Emerging Trends and Techniques in Biofuel Production from Agricultural Waste (Clean Energy Production Technologies) 981998243X, 9789819982431

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Clean Energy Production Technologies Series Editors: Neha Srivastava · P. K. Mishra

Pardeep Singh   Editor

Emerging Trends and Techniques in Biofuel Production from Agricultural Waste

Clean Energy Production Technologies Series Editors Neha Srivastava, Department of Chemical Engineering and Technology,  IIT (BHU) Varanasi, Varanasi, Uttar Pradesh, India P. K. Mishra, Department of Chemical Engineering and Technology,  IIT (BHU) Varanasi, Varanasi, Uttar Pradesh, India

The consumption of fossil fuels has been continuously increasing around the globe and simultaneously becoming the primary cause of global warming as well as environmental pollution. Due to limited life span of fossil fuels and limited alternate energy options, energy crises is important concern faced by the world. Amidst these complex environmental and economic scenarios, renewable energy alternates such as biodiesel, hydrogen, wind, solar and bioenergy sources, which can produce energy with zero carbon residue are emerging as excellent clean energy source. For maximizing the efficiency and productivity of clean fuels via green & renewable methods, it’s crucial to understand the configuration, sustainability and techno-­ economic feasibility of these promising energy alternates. The book series presents a comprehensive coverage combining the domains of exploring clean sources of energy and ensuring its production in an economical as well as ecologically feasible fashion. Series involves renowned experts and academicians as volume-editors and authors, from all the regions of the world. Series brings forth latest research, approaches and perspectives on clean energy production from both developed and developing parts of world under one umbrella. It is curated and developed by authoritative institutions and experts to serves global readership on this theme.

Pardeep Singh Editor

Emerging Trends and Techniques in Biofuel Production from Agricultural Waste

Editor Pardeep Singh Department of Environmental Studies PGDAV College, University of Delhi New Delhi, Delhi, India

ISSN 2662-6861     ISSN 2662-687X (electronic) Clean Energy Production Technologies ISBN 978-981-99-8243-1    ISBN 978-981-99-8244-8 (eBook) https://doi.org/10.1007/978-981-99-8244-8 © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024 This work is subject to copyright. All rights are solely and exclusively licensed by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors, and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, expressed or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. This Springer imprint is published by the registered company Springer Nature Singapore Pte Ltd. The registered company address is: 152 Beach Road, #21-01/04 Gateway East, Singapore 189721, Singapore Paper in this product is recyclable

Preface

The energy demand has been increasing daily in the last two decades. The direction of energy is increasing manyfold. To fulfil the present energy demands, the utilisation of fossil fuels is growing, which ultimately causes various environmental issues like the emission of greenhouse gasses and other environmental pollutants. With dual pressures to avoid environmental deterioration and encourage energy security, a low-carbon, sustainable energy structure is becoming increasingly important in developing countries. We must convert large quantities of primary energy into electricity. In thermal power plants, fossil fuels release greenhouse gas emissions and other atmospheric pollutants. Therefore, there is a need for sustainable and clean energy. Agricultural activities lead to abundant agricultural waste generation, and it is projected that most Asian countries, particularly India, have a significant problem managing this waste. Different environmental issues emerge from the mismanagement of agricultural waste. Natural biodegradation of agricultural waste causes the emission of greenhouse gases. In India, waste is mainly burned in the fields, causing air pollution. Agriculture waste is a renewable source of lignocellulosic feedstock for value-­ added products. Considering the non-replaceable fossil fuel reservoir, the exponentially growing human population urges an immediate search for alternative renewable energies. To confront the upcoming energy crisis, lignocellulosic agricultural waste is expected to be a sustainable, renewable, low-cost resource to derive bioenergy because of its high availability. This book primarily focuses on the potential of biofuel production from agricultural waste, such as biogas generation, biohydrogen production, and research trends in managing or converting agricultural waste into biofuel. This book also draws attention to technological equipment and generated biofuels from agricultural waste through various biological and chemical processes and even to the multiple factors responsible for biofuels from agricultural waste generation. This book has 13 chapters, all authored by eminent scholars in the field. The first chapter is an introductory chapter on biofuel production from agricultural waste, discussing global trends. The second chapter is based on the utilisation of Agricultural Waste from a Circular Economy perspective. The third and fourth chapters elaborate on the role of various microbes in biofuel generation from v

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Preface

agricultural waste. The fifth and sixth chapters deal with biohydrogen production from various feedstocks. The seventh chapter is based on biomethane production as an alternative for valorising agricultural residues. The eighth chapter discusses biofuel production from agricultural waste through various effective and sustainable approaches, and the ninth chapter describes the production and characterisation of bio-alcohols. In the tenth and eleventh chapters, the authors discuss the technological advancement for bio-hydrogen production from agricultural waste. The twelfth chapter is based on the various parameters responsible for biomass energy production. In the last chapter, government initiatives and policies for agricultural waste utilisation as biofuel were discussed. This book will be the key guide for researchers, policymakers and organisations working on biofuel production and agriculture waste management through the circular economy perspective. New Delhi, Delhi, India

Pardeep Singh

Contents

1

 Biofuel Production from Agricultural Waste: A Global Trend������������    1 Bhupinder Dhir

2

 Agricultural Waste in Circular Economy: An Indian Scenario����������   15 Nijara Baruah, Abhijit Bora, and Nirmali Gogoi

3

 Application of Methano Bacteria for Production of Biogas����������������   43 Sonal Singh, Kuldip Dwivedi, Shashank Gupta, and Nidhi Shukla

4

Microbial Advancements in Dark Fermentative Biohydrogen Production: Applications and Innovations��������������������������������������������   57 D. M. Tripathi and Smriti Tripathi

5

 Biohydrogen Production from Various Feedstocks: Biohydrogen Generation from Biomass������������������������������������������������������������������������   81 Manmohan Kumar, Shagun Sharma, Jai Kumar, Shibnath Mazumder, and Usha Kumari

6

Biohydrogen from Agricultural Waste��������������������������������������������������  101 Taciana Carneiro Chaves, Fernanda Santana Peiter, and Eduardo Lucena Cavalcante de Amorim

7

Biomethane Production as an Alternative for the Valorization of Agricultural Residues: A Review on Main Substrates Used as Renewable Energy Sources����������������������������������������������������������������  119 Georgia Nayane Silva Belo Gois, Amanda Santana Peiter, Norma Candida dos Santos Amorim, and Eduardo Lucena Cavalcante de Amorim

8

Biofuel Production from Agricultural Residue: An Effective and Sustainable Approach for Management of Agro-waste����������������  131 Swati Sachdev

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Contents

Production and Characterization of Bio-­alcohols from Agricultural Wastes ��������������������������������������������������������������������������������  147 Dharitri Borah, Baldev Edachery, Jayashree Rout, and Thajuddin Nooruddin

10 Technological  Advancement for Biohydrogen Production from Agricultural Waste��������������������������������������������������������������������������  175 Anudeb Ghosh, Apurba Koley, Saradashree Pal, Nitu Gupta, Binoy Kumar Show, Gaurav Nahar, and Srinivasan Balachandran 11 Recycling  of Agricultural Waste for Biohydrogen Production������������  223 Zeenat Arif and Pradeep Kumar 12 Parameters  Responsible for Biomass Energy Production��������������������  241 Gopal Sonkar 13 Government  Initiative and Policy for Agricultural Waste Utilization as Biofuel��������������������������������������������������������������������������������  273 Prateek Srivastava

Editor and Contributors

About the Editor Pardeep Singh  currently serves as an Assistant Professor within the Department of Environmental Science at PGDAV College, University of Delhi, New Delhi, India. He earned his Master's degree in Environmental Science from Banaras Hindu University, Varanasi, India, and completed his Ph.D. at the Indian Institute of Technology, Banaras Hindu University, Varanasi. Dr. Singh has contributed to over 75 publications in international journals specialising in waste management and has also edited 40 books in the field of environmental management with publishers of international repute.

Contributors Zeenat Arif  Harcourt Butler Technical University, Kanpur, Uttar Pradesh, India S.  Balachandran  Department Santiniketan, India

of

Environmental

Studies,

Visva-Bharati,

Nijara  Baruah  Plant Physiology and Biochemistry Laboratory, Department of Environmental Science, Tezpur University, Tezpur, Assam, India Abhijit  Bora  Plant Physiology and Biochemistry Laboratory, Department of Environmental Science, Tezpur University, Tezpur, Assam, India Dharitri Borah  Department of Environmental Science, Arunachal University of Studies, Namsai, Arunachal Pradesh, India Taciana Carneiro Chaves  Environmental Control Laboratory, Technology Center, Federal University of Alagoas, Maceió, Alagoas, Brazil Eduardo  Lucena  Cavalcante  de Amorim  Environmental Control Laboratory, Technology Center, Federal University of Alagoas, Maceió, Alagoas, Brazil ix

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Editor and Contributors

Bhupinder  Dhir  School of Sciences, Indira Gandhi National Open University, New Delhi, India Norma Candida dos Santos Amorim  Federal Institute of Alagoas, Satuba, Brazil Kuldip  Dwivedi  Department of Environmental Science, Amity School of Life Science, Amity University Madhya Pradesh, Gwalior, India Baldev  Edachery  Research and Development, Sreedhareeyam Farmherbs India Pvt. Ltd., Ernakulam, Kerala, India Anudeb  Ghosh  Department Santiniketan, India

of

Environmental

Studies,

Visva-Bharati,

Nirmali  Gogoi  Plant Physiology and Biochemistry Laboratory, Department of Environmental Science, Tezpur University, Tezpur, Assam, India Georgia Nayane Silva Belo Gois  Environmental Control Laboratory, Technology Center, Federal University of Alagoas, Maceió, Brazil Nitu  Gupta  Department of Environmental Science, Tezpur University, Tezpur, Assam, India Shashank Gupta  Department of Civil Engineering, ITM University, Gwalior, India Apurba  Koley  Department Santiniketan, India

of

Environmental

Studies,

Visva-Bharati,

Usha Kumari  Department of Zoology, Gargi College, University of Delhi, New Delhi, India Jai  Kumar  Immunobiology Laboratory, Department of Zoology, University of Delhi, New Delhi, India Manmohan  Kumar  Immunobiology Laboratory, Department of Zoology, University of Delhi, New Delhi, India Pradeep  Kumar  Indian Institute of Technology (BHU), Varanasi, Uttar Pradesh, India Shibanath  Mazumder  Immunobiology Laboratory, Department of Zoology, University of Delhi, New Delhi, India Faculty of Life Sciences and Bio-Technology, South Asian University, New Delhi, India Gaurav Nahar  Defiant Renewables Pvt Ltd, Chinchwad, Pune, India Thajuddin  Nooruddin  Department of Microbiology, Bharathidasan University, Tiruchirappalli, Tamil Nadu, India Saradashree  Pal  Department Santiniketan, India

of

Environmental

Studies,

Visva-Bharati,

Editor and Contributors

xi

Amanda Santana Peiter  Renewable Energy Center, Center of Agrarian Sciences, Federal University of Alagoas, Rio Largo, Brazil Fernanda Santana Peiter  Environmental Control Laboratory, Technology Center, Federal University of Alagoas, Maceió, Alagoas, Brazil Jayashree  Rout  Department of Ecology and Environmental Science, Assam University, Silchar, Assam, India Swati Sachdev  Department of Liberal Education, Era University, Lucknow, Uttar Pradesh, India Shagun Sharma  Immunobiology Laboratory, Department of Zoology, University of Delhi, New Delhi, India Binoy  Show  Department Santiniketan, India

of

Environmental

Studies,

Visva-Bharati,

Nidhi  Shukla  Department of Environmental Science, Amity School of Life Science, Amity University Madhya Pradesh, Gwalior, India Sonal Singh  Department of Environmental Science, Amity School of Life Science, Amity University Madhya Pradesh, Gwalior, India Gopal Sonkar  Department of Geography, University of Delhi, Delhi, India Prateek  Srivastava  Forestry and Compliance, Natural Resources Development S.A., Mauren, Principality of Liechtenstein D. M. Tripathi  Department of Microbiology, Bundelkhand University, Jhansi, India Smriti Tripathi  Institute of Environment and Development Studies, Bundelkhand University, Jhansi, India

Chapter 1

Biofuel Production from Agricultural Waste: A Global Trend Bhupinder Dhir

Abstract Conversion of waste into fuel has emerged as an eco-friendly, economical, and sustainable way of handling waste. Agricultural wastes and residues form an important source for the production of fuels. Straw from rice and wheat, husk from rice and wheat, maize cobs, sugarcane bagasse, oil cakes, and banana peel are some of the agro residues used in the generation of fuels. The fuels generated from biological waste include bioethanol, biobutanol, biodiesel, biomethane, and biohydrogen. Biofuels offer a renewable, sustainable clean energy option because of reduced emissions of greenhouse gases and particulates. The dependency on biofuels has increased tremendously during the last decade, with global production reaching approximately 40 million metric tons. The United States, Brazil, Germany, China, Argentina, and France are some of the countries leading in biofuel production. Biofuels offer a good alternative to conventional fuels such as petroleum; therefore, their production needs to be enhanced significantly for a sustainable future. Keywords Agricultural residues · Biodiesel · Bioethanol · Biofuel · Biohydrogen · Sustainable

1.1

Introduction

Exhaustion of fossil fuels and energy resources, environmental problems resulting from their overuse, and increasing demand for fuels and energy sources have generated a search for alternate sources of energy and fuel (Robak and Balcerek 2018; Machineni 2019; Manfred 2020; Leong et al. 2021). Researchers have tried various materials for generating energy sources and have successfully generated fuels/ B. Dhir (*) School of Sciences, Indira Gandhi National Open University, New Delhi, India © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024 P. Singh (ed.), Emerging Trends and Techniques in Biofuel Production from Agricultural Waste, Clean Energy Production Technologies, https://doi.org/10.1007/978-981-99-8244-8_1

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energy sources from agricultural waste (Demirbas 2009). The fuels generated from agricultural products and residues/wastes are termed biofuels. These fuels are a cheaper, eco-friendly, and sustainable energy source compared to conventional fuels. Bioethanol, biobutanol, biohydrogen, and biodiesel are major biofuels produced from agricultural wastes and residues. Generation of about 350 million tons of agricultural waste is reported from all over the world every year. Out of such a huge amount, only a small amount is used by farmers for feeding livestock, and the rest is either burned or dumped in the soil. Burning of the waste results in the generation of large quantities of harmful gases such as carbon monoxide, nitrogen oxide, and hydrocarbons. These gases exert a negative impact on the environment. Accumulation of agro-wastes leads to environmental pollution. Therefore, its processing and conversion into valuable products like fuel was conceptualized (Leong et al. 2021). The use of these residues in the production/generation of fuels which cause comparatively less harm to the environment proved to be a sustainable option for their disposal. Agricultural residues include waste or by-products left after processes such as harvesting and processing of agricultural output. These residues are carbon-based materials and can be used in the generation of biofuels. These mainly include straw, husk, hull, leaves, and other materials left after harvesting of crops and their processing at the mills. Wastes from sugarcane, maize which are rich sources of starch and sugar, soybean, and sunflower which is rich source of oil have been exploited for the production of biofuels. Bagasse residues from sugarcane have been specifically used to produce ethanol. Biomass, residues obtained from forest (like branches, leaves, dry flowers, fruits), hulls (from rice, palm, coconut, groundnut, cashew), stalks and leaves of maize, millet and sorghum are some of the other waste materials used in the production of renewable biofuels. At the commercial level, corn and sugarcane have been exploited as a feedstock used for the generation of biofuels at the commercial level (Abdeshahian et al. 2010).

1.2 Synthesis of Biofuels Agricultural residues/wastes like sugarcane bagasse, peel, bran, straw, husk, cobs, and shells (coconut, groundnut) are good sources of lignocellulose which is the main source of biofuel (Sarangi and Nanda 2019, 2020; Yadav et  al. 2021). Lignocellulose contains about high quantities of cellulose (40–50%), hemicellulose (20–30%), and some amount of lignin (10–25%). Lignocellulose is one of the major components of biomass that is used in biofuel production (Ullah et al. 2015; Eckert et al. 2018; Hassan et al. 2018) (Table 1.1). The presence of strong covalent bonds, hydrogen bonding, and extensive van der Waal forces make the lignocellulose molecules recalcitrant. Because of all these properties, lignocellulosic biomass is resistant to breakdown. Hence, pretreatment is done to disrupt the structure of lignocellulose. Pretreatment of residues removes lignin and results in the release of

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Table 1.1  Proportion of various components of lignocelluloses present in various crop residues Crop residue Rice residues Maize residues Corn husk Soybean residues Groundnut husk Hazelnut shell Tobacco leaf Almond shell Wheat stalk Cotton residues Grass straw Barley straw The straw of pulses, cereals

Composition (% dry weight) Cellulose Hemicellulose 0.42 0.21 0.35 0.23 0.35 0.37 0.40 0.16 0.22 0.27 0.28 0.24 0.36 0.34 0.51 0.29 0.38 0.27 0.80 0.20 0.40 0.50 0.46 0.23 0.37 0.29

Lignin 0.19 0.19 0.17 0.16 0.36 0.49 0.12 0.20 0.18 – 0.10 0.16 0.14

lignocellulosic components of biomass such as cellulose (Sun and Cheng 2002). Pretreatment of lignocellulosic biomass is followed by hydrolysis so that sugars can easily be used in the generation of fuel (Mosier et al. 2005a, b). The general procedure for biofuel production involves pretreatment of residues followed by hydrolysis. Hydrolysis is done using enzymes such as cellulases (used for cellulose) or hemicellulase (used for hemicellulose) or acids (such as sulfuric acid). This results in the release of free sugars (Ibrahim et al. 2021; Özbek et al. 2021). The biological processes involved in biofuel production include fermentation, digestion, and microbial processing (Malode et al. 2021). Physical, chemical, physicochemical, and biological methods can be followed for the pretreatment of biomass (Cheah et al. 2020; Özbek et al. 2021; Ibrahim et al. 2021). The physical methods of lignocellulosic biomass pretreatment involve a reduction in the size of the residues through processes such as milling, grinding, or chipping. These processes decrease the particle size but increase the surface area. Lignocellulosic biomass is also treated by the pyrolysis method, which involves heating of biomass at high temperatures (above 300 °C). The process leads to the rapid degradation of cellulose. The carbon in the leachate supports the growth of microbes that help in fermentation during the production of bioethanol. Thermal pretreatment of biomass releases acetic acid. These processes reduce the polymerization and crystallinity of cellulose, hydrolyze hemicellulose, and cause partial depolymerization of lignin. Physicochemical methods such as steam treatment or CO2 exposure are also done for the delignification of biomass. The pretreatment of lignocellulosic biomass can also be done by auto-hydrolysis method (Sun and Cheng 2002). The process involves the conversion of lignocellulosic biomass into levulinic acid, xylitol, and alcohols without the use of a catalyst. Biomass is subjected to heat treatment (steam at a pressure of 20–50 bar and temperature of 160–290 °C) for a few minutes (Balat

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et al. 2008; Sanchez and Cardona 2008). Hemicellulose gets hydrolyzed, and oligomeric sugars get separated from hemicellulose after this treatment (Neves et  al. 2007). A high temperature of 170–230  °C and pressure of more than 5  MPa for 20 min are required for the process. About 45–65% of xylose can be recovered after this method of lignocellulosic biomass pretreatment. Biomass is treated with water, air, or oxygen at high temperatures (above 120  °C) in the wet oxidation method (Martín et al. 2007). Acid, alkali, ammonia, organic solvent, sulfur dioxide, carbon dioxide, and other chemicals are used in chemical pretreatment methods. This method converts hemicellulose into monomeric xylose and cellulose. This method is easy and has better conversion efficiency. Sulfuric acid brings about hydrolysis of hemicelluloses resulting in the release of sugars at temperatures between 130 and 210 °C (Cardona et al. 2009). Alkali treatment of lignocellulose results in solubilization of hemicellulose, lignin, and silica. Organic solvents such as methanol, ethanol, acetic acid, performic acid, peracetic acid, and acetone also play a role in the delignification of lignocellulosic biomass (Zhao et al. 2009). In the biological method, lignocellulose is treated with brown-rot and white-rot fungi that attack cellulose and lignin. They liberate cellulose from the lignocellulose complex. Biological pretreatment results in less yield, and rate of hydrolysis is also low (Balat et al. 2008). The pretreatment method varies according to the properties of the substrate. Pretreatment results in the release of cellulose and hemicelluloses from the lignocellulosic biomass. Pretreatment speeds up the process of release of cellulose and sugars required for metabolism. After pretreatment, cellulose is hydrolyzed to release sugars. Sugars like glucose, xylose, and galactose are fermented to synthesize ethanol. The fermentation is carried out with the help of microorganisms (Kabel et al. 2007). Fermentation used in biofuel production can be batch, fed-batch, or continuous. Plant oils can also be used to generate fuel. Plant oils are obtained by crushing of seeds of oil crops such as soybean, canola, and mustard. After extraction, transesterification of oil is done to produce biodiesel. Anaerobic digestion of crop residues helps in producing methane and other combustible gases. Waste produced from industrial processes, sewage, and microalgae can also serve as raw material for the generation of biohydrogen and other biofuels.

1.3 Types of Biofuels Agricultural biomass is categorized into different generations depending upon the source used in biofuel production. First-generation biomass includes food crops, whereas second-generation biomass includes lignocellulosic residues obtained from agriculture, forest, domestic, and industrial wastes (Fig. 1.1). Microalgae as feedstock are considered as third- and fourth-generation biomass (Sanchez and Cardona 2008; Tse et al. 2021). The nonfood feedstock used for second-generation biofuels

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Fig. 1.1  Various generations of bioethanol production

includes grasses and municipal waste. Algae are used in the generation of third-­ generation biofuels. About 50% oil can be extracted and processed to produce biodiesel, and the residue left after oil extraction can be used in ethanol production. Biofuels are broadly categorized as first generation, second generation, third generation, and fourth generation. This categorization of biofuels is based on the material used in biofuel production. Sugar and starch obtained from crops are used in the synthesis of first generation of biofuels. These materials produce ethanol by transesterification or yeast fermentation which results in formation of ethanol. Small quantities of butanol and propanol are also produced during the process.

1.4 Major Biofuels 1.4.1 Bioethanol Agricultural residues such as sugarcane bagasse, wheat and rice straw, corn stover, and sugar beet are used in production of bioethanol (Kim and Dale 2004; Sarkar et al. 2012). Bagasse is the most abundant agricultural residues used in synthesis of bioethanol (Canilha et al. 2012). Pretreatment, hydrolysis, and fermentation of sugars are the basic steps involved in production of bioethanol (Bušić et  al. 2018; Badamchizadeh et al. 2021). Biomass containing high levels of starch (e.g., wheat, corn) and/or sugar (e.g., sugarcane, sugar beet) is fermented to produce

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first-­generation bioethanol. Corn and cassava contain 50–70% starch which is predominantly used for bioethanol production. The production of bioethanol from lignocellulosic biomass is primarily an anaerobic process which involves role of enzymes. The cellulose from the biomass gets transformed into glucose through hydrolysis carried out with the help of enzymes. Microorganisms convert glucose into ethanol. Hexose sugars produce ethanol after fermentation. Sugars from monosaccharides, disaccharides, or polysaccharides act as the substrate for synthesis of bioethanol. Polysaccharides produce ethanol via fermentation directly or digestion or chemical degradation and subsequent fermentation. Lignocellulosic biomass obtained from specific biomass requires specific pretreatment followed by enzymatic hydrolysis and fermentation to produce bioethanol. Fermentation is carried out by microbes such as Saccharomyces cerevisiae, Escherichia coli, Zymomonas mobilis, Candida brassicae, Mucor indicus, etc. Saccharification process converts complex carbohydrates into monomeric units which are used in bioethanol production. Cellulose and hemicellulose present in lignocellulosic biomass are degraded with the help of cellulase and hemicellulase enzymes (Neves et al. 2007). Cellulose degrading enzymes mainly include endoglucanase, exo-glucanase, and β-glucosidase. Endoglucanase specifically helps in breakdown of crystalline regions of cellulose fibers, while exo-glucanase helps in the formation of glucose by removing cellobiose units (Banerjee et  al. 2010). Cellulase enzyme is costly; therefore, pretreatment technology needs to be designed in a way that crystallinity of cellulose and lignin removal can be achieved to maximum extent. Surfactants that adsorb lignin, and modify cellulose surface, ultimately reducing requirement of enzyme are also being tried (Eriksson et  al. 2002). Pretreatment of wheat straw with alkaline peroxide decomposed about 96.75% of lignocellulose after enzymatic hydrolysis, while organic solvent pretreatment resulted in about 75% degradation (Saha and Cotta 2006). Second-generation bioethanol typically uses nonedible feedstocks such as lignocellulosic materials and agricultural forest residues (e.g., wood), and third-­ generation bioethanol uses algal biomass for ethanol production. Chemical mainly acid or physical pretreatment is required to disrupt algal cell walls required for generation of third-generation bioethanol production. Pretreatment converts complex carbohydrates to simple sugars that can be fermented. Enzymatic hydrolysis occurs through a process known as saccharification. Genetically engineered organisms are used in generation of fourth-generation bioethanol. They show enhanced fermentation efficiency. Higher octane value of bioethanol increases the efficiency of the engine, hence preferred as a fuel (Safarian and Unnthorsson 2018).

1.4.2 Biodiesel Biodiesel is synthesized mainly from vegetable oils, animal fats, and alcohol. It is produced by transesterification of plant oil or animal fat (Singh and Singh 2010). Oils and methanol react in the presence of a catalyst to produce biodiesel (Pasha

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et al. 2021). It is either used singly as a fuel or blended with diesel oil. It shows low toxicity, degrades easily, and has easy blending capacity and good lubrication potential. Low emission of carbon monoxide, particulate matter, and polycyclic aromatic hydrocarbons helps in reducing environmental pollution. Lower health risk, due to reduced emissions, makes biodiesel a preferred fuel in many countries of the world.

1.4.3 Biobutanol Biobutanol is synthesized manly from agro-waste rich in sugar, starch, or lignocellulose (Alias et al. 2020). The lignocellulosic biomass is converted to butanol after pretreatment and fermentation. Microorganisms such as Escherichia coli, Clostridium acetobutylicum, Clostridium beijerinckii, Bacillus subtilis, Pseudomonas putida, and Saccharomyces cerevisiae produce biobutanol through aerobic and anaerobic fermentation. Biobutanol possesses high calorific value and low hydrophilicity. Biobutanol possesses high energy content and produces fewer emissions; hence, it can easily be used as a transport fuel. It is highly volatile and highly polar, possesses high combustion value and high octane rating, and is less corrosive. It shows properties similar to gasoline; hence, it can easily get substituted without alteration in vehicle engine. In addition, it has less ignition problems because of the low heat of vaporization (Visioli et al. 2014).

1.4.4 Biohydrogen Biohydrogen is produced predominantly by microalgae. Wheat, corn, rice, barley, sugarcane, sugar beet, potato, and oat residues are also used as raw material in synthesis of biohydrogen. Fermentation of biomass results in the production of the fuel (Alavijeh et  al. 2020; Ahmed et  al. 2021). Biohydrogen production using algae involves low productivity, oxygen sensitivity, and high operational costs; therefore, commercialization of microalgae-based biohydrogen production is restricted (Osman et al. 2023).

1.4.5 Bio-Oils Crop and algal biomass and agricultural and forestry by-products are subjected to thermochemical process for bio-oil production (Demirbas 2007). Pyrolysis, liquefaction, and gasification are the processes involved in the conversion of biomass to bio-oil. It possesses high volatility and combustibility (Xu et al. 2011).

