lett. 16 (1) (2018) 239–250, https://doi.org/10.1007/S10311-017-0669-4/FIGURES/1. [106] M. Fatima, R. Farooq, R.W. Lindstr€ om, M. Saeed, A review on biocatalytic decomposition of azo dyes and electrons recovery, J. Mol. Liq. 246 (2017) 275–281, https://doi.org/10.1016/J. MOLLIQ.2017.09.063. [107] A. Yadav, P. Kumar, D. Rawat, S. Garg, P. Mukherjee, F. Farooqi, A. Roy, S. Sundaram, R.S. Sharma, V. Mishra, Microbial fuel cells for mineralization and decolorization of azo dyes: recent advances in design and materials, Sci. Total Environ. 826 (2022), 154038, https://doi.org/ 10.1016/J.SCITOTENV.2022.154038.

Bioremediation by MFC technology

[108] W. Logron˜o, M. P
erez, G. Urquizo, A. Kadier, M. Echeverrı´a, C. Recalde, G. Ra´khely, Single chamber microbial fuel cell (SCMFC) with a cathodic microalgal biofilm: a preliminary assessment of the generation of bioelectricity and biodegradation of real dye textile wastewater, Chemosphere 176 (2017) 378–388, https://doi.org/10.1016/j.chemosphere.2017.02.099. [109] Y. Li, H.Y. Yang, J.Y. Shen, Y. Mu, H.Q. Yu, Enhancement of azo dye decolourization in a MFC– MEC coupled system, Bioresour. Technol. 202 (2016) 93–100, https://doi.org/10.1016/J. BIORTECH.2015.11.079. [110] M.H. Cui, W.Z. Liu, Z.E. Tang, D. Cui, Recent advancements in azo dye decolorization in bioelectrochemical systems (BESs): insights into decolorization mechanism and practical application, Water Res. 203 (2021), 117512, https://doi.org/10.1016/J.WATRES.2021.117512. [111] H. Li, Q. Zhang, X.L. Wang, X.Y. Ma, K.F. Lin, Y.D. Liu, J.D. Gu, S.G. Lu, L. Shi, Q. Lu, T.T. Shen, Biodegradation of benzene homologues in contaminated sediment of the East China Sea, Bioresour. Technol. 124 (2012) 129–136, https://doi.org/10.1016/J.BIORTECH.2012.08.033. [112] D.C. Hao, X.J. Li, P.G. Xiao, L.F. Wang, The utility of electrochemical systems in microbial degradation of polycyclic aromatic hydrocarbons: discourse, diversity and design, Front. Microbiol. 11 (2020) 2581, https://doi.org/10.3389/FMICB.2020.557400/BIBTEX. [113] Y. Zhou, Q. Zou, M. Fan, Y. Xu, Y. Chen, Highly efficient anaerobic co-degradation of complex persistent polycyclic aromatic hydrocarbons by a bioelectrochemical system, J. Hazard. Mater. 381 (2020), 120945, https://doi.org/10.1016/j.jhazmat.2019.120945. [114] B. Thulasinathan, T. Jayabalan, M. Sethupathi, W. Kim, S. Muniyasamy, N. Sengottuvelan, S. Nainamohamed, K. Ponnuchamy, A. Alagarsamy, Bioelectricity generation by natural microflora of septic tank wastewater (STWW) and biodegradation of persistent petrogenic pollutants by basidiomycetes fungi: an integrated microbial fuel cell system, J. Hazard. Mater. 412 (2021), 125228, https://doi.org/10.1016/J.JHAZMAT.2021.125228. [115] A. Mukherjee, P. Zaveri, R. Patel, M.T. Shah, N.S. Munshi, Optimization of microbial fuel cell process using a novel consortium for aromatic hydrocarbon bioremediation and bioelectricity generation, J. Environ. Manage. 298 (2021), 113546, https://doi.org/10.1016/J.JENVMAN. 2021.113546. [116] J.M. Morris, S. Jin, Enhanced biodegradation of hydrocarbon-contaminated sediments using microbial fuel cells, J. Hazard. Mater. 213–214 (2012) 474–477, https://doi.org/10.1016/J. JHAZMAT.2012.02.029. [117] J.O. Duruibe, M.O.C. Ogwuegbu, J.N. Egwurugwu, Heavy metal pollution and human biotoxic effects, Int. J. Phys. Sci. 2 (2007) 112–118. 5 SRC-GoogleScholar FG-0. [118] V. Masindi, K.L. Muedi, Environmental contamination by heavy metals, Heavy Metals 10 (2018) 115–132, https://doi.org/10.5772/intechopen.76082. [119] C.F. Carolin, P.S. Kumar, A. Saravanan, G.J. Joshiba, M. Naushad, Efficient techniques for the removal of toxic heavy metals from aquatic environment: a review, J. Environ. Chem. Eng. 5 (3) (2017) 2782–2799, https://doi.org/10.1016/j.jece.2017.05.029. [120] S. Pandit, D. Das, Principles of microbial fuel cell for the power generation, in: Microbial Fuel Cell: A Bioelectrochemical System that Converts Waste to Watts, Springer, 2017, pp. 21–41, https://doi. org/10.1007/978-3-319-66793-5_2. [121] Z. Chen, X. Lu, R. Yin, Y. Luo, H. Mai, N. Zhang, J. Xiong, H. Zhang, J. Tang, D. Luo, Research on treatment of wastewater containing heavy metal by microbial fuel cell, in: IOP Conference Series: Earth and Environmental Science, vol. 121, IOP Publishing, 2018, p. 32022, https://doi.org/ 10.1088/1755-1315/121/3/032022. [122] M. Zhou, M. Chi, J. Luo, H. He, T. Jin, An overview of electrode materials in microbial fuel cells, J. Power Sources 196 (10) (2011) 4427–4435, https://doi.org/10.1016/j.jpowsour.2011.01.012. [123] M. Ghasemi, S. Shahgaldi, M. Ismail, B.H. Kim, Z. Yaakob, W.R. Wan Daud, Activated carbon nanofibers as an alternative cathode catalyst to platinum in a two-chamber microbial fuel cell, Int. J. Hydrogen Energy 36 (21) (2011) 13746–13752, https://doi.org/10.1016/j.ijhydene. 2011.07.118. [124] E. Martin, B. Tartakovsky, O. Savadogo, Cathode materials evaluation in microbial fuel cells: a comparison of carbon, Mn2O3, Fe2O3 and platinum materials, Electrochim. Acta 58 (1) (2011) 58–66, https://doi.org/10.1016/j.electacta.2011.08.078.

413

414

Biological fuel cells

[125] F. Harnisch, U. Schr€ oder, From MFC to MXC: chemical and biological cathodes and their potential for microbial bioelectrochemical systems, Chem. Soc. Rev. 39 (11) (2010) 4433–4448, https://doi. org/10.1039/c003068f. [126] D.H. Park, J.G. Zeikus, Improved fuel cell and electrode designs for producing electricity from microbial degradation, Biotechnol. Bioeng. 81 (3) (2003) 348–355, https://doi.org/10.1002/bit.10501. [127] S. Khilari, D. Pradhan, Role of cathode catalyst in microbial fuel cell, in: Microbial Fuel Cell: A Bioelectrochemical System that Converts Waste to Watts, Springer International Publishing, Cham, 2017, pp. 141–163, https://doi.org/10.1007/978-3-319-66793-5_8. [128] L. Joseph, B.M. Jun, J.R.V. Flora, C.M. Park, Y. Yoon, Removal of heavy metals from water sources in the developing world using low-cost materials: a review, Chemosphere 229 (2019) 142–159, https://doi.org/10.1016/j.chemosphere.2019.04.198. [129] M. Zhao, Y. Xu, C. Zhang, H. Rong, G. Zeng, New trends in removing heavy metals from wastewater, Appl. Microbiol. Biotechnol. 100 (15) (2016) 6509–6518, https://doi.org/10.1007/s00253016-7646-x. [130] M.J.K. Ahmed, M. Ahmaruzzaman, A review on potential usage of industrial waste materials for binding heavy metal ions from aqueous solutions, J. Water Process Eng. 10 (2016) 39–47, https://doi.org/ 10.1016/j.jwpe.2016.01.014. [131] F. Pepe, B. de Gennaro, P. Aprea, D. Caputo, Natural zeolites for heavy metals removal from aqueous solutions: modeling of the fixed bed Ba2+/Na + ion-exchange process using a mixed phillipsite/chabazite-rich tuff, Chem. Eng. J. 219 (2013) 37–42, https://doi.org/10.1016/j.cej.2012.12.075. [132] H. Figueiredo, C. Quintelas, Tailored zeolites for the removal of metal oxyanions: overcoming intrinsic limitations of zeolites, J. Hazard. Mater. 274 (2014) 287–299, https://doi.org/10.1016/j.jhazmat. 2014.04.012. [133] K. Tanong, L.H. Tran, G. Mercier, J.F. Blais, Recovery of Zn (II), Mn (II), Cd (II) and Ni (II) from the unsorted spent batteries using solvent extraction, electrodeposition and precipitation methods, J. Clean. Prod. 148 (2017) 233–244, https://doi.org/10.1016/j.jclepro.2017.01.158. [134] F. Fu, Q. Wang, Removal of heavy metal ions from wastewaters: a review, J. Environ. Manage. 92 (3) (2011) 407–418, https://doi.org/10.1016/j.jenvman.2010.11.011. [135] H. Tounsadi, A. Khalidi, A. Machrouhi, M. Farnane, R. Elmoubarki, A. Elhalil, M. Sadiq, N. Barka, Highly efficient activated carbon from Glebionis coronaria L. biomass: optimization of preparation conditions and heavy metals removal using experimental design approach, J. Environ. Chem. Eng. 4 (4) (2016) 4549–4564, https://doi.org/10.1016/j.jece.2016.10.020. [136] S.A. Northey, G.M. Mudd, T.T. Werner, N. Haque, M. Yellishetty, Sustainable water management and improved corporate reporting in mining, Water Resour. Ind. 21 (2019), 100104, https://doi.org/ 10.1016/j.wri.2018.100104. [137] A. Shafaei, M. Rezayee, M. Arami, M. Nikazar, Removal of Mn2+ ions from synthetic wastewater by electrocoagulation process, Desalination 260 (1–3) (2010) 23–28, https://doi.org/10.1016/j. desal.2010.05.006. [138] C. Trellu, E. Mousset, Y. Pechaud, D. Huguenot, E.D. van Hullebusch, G. Esposito, M.A. Oturan, Removal of hydrophobic organic pollutants from soil washing/flushing solutions: a critical review, J. Hazard. Mater. 306 (2016) 149–174, https://doi.org/10.1016/j.jhazmat.2015.12.008. [139] S. Bajracharya, M. Sharma, G. Mohanakrishna, X. Dominguez Benneton, D.P.B.T.B. Strik, P.M. Sarma, D. Pant, An overview on emerging bioelectrochemical systems (BESs): technology for sustainable electricity, waste remediation, resource recovery, chemical production and beyond, Renew. Energy 98 (2016) 153–170, https://doi.org/10.1016/j.renene.2016.03.002. [140] D.A. Jadhav, S.C. Jain, M.M. Ghangrekar, Cow’s urine as a yellow gold for bioelectricity generation in low cost clayware microbial fuel cell, Energy 113 (2016) 76–84, https://doi.org/10.1016/j. energy.2016.07.025. [141] L. Fang, L. Li, Z. Qu, H. Xu, J. Xu, N. Yan, A novel method for the sequential removal and separation of multiple heavy metals from wastewater, J. Hazard. Mater. 342 (2018) 617–624, https://doi. org/10.1016/j.jhazmat.2017.08.072. [142] N. Abdullah, N. Yusof, W.J. Lau, J. Jaafar, A.F. Ismail, Recent trends of heavy metal removal from water/wastewater by membrane technologies, J. Ind. Eng. Chem. 76 (2019) 17–38, https://doi.org/ 10.1016/j.jiec.2019.03.029.

Bioremediation by MFC technology

[143] W. Teng, G. Liu, H. Luo, R. Zhang, Y. Xiang, Simultaneous sulfate and zinc removal from acid wastewater using an acidophilic and autotrophic biocathode, J. Hazard. Mater. 304 (2016) 159–165, https://doi.org/10.1016/j.jhazmat.2015.10.050. [144] M. Malakootian, H. Mahdizadeh, A. Nasiri, F. Mirzaienia, M. Hajhoseini, N. Amirmahani, Investigation of the efficiency of microbial desalination cell in removal of arsenic from aqueous solutions, Desalination 438 (2018) 19–23, https://doi.org/10.1016/j.desal.2018.03.025. [145] H. Luo, G. Liu, R. Zhang, Y. Bai, S. Fu, Y. Hou, Heavy metal recovery combined with H2 production from artificial acid mine drainage using the microbial electrolysis cell, J. Hazard. Mater. 270 (2014) 153–159, https://doi.org/10.1016/j.jhazmat.2014.01.050. [146] Y. Li, B. Zhang, M. Cheng, Y. Li, L. Hao, H. Guo, Spontaneous arsenic (III) oxidation with bioelectricity generation in single-chamber microbial fuel cells, J. Hazard. Mater. 306 (2016) 8–12, https://doi.org/10.1016/j.jhazmat.2015.12.003. [147] T.S. Song, Y. Jin, J. Bao, D. Kang, J. Xie, Graphene/biofilm composites for enhancement of hexavalent chromium reduction and electricity production in a biocathode microbial fuel cell, J. Hazard. Mater. 317 (2016) 73–80, https://doi.org/10.1016/j.jhazmat.2016.05.055. [148] X. Wu, F. Tong, X. Yong, J. Zhou, L. Zhang, H. Jia, P. Wei, Effect of NaX zeolite-modified graphite felts on hexavalent chromium removal in biocathode microbial fuel cells, J. Hazard. Mater. 308 (2016) 303–311, https://doi.org/10.1016/j.jhazmat.2016.01.070. [149] L. Huang, X. Chai, S. Cheng, G. Chen, Evaluation of carbon-based materials in tubular biocathode microbial fuel cells in terms of hexavalent chromium reduction and electricity generation, Chem. Eng. J. 166 (2) (2011) 652–661, https://doi.org/10.1016/j.cej.2010.11.042. [150] J.K. Im, I.H. Cho, S.K. Kim, K.D. Zoh, Optimization of carbamazepine removal in O3/UV/H2O2 system using a response surface methodology with central composite design, Desalination 285 (2012) 306–314, https://doi.org/10.1016/j.desal.2011.10.018. [151] Y. Dong, J. Liu, M. Sui, Y. Qu, J.J. Ambuchi, H. Wang, Y. Feng, A combined microbial desalination cell and electrodialysis system for copper-containing wastewater treatment and high-salinity-water desalination, J. Hazard. Mater. 321 (2017) 307–315, https://doi.org/10.1016/j.jhazmat.2016.08.034. [152] E. Leiva, E. Leiva-Aravena, C. Rodrı´guez, J. Serrano, I. Vargas, Arsenic removal mediated by acidic PH neutralization and iron precipitation in microbial fuel cells, Sci. Total Environ. 645 (2018) 471–481, https://doi.org/10.1016/j.scitotenv.2018.06.378. [153] O.C. T€ urker, Simultaneous boron (B) removal and electricity generation from domestic wastewater using duckweed-based wastewater treatment reactors coupled with microbial fuel cell, J. Environ. Manage. 228 (2018) 20–31, https://doi.org/10.1016/j.jenvman.2018.08.112. [154] N. Colantonio, Y. Kim, Cadmium (II) removal mechanisms in microbial electrolysis cells, J. Hazard. Mater. 311 (2016) 134–141, https://doi.org/10.1016/j.jhazmat.2016.02.062. [155] X. Wu, X. Zhu, T. Song, L. Zhang, H. Jia, P. Wei, Effect of acclimatization on hexavalent chromium reduction in a biocathode microbial fuel cell, Bioresour. Technol. 180 (2015) 185–191, https://doi. org/10.1016/j.biortech.2014.12.105. [156] K.S. Aiyer, Recovery of chromium, copper and vanadium combined with electricity generation in two-chambered microbial fuel cells, FEMS Microbiol. Lett. 367 (2020) fnaa129, https://doi.org/ 10.1093/femsle/fnaa129. [157] A. Ter Heijne, F. Liu, R. van der Weijden, J. Weijma, C.J.N. Buisman, H.V.M. Hamelers, Copper recovery combined with electricity production in a microbial fuel cell, Environ. Sci. Technol. 44 (2010) 4376–4381, https://doi.org/10.1021/es100526g. [158] A. Singh, A. Kaushik, Removal of Cd and Ni with enhanced energy generation using biocathode microbial fuel cell: insights from molecular characterization of biofilm communities, J. Clean. Prod. 315 (2021) 127940, https://doi.org/10.1016/j.jclepro.2021.127940. [159] Y. Hubenova, E. Chorbadzhiyska, K.L. Kostov, M. Mitov, Efficient gold recovery by microbial electrochemical technologies, Bioelectrochemistry 149 (2023) 108311, https://doi.org/10.1016/j. bioelechem.2022.108311. [160] T. Kamperidis, A. Tremouli, E. Remoundaki, G. Lyberatos, Silver recovery from wastewater, simulating the chemical extract originating from a PV panel using microbial fuel cell technology, Waste Biomass Valorization 13 (2022) 4073–4083, https://doi.org/10.1007/s12649-02201793-y. [161] N. Hu, Y. Cui, C. Choi, Recovery of platinum-group metals using a microbial fuel cell, Trends Diabetes Metab. 2 (2019), https://doi.org/10.15761/TDM.1000115.

415

416

Biological fuel cells

[162] X.Q. Wang, C.P. Liu, Y. Yuan, F.B. Li, Arsenite oxidation and removal driven by a bio-electrofenton process under neutral PH conditions, J. Hazard. Mater. 275 (2014) 200–209, https://doi. org/10.1016/j.jhazmat.2014.05.003. [163] N. Pous, B. Casentini, S. Rossetti, S. Fazi, S. Puig, F. Aulenta, Anaerobic arsenite oxidation with an electrode serving as the sole electron acceptor: a novel approach to the bioremediation of arsenicpolluted groundwater, J. Hazard. Mater. 283 (2015) 617–622, https://doi.org/10.1016/j. jhazmat.2014.10.014. [164] Y.-H. Wang, B.-S. Wang, B. Pan, Q.-Y. Chen, W. Yan, Electricity production from a bioelectrochemical cell for silver recovery in alkaline media, Appl. Energy 112 (2013) 1337–1341, https://doi.org/10.1016/j.apenergy.2013.01.012. [165] I.A. Katsoyiannis, A.I. Zouboulis, Application of biological processes for the removal of arsenic from groundwaters, Water Res. 38 (1) (2004) 17–26, https://doi.org/10.1016/j.watres.2003.09.011. [166] C.H. Feng, F.B. Li, H.J. Mai, X.Z. Li, Bio-electro-fenton process driven by microbial fuel cell for wastewater treatment, Environ. Sci. Technol. 44 (5) (2010) 1875–1880, https://doi.org/10.1021/ es9032925. [167] H. Wang, Z.J. Ren, Bioelectrochemical metal recovery from wastewater: a review, Water Res. 66 (2014) 219–232, https://doi.org/10.1016/j.watres.2014.08.013. [168] P. Lai, H.Z. Zhao, C. Wang, J.R. Ni, Advanced treatment of coking wastewater by coagulation and zero-valent iron processes, J. Hazard. Mater. 147 (1–2) (2007) 232–239, https://doi.org/10.1016/j. jhazmat.2006.12.075. [169] Y. Chen, J. Shen, L. Huang, Y. Pan, X. Quan, Enhanced Cd (II) removal with simultaneous hydrogen production in biocathode microbial electrolysis cells in the presence of acetate or NaHCO3, Int. J. Hydrogen Energy 41 (31) (2016) 13368–13379, https://doi.org/10.1016/j.ijhydene. 2016.06.200. [170] Y.V. Nancharaiah, C. Dodge, V.P. Venugopalan, S.V. Narasimhan, A.J. Francis, Immobilization of Cr(VI) and its reduction to Cr(III) phosphate by granular biofilms comprising a mixture of microbes, Appl. Environ. Microbiol. 76 (8) (2010) 2433–2438, https://doi.org/10.1128/AEM.02792-09. [171] D.A. Eastmond, J.T. Mac Gregor, R.S. Slesinski, Trivalent chromium: assessing the genotoxic risk of an essential trace element and widely used human and animal nutritional supplement, Crit. Rev. Toxicol. 38 (3) (2008) 173–190, https://doi.org/10.1080/10408440701845401. [172] Z. Li, X. Zhang, L. Lei, Electricity production during the treatment of real electroplating wastewater containing Cr6 + using microbial fuel cell, Process Biochem. 43 (12) (2008) 1352–1358, https://doi. org/10.1016/j.procbio.2008.08.005. [173] W. Xu, H. Zhang, G. Li, Z. Wu, A Urine/Cr(VI) fuel cell- electrical power from processing heavy metal and human urine, J. Electroanal. Chem. 764 (2016) 38–44, https://doi.org/10.1016/j. jelechem.2016.01.013. [174] J. Shi, W. Zhao, C. Liu, T. Jiang, H. Ding, Enhanced performance for treatment of Cr (VI)containing wastewater by microbial fuel cells with natural pyrrhotite-coated cathode, Water 9 (12) (2017) 979, https://doi.org/10.3390/w9120979. [175] P. Singhvi, M. Chhabra, Simultaneous chromium removal and power generation using algal biomass in a dual chambered salt bridge microbial fuel cell, J. Bioremed. Biodegr. 04 (05) (2013), https://doi. org/10.4172/2155-6199.1000190. [176] A.C. Sophia, S. Saikant, Reduction of chromium(VI) with energy recovery using microbial fuel cell technology, J. Water Process Eng. 11 (2016) 39–45, https://doi.org/10.1016/j. jwpe.2016.03.006. [177] Y. Li, A. Lu, H. Ding, S. Jin, Y. Yan, C. Wang, C. Zen, X. Wang, Cr(VI) reduction at rutile-catalyzed cathode in microbial fuel cells, Electrochem. Commun. 11 (7) (2009) 1496–1499, https://doi.org/ 10.1016/j.elecom.2009.05.039. [178] Y. Pang, D. Xie, B. Wu, Z. Lv, X. Zeng, C. Wei, C. Feng, Conductive polymer-mediated Cr(VI) reduction in a dual-chamber microbial fuel cell under neutral conditions, Synth. Met. 183 (2013) 57–62, https://doi.org/10.1016/j.synthmet.2013.09.019. [179] P. Gangadharan, I.M. Nambi, J. Senthilnathan, Liquid crystal polaroid glass electrode from E-waste for synchronized removal/recovery of Cr +6 from wastewater by microbial fuel cell, Bioresour. Technol. 195 (2015) 96–101, https://doi.org/10.1016/j.biortech.2015.06.078.

Bioremediation by MFC technology

[180] D. Wu, L. Huang, X. Quan, G. Li Puma, Electricity generation and bivalent copper reduction as a function of operation time and cathode electrode material in microbial fuel cells, J. Power Sources 307 (2016) 705–714, https://doi.org/10.1016/j.jpowsour.2016.01.022. [181] L. Liu, Y. Yuan, F. Li, C. Feng, In-situ Cr(VI) reduction with electrogenerated hydrogen peroxide driven by iron-reducing bacteria, Bioresour. Technol. 102 (3) (2011) 2468–2473, https://doi.org/ 10.1016/j.biortech.2010.11.013. [182] H. Xue, P. Zhou, L. Huang, X. Quan, J. Yuan, Cathodic Cr(VI) reduction by electrochemically active bacteria sensed by fluorescent probe, Sens. Actuators B 243 (2017) 303–310, https://doi. org/10.1016/j.snb.2016.11.154. [183] Z. An, H. Zhang, Q. Wen, Z. Chen, M. Du, Desalination combined with hexavalent chromium reduction in a microbial desalination cell, Desalination 354 (2014) 181–188, https://doi.org/ 10.1016/j.desal.2014.10.006. [184] G.M. Keegan, I.D. Learmonth, C.P. Case, A systematic comparison of the actual, potential, and theoretical health effects of cobalt and chromium exposures from industry and surgical implants, Crit. Rev. Toxicol. 38 (8) (2008) 645–674, https://doi.org/10.1080/10408440701845534. [185] L. Huang, R. Guo, L. Jiang, X. Quan, Y. Sun, G. Chen, Cobalt leaching from lithium cobalt oxide in microbial electrolysis cells, Chem. Eng. J. 220 (2013) 72–80, https://doi.org/10.1016/j.cej.2012.12.092. [186] L. Huang, Y. Liu, L. Yu, X. Quan, G. Chen, A new clean approach for production of cobalt dihydroxide from aqueous Co(II) using oxygen-reducing biocathode microbial fuel cells, J. Clean. Prod. 86 (2015) 441–446, https://doi.org/10.1016/j.jclepro.2014.08.018. [187] L. Huang, L. Jiang, Q. Wang, X. Quan, J. Yang, L. Chen, Cobalt recovery with simultaneous methane and acetate production in biocathode microbial electrolysis cells, Chem. Eng. J. 253 (2014) 281–290, https://doi.org/10.1016/j.cej.2014.05.080. [188] L. Jiang, L. Huang, Y. Sun, Recovery of flakey cobalt from aqueous Co(II) with simultaneous hydrogen production in microbial electrolysis cells, Int. J. Hydrogen Energy 39 (2) (2014) 654–663, https:// doi.org/10.1016/j.ijhydene.2013.10.112. [189] Y.V. Nancharaiah, S. Venkata Mohan, P.N.L. Lens, Metals removal and recovery in bioelectrochemical systems: a review, Bioresour. Technol. 195 (2015) 102–114, https://doi.org/10.1016/j. biortech.2015.06.058. [190] S.A. Cheng, B.S. Wang, Y.H. Wang, Increasing efficiencies of microbial fuel cells for collaborative treatment of copper and organic wastewater by designing reactor and selecting operating parameters, Bioresour. Technol. 147 (2013) 332–337, https://doi.org/10.1016/j.biortech.2013.08.040. [191] H.C. Tao, W. Li, M. Liang, N. Xu, J.R. Ni, W.M. Wu, A Membrane-free baffled microbial fuel cell for cathodic reduction of Cu(II) with electricity generation, Bioresour. Technol. 102 (7) (2011) 4774–4778, https://doi.org/10.1016/j.biortech.2011.01.057. [192] P.R. Motos, R.V. Weijden, A. ter Heijne, M. Saakes, C.J. Buisman, T.H. Sleutels, High rate copper and energy recovery in microbial fuel cells, Front. Microbiol. 6 (2015) 527, https://doi.org/10.3389/ fmicb.2015.00527. [193] L.J. Zhang, H.C. Tao, X.Y. Wei, T. Lei, J.B. Li, A.J. Wang, W.M. Wu, Bioelectrochemical recovery of ammonia-copper(II) complexes from wastewater using a dual chamber microbial fuel cell, Chemosphere 89 (10) (2012) 1177–1182, https://doi.org/10.1016/j.chemosphere.2012.08.011. [194] K.K. Fedje, O. Modin, A.M. Str€ omvall, Copper recovery from polluted soils using acidic washing and bioelectrochemical systems, Metals 5 (3) (2015) 1328–1348, https://doi.org/10.3390/met5031328. [195] E. Ntagia, P. Rodenas, A. Ter Heijne, C.J.N. Buisman, T.H.J.A. Sleutels, Hydrogen as electron donor for copper removal in bioelectrochemical systems, Int. J. Hydrogen Energy 41 (13) (2016) 5758–5764, https://doi.org/10.1016/j.ijhydene.2016.02.058. [196] T. Watanabe, H. Motoyama, M. Kuroda, Denitrification and neutralization treatment by direct feeding of an acidic wastewater containing copper ion and high-strength nitrate to a bio-electrochemical reactor process, Water Res. 35 (17) (2001) 4102–4110, https://doi.org/10.1016/S0043-1354(01) 00158-0. [197] Z. Wang, B. Lim, C. Choi, Removal of Hg2+ as an electron acceptor coupled with power generation using a microbial fuel cell, Bioresour. Technol. 102 (10) (2011) 6304–6307, https://doi.org/10.1016/ j.biortech.2011.02.027. [198] APHA, Standard Methods for the Examination of Water and Wastewater, American Public Health Association, 1998.

417

418

Biological fuel cells

[199] C. Choi, N. Hu, The modeling of gold recovery from tetrachloroaurate wastewater using a microbial fuel cell, Bioresour. Technol. 133 (2013) 589–598, https://doi.org/10.1016/j.biortech.2013.01.143. [200] B. Qin, H. Luo, G. Liu, R. Zhang, S. Chen, Y. Hou, Y. Luo, Nickel ion removal from wastewater using the microbial electrolysis cell, Bioresour. Technol. 121 (2012) 458–461, https://doi.org/ 10.1016/j.biortech.2012.06.068. [201] A.P. Borole, C.Y. Hamilton, T.A. Vishnivetskaya, D. Leak, C. Andras, J. Morrell-Falvey, M. Keller, B. Davison, Integrating engineering design improvements with exoelectrogen enrichment process to increase power output from microbial fuel cells, J. Power Sources 191 (2) (2009) 520–527, https://doi.org/10.1016/j.jpowsour.2009.02.006. [202] T. Catal, H. Bermek, H. Liu, Removal of selenite from wastewater using microbial fuel cells, Biotechnol. Lett. 31 (8) (2009) 1211–1216, https://doi.org/10.1007/s10529-009-9990-8. [203] H.C. Tao, Z.Y. Gao, H. Ding, N. Xu, W.M. Wu, Recovery of silver from silver(I)-containing solutions in bioelectrochemical reactors, Bioresour. Technol. 111 (2012) 92–97, https://doi.org/ 10.1016/j.biortech.2012.02.029. [204] C. Choi, Y. Cui, Recovery of silver from wastewater coupled with power generation using a microbial fuel cell, Bioresour. Technol. 107 (2012) 522–525, https://doi.org/10.1016/j.biortech.2011.12.058. [205] A.P. Yelton, K.H. Williams, J. Fournelle, K.C. Wrighton, K.M. Handley, J.F. Banfield, Vanadate and acetate biostimulation of contaminated sediments decreases diversity, selects for specific taxa, and decreases aqueous V5 + concentration, Environ. Sci. Technol. 47 (12) (2013) 6500–6509, https:// doi.org/10.1021/es4006674. [206] B. Zhang, C. Tian, Y. Liu, L. Hao, Y. Liu, C. Feng, Y. Liu, Z. Wang, Simultaneous microbial and electrochemical reductions of vanadium (V) with bioelectricity generation in microbial fuel cells, Bioresour. Technol. 179 (2015) 91–97, https://doi.org/10.1016/j.biortech.2014.12.010. [207] R.K. Thauer, K. Jungermann, K. Decker, Energy conservation in chemotrophic anaerobic bacteria, Bacteriol. Rev. 41 (1) (1977) 100–180, https://doi.org/10.1128/br.41.1.100-180.1977. [208] J.J. Heijnen, Bioenergetics of microbial growthmicrobial growth, in: Encyclopedia of Bioprocess Technology, John Wiley & Sons, Ltd, 2002, https://doi.org/10.1002/0471250589.ebt026. [209] V. Kumaravel, J. Bartlett, S.C. Pillai, Photoelectrochemical conversion of carbon dioxide (CO2) into fuels and value-added products, ACS Energy Lett. 5 (2) (2020) 486–519, https://doi.org/10.1021/ acsenergylett.9b02585. [210] P. Clauwaert, K. Rabaey, P. Aelterman, L. De Schamphelaire, T.H. Pham, P. Boeckx, N. Boon, W. Verstraete, Biological denitrification in microbial fuel cells, Environ. Sci. Technol. 41 (9) (2007) 3354–3360, https://doi.org/10.1021/es062580r. [211] M. Rodrı´guez Arredondo, P. Kuntke, A.W. Jeremiasse, T.H.J.A. Sleutels, C.J.N. Buisman, A. Ter Heijne, Bioelectrochemical systems for nitrogen removal and recovery from wastewater, Environ. Sci. Water Res. Technol. 1 (1) (2015) 22–33, https://doi.org/10.1039/c4ew00066h. [212] T. Tanaka, M. Kuroda, Improvement of submerged biofilter process by bioelectrochemical method, J. Environ. Eng. 126 (6) (2000) 541–548, https://doi.org/10.1061/(asce)0733-9372(2000)126:6(541). [213] T. Parvanova-Mancheva, V. Beschkov, Microbial denitrification by immobilized bacteria pseudomonas denitrificans stimulated by constant electric field, Biochem. Eng. J. 44 (2–3) (2009) 208–213, https://doi.org/10.1016/j.bej.2008.12.005. [214] B. Virdis, K. Rabaey, Z. Yuan, J. Keller, Microbial fuel cells for simultaneous carbon and nitrogen removal, Water Res. 42 (12) (2008) 3013–3024, https://doi.org/10.1016/j.watres.2008.03.017. [215] B. Virdis, K. Rabaey, R.A. Rozendal, Z. Yuan, J. Keller, Simultaneous nitrification, denitrification and carbon removal in microbial fuel cells, Water Res. 44 (9) (2010) 2970–2980, https://doi.org/ 10.1016/j.watres.2010.02.022. [216] F. Zhang, Z. He, Integrated organic and nitrogen removal with electricity generation in a tubular dual-cathode microbial fuel cell, Process Biochem. 47 (12) (2012) 2146–2151, https://doi.org/ 10.1016/j.procbio.2012.08.002. [217] Z. Yang, H. Pei, Q. Hou, L. Jiang, L. Zhang, C. Nie, Algal biofilm-assisted microbial fuel cell to enhance domestic wastewater treatment: nutrient, organics removal and bioenergy production, Chem. Eng. J. 332 (2018) 277–285, https://doi.org/10.1016/j.cej.2017.09.096. [218] J. Li, Z. Ge, Z. He, A fluidized bed membrane bioelectrochemical reactor for energy-efficient wastewater treatment, Bioresour. Technol. 167 (2014) 310–315, https://doi.org/10.1016/j. biortech.2014.06.034.

CHAPTER 16

MFC-based biosensors Hoda Ezojia and Mostafa Rahimnejadb a

Faculty of Research and Development of Energy and Environment, Research Institute of Petroleum Industry (RIPI), Tehran, Iran b Biofuel and Renewable Energy Research Center, Chemical Engineering Department, Babol Noshirvani University of Technology, Babol, Mazandaran, Iran

16.1 Measurement and sensors Measurement is the procedure of connecting numbers to physical amounts and happenings. It is essential to all branches of science and approximately all human beings’ daily activities. In point of fact, measurement is the oldest approach that humans use to realize better and manage the world. In consequence, over the years, the theoretical and practical basis of measurement has been widely considered [1]. In this respect, the first major constituent of measurement is sensors, devices that respond to the chemical or physical phenomena occurring around (Fig. 16.1). In other words, sensors can be described as systems that can detect the characteristics and usually transform the sensed input information into the optical or electrical output signals that can be received and read either by electronic instruments or human beings. They are employed to determine and measure various chemical and physical attributes of compounds, namely, odor, force, light intensity, pressure, pH, temperature, etc. Sensors utilizations have enhanced since around 1980. This advancement was a result of technological advancements due to the technical revolution, which continues till today. Nowadays, sensors are of vital importance in lots of industries and our everyday lives. They utilize appropriate elements to convert the chemical or physical properties into the variables of diverse nature that are much more suitable for other elucidations with the electronic systems. A sensor sensitivity demonstrates the rate of variation in the output signal in relation to variation in the measured physical or chemical item. The use of sensors for various purposes is based on their fundamental characteristics, including, sensitivity, selectivity, calibration range, linearity, response time, etc. [2–6].

16.2 Types of sensors Based on the number of the employed transduction mechanism, sensors can be classified into direct and indirect ones. As, for instance, in mercury thermometers, temperature changes result in variation of the mercury volume through thermal expansion; however, the outcome is a mechanical shift. Thus, another mechanism should be used to transduce Biological Fuel Cells https://doi.org/10.1016/B978-0-323-85711-6.00013-8

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Fig. 16.1 Schematic diagram of a sensor.

it to an electrical signal. Nevertheless, it can be known as a sensor because the human eyes can read the variations in mercury volume as the secondary transducer. Sensors classification can be performed in accordance with numerous approaches. Another classification of sensors is based on the variety of the nonelectrical variables that should be measured; in this regard, sensors can be grouped into four major classes of sensors for hydraulic, mechanical, electromagnetic, and environmental phenomena. Additionally, sensors are usually divided into two basic groups, according to electronic circuits, which should be merged on the uniform chip as the primary analog front-end: active sensors that need an external source of power to produce an operational output signal (either voltage or current) directly, and passive sensors that directly improve their internal components if an external event happens. In active sensors, either capacitive or resistive bridges can be connected to the conditioning and signal processing circuits as current amplifiers. In the latter case, the main part of the passive sensors as resistance and capacitance can be evaluated (based on their alteration range) directly or via a number of appropriate circuits, namely, charge amplifier, bridges, oscillators, and converters based on the switched capacitors [2,4,7,8]. Moreover, depending on the recognition method, construction, and analyte characteristics, sensors can be generally classified into chemical and physical sensors. Physical sensors are devices that measure or/and detect physical features such as pressure, temperature, conductivity, distance, magnetic field, etc. Fig. 16.2 shows various types of physical sensors. The chemical ones are analyzers with a selective layer that provide data about a special analyte in a reversible and selective manner. The aforementioned chemical data may emanate from the analyte (chemical compound, biomaterials, etc.) chemical reaction at the surface of the transducer, which is an important component of the sensor. In spite of the fact that these kinds of sensors are not very old, but due to their numerous supreme features, namely, small size, desirable sensitivity, cost-effectiveness, wider dynamic range, ease of use, and continuous and in situ or online detection, they have gained lots of attention in medicine, industrial process and

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Fig. 16.2 Different kinds of physical sensor.

environmental monitoring, analyses of gas composition, public security and national defense and on-site emergency access applications. Therefore, today, chemical sensors are known as one of the most influential and active orientations of the technology of modern sensors. A chemical sensor, indeed, is composed of two main components: a recognition layer (receptor) and a transducer. Actually, the reaction mentioned above is the interaction occurring between the analyte and the recognition element. The transducer transforms the produced signal into an analytically electrical form. If needed, the output signal will be amplified using an amplifier [3,6,9–11].

16.3 Recognition element In lots of cases, the receptor operation is fulfilled using a thin layer that has the ability to interact with the molecules of the analyte, take part in equilibrium simultaneously with the molecules of the analyte, or catalyzes the reaction in a selective manner. It can answer to specific substances or a group of them selectively. This behavior is described by the term “molecular recognition.” In particular, for biosensors, the molecules can be recognized based on their dimension or size, namely, through steric recognition. In the midst of the interaction processes, the most important ones for chemical sensors are liquidliquid extraction and ion exchange. These phenomena, first and foremost, operate between the receptor surface and the analyte (both are in equilibrium), which is known as the interface. Actually, a chemical reaction, in lieu of the equilibrium, may be the information source, too. Processes performed at the interface of the analyte-receptor

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can be divided into two classes of chemical reaction and interaction equilibria. To use sensors, the differences between these groups are negligible. As an example, in electrochemical sensors where analytes and receptors are partners of the unique redox pair, an actual chemical equilibrium can be established. Moreover, the receptor part of chemical sensors may be based on different principles: (a) physical, where no chemical reaction occurs. Receptors based on measurement of conductivity, absorbance, mass change, refractive index, and temperature are examples of this group, (b) chemical, where the participation of analytes in chemical reactions leads to the production of analytical signals, (c) biochemical, where the source of the output analytical signal is a biochemical process. Immunosensors or microbial potentiometric sensors are typical examples of this group. They may be considered as a subset of the chemical receptors. In this case, they are called biosensors [12].