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1.5 Status of Biofuels All over the Globe The United States, Brazil, the European Union, China, and India lead in the production of biofuels among the other countries of the world (Table  1.2). The biofuel production from these countries accounts to 90% of the global production. The United States alone produced about 2616  thousand  barrels/day of biofuels, 1890  thousand  barrels/day of biogasoline, and 702  thousand  barrels/day of biodiesel in 2018. According to the Energy Information Administration (EIA) report, the United States produced around 16.061 billion gallons of ethanol in 2018. The United States leads the production of biogasoline with 55.4% share of the total world. In the year 2019, the United States produced about 15.7 billion gallons of bioethanol. Brazil is the second largest producer of biofuel. The country produced 693.2 thousand barrels/day of biofuel in 2018. It is also the second largest country for biodiesel production. High production of 99,000 barrels/day has been reported by the country (Table 1.3). The United States and Brazil contributed about 87% of the world’s total biofuel production. In the United States, feedstocks that are used in bioethanol production for corn and soybean are used for biodiesel production. According to an estimate, country is likely to use 680  million  tons of biomass resources annually by the year 2030 that would be able to generate about 10 billion gallons of ethanol. Germany occupies third position among the biofuel producing countries in the world. Annual production of 75.8 thousand barrels/day was reported in 2018. The country’s contributed about 2.9% of the global biofuel production. Argentina is fourth largest country showing high biofuel production (mainly bioethanol and biodiesel). The country produced 70.6 thousand barrels/day of biofuels Table 1.2  Countries leading in biofuel production as noted in 2021

Table 1.3  Top 10 biodiesel producing countries of the world

Country Brazil Indonesia China

Rank 1 2 3 4 5 6 7 8 9 10

Country Indonesia Argentina United States Brazil Netherlands Germany Malaysia Philippines Belgium Spain

Production (petajoules) 839.5 311.9 142.7

Volume (L) 7,595,000,000 5,255,000,000 3,212,000,000 2,567,000,000 2,496,000,000 2,024,000,000 14,540,000,000 1,234,000,000 1,213,000,000 1,073,000,000

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in 2018 which accounts for 2.7% of the global production. According to a USDA report, the country produces 1.4 billion L of bioethanol and 700 million L of biodiesel every year. China, India, Brazil, and Indonesia dominate in biofuel production among the developing countries of the world. China is fifth largest biofuel producer in the world. It produced about 68,000 barrels/day in 2018 which accounted for 2.6% of total biofuel production. China is the fourth largest ethanol producing country of the world. It is also one of the biggest consumers after the United States, Brazil, and the European Union. China aims for getting a 10% ethanol-gasoline blend-use nationwide by 2020. Iran produces 6542  million  m3 of biogas, 2443  million  L of bioethanol, and 2082  million  m3 of biohydrogen from 24.3  million  tons of agricultural waste (Ahmadi et al. 2020). The country aims to produce about 5 billion L of bioethanol from the agricultural waste by the year 2026. Demand for biofuels is likely to increase by 41 billion L (i.e., about 28%) over 2021–2026. Annual bioethanol production increasing and worldwide bioethanol production and consumption will increase to 134.5 billion L by 2024. According to predictions, the United States, Brazil the European Union, and China will continue to be the major bioethanol producers of the world. Sugarcane and sugar beet will be major source of agro residues or feedstocks used in bioethanol. The feedstocks used for bioethanol production in Europe mainly include wheat and sugar beet. In terms of consumption of biofuels, China and India are the largest consumers all over the world followed by Brazil (Fig. 1.2). According to estimates, the United States, India, China, Brazil, and the EU will use 90% of global biofuel by the year 2035. The highest demand for biofuels is likely to include. Biofuels are expected to meet requirement of about 8% of total fuel required for road transport by the year 2035. Bioethanol makes about 75% of the total biofuel.

Fig. 1.2 Prediction for biofuel consumption by various countries of the world, 2030

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The demand for bioenergy production is rising day by day. The production of biofuels from agricultural residues depends largely on the availability of residues at regional and a global scale. Different countries of the world produce different agricultural crops, and hence the availability of the residues for biofuel production also differs. Corn (maize), one of the crops grown in tropical to temperate climates, provides feedstock for ethanol and is available in large quantities in the United State. Jatropha, another perennial crop, is another good option for biofuel production available in countries like Mexico, Sudan, Ethiopia, and India. Palm, a feedstock for biodiesel, is produced in large quantities by Indonesia, Malaysia, and other countries of Southeast Asia (Table 1.4). Sugarcane is the second largest feedstock for ethanol production. It is easily available in Brazil, India, and the United States. Sorghum is a grass crop produced mostly by the United States, Nigeria, and India. Soybeans are largely produced by the United States and Brazil. The United States is expected to have 155 million tons of residues that will be used for producing biofuels and bioenergy in 2030.

1.5.1 Benefits Biofuels significantly reduce dependence on fossil fuels (Ahorsu et  al. 2018; Alalwan et  al. 2019). Biofuels provide an eco-friendly clean energy source and reduce the problem of pollution by reducing greenhouse gas emissions, global warming, and greenhouse effect (Leong et  al. 2021; Liu et  al. 2021). Waste can provide promising material for global energy production (Sarangi and Nanda 2020). Bioconversion of lignocelluloses from waste for the production of biofuel can make significant contribution in terms of environmental, socioeconomic benefits. Fossil

Table 1.4  Availability of agricultural residues for biofuel production in countries of Asia

Country Indonesia Thailand Bangladesh Vietnam Philippines Myanmar Middle East Afghanistan Pakistan Turkey China India Whole Asia

Availability of residue (Tg DM) 88 57 41 29 30 29 117 7 51 43 632 347 1471

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fuels with 30% of bioethanol can be used in vehicles without any alteration in vehicle (Safarian and Unnthorsson 2018).

1.6 Conclusion and Future Prospects Biofuel is a good alternate in the today’s scenario increasing demand for fuel. Biofuels are a good option for reducing our requirement and dependency on fossil fuels. Agricultural wastes/residues are considered good sources/feedstocks that are available in abundant amount around the world and can help in synthesis of sustainable biofuel and bioenergy. Wheat, corn, sugarcane, and sugar beet are the major agricultural materials used in biofuel production. Bioethanol and biodiesel are clean fuels produced through enzymatic digestion of sugars followed by fermentation. Biofuels derived from starch, sugar, and vegetable oil and processing a range of nonfood crops and biowastes comprise of first- and second-generation biofuels. Algae act as the feedstock for third generation of biofuels. Fourth-generation biofuel production involves the use of genetically engineered organisms in combination with other innovative approaches such as methods of improving fermentation process. Integration of first- and second-generation biofuels to maximize ethanol yield has been tried as this is expected to reduce capital investment required for integration of lignocellulose processes into industrial processes. Researchers around the world are searching for approaches/ways to maximize conversion of agricultural residues and related feedstocks into biofuels. Considerable research is being carried out to optimize synthesize of biofuels on a larger scale using cost-effective method. Research is also been carried out to find an easy and cost-effective method for extraction of sugars from the residues. Improvement has also been made in the protocol for hydrolysis of lignocellulosic materials by including pretreatment step for removal of lignin and hemicellulose and by optimizing the enzymes required for lignocellulose degradation. Research studies related to improvement in cultivation of biological products via improvement in soil and fertilizer application, upgrading biomass pretreatment, are under progress. Hence, all these measures can reduce costs and increase the economic sustainability of the feedstocks.

References Abdeshahian P, Dashti MG, Kalil MS, Yusoff WMW (2010) Production of biofuel using biomass as a sustainable biological resource. Biotechnol 9:274–282 Ahmadi A, Esmaeilion F, Esmaeilion A, Ehyaei MA, Silveira JL (2020) Benefits and limitations of waste-to-energy conversion in Iran. Renew Energy Res Appl 1:27–45 Ahmed SF, Rafa N, Mofijur M, Badruddin IA, Inayat A, Ali MS, Farrok O, Khan YTM (2021) Biohydrogen production from biomass sources: metabolic pathways and economic analysis. Front Energy Res 9:753878. https://doi.org/10.3389/fenrg.2021.753878

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Malode SJ, Prabhu KK, Mascarenhas RJ, Shetti NP, Aminabhavi TM (2021) Recent advances and viability in biofuel production. Energy Convers Manag 10:100070 Manfred K (2020) Bioeconomy—present status and future needs of industrial value chains. New Biotechnol 60:96–104 Martín C, Klinke HB, Thomsen AB (2007) Wet oxidation as a pretreatment method for enhancing the enzymatic convertibility of sugarcane bagasse. Enzyme Microb Technol 40:426–432 Mosier N, Hendrickson R, Ho N, Sedlak M, Ladisch MR (2005a) Optimization of pH controlled liquid hot water pretreatment of corn stover. Bioresour Technol 96:1986–1993 Mosier N, Wyman C, Dale B, Elander R, Lee YY, Holtazapple M (2005b) Features of promising technologies for pretreatment of lignocellulosic biomass. Bioresour Technol 96:673–686 Neves MA, Kimura T, Shimizu N, Nakajima M (2007) State of the art and future trends of bioethanol production. Dyn Biochem Process Biotechnol Mol Biol 1:1–13 Osman AI, Deka T, Baruah DC, Rooney DW (2023) Critical challenges in biohydrogen production processes from the organic feedstocks. Biomass Conv Bioref 13:8383–8401. https://doi. org/10.1007/s13399-­020-­00965-­x Özbek HN, Koçak Yanık D, Göğüş FSF (2021) Effect of microwave assisted alkali pre-treatment on fractionation of Pistachio shell and enzymatic hydrolysis of cellulose-rich residues. J Chem Technol Biotechnol 96:521–531 Pasha MK, Dai L, Liu D, Guo M, Du W (2021) An overview to process design, simulation and sustainability evaluation of biodiesel production. Biotechnol Biofuels 14:129 Robak K, Balcerek M (2018) Review of second generation bioethanol production from residual biomass. Food Technol Biotechnol 56:174–187 Safarian S, Unnthorsson R (2018) An assessment of the sustainability of lignocellulosic bioethanol production from wastes in Iceland. Energies 11:1493 Saha BC, Cotta MA (2006) Ethanol production from alkaline peroxide pretreated enzymatically saccharified wheat straw. Biotechnol Prog 22:449–453 Sanchez OJ, Cardona CA (2008) Trends in biotechnological production of fuel ethanol from different feedstocks. Bioresour Technol 99(13):5270–5295 Sarangi PK, Nanda S (2019) Recent advances in consolidated bioprocessing for microbe-assisted biofuel production. In: Nanda S, Sarangi PK, Vo DVN (eds) Fuel processing and energy utilization. CRC Press, Boca Raton, pp 141–157 Sarangi PK, Nanda S (2020) Bioprocessing of biofuels. CRC Press, Boca Raton Sarkar N, Ghosh SK, Bannerjee S, Aikat K (2012) Bioethanol production from agricultural wastes: an overview. Renew Energy 37:19–27 Singh SP, Singh D (2010) Biodiesel production through the use of different sources and characterization of oils and their esters as the substitute of diesel: a review. Renew Sust Energ Rev 14:200–216 Sun Y, Cheng JY (2002) Hydrolysis of lignocellulosic materials for ethanol production: a review. Bioresour Technol 83:1–11 Tse TJ, Wiens DJ, Reaney MJT (2021) Production of bioethanol—a review of factors affecting ethanol yield. Fermentation 7:268 Ullah K, Kumar SV, Dhingra S, Braccio G, Ahmad M, Sofia S (2015) Assessing the lignocellulosic biomass resources potential in developing countries: a critical review. Renew Sustain Energy Rev 51:682–698 Visioli LJ, Enzweiler H, Kuhn RC, Schwaab M, Mazutti MA (2014) Recent advances on biobutanol production. Sustain Chem Process 2:15 Xu Y, Hu X, Li W, Shi Y (2011) Preparation and characterization of bio-oil from biomass. In: Shaukat S (ed) Progress in biomass and bioenergy production. IntechOpen, London, pp 197–222 Yadav D, Kumari R, Kumar N, Sarkar B (2021) Reduction of waste and carbon emission through the selection of items with cross-price elasticity of demand to form a sustainable supply chain with preservation technology. J Clean Prod 297:126298 Zhao X, Cheng K, Liu D (2009) Organosolv pretreatment of lignocellulosic biomass for enzymatic hydrolysis. Appl Microbiol Biotechnol 82:815–827

Chapter 2

Agricultural Waste in Circular Economy: An Indian Scenario Nijara Baruah, Abhijit Bora, and Nirmali Gogoi

Abstract The increasing food, water, and energy demand and the earnestness of fulfilling the same in a sustainable way make circular economy a promising approach particularly for the developing and urbanized society. Reverse to the existing usual model of linear economy, circular economy will decelerate the depletion of natural resources and lower the environmental damages. India generates a huge quantity of agricultural waste. Immediate disposal of this agricultural waste can lead to loss of their probable economic value. However, by adopting circular economy, the agricultural waste can be reduced as it focuses on recycling and reuse of wastes to prevent the economic loss. The agricultural waste can be utilized as resources for other processes to improve their value. This chapter attempts to discuss the role of circular economy on agriculture, valorization of agricultural waste, and the effective management strategies to reduce agricultural waste. It also highlights the various challenges to agricultural waste management and adaptation potentiality of circular economy in India. Keywords Circular economy · Agricultural waste · Energy · Agro-waste valorization · Biomaterials · Additives · Soil amendments

N. Baruah Plant Physiology and Biochemistry Laboratory, Department of Environmental Science, Tezpur University, Tezpur, Assam, India Department of Botany, Moridhal College, Moridhal, Dhemaji, Assam, India A. Bora · N. Gogoi (*) Plant Physiology and Biochemistry Laboratory, Department of Environmental Science, Tezpur University, Tezpur, Assam, India © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024 P. Singh (ed.), Emerging Trends and Techniques in Biofuel Production from Agricultural Waste, Clean Energy Production Technologies, https://doi.org/10.1007/978-981-99-8244-8_2

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2.1 Introduction World population is growing and predicted to reach about 9.8 billion by 2050 (UN 2022). The growing population increases the demand of sustainable agricultural production as agriculture imposes enormous pressure on environment and natural resources (Laik et al. 2021; Sial et al. 2021). Earlier traditional agriculture was performed using available plants and resources for survival of local communities. The small amount of waste generated was recycled to soil as fertilizers (Jimenez-Lopez et  al. 2020). Currently, under the scenario of global warming, climate change, reduction and degradation of natural resources, it is highly difficult to increase the agricultural productivity in a sustainable way. Promotion of modern agriculture through Green Revolution in the 1950s increased the application of synthetic fertilizer, pesticide, and productive plant varieties (Duque-Acevedo et  al. 2020a; Ramankutty et al. 2018). It was recently estimated that globally crop yield would reduce by 42% if we exclude use of pesticides completely (Adejumo and Adebiyi 2020). Interestingly, modern agriculture improved the crop productivity more than threefold in the last five decades. Thus, it has the capability to meet the demand of global food requirements. However, modern agriculture also overexploits soil, water, and energy. These natural resources are finite and have limitation to fulfill the growing demand. Another biggest drawback of modern agriculture is generation of huge quantity of waste. India is an agrarian country and its economy is highly controlled by agriculture. Every year India is estimated to generate waste biomass of about 500 million tons including waste from agriculture, plantations, and forestry (Aradhey 2011). According to a report of the Ministry of New and Renewable Energy (MNRE  2009), Government of India, India generates about 500 metric tons (Mt) of agricultural waste per year (Bhuvaneshwari et al. 2019). The agricultural waste production was recorded higher from Uttar Pradesh (60 Mt) compared to Punjab and Maharashtra (51 and 46 Mt, respectively) (Dadlani 2012). These agricultural wastes are mainly produced during growth, processing, and consumption of fruit, vegetables, crops, dairy, poultry, meat, fish, etc. The unutilized residue accumulation creates health, safety, and esthetic concern. The agricultural waste also leads to critical environmental problem due to release of methane, nitrous oxide, sulfur dioxide, etc. (Nagendran 2011; He et al. 2019). It was reported that agriculture contributes approximately 21% of greenhouse gas emission (Adejumo and Adebiyi 2020). Hence, management of agricultural waste is a great concern. The circular economy concept has received significant popularity in recent times due to use of renewable resources as an alternative to finite resources (fossil fuels). The growing population, urbanization, environmental degradation, and changing climate depict the urgency of India to shift toward a circular economy. Circular economy can separate economic growth from consumption by utilizing waste biomass in generation of energy and chemicals so that waste of one process acts as raw material for another process (Bracco et al. 2018). Circular economy classifies materials into two types: biological and technical. Biological materials are easily returned to the natural environment after their use-life through biodegradation. Technical materials

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are nonconsumable and cannot be returned into the biosphere. Thus, technical material should be reusable, durable, and easily upgradable. For creating value or repeated recycle, technical products can be leased or rented to promote maintenance and reduce disposal. Adoption of circular economy by utilizing organic waste reduces greenhouse gas emission and fossil fuel requirement, creates job opportunities, and generates new green market (McCormick and Kautto 2013; Scarlat et al. 2015). According to FAO (2015) for maintaining food supply chain to the growing population, about 30% of total global energy produced is used. Valorization of large amount of agricultural waste generated in India has the potential to reduce the demand of nonrenewable energy, benefits the environment by lowering emission and pollution, and, thus, improves circular economy. It also assists production model to shift toward a sustainable mode. This chapter focuses to provide an overview of circular economy in agriculture, flow of nutrient in loop, and agricultural waste valorization. It also provides an introduction of how to effectively manage agricultural waste in production of energy, biomaterials, additives, and soil amendments. This chapter also discusses the critical aspects of agricultural waste management challenges and adoption of circular economy in India.

2.2 Circular Economy in Agriculture Agriculture has rigorous impact on the environment that affects ecosystems. It consumes a huge portion of natural resources such as water and energy (Chen et al. 2020; Brunner and Rechberger 2016). Intensive farming result in deterioration of soil,  water, air, biodiversity, loss of habitat and food quality, and provoke health crisis due to exposure to toxic pesticides (EMF 2019a, b; Castillo-Díaz et al. 2022; Kanter et al. 2015; Augustyn et al. 2021). Likewise, immediate discarding of agri-­ food industry waste leads to loss of possible economic value that can be earned from the waste (Nattassha et al. 2020). To deal with these consequences of intense agriculture, society is adopting novel models of agriculture, like permaculture, precision, restorative, regenerative, and organic agriculture with sustainable soil management. Thus, resource scarcity, environmental degradation, and increasing food demand (70% hike by 2050) under changing climatic condition accentuate identification of promising strategy to enhance resource efficiency and sustainable crop production. Alliance of agriculture and sustainability will assist growth of circular economy (Lindblom et al. 2017; Batlles-delaFuente et al. 2022). Present linear economic system with take-make-dispose pattern limits available resources in the globe. It does not anticipate any awareness toward environment during production either at business or government level (Corral et al. 2022). However, the circular economy is a promising strategy to save concerned resources and environmental degradation accompanied by economic prosperity (Stegmann et  al. 2020). It has proper planning for reuse, recycle, reduction, and regeneration of economy. Figure 2.1 shows the comparison between linearity and circularity in agriculture. Circular economy can be defined as an economic system with close loops, where

Fig. 2.1  Comparison between linearity and circularity in agriculture

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resources are renewable energy source, and products maintain their value and quality for longer duration (EMF 2013a). Circular economy aims to manufacture goods and services promoting waste minimization and reuse of waste or by-product as sources of energy and thus reduces energy and water consumption. The circular economic model for agriculture targeting zero waste and zero pollution can deliver numerous benefits for health, environment, economy, and social growth by creating job opportunities and saving cost, material, and biodiversity (Corral et al. 2022). Adoption of circular economy will fulfill the needs of current generations without negotiating the future in terms of economy, environment, society, and temporal dimensions. Practicing circular economy model in developing nations like India is a forefront for potential change toward sustainable life on the planet. Involvement of circular economy in agriculture reduces use of excessive chemical fertilizers and curtails greenhouse gas emission. For example, Castillo-Díaz et al. (2022) reported 100% reduction in inorganic fertilization by reuse of crop waste along with other organic materials that in turn lowered production cost up to 4.8%. Thus, reuse, recycle, and reduction are three major measures of circular economy in agriculture. This includes use of agricultural waste for fertilizer, improvement in irrigation, reuse of water, transformation of debris into packaging material, recycling of plastics and package, etc. The reuse of agricultural waste as fertilizer becomes more efficient and economic when bio-solarization and biofumigation techniques are used for disinfection (Castillo-Díaz et  al. 2021; Salinas et  al. 2020; Duque-Acevedo et  al. 2020b; Kirkegaard et al. 1993). Agricultural waste as soil fertilizer improves soil physiochemical properties resulting in increase in crop production (Marín-Guirao et al. 2016). Furthermore, flow of nutrients in close loop and valorization of waste and by-product lower the external input of nutrients in agriculture. Thus, it helps in scaling up the economic sustainability.

2.2.1 Close Input and Flow of Nutrients in a Loop Intensive agriculture with inadequate management of nutrient in agro-food waste system leads to nutrient pollution in soil and water bodies of the proximate areas. The growing demand of food due to increase population has promoted dependency on chemical fertilizers, which increased the irrelevancy of internal nutrient recycling system of the agroecosystem for sustainable yield (Arizpe et al. 2011). This violation of nutrient cycles gets worsen during agricultural activities due to rapid industrialization, international trading of agricultural products, and globalization of economy (Nesme et al. 2018). Moreover, specialization of agriculture in terms of specialized farms and production of animals or crops in a particular region cause larger flow of nutrients and animal feed between distant areas (Renner et al. 2020). Thus, the nutrient flow becomes dramatically linear across the globe. This necessitates proper management of agricultural wastes that can promote nutrient cycle and conserve the soil carbon and balance between animal and crop production. In this regard, the consumption, trade (international market), and agricultural waste

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management should be given equal weightage (Van der Wiel et al. 2021). Production of commodities under intensive agriculture heavily relies on external inputs of inorganic fertilizers: nitrogen, phosphorous, and potassium (Kuokkanen et  al. 2017). Synthesis of these inorganic fertilizers requires higher investment of fossil fuels. Additionally, for phosphorous fertilizers, most of the nations need to depend on finite reserves (phosphate rock) present in a few countries (Cordell and White 2015; Buckwell and Nadeu 2016). Thus, the availability crises and use of fossil fuel imply that any significant rise in price of fuel can increase fertilizer price and risk food security especially in low income nations. Furthermore, mineral fertilizer carries no organic matter and plays little role in soil carbon stock and soil quality and structure (Valve et al. 2020). Thus, to overcome the unequal distribution of nutrients around the world and nutrient pollution in soil and water and to improve the economy, the recovery of nutrients from agricultural waste to reuse in crop production is extremely necessary. Close input in circular economy is achieved through two different circular modes, namely, biological and technical. In biological cycle, agricultural waste and by-product act as input to support and produce crop, food, feed, and energy, along with pharmaceutical and cosmetic industries (Ribeiro et al. 2022). However, technical cycle involves reusing, renewing, and maintaining agro-processing technologies to continue agricultural efficiency. This also includes non-natural packaging materials. For example, the bans in single use plastic bags is creating opportunities for the production of renewable packaging materials. Thus, closing of input loops lowers the demand for resources, reduces waste, improves resource efficiency, and creates circular economy. Global trading of agricultural commodities leads to gathering of nutrients in areas where foods and feeds are consumed in contrast to nutrient depletion in the production sites. Consequently, aggravated linearization in nutrient flows due to specialization of agriculture, urbanization, and globalization creates nutrient imbalance on both sink and supply sides and raises nutrient insecurity (Razon 2018). It also affects water quality and soil health (Jones et  al. 2013; Steffen et  al. 2015), which causes loss in biodiversity (Van Grinsven et al. 2010). Thus, extracting nutrients from organic residue in consumption site and sending back to production site are extremely necessary to maintain circularity of nutrients. For achieving sustainable circular economy, nutrient recycling should perform in right place and right mix, solely using renewable energy. The close loop concept of nutrient flow addresses the continuous movement of biological and technical material in the circular system; it reduces waste and maintain products and materials at highest utility (Harder et  al. 2021). Flow of nutrient in a loop focuses on minimizing external inputs to maintain soil health, thus lowering impact on the environment. Nutrient circularity has received steep attention in recent time particularly in the area of food and waste management. Nutrient circularity primarily comprises of (a) reduction in nutrient loss and (b) enhance rescue of nutrient from waste organic materials for reuse in agriculture (Harder et al. 2021). Briefly, the nutrient circularity is a comparison among nutrient inputs for agriculture production and nutrient content in agricultural residuals (Akram et al. 2019; Trimmer and Guest 2018; Metson et al.

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2016). Thus, flow of nutrient in a loop limits chemical fertilization in agriculture (Wysokińska 2020; Lima et al. 2021).

2.2.2 Valorization of Agricultural Waste Valorization of agricultural wastes produces energy, fuel, and chemical while reducing waste and greenhouse gas emission. Circular economy promotes continuous recycling of biological and technical materials by enhancing the value cycle (EMF 2013b; Murray et al. 2017). The model of circular economy was established based on the idea of conversion of waste into value added product making zero waste. Thus, it circulates waste to resource in a close loop. Huge quantity of agricultural waste produced in India is a potential resource for product valorization (Kapoor et al. 2020). India is reported as the world biggest producer of jute and second biggest producer of rice, wheat, sugarcane, groundnut, and cotton. It produces around 130 million MT of rice straw and 50 million MT of sugarcane trash every year. Some other wastes generated are stalks of maize, cotton, millets, pulse, and sunflower; shells of groundnut and coconut; etc. The agriculture waste biomass acts as a carbon neutral feedstock for approximately 9% primary energy supply globally (Antunes et al. 2017). Until the previous decade, first generation feedstocks were used for energy production. Earlier, single resource was used for valorization of a product. Recently, cross-chain waste valorization is capturing attention for product diversification in large scale industries (Gontard et al. 2018). However, the existing heterogeneity in the resources makes it difficult for valorization. Again, consumer’s acceptability of waste derived product is another challenge. Agricultural waste (second generation feedstock) inherent energy in the form of lignocellulose, cellulose, starch, etc. is a potential source for different product valorization (Kumar et  al. 2019; Mohan et  al. 2018). Several technologies are available for valorization of agricultural waste, and they can be categorized as mechanical, biochemical, and thermochemical (Fig.  2.2). For example, pelletization is a mechanical method to produce high density biomass (pellets) with solid energy. Pellets are utilized in cooking, heating, and boiling and also have application in power plants. Likewise, biomass combustion, gasification, and pyrolysis are thermochemical waste valorization techniques (Kumar et  al. 2015). In the combustion process, the inherent chemical energy in biomass is converted to heat, mechanical power, or electricity in the presence of air (Kapoor et al. 2020). Steam turbines, furnaces, boiler, etc. are used for combustion of biomass. However, gasification process converts biomass to a mix of combustible gases including methane, carbon monoxide, hydrogen, nitrogen, etc. by using gasifier (maintaining control oxidation) at a temperature range of 800 to 1100 °C. The produced gases are used as fuel in thermal application or for mechanical or electrical power generation or to produce value added chemicals. Pyrolysis is performed in oxygen deficient environment at a temperature range of about 300–900 °C. In this process, the biomass is transformed to biochar (solid) and bio-oil (liquid) along with a mixture of gases (H2, CO2, CO, CH4, etc.) (Singh et al.

Fig. 2.2  Technologies for agricultural waste valorization and their products and applications

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2014). Pyrolysis condition have significant role in the type of product yield from the process. For example, slow pyrolysis produces higher quantity of biochar for agricultural application. However, flash pyrolysis yields greater amount of bio-oil. The produced bio-oils are used to run various engines. Sometimes upgradation of bio-oil is required to improve stability and to eliminate corrosive property. Another method of waste valorization is biochemical conversion. This includes fermentation, transesterification, and digestion. Agricultural waste can be converted to bioethanol through fermentation process. However, esterification and transesterification can be employed to produce biodiesel from biomass such as waste cooking oil, animal fats, nonedible oil, vegetable oil, etc. By-product of transesterification such as glycerol is used in cosmetics and pharmaceutical industries. Anaerobic digestion (in the absence of air) of crop waste, food waste, animal waste, etc. produces biogas which is used for cooking, electricity, and mechanical power generation, as well as fuel in vehicles. Anaerobic digestion is a cost-effective agricultural waste valorization technique as it does not require any power, and the technology is scalable depending on the availability of the feedstock. Moreover, relative to combustion, pyrolysis, and gasification, anaerobic digestion emits lowest quantity of greenhouse gases and other air pollutants (Kapoor et al. 2020). Agricultural residues are also rich in bioactive compounds like phenolics, which have antioxidant, antimicrobial, anticancer, anti-inflammatory, and cardioprotective properties (Tian et al. 2017; López et al. 2018; Lopes et al. 2018). Functional phenolic compounds can be recovered from it and reutilized as feed and food additives, cosmeceuticals, preservatives, etc. to boost the economy (Jimenez-Lopez et  al. 2020). Besides their application as additives, direct intake of phenolic compounds possesses numerous health benefits against metabolic disorders (diabetes, obesity, etc.), cardiovascular diseases, tumor, neurological disorder, etc. (Salehi et al. 2019; Khan et al. 2020; Preethi Pallavi and Sampath Kumar 2018). India being an agrarian country produces a huge quantity of rice (104.99 million tons in 2022). Rice industry generates large amount of by-products which include husks, straw, and rice bran (Moraes et  al. 2014). From the rice bran, oil is extracted for food and cosmetic industry. The residue from oil extraction, i.e., the defatted rice bran (DRB) is also bio-converted to chemicals and value added products to use as food additives. The conversion includes pretreatment, hydrolysis (use enzymes), and fermentation (use microorganisms). The products obtained are bioethanol, lactic acid, biobutanol, biohydrogen, enzyme, etc. (Alexandri et al. 2020). Lactic acid produced from different feedstock such as DRB, municipal solid waste, food waste, coffee by-product, etc. is extensively utilized in cosmetic, chemical, food, and pharmaceutical industries. Poly lactic acid produced from lactic acid is a great option for petroleum based plastic in global market (Djukić-Vuković et  al. 2019). Similarly, biobutanol produced has advantage over ethanol in fuel industry due to higher energy content and lower miscibility with water. Thus, it can be mixed in higher proportion with gasoline relative to ethanol (Lee et al. 2009; Alexandri et al. 2020). Therefore, valorization of agricultural waste to value added product has great advantage to environment and economic sustainability.

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2.3 Effective Management of Agricultural Waste India has 159.7 million hectares of agricultural land that ranks second biggest in the world after the USA (Patel et al. 2020). India generates a huge amount of agricultural waste and by-products mainly from agro-industries, agricultural products, horticulture, aquaculture, animal feeds, etc. (Sindhu et al. 2015; Ungureanu et al. 2017). Change in lifestyle and food habits, for example, ready to consume food with rich protein under rapid industrialization and urbanization, adds to agricultural waste and by-products. India produces ≈ 500 metric tons of agricultural waste annually (Mahawar et al. 2015). Inappropriate handling of agricultural waste biomass contributes in climate change and soil, air, and water contamination (Prasad et al. 2020). Both rotten agricultural waste and burning of crop residue release noxious gases such as CH4, N2O, CO2, NH3, H2S, O3, etc. that cause air pollution, affect human and plant health, and deteriorate soil physiochemical and biological health (Patel et al. 2020). Effective management of agricultural waste can solve various environmental issues associated with it. The organic nature of agricultural by-products and waste demands effective management using extreme safety with least environmental impact (Prasad et  al. 2020). With application of adequate managing technique, quantity of agricultural waste is reduced and the organic matter is recycled (Koul et al. 2022). According to the USDA (1992, 2012), the complete set of agricultural waste management system has six prime functions, namely, production, collection, storage, treatment, transportation, and application. In India, the management of waste adopting circularity principles could generate huge revenue and employment. It also supports effective resource recovery from agricultural waste. Agricultural waste can be managed effectively by recycling, reducing, and reusing agricultural waste for biocompost, energy, bioethanol, biogas, electricity, biofuel, biomaterials, additives, animal feed, soil amendments, mulching, heavy metal removal, etc. (Lim and Matu 2015; Nandi et al. 2022; Adejumo and Adebiyi 2020).

2.3.1 Energy Source Energy has a crucial role in economic growth and development of an individual, society, and the nation as a whole (Mabel and Fernandez 2008). Use of fossil energy is a limitation factor for sustainable development of environment and economy (Wei et al. 2020). Burning of fossil fuels emits greenhouse gases causing climate change (Azouma et al. 2018). The nonrenewable energy sources produced from decomposition of fossils like petrol, diesel, kerosene, and coal are being exhausted due to rapid urbanization and population growth which results in environmental pollution. Thus, there is an urgent need of substitute sources for energy generation that should be secure, reliable, and affordable. Agricultural waste can be utilized as a source of fuel to enhance circular economy. It is a footstep toward clean and sustainable development. India requires a large quantity of energy to support the activities of its huge

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population. There is a big gap between supply and demand of energy in India. The huge agricultural waste in India can be utilized to obtain clean energy. Annual production of approximately 350 million tons of agricultural waste has the ability to generate 17,000 MWe power (Singh and Raghuwanshi 2017; Kaur 2019; Sharma et al. 2015). Currently, India produces about 15.8% of the total energy from renewable sources (NAAS 2018). As a source of renewable energy, agricultural waste has massive advantage over the nonrenewable energy. It provides low cost energy with least emission of greenhouse gases and reduces risk of climate change, global warming, and degradation of air quality. Agricultural waste biomass can be used in both large and small scale industries (Kaur 2014). Installation of industries for renewable energy can provide employment for people and help in skill development of the youth (Kaur 2019). These energy plants should be installed in vicinity to agricultural farm to avoid transportation cost for the raw materials. Agricultural waste including crop residue, food waste, green waste, manure, etc. can be processed to biogas, biohydrogen, syngas, producer gas, bioethanol, biobutanol, biodiesel, bio-kerosene, bio-gasoline, electricity, etc. (Srivastava 2019; Wei et al. 2020; Klass 2004). Biogas technology produces methane rich gas (55–70%) combined with carbon dioxide (35–40%), hydrogen, hydrogen sulfide (0.5–1%), oxygen, nitrogen, ammonia, and silicon dioxide (Vispute and Dabhade 2018; Kaur 2019). Animal manure is mainly used as a raw material in Indian household biogas plants (Bhat et al. 2001; Chen et al. 2012). Biogas also known as gobar gas in India can replace fossil fuel, and it can be utilized to produce electricity and thermal energy. Conversion of agricultural waste biomass into biogas includes a series of biochemical process such as hydrolysis, acidogenesis, acetogenesis, and methanogenesis. The processes are carried out by different microbes under anaerobic environment known as anaerobic digestion. Hydrolysis breaks complex solid organic material into soluble compound; following it, acidogenesis converts the same into alcohols and short chain acids. Simultaneously, acetogenesis reduces organic acids to acetate, and at last methanogenesis converts the products of acidogenesis and acetogenesis to biogas (Singh and Raghuwanshi 2017). Waste materials rich in lignocellulose are effectively used in the production of biohydrogen (Chong et  al. 2009). Hydrogen has no odor, color, taste, and poisonous effect. Thus, as a fuel, it does not evolve pollutants and acts as a clean energy. Biohydrogen generation involves photosynthetic or anaerobic microbes. Photosynthetic microbes produce hydrogen by utilizing carbon dioxide and water. However, anaerobic microbes produce hydrogen by utilizing organic acids or carbohydrates (Vispute and Dabhade 2018). Another source of bioenergy, the bioethanol is produced by fermentation of starchy biomass with the aid of microorganisms primarily anaerobic microbe (e.g., Saccharomyces cerevisiae). Distillation process is used to recover and concentrate the ethanol. Presently, ethanol is introduced as an eco-friendly fuel for vehicles in many developing countries including India. Similar to bioethanol, biobutanol is also produced by the action of Clostridium acetobutylicum. Agricultural waste can be pyrolyzed to produce bio-oil and char (Hawash et al. 2017). Gasification process is also used to convert agricultural waste into biogas, where the composition of the produced gas varies based on biomass type, reaction rate, and temperature. The

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thermochemical processes, gasification, and pyrolysis are implemented in woody type of agricultural residue with higher lignocellulosic component. Biomass briquetting is another technology to covert waste biomass into fuel briquettes with high energy density or calorific value (Shahapur et al. 2017). Furthermore, agricultural waste based charcoal can be used to generate electricity (Singh et al. 2013). Bio-coal can be formed from waste biomass using frictional pyrolysis method (NAAS 2018). In biomass power plant, biomass is burned that releases heat energy, which transforms water to steam to turn on turbine to generate electricity. Currently approximately 16% of Indian electricity is generated from renewable sources like solar, wind, and biomass (Azouma et al. 2018). Thus, agricultural waste is a great source for energy generation in India.

2.3.2 Biomaterials Biomaterials are specially designed material to interact with the biological systems. They are bioactive in nature and effortlessly compactable with human tissues and organs. The biomaterials possess a higher degree of biodegradability. Biomaterials are frequently used in manufacturing applications commonly in building of human body parts, medicines, and tissue engineering. Biomaterials replace artificial and natural based tissues and organs in the body. Utilization of agricultural waste for production of biomaterial can boost the economy by assisting waste management and adding value to it. Agricultural waste can be converted into biomaterials either through extraction or fermentation processes with or without pretreatment (Gutierrez-Macias et al. 2017). Several sustainable biomaterials are manufactured by nanotechnology utilizing agricultural waste like fish scale powder, chicken egg shell powder, prawn shell powder, crop residues, seafood waste, marine wastes, etc. Numerous biocomposite materials (consists of biodegradable polymer and supplements) are also synthesized from various natural fibers such as banana, jute, flax, kenaf, coir, blast fiber, etc. and synthetic polymer or biopolymer as matrix. The produced biocomposite materials serve a number of medical applications. India being a rice producer country generates two most important by-products, i.e., rice straw and husk, during harvesting and processing of rice. It is estimated that India generates almost 16 million tons of these by-products annually. Rice husks contain higher quantity of silica (SiO2) that is extracted with alkali solutions. Silica is a major component of bioactive glasses, which are basically used in medical sector particularly in dental fillings, composite, and prosthesis applications (Özocak 2020). The underutilized residues of rice (straw and husk) are also utilized for building polymer based biocomposite materials. Thus, utilization of these residues in biocomposite production can save wood and petroleum from the nature (Permatasari et al. 2016; Babaso and Sharanagouda 2017). Similarly, storage, recycling, management, utilization, and disposal of tobacco waste are an issue of great concern in both developed and developing nations. Majority of these wastes is burned or disposed to the landfill areas. However, nanocomposites and composites of these wastes with

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polymer matrix retain great antimicrobial property. These composites are used for packaging of drugs and medical devices. Similarly, during processing and production of orange juice, a huge quantity of solid waste is generated. These wastes contain significant quantity of soluble sugars and insoluble carbohydrates, for example, cellulosic materials, pectin, and essential oils (Zahid et  al. 2018; Hieu 2017). Cellulose, a structural polysaccharide of cellobiose (disaccharide), is a biodegradable, biocompatible material with no toxicity and great mechanical properties. Nanocellulose is produced from cellulosic substances using acidic hydrolysis. The nanocrystal cellulose produced from citrus or orange peels can be successfully utilized in production of functional fibers. Hydroxyapatite [Ca10(PO4)6(OH)2, HAp] is effectively synthesized from eggshell by a simple hydrothermal method (Elizondo-­ Villarreal et al. 2012). It is the main inorganic component of bone and teeth tissue and used for developing bone grafts. Thus, use of agricultural waste in production of biomaterial is a sustainable solution for circular economy.

2.3.3 Additives Agricultural waste can be recycled, reused, and reduced in many ways. One such application is use of organic waste as additives in various products. In the era of rapid industrialization and development, cement is a crucial element. The production of ordinary Portland cement (OPC) emits CO2 (about 800  kg/ton) into the atmosphere accounting approximately 7% of the anthropogenic carbon emission (Frías et al. 2017). However, the use of agricultural waste such as rice husk ash and oat husk ash can partially replace OPC as they contain higher amount of reactive silica, having potential for pozzolans (siliceous and aluminous material). According to Marchetti (2020), rice husk ash concrete possesses same resistance as ordinary concrete. Agricultural waste ash in cement even can perform greater under exposure to hydrochloric acid solution (Alnahhal et al. 2018). Both rice husk ash and oat husk ash are suitable as supplementary cementitious material (up to 5–20% substitution). Some other examples of agricultural waste which are used in concrete production include sugarcane bagasse ash, saw dust, oyster shell, groundnut shell, oil palm shell, coconut shell, and cork waste ash (Sokolova et al. 2018). In concretes, the agricultural wastes are mainly used for replacement of fine and coarse aggregates, cement, and admixture and to make lightweight or high strength concretes (Li et al. 2015; Ramos et al. 2014; Anbazhagan and Gopinath 2017). Rice husk ash is also used to stabilize and treat kaolinite clay, which subsequently enhances its compaction characteristic. It is a cost-effective method used in landfill liners. Use of these wastes in construction industry is a cost-effective alternative for the developing countries. Moreover, use of such waste material can reduce global warming potential by lowering the CO2 emission and improve the economy. Growing awareness of society toward balanced and healthy diet enhances the demand of natural additives with least side effect compared to the synthetic elements (Traka and Mithen 2011; Wojdyło et al. 2017). Agricultural by-product such

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as kiwi by-product contains useful biochemicals like citric acid, pectin, phenolic compound, actinidin enzyme, etc. These compounds are use as food additives. Citric acid extracted from agricultural waste has beneficial use as acidifying agent or as flavor enhancer in pharmaceutical and food industries. Citric acid can prevent browning of food by inhibiting enzymatic reaction during food processing (Bhat et  al. 2021). Phenolic compounds recovered from agricultural waste are used as antioxidant in cosmetic, food, and pharmaceutical industries (Guthrie et al. 2020). Antioxidants as food additives prevent lipid oxidation and microbial growth (Pinto et al. 2020). Similarly, actinidin enzyme is utilized for fortification of beef meat, where this enzyme improves water holding capacity and nitrogen solubility index of the meat (Toohey et al. 2011). Actinidin enzyme can tenderize pork meat, degrade desmin protein, and increase heat soluble collagen and myofibrillar particles (Christensen et al. 2009). It is also an economic coagulant for milk. Pectin extracted from agricultural waste is used as a preservative agent. Likewise, biomolecules inherent in food waste extracted with physical or chemical method can be used as food components such as lipids, proteins, starch, fibers, vitamins, minerals, and antioxidants. However, care is necessary to eliminate antinutritional factors and toxic compounds (Capanoglu et  al. 2022). Consumer acceptance is one essential criterion for such additives in food (Torres-León et  al. 2018). Some example of agricultural waste used to extract food additives are tomato residues, olive pomace, citrus fruit waste, etc. Another agricultural waste, i.e., defatted rice bran, is used as a supplement in breads, cakes, etc., to increase dietary fiber content and antioxidant activity (Sairam et al. 2011). Natural additives are gaining attention for making novel active packaging materials to meet the demand of food preservation, protection, smart communication with consumer, and marketing. Biocomposites produced from agricultural waste are great active food packaging materials that enhance antimicrobial and antioxidant properties and mechanical barrier (Valdés et  al. 2014). Naturally biodegradable agricultural waste is fabricated to sustainable material (bio-blocks) with tunable characteristics. In the fabrication process, microbes are used as natural adhesive material. The biodegradable fabricated bio-blocks possess great thermal stability, mechanical strength, and hydrophobicity (Joshi et al. 2020). The bio-blocks used in packaging application have higher compressive strength (five to sixfold) than regularly used polystyrene packaging substances. Bio-blocks can be also used in filtration of toxic waste and wall panelling. Similarly, wood pellets made from compressed sawdust can replace use of coal in various processes and reduce emission (Blake 2018).

2.3.4 Soil Amendments Agricultural wastes are rich in nutrient content; thus, on processing to soil amendments, it aids in recycling of the nutrients. Under the umbrella of organic agriculture, these soil amendments enhance crop yield and maintain soil fertility and

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environmental quality (Aliku et al. 2019; Raza et al. 2021). It encourages circular economy by sustainable management of agricultural waste biomass to value added product (EMF 2013b; Donia et al. 2018). Conversion of agricultural waste to biochar by pyrolysis under anaerobic environment aids in management of the organic waste, which reduces greenhouse gas emission and air pollution by sequestering carbon for long duration (Choudhary et  al. 2021; Enaime and Lübken 2021). Biochar can reside in soil for thousands of years (Kumar et al. 2013; Xu et al. 2013). Composting of agricultural waste to organic fertilizer by biological oxidative transformation is a promising strategy to reduce the organic waste, nasty odors, and growth of pathogenic microbes. Composting is a complex process performed by diverse group of microbes including bacteria, fungi, and actinomycetes in defined environmental condition of temperature, moisture, and aeration (Nandi et al. 2022). It significantly reduces pathogens in waste due to the temperature generated during the process (Sahu et al. 2020). In this process, the organic waste is transformed to humus (Atalia et al. 2015). Co-composting of different agricultural waste such as food waste and wheat straw is done to improve the ambient condition for composting (Mironov et al. 2021). Vermicomposting is another method of converting agricultural waste to value added soil amendment. In vermicomposting, activities of both earthworms and microbes are involved to convert the waste to organic fertilizer (Sahu et al. 2020). The agricultural waste as manure, compost, vermicompost, green manure, farmyard manure, mulch, and biochar improves soil properties including soil organic carbon, available nitrogen, hydraulic conductivity, water holding capacity, nutrient holding capacity, microbial diversity, etc. (Velmourougane 2016; Triberti et al. 2008; Enaime and Lübken 2021; Mekki et al. 2013), thus assisting in enhancement of plant growth and yield. In a study, Blanchet et  al. (2016) documented improvement in soil organic carbon content under application of farmyard manure and crop residues relative to mineral fertilizer. The chemical fertilizers have several negative effect on soil quality, crop genetic diversity, atmosphere, and groundwater sources (Erana et al. 2019; Folberth et al. 2014). However, the organic amendments derived from the agricultural waste have advantage over it. Variation in application rate and type of the waste derived soil amendment affects differently on the physicochemical and biological properties of soil (Bhogal et  al. 2009). For example, Erana et  al. (2019) documented effectiveness of agro-industrial waste compost to improve soil total organic carbon; nitrogen; potassium; exchangeable Na, Mg, Ca, Cu, Zn, and Fe; soil pH; available water content; field capacity; permanent wilting point; and cultivable fungi and bacterial count. They also observed enhancement of onion (Allium cepa L.) yield under the compost application. Compost prepared from Terminalia catappa leaves and poultry manure was efficient to improve okra yield when applied both as compost and mulch (Aiyelari et al. 2011). Likewise, biochar application in soil improves crop productivity and reduces stress associated with toxic contaminates, heavy metal, pesticides, and salinity (Boro et al. 2021; Dugdug et al. 2018; Rizwan et al. 2018). Biochar remediates the toxic pollutant in soil through sorption or complexation on its surface (Ahmad et al. 2014; Bashir et al. 2018; Baruah et al. 2020). Biochar improves soil properties such as nutrient content, pH, EC, CEC, porosity, bulk density, surface area, etc. and

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encourages growth of microbial population (Baruah et  al. 2020; Lehmann et  al. 2011; El-Naggar et al. 2018; Manolikaki and Diamadopoulos 2017). Drought stress due to global climate change can be reduced by application of biochar as it improves water retention capacity of the soil (Igalavithana et  al. 2017; Rasa et  al. 2018; Paetsch et al. 2018). Several reports are there on reduced CO2, CH4, and N2O emission under application of biochar derived from agricultural waste (Karhu et  al. 2011; Zhang et al. 2012). Efficacy of biochar to mitigate greenhouse gas emission highly depends on origin of biochar, its preparation method, type of soil, and cultivated crop (Lehmann et al. 2011; Kalu et al. 2022). Dong et al. (2013) in a study documented higher efficiency of rice straw derived biochar than bamboo derived biochar on mitigation of CH4 emission from paddy field. Biochar can alter denitrification process and thus effectively reduce N2O emission from agricultural soil (Cayuela et al. 2013; Kalu et al. 2022). Use of agricultural waste such as straw and cocoa husk as mulch was reported to enhance yield of watermelon and tomato fruit, respectively, compared to unmulched plots (Johnson et al. 2004). The slurry produced from biogas plant is rich in nutrient (N, P, Zn, Fe, etc.) and also used as soil amendment to boost soil quality and plant growth (Kaur 2019). Similarly, by-­ product generated during ethanol production may also be used as novel source of soil additive after characterization for nutrient content (Sahu et al. 2020). Despite the benefits obtained from recycling of agricultural waste to soil amendment, it may also pose risk to the environment. Sometimes the agricultural waste may contain toxic elements like heavy metals (Cd, Cr, Pb, Cu, Hg, Zn, Ni, As, etc.) and organic pollutants, which may re-invite the threat to food chain contamination, diseases, and disorders associated with it. Thus, before preparing soil amendment from agricultural waste or prior to applying in soil, it should be checked for presence of any toxic contaminant to prevent soil, water, and food chain contamination.

2.4 Agricultural Waste Management Challenges and Risk Identification of major challenges and risk in agricultural waste management system is difficult as it includes interdisciplinary areas such as agronomy, microbiology, soil science, plant physiology, ecology, environment and engineering, etc., which have different priorities and point of views. However, some of the key challenges associated with waste management are huge volume, poor collection rate, transportation, and treatment issues. Development of adequate technology to reduce contaminant in waste and food safety is another challenge (Bernal 2017). Both collection and storage of agricultural waste is challenging as it is accompanied with risk of degradation, bad odors, greenhouse gas emission, pathogens, etc. Anaerobic digestion is a mature and effective technology to convert residue biomass to bioenergy and biogases. However, owing to transportation and economic constrains, dedicated energy crops are cultivated in huge areas, which limits agricultural waste utilization in this process (Gontard et al. 2018). It also increases land use, emission, and contamination from agrochemicals. Another challenge associated to use of anaerobic digestion for valorizing agricultural waste is higher content of

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lingo-­cellulose, which reduces the product yields due to its complex recalcitrant nature resisting microbial attack. To deal with this issue, several lignocellulosic pretreatment methods are developed, which shows different efficacy on yields. Similarly, management of agricultural waste through valorization to various value added products and services has some limitations. For example, if agricultural residue is used for paper making by adding strong alkali for pulp preparation, silica in waste materials dissolves in the alkali. Thereby, on the alkali/liquor recovery step, the silica gets precipitates on equipment (Babyloni et al. 2022). Similarly, bioplastic is a value added product of waste valorization. However, the degradation of disposed bioplastics releases greenhouse gases such as carbon dioxide and methane. Therefore, it is necessary to design techniques to collect the released methane during the degradation, so that it can be used as fuel. This greenhouse gas emission can be also controlled by designing slow degrading bioplastics. Another prime challenge of agricultural waste management is heterogeneity of waste in terms of chemical and physical properties. Moreover, some waste valorization techniques are validated solely in lab scale. Therefore, optimization of the methods and development of revolutionary technologies is essential for promoting agricultural waste management, value addition to the waste, and economy of the nation. Some of the risk and challenges of application of organic waste in urban agriculture includes lack of land tenure rights, supporting policy, climate variation, struggle in segregating waste, contamination of soil, food safety, etc. (Menyuka et al. 2020). Although policy and regulations on minimizing agricultural waste burning are formulated in India, however, due to existing execution challenges, lack of awareness, clarity, and social consciousness regarding profitability, agricultural waste burning is continued till date (Kapoor et al. 2020). Therefore, awareness and training drives are needed to empower and educate the farmers and stakeholders about advantages of agricultural waste management and value addition for ensuring sustainability and monetary gain of communities (Donner et al. 2021). Acceptance of recycled waste based material is another challenge. For efficient agricultural waste and by-product management, development of new business model alliance with innovative upgrading technologies and marketing strategies is highly essential. Establishment of a new business model is challenging, as it needs new vision for customer and supplier relationships. For a proper assessment of waste management chains, a cross-­ sectional discussion between end users, converters, academicians, local and national policy-maker, etc. is required to tackle the challenges sustainably depending on political, geographical, and historical constraints. Despite the existing risk and challenges, agricultural waste can be managed significantly by bridging the gaps between innovative upgrading technologies with business opportunities.

2.5 Adoption of Circular Economy in India Circular economy is considered as a prototypical of manufacture and consumption to ensure long-term growth. By adopting circular economy, India can support resource optimization and reduce and recover waste by providing a second life to

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the product through recycling. It is projected that adoption of circular economy in India will result in a yearly profit of 40 lakh crores ($624 billion) by 2050, and it will also reduce greenhouse gas emissions by approximately 44% with a significant reduction in congestion and pollution (Ellen MacArthur Foundation 2016; ICEF 2022). Thus, circular economy has a crucial role in conserving the environmental condition while forming a reward system to promote product recycling. Although improved production and alteration in consumption patterns create new employment and increase per capita income, effects of increased production on the environment also needs to manage effectively. India contains only 4% of the world’s freshwater resources and 2% landmass. In this scenario, linear economic model with take-make-dispose pattern will limit India’s goods and service production, which will affect the overall economy. Thus, it is necessary to shift the Indian economy toward circularity by identification and revolution of material flow during the manufacturing processes. It will provide long-lasting ecological and economic benefits (NITI Aayog 2021). India ranked third in terms of raw materials consumer in the world. India’s raw materials necessities are estimated as 15 billion tons by the end of 2030 and more than 25 billion tons by the end of 2050. To meet the demand of resources, it is crucial for India to adopt circular economy model over the linear economy (Ministry of Electronics and Information Technology Government of India, (MeitY) 2021). Adoption of circular economy in India will bring significant annual benefits, and it will also reduce pollution that would subsequently promote the growth of the economy (NITI Aayog 2021). To accelerate the shifting of India’s economy toward circularity, a total of 11 committees have been designed. The committees are led by ministries, officials from NITI Aayog and MoEFCC, domain experts, industry representatives, and academicians from the all 11 focus areas (NITI Aayog 2021). Currently, India is witnessing increased manufacturing and change in its consumption patterns resulting in rising per capita income. However, merely with 2% of the Earth’s landmass and almost 18% of the world population, it is paramount for India to tackle harmful linear material flows and shift toward a circular model. During the 2022–2023 union budget, Indian government recognized the importance of sustainable growth in sync with a circular economy. Based on this, Indian government formulated the Plastic Waste Management (Amendment) Rules 2022, Battery Waste Management Rules 2022, and e-Waste Management Rules 2022 to set out target waste disposal standards. This will be helpful for manufacturers, producers, importers, and bulk consumers. It will enable easy transactions among stakeholders by providing Extended Producer Responsibility (EPR) certificates. Across ten sectors including e-waste, municipal solid waste, scrap metal, life ended vehicles, lithium-ion batteries, etc., action plans were formulated emphasizing the importance of reusing secondary materials (Union Budget speech 2022–23). According to a study by an IT company (Accenture), it is documented that by the adoption of circular economy business models, India can unlock approximately 0.5 trillion USD of economic value by 2030 (Fiksel et al. 2021). For adoption of a circular economy, India requires an enabling ecosystem that can encourage identification and acceptance of new business models. Approximately

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55 million tons of municipal solid waste (MSW) are generated each year by 377 million people living in urban cities of India, and by 2031, it is expected to reach 125 million Mt. However, only a portion (75–80%) of the MSW is collected, while from the collected waste, a small fraction (22–28%) is treated or processed to value added product. Municipal solid waste generation is expected to rise to 436 million tons by 2050. According to IBEF (2023), it is expected that India will become the third largest economy in the world, accounting for about 8.5% of the world’s GDP by 2030. In this context, circular economy can assist India’s growth together with noteworthy environmental benefits. For example, the recycled industry of polyethylene terephthalate (PET) in India is estimated a worth of about 400–550 million USD.  Recycled rate of PET in India is 90% which is greater than Japan (72%), Europe (48%), and the USA (31%). So India has an enormous opportunity for circular economy. On adoption of circular economy, India is expected to become a leading hub for innovation and technology for circular economy due to its dominance in IT sector. The pool of tech talented Indian can construct innovative and advanced circular businesses and dominate the revolution of global circular economy. Secondly, India has the potentiality to earn early success than other global economy because of the fastest economic growth. India will easily take up the circular methods of production, sustainable design, etc. Moreover, as a developing country, India has a relative advantage than mature economies. Thirdly, the easy acceptance of recycled products and the circular mindset in India will help in widespread recovery, repair, overutilization, and recycling of used products at the households. For example, in India the usual lifetime of a car is 9–12 years, whereas, in the USA it is only 7–8 years. Last but not the least, in India due to cost centric market, the cheaper cost of services or product generated through circular path will be widely adopted as the Indian consumers are cost consensus. Therefore, incorporation of circular practice in India could result in lots of price savings across construction, food, agriculture, and mobility (IBEF 2023).

2.6 Conclusion Circular economy is a promising approach to fulfill the demand for basic needs including food, energy, water, medicine, etc. in a sustainable way. It protects the environment from overexploitation while serving long-lasting solution for agricultural waste management. Use of agricultural waste in circular economy promotes rapid economic growth by providing value from waste in the form of energy, biomaterials, soil nutrients, chemicals, medicines, food additives, construction material, etc. The Indian government have identified the importance of sustainable economy and recently formulated new policies for management of plastic, battery, and e-waste in 2022. This will benefit the stakeholders by providing Extended Producer Responsibility (EPR) certificates. India’s dominance in IT sector ensures the probability of establishing a leading hub for innovative and advanced circular business

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model to dominate the global circular economy. Moreover, as a developing nation, India has a higher chance of gaining success in circular methods due to its fastest economic growth rate. Besides, the circular mindset and cost centric market in India trigger easy acceptance of recycled products from waste. Although there are challenges and risk in application of agricultural waste in circular economy in terms of development of technology and businesses, it is possible to manage, reduce, recycle, and recover existing economic potential from the waste through linking innovative upgrading technologies with marketing strategies and business opportunities.