16.4 Transducer Nowadays, signal processing is done almost exclusively through electrical instrumentation. As a consequence, each sensor must contain a transducing element; in other words, a nonelectrical quantity, such as the concentration value, should be converted into an electrical quantity, namely, resistance, current, or voltage. Transducers can be categorized in various ways. Based on the transducer output quantity, the transducers can be classified as current transducers or voltage transducers. In the existing international documentation, there is no systematic and explicit theory for the classification of transducers. The aforementioned classes are: (1) Energy-conversion transducers in which the principle is that the sensors generate electrical energy. Many of these sensors do not require an external voltage source to operate. (2) Limiting current transducers; in these kinds of transducers, voltage sources in short-circuit mode can attain the limiting state. Many of energyconversion transducers demonstrate this behavior, too. In the limiting state, there is the maximum amount of current that cannot be enhanced even in the presence of additional voltage. (3) Resistive transducers, usually by the environmental properties variations, electrically conductive materials vary their conductivity (resistivity). Specific conductivity of metals decreases with the increase in temperature, while the conduction of semiconductors increases with increase in temperature. In both the aforesaid cases, the variation in resistance can be employed for the determination of temperature. The wellknown and common semiconductor thermistors are sensitive to small changes in temperature [13].

16.5 Classification of chemical sensors The advancements of computers, instrumentation, and microelectronics result in the design and fabrication of sensors using most of the biological, chemical, and physical

MFC-based biosensors

principles which have been employed in chemistry. Chemical sensors can be categorized based on their transducer working principle: (1) electrochemical sensors convert the information related to the electrochemical interaction between the analyte and the electrode into a useful analytical signal. The aforementioned information may be electrically stimulated or lead to a spontaneous interaction in a zero-current state. The subgroups of these sensors are: (a) Voltammetric devices, containing amperometric sensors that measure the current in the a.c. or d.c. mode. This kind of devices may comprise sensors on the basis of chemically active, chemically inert, and modified electrodes. There are devices with and without external current supply in this group. (b) Potentiometric devices, in which the indicator electrode (redox, metal/metal oxide, and ion-selective) potential is gauged versus a reference electrode. (c) Potentiometric gas sensors based on solid electrolytes, which are different from the previous subgroup in view of the fact that they are generally employed for gas sensing applications. Additionally, these devices work in solid electrolytes with high temperature. (d) Chemically sensitive field effect transistor (ChemFet), which transforms the output of the interaction between the active coating and the analyte into a variation in the current of the source drain. The aforesaid interactions are similar to the interactions in ion-selective sensors from chemical point of view. (2) Optical sensors, which convert the variations in the optical phenomena that are a consequence of the interaction between the analyte and the receptor element into a signal. Based on the kind of optical features that have been employed in chemical sensors, this type of sensors can be further classified into: (a) Absorbance, evaluated in a transparent medium, induced by the absorptivity of the target analyte or a reaction with a number of appropriate indicators. (b) Reflectance, which is determined in a nontransparent medium, commonly utilizing the immobilized indicators. (c) Luminescence, which is based on the intensity of the light emitted by the chemical reaction that occurred in the receptor system. (d) Refractive index, which is gauged as the outcome of a change in the composition of the solution [12,14]. It may also contain the effect of a surface plasmon resonance. (e) Fluorescence, which monitors the influence of the positive emission induced by irradiation. Moreover, such systems may be on the basis of fluorescence selective quenching. (f ) Optothermal effect, according to the measurement of the thermal effect created by light absorption. The application of optical fibers in different configurations made it possible to use many of the abovementioned phenomena in sensors. (g) Light scattering on the basis of effects induced by the presence of particles with definite size in the sample. (3) Electrical apparatus based on measurements in which no electrochemical reactions occur and the signal is the output of the variation in electrical characteristics induced by the analyte interaction. The subgroups are (a) semiconductor metal oxides sensors employed basically as detectors of gas phase on the basis of reversible redox reactions of gas components of the analyte. (b) Sensors based on organic semiconductors, based on the constitution of charge transfer (CT) complexes that improve the density of the charge carrier. (c) Permittivity sensors, and (d) electrolyte conductivity

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sensors. (4) Magnetic systems constructed based on the variations in paramagnetic features of the gas being studied. These are demonstrated by specific kinds of oxygen monitors. (5) Mass-sensitive sensors that convert the change of mass at a particular modified surface into the variation in the characteristic of the support material. The analyte accumulation is the reason for this mass change. The subgroups of this class of sensors are (a) surface acoustic wave systems based on correction of the propagation velocity of a produced acoustic wave influenced by deposition of a certain mass of analyte. (b) Piezoelectric sensors that are utilized mostly in the gaseous phase, additionally in solutions, evaluate the conversion of the quartz oscillator plate frequency as a consequence of the analyte bulk at the oscillator. (6) Thermometric apparatuses used for measuring the heat efficacies of the special chemical adsorption or reaction that implicate the analyte. In these kind of sensors, various approaches can be employed to measure the health effects, for instance, the heat generated by an enzymatic or a combustion reaction in catalytic sensors is measured via a thermistor. Also, devices that measure optothermal effects may be placed in this group, too. (7) Other kinds of physical features such as Γ-, X-, and β-radiations, if used to investigate the chemical compositions, can be the basis of a chemical sensor. The aforementioned classification demonstrates only one of the probable methods. Sensors also have been categorized according to the method employed for the measurement of the primary effect. The commonly named catalytic devices that measure the heat effect developed in the initial process through a change in a thermistor conductivity are examples of this type of classification. Moreover, the electrical and electrochemical ones are often grouped together. Furthermore, sensors have been categorized based on their application for the detection or investigation of a certain analyte. Examples of this group are sensors for metal ions, pH, or the determination of gases such as oxygen. Additionally, they can be classified based on their application mode, namely, sensors employed for utilization in vivo or sensors for monitoring various processes, etc. Of course, sensors can be grouped based on different classifications and according to logically arranged and clearly specified principles [15,16] (Fig. 16.3).

16.6 Biosensors and their classification Biosensors are not introduced as a particular group because they are made based on the same processes as the chemical sensors. They may also be distinguished from each other based on the biological components employed as the receptor. The biological element may be tissues, organisms, cells, membranes, organelles, antibodies, enzymes, etc. As mentioned before, the biosensor is one of the main streams of the prevalent chemical sensors. The present century is the biology century. Biosensors, as one of the most important components of biology, present vital support for the technology of biology. They are not only a significant aspect of the high-tech international competition but also an opening to assess the biological level of different countries. Today, the investigations in this

MFC-based biosensors

Fig. 16.3 A classification of chemical sensor.

field are strengthened in numerous countries in order to adapt to the fast progress in biology. Based on the foregoing, biosensors, according to IUPAC, are devices that belong to the group of chemical sensors and employ special biochemical reactions mediated by tissues, immunosystems, isolated enzymes, whole cell, or organelles to detect chemicals generally via optical, electrical, or thermal signals (Fig. 16.4). The basis of biosensor discrimination as the chemical sensors subgroup is the receptor character. Biosensors typically use the receptors from the natural biological sources or mimic natural chemicals, whereas the other kinds of chemical sensors employ artificial organic or inorganic ligands in their receptor layer. Principally, the word “biosensor” referred to a wider range. The definitions point out the sensors used for determining any element of the biological

Fig. 16.4 Schematic of a biosensor.

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substances. Nowadays, the prefix “bio” specifies the character of the reaction which results in the output signal [17,18]. In essence, devices are considered sensors which are capable of innumerable analyses and persistent control of the target parameter (rather than the ones which are disposable and known as single-use devices). Selectivity is the vital property of sensors which makes it possible to determine specific components in complex samples (without the need to separate the sample components). This feature is due to the presence of the receptor layer. Short analysis time is the other considerable superiority of these kinds of sensors (chemical sensors containing biosensors) as compared to other standard analytical methods. In simple terms, biosensors are analytical apparatuses which use biological entities for detecting any analyte through the generation of a detectable response or signal. The output response is proportional to the concentration of the target analyte, which allows accurate determination of the analyte. Basically, biosensors are made up of three main components. The first part of the biosensor the biological element (bio-receptor) is responsible for the detection of the target analyte and producing the response signal. Afterward, the generated signal is converted into a detectable analytical response using the second part which is known as the transducer and is the most important element in any biosensing system. The third part is the detector that processes and amplifies the response prior to displaying them, employing an electrical display device. Employing an appropriate immobilization method (either reversible or irreversible) for bioreceptors immobilization at the surface of the desired transducer is the prerequisite to biosensor stability. To this end, various strategies can be utilized, which are grouped into the covalent binding, surface adsorption, cross-linking, bio-affinity, metal binding or chelation, and entrapment (fibers or beads) based on criteria such as sample type, desired selectivity, ranging, and difficulty. As a component for transforming energy (which produced through a physical variation accompanying a reaction) from one form into the other one, a transducer in a biosensor converts the bio-recognition phenomenon into a measurable response through a process which is called signalization. There are various types of transducers, namely, electrochemical, optical, quartz crystal piezoelectric, thermal, and colorimetric types. Nevertheless, most of the transducers, proportionate to the bioreceptor-analyte interactions, generate either electrical or optical signals. As mentioned before, biosensors are made up of three main elements. Accordingly, they can be classified based on two main components: (1) the bioreceptor and (2) the transducer. Fig. 16.5 demonstrates the biosensors classifications based on their transducers and bioreceptors [19,20]. Generally, bioreceptors can be categorized into five major groups, which are also the most common ones: (1) Enzymes (enzymatic interactions). (2) Antibodies/antigens (nntibodies/antigens interactions). (3) Nucleic acid/DNA (nucleic acid interactions). (4) Cellular structure/cell (cellular interactions such as microorganisms). (5) Biomimetic materials (such as interactions based on synthetic bioreceptors).

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Fig. 16.5 Classification of biosensors.

Among the abovementioned bio-recognition elements, the antibodies and enzymes are the main groups of bioreceptors which are broadly employed for biosensor applications.

16.6.1 Enzyme-based biosensors Up until now, enzymes have been the most broadly applied bioreceptor in biosensors. They have often been employed as bio-recognition elements due to their excellent catalytic activities as well as their special binding abilities. In these kinds of biosensors, the detection mechanism is amplified through a catalytic reaction. Enzymes, as natural proteins, are selected for biosensing applications and catalyze the conversion reaction of a special substrate to the product without being consumed during the reaction. They recognize a specific target analyte based on the lock-key strategy. Enzymes are quick acting as compared to other bioreceptors, and they can be applied simultaneously with various transduction mechanisms. More importantly, they are highly sensitive and selective in comparison to chemical reactions. The operation mechanisms of these kinds of bioreceptors include: (1) transformation of the target analyte into a product which is detectable in the sensor, (2) determination of the analytes that play the role as the activators or inhibitors of enzymes, and (3) investigation of the correction of the enzymes features during their interactions with target analytes [21].

16.6.2 Antibody/antigen-based biosensors (Immunosensors) Immunosensors employed antibodies as the bioreceptor with the aim of detecting particular antigens. Immunoassays are considered the most special analytical methods, can be

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applied for a broad range of analytes, and present extraordinary low limits of detection. They are widely used for monitoring proteins. The antibodies bind to their target antigen with excellent affinity; thus, they have the ability to identify the target analyte in the presence of various interference [22,23].

16.6.3 Nucleic acid-based biosensors These kinds of biosensors work based on the hybridization of RNA or DNA. Application of sequencing of nucleic acids for the special diagnostics usages has increased from early 1953 and is growing extensively till now. The binding reactions with the excellent specific affinity between two single-stranded DNA (ssDNA) to create double-stranded DNA (dsDNA) are applied in these kinds of biosensors with nucleic acids as bioreceptor. DNA biosensors (genosensors), which can determine single nucleotides comprising a DNA molecule, have attracted remarkable attention by virtue of their potential usages, including forensic study, clinical diagnostics, gene analysis, and some other medical utilizations. Also, the main goal of their rapid development is providing low-cost and fast testing approach for infectious and genetic diseases. Aptasensors are the other group of these biosensors which use aptamers as bioreceptors. Aptamers are single-stranded DNA or RNA molecules that bind to the analyte with high affinity and specificity. Because of the special characteristics of aptamers, aptasensors have more stability and will be well adapted to the real samples conditions [22,24].

16.6.4 Microbial biosensors Microbial biosensors are analytical devices that detect target analytes through the immobilization of microorganisms onto the transducers. Fungi and bacteria are microorganisms that can be employed as biosensors for the detection of special molecules or for totally monitoring the surrounding environment. Microorganisms contain several enzymes. These enzymes as bioelements in the living cells can generate the response to the target analytes selectively. Moreover, proteins of cells can be applied as bioreceptors for the determination of particular analytes. Integration of the microorganisms with the transducers is essential for constructing reliable microbial biosensors. In this regard, microorganisms have been merged with several transducers, namely, potentiometric, amperometric, conductometric, luminometric, fluorimetric, calorimetric, and colorimetric. The transducers are biosensor components with important role in the process of signal detection. They convert the biorecognition output signal into detectable ones. These detectable signals can be optical (luminescence, interferometry, fluorescence, and colorimetric), electrochemical (voltammetry, amperometry, conductometry, potentiometry, and impedimetry), mass change (acoustic wave/piezoelectric), or magnetic. As

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mentioned before, biosensors can be categorized on the basis of transducers that they employ. Transduction can be performed via various methods. Most forms of transducers can be classified into three major groups [25–27]: (1) Optical transducers. (2) Electrochemical transducers. (3) Mass-based transducers.

16.7 Biosensors applications Nowadays, biosensors have found vast applications in many fields (Fig. 16.6) such as food (genetic modifications, contaminations, toxins) and chemical industries, military (chemical and biological warfare), medical diagnosis (biomarkers, pathogens), clinical analysis, environmental monitoring (pollutants), etc., and present better sensitivity and stability as compared to the traditional approaches [22].

16.8 Self-powered biosensors As mentioned before, electrochemical biosensors are one of the most common class of biosensors. However, these type of biosensors and also others require instruments (i.e., potentiostat/galvanostat, signaling, and signal processing devices) that need external power sources. To solve this issue, in 2001, Katz and Willner introduced a group of

Fig. 16.6 Different application of biosensors.

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Fig. 16.7 Different applications of MFCs.

sensors named “self-powered biosensors.” This was the beginning of a modern kind of electrochemical biosensors and also the integration of the sensors and the fuel cell fields. In self-powered electrochemical biosensors, biofuel cells play an important role as the biosensor and the power source simultaneously. They make the biosensor systems simpler because they do not need potentiostat or external power sources for the instruments. Actually, self-powered biosensors determine the target analyte concentration by monitoring the output current or power signal of the biofuel cells. Therefore, they are appropriate alternatives for expensive and sophisticated equipment and decrease the demand for skilled operators. The variations in the value of power or current signals are owing to either inhibition or activation at one of the anode or cathode electrodes, depending on the type of the target analyte. It is interesting to note that prior to the introduction of this type of biosensors, this method had been employed in former microbial fuel cells (MFCs). Fig. 16.7 indicates different applications of MFCs. On the other hand, according to the IUPAC electrochemical biosensors are self-contained integrated systems that have the ability to present special analytical data (quantitative or semiquantitative) employing the bioreceptors which are in direct spatial relation with the electrochemical transducers. Accordingly, MFCs that apply bacteria as the bioreceptor in the anodic chamber in order to produce electrical output signals directly in response to the target analyte, which are added into the chamber exogenously, can be called biosensors. Enzymatic, organelle, logic-Gate, and microbial self-powered biosensors are examples of various types of biosensors in this classification [28].

16.9 MFC-based biosensors Microbial self-powered biosensors (Fig. 16.8) are outstandingly interesting types for special applications in the real world. As previously described, microbial self-powered biosensors depend on the microorganisms’ ability to exchange electrons with the surfaces of the electrodes that lead to obtaining MFCs. In fact, capability of MFCs to use microbial catabolism with the aim of transforming the organic substrates into electrical energy makes it possible to apply them as transducers in the microbial type of biosensors. A typical MFC consists of a cathodic and an anodic chamber where a proton exchange membrane (PEM) separates them from each other. In the anodic chambers of the MFCs,

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Fig. 16.8 Schematic diagram of an MFC as biosensor.

microorganisms oxidize substrates and generate protons and electrons. The produced protons are transferred to the cathodic compartment via the PEM. But, the electrons move to the surface of the anode electrode and then generate power by flowing to the cathode through the external electric circuit. In this way, a measurable power/ current output signal is gained. Various amounts of the organic substances, as well as the presence of different chemicals (i.e., toxic) that decrease or inhibit the activity of the microorganisms, can affect power generation and efficiency of the MFCs. Therefore, they can be applied as both turn-off and turn-on biosensors. The first turn-on biosensor, which employed an MFC, was constructed by Karube et al. in 1977 for monitoring the biological oxygen demand (BOD) [29]. A significant property of these kinds of biosensors is their long-time operational stability. The operation of these biosensors on the remarkably long-time scale is the result of continuing growth of new bacterial cells and replacement of old or dead cells by new ones. Moreover, in MFC-based biosensors, the microorganisms sense the target analytes and the corresponding responses are their output signals. Thus, in these devices, the sensing and signal conversion steps are merged in one step with no need for the transduction element and the external power source. More importantly, MFC-based biosensor does not require transducer for converting the output signal into its electrical version because it is already the electrical one. These characteristics simplify the construction of portable and disposable biosensing systems which provide remote and long-term sensing procedures [30].

16.9.1 The operation mechanism of MFCs as biosensors In MFCs, the electrochemically active microorganisms (EAMs) catalyze the process of degradation of the organic substances. Subsequently, the electrons that are released in

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the course of this procedure are transferred to the surface of the anode electrode [31]. So, the MFC generated electricity is the main factor that demonstrates the metabolic activity of the special microorganisms at the surface of the anode. Therefore, realizing the electron production mechanism in MFCs is of great importance for understanding the operation procedures and analytical applications of MFC-based biosensors. According to the literature, there are two mechanisms for the transfer of charge from biofilms to the surface of the anode: (1) direct electron transfer (DET) and (2) mediated electron transfer (MET) [32,33]. Additionally, the current generation efficiency of MFCs can be affected by different operational parameters, including pH, the anode potential, salinity, and temperature [34]. If the operations of MFC, in the presence of the abovementioned factors and in nonsaturated organic materials, continue to be constant, the biocatalytic activity is in direct association with the organic substances which feed into the system. Until the organic matter concentration attains a saturated point, the number of electrons transferred to the anode increases. Contrastingly, applying saturated organic matters and different amounts of toxic substances in the MFC input stream results in the inhibition of the substrate consumption and the microbial metabolism activity and variations in produced current [35,36]. Moreover, in the anodic chamber of the MFC-based biosensor, enrichment of EAM has a significant role as the bioreceptor that provides the response output signal to different concentrations of toxic matters in addition to playing the role as the biocatalyst for generating current from organic substrates. In this context, there are two strategies for the EAM inoculations. In the first one, a compound substance like soil, domestic wastewater, or anaerobic sludge is the source of inoculum, which supplies a consortium of bacteria for the anodic chamber [37–39]. As an alternative, recently, researchers have employed pure cultures as the anode inoculum [40–42]. However, the analytical operation factors of these biosensors, namely, detection range and time, and saturation signal, demonstrate no remarkable differences in the presence of either a particular bacteria or a bacterial consortium as the inoculum source; pure cultures have the capability to retain high uniformity and stability. Unlike the times employing an individual bacterial type in the anodic chamber, the variety of the bacterial consortium may be affected by various substrates which are fed into the MFCs. Consequently, the performance of the MFC as the biosensor, may be influenced, too [43,44]. On the other hand, the sole bacteria are appropriate to be manipulated for the fabrication of a viable and stable toxicant detector. Thus, applying the single strain as the biological sensing element of the anode could demonstrate the further research pathways toward the development of the MFC-based biosensors (Fig. 16.9).