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in rice (Oryza sativa L.) under Cd stress with different water conditions. J Environ Manag 206:676–683 Sahu KK, Rout S, Kar S, Prusty AK (2020) Waste management through soil amendments: A sustainable agricultural approach for climate change mitigation. In: Babu KR, Nakkella AK (eds) Global environmental governance, policies and ethics – II, vol 2. Immortal Publications, Andhra Pradesh, India, pp 376–391 Sairam S, Gopala Krishna AG, Urooj A (2011) Physico-chemical characteristics of defatted rice bran and its utilization in a bakery product. J Food Sci Technol 48:478–483 Salehi B, Vlaisavljevic S, Adetunji CO, Adetunji JB, Kregiel D, Antolak H, Pawlikowska E, Uprety Y, Mileski KS, Devkota HP, Sharifi-Rad J, del Mar Contreras M (2019) Plants of the genus Vitis: phenolic compounds, anticancer properties and clinical relevance. Trends Food Sci Technol 91:362–379 Salinas J, Meca D, del Moral F (2020) Short-term effects of changing soil management practices on soil quality indicators and crop yields in greenhouses. Agronomy 10:582 Scarlat N, Dallemand JF, Monforti-Ferrario F, Nita V (2015) The role of biomass and bioenergy in a future bioeconomy: policies and facts. Environ Dev 15:3–34 Shahapur A, Desai N, Kader A (2017) Agricultural wastes as a supplementary source of energy: an economic assessment of a briquette making facility. J South Pacific Agric 20:25–33 Sharma M, Gohil P, Sharma N (2015) Biomass briquette production: A propagation of non-­ convention technology and future of pollution free thermal energy sources. Am J Eng Res 4(2):44–50 Sial AK, Shankar T, Praharaj S, Sahoo U, Maitra S (2021) Intensive farming: It’s effect on the environment. Indian J Nat Sci 12(69):37480–33748 Sindhu NP, Seharawat SP, Malik JS (2015) Strategies of agricultural waste management for better employment and environment. Int J Curr Res 7(12):24604–24608 Singh CS, Raghuwanshi RK (2017) Agricultural waste to energy for rural India: A smart way to clean energy. Int J Sci Res 6(4):2241–2245 Singh N, Singh H, Singh S (2013) Agri charcoal as a fuel for power generation: an initiative. Fuel 2(5):1–6 Singh NB, Kumar A, Rai S (2014) Potential production of bioenergy from biomass in an Indian perspective. Renew Sust Energ Rev 39:65–78 Sokolova LS, Ermakova EV, Rynkovskaya M (2018) A review of agro-waste materials as partial replacement of fine aggregate in concrete. In IOP Conference Series: Materials Science and Engineering (Vol. 371, No. 1, p. 012012). IOP Publishing Srivastava RK (2019) Bio-energy production by contribution of effective and suitable microbial system. Mater Sci Energy Technol 2(2):308–318 Steffen W, Richardson K, Rockstrom J, Cornell SE, Fetzer I, Bennett EM, Biggs R, Carpenter SR, De Vries W, De Wit CA, Folke C, Gerten D, Heinke J, Mace GM, Persson LM, Ramanathan V, Reyers B, Sörlin S (2015) Planetary boundaries: guiding human development on a changing planet. Science 347(6223):1259855 Stegmann P, Londo M, Junginger M (2020) The circular bioeconomy: its elements and role in European bioeconomy clusters. Resour Conser Recycl X 6:100029 Tian Y, Liimatainen J, Alanne AL, Lindstedt A, Liu P, Sinkkonen J, Kallio H, Yang B (2017) Phenolic compounds extracted by acidic aqueous ethanol from berries and leaves of different berry plants. Food Chem 220:266–281 Toohey ES, Kerr MJ, Van Ven R, De, & Hopkins, D. L. (2011) The effect of a kiwi fruit based solution on meat traits in beef M. Semimembranosus (topside). Meat Sci 88(3):468–471 Torres-León C, Ramírez-Guzman N, Londoño-Hernandez L, Martinez-Medina GA, Díaz-Herrera R, Navarro-Macias V, Alvarez-Pérez OB, Picazo B, Villarreal-Vázquez M, Ascacio-Valdes J, Aguilar CN (2018) Food waste and byproducts: an opportunity to minimize malnutrition and hunger in developing countries. Front Sustain Food Syst 2:52 Traka MH, Mithen RF (2011) Plant science and human nutrition: challenges in assessing health-­ promoting properties of phytochemicals. Plant Cell 23(7):2483–2497

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Triberti L, Nastri A, Giordani G, Comellini F, Baldoni G, Toderi G (2008) Can mineral and organic fertilization help sequestrate carbon dioxide in cropland? Eur J Agron 29(1):13–20 Trimmer JT, Guest JS (2018) Recirculation of human-derived nutrients from cities to agriculture across six continents. Nat Sustain 1(8):427–435 UN (2022) World population projected to reach 9.8 billion in 2050, and 11.2 billion in 2100. Department of Economic and Social Affair, United Nations, https://www.un.org/en/desa/world-­ population-­projected-­reach-­98-­billion-­2050-­and-­112-­billion-­2100. Accessed 20 Feb 2023 Ungureanu G, Ignat G, Vintu CR, Diaconu CD, Sandu IG (2017) Study of utilization of agricultural waste as environmental issue in Romania. Rev Chim 68(3):570–575 Union Budget speech (2022–23). https://www.indiabudget.gov.in/doc/bspeech/bs202223.pdf. Accessed 5 Feb 2 2023 USDA (1992) Agricultural waste management field handbook. Part 651 of National engineering handbook, USA.  Department of Agriculture (Washington). Soil Conservation Service, Washington, DC, pp 1–431 USDA (2012) Agricultural waste management field handbook. United States Department of Agriculture, Soil Conservation Service, Washington, DC Valdés A, Mellinas AC, Ramos M, Garrigós MC, Jiménez A (2014) Natural additives and agricultural wastes in biopolymer formulations for food packaging. Front Chem 2:6 Valve H, Ekholm P, Luostarinen S (2020) The circular nutrient economy: needs and potentials of nutrient recycling. In Handbook of the circular economy. Edward Elgar Publishing, pp. 358–368 Velmourougane K (2016) Impact of organic and conventional systems of coffee farming on soil properties and culturable microbial diversity. Scientifica 1-9. https://doi.org/10.1155/2016/3604026 Vispute P, Dabhade S (2018) A review: utilization of agricultural waste in India. Int J Sci Res 7(1):1879–1883 Wei J, Liang G, Alex J, Zhang T, Ma C (2020) Research progress of energy utilization of agricultural waste in China: bibliometric analysis by citespace. Sustainability 12(3):812 van der Wiel BZ, Weijma J, van Middelaar CE, Kleinke M, Buisman CJN, Wichern F (2021) Restoring nutrient circularity in a nutrient-saturated area in Germany requires systemic change. Nutr Cycl Agroecosyst 121(2):209–226 Wojdyło A, Nowicka P, Oszmia’nski, J., & Golis, T. (2017) Phytochemical compounds and biological effects of Actinidia fruits. J Funct Foods 30:194–202 Wysokińska Z (2020) A review of transnational regulations in environmental protection and the circular economy. Comp Econ Res Central Eastern Europe 23(4):149–168 Xu G, Wei LL, Sun JN, Shao HB, Chang SX (2013) What is more important for enhancing nutrient bioavailability with biochar application into a sandy soil: direct or indirect mechanism? Ecol Eng 52:119–124 Zahid MU, Pervaiz E, Hussain A, Shahzad MI, Niazi MBK (2018) Synthesis of carbon nanomaterials from different pyrolysis techniques: a review. Mater Res Express 5(5):052002 Zhang A, Bian R, Pan G, Cui L, Hussain Q, Li L, Zheng J, Zheng J, Zhang X, Han X, Yu X (2012) Effects of biochar amendment on soil quality, crop yield and greenhouse gas emission in a Chinese rice paddy: a field study of 2 consecutive rice growing cycles. Field Crop Res 127:153–160

Chapter 3

Application of Methano Bacteria for Production of Biogas Sonal Singh, Kuldip Dwivedi, Shashank Gupta, and Nidhi Shukla

Abstract A competitive, practical, and typically sustainable energy source is biogas. Since 2010, there has been a considerable growth in the capacity of biogasbased electricity; with 65 GW in 2010 to 120 GW in 2019, there has been a 90% increase in the ability of biogas-based energy generation. Biogas is a crucial component of the development of environmentally friendly energy because it may be utilised as a raw material to produce hydrogen, fuel for vehicles, and electricity directly in fuel cells. Refined bioenergy or biomethane can be put in containers or injected into gas supply mains for use as renewable natural gas. It is feasible to use biogas directly for power generation, cooking, and lighting. As they develop and function, microbes produce a variety of gaseous by products. Particular bacteria that grow anaerobically on cellulose materials also produce substantial volumes of methane, along with other gases like carbon dioxide and hydrogen sulphide. Methanobacterium is an example of a type of bacteria known as a methanogen, which produces a variety of gases. The aforementioned bacteria are typically found in the anaerobic sludge after sewage treatment. Additionally, cattle rumens contain methano bacteria. The rumen is where cellulose-rich food is kept. These rumen bacteria help break down cellulose and are essential for the nutrition of cattle. These bacteria are common in gobar, which is another name for cow or cattle dung. Biogas also referred to as gobar gas, can be produced from dung. We discussed numerous bacterial species and how they might be used to make biogas, different factors involved in biogas production in this essay. Keywords Methanobacteria · Cellulose · Biomethane · Anaerobic digestion · Methane

S. Singh · K. Dwivedi (*) · N. Shukla (*) Department of Environmental Science, Amity School of Life Science, Amity University Madhya Pradesh, Gwalior, India S. Gupta Department of Civil Engineering, ITM University, Gwalior, India © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024 P. Singh (ed.), Emerging Trends and Techniques in Biofuel Production from Agricultural Waste, Clean Energy Production Technologies, https://doi.org/10.1007/978-981-99-8244-8_3

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3.1 Introduction Biogas, a renewable fuel, is produced by the anaerobic digestion, or AD, of organic feedstocks such municipal waste, agricultural waste, food waste, and energy crops. The main components of raw biogas are methane (50–75%), carbon dioxide (25–50%), and nitrogen (2–8%). In trace levels, biogas may also contain hydrogen sulphide, ammonia, hydrogen, and various volatile organic compounds, depending on the feedstock (Wellinger et al. 2013). Implementing biogas technology may significantly decrease the release of greenhouse gases (GHG) as well as as a result, the environmental impact of energy consumption, according to life cycle assessment research (Poeschl et al. 2012a, b; Hijazi et al. 2016). As stated by CalEPA (California Environmental Protection Agency n.d.), biogas generation and utilisation techniques also help sustainable waste management strategies while diversifying energy systems. California is promoting the use of this fuel by requiring low-carbon fuels, providing incentives to establish biogas production plants, and facilitating access to pipeline infrastructure (Parker et al. 2017; Milbrandt 2013. Animal and plant waste can both be used to make biogas. In anaerobic digesters, they are processed with liquid or slurry and water. Anaerobic digesters typically feature a feedstock supply container, a decomposition tank, as well as the biogas recover unit, and heat exchangers in order to keep the temperature necessary for bacterial digestion. Small-scale domestic digesters with a capacity of just as 757 L (200 Gallons) may be used to provide cooking fuel or electricity in rural homes. According to estimates, household digesters are used as a renewable energy source in millions of houses throughout less developed nations like China and some parts of Africa (Fig. 3.1). An environmentally friendly way to utilise the enormous amounts of organic waste being produced globally is anaerobic digestion (AD), which generates biogas. This technology can be applied to a wide variety of garbage waterways, such as waste from industries and municipal waterways, farming, local, and commercial

Fig. 3.1  Flow chart of biogas production

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waste from industries, along with plant residues. It provides a number of benefits over many other waste treatment techniques. The biogas produced as a result of this treatment is a sustainable energy source, whereas the digester residue, which is a by-product, can be used as fertiliser due to the high nutritional content it has for plants (Ward et al. 2008). The performance of the AD process is significantly influenced by the characteristics of the feedstock and the metabolism of the microorganisms that participate in the different degrading processes (Batstone et al. 2002). The conversion of naturally occurring substances into biogas can be broken down into three stages: hydrolysis, acid creation, and methane production. The output of one bacterial group acts as the substrate for the products of another group in an anaerobic food chain that is created when several bacterial groups collaborate in these multiple, simultaneous activities. The procedure proceeds well if the levels of degradation at each stage are evenly distributed (Yong et al. 2015).

3.2 Methanobacteria for the Production of Biogas Microorganisms naturally produce biogas through a process called anaerobic fermentation from biodegradable substrate. It can be found in wetlands, marshes, river sediments, and ruminant gastrointestinal tracts (Krich et  al. 2005; Kushkevych 2016). The microorganisms play a role in the degradation of biodegradable waste in landfills as well (Krich et al. 2005; Barton and Hamilton 2010). The end result of anaerobic metabolism is biogas. According to Ahring et al. (2001) and Ziemiński and Frąc (2012), the process takes place in an anaerobic environment by the sequential biochemical breakdown of polymers to methane and carbon dioxide. This is the outcome of several microorganisms’ metabolism, including fermentative microbes (acidogens), microbes that produce hydrogen and acetate (acetogens), and microbes that produce methane (methanogens). Methanotrophic bacteria, which can use methane (CH4), the primary component of natural gas and biogas produced by anaerobic digestion (AD), as their sole source of carbon and energy, are a suitable biological pathway for atmospheric methane sequestration, bioremediation, and gas-to-liquid conversion for industrial applications (Kalyuzhnaya et  al. 2015; Strong et  al. 2015, 2016; Pieja et  al. 2017). Biocatalytic pathway or methane conversion to lipid fuel intermediates and platform chemicals, as well as metabolic engineering techniques to increase the efficiency of carbon conversion in biological gas-to-liquid conversion processes (Henard et al. 2016, 2017). Further highlighting the potential strength of methanotrophic bioconversion strategies are recent studies that have shown methane bioconversion to a variety of products, including single cell protein, methanol, carboxylic acids, polyhydroxybutyrate, and 2,3-butanediol (Garg et al. 2018) (see Fig. 3.2). Methane can be used as a better option for non- renewable fuel sources in the generation of electricity, heat and fuel which is used for transportation. AD of wastes, energy crops, and residues is more and more important for reduction of greenhouse gases and support the sustainable development of the energy supply

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Climate change mitigation

Proper management

Co-digestion with other feedstocks

Animal manure

Enhance biogas production

Biogas production process

Sources and characteristics

Factors affecting production process

Microbes Hydrolysis

Water scrubbing Pressure swing adsorption

Acidification

Acidogenesis

Biogas

Biogas upgradation

Methanogenesis

Advantages and disadvantages of biogas production Electricty

Amine scrubbing Membrane separation

Heat and stream Biogas application Biofuel and biodiesel Biomethane

Fig. 3.2  Steps involved in biogas production, application and limitations

(Abbasi et al. 2012). Anaerobic digestion is a frequently employed method with a proven track record for stabilising sewage sludge, animal manure, municipal solid waste, and industrial wastewater (Treichel and Fongaro 2019). As long as it has cellulose, hemicelluloses, carbohydrates, proteins, and lipids as its main components, biomass can be used as a source of substrate for the production of biogas. Only strongly lignified organic materials, like wood, are unsuitable due to the decomposition that occurs slowly under anaerobic conditions. The kind of feedstock, the digestion mechanism, and the retention duration all affect the composition of biogas and the methane yield (Braun 2007). The substrates for biogas production with the highest gas yields and potential methane concentrations are carbohydrates, which produce 790–800  biogas (Nm3/t TS), 50% CH4, and 50% CO2. Raw protein is converted into 700 Nm3/t TS of biogas, which contains 70–71% CH4 and 30–33% CO2. Raw fat is converted into 1200–1500 Nm3/t TS of biogas, which contains 67–68% CH4 and 32–33% CO2 (Baserga 1998). In anaerobic digestion, organic wastes are fermented by bacteria without the presence of free oxygen.

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Complex organic Matter Carbohydrates, proteins, fats

1 Hydrolysis Complex organic molecules to solube

1 2 Acidogenesis

Soluble Organic Molecules Sugars, amino acids, fatty acids

Small organic molecules to fatty acids

2

3 Acetogenesis Conversion to acetic acid and CO2

Vloatile fatty acids

4 Methanogenesis Final conversion to methane (CH4)

Acetic acid

3

H2,CO2 4

4 CH4 + CO2 Methane + Carbon dioxide Fig. 3.3  Process involved in the biogas production process

It takes four stages to break down complex biodegradable organics throughout the complicated Methanogenesis (Meisam Tabatabaei 2018; Abbasi et al. 2012; Agler et al. 2011).

3.2.1 Hydrolysis Process Large protein macromolecules, lipids, and carbohydrate polymers (such as cellulose and starch) are broken down into amino acids, long-chain fatty acids, and sugars by a process called hydrolysis (Fig. 3.3).

3.2.2 Acidogenesis Process It is a fermentation process which produces volatile fatty acids, valeric acid, propionic acid, and predominantly lactic and butyric acid from the first-step products.

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3.2.3 Acetogenesis Acetic acid, hydrogen, and carbon dioxide are created by bacteria as they consume this fermentation by products.

3.2.4 Methanogenesis Methanogens perform the action below using three metabolic pathways to make methane by feeding on hydrogen, acetate, and a little quantity of carbon dioxide (Rapport et al. 2008).

( acetotrophic pathway ) (3.1) CO 2 + 4H 2 → CH 4 + 2H 2 O ( hydrogenotrophic pathway ) (3.2) 4CH 3 OH + 6H 2 → 3CH 4 + 2H 2 O ( methylotrophic pathway ) (3.3) 4CH 3 COOH → 4CO 2 + 4CH 4

Methane gas or biogas is a versatile green source of energy green that may easily be used to replace non-renewable energy sources in the production of fuel and electricity as well as heat. Natural gas can be replaced by biomethane when used as a feedstock to make chemicals. Anaerobic digestion (AD) produces biogas, which has significant advantages over other bioenergy producing processes. It is acknowledged as one of the most environmentally friendly and energy-efficient technologies for the production of bioenergy (Turco et  al. 2016; Fehrenbach et  al. 2008). A widely used technology, anaerobic digestion has some advantages over other methods of producing biofuels, including sustainable biogas production, the ability to use wastewater and seawater, lower operating costs, maximum biomass utilisation, minimal sludge production, lower energy consumption, and the ability to recycle nutrients (Zabed et  al. 2020; Adarme et  al. 2017; Saratale et  al. 2018). The AD (Anaerobic Digestion) of animal manure offers some socioeconomic, environmental, and agricultural benefits through the inactivation of pathogens, improved fertiliser quality, significant odour reduction, and last but not least, the generation of biogas, a green renewable fuel with numerous applications. The slurry or digestate from the reactor, which is utilised as an organic fertiliser, is rich in ammonium and other nutrients (Rajendran et al. 2012; NAS 1977). The goal of the renewable energy policy in the European Union is to replace between 27% and 30% of all energy consumption with renewable sources by 2030. Fourteen to twenty-six percent of this green power is expected to come from biogas produced from waste from farms and forests (Nielsen et al. 2009; Meyer et al. 2018). Biogas is generated and used in Europe. The UK came in second utilising largely waste sources, whereas Germans manufactured the most bioenergy in Europe in 2007 employing primarily energy crops (Meisam Tabatabaei 2018).

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3.3 Factors Affect Biogas Production The generation of natural gas includes a series of four complex biochemical processes, such as the processes of hydrolysis, acidogenesis, acetogenesis, and methanogenesis, depending on a number of factors, including the type of material, substrate particle dimension, temperature range, pH, carbon/nitrogen (C/N) ratio, and bacteria concentration (Kadam and Panwar 2017; Chen et al. 2015; Van Stephan et al. 2016). Numerous factors affect the capacity of anaerobic digestion to generate biogas. 1. Hydrogen-ion (pH) concentration control: The hydrogen-ion (pH) level of the item being digested affects its anaerobic breakdown. The hydrogen-ion amount in the incubation environment has an immediate effect on microbial development because too much acidity inhibits digestion (Viessman Jr and Hammer 1993; Steadman 1975). Environments ranging from balanced to slightly salty are ideal for methanogen growth. The environment’s acidity kills them. The pH of the system should be between 7 and 8.5 once the aerobic digestion process has stabilised; values close to 7 indicate acceptable activity (Weiland 2010; Eckenfelder Jr. 2009; Ward et al. 2008; Jain and Mattiasson 1998). 2. Temperature control: Because the anaerobes that break down waste have temperature-­dependent activity, the temperature of MSW (municipal sewage waste) affects how well the digestion process works. The operating temperatures of the reactor have a significant impact on an aerobic digestion system’s ability to function at its best. According to Meisam Tabatabaei (2018) and Choorit and Wisarnwan (2007), there are actually three basic ranges of temperatures, each of which supports a particular type of microbe. The three temperature ranges are psychrophilic (10–20 °C, or less than 30 °C), mesophilic (40–50 °C), and thermophilic (50–55 °C, or up to 60 °C). According to earlier studies (Kumar 2012), mesophilic and thermophilic regions are where bacteria that are anaerobic are most active. Extremely high or extremely low temperatures can kill anaerobes, which hinders the whole procedure for AD (Kigozi et al. 2014). High temperatures have a tendency to hasten the process of material breakdown and gas production (Maciejewska et  al. 2006; Igoni et  al. 2008). According to Steadman (1975) and Kahaynian et al. (1991), 35 °C is the optimal temperature. A digester can generate or transmit heat with the aid of process reaction, agitation (impellers), and heat transfer systems (hot water or steam) (Meisam Tabatabaei 2018). 3. Feedstock composition and nutrients: It is possible to process organic waste anaerobically using a variety of digesters. A wide range of biomass feedstocks, such as biological waste, crop residue, garbage from humans, municipality sewage disposal, and animal manure, could be used in anaerobic digestion systems. Both the amount and the grade of the methane produced are influenced by the form of feedstock used. The vital nutrients as well as carbon that allow microorganisms thrive sustainably are also produced by biomass in addition to biogas (Kigozi et al. 2014; Kumar 2012; Kumar et al. 2006). The kind that is chosen is influenced by operational factors, such as the type of trash that needs to be treated

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and its solid content. According to the state of Oregon Department of Energy, plug-flow digestion systems, which were introduced in 2002, serve the purpose for compost with solid concentrations of 2–10%, complete-mix digesters are suitable for manure with solid concentrations of 11–13%, and wrapped a lagoon digestion systems are utilised over liquid animal waste with solid levels of less than 2%. According to Igoni et al. (2008), the amount and kind of solids in the wastes they considered were such that they could either flow on their own or flow after producing slurries with water. They could thus be utilised in continuous operations. 4. Carbon/Nitrogen (C/N) Proportion: Carbon and nitrogen concentrations have an impact on how well anaerobic digestion works. A C/N ratio around 20:1 and 30:1 is suitable for anaerobic digestion. The amount of carbon to nitrogen in the raw material has to be close to 30:1 for maximum efficiency. Nitrogen is used by methanogenic bacteria to fulfil their protein needs. While carbon provides the microorganisms with energy, nitrogen aids in the development of microbes. If there is a shortage of nitrogen, the number of microbes will remain small and the surplus carbon will take lengthier to decompose (Igoni et al. 2008). Therefore, in circumstances where the C/N ratio exceeds the optimal limits, the nitrogen will be quickly consumed by the bacteria that lack of time to react with the additional carbon in the feedstock, decreasing the biogas yield. According to Kigozi et al. (2014) and Kumar (2012), lower ratios than the allowed range may result in the production of ammonia, which has a solid base, which would elevate the working pH over the required 8.5, suppressing bacteria and ultimately lowering gas generation rates. Igoni et al. (2008) found that the rate at which the microbes that help in digestion utilise the available carbon is 30–35 times higher than the rate at which they change the nitrogen. Because of the high C/N ratio of animal manures, their use in anaerobic digestion for the production of biogas is limited (Chozhavendhan et al. 2020; Tufaner and Avşar 2016). Before the AD process begins, the carbon content of the animal dung is increased using a nitrogen-free raw material or a source high in carbohydrates to address this issue (Chozhavendhan et al. 2020). 5 . Substrate particle size: The generation of biogas should be increased through co-digestion after pretreatment of the biomass to minimise particle size (Chozhavendhan et al. 2020; Gomez-Lahoz et al. 2007). A substrate with digestible particle sizes is necessary for anaerobic digestion. Smaller particles have more surface area available for the methanogens’ microbial activity, which speeds up the biodegradation of the feedstock and the production of biogas. Conversely, larger particles that may clog the digester have the opposite effect (Kigozi et al. 2014; Mshandete et al. 2006; Sharma et al. 1988).

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3.4 Advantages of Biogas 1. To begin with, biogas is regarded as a renewable energy source. We must stop producing waste because the majority of the waste materials are created when the environment is at its most vulnerable. 2. Use waste materials from agricultural land, dumps, and landfills around the country to reduce landfill waste and water and soil contamination. 3. Additionally, it is meant to be environmentally friendly. Since oxygen is not required for the creation of biogas, resources are not utilising any more fuel. 4. In any case, thousands of individuals have employment chances thanks to the plants. The blessing of finding career in rural areas, where bioenergy is used. Biogas is actually easily decentralised, which makes it available to people who live far away or frequently lack power. 5. Better biogas uses for the technology will be made possible. Both heating and producing electricity are possible with it. Both compressed biogas and compressed natural gas (CNG) can be used as automotive fuel. Either a large factory or a multitude of small plants can be used to produce goods. 6. Using landfill gas as a source of energy lowers greenhouse gas emissions. This is a significant contributing factor to the rising acceptance of using methane gas. Biodegradable garbage recycles a variety of shapes and is developing straightforward technologies. 7. Low upfront costs: Biogas is inexpensive to start up and operate on a modest scale. In fact, many farms may utilise biogas plants and the waste materials created daily by their cattle. A light bulb can only be constantly powered by cow excrement for 1 day.

3.5 Disadvantages 1. Technology has made little progress: To start; the technologies that are presently in place to create biogas are not very effective. A small amount of new technology has been introduced to streamline the process and lower the cost. Large-scale industrial biogas generation continues to remain on the energy map as a result of this. Although the fact that it has the potential to resolve the energy problems that nations all over the globe confront, few investors are ready to put up the first capital. The best course of action is to construct a plant to produce biogas at home, which calls for the development of some type of decentralised infrastructure. 2. Contain impurities: Even if refinement techniques are used, biogas still has a lot of contaminants in it. If used as compression fuel, it can damage engine metal components. 3. Due to the nature of the methane and how combustible it has become, this is not entirely sustainable and is prone to explosion.

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4. Although it doesn’t seem economically feasible and it is extremely difficult to increase the effectiveness of the biogas system, widespread use of biogas is not tempting.

3.6 Application of Biogas Mass reduction, odour removal, pathogen reduction, reduced energy use, and— most significantly—energy reclamation in the form of methane are only a few advantages of anaerobic digestion technology (Mudhoo 2012; Venkata Mohan et al. 2008). Anaerobic digestion aims to produce methane-rich biogas by biologically degrading material that is organic in an atmosphere without oxygen. As a low-cost, environmentally friendly waste management technique, AD is recognised to reduce greenhouse gas emissions. Mass reduction, odour removal, pathogen reduction, reduced energy use, and—most significantly—energy reclamation in the form of methane are only a few advantages of anaerobic digestion technology (Mudhoo 2012; Venkata Mohan et al. 2008). Anaerobic digestion aims to produce methane-­ rich biogas by biologically degrading material that is organic in an atmosphere without oxygen. As a low-cost, environmentally friendly waste management technique, AD is recognised to reduce greenhouse gas emissions. The biogas which is generated by methano bacteria can be advanced and utilised in the transportation industry for vehicle fuel, or biogas also used to produce heat and electricity. Additionally, “digestate residue,” a by-product of anaerobic digestion (AD), can be used as fertiliser on agricultural land.

3.7 Conclusion Biogas is the most promising source of renewable energy which is environmental friendly or has no negative effects on environment. The raw materials used to produce the biogas have a direct impact on its output, contaminants, and composition. Compared to natural gas, biogas provides a number of advantages. As a result, it is today utilised in a wide range of applications, from small-scale use in homes to large-scale use in a number of sectors, including power plants. In this chapter we have discussed about biogas production method by methano bacteria, its application, advantages and disadvantages.

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References Abbasi T, Abbasi SA, Tauseef SM (2012) Biogas energy. Springer Science, New York Adarme OFH, Baêta BEL, Lima DRS, Gurgel LVA, de Aquino SF (2017) Methane and hydrogen production from anaerobic digestion of soluble fraction obtained by sugarcane bagasse ozonation. Ind Crop Prod 109:288–299 Agler MT et al (2011) Waste to bioproduct conversion with undefined mixed cultures: the carboxylate platform. Trends Biotechnol 29(2):70–78 Ahring B, Ibrahim AA, Mladenovska Z (2001) Effect of temperature increase from 55 to 65°C on performance and microbial population dynamics of an anaerobic reactor treating cattle manure. Water Resour 35:2446–2452 Barton LL, Hamilton WA (2010) Sulphate-reducing bacteria: environmental and engineered systems. Cambridge University Press, Cambridge Baserga U (1998) Landwirtschaftliche Co-Vergärungs-biogasanlagen, Biogasaus organischen Reststoffen und Energiegras, FATBerichte no. 512. Eidgenössische Forschungsanstalt für Agrarwirtschaft und Landtechnik (FAT), Tänikon Batstone DJ, Keller J, Angelidaki I, Kalyuzhnyi SV, Pavlostathis SG, Rozzi A, Sanders WTM, Siegrist H, Vavilin VA (2002) The IWA anaerobic digestion model no 1 (ADM 1). Water Sci Technol 45(10):65–73 Braun R (2007) Anaerobic digestion: a multi-faceted process for energy, environmental management and rural development. In: Ranalli P (ed) Improvement of crop plants for industrial end uses. Springer, Dordrecht, pp 335–415 California Environmental Protection Agency (n.d.) Recommendations to the California Public Utilities Commission Regarding Health Protective Standards for the Injection of Biomethane into the Common Carrier Pipeline Chen C, Zheng D, Liu GJ, Deng LW, Long Y, Fan ZH (2015) Continuous dry fermentation of swine manure for biogas production. Waste Manag 38:436–442 Choorit W, Wisarnwan P (2007) Effect of temperature on the anaerobic digestion of palm oil mill effluent. Electron J Biotechnol 10:376–385 Chozhavendhan S, Gnanavel G, Karthiga DG, Subbaiya R, Praveen Kumar R, Bharathiraja B (2020) Enhancement of feedstock composition and fuel properties for biogas production. In: Praveen Kumar R, Bharathiraja B, Kataki R, Moholkar V (eds) Biomass valorization to bioenergy, Energy, environment, and sustainability. Springer, Singapore, pp 113–131 Eckenfelder WW Jr (2009) Industrial water-pollution control. McGraw-Hill Higher Education, Boston Fehrenbach H, Giegrich J, Reinhardt G, Sayer U, Gretz M, Lanje K et al (2008) Kriterien einer nachhaltigen Bioenergienutzung im globalen Maßstab. UBA-Forschungsbericht 206:41–112 Garg S, Clomburg JM, Gonzalez R (2018) A modular approach for high-flux lactic acid production from methane in an industrial medium using engineered methylomicrobium buryatense 5GB1. J Ind Microbiol Biotechnol 45:379–391 Gomez-Lahoz C, Fernandez GB, Garcia HF, Rodriguez MJM, Vereda AC (2007) Biomethanization of mixtures of fruits and vegetables solid wastes and sludge from a municipal waste water treatment plant. J Environ Sci Health A Tox Hazard Subst Environ Eng 42(4):481–487 Henard CA, Smith H, Dowe N, Kalyuzhnaya MG, Pienkos PT, Guarnieri MT (2016) Bioconversion of methane to lactate by an obligate methanotrophic bacterium. Sci Rep 6:1–9 Henard CA, Smith HK, Guarnieri MT (2017) Phosphoketolase overexpression increases biomass and lipid yield from methane in an obligate methanotrophic biocatalyst. Metab Eng 41:152–158 Hijazi O, Munro S, Zerhusen B, Effenberger M (2016) Review of life cycle assessment for biogas production in Europe. Renew Sustain Energy Rev 54:1291–1300 Igoni AH, Ayotamuno MJ, Eze CL, Ogaji SOT, Probert SD (2008) Designs of anaerobic digesters for producing biogas from municipal solid-waste. Appl Energy 85:430–438 Jain SR, Mattiasson B (1998) Acclimatization of methanogenic consortia for low pH biomethanation process. Biotechnol Lett 20:771–775

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Kadam R, Panwar NL (2017) Recent advancement in biogas enrichment and its applications. Renew Sust Energ Rev 73:892–903 Kahaynian M, Lindenauer K, Hardy S, Tchobanoglous G (1991) Two-stage process combines anaerobic and aerobic methods. Biocycle 32:48 Kalyuzhnaya MG, Puri AW, Lidstrom ME (2015) Metabolic engineering in methanotrophic bacteria. Metab Eng 29:142–152 Kigozi R, Muzenda E, Aboyade AO (2014) Biogas technology: current trends, opportunities and challenges. In: Proceedings of 6th international conference on Green Technology, Renewable Energy and Environmental Engineering (ICGTREEE’2014), 24–28 Nov 2014, Cape Town, South Africa, pp 311–317 Krich K, Augenstein D, Batmale JP, Benemann J, Rutledge B, Salour D (2005) Biomethane from dairy waste: a sourcebook for the production and use of renewable natural gas in California. USDA Rural Development, Washington, DC Kumar S (2012) Biogas. Rijeka, Intech. https://www.intechopen.com/books/biogas Kumar A, Miglani P, Gupta RK, Bhattacharya TK (2006) Impact of Ni (II), Zn(II) and Cd(II) on biogassification of potato waste. J Environ Biol 27(1):61–66 Kushkevych I (2016) Dissimilatory sulfate reduction in the intestinal sulfate-reducing bacteria. Studia Biologica 10(1):197–228 Maciejewska A, Veringa H, Sanders J, Peteves SD (2006) Co-firing of biomass with coal: constraints and role of biomass pretreatment. DG JRC Institute for Energy Report, EUR 22461 EN Meisam Tabatabaei HG (2018) Biogas: fundamentals, process and operation, Biofuel and biorefinery technologies, vol 6. Springer, Cham Meyer A, Ehimen E, Holm-Nielsen J (2018) Future European biogas: animal manure, straw and grass potentials for a sustainable European biogas production. Biomass Bioenergy 111:154–164 Milbrandt A (2013) A biogas potential in the United States (fact sheet), energy analysis. National Renewable Energy Laboratory, Golden Mshandete A, Bjornsson L, Kivaisi AK, Rubindamayugi MST, Mattiasson B (2006) Effect of particle size on biogas yield from sisal fibre waste. Renew Energy 31:2385–2392 Mudhoo A (2012) Anaerobic digestion: pretreatments of substrates. In: Biogas production: pretreatment methods in anaerobic digestion. Wiley, Hoboken, pp 199–212 NAS (1977) Methane generation from human, animal and agricultural waste. National Academy of Sciences, Washington, DC Nielsen JBH, Seadi TA, Popiel PO (2009) The future of anaerobic digestion and biogas utilization. Bioresour Technol 100(22):5478–5484 Parker N, Williams R, Dominguez-Faus R, Scheitrum D (2017) Renewable natural gas in California: an assessment of the technical and economic potential. Energy Policy 111:235–245 Pieja AJ, Morse MC, Cal AJ (2017) Sciencedirect methane to bioproducts: the future of the bioeconomy? Curr Opin Chem Biol 41:123–131 Poeschl M, Ward S, Owende P (2012a) Environmental impacts of biogas deployment—part II: life cycle assessment of multiple production and utilization pathways. J Cleaner Product 24:184–201 Poeschl M, Ward S, Owende P (2012b) Environmental impacts of biogas deployment—part I: life cycle inventory for evaluation of production process emissions to air. J Cleaner Product 24:168–183 Rajendran K, Aslanzade S, Taherzadeh J (2012) Household biogas digesters: a review. Energies 5(8):2911–2942 Rapport J, Zhang R, Jenkins BM, Williams RB (2008) Current anaerobic digestion technologies used for treatment of municipal organic solid waste. Contractor report to the California Integrated Waste Management Board. Department of Biological and Agricultural Engineering, University of California, Davis Saratale RG, Kumar G, Banu R, Xia A, Periyasamy S, Saratale GD (2018) A critical review on anaerobic digestion of microalgae and macroalgae and co-digestion of biomass for enhanced methane generation. Bioresour Technol 262:319–332

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Sharma SK, Mishra IM, Sharma MP, Saini JS (1988) Effect of particle size on biogas generation from biomass residues. Biomass 17:251–263 Steadman P (1975) Energy, environment and building: a report to the Academy of Natural Sciences of Philadelphia. Cambridge University Press, Cambridge Strong PJ, Xie S, Clarke WP (2015) Methane as a resource: can the methanotrophs add value? Environ Sci Technol 49:4001–4018 Strong PJ, Kalyuzhnaya M, Silverman J, Clarke WP (2016) A methanotroph-based biorefinery: potential scenarios for generating multiple products from a single fermentation. Bioresour Technol 215:314–323 Treichel H, Fongaro G (2019) Improving biogas production: technological challenges, alternative sources, future developments, Biofuel and biorefinery. Springer, Cham Tufaner F, Avşar Y (2016) Effects of co-substrate on biogas production from cattle manure: a review. Int J Environ Sci Technol 13:2303–2312 Turco M, Ausiello A, Micoli L (2016) Treatment of biogas for feeding high temperature fuel cells: removal of harmful compounds by adsorption processes. Springer, Cham Van Stephan F, Mathot M, Decruyenaere V, Loriers A, Delcour A, Planchon V et  al (2016) Consequential environmental life cycle assessment of a farm-scale biogas plant. J Environ Manag 175:20–32 Venkata Mohan S, Lalit Babu V, Sarma PN (2008) Effect of various pretreatment methods on anaerobic mixed microflora to enhance biohydrogen production utilizing dairy wastewater as substrate. Bioresour Technol 99:59–67 Viessman W Jr, Hammer MJ (1993) Water supply and pollution control. Harper Collins College Publishers, New York Ward AJ, Hobbs PJ, Holliman PJ, Jones DL (2008) Optimisation of the anaerobic digestion of agricultural resources. Bioresour Technol 99(17):7928–7940 Weiland P (2010) Biogas production: current state and perspectives. Appl Microbiol Biotechnol 85:849–860 Wellinger A, Murphy J, Baxter D (2013) The biogas handbook: science, production and applications. Woodhead Publishing, Oxford Yong Z, Dong Y, Zhang X, Tan T (2015) Anaerobic codigestion of food waste and straw for biogas production. Renew Energy 78:527–530 Zabed HM, Akter S, Yun J, Zhang G, Zhang Y, Qi X (2020) Biogas from microalgae: technologies, challenges and opportunities. Renew Sust Energ Rev 117:109503 Ziemiński K, Frąc M (2012) Methane fermentation process as anaerobic digestion of biomass: transformations, stages and microorganisms. Afr J Biotech 11(18):4127–4139

Chapter 4

Microbial Advancements in Dark Fermentative Biohydrogen Production: Applications and Innovations D. M. Tripathi and Smriti Tripathi

Abstract Direct or indirect biophotolysis, photo-fermentation, and dark fermentation are all methods of biohydrogen production (BHP), with the latter being the only one that doesn’t require the addition of light energy. The significant research on the application of pure and defined coculture dark fermentative biohydrogen production is compiled in this chapter. The recent advances in microbiology, including biochemistry, enzymology, microbial modification, and the identification of the microbial community structure, for the production of hydrogen through dark fermentation are discussed. By altering metabolic pathways, metabolic engineering can improve the biological production of hydrogen by removing constraints on hydrogen synthesis in various systems, increasing electron flow to hydrogen-producing pathways, boosting substrate utilization, and designing more effective enzymes. Moreover, leading biohydrogen-producing microbes like Clostridium spp., Escherichia coli, Enterobacter spp., Bacillus spp., etc. are also covered, as well as innovative methods used to increase biohydrogen production. Keywords Hydrogen yield, biohydrogen · Metabolism · Microbiology · Organic waste

D. M. Tripathi Department of Microbiology, Bundelkhand University, Jhansi, Uttar Pradesh, India e-mail: [email protected] S. Tripathi (*) Institute of Environment and Development Studies, Bundelkhand University, Jhansi, Uttar Pradesh, India © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024 P. Singh (ed.), Emerging Trends and Techniques in Biofuel Production from Agricultural Waste, Clean Energy Production Technologies, https://doi.org/10.1007/978-981-99-8244-8_4

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4.1 Introduction Bioenergy has shown good potential as a green and low-carbon emission energy generation technology (including biodiesel, bioethanol, biomethane, and bio-H2). Hydrogen has the highest calorific value of any clean and sustainable energy source, making it the most viable alternative fuel. It also has zero emissions. In addition to producing energy, hydrogen can be used as a feedstock to produce several compounds, hydrogenate fats and oils, and produce methanol. H2 has numerous advantageous qualities, including being acceptable for mammals and the environment and being a clean fuel because water is produced after combustion. The first speculative creation of biological H2 was proposed in the early nineteenth century. The H2 production from anaerobic digestion of cellulose in the ruminant tract, however, was not clearly understood until the 1930s, when Woodman and his coworkers published their initial research findings. Since then, extensive research on H2 production has been conducted, and numerous ways have been put into practice to overcome associated disadvantages (Woodman and Evans 1938). Currently, the main techniques used to generate H2 are the steam reformation of methane and electrolysis of water. Although exceedingly energy-intensive, these operations are easily carried out. Although biological processes can function at ambient temperature, they are more complex in both design and operation. Direct or indirect biophotolysis, photo-fermentation, and dark fermentation are methods for achieving it (see Fig. 4.1). In the year 1942, it was found that algae could produce fermentative H2 in the presence of sugar. Later, it was shown that Rhodospirillum rubrum’s anaerobic growth in the absence of light results in the anaerobic metabolism of pyruvate (Hallenbeck and Ghosh 2009). Following this, numerous attempts have been made to increase the efficiency of H2 production using various microbiological vantage points (see Table 4.1), including coculture of photosynthetic bacterial species and dark fermentative bacterial species optimization of physicochemical conditions, application of fermentative immobilized bacterium, use of hydrogenase enzymes, isolation of efficient H2 producers from various sources, and employing nanotechnological approach. A study on the impact of metal ions on H2, CH4, and CO2 generation during batch anaerobic sludge digestion is one of the latest advancements. The dark fermentation technique is increasingly popular because of its lack of reliance on light, high hydrogen production rate, affordable reactor setup, and simplicity of operation. Furthermore, using organic waste as a substrate allows for the double benefits of clean energy production and waste management. The downside is the insignificant H2 production per substrate consumed in dark fermentative biohydrogen synthesis. Additionally, the concurrent generation of CO2 and carbon metabolites also takes place during the process. In comparison with ethyl alcohol (i.e., 2 mol/mol of glucose) and methane (i.e., 3 mol/mol of glucose), hydrogen has a relatively high theoretical yield of 4  mol/mol of glucose for the production of bioenergy through microbial fermentation. The hydrogen yield, though, is still well below the 12 mol H2/mol glucose theoretical maximum yield.

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Fig. 4.1  Various processes representing hydrogen production. (Based on Kumar et al. 2019)

When glucose was utilized as the substrate for dark biohydrogen production, the maximum hydrogen output was 3.47 mol hydrogen/mol glucose (Ortigueira et al. 2015). There are several process modes including batch, fed-batch, closed batch, chemostat culture, and other modes which utilize microorganisms in biohydrogen production (Wang and Yin 2019). This chapter reviews the use of microorganisms in the production of dark fermentative hydrogen, with a focus on inoculum sources, widely utilized hydrogen producers, microbial metabolic steps, critical microbial enzymes, and advanced microbial modification for higher hydrogen production.

4.2 Hydrogen-Producing Microorganisms Microorganisms that create hydrogen include those that are photosynthetic, photo-­ fermentative, and dark fermentative. Photoautotrophic microbes like blue-green algae and green algae break water into oxygen and hydrogen. Purple nonsulfur bacteria (Rhodobacter), gliding bacteria, purple sulfur bacteria (Chromatium), and green sulfur bacteria (Chlorobium) are examples of photo-fermentative microorganisms (e.g., Chloroflexus). When exposed to light, they can change small organic compounds like short-chain volatile fatty acids (VFA) into hydrogen. Different types of microbes from soil, sludge, etc. can produce biohydrogen, and due to their presence in various environmental conditions, they may be mesophiles (Clostridium

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Table 4.1  Major works in the generation of fermentative H2 The early 1900s 1930

Initial studies showed that bacteria and algae may create H2

Benemann (1996) Woodman (1930)

1942

Demonstration of the existence of two distinct anaerobic cellulose-fermenting organisms Fermentative photochemical production of H2 in algae

Gaffron and Rubin (1942) Dark fermentative metabolism of pyruvate by Rhodospirillum Gorrell and Uffen rubrum for H2 production (1977) Photoproduction of H2 from glucose by a coculture of a Miyake et al. photosynthetic bacterium and Clostridium butyricum (1984) Hydrogenase enzyme in Chlorella Mahro et al. (1986) Fermentative H2 production from Enterobacter aerogenes Tanisho et al. (1987) The effect of metal oxides on H2 production Hickey et al. (1989) H2 production by photosynthetic microorganisms Kumar et al. (1995) H2 production using coculture of strict and facultative anaerobes Yokoi et al. (1998) Characterization of an H2 producer from sludge Fang et al. (2002) Microbial H2 production with Bacillus coagulans isolated from Kotay and Das anaerobic sewage sludge (2007) H2 production using immobilized mixed culture Singh et al. (2013) H2 production by metabolically engineered Escherichia coli Maeda et al. (2007) Bioreactor design for continuous dark fermentative H2 Jung et al. (2011) production Mishra et al. Nanometal application for H2 production (2019) Dark fermentative hydrogen production by a newly isolated Litti et al. (2022) Thermoanaerobacterium thermosaccharolyticum Dark fermentative hydrogen gas production from molasses Ören et al. (2022) using hot spring microflora

1977 1984 1986 1987 1989 1995 1998 2002 2007 2013 2007 2011 2018 2022 2022

spp.), thermophiles (Thermoanaerobacterium spp.), (Polaromonas spp.); and anaerobic species (Citrobacter spp.) as well as facultative anaerobic strains (Enterobacter spp.). When it comes to practical application, mixed cultures are favored since they result in a more efficient process and a wider range of feedstock options than pure cultures. On the other hand, producing hydrogen using only specific microbial strains can give researchers greater information about the reactions taking place throughout the process and reactions in the metabolic pathways and suggest practical approaches to increase the efficiency of hydrogen production (Wang and Yin 2019).

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Numerous microbial pure culture genera are capable of dark fermentation, which produces hydrogen (see Table  4.2). The most generally used strains are Enterobacter spp. (E. asburiae, E. aerogenes, and E. cloacae) and Clostridium spp. (C. butyricum, C. beijerinckii, C. pasteurianum). There are some other genera which are also utilized for biohydrogen production like Thermoanaerobium, Rahnella, Bacillus, Klebsiella, and Ethanoligenens. According to the growth temperature, the hydrogen-producing strains are divided into mesophiles, thermophiles, and psychrophiles. Besides temperature, based on O2 resistance level, the strains are classified into aerobes (Bacillus licheniformis), anaerobes (Clostridium spp.), and facultative anaerobes (Enterobacter spp.). Here it is worth mentioning that the anaerobes have been found to generate more hydrogen, while facultative anaerobes and aerobes assist by consuming the oxygen in a system to maintain a suitable environment for anaerobes. Mesophiles are the most frequently used in dark fermentative hydrogen production. Most commonly used strains such as Clostridium butyricum has shown the highest efficiency in hydrogen production. Other Clostridium spp. like C. beijerinckii and C. pasteurianum also displayed good potential in hydrogen generation. Species belonging to Enterobacter spp. and Bacillus spp. showed comparatively lower hydrogen production, but their resistance to oxygen makes them more applicable in practical use. Additionally, Kotay and Das (2009) concluded that hydrogen generation efficiency can be considerably increased by incorporating highly effective pure cultures into mixed-culture systems. Gamma radiation can also be utilized as a treatment method to enrich hydrogen producers and induce mutation (Yin and Wang 2016; Wang and Yin 2017a, b). With this process, the two new strains named Clostridium butyricum INET1 and Enterococcus faecium INET2 were obtained. Considerable research has attempted to find microorganisms that can create hydrogen utilizing different substrates; generally, the isolates were derived from the target wastes. For instance, cow dung, which is rich in cellulosic components, was chosen by Zhang et al. (2015a, b) as a source of bacteria. When synthesizing hydrogen from cellulosic biomass, the isolated strain of Clostridium sartagoforme demonstrated remarkable efficiency. Harun et al. (2012) sought to create a strain with high efficiency in generating hydrogen from lignocellulosic biomass from termite guts since termites are widely known for degrading lignocellulosic materials. In addition to the impact of various operational circumstances and substrates, microorganisms differ in their capacity to produce hydrogen. Different Clostridium species like C. beijerinckii, C. pasteurianum, etc. are also taken into account, and H2 production of 0.52–3.0 mol H2/mol hexose was obtained. Enterobacter spp. and Bacillus spp. are among the highly studied microorganisms, and according to Long et al. (2010), the maximum yield of 2.4  mol H2/mol hexose was given by Enterobacter sp. CN1. Mostly the facultative anaerobic strains have comparatively lower hydrogen yield, and some thermophiles, e.g., Klebsiella pneumoniae, Caloranaerobacter azorensis, and Thermoanaerobacterium thermosaccharolyticum, produce 0.43–2.6 mol hydrogen/ mol hexose which may go up to 2.5 mol H2/mol hexose for some strains, which is more than the production value given by mesophiles. The substantial cost of

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Table 4.2  Hydrogen production by various potential microorganisms S.N. Microorganisms Substrate Obligate anaerobes 1 Clostridium acetobutylicum Glucose

Yield

References

1.8 mol/mol substrate Glucose 2.81 mol/mol substrate Glucose 2.29 mol/mol substrate Sugar rich cassava 2.41 mol H2/ wastewater mol glucose Raw food waste 38.9 mL H2/g-volatile solids added De-oiled Jatropha 20 mL H2/g waste volatile soilids Peanut shell biomass 6.4–39.9 mL H2/g

Lin et al. (2007)

Facultative anaerobes 8 E. coli

Glucose

Seppala et al. (2011)

9

E. coli MG1655

Crude glycerol

10

E. coli HD701 strain

Molasses (glucose)

11

E. coli strain ZH-4

Pang et al. (2017)

12

Engineered E. coli BW25113

13

E. coli + Enterobacter aerogenes

14

E. aerogenes

15

E. cloacae

16

Klebsiella oxytoca

17

K. pneumoniae

Cellulose and lignocellulosic material Palm oil mill effluent 0.66 mol H2/ (pome) mol total monomeric sugar The organic fraction 1.96 L/L of municipal solid substrate waste (OFMSW) + alanine Xylose 1.92 mol/mol substrate Glucose 3.1 mol/mol substrate Glucose 1.01 mol/mol substrate Glucose 2.07 mol/mol substrate Cellulose

Liu et al. (2008)

2

Clostridium beijerinckii

3

Clostridium butyricum

4

C. acetobutylicum

5

C. beijerinckii

6

Clostridium sp.

7

C. guangxiense ZGM211T

Thermophilic 18 Thermoanaerobacterium thermosaccharolyticum

1.44 mol/mol substrate 0.56 mol/mol glycerol 0.48 mol/mol glucose 4.71 mL/g corn

1.8 mol/mol substrate

Lin et al. (2007) Lin et al. (2007) Cappelletti et al. (2011) Hu et al. (2014)

Kumar et al. (2015) Qi et al. (2018)

Cofre et al. (2016) Morsy (2017)

Taifor et al. (2017)

Sharma and Melkania (2018)

Jayasinghearachchi et al. (2009) Khanna et al. (2011a, b) Minnan et al. (2005) Niu et al. (2010)

(continued)

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Table 4.2 (continued) S.N. Microorganisms 19 Thermotoga neapolitana

Substrate Carrot pulp

20

Glucose

Thermoanaerobacter mathranii

Yield 2.4 mol/mol substrate 2.64 mol/mol substrate

References de Vrije et al. (2010) Jayasinghearachchi et al. (2012)

continuous high-temperature (40–60 °C) maintenance prevents thermophiles from being extensively employed, although they can be a suitable choice when hot industrial wastes are used as substrates. Numerous trials have been made to improve the capacity for producing hydrogen through genetic engineering in addition to isolating more effective strains from nature. This entails the overexpression of genes that produce hydrogen (both native and heterologous), the elimination of competitive pathways, the development of novel productive pathways, and other techniques. Wide-ranging natural ecosystems can provide mixed cultures for the synthesis of hydrogen. The most typical inoculum is anaerobic sludge, which is followed by animal compost (mostly from cows and poultry) (Li et al. 2016) and soil (Garcıa et  al. 2012). Different approaches have been examined to improve the hydrogen generation capability of these systems. H2 producers, substrate competitors, and H2 consumers may coexist in a culture. For example, heat, acid, and base pretreatment were favorable to enriching the hydrogen producers, like Clostridium spp., Enterococcus spp., and Bacillus spp. (Liu et al. 2009); Bacillus species predominated in the mixed culture that was treated with 2-bromo-ethano-sulfonic acid (BESA) (O-Thong et  al. 2009). In addition to the techniques of treatment, the sources of the inoculum play a significant role on the diversity of microbes found in a fermentation system. When anaerobic sludge was introduced, Clostridium spp. typically took dominance (Chu et al. 2011). Activated sludge is the most commonly utilized inoculum source and typically produces a high H2 output, according to a study of numerous research. Compost from animals is also frequently used and then naturally occurring microbes from organic wastes. In a system of mixed cultures, non-hydrogen producers as well as hydrogen producers coexist. The term “non-hydrogen producers” describes microorganisms that cannot generate H2 but indirectly help in the hydrogen production process. They can be divided into three categories. H2−consumers are undesirable bacteria because they can break down the hydrogen produced into methane or acetate, decreasing the system’s ability to produce H2 (Wang and Yin 2019). Although substrate competitors don’t utilize H2, they compete with H2−producers for food, which lowers the system’s overall H2 yield. Beneficial bacteria, such as those in this class, contribute to the creation of hydrogen by maintaining system stability or improving fermentation efficiency, such as by removing oxygen from the system and hydrolyzing complex organic materials into simple sugar molecules. When complex organic wastes are utilized as the substrate, several non-hydrogen producers help the system maintain stability or provide suitable combinations of metabolic pathways for hydrogen synthesis. For instance, some facultative anaerobes or aerobes can

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consume the O2 in a system and maintain an anaerobic condition (Hung et  al. 2011a); microorganisms (Streptococcus spp.) can result in the formation of a structure, which improves the retention of microbes and increases H2 yield; and certain cultures are adept at breaking down complex macromolecules, which can help to supply simple carbohydrates for hydrogen producers. In addition to the helpful microorganisms, some microbes are unfavorable for the generation of hydrogen, such as H2−consumers, bacteria which produce acidic substances and so forth. By turning the generated hydrogen into methane or acids, hydrogen consumers can drastically lower the efficiency of hydrogen production. Methanogens and homoacetogenic bacteria make up the majority of them. Methanogens can create methane from hydrogen and carbon dioxide, whereas homoacetogenic bacteria use hydrogen to create acetate.

4.3 Fermentative Hydrogen Production Primary substrates for the fermentative H2 production to accomplish energy generation and waste management are organic wastes. It typically has complex constituents, primarily polysaccharides, proteins, and lipids. While proteins and lipids have a poorer energy conversion efficiency and a lower hydrogen output than polysaccharides, they are nevertheless important for microbial growth. It is evident that during the dark fermentative H2-generating metabolism, complex polymers are initially hydrolyzed to glucose through the metabolism of microorganisms. Adenosine triphosphate (ATP) is then formed by the glycolytic pathway, which results in the generation of pyruvate. Then, pyruvate is converted into hydrogen in two routes. The first occurs in obligate anaerobes like Clostridium spp. (Eqs. 4.1 and 4.2), and the second occurs in facultative anaerobic bacteria like E. coli (Eqs. 4.3 and 4.4) (Bundhoo and Mohee 2016). Equations 4.1 and 4.2 describe how obligate anaerobes like Clostridium spp. produce hydrogen. Pyruvate dehydrogenase (PDH) catalyzes this process, releasing electrons from pyruvate to create acetyl-CoA. The released electrons from ferredoxin are united with H+ forming H2, which is catalyzed by hydrogenase. The action of alcohol dehydrogenase (ADH) and acetate kinase causes the acetyl-CoA produced and its breakdown into acetate and ethanol. In the process of H2 production by facultative anaerobes like Enterobacter spp., pyruvate formate-lyase (PFL) catalyzes the conversion of pyruvate into formate and acetyl-CoA (Eqs.  4.3 and 4.4). Formate hydrogen lyase (FHL) and hydrogenase then convert formate into H2 and CO2. Two mol H2 can be obtained from single mol pyruvate through Eqs. 4.1 and 4.2, while 1 mol H2 is formed through Eqs. 4.3 and 4.4. Obligate anaerobes can produce more hydrogen than facultative anaerobes, proving that variable microbial concentration can result in varying hydrogen production efficiencies. H2 yield of 3.47  mol H2/mol sugar can be obtained by the Clostridium, while not more than 2.6  mol H2/mol sugar can be produced by the Enterobacter and Bacillus (Sinha and Pandey 2014; Ortigueira et al. 2015).

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Pyruvate + CoA + 2Fd ( oxidised ) → AcetylCoA + 2Fd ( reduced ) + CO 2 (4.1)



4H + + 2Fd ( reduced ) → 2H 2 + 2Fd ( oxidised ) (4.2)



Pyruvate + CoA → AcetylCoA + HCOOH (4.3)



HCOOH → CO 2 + H 2 (4.4)

Rapid microbial growth and the generation of by-products check energy transfer from sugar to H2 in a fermentation system. The maximum hydrogen output is just 4 mol H2/mol glucose, even though theoretically 12 mol H2 can be produced from 1 mol of glucose. The content of the generated volatile fatty acids (VFA), which are crucial by-products of the dark fermentation process, has a significant impact on the hydrogen yield, and it is possible to infer the microbial metabolism pathways from the composition of the volatile fatty acids. Fermentation types for hydrogen production can be divided into four groups based on the dominating VFA formation: ethanol-type fermentation, butyrate-type fermentation, propionate-type fermentation, and mixed-type fermentation (Wang and Yin 2019). Ethanol and acetate acid make up the majority of the liquid metabolites in ethanol-­type fermentation. In butyrate-type fermentation, butyrate acid and acetate acid dominate the liquid metabolites. The ratio of butyric to acetic acid that is produced is 2. Studies have shown that Clostridium spp. dominated conditions cause butyrate-type fermentation. Similarly, propionate-type fermentation is characterized when the dominant liquid metabolites are propionate acid and acetate acid. Studies typically strive to avoid propionate-type fermentation because there is a very low amount of hydrogen output produced here. A fermentation system is classified as mixed-type fermentation when there is no significant liquid metabolite present. When no discernible dominating bacterial community has yet been established during the start-up phase of a fermentation process, mixed-type fermentation typically occurs. Mixed-type fermentation is an example of the unpredictability of the fermentation process because there is no theory of microbial metabolism for it.