16.9.2 Applications of MFC-based biosensors As mentioned in previous sections, the MFC-based biosensors are analytical devices that when integrated with bacteria as bioreceptors generate the output signals proportional to

MFC-based biosensors

Fig. 16.9 Schematic representation of the operation mechanism of MFC-based biosensors.

the concentrations of the target analytes. In comparison with the common biosensors, namely, algal-, enzyme-, or bluegill-based biosensors, MFC-based ones exhibit advantages in respect of simplicity and stability. Thus, they have been offered as promising devices for analytical applications. Today, they are considered as one of the most practical and effective instruments for monitoring clinical, food, and environmental samples [45,46]. 16.9.2.1 BOD monitoring BOD is an essential parameter in the monitoring water quality which refers to the amount of dissolved oxygen that microorganisms use throughout the oxidation process of substances [47]. As a result of the considerable increase in population and increasing civilization and industrialization, large amounts of industrial or domestic wastewaters are released into ponds, rivers, water reservoirs, or other kinds of surface waters. Mostly, the abovementioned effluents possess very high levels of BOD that can lead to intense water quality difficulties resulting in the aquatic organisms’ death, reduction in dissolved oxygen, or eutrophication [48]. Nevertheless, conventional approaches are not appropriate for real-time monitoring of BOD, and even they need external powered apparatus. Therefore, many efforts have been made for the development of MFC-based BOD biosensors. The first proposed MFC-based biosensor for BOD monitoring could only present an approximate value for BOD in industrial wastewater. But, another study performed more than 5 years revealed that the MFC demonstrated stable efficiency for

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monitoring BOD with the limit of detection (LOD) of 2.58 mg/L [29,49]. Although approximately all BOD biosensing devices were employed for monitoring high levels of BOD in industrial wastewater, a lot of research focused on monitoring its low values because the surface water and the secondary effluents often include low amounts of organic matters [50]. In these devices, O2-reducing activity at the surface of the cathode is a critical parameter. In this regard, Kang et al. proposed an MFC as a biosensor for low values of BOD in which employing a cathode with more affinity toward O2, the LOD was reported as 5 mg/L [51]. Up until now, several studies have been reported in this regard, and the results demonstrated that the MFC could be applied as a BOD biosensing device continuously. 16.9.2.2 Toxicants monitoring Online monitoring of different toxicants of domestic or industrial wastewaters is necessary for cyclic utilization of water resources and public health. Conventional sensors are sophisticated and expensive. To solve this issue, MFCs can offer low maintenance costs and long-term stability. Toxicants can influence the electrogenic microorganisms’ activities in biofilms leading to a sudden variation (either rise or fall) in voltage. Based on the various types of substrates which should be monitored, these kinds of biosensors can be classified into two major groups: (1) organic matter and (2) heavy metal biosensors. Actually, since microbial metabolism is the only driving force for the transformation of chemical energy to electrical one, the output of MFC is generally related to bacterial activity and viability. Thus, inhibition of the microbial activities will reduce the MFC outputs. Due to the exposure of bacteria to toxicants, the bacterial activity will be inhibited, and so the reduction of the MFC output signal could be determined. Therefore, MFC possesses the capability to be employed as a toxicant biosensor. 16.9.2.3 Food and fermentation monitoring Since the product quality is important for both the government and the customers, the development of fast-response and low-cost approaches to monitor the quality of the products and control the processes is of great importance [52]. Fermentation is broadly employed for the generation of drinks and foodstuffs that need a carefully carried out operation of the fermentation system [53]. MFC-based biosensors are applied to monitor the substances with the aim of controlling the fermentation process. Ethanol is very necessary and crucial in fermentation processes. Therefore, MFC-based biosensors are employed for determining the sensitivity of ethanol with the intention of controlling the fermentation process. In addition, the monitoring of food freshness and quality is of increasing interest to the food industry and consumers [52]. Today, there are growing demands for selective and quick analytical devices for monitoring food contaminants and nutrition factors [54].

MFC-based biosensors

In this regard, MFC-based biosensors are applied as affordable and rapid methods to control the quality of products. 16.9.2.4 Clinical diagnostics Conventional techniques for the diagnosis of different diseases face some obstacles, such as complicated processes, slow response time, and time-consuming operations that lead to difficult critical cares throughout emergencies [55]. In comparison with the enzymebased biosensing devices, MFC-based biosensors need no purification that is expensive and time-consuming. These biosensors provide inexpensive, rapid, and accurate approaches for diagnoses of DNA, hormones, and pathogens, which are factors crucial for living individuals. 16.9.2.5 Microbial activity (MA) monitoring Moreover, MFC-based biosensors can be applied for monitoring the microorganisms’ number and the MA in situ employing the relationships between the output currents and the microorganisms. The basis of in situ microbial biomass quantification and MA monitoring can be divided into two groups. One of the common approaches for MA determination is the monitoring of microbial respiration. The other is monitoring MAs via using the biomass concentration as the expression of the concentrations of the active microorganisms.

16.10 Conclusions MFC technology still meets significant obstacles in real-world usage with the aim of power production utilizing organic substances of wastewaters, excluding power supply for small sensing devices. A number of researchers have proposed other applications for MFCs. One of the promising applications is the utilization of MFCs as biosensors. These kinds of biosensors demonstrate significant promise for controlling the presence of toxicants, monitoring BOD, DO, VFA, corrosivity and the presence of corrosive biofilms, and the performance of anaerobic digester. MFC-based biosensors are often self-powered and low cost, with the ability for real-time monitoring. Some of these sensors may observe real deployment in the near future.

References [1] [2] [3] [4] [5]

J.W. Gardner, P.N. Bartlett, Sensors and Sensory Systems for an Electronic Nose, Springer, 1992. W. G€ opel, J. Hesse, J.N. Zemel, Sensors: A Comprehensive Survey, 1989. A. D’Amico, C. Di Natale, Introduzione ai sensori, Aracne, 2008. R. Pallas-Areny, J.G. Webster, Sensors and Signal Conditioning, John Wiley & Sons, 2012. A.D. Marcellis, G. Ferri, Physical and chemical sensors, in: Analog Circuits and Systems for VoltageMode and Current-Mode Sensor Interfacing Applications, Springer, 2011, pp. 1–35.

435

436

Biological fuel cells

[6] A. D’Amico, C. Di Natale, A contribution on some basic definitions of sensors properties, IEEE Sensors J. 1 (3) (2001) 183–190. [7] S. Middelhoek, et al., Silicon sensors, Meas. Sci. Technol. 6 (12) (1995) 1641. [8] S.D. Senturia, Microsystem Design, Springer Science & Business Media, 2007. [9] S.M. Sze, Y. Li, K.K. Ng, Physics of Semiconductor Devices, John wiley & sons, 2021. [10] R.C. Dorf, The Electrical Engineering Handbook-Six Volume Set, CRC Press, 2018. [11] G. Ferri, N.C. Guerrini, Low-voltage low-power CMOS integrated architectures for sensor interfaces, Electron. World 108 (1799) (2002) 12–20. [12] F.-G. Banica, Chemical Sensors and Biosensors: Fundamentals and Applications, John Wiley & Sons, 2012. [13] P. Gr€ undler, Chemical Sensors: An Introduction for Scientists and Engineers, Springer Science & Business Media, 2007. [14] D. Schuetzle, R. Hammerle, Fundamentals and Applications of Chemical Sensors, 1986. [15] W.R. Seitz, M.J. Sepaniak, Chemical Sensors Based on Immobilized Indicators and Fiber Optics, 1988. [16] R. Nießner, Chemische Sensoren: Prinzipien und Anwendungen, Analytiker Taschenbuch 7 (1988) 55. [17] K. Cammann, Bio-sensors based on ion-selective electrodes, Fresenius’ Z. Anal. Chem. 287 (1) (1977) 1–9. [18] D.R. Thevenot, et al., Electrochemical biosensors: recommended definitions and classification, Pure Appl. Chem. 71 (12) (1999) 2333–2348. [19] P. Mehrotra, Biosensors and their applications—a review, J. Oral Biol. Craniofac. Res. 6 (2) (2016) 153–159. [20] J.H. Luong, K.B. Male, J.D. Glennon, Biosensor technology: technology push versus market pull, Biotechnol. Adv. 26 (5) (2008) 492–500. [21] A.A. Ensafi, An introduction to sensors and biosensors, in: Electrochemical Biosensors, Elsevier, 2019, pp. 1–10. [22] C. Karunakaran, K. Bhargava, R. Benjamin, Biosensors and Bioelectronics, Elsevier, 2015. [23] A.L. Ghindilis, et al., Immunosensors: electrochemical sensing and other engineering approaches, Biosens. Bioelectron. 13 (1) (1998) 113–131. [24] H.-M. So, et al., Single-walled carbon nanotube biosensors using aptamers as molecular recognition elements, J. Am. Chem. Soc. 127 (34) (2005) 11906–11907. [25] S. D’souza, Immobilization and stabilization of biomaterials for biosensor applications, Appl. Biochem. Biotechnol. 96 (1) (2001) 225–238. [26] S. Choi, J. Chae, Optimal biofilm formation and power generation in a micro-sized microbial fuel cell (MFC), Sensors Actuators A Phys. 195 (2013) 206–212. [27] Z. Du, H. Li, T. Gu, A state of the art review on microbial fuel cells: a promising technology for wastewater treatment and bioenergy, Biotechnol. Adv. 25 (5) (2007) 464–482. [28] E. Katz, A.F. B€ uckmann, I. Willner, Self-powered enzyme-based biosensors, J. Am. Chem. Soc. 123 (43) (2001) 10752–10753. [29] I. Karube, et al., Microbial electrode BOD sensors, Biotechnol. Bioeng. 19 (10) (1977) 1535–1547. [30] C. Dai, S. Choi, Technology and Applications of Microbial Biosensor, 2013. [31] B.E. Logan, et al., Microbial electrolysis cells for high yield hydrogen gas production from organic matter, Environ. Sci. Technol. 42 (23) (2008) 8630–8640. [32] K.P. Nevin, et al., Anode biofilm transcriptomics reveals outer surface components essential for high density current production in Geobacter sulfurreducens fuel cells, PLoS One 4 (5) (2009), e5628. [33] K. Inoue, et al., Purification and characterization of OmcZ, an outer-surface, octaheme c-type cytochrome essential for optimal current production by Geobacter sulfurreducens, Appl. Environ. Microbiol. 76 (12) (2010) 3999–4007. [34] J. Chouler, M. Di Lorenzo, Water quality monitoring in developing countries; can microbial fuel cells be the answer? Biosensors 5 (3) (2015) 450–470. [35] X.C. Abrevaya, et al., Analytical applications of microbial fuel cells. Part I: Biochemical oxygen demand, Biosens. Bioelectron. 63 (2015) 580–590.

MFC-based biosensors

[36] M. Di Lorenzo, et al., A small-scale air-cathode microbial fuel cell for on-line monitoring of water quality, Biosens. Bioelectron. 62 (2014) 182–188. [37] D. Yu, et al., Toxicity detection in water containing heavy metal ions with a self-powered microbial fuel cell-based biosensor, Talanta 168 (2017) 210–216. [38] H. Deng, et al., Using electrical signals of microbial fuel cells to detect copper stress on soil microorganisms, Eur. J. Soil Sci. 66 (2) (2015) 369–377. [39] L. Zeng, et al., FePO4 based single chamber air-cathode microbial fuel cell for online monitoring levofloxacin, Biosens. Bioelectron. 91 (2017) 367–373. [40] G.-H. Wang, et al., Utility of Ochrobactrum anthropi YC152 in a microbial fuel cell as an early warning device for hexavalent chromium determination, Sensors 16 (8) (2016) 1272. [41] D. Da´vila, et al., Silicon-based microfabricated microbial fuel cell toxicity sensor, Biosens. Bioelectron. 26 (5) (2011) 2426–2430. [42] X. Wang, N. Gao, Q. Zhou, Concentration responses of toxicity sensor with Shewanella oneidensis MR-1 growing in bioelectrochemical systems, Biosens. Bioelectron. 43 (2013) 264–267. [43] Z. Chen, et al., A novel biosensor for p-nitrophenol based on an aerobic anode microbial fuel cell, Biosens. Bioelectron. 85 (2016) 860–868. [44] K.-J. Chae, et al., Effect of different substrates on the performance, bacterial diversity, and bacterial viability in microbial fuel cells, Bioresour. Technol. 100 (14) (2009) 3518–3525. [45] Y. Lei, W. Chen, A. Mulchandani, Microbial biosensors, Anal. Chim. Acta 568 (1–2) (2006) 200–210. [46] H. Yang, et al., Microbial fuel cells for biosensor applications, Biotechnol. Lett. 37 (12) (2015) 2357–2364. [47] M.R. Penn, J.J. Pauer, J.R. Mihelcic, Biochemical oxygen demand, Environ. Ecol. Chem. 2 (2009) 278–297. [48] T. Zhou, et al., Microbial fuels cell-based biosensor for toxicity detection: a review, Sensors 17 (10) (2017) 2230. [49] B.H. Kim, et al., Novel BOD (biological oxygen demand) sensor using mediator-less microbial fuel cell, Biotechnol. Lett. 25 (7) (2003) 541–545. [50] H.-S. Moon, et al., On-line monitoring of low biochemical oxygen demand through continuous operation of a mediator-less microbial fuel cell, J. Microbiol. Biotechnol. 15 (1) (2005) 192–196. [51] K.H. Kang, et al., A microbial fuel cell with improved cathode reaction as a low biochemical oxygen demand sensor, Biotechnol. Lett. 25 (16) (2003) 1357–1361. [52] L.D. Mello, L.T. Kubota, Review of the use of biosensors as analytical tools in the food and drink industries, Food Chem. 77 (2) (2002) 237–256. [53] Y.-H. Kim, J.-S. Park, H.-I. Jung, An impedimetric biosensor for real-time monitoring of bacterial growth in a microbial fermentor, Sens. Actuators B 138 (1) (2009) 270–277. [54] S. D’souza, Microbial biosensors, Biosens. Bioelectron. 16 (6) (2001) 337–353. [55] B.D. Malhotra, A. Chaubey, Biosensors for clinical diagnostics industry, Sens. Actuators B 91 (1–3) (2003) 117–127.

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CHAPTER 17

Sediment microbial fuel cell (SMFCs) Atieh Zabihollahpoor and Mostafa Rahimnejad

Biofuel and Renewable Energy Research Center, Chemical Engineering Department, Babol Noshirvani University of Technology, Babol, Mazandaran, Iran

17.1 SMFCs and constructed wetland (CW) associated with it SMFC or benthic MFC is a bioelectrochemical and in situ system, which can harvest electricity along with pollutant treatment of sediments. The main parts of the SMFC system are an anoxic anode buried in organic-rich sediment and an oxic cathode positioned in the water compartment of SMFCs (Fig. 17.1) [1]. Microorganisms as biocatalysts on the anode surface reduce organic substrates in the sediment or wastewater and produce protons and electrons [2]. In SMFCs, the separator of anodic and cathodic parts is a naturally occurring oxygen gradient. The protons are directed to the cathode by sediments and the electrons are transferred to the cathode across a load. Oxygen (nitrate, iron, etc.) as a redox electron acceptor on the cathode surface combines with the transferred electron and protons to produce the related reduced product [3,4]. Recently, SMFCs have been applied for wastewater treatment, environmental remediation projects of organic matter-rich sediments, and powering remote oceanographic instruments such as sensors, telemetry systems, and monitoring devices [3,5]. Applying plants into SMFCs leads to a CW-MFC mimetic structure. The CW-MFC is also a wastewater phytoremediation system similar to plant SMFCs. The plant rhizosphere microorganisms convert solar energy to biological energy (bioelectricity) (Fig. 17.1) [5]. The role of plants in these systems are as a carbon source for microorganisms, supplying other nutrients by up-taking the contaminants, a base material for biofilm formation and regulating water flow in the wetland [6]. It has also been observed that the presence of plants can increase the microbial density in the cathode zone and stimulate the electricigenic microbial population in the anode zone [6]. In compared with the freshwater SMFCs, using plants in the cathode zone can produce as much as 18 times higher current density [2]. The microorganism in the roots of plants oxidizes the exudate organic compounds by the plants and produce CO2, electrons, and protons. Same as the SMFC system, the proton are flown from the anode to the cathode by sediments as a natural redox gradient and the electrons are attached to the anode [5]. The significant difference of plant SMFCs and CW-MFCs is that in plant SMFCs, the electrogenic microorganisms in the rhizosphere of a plant are just fed by the exudate organic compounds by the plants and rhizodeposits while in CW-MFCs, microorganisms are fed with both wastewater and organic compounds [3]. Biological Fuel Cells https://doi.org/10.1016/B978-0-323-85711-6.00004-7

Copyright © 2023 Elsevier Inc. All rights reserved.

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Fig. 17.1 Schematic diagram of SMFCs (left), and CW-MFCs (right).

Improving the oxygen reduction at the cathode can better the function of SMFC and CW-MFC systems. The purpose of this chapter is to better understand the factors affecting the improvement of SMFC and CW-MFC performance.

17.1.1 Fundamentals of SMFCs and CW-MFCs The SMFCs as a kind of MFCs can produce bioelectricity by oxidation of the sediment’s organic matter content based on the oxidation function of autochthonous electrogenic microorganisms [7]. SMFC is made of a cathode installed at the water phase with high dissolved oxygen (DO) and an anode which is buried in an anoxic marine sediment. Electrochemically active bacteria such as the genera Geobacter and Desulfuromonas degrade the organic content of sediments thereby releasing the electron and proton [8]. Some of the half-cell anodic and cathodic equations are shown in Table 17.1. The mechanisms of electron displacement from electrogenic microorganisms to the anode are composed of direct mechanisms based on membrane-associated cytochromes, conductive pili, Table 17.1 Some of half-cell anodic and cathodic equations in SMFCs and CW-MFCs [2,3]. Anodic reaction

Cathodic reaction

CH3COOH + 2H2O ! 2CO2 + 8H + 8e +  HS + 4H2O ! SO2 4 + 9H + 8e 2+ + 2Fe + 3H2O ! Fe2O3 + 6H + 2e +  H2S + 4H2O ! SO2 4 + 6H + 8e 0 +  H2S ! S + 2H + 2e CH2O + H2O ! CO2 + 4H+ + 4e +



2O2 + 8H+ + 8e ! 4H2O +  2NO 3 + 12H + 10e ! N2 + 6H2O +   NO3 + 2H + 2e ! NO2 + H2O MnO2 + 4H+ + 2e ! Mn2+ + 2H2O +  2+ MnO 4 + 8H + 5e ! Mn + 4H2O

Sediment microbial fuel cell (SMFCs)

and nanowires or mediated mechanism by exogenous soluble redox compounds or electron shuttles [9]. The produced electrons move to the cathode via the outer circuit, while the protons travel to the cathode via sediments as proton-permeable natural media [10]. Based on recent studies, the performance of SMFCs are affected by parameters such as electrode materials, distance between electrodes, temperature, pH, salinity, DO near the cathode, organic matter in the sediment, bacteria, etc. [2,3]. CW-MFC is a new engineered systems and a subclass of SMFCs designed for wastewater treatment with a synergistic combination of biological, chemical, and physical functions of plant, sediment, electrogenic microorganisms, and organic content of wastewater [2,11]. Pollutants in wastewater can improve the growth of plants and provide the source of protons and electrons needed to generate electricity at the same time. The main advantages of CW-MFC are their comparatively easy and inexpensive installation, operation, and maintenance [11,12]. Plant-applied SMFCs are a CW-MFC similar system. So, both the systems are considered in the same category in some literatures. Therefore, a CW-MFC is constructed by installing an anode in the deep layer of sediment and a cathode in rhizosphere or in water containing dissolved oxygen.

17.1.2 Factors affecting the performance of SMFCs and CW-MFCs 17.1.2.1 Electrode materials In SMFCs and CW-MFCs as previously noted, the energy produced by the reduction of organic matters in sediments is converted to electrons. The electrons are transferred to a buried working electrode (anode) and then flow across a load to the counter-electrode (cathode). The significant parameters in improving SMFC performance to harvested electricity from sediments are electrode material, geometry, and surface modification [7,13]. These factors affect electron transfer, microbial adhesion to electrode surface, and substrate oxidation. Until now, several different anode and cathode materials have been investigated in SMFC systems, including different geometries of graphite, activated carbon, carbon, stainless steel, and their modification surfaces [7]. Table 17.2 shows the brief summary of current and power densities of several different electrode materials, geometries, and surface modification that were applied in SMFCs and CW-MFCs. As can be seen, a graphite tank as the anode with a stainless steel cathode electrode in SMFCs [24] and granules of graphite as an anode with Pt-coated carbon cloth as the cathode in CW-MFCs [44], both without surface modification, demonstrated an ever highest power density of 100 and 320 mW/m2, respectively. In addition to electrode material, the geometry of the electrode also is effective for the function of SMFCs and CW-MFCs. Selecting a shape of electrode with higher surface area can enhance the power performance of SMFCs due to more substrate diffusion [2]. To improve adhesion of microorganism onto the anode surface, several hydrophilic groups must be introduced onto it to change the contact angle and wettability of the anode surface [7]. As can be observed in Table 17.2, surface modification of the electrode

441

Table 17.2 Various geometry of anode and cathode materials for the design of SMFCs and CW-MFCs. Type of No. MFC

Anode material/ geometry

Anode surface modification

1

PlantSMFC

Graphite/ felt

–

2

SMFC

Carbon/ fiber brush

–

3

SMFC

4

SMFC

5

SMFC

Graphite felt Graphene (GR) Graphene oxide (GO) carbon nanotubes (CNTs) Carbon/ Heat treated cloth carbon/ – cloth

6

CW-MFC Gravel

7

CW-MFC Carbon – fiber/felt stainless steel/mesh graphite/rod nickel/ foamed

–

Cathode material/ geometry

Cathode surface modification

Stainless Magnetic steel/mesh particle of palladiumchitosan polymer Stainless Manganese steel/mesh dioxide/ tourmaline composite Graphite/ – felt

Carbon/ cloth Carbon/ clothcomb type Graphite/ felt Carbon fiber/felt stainless steel/mesh graphite/ rod nickel/ foamed

Heat treated

COD removal efficiency %

Power density

–

1298

[14]

–

368.99

[15]

Current density

–

–

Reference

[16]

23.43

[13]

–

3.77  102

[17]

–

288 mV/m3

1.17 A/m3

[18]

–

–

[19]

–

–

8

SMFC

9

SMFC

10

SMFC

11

SMFC

12

SMFC

13

SMFC

14

SMFC

15

SMFC

16

SMFC

Graphite/ plate Graphite/ felt Activated carbon/fiber felt (ACFF) Graphite/ felt Carbon/ paper Graphite/ tank Graphite/ rode Graphite/ disk Stainless steel Carbon sponge carbon cloth carbon fiber reticulated vitreous carbon (RVC) Graphite/ disk Graphiteceramic composite Graphite paste

–

– – – – –

– –

adsorption of AQDS or NQ Mn2+ and Ni2+,

Fe3O4 or Fe3O4 and Ni2+

Graphite/ plate Graphite/ felt Graphite/ felt

–

–

4.08 mW/m2

–

–

74.5 mW/m2

Graphite/ felt Carbon/ paper Stainless steel –

–

–

4 mW/m2

–

–

1 mW/m2

–

–

100 mW/m2

3500 mA/m2

[24]

–

–

19.57  0.35 8.72  1.39

23.72 5.39

[25]

–

–

23

140

[26]

–

–

55 19–27.5 4.5 0.2

100 50 5 0.8

[27]

–

–

98

–

[28]

105

–

–

–

Stainless steel carbon cloth

Graphite/ disk

3 mA/m2 10 mA/m2

[20]

[21] 45.4 mA/m2

[22] [23]

Continued

Table 17.2 Various geometry of anode and cathode materials for the design of SMFCs and CW-MFCs—cont’d Type of No. MFC

Anode material/ geometry

17

SMFC

Graphite/ rod

18

SMFC

Graphite/ plate or GC Graphite/ plate

19

20

SMFC

SMFC

Graphite paste or GC Graphite paste

Graphite/ cloth

Anode surface modification

Electrodeposited with Fe/Ferric oxide oxidize

Cathode material/ geometry

Cathode surface modification

COD removal efficiency %

Power density

Graphite

–

–

740

Graphite

–

–

Graphite

–

–

Current density

Reference

[29]

[30]

Oxidize and modified with AQDS Sb(V) complex PTFE solution sulfonated polyaniline and PTFE sulfonated polyaniline/ vanadate composite and PTFE –

48.9 129.1

187.1

Carbon/ cloth carbon/ paper carbon/ sponge graphite/ thick disk RVC Pt/C Pt/Ti mesh CoTMPP Fe– CoTMPP

–

–

25 0.2 38 7 12 8 – 32 62

2.5896  107 A/cm2 2.3015  106 A/cm2

[31]

5.9863  106 A/cm2

[32]

Stainless – steel/ cylindrical Graphite felt –

Activated carbon/ granule Graphite/ felt

–

Graphite/ felt

– –

Carbon Graphite/ plate Graphite Activated carbon/ granule Carbon/ felt Carbon/ cloth Graphite/ granular Graphite/ rod Activated carbon/ granule Graphite/ granular Ptcarbon/ cloth Ptcarbon/ cloth

21

SMFC

22

SMFC

23

SMFC

24 25

CW-MFC Carbon CW-MFC Graphite/ plate CW-MFC Graphite CW-MFC Activated carbon/ granule CW-MFC Carbon/felt

26 27

28 29 30 31 32

Graphite/ felt

CW-MFC Graphite/ disk CW-MFC Graphite/ granular CW-MFC Graphite/ rod CW-MFC Activated carbon/ granule Graphite/ granular Graphite/ granular Activated carbon/ granule

– – – – – – –

–

–

3.5

–

[33]

Polyaniline graphene nanosheets Multiwalled carbon nanotubes – –

65.7

99

479.8

[34]

–

38

270

[35]

75 76.5

15.73 12.37

69.75 –

[36] [37]

– –

100 85.55

2 0.852 W/m3

8

[38] [39]

–

100

6.12

–

–

18

105

[41]

–

64

0.268

0.408 A/m3

[42]

–

61

36

219 mA/m2

[43]

–

90.9

43.63

125

[44]

80.9

0.1

5

84

320.8

422.2

91.4

92.48

225

[40]

Continued

Table 17.2 Various geometry of anode and cathode materials for the design of SMFCs and CW-MFCs—cont’d Type of No. MFC

33 34

35

36 37

38

39

40

Anode material/ geometry

Anode surface modification

CW-MFC Carbon – fiber/felt CW-MFC Activated – carbon/ granule CW-MFC Carbon fiber – felt Stainless steel (SS) mesh Graphite rod Foamed nickel CW-MFC Activated carbon CW-MFC Activated carbon/ granule CW-MFC Activated carbon/ granule CW-MFC Activated carbon/ granule CW-MFC Magnesium

– – – – –

Cathode material/ geometry

Cathode surface modification

COD removal efficiency %

Power density

Current density

Reference

Carbon fiber/felt Activated carbon/ granule Carbon fiber felt Stainless steel (SS) mesh Graphite rod Foamed nickel Activated carbon Activated carbon/ granule Activated carbon/ granule Activated carbon/ granule Graphite

–

80.7

8.08

53.74

[45]

–

–

87.79

–

[46]

–

42.30 37.42

4.80 mW/m2 2.30 mW/m2

[47]

48.78 35.73

3.35 mW/m2 5.11 mW/m2

48.12 19.19 35.59 39.79 mA/m2

–

98–99

184.75  7.50 mW/m3 –

[48]

–

–

0.88 W/m3

0.310 A/m2

[49]

–

94.90

0.15 W/m3

0.49 A/m3

[50]

–

82.32  12.85 3.71 W/m2

16.63 mA/m2

[51]

–

85.10–88.25

1.19–7.49 W/m2

10.6–25.2 mA/m2 [52]

AQDS, anthraquinone-1,6-disulfonic acid; NQ, 1,4-naphthoquinone; GC, glassy carbon; PTFE, Polytetrafluoroethylene; RVC, reticulated vitreous carbon; CoTMPP, Cobalt tetramethoxyphenyl porphyrin; Pt/C, platinised carbon; Pt/Ti, platinised titaniu.

Sediment microbial fuel cell (SMFCs)

surface has significantly increase the power density of the SMFCs in most cases, such as a graphite rod anode electrode, which was electrodeposited with Fe/Ferric oxide [29] and magnetic particles of palladium and chitosan polymer-modified stainless steel cathode electrode [14]. Oxygen reduction rate as the acceptor of electron on the cathode surface is vital for the power production of SMFC and CW-MFCs. As cathode electrodes catalyze the oxygen reduction reaction, carbon-based materials such as carbon, graphite, and activated carbon are commonly applied materials as cathode electrodes due to their high conductivity in compare with nonnoble metals [15]. To increase the oxygen reduction rate, the concentration of DO of the cathode chamber must be improved. Researchers have proposed several kinds of cathodes such as rotating, floating, air, algae, and plant rhizosphere cathodes to increase the dissolved oxygen [17]. Various geometry of anode and cathode materials have been investigated for the design of SMFCs and CW-MFCs (Table 17.2). For example, carbon sponge as the anode in SMFC meliorate a power density of 55 mW/m2 compared with 0.2 mW/m2 with a reticulated vitreous carbon (RVC) anode [27]. In another investigation by Scott et al. [32], a higher power density achieved was 38 mW/m2 with carbon sponge as the cathode electrode, which was higher than that obtained with carbon paper and cloth. 17.1.2.2 Electrode spacing and external resistance The spacing between the cathode and anode electrodes in SMFC and CW-MFCs affects the maximum power production. The longer distance of the electrons from the anode to cathode causes less current produced due to the higher loss of electrons [53,54]. In other word, by reducing the electrode distance the power generation increased due to decreasing in ohmic resistance [55]. For example, it was investigated that when the electrode spacing was varied from 12 to 100 cm in the SMFCs, the average current density was decreased from 11.5 to 2.11 mA/m2 and the maximum power density decreased from 1.01 to 0.37 mW/m2 [56]. So, spacing the electrodes near to each other could increase the current production. Sajana et al. [55] observed a similar trend on the reduction of power generation of SMFCs operated with the same external resistance and feed pH. The SMFC with lower electrode spacing (50 cm) gave higher power generation (3.96 mW/m2) in comparison with power generated (3.57 mW/m2) with the higher distance between the electrodes (100 cm) under the same operating condition [55]. In different types of MFCs such as SMFCs, the external resistance (Rex) could control the transfer of electrons from the anode to the cathode electrode [55]. So, the optimal external resistance is a key point, which influences the outputs of fuel cells such as power production, COD removal, and exoelectrogenic microorganism’s activity. This parameter is specified by the potential difference of anode and cathode electrode and current, which is flown through the circuit [57]. At low resistance, which is equivalent to higher current resulting from the highest electron transfer to the cathode, exoelectrogenic

447

448

Biological fuel cells

microorganisms can improve the cathode reaction. As a result, the growth of electrogenic bacteria and the power and current generation of SMFCs could increase at low external resistance [55]. The MFC operated with lower Rex (20 Ω), generate higher power density of 66 mW/m2 in compared with the MFCs operated with 249, 480, and 1000 Ω Rex [58]. Corbella et al. [18] investigated that the treatment efficiency of CW-MFC was higher at 220 Ω when Rex was increased from 50 to 1000 Ω (50, 220, 402, 604, and 1000 Ω). In a similar trend, power density generated from SMFC operated with lower Rex was higher (3.96 mW/m2) than those operated with higher Rex (3.09 mW/m2) [55]. 17.1.2.3 Effect of catalysts and mediators It was investigated in the literature that SMFC and CW-MFC systems with catalyzed cathode and anode electrodes can significantly improve power generation in comparison with noncatalyzed electrodes. As, for example, a Fe/Ferric oxide electrodeposited graphite electrode produced the power density of 740 mW/m2 in comparison with plain graphite (17.4-fold higher) in SMFC [29]. Results also indicate that higher power densities (1.9 and 218, respectively) were obtained applying anthraquinone-1,6-disulfonic acid (AQDS)-modified glassy carbon graphite and oxidized and subsequently AQDS modified graphite electrodes in SMFC [30]. YuBin et al. [31] developed a unique sulfonated polyaniline/vanadate composite anode and used in ocean floor (BMFCs), which produced the power density of 187.1 mW/m2. Anthraquinone-1,6-disulfonic acid (AQDS) or 1,4-naphthoquinone (NQ)-modified graphite, Mn2+ and Ni2+ containing graphite-ceramic composite and Fe3O4 or Fe3O4 and Ni2+ modified graphite paste anode electrodes in comparison with plain graphite significantly improve the kinetic activity of SMFC [28]. As mentioned before, the power generation in SMFCs or CW-MFCs depends on the reduction kinetics of oxygen (nitrate, iron, etc.) as redox electron acceptors occur at the cathode [3]. So, applying a catalyst or nonsoluble artificial electron mediators at the cathode material can improve the slow kinetics of oxygen reduction reactions, which is a surface electrochemical phenomenon [59]. Different catalyst materials applied in SMFCs and CW-MFCs are presented in Table 17.2. One of the commonly used materials as catalysts in cathode electrodes is platinum (Pt)-coated carbon due to their low catalytic overpotential and low activation energy to accomplish the oxygen reduction reaction [60]. Srivastava et al. [44] reported the maximum power density of 320.8 mW/m3 using a Pt-coated carbon cloth cathode in CW-MFC. Also, a marine SMFCs produced power density of 207 mWm2 from a platinum (Pt)-modified carbon felt cathode [61]. But, Scott et al. [32] demonstrated that applying mediators such as cobalt tetramethoxyphenyl porphyrin (CoTMPP), platinized carbon (Pt/C), and platinized titanium (Pt/Ti) for easy movement of electrons can generate a higher power density than carbon catalyst in SMFCs. A maximum power density of 62 mW/m2 was obtained from a carbon paper catalyzed with Fe-CoTMPP.

Sediment microbial fuel cell (SMFCs)

Pt-coated material for catalysts are expensive due to high energy requirement for the production and limited reserves, and poisoning due to the presence of H2S and other organics [60]. So, microbially mediated cathodes (biocathodes), which applied oxidizing bacteria, are a good alternative option due to their sustainable cathode operation and low costs [62]. As for example, Wang et al. [60] reported that the floating biocathodes after a start-up of 10 days produced the maximum power density of 1.00 W/m3, which was better than Pt-catalyzed carbon paper cathode. Algal biocathodes can also overcome oxygen depletion by producing oxygen in the cathode compartment [2]. Najafgholi et al. [63] reported the maximum power density of 46.148 mW/m2 (twofold higher power output) in SMFC, which was produced by applying seaweed as a biocathode. 17.1.2.4 Effect of pH, dissolved oxygen, and temperature The operating pH in the anodic compartment affects the power generation and contaminant remediation in CW-MFCs and SMFCs. He et al. [64] observed that the highest current value happens between pH of 7 and 8 and current decreases at pH below 7 and at a pH of 9 [55]. The operating pH in SMFCs is a crucial factor in optimizing bacterial growth conditions by impact on the formation of biofilm, proton shuttling, and the pH of microbial cytosolic and ionic concentrations [1]. Sajana et al. [55] investigated that in a SMFC operated at pH of 6.5, a power output of 3.96 mW/m2 was produced while a higher power output of 4.52 mW/m2 was obtained at pH of 8.5. The biofilm formation of electrogenic bacteria at lower pH is decreased. Zhang et al. [65] also obtained the faster COD removal with lower power (95–116 mW/m2 vs 182–237 mW/m2) and voltage output under acidic pH conditions (pH range of 6.7–7.2) due to better growth of methanogenic bacteria and undesirable growth of electrogens. Supporting these findings, it was reported that COD removal efficiencies and the maximum power densities of 76.2% and 63 mW/m2 were achieved for an SMFC fed with the acidic fermentation broth of cyanobacteria [66]. The performance of CW-MFC is strongly influenced by pH. As for example, for a CW-MFC operated at neutral influent condition, higher bioenergy production (8.08 mW/m2) and COD removal efficiency was obtained in comparison with acidic and alkaline pH [45]. As mentioned earlier, the concentration of DO of the cathode chamber is an important factor to increase the oxygen reduction rate. It was investigated that using several kinds of cathodes such as rotating, floating, air, algae, and plant rhizosphere cathodes could enhance the DO followed by power production [17]. He et al. [67] applied a rotating cathode in a river SMFC and as a result increased the DO in the water from 0.4 to 1.6 mg/L. Increasing the dissolved oxygen concentration resulted in a higher power yield (49 mW/m2) versus the nonrotating cathode (29 mW/m2). Wang et al. [60] applied the floating biocathodes after start-up of 10 days produced the maximum power density of 1.00 W/m3, which was better than a Pt-catalyzed carbon-paper cathode. Wang et al. [35] studied the effect of photosynthetic process of the algae (Chlorella vulgaris) on the

449

450

Biological fuel cells

DO level and subsequently power generation in an SMFC. It was investigated that the maximum power density increased to 21 mW/m2 with the algae-assisted cathode. The use of an air cathode can also increase the DO concentration (1–2 mg/L higher) in comparison with submerged cathode in SMFCs [68]. Yan et al. [69] found that using an air cathode can significantly increase chemical oxygen demand (COD), NH3-N removal efficiency and the bioenergy output (4.21 mW/m2) of a CW-MFC compared with a nonair cathode system (0.005 mW/m2). Algae-assisted cathode have also been used in CW-MFC to increase the DO as was reported by Gupta et al. [70] and Srivastava et al. [71]. Temperature can also affect SMFC and CW-MFCs performance by impact on their kinetics, thermodynamics, mass transfer coefficient, and finally nature and distribution of the microbial community [1]. Most of the microorganism in the sediments are mesophilic and as a result their optimum temperature is around 35°C. Their metabolism also slows at temperature between 10°C and 20°C. Hong et al. [56] investigated that the maximum current density of an SMFC is negatively affected by low temperature. The maximum current production was 52.6 mA/m2, which was obtained at temperature 35°C in comparison with 15.6 and 35.9 mA/m2 at temperatures of 10 and 20°C, respectively. A costeffective and related mechanism for enhanced NH4+ removal was applied in CW-MFC at different temperatures. CW-MFC completely removed NH4+ at 12.8–16.8°C [72]. 17.1.2.5 Plants Plants which are composed of biomass, root, and stem parts in constructed wetlands are crucial in pollutant degradation and generation of electricity [73]. The roles of roots in wetland plants are photosynthesis, oxygen secretion (by radial oxygen loss), and excretion of organic compounds to provide carbon source [74,75] for the microorganisms in the rhizosphere. The mechanism of pollutant degradation by roots of plants are absorption, adsorption, and enrichment. Creating surface area for biofilm formation, and preventing the blocking of the subsurface of the wetland are the other tasks of plant’s root. Some of different wetland plants used in CW-MFC are summarized in Table 17.3. As for example, Liyan Di et al. [78] exhibited the positive effect of roots of wetland plants on electricity production and pollutant degradation in CW-MFCs. Scirpus validus showed highest power density, voltage, and nitrobenzene (NB) removal efficiency (19.5 mW/m2, 590 mV, 93.9%) as a result of higher DO (2.57  0.17 mg/L) and root biomass (16.42  0.18 g/m2). Liu et al. [74] developed an integrated, vertical flow CW-MFC to investigate the effect of three commonly used plants on swine wastewater treatment and power generation. Canna indica and Ipomoea aquatica have the higher decontamination capability (ammonium nitrogen removal of 75.02%) and the largest effect on electricity production (maximum power density of 0.4964 W/m3), respectively. As shown in Table 17.3, C. indica and Iris pseudacorus are mostly evaluated for wastewater phytoremediation in the CW-MFCs.