4.4 Microbial Applications in Fermentative Hydrogen Production Through conventional dark fermentation, the theoretical maximum yield of hydrogen is only 4 mol hydrogen/mol glucose, which is much less than the theoretical maximum yield of 12 mol hydrogen/mol glucose. As a result, research attempts to create synthetic enzymatic hydrogen production pathways, which significantly boost the amount of hydrogen. By using 13 enzymes in an enzymatic hydrogen production process, Zhang et al. (2007) achieved hydrogen generation from glucose and starch of 70% and 43%, respectively. Hydrogen was produced from cellobiose using 13 enzymes, and it was 93.1% more successful than anticipated (Ye et  al.

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2009). By combining a 17 thermophilic enzyme pathway and a 5 thermophilic enzyme pathway, Kim et al. (2017) theoretically got a complete conversion of starch to glucose and then to hydrogen. According to these findings, fermentative hydrogen production constraints can be overcome by synthetic enzymatic hydrogen production, resulting in hydrogen yields that are close to the theoretical maximum. Hydrogenase is an important enzyme in the process of producing hydrogen from protons. The redox potential of the electron donors that can interact with hydrogenase determines the equation’s direction, which is reversible. The activity of hydrogenase has a significant impact on the efficiency of the process.

2 H + + 2e − → H 2

According to the amount of metal in the active site, hydrogenases are divided into three groups: [Fe], [FeFe], and [NiFe] hydrogenases. Some of these hydrogenases, such as [FeFe] hydrogenases and [Fe] hydrogenases, can be irreversibly inactivated when exposed to oxygen. Other hydrogenases, such as [NiFe] hydrogenases, can be checked by oxygen but can regain activity when the oxygen is removed. A few hydrogenases are aerobically active and oxygen-tolerant and catalyze hydrogen oxidation. While some hydrogenases are only active in either hydrogen consumption or hydrogen synthesis, others catalyze both reversible hydrogen oxidation and hydrogen synthesis. Many hydrogenases are typically present in microorganisms, and each one has a distinct function. Other names for [Fe] hydrogenase include iron-sulfur-cluster-free hydrogenase and H2-forming methylene-tetrahydromethanopterin dehydrogenase. The most researched classes of hydrogenases are [NiFe] hydrogenases. The breakdown of molecular hydrogen into two protons and two electrons, which results in the breakdown of hydrogen, can be catalyzed by [NiFe] hydrogenases. On the other hand, under sufficiently reducing conditions, they can also catalyze the synthesis of hydrogen from two protons and two electrons. Two families of [FeFe] hydrogenases can be distinguished: the first one is monomeric [FeFe] hydrogenases. These are oxygen-sensitive, cytoplasmic, and soluble and present in strict anaerobes like Clostridium pasteurianum and Megasphaera elsdenii. They function both in hydrogen production and consumption. The second one is heterodimeric and periplasmic. It is found in Desulfovibrio spp. They catalyze the oxidation of hydrogen and reduce sulfate to sulfide. A strategy that has the potential to enhance the electron pathways and, consequently, the effectiveness of biological hydrogen synthesis is the genetic and metabolic changes in hydrogenase. The main modifications made to the dark fermentative hydrogen production system are the deletion of the gene for H2-uptake hydrogenase, the insertion of a gene for enzyme expressions such as an increase in the efficiency of some hydrogen-producing enzymes or overexpression of one particular hydrogen-producing enzyme, and the improvement of hydrogenase’s oxygen tolerance. The key issue in attaining an acceptable hydrogen generation is hydrogenase, a hydrogen-consuming enzyme that reoxidizes the hydrogen produced. Studies have

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shown that mutants with uptake hydrogenase gene deficiencies (deletion of hydrogen-­uptake hydrogenase) had higher hydrogen generation rates and efficiency. In Enterobacter aerogenes IAM1183, Zhao et al. (2009) took two hydrogen absorption genes for the genetic knockout, resulting in three mutant strains. The findings demonstrated that both hydrogen yield and production rate had greatly increased. Sequential dark-photo-fermentations were carried out by Wu et al. (2010) to produce hydrogen from bagasse, and the hydrogen yield was increased by inactivating an acetaldehyde dehydrogenase in Klebsiella oxytoca HP1 to lower the alcohol concentration. The genetic insertion of an enzyme to facilitate hydrogenase is another good modification to strengthen the process. According to studies, hydrogenase can be cloned into a heterologous host to increase hydrogen generation. When the Hydrogenovibrio marinus [NiFe] hydrogenase was heterologously expressed in E. coli, oxygen tolerance was greatly improved, according to Kim et  al. (2011). Thus, the need for strictly anaerobic infrastructure can be reduced by using oxygentolerant hydrogenases for in vivo biohydrogen generation. A new strategy to increase H2 productivity by genetic engineering is implemented through manipulation of the microbial metabolic process and thus regulating the generation of the unwanted microbial product. By turning off or changing particular genes that hinder H2 generation, the metabolic engineering technique increases H2 productivity. Nath and Das (2004) provided a summary of the potential genetic engineering strategy to increase H2 production, which includes (a) overexpressing H2 evolving hydrogenases, (b) eliminating uptake hydrogenases, and (c) overexpressing enzymes that maintain substrate availability, such as cellulases, hemicellulases, and ligninases (Nath and Das 2004). The formate pathway and the NADH pathway are two well-known metabolic routes for hydrogen synthesis. Researchers have independently looked into both pathways and found a linear link between the H2 yield and the relative change in NADH pathways. Pyruvate formate-­ lyase (PFL) and formate hydrogen lyase (FHL) enzyme complexes catalyze formate metabolic processes. The formate pathway’s primary enzymes include hydrogenase, formate dehydrogenase, and the FHL enzyme complex. The majority of genetic tampering has been done on FHL-related genes to control the formate pathway and boost H2 synthesis (McDowall et al. 2014). The successfully increased H2 production through in  vivo genetically engineered modes using E. coli strains has been investigated by several researchers and comprehensively reviewed by Maeda and his coauthors (Maeda et al. 2008), and these included some metabolic modifications such as the overexpression of particular genes such as cellulases, hemicellulases, and ligninases which increases the complex carbohydrate-consuming ability of microbial strains and resulted in increased H2 productivity (Vardar-Schara et al. 2008). Microbes’ ability to survive in the presence of oxygen is determined by their oxygen tolerance, whereas hydrogenase’s ability to produce hydrogen under oxygen-­rich conditions is determined by its oxygen resistance. The majority of hydrogenases, though, are oxygen-sensitive. It has been established that the majority of well-known hydrogen producers, such as Clostridium butyricum, Clostridium

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beijerinckii, etc., can only produce hydrogen with high production efficiency in a strictly anaerobic environment. In comparison with Clostridium spp., the O2-tolerant Enterobacter spp. can produce 50% of the total hydrogen production. Additionally, as substrate sources for hydrogen production increase, more microbial species must produce hydrogen to attain high hydrogen production from a variety of substrates, including facultative and anaerobic ones. Since there are no bacteria that consume hydrogen or competitors that degrade the substrate, pure hydrogen-producing cultures can typically produce higher yields of hydrogen. Pure cultures are capable of converting sugar into hydrogen with high efficiency, particularly when using pure sugars as the substrate. However, mixed cultures exhibit benefits in both H2 production and substrate degradation when complex organic wastes are utilized as the substrate. This may be due to the biological interactions found in mixed cultures. However, due to the diverse microbial configurations found in the various consortia sources, the hydrogen productivity by mixed cultures is not constant. Finding the advantageous biological interactions by microbial community modification is therefore important for increasing the effectiveness of hydrogen production. To satisfy various needs, synthetic microbial consortia are constructed. This approach involves integrating many characterized microbial populations with complementary metabolic functions. The process is known as cocultivation. According to studies, well-designed consortia can execute better than traditional monocultures (Bernstein and Carlson 2012). The field of synthetic microbial consortiums has been employed extensively in the fields of food, medicine, and biofuel (Bagi et al. 2007). The investigated advantageous biological interactions in the area of dark fermentative hydrogen production generally fall into two categories: oxygen depletion and macromolecule breakdown. Most hydrogenases are sensitive to O2, and facultative anaerobes like Enterobacter spp. can only create hydrogen in anaerobic environments, in addition to obligate anaerobes like Clostridium spp. Therefore, to ensure the steady operation of systems that produce hydrogen, maintaining a strict anaerobic state must be done for efficient production. However, oxygen frequently enters the system with the feedstock, and it would be impractical to expect to completely remove oxygen from the substrate, particularly when operating in continuous mode and using actual organic wastes. As a result, the solutions are brought by a system that may consume oxygen by itself. In systems that produce hydrogen, inoculating facultative anaerobes can avoid oxygen shock. In this case, both facultative anaerobic hydrogen producers and non-hydrogen-producing ones can be used. Mixed culture of Bacillus spp., Enterobacter spp., and Klebsiella spp. with Clostridium spp. was used to achieve hydrogen (Hung et  al. 2011b). Similarly, coculturing of a hydrogen-producing Candida maltosa HY-35 with a facultative anaerobe Enterobacter aerogenes W-23 generates hydrogen 1.74 L H2/L medium, which was enhanced by 0.17 and 1.19 times more than the monoculture of E. aerogenes and C. maltosa, respectively (Lu et al. 2007). In addition to taking into account the various traits of microorganisms treated using various methods, variously treated mixed cultures are also cocultured. For instance, facultative anaerobic microorganisms have been shown to predominate in aeration-treated cultures, but Clostridium spp. is more likely to survive in

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high-temperature therapy. As a result, cocultivating a consortium that has been heating and aeration-treated can be a promising option for getting high hydrogen generation and oxygen resistance (Zhu and Beland 2006). Organic wastes may be employed as the substrate for a larger application of fermentative hydrogen production to increase its economic and environmental advantages. Agricultural waste, food waste, municipal garbage, and highly concentrated organic effluent from breweries and dairies are among the most often used organic wastes. Actual wastes contain organic materials that are mostly made up of large molecules like starch, cellulose, and protein. Here, it must be mentioned that the hydrolysis of complex organic substrates is primarily the rate-limiting phase. There have been numerous attempts to speed up the hydrolysis by the processing of wastes, including heat treatment, ultrasonication, acid, and base-improved oxidation treatment, among others (Karthikeyan et al. 2018). However, the majority of treatment techniques use a lot of energy, which lessens their economic and environmental advantages. To improve the hydrogen generation process, cocultivating H2 producers with hydrolyzing strains can be a suitable option. For instance, cellulose, cellobiose, and lignin make up the majority of the carbon supply when lignocellulosic wastes are utilized as a substrate. Coculture of Caldicellulosiruptor saccharolyticus and Caldicellulosiruptor kristjanssonii improved the hydrogen production rate from 19 mmol to 40 mmol H2/g cell dry weight/h, and xylose was degraded simultaneously (Zeidan and Van Niel 2009). Li and Liu (2012) achieved the highest hydrogen yield from corn stalks through the coculture of Clostridium thermocellum and Clostridium thermosaccharolyticum, which was 94% higher than the monoculture. In addition to lignocellulose, Pachapur et al. (2016) revealed that crude glycerol can be used to produce hydrogen. In comparison with mono- and coculture systems, they discovered that the multi-culture system had greater natural acclimation activity for digesting glycerol and removing inhibitors. To strengthen their stability and enable their repeated or ongoing use, microbial cells, enzymes, organelles, or other proteins may be physically or chemically fixed into a solid matrix, onto a solid substrate, or maintained by a membrane, known as microbial immobilization. The use of microbial cells or enzymes can be improved by the immobilization approach. For instance, it is possible to coculture microorganisms with various development cycles in a single reactor; the immobilized biocatalyst is easily reusable and increases product yield; the attached biocatalyst is protected from environmental impacts and is less sensitive to contamination. They can be divided into groups based on the natural or artificial materials employed and the biocatalyst fixation mechanism, such as confinement, entrapment, adsorption, and aggregation. The most popular techniques are entrapment and adsorption. An efficient and simple physical technique for immobilizing microbial cells is entrapment. By using 3D matrices such as an electro-polymerized film and network, microbial cells can be immobilized through this technique (see Table  4.3). The microorganisms’ operational and storage stability can typically be improved by entrapment. Entrapment, especially for macromolecular compounds, can also make the mass transfer more difficult and cause problems with substrate/product diffusion. The most popular and straightforward immobilization technique is

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Table 4.3  Immobilization of pure and mixed cultures on various matrices for the generation of bio-H2 Supportive/ matrices Polymethyl methacrylate

Fermentative inoculum Acid-pretreated acclimated sludge

Agar

E. coli SH5

Polyethylene-­ Acid-pretreated octene-­elastomer anaerobic sludge Polyester fiber Heat- and acid-pretreated anaerobic sludge Heat- and Metal mesh-­ acid-pretreated covered plastic scouring sponge anaerobic sludge pad Calcium alginate Enterobacter aerogenes MTCC 2822

Feed Sucrose-­ based synthetic wastewater Sodium formate

Reactor Continuous-­ flow reactor

H2 yield 2.25 mol H2/mol sucrose

References Wu and Chang (2007)

Batch mode (serum vial)

Seol et al. (2011)

Sucrose

Continuously stirred tank bioreactor Batch mode (glass serum bottles)

1 mol H2/ mol formate 1.7 mol H2/mol sucrose 1.96 mol H2/mol glucose 2.1 mol H2/mol glucose

Kirli and Kapdan (2016)

3.45 mol H2/mol lactose

Rai et al. (2012)

Acid-­ hydrolyzed wheat starch Acid-­ hydrolyzed wheat starch

Batch mode (serum bottles)

Cheese whey Batch mode

Wu et al. (2007) Gokfiliz and Karapinar (2017)

adsorption, which is a type of physical immobilization. The adsorption mechanisms are based on electrostatic and/or hydrophobic interactions and van der Waal forces. Microbial adsorption is typically not harmful to microbial activity when it doesn’t involve a functionalized support. There may be only very few attached microorganisms, and the cells may only be loosely connected. For adsorption immobilization techniques, cell desorption appears to be a crucial problem. Dark fermentative hydrogen generation has made use of both trapping and adsorption. To tackle bacterial washout, which is common in the conventional continuous stirred tank reactor (CSTR) systems (see Table 4.4) at low hydraulic retention time, the effect of different aspect ratios, height to diameter of 1:1, 3:1, and 5:1, of a CSTR with immobilized anaerobic sludge (HRT) was investigated (Wu et al. 2013). The silicone gel entrapment technique was used to immobilize the thermally treated sludge. At a low HRT, the entrapped sludge system maintained stability without experiencing cell washout. As a result, increasing organic loading rates increased the rate at which hydrogen was produced. The findings demonstrated that the rate of granulation and hydrogen production was both increased by over ten times. In a continuous mixed immobilized sludge reactor, Han et al. (2015) employed activated carbon in the H2 generation from enzymatically hydrolyzed food waste. In an upflow anaerobic sludge bed system, Sun et al. (2016) investigated fermentative H2 production from an effluent herbal medicine plant. To keep the microorganisms in the sludge, they immobilized it on granular activated

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Table 4.4  Bioreactors used for fermentative H2 production S.N. Reactor type Advantages 1 Continuous stirred Capable of providing effective gas transfer tank reactor (CSTR) to cells; simple to monitor, and easy controlling scale-up An impeller is used for mixing, and the impeller speed will be high enough to ensure that the composition of the vessel’s contents is consistent Effective treatment and the capacity to 2 Upflow anaerobic maintain high biomass concentration sludge blanket reactor (UASB) 3 Granular sludge bed Compared to the CSTR, the hydraulic reactor (GSBR) mixing regime is less turbulent, which increases the mass transfer resistance Good biomass retention 4 Anaerobic packed bioreactor (APB)

Disadvantages Low biomass retention

Slow development of granules Excessive shear stress can detach biomass Clogging and lower mass transfer than FBR

Based on Bakonyi et al. (2014)

carbon. They next investigated how different organic loading rates affected hydrogen generation. In their investigation, Yin and Wang (2016) used PVA-sodium alginate to capture Enterococcus faecium INET2 strain for the formation of dark fermentative hydrogen. Immobilization has been proven to be beneficial in the hydrogen production system because it can reduce end-product inhibition (Hawkes et  al. 2002), shield microorganisms from the harmful effects of pollutants (Guo et al. 2008), and also stop biomass washout. Through metabolic engineering, pathways can be changed to boost the synthesis of biological hydrogen. The important enzyme activity can be improved, the flow of electrons can be increased, and the expression of genes can be changed by metabolic engineering. It has immense potential to get over the hurdles (Hallenbeck et al. 2012). Metabolic engineering could be applied at many levels to dark fermentation for enhancing the process. The two fundamental phases in producing hydrogen from organic wastes are the conversion of complex substrates into important metabolic intermediates and the conversion of those intermediates into hydrogen. Both of the above steps may include metabolic engineering. A wide variety of complex substrates, such as lignocellulosic substrates, can be used directly by an organism by adding pathways through metabolic engineering. In addition, it can add pathways to encourage the conversion of a wider variety of monomers, such as hexose, xylose, pentose, etc., to important metabolic products (pyruvate). By modifying the already existing routes or giving common microorganisms new pathways to use, it is possible to increase the creation of hydrogen throughout the fuel generation process. Today, a wide range of tools are accessible to accomplish all these different forms of alteration. Khanna et al. (2011a, b) investigated how Enterobacter cloacae could increase the production of H2 by rerouting metabolic pathways, because NADH is often formed in glycolysis and because NADH is then oxidized

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to make hydrogen. However, NADH is depleted during the change of pyruvate to ethanol and acids such as lactic and butyric acid. Thus, they tried to reroute the pathways to stop the formation of alcohol and acids in E. cloacae IIT-BT 08, increase the available NADH for H2 production, and obtain H2 yield and H2 production rate that were, respectively, 1.2 and 1.6 times higher than the wild type of strain. These values were 2.26  mol H2/mol hexose and 1.25  L H2/L/h. Coproduction of hydrogen and ethanol from glucose in Escherichia coli was improved by deleting phosphoglucose isomerase and overexpressing glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase (Sekar et al. 2017). The use of nanotechnology-based methods has taken on a new thrust to increase H2 productivity by enhancing microbial bioactivity along several pathways (Patel et al. 2018). The formation of microbial H2 is mediated by the enzymes nitrogenase and hydrogenase, and the presence of metal ions (such as Ni and Fe) at their active sites is modulated by the addition of nanoparticles to the growth medium (Mishra et al. 2019). Several studies have looked into the applications of improved nanometals and their oxides for improving fermentative H2 production during the past few years. To improve the production of H2 through the fermentative process, various researchers have looked into the extraordinary range of unusual structures and exceptional catalytic activity of nanoscale materials (Mudhoo et  al. 2018). Ag-oxides, Au-oxides, CuO2, Fe, Fe2O3, Fe3O4, Ni, NiO, CoO, Pd-oxides, SiO2, carbon nanotubes, and TiO2 have all been studied and used as the catalyst for fermentative H2 synthesis among the multitude of nanoscale materials. According to Zhang and Shen’s investigation into the use of gold oxide nanoparticles, the inclusion of 5-nm gold nanoparticles increased H2 productivity from synthetic wastewater by 46% (Zhang and Shen 2007). The increased affinity for electrons of the gold nanoparticles, which operated as an electron sink and enabled the further reduction of protons into H2 in the fermentative medium, was hypothesized to account for the increase in yield. The ability of the nanoparticles to quickly permeate cell membranes and cause cell lysis makes them act as antibacterial agents as well. Thus, the immobilization of nanoparticles had a favorable effect on the generation of H2 by microbes. The inclusion of nanoparticles of Pd, Ag, Cu, and Fe oxides immobilized in a porous silica matrix has been reported to significantly improve H2 yield (Beckers et al. 2013). Furthermore, it has been shown that the addition of NiO2 and CoO2 nanoparticles to the substrate significantly increased H2 production by 1.51- and 1.61-fold, respectively (Mishra et al. 2019). In addition to these, a significant impact on the improvement of H2 yield was seen while studying several nanoparticles of metal ions and oxides using various carbon sources. Nanoparticles primarily boost H2 production by having significant effects on microbial metabolism, substrate conversion efficiency, and microbial growth. In the presence of nanoparticles, the production of intermediate metabolites such as acetate and butyrate moves toward greater levels, whereas the formation of alcohol decreases which is an inhibitor of H2 generation (Nath and Das 2004). As the least amount of toxicity of nanoparticles on fermentative microorganisms is essential, there are still questions about the appropriate nanoparticle concentrations. To balance their catalytic activity and avoid feedback inhibitions, the metalloenzymes require the proper doses

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(Shanmugam et al. 2020). For better H2 generation, it is also necessary to investigate the identification of novel nanoparticles with significant physicochemical features from different sources. Along with attempting to speed up the substrate breakdown rate, attention is drawn to energy that is still in the liquid state. There is still a significant amount of energy in the liquid metabolites following dark fermentation. To increase the rate of energy recovery, various procedures are combined into a multistage fermentation process to recover the remaining energy that is present in the liquid phase. Two-­ stage H2 and CH4 synthesis alternate dark and photo-fermentation, and H2 production and other by-products are the critical elements of the combination. The dark fermentative H2 generation procedure transforms raw materials into H2, volatile fatty acids, and alcohols. The use of these soluble metabolites in photo-­ fermentation can increase the hydrogen output of the overall hydrogen production process. Additionally, by integrating photo-fermentation, high-acid and high-­ alcohol organic wastes can be used, broadening the range of substrate supplies (Argun and Kargi 2011). Twelve mol H2/mol hexose is the simulated value yield for two-phase dark and photo-fermentation. Therefore, it is possible to boost hydrogen generation while also regulating effluent by sequential mixing of dark and photo-fermentation. By including a photo-fermentation procedure following the dark fermentation, Chen et al. (2008) were able to enhance the hydrogen generation from 1.9 to 7.1 mol H2/mol hexose, and they also acquired a COD elimination of about 90%. The hydrogen yield and heat value conversion efficiency increased from 1.59 to 5.48 mol H2/ mol glucose and from 13.3% to 46.0%, respectively, through the combination of dark and photo-fermentation (Su et  al. 2009). By combining dark and photo-­ fermentation, Morsy (2017) was able to constantly create hydrogen from molasses, yielding 5.65 mol H2/mol glucose. For the first time, Zhang et al. (2018) investigated the synthesis of hydrogen from maize stover using a pilot-scale dark and photo-fermentative process. The output can also be employed for CH4 production in addition to photo-­ fermentation, maximizing the process’s capacity to retrieve energy. When compared to conventional methane fermentation, two-step H2-CH4 fermentation can help maximize the production of both hydrogen and methane independently depending on the appropriate conditions and prevent the reformation of hydrogen to methane. In a two-stage process, H2 and CH4 were produced from house waste by Liu et al. (2006). The hydrogen yield was 43 mL H2/g VS and the methane yield was 500 mL CH4/g VS, which was 21% greater than the methane yield from the one-stage procedure. When palm oil mill effluent was used as the substrate for a two-stage hydrogen-­methane fermentation, Krishnan et al. (2017) got hydrogen and methane yields of 1.73 mol H2/mol hexose and 2.57 mol CH4/mol hexose, and the overall COD removal efficiency was 94%. Studies also look into the potential for manufacturing other bioproducts in addition to hydrogen. These goods mostly consist of acids and alcohols like butyrate and ethanol. The dark-photo-fermentative reactor created by Liu et al. (2015) produced 4.96 mol H2/mol sugar and 0.82 mol ethanol/mol sugar. Islam et al. (2018)

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studied the synthesis of hydrogen and volatile fatty acids from a two-step dark fermentation with acid treatments using diluted solutions. According to the results, hydrogen, butyric acid, and acetic acid had the highest yields at 5.77 mmol/g substrate, 2.07 g/L, and 2.17 g/L, respectively. Production of hydrogen, acetic acid, and butyric acid increased by 76%, 113%, and 84% when compared to the single step, respectively. A fresh approach to improving the value and energy recovery effectiveness of dark fermentative H2 production is the creation of valuable organic acids or alcohols. The majority of organic acids and alcohols are soluble, which makes their purification, separation, and recovery challenging. Separation of acid and alcohol and the fermentation process may be beneficial to improve the simultaneous production of hydrogen and by-products, taking into account the product-­ inhibitive effect.

4.5 Conclusion With a high rate of hydrogen production, an easy reactor design, and simple management and operation, dark fermentation offers the highest chances for a practical application. Environmental and financial advantages can be increased, particularly when organic wastes are employed as the substrate. The effectiveness of the entire system’s hydrogen production is largely dependent on the microbes present because it is a process that is dominated by microbial metabolism. To increase the hydrogen yield, a lot of work has been put into understanding the microbiological side of the H2 production process, beginning with microbes. Pure cultures yield a lot of hydrogen. Although newer H2 producers have been obtained and identified, little is known about the mechanisms that underlie the highly effective hydrogen producers of some isolates. Mixed cultures are more suitable for practical applications, and various inoculum sources and treatment techniques have been investigated to produce a lot of hydrogen. The critical elements that influence the evolution of dominant microorganisms and the interactions among dominant microbial communities, however, are still lacking in research. Second, four different types of fermentation and two typical metabolic pathways have been identified. However, the hydrogen yield of 4 mol H2/mol hexose cannot be easily overcome by conventional approaches for hydrogen generation. To attain both a significant hydrogen yield and a fast rate of substrate degradation, synthetic enzymatic hydrogen synthesis appears to be a good option. This technology is still in its infancy, though. Further research must be done to see whether the synthetic enzymes can be produced in large quantities, recovered, and used again. Third is genetic engineering. Without hydrogenases’ catalysis, it is impossible to produce hydrogen. Deletion of hydrogen-uptake hydrogenase, genetic insertion of heterologous hydrogenase, and overexpression of hydrogenase are examples of genetic manipulation targeting the expression and activity of hydrogenases. To comprehend oxygen-tolerant hydrogenase and provide guidance for molecularly altering hydrogen producers, oxygen tolerance of hydrogenase is also investigated. All of these techniques are successful in increasing hydrogen yield, but

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more research is needed to understand how modified microorganisms spread and remain stable. Fourth is the cooperation of microbes. Multiple microorganisms must work together for the multistep process of converting organic materials to hydrogen. Degradation processes can be more complicated, particularly when actual organic wastes are employed as the substrate. In this situation, inoculating strains by the substrate can aid in reducing the time needed for adaptation and improving hydrogen generation. Numerous research have examined the roles played by various strains in the production of hydrogen, but few have investigated how to increase hydrogen production by manually modifying microbial cooperation. The fifth point is multistage energy recovery. Dark-photo-fermentation and hydrogen-­ methane fermentation are the two types of multistage fermentations that have been used to increase the efficiency of energy conversion. Liquid metabolite recovery can improve hydrogen yield and by-product recovery at the same time. However, as this technology is still in its early stages, other technologies, such as microbial fuel cells, can be taken into account for the separation and concentration of the by-products.