Table 17.3 Some of different wetland plants investigated in CW-MFC for phytoremediation of wastewater. No.

1 2

3 4

5 6

7

8

Plant

Canna indica Iris pseudacorus Lythrum salicaria Phragmites australis Eichhornia crassipes Scirpus validus Typha orientalis I. pseudacorus Chlorella vulgaris sp C. indica Acorus calamus Ipomoea aquatica Cyperus prolifer Wachendorfia thyrsiflora P. australis Typha latifolia L. Typha angustifolia L. Juncus gerardii Carex divisa

Wastewater

COD removal (%)

Max power density

Max current density

CE%

Reference

75–90 61.3  8.7% 56.8  10.1%

124.89 mW/m 1.67–8.51 mW/m2 3.15–5.67 mW/m2

– 99.07–105.26 mA/m2 58.82–77.39 mA/m2

4.64–9.24 6.8–8.96

48.5  5.3%

7.59–14.71 mW/m2

71.2–145.5 mA/m2

9.71–19.85

Synthetic

99

45.46  3.83 mW/m3

370 mA/m2

2.15

[77]

Nitrobenzene

94.2%, 95.1% 93.1% 96.37  2.6%

19.5 mW/m2 – 62.8 mW/m2 33.14 mW/m3

56.9 mA/m2 – 100.6 mA/m2 235.0 mA/m3

– – – –

[78]

Swine

88.07% 84.70% 82.20%

0.4136 W/m3 0.3614 W/m3 0.4964 W/m3

– – –

– – –

[74]

Settled sewage

97  1% 93%  1%

229  52 mW/m3 106  21 mW/m3

1250 mA/m3 950 mA/m3

– –

[79]

Synthetic

93%  1% 85–88%

109  29 mW/m3 13.4 mW/m2

800 mA/m3 31.4 mA/m3

– 6.074  8.42

18.1 mW/m2

33.8 mA/m3

8.28  10.4%

8.1 mW/m2 8.8 mW/m2

21.6 mA/m3 29.5 mA/m3

6.57  6.84 6.13  5.68

Municipal Synthetic

Synthetic

3

[76] [75]

[70]

[52]

Continued

Table 17.3 Some of different wetland plants investigated in CW-MFC for phytoremediation of wastewater—cont’d No.

9 10

Plant

Water hyacinth C. indica Cyperus alternifolius L. A. calamus Arundo donax

Wastewater

COD removal (%)

Municipal

72.72  4.53%

6.5 mW/m

Urban

– – – –

Max power density

Max current density

CE%

Reference

–

–

[80]

18.56 mW/m2 6.92 mW/m2

85 mA/m3 32 mA/m3

– –

[73]

2.26 mW/m2 17.41 mW/m2

22 mA/m3 84 mA/m3

– –

2

Sediment microbial fuel cell (SMFCs)

17.1.2.6 Operating conditions Free water surface and subsurface flow wetlands are the two important types of CW-MFC on the basis of water flow regime, which affects the formed elements in it such as biofilm and wetland plants [81]. Subsurface wetlands are also classified in two forms of horizontal (HF) and vertical flow (VF) [82]. In surface flow wetlands, the water just flows horizontally over the sediment [38]. Schematic layouts of different types of CW-MFCs are shown in Fig. 17.2. Doherty et al. [83] constructed four CW-MFC configurations with different architectures and flow regimes. Maximum power densities of 0.276 W/m3 was produced with simultaneous up-flow into the anode and down-flow into the cathode chamber. Doherty et al. [42] also runs a two-stage system to improve power production and COD removal (85  5.2%) and also the effect of electrode separation and flow regimes was evaluated. The advantages of horizontal subsurface-constructed wetlands in comparison with conventional settling is to supply higher amount of biodegradable substrates [43]. A pilot plant based on two horizontal subsurface-constructed wetlands (settler and

Fig. 17.2 Various types of constructed wetlands: (A) free water surface flow, (B) horizontal subsurface flow; and (C) vertical subsurface flow.

453

454

Biological fuel cells

hydrolytic up-flow sludge blanket reactor(HUSB)) were constructed by Corbella et al. [43] and a maximum power density of 36 mW/m2 and current density of 219 mA/m2 were obtained with a HUSB line. 17.1.2.7 Effect of electrode surface The electrodes applied in SMFCs and CW-MFCs are classified in two types of chemical and bio-electrodes (anode and cathodes). The properties of the electrode surface including contact angle, wettability, conduction, chemical stability, and mechanical strength are important to improve the performance of various types of MFCs [7,84]. The electrode surface characterization is also essential for bio-electrode activity including biocompatibility, good electron transfer between the electrode surface and bacteria, and surface roughness. So, surface modification of electrodes can improve the performance of SMFCs and CW-MFCs. As mentioned before (Table 17.2), surface modification of electrode surface has significantly increased the power density of the SMFCs in most cased such as graphite rode anode electrode, which was electrodeposited with Fe/ferric oxide [29]. The anode to cathode surface area ratio (SARa/c) is also essential to increase the power generation of SMFCs and CW-MFCs. As for example, Yang et al. [85] investigated the effect of surface areas on the performance of single and serially stacked SMFCs. The results showed that for both of them, the optimal SARa/c is between 1 and 1.33.

17.1.3 Electricity generation as a function of wastewater treatment CW-MFC systems have a good capacity for the wastewater treatment as the bioelectricity production is low in compared with traditional CWs [5]. CW-MFCs can be used to purify the azo dye [36,39,49,86], urban wastewater treatment [87], industrial effluent, domestic sewage [88,89], trace contaminants in river water, and reducing the CH4 emission from the CW [88]. Colares et al. [87] developed a CW-MFC for the production of bioelectricity and wastewater treatment. The system shown the COD removal of 71.4% and maximum power density of 0.93 mW/m2. Fang et al. [39] reported that the calculated COD concentration (as reactive brilliant red X-3B (ABRX3) proportion) plays an important role in bioelectricity generation and decolorization rate. The highest power generation and decolorization rate (0.852 W/m3 and 95.6%, respectively) were obtained at a COD concentration of 300 mg/L (ABRX3 proportion of 30%). An integrated system of MFC and CW was also evaluated for the treatment of wastewater produced at a hospital laundry [89], which shown good results to reduce the overall toxicity of hospital laundry wastewaters. Xu et al. [51] observed that the removal percentage of total nitrogen (82.46  4.74%) and COD removal rate (82.32  12.85%) in CW-MFC as compared with CW was significantly high with the highest power density of 3714.08 mW/m2. Araneda et al. [90] evaluated a CW-MFC planted with Phragmites australis to effective

Sediment microbial fuel cell (SMFCs)

greywater treatment while producing energy and the results showed that this combined system can produce energy with good wastewater treatment.

17.2 Photosynthetic sediment microbial fuel cells (PSMFCs) Sunlight as an abundant source of energy can be used to power the oxygenation of the cathode [91]. A new construction of SMFCs can be produced by switching the cathode electrode to a biogenic one (by applying microalgae in the cathode compartment) (Fig. 17.3), which leads to direct production of oxygen at the cathode. In this system, which is known as photosynthetic sediment microbial fuel cells (PSMFCs), the bacterial activity of the anodic chamber produced CO2, which is then consumed by algal cells at cathodic chamber. Then, the algal cells produced O2, which was consumed at cathode electrode for energy production. In PSMFCs, a sunlight source is essential for the photosynthesis of algal cells [92]. The photosynthetic MFC system was first developed by Berk and Canfield [93] by applying Rhodospirillum rubrum at the anode and blue-green marine algae at the cathode compartment. Jeon et al. [94] showed that inoculation of Chlorella vulgaris at the cathode compartment produced energy and the biomass production was related to current production. In another similar investigation by Wang et al. [35], C. vulgaris was introduced to the cathode, which increased the dissolved oxygen concentration at the cathode chamber. Power generation of SMFC with an algae-assisted cathode was also increased (2.4 fold) in compared with the SMFC with a bare cathode. An algal-cultivated SMFC system was also developed by Neethu et al. [95] for power generation. The PSMFC reached a higher power density of 22.19 mW/m2 (3.65 times higher) and organic matter removal efficiencies (1.21%) than the SMFC with bare cathode.

Fig. 17.3 Schematic layout of photosynthetic Sediment MFC (PSMFC).

455

456

Biological fuel cells

17.3 SMFCs and removal of heavy metals Today, large amounts of heavy metals (liod) are introduced into water and sediments in rivers and lakes, which can affect the soil and food quality [96,97]. Accumulation of these toxic metals can also poses a severe risk to the health of living organisms and human health [98]. High level of toxicity, bio accumulation, and nonbiodegradability are the main characterizations of liod. Different physical, chemical, and biological techniques such as ozonation, amended capping, electrochemical degradation, etc. were developed to treat the heavy metal pollutants in sediments, but most of them are not affective for low concentration of liod [97,99]. MFC, as mentioned before, is a bio-electrochemical system in which heavy metals and organic matters are degraded and converted to energy by microbial degradation attached on the anode electrode. As for example of an in situ bio-degradation of heavy metals in sediments, a lab-scale SMFC was applied by Wu et al. [97] and achieved good removal efficiencies of Ag(I) (98.5  1.2%), Cu(II) (87.7%  3.2%), and Hg(II) (97.3  2.6%) after about 60 days’ operation. Abbas et al. [98] constructed aerated and nonaerated SMFCs to the bio-remediation of chromium, copper and nickel in Penang, Malaysia, coupled with electricity production. After 60 days, %); the optimum remediation efficiencies of Cr, Cu, and Ni ions were 80.70%, 72.72%, and 80.37%, respectively, in aerated SMFC. After 80 days, the nonaerated SMFC achieved the removal efficiencies of 67.36%, 59.36%, and 52.74% of Cr (VI), Cu (II), and Ni (II) ions. Zhang et al. [100] developed a three-chamber MFC for the bio-degradation of copper from soil in the presence of HCl, citric acid, and acetic acid as auxiliary reagents. After 74 days of treatment, the total removal efficiency of copper was 32.27%, 41.56%, and 16.64%, for 1 mol/L of citric acid, HCl, and acetic acid, respectively. To calculate the removal efficiency (RE, %) of heavy metals, Eq. (17.1) can be used where HMi and HMop are the heavy metal concentrations before and after SMFC operation, respectively, with a range of external resistance from 60 U to 2 kU [98]. RE ¼

HM i  HM op  100 HM i

(17.1)

References [1] S.Z. Abbas, M. Rafatullah, N. Ismail, M.I. Syakir, A review on sediment microbial fuel cells as a new source of sustainable energy and heavy metal remediation: mechanisms and future prospective, Int. J. Energy Res. 41 (9) (2017) 1242–1264. [2] M.T. Noori, M. Ghangrekar, C. Mukherjee, Sediment microbial fuel cell and constructed wetland assisted with it: challenges and future prospects, in: Microbial Fuel Cell, Springer, 2018, pp. 335–352. [3] T. Sajana, S. Pandit, D.A. Jadhav, M. Abdullah-Al-Mamun, E. Fosso-Kankeu, Sediment microbial fuel cell for wastewater treatment: a new approach, in: Nano and Bio-Based Technologies for Wastewater Treatment, 2019, p. 303. [4] N. Song, H. Jiang, Z. Yan, Contrasting effects of sediment microbial fuel cells (SMFCs) on the degradation of macrophyte litter in sediments from different areas of a shallow eutrophic lake, Appl. Sci. 9 (18) (2019) 3703.

Sediment microbial fuel cell (SMFCs)

[5] O. Guadarrama-P
erez, T. Guti
errez-Macı´as, L. Garcı´a-Sa´nchez, V.H. Guadarrama-P
erez, E.B. Estrada-Arriaga, Recent advances in constructed wetland-microbial fuel cells for simultaneous bioelectricity production and wastewater treatment: a review, Int. J. Energy Res. 43 (10) (2019) 5106–5127. [6] B. Xu, Z. Ge, Z. He, Sediment microbial fuel cells for wastewater treatment: challenges and opportunities, Environ. Sci.: Water Res. Technol. 1 (3) (2015) 279–284. [7] A. Zabihallahpoor, M. Rahimnejad, F. Talebnia, Sediment microbial fuel cells as a new source of renewable and sustainable energy: present status and future prospects, RSC Adv. 5 (114) (2015) 94171–94183. [8] K. Kubota, T. Watanabe, H. Maki, G. Kanaya, H. Higashi, K. Syutsubo, Operation of sediment microbial fuel cells in Tokyo Bay, an extremely eutrophicated coastal sea, Bioresour. Technol. Rep. 6 (2019) 39–45. [9] S. Yang, F. Du, H. Liu, Characterization of mixed-culture biofilms established in microbial fuel cells, Biomass Bioenergy 46 (2012) 531–537. [10] F.T. Kabutey, et al., Pollutant removal and bioelectricity generation from urban river sediment using a macrophyte cathode sediment microbial fuel cell (mSMFC), Bioelectrochemistry 128 (2019) 241–251. [11] W. Wang, et al., Operation mechanism of constructed wetland-microbial fuel cells for wastewater treatment and electricity generation: a review, Bioresour. Technol. (2020), 123808. [12] Y. Shi, X. Yang, X. Ning, Q. Yang, Research progress of microbial fuel cell and constructed wetland coupling system, IOP Conf. Ser.: Earth Environ. Sci. 199 (5) (2018) 052014. IOP Publishing. [13] T. Tran, I. Lee, K. Kim, Electricity production characterization of a sediment microbial fuel cell using different thermo-treated flat carbon cloth electrodes, Int. J. Hydrogen Energy 44 (60) (2019) 32192–32200. [14] O.C. T€ urker, T. Baran, A. Yakar, C. T€ ure, C ¸ . Saz, Novel chitosan based smart cathode electrocatalysts for high power generation in plant based-sediment microbial fuel cells, Carbohydr. Polym. 239 (2020), 116235. [15] W. Li, et al., MnO2/tourmaline composites as efficient cathodic catalysts enhance bioelectroremediation of contaminated river sediment and shape biofilm microbiomes in sediment microbial fuel cells, Appl. Catal. Environ. 278 (2020), 119331. [16] Y. Liang, H. Zhai, B. Liu, M. Ji, J. Li, Carbon nanomaterial-modified graphite felt as an anode enhanced the power production and polycyclic aromatic hydrocarbon removal in sediment microbial fuel cells, Sci. Total Environ. 713 (2020), 136483. [17] C.-T. Wang, et al., Exposing effect of comb-type cathode electrode on the performance of sediment microbial fuel cells, Appl. Energy 204 (2017) 620–625. [18] C. Corbella, J. Puigagut, Improving domestic wastewater treatment efficiency with constructed wetland microbial fuel cells: influence of anode material and external resistance, Sci. Total Environ. 631 (2018) 1406–1414. [19] J. Wang, et al., Microbial community structure of different electrode materials in constructed wetland incorporating microbial fuel cell, Bioresour. Technol. 221 (2016) 697–702. [20] S.-W. Hong, H.-J. Kim, Y.-S. Choi, T.-H. Chung, Field experiments on bioelectricity production from lake sediment using microbial fuel cell technology, Bull. Korean Chem. Soc. 29 (11) (2008) 2189–2194. [21] T.S. Song, W.M. Tan, X.Y. Wu, C.C. Zhou, Effect of graphite felt and activated carbon fiber felt on performance of freshwater sediment microbial fuel cell, J. Chem. Technol. Biotechnol. 87 (10) (2012) 1436–1440. [22] S.W. Hong, I.S. Chang, Y.S. Choi, B.H. Kim, T.H. Chung, Responses from freshwater sediment during electricity generation using microbial fuel cells, Bioprocess Biosyst. Eng. 32 (3) (2009) 389–395. [23] G. Martins, L. Peixoto, D.C. Ribeiro, P. Parpot, A.G. Brito, R. Nogueira, Towards implementation of a benthic microbial fuel cell in lake Furnas (Azores): phylogenetic affiliation and electrochemical activity of sediment bacteria, Bioelectrochemistry 78 (1) (2010) 67–71. [24] C. Dumas, A. Mollica, D. F
eron, R. Basseguy, L. Etcheverry, A. Bergel, Checking graphite and stainless anodes with an experimental model of marine microbial fuel cell, Bioresour. Technol. 99 (18) (2008) 8887–8894.

457

458

Biological fuel cells

[25] N.J. Sacco, E.L. Figuerola, G. Pataccini, M.C. Bonetto, L. Erijman, E. Corto´n, Performance of planar and cylindrical carbon electrodes at sedimentary microbial fuel cells, Bioresour. Technol. 126 (2012) 328–335. [26] C. Dumas, A. Mollica, D. F
eron, R. Bass
eguy, L. Etcheverry, A. Bergel, Marine microbial fuel cell: use of stainless steel electrodes as anode and cathode materials, Electrochim. Acta 53 (2) (2007) 468–473. [27] K. Scott, I. Cotlarciuc, D. Hall, J. Lakeman, D. Browning, Power from marine sediment fuel cells: the influence of anode material, J. Appl. Electrochem. 38 (9) (2008) 1313. [28] D.A. Lowy, L.M. Tender, J.G. Zeikus, D.H. Park, D.R. Lovley, Harvesting energy from the marine sediment–water interface II: kinetic activity of anode materials, Biosens. Bioelectron. 21 (11) (2006) 2058–2063. [29] Y. Fu, Q. Xu, X. Zai, Y. Liu, Z. Lu, Low electrical potential anode modified with Fe/ferric oxide and its application in marine benthic microbial fuel cell with higher voltage and power output, Appl. Surf. Sci. 289 (2014) 472–477. [30] D.A. Lowy, L.M. Tender, Harvesting energy from the marine sediment–water interface: III. Kinetic activity of quinone-and antimony-based anode materials, J. Power Sources 185 (1) (2008) 70–75. [31] Y. Fu, Z. Zhao, J. Liu, K. Li, Q. Xu, S. Zhang, Sulfonated polyaniline/vanadate composite as anode material and its electrochemical property in microbial fuel cells on ocean floor, Sci. China Chem. 54 (5) (2011) 844–849. [32] K. Scott, et al., Fuel cell power generation from marine sediments: investigation of cathode materials, J. Chem. Technol. Biotechnol. 83 (9) (2008) 1244–1254. [33] T.-S. Song, Z.-S. Yan, Z.-W. Zhao, H.-L. Jiang, Construction and operation of freshwater sediment microbial fuel cell for electricity generation, Bioprocess Biosyst. Eng. 34 (5) (2011) 621–627. [34] Y. Ren, D. Pan, X. Li, F. Fu, Y. Zhao, X. Wang, Effect of polyaniline-graphene nanosheets modified cathode on the performance of sediment microbial fuel cell, J. Chem. Technol. Biotechnol. 88 (10) (2013) 1946–1950. [35] D.-B. Wang, T.-S. Song, T. Guo, Q. Zeng, J. Xie, Electricity generation from sediment microbial fuel cells with algae-assisted cathodes, Int. J. Hydrogen Energy 39 (25) (2014) 13224–13230. [36] A.K. Yadav, P. Dash, A. Mohanty, R. Abbassi, B.K. Mishra, Performance assessment of innovative constructed wetland-microbial fuel cell for electricity production and dye removal, Ecol. Eng. 47 (2012) 126–131. [37] Y. Zhao, S. Collum, M. Phelan, T. Goodbody, L. Doherty, Y. Hu, Preliminary investigation of constructed wetland incorporating microbial fuel cell: batch and continuous flow trials, Chem. Eng. J. 229 (2013) 364–370. [38] J.V. Camacho, M.D.C.M. Vico, M. Andr
es, R. Rodrigo, F.J.F. Morales, P.C. Can˜izares, Energy production from wastewater using horizontal and vertical subsurface flow constructed wetlands, Environ. Eng. Manag. J. 13 (10) (2014) 2517–2523. [39] Z. Fang, H.-L. Song, N. Cang, X.-N. Li, Electricity production from azo dye wastewater using a microbial fuel cell coupled constructed wetland operating under different operating conditions, Biosens. Bioelectron. 68 (2015) 135–141. [40] Y.-L. Oon, et al., Hybrid system up-flow constructed wetland integrated with microbial fuel cell for simultaneous wastewater treatment and electricity generation, Bioresour. Technol. 186 (2015) 270–275. [41] L. Lu, D. Xing, Z.J. Ren, Microbial community structure accompanied with electricity production in a constructed wetland plant microbial fuel cell, Bioresour. Technol. 195 (2015) 115–121. [42] L. Doherty, Y. Zhao, Operating a two-stage microbial fuel cell–constructed wetland for fuller wastewater treatment and more efficient electricity generation, Water Sci. Technol. 72 (3) (2015) 421–428. [43] C. Corbella, M. Guivernau, M. Vin˜as, J. Puigagut, Operational, design and microbial aspects related to power production with microbial fuel cells implemented in constructed wetlands, Water Res. 84 (2015) 232–242. [44] P. Srivastava, A.K. Yadav, B.K. Mishra, The effects of microbial fuel cell integration into constructed wetland on the performance of constructed wetland, Bioresour. Technol. 195 (2015) 223–230.

Sediment microbial fuel cell (SMFCs)

[45] J. Wang, et al., Nitrate removal and bioenergy production in constructed wetland coupled with microbial fuel cell: establishment of electrochemically active bacteria community on anode, Bioresour. Technol. 221 (2016) 358–365. [46] L. Xu, Y. Zhao, L. Doherty, Y. Hu, X. Hao, Promoting the bio-cathode formation of a constructed wetland-microbial fuel cell by using powder activated carbon modified alum sludge in anode chamber, Sci. Rep. 6 (1) (2016) 1–9. [47] J. Wang, X. Song, Y. Wang, Z. Zhao, B. Wang, D. Yan, Effects of electrode material and substrate concentration on the bioenergy output and wastewater treatment in air-cathode microbial fuel cell integrating with constructed wetland, Ecol. Eng. 99 (2017) 191–198. [48] Y.-L. Oon, et al., Role of macrophyte and effect of supplementary aeration in up-flow constructed wetland-microbial fuel cell for simultaneous wastewater treatment and energy recovery, Bioresour. Technol. 224 (2017) 265–275. [49] Z. Fang, X. Cao, X. Li, H. Wang, X. Li, Electrode and azo dye decolorization performance in microbial-fuel-cell-coupled constructed wetlands with different electrode size during long-term wastewater treatment, Bioresour. Technol. 238 (2017) 450–460. [50] H. Song, S. Zhang, X. Long, X. Yang, H. Li, W. Xiang, Optimization of bioelectricity generation in constructed wetland-coupled microbial fuel cell systems, Water 9 (3) (2017) 185. [51] F. Xu, et al., Electricity production and evolution of microbial community in the constructed wetland-microbial fuel cell, Chem. Eng. J. 339 (2018) 479–486. [52] C ¸ . Saz, C. T€ ure, O.C. T€ urker, A. Yakar, Effect of vegetation type on treatment performance and bioelectric production of constructed wetland modules combined with microbial fuel cell (CWMFC) treating synthetic wastewater, Environ. Sci. Pollut. Res. 25 (9) (2018) 8777–8792. [53] A.I.C. Muler, Effect of Experimental Parameters on the Voltage Output of a Sediment Microbial Fuel Cell, 2016. [54] T. Sajana, M. Ghangrekar, A. Mitra, Effect of pH and distance between electrodes on the performance of a sediment microbial fuel cell, Water Sci. Technol. 68 (3) (2013) 537–543. [55] T. Sajana, M. Ghangrekar, A. Mitra, Effect of operating parameters on the performance of sediment microbial fuel cell treating aquaculture water, Aquacult. Eng. 61 (2014) 17–26. [56] S.W. Hong, I.S. Chang, Y.S. Choi, T.H. Chung, Experimental evaluation of influential factors for electricity harvesting from sediment using microbial fuel cell, Bioresour. Technol. 100 (12) (2009) 3029–3035. [57] A.G. del Campo, P. Can˜izares, J. Lobato, M. Rodrigo, F.F. Morales, Effects of external resistance on microbial fuel cell’s performance, in: Environment, Energy and Climate Change II, Springer, 2014, pp. 175–197. [58] H. Rismani-Yazdi, A.D. Christy, S.M. Carver, Z. Yu, B.A. Dehority, O.H. Tuovinen, Effect of external resistance on bacterial diversity and metabolism in cellulose-fed microbial fuel cells, Bioresour. Technol. 102 (1) (2011) 278–283. [59] L. De Schamphelaire, K. Rabaey, P. Boeckx, N. Boon, W. Verstraete, Outlook for benefits of sediment microbial fuel cells with two bio-electrodes, J. Microbial. Biotechnol. 1 (6) (2008) 446–462. [60] A. Wang, H. Cheng, N. Ren, D. Cui, N. Lin, W. Wu, Sediment microbial fuel cell with floating biocathode for organic removal and energy recovery, Front. Environ. Sci. Eng. 6 (4) (2012) 569–574. [61] B. Mathis, C. Marshall, C. Milliken, R. Makkar, S. Creager, H. May, Electricity generation by thermophilic microorganisms from marine sediment, Appl. Microbiol. Biotechnol. 78 (1) (2008) 147–155. [62] Z. Chen, Y.-C. Huang, J.-H. Liang, F. Zhao, Y.-G. Zhu, A novel sediment microbial fuel cell with a biocathode in the rice rhizosphere, Bioresour. Technol. 108 (2012) 55–59. [63] Z. Najafgholi, M. Rahimnejad, Improvement of sediment microbial fuel cell performance by application of sun light and biocathode, Korean J. Chem. Eng. 33 (1) (2016) 154–158. [64] Z. He, Y. Huang, A.K. Manohar, F. Mansfeld, Effect of electrolyte pH on the rate of the anodic and cathodic reactions in an air-cathode microbial fuel cell, Bioelectrochemistry 74 (1) (2008) 78–82. [65] L. Zhang, C. Li, L. Ding, K. Xu, H. Ren, Influences of initial pH on performance and anodic microbes of fed-batch microbial fuel cells, J. Chem. Technol. Biotechnol. 86 (9) (2011) 1226–1232.

459

460

Biological fuel cells

[66] J. Zhao, X.F. Li, Y.P. Ren, X.H. Wang, C. Jian, Electricity generation from Taihu Lake cyanobacteria by sediment microbial fuel cells, J. Chem. Technol. Biotechnol. 87 (11) (2012) 1567–1573. [67] Z. He, H. Shao, L.T. Angenent, Increased power production from a sediment microbial fuel cell with a rotating cathode, Biosens. Bioelectron. 22 (12) (2007) 3252–3255. [68] J.M. Morris, S. Jin, Enhanced biodegradation of hydrocarbon-contaminated sediments using microbial fuel cells, J. Hazard. Mater. 213 (2012) 474–477. [69] D. Yan, X. Song, B. Weng, Z. Yu, W. Bi, J. Wang, Bioelectricity generation from air-cathode microbial fuel cell connected to constructed wetland, Water Sci. Technol. 78 (9) (2018) 1990–1996. [70] S. Gupta, A. Nayak, C. Roy, A.K. Yadav, An algal assisted constructed wetland-microbial fuel cell integrated with sand filter for efficient wastewater treatment and electricity production, Chemosphere 263 (2021), 128132. [71] P. Srivastava, S. Gupta, V. Garaniya, R. Abbassi, A.K. Yadav, Up to 399 mV bioelectricity generated by a rice paddy-planted microbial fuel cell assisted with a blue-green algal cathode, Environ. Chem. Lett. 17 (2) (2019) 1045–1051. [72] B. Yu, C. Liu, S. Wang, W. Wang, S. Zhao, G. Zhu, Applying constructed wetland-microbial electrochemical system to enhance NH4+ removal at low temperature, Sci. Total Environ. 724 (2020), 138017. [73] Y. Zhou, et al., Relationship between electrogenic performance and physiological change of four wetland plants in constructed wetland-microbial fuel cells during non-growing seasons, J. Environ. Sci. 70 (2018) 54–62. [74] F. Liu, et al., Performance of different macrophytes in the decontamination of and electricity generation from swine wastewater via an integrated constructed wetland-microbial fuel cell process, J. Environ. Sci. 89 (2020) 252–263. [75] Y. Yang, Y. Zhao, C. Tang, R. Liu, T. Chen, Dual role of macrophytes in constructed wetlandmicrobial fuel cells using pyrrhotite as cathode material: a comparative assessment, Chemosphere 263 (2021), 128354. [76] H. Wen, H. Zhu, B. Yan, Y. Xu, B. Shutes, Treatment of typical antibiotics in constructed wetlands integrated with microbial fuel cells: roles of plant and circuit operation mode, Chemosphere 250 (2020), 126252. [77] T.-P. Teoh, et al., Up-flow constructed wetland-microbial fuel cell: influence of floating plant, aeration and circuit connection on wastewater treatment performance and bioelectricity generation, J. Water Process Eng. 36 (2020), 101371. [78] L. Di, Y. Li, L. Nie, S. Wang, F. Kong, Influence of plant radial oxygen loss in constructed wetland combined with microbial fuel cell on nitrobenzene removal from aqueous solution, J. Hazard. Mater. 394 (2020), 122542. [79] A. Oodally, M. Gulamhussein, D.G. Randall, Investigating the performance of constructed wetland microbial fuel cells using three indigenous south African wetland plants, J. Water Process Eng. 32 (2019), 100930. [80] M. Tao, et al., Enhanced denitrification and power generation of municipal wastewater treatment plants (WWTPs) effluents with biomass in microbial fuel cell coupled with constructed wetland, Sci. Total Environ. 709 (2020), 136159. [81] A. Ghermandi, D. Bixio, C. Thoeye, The role of free water surface constructed wetlands as polishing step in municipal wastewater reclamation and reuse, Sci. Total Environ. 380 (1–3) (2007) 247–258. [82] M. Wang, D. Zhang, J. Dong, S.K. Tan, Application of constructed wetlands for treating agricultural runoff and agro-industrial wastewater: a review, Hydrobiologia 805 (1) (2018) 1–31. [83] L. Doherty, X. Zhao, Y. Zhao, W. Wang, The effects of electrode spacing and flow direction on the performance of microbial fuel cell-constructed wetland, Ecol. Eng. 79 (2015) 8–14. [84] J. Wei, P. Liang, X. Huang, Recent progress in electrodes for microbial fuel cells, Bioresour. Technol. 102 (20) (2011) 9335–9344. [85] Y. Yang, L. Yan, J. Song, M. Xu, Optimizing the electrode surface area of sediment microbial fuel cells, RSC Adv. 8 (45) (2018) 25319–25324. [86] Z. Fang, H.-L. Song, N. Cang, X.-N. Li, Performance of microbial fuel cell coupled constructed wetland system for decolorization of azo dye and bioelectricity generation, Bioresour. Technol. 144 (2013) 165–171.

Sediment microbial fuel cell (SMFCs)

[87] G.S. Colares, et al., Floating treatment wetlands integrated with microbial fuel cell for the treatment of urban wastewaters and bioenergy generation, Sci. Total Environ. 766 (2021), 142474. [88] K. Zhang, et al., CH4 control and associated microbial process from constructed wetland (CW) by microbial fuel cells (MFC), J. Environ. Manage. 260 (2020), 110071. [89] C.A. Lutterbeck, et al., Toxicity evaluation of hospital laundry wastewaters treated by microbial fuel cells and constructed wetlands, Sci. Total Environ. 729 (2020), 138816. /08/10/2020. [90] I. Araneda, N.F. Tapia, K. Lizama Allende, I.T. Vargas, Constructed wetland-microbial fuel cells for sustainable greywater treatment, Water 10 (7) (2018) 940. [91] A. Commault, G. Lear, P. Novis, R.J. Weld, Photosynthetic biocathode enhances the power output of a sediment-type microbial fuel cell, N. Z. J. Bot. 52 (1) (2014) 48–59. [92] A. ElMekawy, H.M. Hegab, K. Vanbroekhoven, D. Pant, Techno-productive potential of photosynthetic microbial fuel cells through different configurations, Renew. Sustain. Energy Rev. 39 (2014) 617–627. [93] R.S. Berk, J.H. Canfield, Bioelectrochemical energy conversion, Appl. Microbiol. 12 (1) (1964) 10. [94] H.J. Jeon, et al., Production of algal biomass (Chlorella vulgaris) using sediment microbial fuel cells, Bioresour. Technol. 109 (2012) 308–311. [95] B. Neethu, M. Ghangrekar, Electricity generation through a photo sediment microbial fuel cell using algae at the cathode, Water Sci. Technol. 76 (12) (2017) 3269–3277. [96] W. Gustave, Z. Yuan, F. Liu, Z. Chen, Mechanisms and challenges of microbial fuel cells for soil heavy metal (loid) s remediation, Sci. Total Environ. (2020), 143865. [97] M. Wu, X. Xu, Q. Zhao, Z. Wang, Simultaneous removal of heavy metals and biodegradation of organic matter with sediment microbial fuel cells, RSC Adv. 7 (84) (2017) 53433–53438. [98] S.Z. Abbas, M. Rafatullah, N. Ismail, F.R. Shakoori, Electrochemistry and microbiology of microbial fuel cells treating marine sediments polluted with heavy metals, RSC Adv. 8 (34) (2018) 18800–18813. [99] S.Z. Abbas, M. Rafatullah, N. Ismail, R.A. Nastro, Enhanced bioremediation of toxic metals and harvesting electricity through sediment microbial fuel cell, Int. J. Energy Res. 41 (14) (2017) 2345–2355. [100] J. Zhang, X. Cao, H. Wang, X. Long, X. Li, Simultaneous enhancement of heavy metal removal and electricity generation in soil microbial fuel cell, Ecotoxicol. Environ. Saf. 192 (2020), 110314.

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CHAPTER 18

Future applications of biological fuel cells Tahereh Jafarya, Anteneh Mesfin Yeneneha, Muna Al Hinaia, Mimi Hani Abu Bakarb, and Mostafa Rahimnejadc a

Engineering Department, International Maritime College Oman, National University of Science and Technology, Muscat, Oman b Fuel Cell Institute, Universiti Kebangsaan Malaysia, Bandar Baru Bangi, Malaysia c Biofuel and Renewable Energy Research Center, Chemical Engineering Department, Babol Noshirvani University of Technology, Babol, Mazandaran, Iran

18.1 Introduction From the discovery of microbial fuel cell (MFC) technology by Potter in 1911 [1], there is no evidence of taking the technology seriously for real-scale applications than only laboratory-scale research. Despite being the only example of a technology for generating energy from the oxidation of organic/inorganic matter under ambient conditions [2–4], the technology has never been regarded as a major candidate in the wastewater treatment field or in the energy sector [5,6]. However, the idea of utilizing MFC for real applications is shifting toward a specific range of applications by considering the potentials of MFC rather the typical large-scale simultaneous wastewater treatment and bioelectricity generation aspects. Allowing the bioelectrochemical bacteria (known as exoelectrogens) to do what they do best, the MFC technology can be used in a range of environments at different scales and in diverse areas [7–9]. Therefore, MFCs can be primarily used in large-scale wastewater treatment applications or in small-scale applications for portable purposes [10]. Hence, this chapter mainly focuses on the areas where MFCs can be used in a small scale for near future applications, i.e., powering low energy devices and remote sensors, robotics, paper-based design, and urine-fed systems.

18.2 Robotics It is a huge engineering obstacle to design autonomous robots that can work efficiently in remote or aquatic areas [11]. Extending the time during which robots can perform autonomously and without the need for human help is one of the major challenges in robotic studies. The energy demand of a robotic system is a major key barrier. Most robots require recharging or refueling, which frequently necessitates human intervention. The majority of miniature mobile robots are powered by chemical batteries or photovoltaic panels, which necessitates periodic intervention or maintenance. The inaccessibility of solar power at night is a key drawback in employing photovoltaic panels as a Biological Fuel Cells https://doi.org/10.1016/B978-0-323-85711-6.00008-4

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power source, and the extent of useable radiation during a day is also impacted by a variety of other parameters such as location, shadow, direction, time of year, and weather conditions. Robots should be developed to operate in a variety of operating situations and have a larger range of power sources to demonstrate superior autonomy. Energetic autonomy will broaden the scope of autonomous systems’ applications in sectors including sea and space exploration, contaminated environment treatment, and remote environmental monitoring. This is especially useful in hazardous circumstances like conflict or pollution zones, when human presence is required [12]. MFCs can be used to supply the robots with the required power by converting energy stored in waste into bioelectricity. Uninterrupted operation, higher substrate conversion, and configuration flexibility are all advantages of employing MFCs over alternative power sources [13].