References Argun H, Kargi F (2011) Bio-hydrogen production by different operational modes of dark and photo-fermentation: an overview. Int J Hydrog Energy 36(13):7443–7459 Bagi Z, Acs N, Balint B, Horvath L, Dob K, Perei KR, Kovacs KL (2007) Biotechnological intensification of biogas production. Appl Microbiol Biotechnol 76(2):473 Bakonyi P, Nemestóthy N, Simon V, Bélafi-Bakó K (2014) Fermentative hydrogen production in anaerobic membrane bioreactors: a review. Bioresour Technol 156:357–363 Beckers L, Hiligsmann S, Lambert SD, Heinrichs B, Thonart P (2013) Improving effect of metal and oxide nanoparticles encapsulated in porous silica on fermentative biohydrogen production by Clostridium butyricum. Bioresour Technol 133:109–117 Benemann J (1996) Hydrogen biotechnology: progress and prospects. Nat Biotechnol 14(9):1 Bernstein HC, Carlson RP (2012) Microbial consortia engineering for cellular factories: in vitro to in silico systems. Comput Struct Biotechnol J 3:e201210017 Bundhoo MAZ, Mohee R (2016) Inhibition of dark fermentative bio-hydrogen production: a review. Int J Hydrog Energy 41(16):6713–6733 Cappelletti BM, Reginatto V, Amante ER, Antonio RV (2011) Fermentative production of hydrogen from cassava processing wastewater by Clostridium acetobutylicum. Renew Energy 36:3367–3372 Chen C, Yang M, Yeh K, Liu C, Chang J (2008) Biohydrogen production using sequential two-­ stage dark and photo fermentation processes. Int J Hydrog Energy 33(18):4755–4762 Chu CY, Wu SY, Wu YC, Sen B, Hung CH, Cheng CH, Lin CY (2011) Phase holdups and microbial community in high-rate fermentative hydrogen bioreactors. Int J Hydrog Energy 36(1):364–373 Cofre O, Ramírez M, Gomez JM, Cantero D (2016) Pilot scale fed-batch fermentation in a closed loop mixed reactor for the biotransformation of crude glycerol into ethanol and hydrogen by Escherichia coli MG1655. Biomass Bioenergy 91:37–47 de Vrije T, Budde MAW, Lips SJ, Bakker RR, Mars AE, Claassen PAM (2010) Hydrogen production from carrot pulp by the extreme thermophiles Caldicellulosiruptor saccharolyticus and Thermotoga neapolitana. Int J Hydrog Energy 35:13206–13213 Fang HH, Liu H, Zhang T (2002) Characterization of a hydrogen producing granular sludge. Biotechnol Bioeng 78(1):44–52

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Gaffron H, Rubin J (1942) Fermentative and photochemical production of hydrogen in algae. J Gen Physiol 26(2):219–240 Garcıa RE, Martınez VL, Franco JI, Curutchet G (2012) Selection of natural bacterial communities for the biological production of hydrogen. Int J Hydrog Energy 37(13):10095–10100 Gokfiliz P, Karapinar I (2017) The effect of support particle type on thermophilic hydrogen production by immobilized batch dark fermentation. Int J Hydrog Energy 42(4):2553–2561 Gorrell T, Uffen R (1977) Fermentative metabolism of pyruvate by Rhodospirillum rubrum after anaerobic growth in darkness. J Bacteriol 131(2):533–543 Guo L, Li X, Bo X, Yang Q, Zeng G, Liao D, Liu J (2008) Impacts of sterilization, microwave and ultrasonication pretreatment on hydrogen producing using waste sludge. Bioresour Technol 99(9):3651–3658 Hallenbeck PC, Ghosh D (2009) Advances in fermentative biohydrogen production: the way forward? Trends Biotechnol 27(5):287–297 Hallenbeck PC, Abo-Hashesh M, Ghosh D (2012) Strategies for improving biological hydrogen production. Bioresour Technol 110:1–9 Han W, Liu DN, Shi YW, Tang JH, Li YF, Ren NQ (2015) Biohydrogen production from food waste hydrolysate using continuous mixed immobilized sludge reactors. Bioresour Technol 180:54–58 Harun I, Jahim JM, Anuar N, Hassan O (2012) Hydrogen production performance by Enterobacter cloacae KBH3 isolated from termite guts. Int J Hydrog Energy 37(20):15052–15061 Hawkes FR, Dinsdale R, Hawkes DL, Hussy I (2002) Sustainable fermentative hydrogen production: challenges for process optimization. Int J Hydrog Energy 27(11–12):1339–1347 Hickey RF, Vanderwielen J, Switzenbaum MS (1989) The effect of heavy metals on methane production and hydrogen and carbon monoxide levels during batch anaerobic sludge digestion. Water Res 23(2):207–218 Hu CC, Giannis A, Chen C-L, Wang J-Y (2014) Evaluation of hydrogen producing cultures using pretreated food waste. Int J Hydrog Energy 39:19337–19342 Hung CH, Chang YT, Chang YJ (2011a) Roles of microorganisms other than Clostridium and Enterobacter in anaerobic fermentative biohydrogen production systems—a review. Bioresour Technol 102(18):8437–8444 Hung CH, Cheng CH, Guan DW, Wang ST, Hsu SC, Liang CM, Lin CY (2011b) Interactions between Clostridium sp. and other facultative anaerobes in a self-formed granular sludge hydrogen-producing bioreactor. Int J Hydrog Energy 36(14):8704–8711 Islam MS, Guo C, Liu C (2018) Enhanced hydrogen and volatile fatty acid production from sweet sorghum stalks by two-steps dark fermentation with dilute acid treatment in between. Int J Hydrog Energy 43(2):659–666 Jayasinghearachchi HS, Sarma PM, Singh S, Aginihotri A, Mandal AK, Lal B (2009) Fermentative hydrogen production by two novel strains of Enterobacter aerogenes HGN-2 and HT 34 isolated from sea buried crude oil pipelines. Int J Hydrog Energy 34:7197–7207 Jayasinghearachchi HS, Sarma PM, Lal B (2012) Biological hydrogen production by extremely thermophilic novel bacterium Thermoanaerobacter mathranii A3N isolated from oil producing well. Int J Hydrog Energy 37:5569–5578 Jung KW, Kim DH, Kim SH, Shin HS (2011) Bioreactor design for continuous dark fermentative hydrogen production. Bioresour Technol 102(18):8612–8620 Karthikeyan OP, Trably E, Mehariya S, Bernet N, Wong JWC, Carrere H (2018) Pretreatment of food waste for methane and hydrogen recovery: a review. Bioresour Technol 249:1025–1039 Khanna N, Kotay SM, Gilbert JJ, Das D (2011a) Improvement of biohydrogen production by Enterobacter cloacae IIT-BT 08 under regulated pH. J Biotechnol 152:9–15 Khanna N, Dasgupta CN, Mishra P, Das D (2011b) Homologous overexpression of [FeFe] hydrogenase in Enterobacter cloacae IIT-BT 08 to enhance hydrogen gas production from cheese whey. Int J Hydrog Energy 36(24):15573–15582

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Sekar BS, Seol E, Park S (2017) Co-production of hydrogen and ethanol from glucose in Escherichia coli by activation of pentose-phosphate pathway through deletion of phosphoglucose isomerase (pgi) and overexpression of glucose-6-phosphate dehydrogenase (zwf) and 6-phosphogluconate dehydrogenase (gnd). Biotechnol Biofuels 10(1):85 Seol E, Manimaran A, Jang Y, Kim S, Oh YK, Park S (2011) Sustained hydrogen production from formate using immobilized recombinant Escherichia coli SH5. Int J Hydrog Energy 36(14):8681–8686 Seppala JJ, Puhakka JA, Yli-Harja O, Karp MT, Santala V (2011) Fermentative hydrogen production by Clostridium butyricum and Escherichia coli in pure and cocultures. Int J Hydrog Energy 36:10701–10708 Shanmugam S, Hari A, Pandey A, Mathimani T, Felix L, Pugazhendhi A (2020) Comprehensive review on the application of inorganic and organic nanoparticles for enhancing biohydrogen production. Fuel 270:117453 Sharma P, Melkania U (2018) Enhancement effect of amino acids on hydrogen production from organic fraction of municipal solid waste using co-culture of Escherichia coli and Enterobacter aerogenes. Energy Convers Manag 163:260–267 Singh L, Siddiqui MF, Ahmad A, Rahim MH, Sakinah M, Wahid ZA (2013) Biohydrogen production from palm oil mill effluent using immobilized mixed culture. J Ind Eng Chem 19(2):659–664 Sinha P, Pandey A (2014) Biohydrogen production from various feedstocks by Bacillus firmus NMBL-03. Int J Hydrog Energy 39(14):7518–7525 Su H, Cheng J, Zhou J, Song W, Cen K (2009) Combination of dark- and photofermentation to enhance hydrogen production and energy conversion efficiency. Int J Hydrog Energy 34(21):8846–8853 Sun C, Hao P, Qin B, Wang B, Di X, Li Y (2016) Co-production of hydrogen and methane from herbal medicine wastewater by a combined UASB system with immobilized sludge (H2 production) and UASB system with suspended sludge (CH4 production). Water Sci Technol 73(1):130–136 Taifor AF, Zakaria MR, Mohd Yusoff MZ, Toshinari M, Hassan MA, Shirai Y (2017) Elucidating substrate utilization in biohydrogen production from palm oil mill effluent by Escherichia coli. Int J Hydrog Energy 42:5812–5819 Tanisho S, Suzuki Y, Wakao N (1987) Fermentative hydrogen evolution by Enterobacter aerogenes strain E. 82005. Int J Hydrog Energy 12(9):623–627 Vardar-Schara G, Maeda T, Wood TK (2008) Metabolically engineered bacteria for producing hydrogen via fermentation. Microb Biotechnol 1(2):107–125 Wang JL, Yin YN (2017a) Biohydrogen production from organic wastes. Springer, Singapore Wang JL, Yin YN (2017b) Principle and application of different pretreatment methods for enriching hydrogen-producing bacteria from mixed cultures. Int J Hydrog Energy 42(8):4804–4823 Wang J, Yin Y (2019) Progress in microbiology for fermentative hydrogenproduction from organic wastes. Crit Rev Environ Sci Technol 49(10):825–865. https://doi.org/10.1080/1064338 9.2018.1487226 Woodman H (1930) The rgle of cellulose in nutrition. Biol Rev 5(4):273–295 Woodman H, Evans R (1938) The mechanism of cellulose digestion in the ruminant organism: IV. Furt vitro studies of the behaviour of rumen bacteria and their bearing on the problem of the nutritive value of cellulose. J Agric Sci 28(1):43–63 Wu KJ, Chang JS (2007) Batch and continuous fermentative production of hydrogen with anaerobic sludge entrapped in a composite polymeric matrix. Process Biochem 42(2):279–284 Wu KJ, Lo Y, Chen S, Chang J-S (2007) Fermentative production of biofuels with entrapped anaerobic sludge using sequential HRT shifting operation in continuous cultures. J Taiwan Inst Chem Eng 38(3–4):205–213 Wu X, Li Q, Dieudonne M, Cong Y, Zhou J, Long M (2010) Enhanced H2 gas production from bagasse using adhE inactivated Klebsiella oxytoca HP1 by sequential dark-photo fermentations. Bioresour Technol 101(24):9605–9611

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Wu S, Chu C, Yeh W (2013) Aspect ratio effect of bioreactor on fermentative hydrogen production with immobilized sludge. Int J Hydrog Energy 38(14):6154–6160 Ye XH, Wang YR, Hopkins RC, Adams MWW, Evans BR, Mielenz JR, Zhang YHP (2009) Spontaneous high-yield production of hydrogen from cellulosic materials and water catalyzed by enzyme cocktails. ChemSusChem 2(2):149–152 Yin YN, Wang JL (2016) Characterization and hydrogen production performance of a novel strain Enterococcus faecium INET2 isolated from gamma irradiated sludge. Int J Hydrog Energy 41(48):22793–22801 Yokoi H, Tokushige T, Hirose J, Hayashi S, Takasaki Y (1998) H2 production from starch by a mixed culture of Clostridium butyricum and Enterobacter aerogenes. Biotechnol Lett 20(2):143–147 Zeidan AA, Van Niel EWJ (2009) Developing a thermophilic hydrogen-producing co-culture for efficient utilization of mixed sugars. Int J Hydrog Energy 34(10):4524–4528 Zhang Y, Shen J (2007) Enhancement effect of gold nanoparticles on biohydrogen production from artificial wastewater. Int J Hydrog Energy 32(1):17–23 Zhang YHP, Evans BR, Mielenz JR, Hopkins RC, Adams MWW (2007) High-yield hydrogen production from starch and water by a synthetic enzymatic pathway. PLoS One 2(5):e456 Zhang JN, Li YH, Zheng HQ, Fan YT, Hou HW (2015a) Direct degradation of cellulosic biomass to bio-hydrogen from a newly isolated strain Clostridium sartagoforme FZ11. Bioresour Technol 192:60–67 Zhang L, Chung JS, Ren NQ, Sun R (2015b) Effects of the ecological factors on hydrogen production and [Fe–Fe]-hydrogenase activity in Ethanoligenensharbinense YUAN-3. Int J Hydrog Energy 40(21):6792–6797 Zhang Q, Zhang Z, Wang Y, Lee D, Li G, Zhou X et al (2018) Sequential dark and photo fermentation hydrogen production from hydrolyzed corn stover: a pilot test using 11 m3 reactor. Bioresour Technol 253:382–386 Zhao H, Ma K, Lu Y, Zhang C, Wang L, Xing XH (2009) Cloning and knockout of formate hydrogen lyase and H-uptake hydrogenase genes in Enterobacter aerogenes for enhanced hydrogen production. Int J Hydrog Energy 34(1):186–194 Zhu HG, Beland M (2006) Evaluation of alternative methods of preparing hydrogen producing seeds from digested wastewater sludge. Int J Hydrog Energy 31(14):1980–1988

Chapter 5

Biohydrogen Production from Various Feedstocks: Biohydrogen Generation from Biomass Manmohan Kumar, Shagun Sharma, Jai Kumar, Shibnath Mazumder, and Usha Kumari Abstract The energy catastrophe has arisen as the utmost momentous obstruction in the development of human civilization. The swift waning of worldwide fossil fuel reserves is posing an inordinate threat to energy security. Therefore, efforts have been made to employ renewable energy sources including biogas and biofuel to shift away from the overdependence on fossil fuels. Hydrogen is a chief feedstock for industries due to its high energy density. While eco-friendly in nature, its commercialization as a fuel faces severe economic, environmental, and technological tailbacks. The employment of microbes for hydrogen synthesis can efficiently address these restrictions. Microbes offer many advantages, such as low-energy requirements, high growth rate, and requirement of costly pretreatment processes. Therefore, this chapter will address the current knowledge on biohydrogen production using microbes. Keywords Hydrogen production: biofuels · Ethanol · Advanced biofuels · Photofermentation

M. Kumar · S. Sharma · J. Kumar Immunobiology Laboratory, Department of Zoology, University of Delhi, New Delhi, India S. Mazumder Immunobiology Laboratory, Department of Zoology, University of Delhi, New Delhi, India Faculty of Life Sciences and Bio-Technology, South Asian University, New Delhi, India U. Kumari (*) Department of Zoology, Gargi College, University of Delhi, New Delhi, India © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024 P. Singh (ed.), Emerging Trends and Techniques in Biofuel Production from Agricultural Waste, Clean Energy Production Technologies, https://doi.org/10.1007/978-981-99-8244-8_5

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5.1 Introduction Today, in this twenty-first century, there is great mandate for chemical fuels as an energy fuel. But the world is facing innumerable challenges in keeping up with this requirement. Fossil fuels are single largest energy source for world’s energy needs and are primary supplier of energy (around 80%). However, these fossil fuels are exhaustible and also emit greenhouse gases (CO2, CO, and CH4) into the environment, ultimately resulting in pollution and global warming. Hence, the notion of sustainable energy development was progressed, where the needs of human are met while keeping the equilibrium with the nature for a livable future. Therefore, the need for clean and renewable energy sources is progressively imperative worldwide to deal with energy crisis issue and environmental deterioration issue. Among technologists, investigations to produce clean and sustainable energy fuel from renewable carbon source are being carried out. Among various alternative clean and renewable sources of energy, hydrogen (H2) is known as a major forthcoming environment friendly fuel. H2 is utmost plentiful element of the universe and, thus, can be a resounding source of energy and most importantly for the clean Earth. Although, as per the Royal Society of Chemistry, H2 is extremely limited in the atmosphere, it escapes quickly into the Earth’s gravity. Currently, the major proportion of H2 is extracted from fossil fuels (approximately 96%), from natural gas (48%), from hydrocarbons (30%), from coal (18%), and from electrolysis (4%), and only 1% is generated by biomass (Imam et al. 2013). H2 is regarded as the most imperative fuel as it is renewable and environment friendly and has low emission rate, no emission of greenhouse gases, high energy content, and high conversion efficiency, i.e., 1 kg of H2 holds approximately 120 mJ (Cheng et al. 2021) energy in comparison with any other known fuel. Thus, it exceeds most other traditional hydrocarbon-based fuels. It is easily convertible into electricity with the help of fuel cell and releases water (H2O) as the by-product on combustion (Das and Veziroglu 2008). H2 generated from renewable sources such as conversion of solid fuels (organic waste [biomass]) and natural gas via thermochemical reaction, water hydrolysis, or electrolysis, either biologically or photobiologically, i.e., green chemical reactions (Mona et al. 2020), is known as biohydrogen (bio-H2). The gaseous form of fuels has more uses than the liquid fuels. These can be used directly as the energy sources or can be used in compressed form such as CNG. Bio-H2 is a proficient energy hauler among various biofuels available in environment because of its huge proficiency in translating into a reusable power with an advanced energy density and lowermost output in pollution (Hallenbeck and Ghosh 2009; Nikolaidis and Poullikkas 2017). The production of biohydrogen via photosynthesis and anaerobic fermentation also has been reported. Photosynthesis requires sunlight; therefore, anaerobic fermentation technique is a choice for biohydrogen production over photosynthesis. In recent years, a wide variety of several microorganisms, e.g., cyanobacteria, microalgae, photosynthetic and fermentative bacteria, are exploited for production of bio-H2.

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5.2 Biofuels Biofuels are the fuels or energy sources generated from live organism or their body parts, biomass, or their waste products especially plants or microalgae by various chemical reactions. Biofuels can be in form of liquid like biodiesel and ethanol or in gaseous form like biohydrogen. Biofuels produced very less amount of greenhouse gases and thus least adverse impact on the environment and human beings. Based on various criteria, biofuels are categorized in various generations: ( A) Conventional biofuels (first generation biofuels) (B) Advanced biofuels (i) Second generation biofuels (ii) Third generation biofuels (iii) Fourth generation biofuels

5.2.1 Conventional Biofuels Conventional fuels are also called as first generation biofuels. These fuels are produced from agricultural crops, which are principally grown for the purpose of feeding. Conventional biofuels are mainly of two types: (i) biodiesel which is extracted from oil producing plants or plant materials (soybean, palm oil) and (ii) ethanol which is extracted from the crops having high content of sugar (e.g., sugar beet or sugarcane). The generation of biofuels with the help of food crops created difficulty in terms of less availability of food crops for feeding purpose and thus increased the probability of scarcity of such food crops for consumption. In order to resolve this challenge, waste food and plant materials which are no longer used for feeding purpose can be used to produce the biohydrogen. And the types of plant materials such as living, dead, or decomposed plant material which are used to generate the biohydrogen by using various methods are called biofuel feedstocks. The sources of feedstocks include products generated from the waste materials such as wood, food, farming crops, and other effluents produced by human and other animals. The criteria to select an appropriate feedstock depend on its availability, cost, carbohydrate contents, and biodegradability. Simple carbohydrate molecules like mono- and disaccharides are preferred for biohydrogen production over polysaccharides (Ziolkowska 2020). Feedstocks can be categorized in various types based on their sources, which are listed below (Fig. 5.1): (a) pure carbohydrates, (b) food and water wastes, (c) wastewater sludge, (d) feedstock supplements, and (e) future feedstocks. • Pure carbohydrate feedstocks. Both the simplest (glucose) and complex (sucrose, maltose, starch) carbohydrate molecules are used to produce the

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Fig. 5.1  Different feedstocks utilized for biohydrogen production. (Source: Author)

h­ ydrogen. Though the complex long chain carbohydrates require more time and energy in breakdown, simplest carbohydrates are preferred over complex. First complex molecules are converted into simplest single unit molecule and then hydrogen produced from them. This process makes the hydrogen production easy, efficient, and cost-effective. • Food and water waste feedstocks. Those food materials which are generated as waste product from industries, kitchen waste residues, and liquid wastes are used to produce hydrogen. As these wastes contain high amount of carbohydrate molecules as well as lipids, these can be converted into biohydrogen (Van Ginkel et al. 2005). Hydrogen can also be produced from fruits, vegetables, sugar production wastes and sugar beet effluents, manufacturing waste products, wheat bran, and other food product waste effluents produced during their processing. These wastes are used as feedstock to produce biofuels. This is important in terms of waste clearance from environment and reuse of wastes as useful material (Hussy et al. 2005). • Wastewater sludge feedstocks. Hydrogen can also be produced from wastewater sludge also. Wastewater contains very high amount of protein compared to carbohydrates. Therefore, the amount of H2 produced from wastewater sludge feedstock is lower than the other feedstocks containing carbohydrate molecules. • Feedstock supplements. Hydrogen production from microbial organisms requires specific microbial cultivation. Essential minerals like nitrogen (N) and phosphate (PO43−) are obligatory for desirable cultivation of microbial culture. Feedstocks can provide these nutrients for the growth of microbial communities and thus hydrogen production.

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5.2.2 Advanced Biofuels Use of feedstocks and many new techniques to produce the fuels from biotic component of environment led to the existence of advanced biofuels. Advanced biofuels are produced from nonfood grown feedstocks and wastes generated from agriculture (green wastes, wood, crop wastes, and energy crops planted primarily for generation of H2). Biofuels from feedstocks are important because these are not competing for natural resources (food crops) and helping in greenhouse gas reduction (Mendiara et al. 2018; Kousoulidou and Lonza 2016; Subramanian et al. 2018). According to global ethanol production by feedstocks 2017–2019 report, highest used feedstocks are coarse grains and sugarcane. The advanced biofuels are also known as developing fuels. There are many generations of advanced biofuels, which include (i) second generation biofuels, (ii) third generation biofuels, and (iii) fourth generation biofuels. 5.2.2.1 Second Generation Biofuels These are synthesized from crops, not meant for food, but grown for hydrogen production only. These are also derived from food wastes and wood. Example of second generation biofuel is ethanol, generated from material having cellulose in high concentration. The important sources of cellulosic ethanol are wheat straw, Jatropha plant, and poplar crops which are specifically grown for energy production. Another source of cellulosic ethanol is green wastes like fallen leaves, damaged stems, seed pods, and wastes obtained from forest. The major advantage of cellulosic biofuels is that wastes which are used to produce such fuels ultimately result in reduction of the accumulation of wastes and protection of the environment and organisms from its harmful effects. Most importantly, these feedstocks used for biofuel production generate the greenhouse gas emission savings. But the limitations of such fuels are that breakdown of cellulose and its processing cost are quite high. As its production cost is high, therefore it is not preferred over fossil fuels. Therefore, to reduce the cost in breaking down the cellulose, microbial or fungal system is used which helped in efficient and effective breakdown of cellulose and process (Bhatia et al. 2017; Ziolkowska 2014). 5.2.2.2 Third Generation Biofuels These fuels are produced by improvement in increasing biomass generation. Microalgae are the most important organisms used as feedstocks. Hence, the third generation biofuels include biofuels generated from microalgae. The microalgae naturally or artificially grown as well as genetically engineered play important role in bio-H2 production. Algal bio-H2 are more cost-effective compared to other

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feedstocks like cellulosic biofuels. The prime aim of these fuels is to improve the production of biomass and more sustainability. The advantages of algae biofuels are the following: 1. Algae growth rate is much higher than the crops; therefore, the amount of biohydrogen produced by algae is much greater than crops. 2. As oil content in algae is much higher than crops, high amount and variety of liquid biofuels like diesel, petrol, or gaseous biofuels like hydrogen can be produced. 3. Algae can grow in closed containers or in open land, so for these fertile land is not needed which can be used for growing crops. 4. Algae also do not need freshwater for growth; they can grow in saline or brackish water, thus helping in saving freshwater. • Most importantly algae reduce the carbon footprint, as they convert more CO2 into biohydrogen (Hon-Nami 2006). • High compatibility with traditional gasoline (Ziolkowska and Simon 2014). Despite having numerous advantages of biofuels generated from algal feedstocks, this is not a very much desirable biofuel due to high production cost. 5.2.2.3 Fourth Generation Biofuels These biofuels are generated by using new techniques like genetic engineering or nanotechnology. These biofuels utilize combinations of variety of techniques, processes, and feedstocks. Genetically engineered microalgae having high oil content can produce large amount of fuels. Metabolically engineered algae which have high oil content can produce good quantity of fuels after its improvement in cultivation, harvesting, and fermentation process. The criteria to select good feedstocks for synthesis of biofuels include its genetic level, high yield biomass production capacity, ratio of cellulose, and lignin content. Fourth generation biofuels are much better than second and third generation as they capture CO2 produced in the environment by different sources, store it, and transform it into biofuels in presence of O2. The remaining fuels after liquefaction produced biohydrogen and biomethane or other fuels that can be utilized in vehicle or electricity generation. Therefore, fourth generation fuels can be called as carbon negative instead of carbon neutral. 5.2.2.4 Future Feedstocks The use of nanotechnology enhances the efficiency of generation of algal biomass and decreases the production cost. Microalgae have been reported as the future feedstocks. There are a large number of advantages of microalgae as feedstocks: • Algae can synthesize and accumulate large amount of neutral fats.

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• Their doubling time is very high, so they grow very fast. • They can survive in saline, brackish, or seawater, so there is no need for freshwater for culture. • They can be grown in desert or semidesert regions. • They can utilize nutrients from wastewater and can help in bioremediation. • During culture, they can produce many useful by-products also like proteins, polysaccharides, and polymers. • Most importantly, they sequester carbon emitted from fossil fuels, therefore helping in greenhouse gas reduction. • Some algae which are the potential candidates for feedstocks are Nannochloropsis, Isochrysis galbana, Scenedesmus, and Schizochytrium limacinum (Singh and Gu 2010). Microalgae represent the good inexhaustible energy source. Bio-H2 and methane can be generated from microalgae, which are cost-effective, renewable, and easy to use for various technologies. Microalgae are used to produce both liquid biofuels like biodiesel and bioethanol and biohydrogen (H2) and biogas (methane). However, the energy consumed in liquid biofuel production is much greater than the gaseous fuel like biohydrogen. The proficiency of bio-H2 production by various processes is different. For example, highest yield and output is high genetically modified organisms, followed by indirect photolysis, dark fermentation, photofermentation, and direct photolysis (Wang et al. 2021). The synthesis of bio-H2 can be done directly or indirectly, depending upon the sunlight, or via thermochemical techniques or fermentation process through conversion of biomass (Limongi et al. 2021). There are four major mechanisms of biohydrogen production (Fig.  5.2): (1) direct photolysis, (2) indirect photolysis, (3) photofermentation, and (4) dark fermentation.

5.2.3 Direct Photolysis This method directly exploits the ability of microalgae and cyanobacteria in transferring the solar energy into chemical energy, i.e., resulting in direct biophotolysis of water via photosynthesis. H2 is produced from engagement of direct sunlight and electron transfer to two diverse enzymes, nitrogenases, and hydrogenases. At the time of anaerobic conditions or storage of undue energy, photosynthetic microbes release excess electrons which transform H- to H2 via hydrogenase (Turner et al. 2008). However, photosynthetic microbes produce O2 other than H2, which ultimately restrict H2 generation (Kapdan and Kargi 2006). Investigation is being carried out to manipulate microbes to utilize solar energy in generation of bio-H2, along with minimum energy requirement for the maintenance of cell to prevent O2 buildup. Biohydrogen can be produced by certain microorganisms such as algae directly under specified circumstances. Green algae induce hydrogenase signaling pathway for the production of biohydrogen via photosynthesis using solar energy

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Fig. 5.2  Four major mechanisms of biohydrogen production. (Source: Author)

under anaerobic and sulfur deprivation conditions. This direct biophotolysis generally occurs for only a short duration, during which light energy is fixed by PS I and PS II, which reduces water molecules by transferring electrons to ferredoxin and producing biohydrogen (Benemann 2000). The benefits of this procedure for biohydrogen production are that it is easily accessible from the environmental as it is readily available in the nature. However, this is long-term procedure in terms of the application because of sensitivity of the hydrogenase pathway to O2 and quite intricate unregulated pathways (Mona et al. 2020). In this line, many investigators are also venturing out to identify or maneuvering of microorganisms which are comparatively resistant to O2, altering the ratio of photosynthesis-respiration. Several reports suggested that sulfate dosage can reduce O2 production, but on the other hand it also halts the biohydrogen production (Turner et al. 2008).

5.2.4 Indirect Photolysis Indirect biophotolysis method has been explored in order to circumvent the difficulties in direct biophotolysis due to inhibitory effect of O2. It has been reported that indirect biophotolysis sustains biohydrogen production, and two-stage procedure has been adopted for segregation of evolution of H2 and photosynthesis (Nagarajan et  al. 2021). First stage is photosynthesis along with production of biomass; and Chlamydomonas reinhardtii (which is sulfur deficient) supported with acetate can sustain H2 separation for long time till antagonistic events of sulfur consumption show up which may lead to reduced yield of biohydrogen (Nagarajan et al. 2021).

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Indirect biophotolysis can be considered for practical use if the proficiency of photon conversion can be improved; high yield of biohydrogen is possible via indirect biophotolysis if 10–15% of light transformation efficiency could be achieved. First stage is influenced by several factors such as temperature, light, nutrients, pH, source of carbon, and bioreactor type (Rashid et al. 2013). Such parameters are also crucial at the second stage as well; in addition, biomass accumulation may also restrict indirect biophotolysis of bio-H2.