18.2.1 Terrestrial and underwater applications Autonomous portable robots fueled by an online bank of MFCs are known, as in the cases of EcoBot robot series [14,15]. The usage of MFCs to power Eco-Bot robot series highlights how robots can generate their own electricity through a symbiotic bacterial connection and reduce their negative environmental impacts. The EcoBot project has created the EcoBot series, EcoBot-I, EcoBot-II, and EcoBot-III, all of which were powered by MFCs and operated on the same basis. EcoBot-I was driven by electricity from the MFC and used artificial muscles to replicate the functions of the stomach and gut. The energy from the MFCs aboard EcoBot-I was temporarily stored in electrolytic capacitors, and once full, the energy was distributed to actuate the motion motors and travel toward the light. EcoBot II was the world’s first robot to be fueled by MFCs made from bacteria extracted from sewage and fed raw insects or fruits, as well as O2 cathode. EcoBot-II used a gas diffusion cathode and was built in the same way as its predecessor. It could communicate data about temperature, toxicity, humidity, and other environmental parameters. It also sent information about its internal state, including pH and the amount of fluid substrate in the system. It consisted of an eight-MFC stack that worked in parallel to provide enough power for ecological monitoring applications [14]. Ecobot-I was the first successful display of a robot powered entirely by stacked MFC (8 units), while Ecobot-II was a more sophisticated robot with 8 MFC units and a 12-day operational cycle. All of these instances of autonomous robots controlled by stacked MFCs might be considered energetically self-sufficient and self-sustaining ways to be used for space applications, underground environments, and remote sites within the controlled limitations of the working environment [6]. EcoBot-III was the first robot to organically integrate actual life with the technology for autonomous operation, and it was fitted with a synthetic digestion system. It was built to accept nutrients from the environment, oxidize it within MFCs, and then discarded the waste at the end of the metabolic cycle. When given nutrient-rich liquid feedstock, it displayed energy autonomy within its environmental constraints [15]. Using ambient oxygen at the cathode side, EcoBots have been

Future applications of biological fuel cells

effective for terrestrial applications [13]. Underwater MFCs were started by Melhuish et al. [16], who connected the cathodic half-cell to an artificial gill for dissolved oxygen extraction. Moreover, the MFC power sources have been used in biomimetic robots such as the Row-bot, an insect-inspired swimming robot powered solely by a single MFC ‘artificial stomach’ [12]. The robots, however, can only work within a structured arena, confining their process to within range of the specially constructed feeding station. The Ecobot series was based on stacked MFCs to provide their required energy. However, stacking MFCs for enhanced power output could increase the size and complexity of the robots, as well as the issues that come with stacking cells, such as voltage reversal [17]. Rowbot was the first practical robotic application to employ a single MFC, demonstrating the technology’s promise as an energy source [12]. The water boatman beetle’s biomimicry has influenced critical design elements, including as morphology to meet the drag profile necessary for power and recovery propulsion phases, as well as integrated floatation and oxygen delivery. Row-bot offered an appropriate system for robots functioning independently in the environment for a prolonged operational time, and it opened up many possibilities for the various subsystems and the robot as a whole. However, there is no other work on using single units of the MFC for supplying the power required for the robotic function, which highlights the need for more studies in this area.

18.2.2 Modeling and outer space applications MFCs are an innovative alternative to hazardous materials for energy storage in soft robotics. Because they are made of biodegradable and biocompatible materials, the entire soft robot entity is not harmful to the environment [18,19]. MFCs, on the other hand, are difficult to model and their outputs are difficult to recreate precisely. As a result, the application of machine learning and, in particular, the “nonlinear autoregressive model with exogenous inputs” (NARX), for the prediction of their outputs, could be employed. The effective usability of MFCs as energy suppliers for soft robotics will be enhanced by applying this smart method of tracking MFC outputs and forecasting behavior once additional feedstock is supplied. Tsompanas et al. (2021) selected the NARX model because it was simple to construct and can be switched between open- and closed-loop circuits depending on the application phase. Open-loop networks, in particular, allowed for more precise training, whereas closed-loop networks allowed for multistep predictions. In other words, the closed-loop mode used internal feedback to continue to anticipate while external feedback was lost or unavailable at the critical moment. Depending on the availability of the last interval data, the same network can switch between open- and closed-loop modes [20]. Future modeling studies should include evaluating this and other models’ efficacy for estimating feed times in energy-autonomous robots, as well as the efficiency of the manner of feeding rate

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compared to sampling the MFC voltage with higher frequency. This will be used in the creation of self-feeding soft robots in the future. A variety of robots have been built and developed with a degree of autonomy, not only primarily in the form of computational autonomy, but also in the form of energy autonomy. An indoor robot that can park at a docking station, for example, may be considered energetically autonomous [21]. Similarly, a photovoltaic-powered outdoor terrestrial robot may be deemed energetically self-sufficient [22]. There are numerous examples of radioisotope thermoelectric generators being utilized in space-exploration projects, such as the Viking mission to Mars and the Pioneer, Voyager, Ulysses, Galileo, and Cassini missions to the outer solar system. All of these instances could be regarded independently autonomous within the confines of the environment in which they operate [23–25]. A robot powered by MFCs, on the other hand, which allows for the opportunistic use of the largest variety of substrate sources, will be able to function in a variety of situations, including terrestrial, underground, underwater, and space. When the accessible organic matter is waste, such robots can play a positive role in the environment, like cleaning up organic pollution [9,26]. Future research can shed light on the prospects and challenges of the technology in this context.

18.3 Powering low-energy devices Moving forward to achieve ultralow/low power device technology resulted in widespread use of a large number of such electronic gadgets and appliances in the current era. Low-power density devices, such as digital clocks, portable computing tools, display devices, sensor nodes, and cellphones, have low energy costs in terms of battery while being portable. As the mission of developing low power devices was almost achieved, the current challenge is to provide continuous and long-term power supplies for remote applications of such devices. Especially, after developing Internet of Things (IoT)-based devices with ultralow power requirement, continuous power supplying source seems to be the main concern due to high cost of batteries and specially their replacement in remote and inaccessible areas. MFC is currently favored over other technologies for powering compact electrical devices in the field due to its lower environmental imprint and longer operating duration using local resources. In situ exploitation of bioelectricity created by MFC to run low-power devices is a feasible technique to harness bioelectricity since there is no requirement for human intervention for replenishment. In the recent decades, a surprising number of promising applications of MFC as a long-term power supply have been reported in both the laboratory and the commercializing level. Uria-Molto et al. [27] have developed and implemented three different configurations of MFC (plant, soil, and hybrid—MFC) to compare in terms of power supply and longterm stability for low-power field electronic devices. Due to the rapid and sudden fall in the anode potential caused by oxygen coming from the aerenchyma of the plant roots,

Future applications of biological fuel cells

the plant MFC (PMFC) showed lower performance (0.6 μW cm 2). The performance of soil MFC was significantly superior (2.0 μW cm 2); however, it was not sustained for a long time due to organic matter depletion. When a soil MFC and a plant MFC were placed in different compartments of a single container, the result was a hybrid MFC with higher performance in both power output (2.7 μW cm 2) and operation longevity (>1 month). As a portable power device, the hybrid MFC proved to be an excellent choice for the long-term power supply of low-power field electronic equipment such as meteorological sensors and LED lights. Moore et al. [28] have designed an integrated power supply for powering microchip-based biofuel cells. They showed implementing a microchip-based biofuel cell as a power supply for lab-on-a-chip technology purposes. A micromolded carbon ink anode has been upgraded with two layers in the bioanode. The first layer was poly(methylene green), which acted as an electrocatalyst for NADH oxidation; the second layer was a membrane containing alcohol dehydrogenase, which was immobilized. The biofuel cell had a maximum open-circuit potential of 0.34 V and a maximum current density of 53 μA cm 2 when an external platinum cathode was used. Walter et al. [29] studied the use of an MFC system that directly and continuously powered an exemplar microcomputer and its screen without the use of any power management electronic circuitry. They designed a stack comprising a single cascade consisting of four self-stratifying membrane-less MFC modules that were connected in series. This design took advantage of complex microbial consortia’s ability to structure themselves and the environment in which they thrived in a series of horizontal layers that followed a redox gradient: the more reduced layers were at the bottom of the electrolyte column, while the more oxidized layers were on the top. The stack MFC produced an average of 62 mA at 2550 mV and was used to directly power a microcomputer. Mohamadifar et al. [30] investigated a sweat-powered battery-based MFC, using the sweat-digesting microorganism (Staphylococcus epidermidis) to convert the chemical energy stored in sweat into electrical power through biocatalytic activity. Sweat bacteria can be used as a biocatalyst to convert chemical energy from sweat into electrical energy via bacterial metabolism. Their research aimed to develop smart, stand-alone, always-on wearable electronic systems by connecting a realistic and accessible power source. Moreover, the device can be useful for self-powered medical equipment. The sweat-powered battery-based MFC generated up to 500-mV operational voltage, and then connected the biobattery to a low input voltage booster to achieve a more practical range of voltage (>3 V) for powering a thermometer. Another self-sustaining power supply system capable of smart sensing and long-range communication using a PMFC was developed by Rossi et al. [31]. They reported a single-sediment MFC with very stable performance over a long time to power wireless sensor network (WSN) nodes. The used PMFC generated an average output voltage of 0.5 V, which needed a boost converter to be enhanced. Using Texas Instruments BQ25505 energy harvesting IC, the output voltage crossed 3 V. The designed hybrid PMFC for smart wireless sensor node can be used to realize self-sustainable

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IoT power to enabled remote sensors. Thomas et al. [32] also reported a single-sediment MFC to power WSN nodes through the PowWow platform (power optimized hardware/software frameWOrk for wireless sensor nodes). The MFC low-voltage output (0.3 V) was boosted up to 1.7–3.3 V using a LTC3108 converter. The developed WSN was successfully powered by the MFC, and the results showed very stable performances over a long-time operation with a high rate of transmitting signals from a source to a computer-connected receptor. In a commercialized level, a group of students and professors from the University of Engineering and Technology in Lima (UTEC) developed Planta La´mpara (https://www.utec.edu.pe/plantalamparas-plantas-que-dan-luz). This product is a plant to run a LED light with a low-cost and green energy supply. The pot-lamp used Geobacteria for its function, which is a type of microorganism existing in the soil. Electron-producing organisms utilize the nutrients released from the plant in the soil and produce electrons as a result. The energy generated through the oxidation of nutrients is then conducted to supply LED power by this specific type of bacteria. As another commercialized example, the inventors of Arkyne Technologies (https:// www.sleepgreenhotels.com/knowledge/bioo-lite-the-green-phone-charger/) created a system that uses a plant’s natural processes to collect energy, which can then be used to charge phones through a USB up to three times a day. The pot called the Bioo Lite as their product employs the energy produced by photosynthesis to power smartphones. The chemicals are broken apart by microorganisms in the pot, releasing electrons that flow via nanowires.

18.4 MFCs powering remote sensors The rapid negative effects of pollution (e.g., climate change and global warming) necessitate continual environmental monitoring. As a result, sensors are being installed in a variety of sites for environment and weather monitoring, agricultural applications, and fisheries research, among other things. Sensors must frequently be deployed at remote areas in the majority of circumstances. The biggest challenge in deploying sensors in remote areas is supplying continuous power to the sensors over a long period of time. With an increase in the number of sensors, the power supplying methods need to be improved. The type of power source could affect the sensors’ reliability, durability, and repetition rate. Renewable energy sources, which do not require human involvement, are favored. While many different types of power sources are available, batteries, which are relatively inexpensive, are used to provide the power requirements of the sensors, particularly in marine situations. However, the need for adequate pressure housing and the battery’s limited lifetime (which is usually about 3 years) adds to the cost. Additional costs for transportation during battery replacement are significant in the case of sensors located in deep waters. Furthermore, batteries are thought to be harmful to the environment. As a result, alternative power sources for remote sensors are required.

Future applications of biological fuel cells

MFCs would be an excellent alternative source of power since they can run for a long period on local existing resources. The SUR, or submersible ultrasonic receiver, is an underwater sensor device that detects ultrasonic signals and logs the movement of fish and other species [33]. Among different components of a standalone SUR (memory, real-time clock, ultrasonic receiver, battery, etc.), the sensor’s operation time is limited by its battery system [34]. To overcome the limitations of other power-suppling technologies like limited life time of seawater batteries, inaccessibility of wind in deep water of wind turbines, and daytime limited application of solar panels, Donovan et al. [34] deployed sediment MFC (SMFC) and power management system (PMS) to power a remote underwater ultrasonic sensor. The PMS has been used to increase the power output of the MFC system because the power output of MFCs is typically insufficient to drive electronic loads continuously [35]. Additionally, SMFCs are low-maintenance and membrane-less type of MFCs with an anode usually inserted in sediment and a cathode placed on top of the anode [36]. Different zones (anaerobic zone of anode chamber and aerobic zone of cathode chamber) are created naturally in an SMFC by a dissolved oxygen gradient along the water depth [37]. The oxidation of organic matters in the sediment results in electrode and proton generation that will be reduced to water in cathode using dissolved oxygen. Donovan et al. [34] showed that the SMFC with a power output of 3–10 mW could drive the real-time clock and the underwater ultrasonic sensor in a continuous and intermittent manner, respectively, without using batteries. Moreover, they have reported that the energy harvesting of the SMFC could be more efficient and reliable by using a PMS with two DC/DC converters (Fig. 18.1A). To power a wireless temperature sensor, Zhang et al. [38] used the SMFC with two different cathodic arrangements, one with a floating cathode and the other with a bottom cathode. When an ultracapacitor was attached to the circuit, the data showed that the SMFC with a floating cathode could produce more electricity and resulting in a shorter charging time (Fig. 18.1B). The PMS (comprising a supercapacitor, a charge pump, and a DC-DC converter) was also designed to control electricity delivery and voltage elevation to a value that can operate a wireless temperature sensor. Both SMFCs could reliably power the wireless temperature sensor for data transfer to a computer with the PMS, despite the fact that the number of collected data during the same period varied. Schievano et al. [39] proposed an interesting design of sediment-based MFC named a floating garden with a PMS to supply power for remote environmental sensors and data transmission (Fig. 18.1C). The results showed the feasibility of using DC/DC converters to collect the power of 40 mW/h/d, which was sufficient to power environment-sensing signals. The data transmission rate offered by a continuous type of PMS (C-PMS), on the other hand, was reported to be insufficient to meet the requirement of the real-time monitoring and recording of the temporal fluctuation of toxins (e.g., ammonium and organic compounds) in onsite wastewater treatment plants. In other words, MFC power

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Fig. 18.1 Integration of SMDC and PMS to supply power of (A) remote submersible ultrasonic receiver, (B) wireless temperature sensor, and (C) remote environmental sensors and data transmission. Panel (A) reprinted with permission from C. Donovan, A. Dewan, D. Heo, Z. Lewandowski, H. Beyenal. Sediment microbial fuel cell powering a submersible ultrasonic receiver: new approach to remote monitoring, J. Power Sources 233 (2013) 79–85, Elsevier, (B) from F. Zhang, L. Tian, Z. He. Powering a wireless temperature sensor using sediment microbial fuel cells with vertical arrangement of electrodes, J. Power Sources 196 (2011) 9568–73. https://doi.org/10.1016/J.JPOWSOUR.2011.07.037, Elsevier, (C) from A. Schievano, A. Colombo, M. Grattieri, S.P. Trasatti, A. Liberale, P. Tremolada, et al., Floating microbial fuel cells as energy harvesters for signal transmission from natural water bodies, J. Power Sources 340 (2017) 80–88. https://doi.org/10.1016/J.JPOWSOUR.2016.11.037, Elsevier.

Future applications of biological fuel cells

generation is often affected by toxic pollutants in wastewater, resulting in a decrease in sensor data transmission frequency [40,41]. Hence, Fan et al. [42] designed a new triggered PMS (T-PMS) (consisting of a charge pump, boost converter, super capacitors, voltage trigger, and data trigger) to improve the power-harvesting efficiency and stability of MFCs, providing adequate energy for frequent data transfer of water sensors under transient wastewater shocks. When compared to typical C-PMS, which required constant active operation, the unique “power discharge prompted by event” function of T-PMS saved a lot of energy and increased the data transmission rate from 0.23 min 1 in C-PMS to 16.23 min 1 in T-PMS after the onset of shock (Fig. 18.2). Piyaret et al. [43] established a proof of concept using plant type of MFC (PMFC) as a power source for sustainable wireless sensing. The PMFC was coupled with an ultralow power wake-up receiver utilized as a trigger for sampling and transmission of the sensed values to match its very low power output capabilities. The arrangement resulted in a system that can be maintained for appropriate data rates. This work showed the initial steps for large-scale wireless sensor networks in situations where sensors were surrounded by living plants and which can provide a green and continuous power supply. Despite the critical role of crude oil in industrialization, oil leakage during the product lifecycle (e.g., drilling, storing, transportation, and pipeline) has resulted in significant environmental damage [44]. Leaked oil could stay in the environment for a long time and pose a health risk to humans and other living creatures [45,46]. In the recent decade, more than 50 big oil leaks have been documented around the world, resulting in 4.7  104 tons of crude oil polluting the ecosystem [47]. For mitigation strategies and ecological restoration, early detection of oil leaks during the crude oil life cycle is critical. Rather than the cost and high energy consumption associated with the existing technologies of UV, infrared, radar, and microwave, they are incapable of detecting slow leaks [48]. Crude oil has been discovered to totally isolate oxygen diffusion to water in a short span of time. As a result, Dai et al. [8] proposed a unique and simple MFC configuration as an in situ oil detection sensor, based on the negative influence of oil on oxygen migration to the cathode and sharp voltage reduction in MFC. The upward open-channel MFC was designed with the cathode directly open to air on the water surface, which could quickly show a potential reduction once the cathode was isolated from air in the presence of oil [8]. The setup showed shorter response time to oil contamination compared to other technologies highlighting its decent sensitivity to oil presence. However, the response time was still quite long: 1.5–12.17 h. The reusability of the sensor, which is an important factor for practical application, was observed through short voltage recovery. This can be attributed to the stability of the anodic catalyst due to the intact of the anodic biofilm. To shorten the sensor response time, a recent study on oil detection using MFC technology, used a sediment type of MFC with a floating cathode for online monitoring of minor oil spill in natural water streams [49]. The detection period was reduced from 10 h to 10–30 min using one-/two-point dynamic identification methods, preventing permanent damage to clean waterways before it is too late [50].

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Fig. 18.2 The circuit implementation of (A) the conventional continuous power management system (C-PMS) vs (B) the innovative triggered power management system (T-PMS). The voltage output and corresponding data transmission of the (C) C-PMS and (D) T-PMS under toxic shock with ammonium shock. Reprinted with permission from Y. Fan, F. Qian, Y. Huang, I. Sifat, C. Zhang, A. Depasquale, et al., Miniature microbial fuel cells integrated with triggered power management systems to power wastewater sensors in an uninterrupted mode, Appl. Energy 302 (2021) 117556. https://doi.org/10.1016/J.APENERGY.2021.117556, Elsevier.

Future applications of biological fuel cells

Sensors and telemetry systems, which are located in remote and inaccessible sites, can be powered by the MFC. The application of various types of MFCs in this regard is still in its infancy, and several crucial issues must be addressed before it can find its place as a commercialized technology. Selecting effective metabolic reactions for the anodic and cathodic reactions in the MFC deployed in natural waters is one of these issues [36,51]. Additionality, reading stability, response rate, and response time of the sensor to different changes of the system, the changes of internal resistance associated with fouling and degradation in the system, the robustness and recovery of the sensor, and simulation of the power storage of the sensors using efficient PMSs are important challenges that need future research to be addressed.

18.5 Paper-based MFC devices Short-term applications with low energy requirements are another category that MFC could easily fit in. Paper-based MFCs could be used in variety of new applications, including portable, lightweight, and backup power supply. To meet with such technology requirements, these systems would require a quick start-up and, ideally, a stable production over their short operational time. If such a device were to be used in a remote places, a readily available fuel would be required for MFC energy production [7]. The application of a paper-based diagnosis device for disease diagnosis and environmental monitoring triggered the invention of paper-based MFC [52]. The first paperbased MFC was fabricated with inexpensive materials to reduce the power source of diagnosis devices and was able of supplying its power by a drop of inoculum added to the device (Fig. 18.3A and B). Therefore, an inexpensive proton exchange membrane was made by infiltrating sodium polystyrene sulfonate into simple filter paper. The anode and cathode electrodes were made of flexible carbon cloth, and the paper chambers were presented by photoresist hydrophobic barriers. The current of 74 μA cm 2 was generated upon adding the solutions to the device, and it gradually diminished over time. The power intensity and duration were enough for diagnosis device for detection function. The advantages of this paper-based MFC included ease of use (one drop of sewage as a fuel), low production costs (