5.2.5 Photofermentation Scientists have developed the use of raw materials such as biomass and residual biomass as prime sources in microbial fermentation for bio-H2 production (Bhatia et al. 2021), to overcome the drawbacks associated with the direct and indirect biophotolysis. The production of H2 can be done via biological pathway by using light-­ driven fermentation mechanism in which light facilitates biomass (such as microalgae) to generate energy by photosynthesis, hence, evading dilapidation of pyruvate, and limit the complications of respiratory ATP production. Photofermentation occurs only in existence of light. The electrons are extracted from organic substrate via photo catabolism coupled with metabolism of oxidative carbon. The efficacy of photoconversion to bio-H2 usually displays standards of approximately 100%, but such estimations normally disregard energy value of organic substrates (Hallenbeck and Benemann 2002). Under ideal light situations (i.e., low light), the efficiency of photosynthesis is much lesser practically. Though hydrogenases are found in photosynthetic microbes, the photoproduction of bio-H2 by such photosynthetic microbes is primarily done via nitrogenase (Basak and Das 2007).

5.2.6 Dark Fermentation Bio-H2 production via organic molecules is a promising technique for the advancement in sustainable energy (Zhang et al. 2021). In comparison with processes for bio-H2 production where energy is derived from sunlight, microorganisms can generate H2 anaerobically by conversion of organic molecules in absence of sunlight (Show et al. 2019a). The rate of fermentation significantly differs in incidence of light and in its absence. At the time of dark fermentation, organic molecules are transformed by diverse phases, e.g., acidogenesis, acetogenesis, and hydrolysis (Show et al. 2019b). Bio-H2 production via dark fermentation has fascinated supplementary attention due to its recompenses of environmental sustainability, huge energy efficiency, and favorable balance in carbon levels. Nevertheless, it is imperative to augment biological activity in addition to advance electron transfer in microbial fermentation to sidestep thermodynamic and kinetic coerces of anaerobic

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fermentation process (Cheng et al. 2021). Growing pieces of evidence demonstrated that the production of biohydrogen can be boosted by using metals or nanoparticles of metal oxide (e.g., NiO, Fe2O3, and FeO), considering that bioactivity of hydrogenase and ferredoxin oxidoreductase is enhanced including electrons transfer as well (Gadhe et  al. 2015). Furthermore, it is also necessary to pretreat biomass beforehand anaerobic fermentation in order to upsurge the bio-H2 generation. Several pretreatment techniques like chemical, physical (hydrodynamic cavitation, bead milling, microwave, ultrasonication, pulse-electric field), thermal (autoclaving, steam explosion, freeze thaw, hydrothermal methods), biological (hydrolysis using bacterial and fungal enzymes), and various combinations are effective for refining the yield of biohydrogen production (Mandotra et al. 2021). For example, acid-hydrogen peroxide-induced microwave process significantly improves production of biohydrogen by Ulva reticulate (Kumar et al. 2019).

5.3 H2-Synthesizing Enzymes The production of biohydrogen from microorganisms relies upon the H2-synthesizing enzymes. Nitrogenase and hydrogenase are the two most vital enzymes which are required for generation of biohydrogen.

5.3.1 Nitrogenase It is a bivalent protein structure which transfers electrons extracted from reduced ferredoxin or flavodoxin and MgATP for reducing different substrates (Hallenbeck and Benemann 2002), but in presence of nitrogen gas. Only cyanobacteria contain these enzymes due to the presence of specialized cells known as heterocyst in them. Nitrogenase catalyzes an irreversible reaction which hydrolyzes four ATP (at least) for each molecule of synthesized H2. In each cycle, MgATP conjugated with MoFe protein which hydrolyzes two ATP via transfer of one electron to MoFe protein (Hallenbeck and Benemann 2002). A massive amount of input energy is mandatory for the synthesis of H2, and thus, in a conclusive scenario, nitrogenase isn’t an effective enzyme system for biohydrogen production.

5.3.2 Hydrogenase It is a critical enzyme required in H2 generation pathways by catalyzing the reduction of H+ to H2, where proton acts as the electron acceptor. The hydrogenase enzymes have been reported in Chlorococcales and Volcocales (Mona et al. 2020). In case of phototrophic microbes, only some genera of green microalgae and

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cyanobacteria contain hydrogenases. However, the activity, functional processing, and variations in structure have been reported in the hydrogenase enzymes belonging to different species. Hydrogenases can be defined as the metalloenzymes which contain iron-sulfur clusters (Fe-S clusters) in their active sites which are responsible for catalyzing reversible oxidation of H+ and electrons (Nagarajan et  al. 2021). Hydrogenase enzymes can be subdivided into different categories based upon metal composition in their active sites—Fe-Fe hydrogenase, Ni-Fe hydrogenase, and metal-free hydrogenase (Gadhe et al. 2015). The reversible activation of H2 occurs at a high rate in case of Fe-Fe hydrogenase due to its prosthetic group, thus suggesting Fe-Fe hydrogenase is proficient producer of biohydrogen. On the other hand, Ni-Fe hydrogenase is more efficient in oxidation of H2 (Lu and Koo 2019). The Fe-Fe hydrogenase enzyme is involved in light fermentation due to the vigorous upsurge in H2 release, and these enzymes are irrevocably deactivated by very less amount of oxygen, whereas the Ni-Fe hydrogenase is also suppressed by the presence of oxygen, but it is reactivated after the elimination of the oxygen (Lu and Koo 2019).

5.4 Factors Affecting Production of Biohydrogen Various factors are responsible which impacts biohydrogen production. These factors are discussed below:

5.4.1 Composition of Substrates Various reports have suggested simple sugars like sucrose and glucose are employed as crucial organic molecules for bio-H2 production, although numerous scientists are increasingly focusing upon usage of several organic wastes like industrial (dairy, distillery, beverage rice slurry, and food processing) and agricultural wastes (wheat straw, corn straw, and sugarcane molasses frequently used for anaerobic fermentation process) for biohydrogen generation. The major components used as substrates for the bio-H2 production include proteins, carbohydrates, and lipids. 5.4.1.1 Carbohydrates The substrates rich in carbohydrates are apt for anaerobic fermentation procedures which comprise processing of food wastes like rice slurry, wastes produced in sugar, distillery, and potato processing. Hydrolytic bacteria produce simple sugars, for example, sucrose and glucose, by hydrolysis of carbohydrate sources; and these simple sugars are then used up by anaerobic bacteria for the synthesis of biohydrogen (Aceves-Lara et al. 2008). H2 generated by glucose fermentation via bacterial

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action is somewhat inadequate at 4 mol/mol, and usually the recoverable amount is 2–3  mol/mol only with respect to the stoichiometric potential of 12  mol/mol (Niessen et al. 2005). Processes for bio-H2 generation from hydrolysis of cellulose and glucose fermentation are comparatively well understood and achievable (Hawkes et  al. 2007). However, additional conversion of residual organic acids (e.g., acetic acid) can’t be attained with the help of bacteria without substituting additional energy sources. Hence, fermentation processes for biohydrogen generation are restricted to sugars only, and maximum yield with such substrate is 33% only (Niessen et  al. 2005). Even, agriculture-based generated wastes are crucial source of celluloses, hemicelluloses, and lignocelluloses. These are also utilized for biohydrogen production (Xiao et al. 2013). However, major disadvantage of using such products involves unusual dilapidation of crystalline lattice by the microbes, and due to this, various chemical treatments such as alkaline and acidic treatment and steam explosion are required. Furthermore, biohydrogen can be generated from other waste substances such as paper mill wastes, molasses, and glycerol-based wastewater, dairy wastes, municipal solid waste, and industrial and domestic wastes. 5.4.1.2 Lipids Sources of lipid molecules for biohydrogen production include oil and dairy products and waste generated during processing of the food. Lipase is the key enzyme responsible for hydrolysis of the lipids. Lipid hydrolysis produces free fatty acids and glycerol, consequently converted to acetyl CoA, acetate, and H2 by NADH oxidation via β-oxidation pathway (Karadag et al. 2015). Accumulation of volatile fatty acids inhibits hydrolysis of lipids by lowering pH. However, the lipid hydrolysis is less efficient in terms of time in generating biohydrogen in comparison with carbohydrates. 5.4.1.3 Proteins The food waste and wastes generated during food processing, for example, cheese whey, fish flesh, eggs, casein, and various additional proteins, are utilized for the synthesis of bio-H2 (Wu et al. 2006). Proteins from these sources are catabolized into polypeptides and then amino acids via proteases of bacteria and finally converted into volatile fatty acids, CO2, and H2. Various protein processing waters derived from brewery and diaries are at present employed for the bio-H2 production as wastewaters from such sources contain nitrate, NH3, phosphates, and proteins.

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5.4.2 Temperature It is one of the most imperative factors required for the production of the biohydrogen. The changes in temperature affect metabolic signaling pathways which significantly influence hydrogenic activity, growth of the bacteria, and thus, biohydrogen generation. High temperature facilitates the production of biohydrogen; however, an increase in the temperature above a certain threshold result in the reduction in the production of biohydrogen (Wang and Wan 2009; Singh and Rathore 2017). Fluctuations in the optimum temperature range impact consumption of substrates and metabolites such as formation of the volatile fatty acids. The production of biohydrogen uses mesophilic conditions (i.e., 30–39 °C) because of the requirement of the least expensive technologies at this temperature range. However, this condition also facilitates the growth of the bacteria responsible for the production of non-­ hydrogen molecules. Furthermore, mesophilic bacterial species can’t exploit cellulose as the substrate, thus necessitating the use of the additional cellulase enzymes for hydrolysis of cellulose for biohydrogen production. In contrast to this, thermophilic (50–64 °C) and hyperthermophilic (>64 °C) conditions appeared more promising in biohydrogen generation. The bacterial species used in these conditions can hydrolyze cellulose, and the hydrolysis of the substrates is also efficient. The frequently employed bacterial species for biohydrogen production are Thermoanaerobacterium, Enterobacter, and Clostridium.

5.4.3 Enzymes Enzymes are considered as the imperative factors responsible for biohydrogen production, and even few minute alterations in operating conditions can significantly influence enzymes’ activity in bio-H2 production process. Two major enzymes in H2 fermentation activity are formate hydrogen lyase and iron-iron hydrogenase. H2 is produced from formic acid under anaerobic environment by formate hydrogen lyase in an acidic environment. In this process, formic acid acts as an electron donor, and H+ acts as electron acceptors. Catalytic activity of formate hydrogen lyase is mainly due to its catalytic activity in bio-H2 production via facultative anaerobic bacteria (Kim et al., 2008).

5.4.4 Partial Pressure of H2 The superfluous generation of biohydrogen triggers a negative impact during fermentation process; therefore, the partial pressure of H2 impacts the bioreactor during generation of biohydrogen (Lin et al. 2009). Partial pressure of H2 is directly proportionate with respect to temperature. Partial pressure of H2 more than 60 Pa is

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unfavorable for H2 production due to significant difference in ratio of H+/H2 which restricts electron transport from reduced ferredoxin to molecular H2 (Monlau et al. 2013). The most favorable conditions for the generation of biohydrogen is 20 kPa at 70 °C, 50 kPa at 60 °C, and 2 kPa at 98 °C (Hawkes et al. 2002; Calusinska et al. 2010). Pretreatment procedure can be categorized into physical, chemical, physiochemical, and biological methods.

5.4.5 Pretreatment of the Substrates The pretreatment is utmost decisive step in the bio-H2 production due to the complex structural dimensions of the substrates utilized in this process. The pretreatment aims to hydrolyze the resistant heteropolymeric chemical structures into monomeric units, which are necessary for the microorganisms for producing biohydrogen. The sources of carbon for bio-H2 generation include xylose, glucose, cellobiose, and arabinose and several inhibitors such as furfural and 5-hydroxymethyl furfural (5-HMF). The negative effects of 5-HMF and furfural depend upon their concentration and the type of microorganisms utilized for fermentation process. Pretreatment process is classified into physicochemical, physical, biological, and chemical mechanisms.

5.4.6 Physicochemical Pretreatment Several physicochemical pretreatment mechanisms such as treatment by water, steam explosion, and hot water treatment are exploited to degrade structures before hydrolysis by enzymes.

5.4.7 Chemical Pretreatment It is the use of various chemicals such as organic solvents such as acids, alkali, and metal chlorides for biomass pretreatment (Ren et  al. 2016). Acid pretreatment is quite effective for biomass, which then releases sugars, lignin precipitates, and inhibitory molecules (Lopez-Hidalgo et  al. 2017). Due to the acid pretreatment, lignocelluloses form 5-HMF and furfural and acetic acid. The pretreated biomass contains levulinic and formic acid from 5-HMF by thermochemical pretreatment of polysaccharides via acid hydrolysis. In acidic environment, undissociated levulinic and formic acids trigger cytotoxicity by penetrating the microorganism body, thus lowering catalytic efficiency (Shobana et al. 2017).

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5.4.8 Biological Pretreatment In the biological pretreatment method, delignification of substrates such as lignocellulose is done with the help of micro-organisms or enzymes. In biological pretreatment, fungi are most effective microorganisms for delignification (Ren et al. 2016). These microorganisms produce several enzymes which digest hemicellulose, lignin, and polyphenol in the biomass. Fungal enzymes such as cellulase, xylanase, and laccase efficiently degrade biomass produced in agricultural wastes. The pretreatment using acids, followed by hydrolysis by enzymes, improves accessibility to cellulose, leading to the production of fermentable sugars.

5.4.9 Physical Pretreatment The most commonly used physical pretreatment methods are grinding, milling, chipping, cutting, and shearing. Such process lowers size of lignocellulosic substrates to enhance surface area. Physical pretreatment of substrates is usually followed by physicochemical, chemical, and biological pretreatments. 5.4.9.1 Mechanism to Enhance Bio-H2 Generation Efficiency 1. Microalgae-bacteria coupling 2. Sodium bisulfide (NaHCO3) addition 3. Mixed-trophic type culture 4. Microalgae immobilization to advance utilization of light In microalgae-bacteria coupling, microalgae and bacteria are coculture in sulfur deficient conditions to increase the anaerobic condition (anaerobic condition created by bacterial consumption of O2). This increases the biohydrogen production efficiency. 5.4.9.2 Advantages • The smaller size of microalgae produces more hydrogen than the large size microalgae. • In presence of bacteria, microalgae grow much faster than the alone. The biomass produced can also be used for methane gas production • Efficiency can also be increased by adding sodium bisulfate. This reduces the oxygen release and thus provides anoxic condition and activates the hydrogenases and induces hydrogen production

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The biohydrogen production can also be increased by improving the design of the bioreactor. Genetic engineering can also increase the biohydrogen production. Some mutations in hydrogenases can increase the biohydrogen production. The biohydrogen production can also be increased by improving the design of the bioreactor. Genetic engineering can also increase the biohydrogen production. Some mutations in hydrogenases can increase the biohydrogen production.

5.5 Conclusion and Future Perspectives Bio-H2 is the promising dream biofuel in the future, primarily because of its recyclable, nonpolluting nature and huge energy content. It has a great potential in reducing the dependence upon the fossil fuels for energy production and, thus, halts emission of greenhouse and other toxic gases in the environment. It is regarded as the cleanest biofuel with negligible emissions The production of bio-H2 is done at ambient temperature, and at apt atmospheric pressure; hence, this process requires less energy and is environmentally friendly in comparison with electrochemical and thermochemical processes. However, several studies also suggest biohydrogen production is quite expensive than gasoline in present scenario. But technological innovations and advancement in technological processes will succeed in limiting the expense of biohydrogen production. A surplus yield in biohydrogen production could be possible by using appropriate processes such as carbon/nitrogen ratio (C/ N2 ratio), intensity of illumination, configuration of bioreactors, and age and size of the inoculum. The wastewater treatment plants can be useful in producing biohydrogen and designing biohydrogen plants in the near future. However, the transition from deriving energy from carbon-based fossil fuel sources to biohydrogen-based energy sources is not easy and isn’t easily feasible as well in short term.

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Chapter 6

Biohydrogen from Agricultural Waste Taciana Carneiro Chaves, Fernanda Santana Peiter, and Eduardo Lucena Cavalcante de Amorim

Abstract The search for renewable and efficient energy sources has been increasingly comprehensive. In this sense, biological hydrogen production outstands as a promising alternative. Studies have evaluated biomasses rich in organic matter that can be converted into hydrogen, the gaseous fuel with the highest energy content per unit of weight and which still has water as a by-product in its combustion. Agricultural waste from harvesting (grains, cereals, straw, husks, and bagasse), livestock (manure and dairy products), industrial processing (fruits, vegetables, vinasse, and cassava wastewater), and domestic activities (leftover food) has a high potential to produce biohydrogen, mainly from anaerobic digestion. Therefore, this chapter presents relevant aspects of biological hydrogen production by dark fermentation using agricultural residues. The objective is to highlight the main interfering factors such as methods of pretreatment of lignocellulosic residues, anaerobic bioreactor configurations, temperature and pH of the medium, type of inoculum and its pretreatment, concentration of the feed, and possible combinations of substrates to increase the production efficiency. Keywords Biohydrogen · Dark fermentation · Anaerobic digestion · Agricultural waste · Lignocellulosic residues · Anaerobic bioreactor

6.1

Biological Hydrogen Production

Hydrogen is the gaseous fuel with the highest energy content per unit of weight (143  kJ/g), considered a promising alternative to reduce greenhouse gas emissions because its combustion generates only water (Chen et al. 2021; Nair et al. 2022). It is a T. C. Chaves · F. S. Peiter · E. L. C. de Amorim (*) Environmental Control Laboratory, Technology Center, Federal University of Alagoas, Maceió, Alagoas, Brazil e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024 P. Singh (ed.), Emerging Trends and Techniques in Biofuel Production from Agricultural Waste, Clean Energy Production Technologies, https://doi.org/10.1007/978-981-99-8244-8_6

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colorless, odorless, and flammable gas with energy efficiency about three times greater than that offered by fuels originating from hydrocarbons. These characteristics make it an efficient, ecological, and renewable energy source (Saravanan et al. 2021, 2022). Besides its use for energy purposes, hydrogen is also applied in sectors such as steel processing, refinery, and the food industry (Yaashikaa et al. 2022). The forms of production include resources such as fossil fuels, water, or biomass, through physical-chemical or biological processes (Chaves et al. 2021). Biological methods of hydrogen production are viable alternatives to minimize the use of fossil fuels. It stands out for its lower energy consumption, use of organic waste and industrial effluents as raw materials, and the possibility of operating at ambient temperature and pressure, facilitating industrial production. The techniques include direct or indirect photolysis, fermentation in the presence or absence of light, and electrochemical methods (Table 6.1) (Prabakar et al. 2018; Ramprakash et al. 2022). In direct photolysis, solar energy converts water molecules into hydrogen and oxygen. The organisms involved are photoautotrophs, such as cyanobacteria and green algae. Conversely, indirect photolysis occurs in two steps, with hydrogen production after the release of oxygen, and cyanobacteria are the preferred organisms. In both methods, the accumulation of oxygen in the medium impairs the hydrogen yield, and the light energy conversion is low (Akhlaghi and Najafpour-Darzi 2020). Electrochemical methods (electro-fermentation) utilize microbial electrolytic cells and varied energy sources to produce biohydrogen. Despite achieving high yields, the investment in electrodes and catalysts is costly, hampering large-scale productions (Yaashikaa et al. 2022). Fermentation in the presence of light (photofermentation) uses sunlight rather than sugar molecules as an energy source for photosynthesis. It is carried out by purple non-sulfur bacteria (PNS) and offers high hydrogen production and light conversion (Yaashikaa et al. 2022). Dark fermentation represents the junction of the three initial phases of the anaerobic digestion process, which occurs in four steps (hydrolysis, acidogenesis, acetogenesis, and methanogenesis). The process ensues in the absence of oxygen, converting complex organic matter into biogas and a stabilized organic effluent that can be applied as a biofertilizer (Cremonez et al. 2021; Khanal et al. 2021). It is a faster process than photolysis and photofermentation, besides requiring less input of external energy. From the proper operational controls, it can have an optimized hydrogen yield (Yaashikaa et al. 2022).

6.1.1 BioH2 via Dark Fermentation Hydrogen is produced in the acidogenic and acetogenic phases of anaerobic digestion. The process promotes the environmental benefits of clean energy generation and the treatment of organic waste used as a cheap source of renewable raw material (Chaves et al. 2021). Besides lessening the dependency on fossil fuels, anaerobic digestion also favors the reduction of organic waste in sanitary landfills and decreases carbon emissions to the atmosphere (Wu et al. 2021).

Easy process Easy process Medium process

Dark fermentation Light fermentation Electrochemical

Medium Low High

High

Cost High

( cyanobacterial and green algal )

C6 H12 O6 + 6H 2 O → 12H 2 + 6CO 2 ( cyanobacterial ) C6H12O6 + 2H2O → 2CH3COOH + 2CO2 + 4H2 (heterotrophs) C6H12O6 + 6H2O → 6CO2 + 12H2  (phototrophic bacteria) C6H12O6 + 2H2O → 2CH3COOH + 2CO2 + 4H2 Anode : CH3COOH + 2H2O → 2CO2 + 8e− + 8H+ Cathode : 8H+ + 8e− → 4H2

Light

6CO 2 + 6H 2 O → C6 H12 O6 + 6O 2

Light

12H 2 O → 12H 2 + 6O 2

Light

General reaction

Source: Adapted from Akhlaghi and Najafpour-Darzi (2020), Prabakar et al. (2018) and Yaashikaa et al. (2022)

Wide range hard process

Continuous operation Difficult process

Indirect photolysis

Production method Direct photolysis

Table 6.1  Biological methods to produce hydrogen

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The hydrogen production via dark fermentation is conducted by strict or facultative anaerobic bacteria. The main responsible species are Clostridium, Enterobacter sp., Klebsiella sp., Citrobacter sp., and bacillus pp. (Banu et al. 2021; Lertsriwong and Glinwong 2020) bacilli. The most competitive microorganisms are the methanogenic, homoacetogenic, propionic acid, and lactic acid producers (Castelló et al. 2020; Dahiya et al. 2021). Hydrogen-consuming organisms can be suppressed through inhibition methanogenesis methods such as inoculum pretreatment and reduction of pH below the appropriate value for methanogenic archaea (Gavazza et al. 2021; Wainaina et al. 2019; Wu et al. 2021). Methods that inhibit methane production are classified as specific or nonspecific. Specific inoculum pretreatments act on microbial cell molecules, such as acidic and basic treatments and the addition of acetylene, 2-BES (2-bromoethanesulfonic acid), and chloroform (CHCl3). On the other hand, nonspecific procedures such as pH adjustment and heat shock influence the general functions of microorganisms (Amorim et al. 2018; Dahiya et al. 2021).

6.2 Agricultural Waste and Biohydrogen Production Agricultural waste originates from various sources: food processing and domestic and commercial activities such as restaurants, slaughterhouses, animal husbandry, brewery, and dairy. In general, the solid parts of these materials are disposed of in landfills and, the liquid, in sewer systems (Nair et al. 2022). Babu et al. (2022) disclose agriculture as the second largest contributor to the release of greenhouse gases, behind only the energy sector. Inadequate disposal of residues of this culture causes problems for human health and the environment. According to Awogbemi and Von Kallon (2022), agricultural waste transformation into valuable products constitutes an economic, ecological, and sustainable strategy for appropriate residue management. Nair et al. (2022) highlight some classes of agricultural waste with potential for biofuel production: crop residues (grains, cereals, straw, husks, and bagasse), livestock residues, industrial processing waste (fruits and vegetables, edible oil, coffee, and breweries), and household residue (leftovers from food). Livestock waste includes animal urine, solid manure (meat, poultry, eggs, seafood, and other aquatic life), wastewater from animal husbandry processes, and dairy waste. Food waste generated by households, retail stores, and processing industries contributes to around 8–10% of global greenhouse gas emissions. The high generated volumes and energy-rich content make these materials suitable for biological treatment through dark fermentation. Techniques such as temperature control in mesophilic ranges and inoculum enrichment can make anaerobic digestion an economically viable technology to produce hydrogen (Luo et al. 2022). Lignocellulosic biomass found in various crop residues such as sugarcane bagasse, straw, and husks (rice, wheat, oats, and corn), leaves and stems of vegetables and fruits, as well as food scraps offered a high potential for biological

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hydrogen production. But in these cases, pretreatment methods are needed to improve the biodegradability of the material (Prabakar et  al. 2018; Ramprakash et al. 2022). Wastewater from the agricultural industry also constitutes a potential source of raw materials to produce biohydrogen via dark fermentation. For example, sugarcane vinasse, an effluent from ethanol production, contains high concentrations of carbon and nutrients, being a great ally in the production of H2 (Fuess et al. 2019; Gois et al. 2021; Piffer et al. 2021, 2022; Ramos et al. 2021). Cassava wastewater (manipueira), a liquid effluent from cassava processing, has also been widely used for the same purpose (Amorim et al. 2018; Gavazza et al. 2021; Tavares et al. 2022), as well as cheese whey wastewater (Lovato et al. 2018, 2021; Marques et al. 2019; Ribeiro et al. 2022).

6.2.1 Pretreatment Methods for Agricultural Waste Lignocellulosic agricultural residues are mainly composed of cellulose (30–40%), hemicellulose (30–50%), and lignin (8–21%), as shown in Table 6.2. The transformation of these complex cellular into simpler monomers that can later be converted Table 6.2  Main constituents of various lignocellulosic agricultural residues Residue Banana stems Barley straw Bean straw Coconut pods Corn cobs Corn stover Maize stalk Napier grass Oat straw Olive tree Peanut shell Rice straw Sorghum bagasse Sorghum stalks Soybean stover Sunflower stalk Sugarcane (top and leaves) Sweet potato Switchgrass Wheat straw

Cellulose (%) 33.3 a 40 31.1 26.1 45 32.75 a 37.5 46.6 a 35 36.5 a 35 a 30 46.6 27 a 45 a 37.5 a 45 a 30 31.8 a 40

Hemicellulose (%) 18.2 a 25 23.9 4.82 35 08.31 a 30 34.1 a 25 21.3 a 12.5 a 35 34.1 25 a 17.5 a 32.5 a 30 a 15 25.0 a 22.5

Source: Adapted from Awogbemi and Von Kallon (2022) and Babu et al. (2022) Average between the minimum and maximum values

a

Lignin (%) 5.5 a 12 9.7 21.29 15 10.07 a 8.5 22.3 a 17.5 24.1 a 30 a 9 22.3 11 a 17.5 a 22.5 a 17.5 a 17.5 31.2 a 17.5

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into products depends on pretreatment techniques. The higher presence of lignin and lower cellulose content in their structure minimizes the digestibility of the material (Awogbemi and Von Kallon 2022; Babu et al. 2022). Decreasing energy consumption during raw material conversion, the direct formation of sugars from biomass, preservation of the sugar produced during degradation, and reduction of costs and inhibitors are some benefits of preprocessing treatment of lignocellulosic biomasses (Areepak et al. 2022). The pretreatment selection must occur according to the characteristics of the substrate, considering the maximum release of fermentable sugar in a short period and minimum use of enzymes, plant material, and drinking water, in addition to avoiding the formation of inhibitors in the fermentation process and allowing the use with large amounts of biomass, favoring the increase in scale (Babu et al. 2022; Hu et al. 2022). Awogbemi and Von Kallon (2022) presented a detailed classification of current methods, reflecting their advantages and disadvantages. The authors cite physical pretreatment (mechanical, ultrasonic, and thermal), chemical pretreatment (acid, alkali, oxidation, and organic solvent), biological pretreatment (fungal, bacterial, thermite, microbial consortium, and enzymes), physicochemical pretreatment (steam explosion, alkali-heat, ammonia fiber explosion, and extrusion), and green solvent-based pretreatment (biochemical, ionic liquid, deep eutectic solvents, and supercritical fluid). Awogbemi and Von Kallon (2022) disclose some observations about pretreatments: physical methods reduce the particle size and improve the surface area; however, they present high cost and low or no lignin removal; chemical techniques increase surface area and biodegradability but can form inhibitors and cause corrosion; biological procedures are time-consuming, despite being efficient and ecologically correct; physicochemical pretreatment combines the beneficial characteristics of physical and chemical treatments by reducing lignin and hemicellulose levels; and finally, green solvent-based methods are more advanced and environmentally friendly. Artificial intelligence and robotics are techniques cited as perspectives for innovative technologies aimed at optimizing these pretreatments.

6.3 Factors Affecting Dark Fermentation of Agricultural Waste Numerous operational factors influence the dark fermentation process, such as inoculum pretreatment, pH control, type of bioreactor, sources of organic matter, co-­ digestion of substrates, type of inoculum, and reactional temperature. The choice of substrates for biological hydrogen production must consider raw material availability, the number of carbohydrates, biodegradability, and reduced cost (Prabakar et al. 2018; Ramprakash et al. 2022), characteristics that make agricultural residues a suitable and renewable material for use in the dark fermentation process (Table 6.3).

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Table 6.3  Hydrogen production in anaerobic reactors from agricultural waste Agriculture waste Sugarcane bagasse

Operating conditions Batch, 55 °C, pH 7.8, alkalization/autoclaving pretreatment

Olive pomace

Batch, 30 °C, 100 rpm, pH 7, basic pretreatment Batch, 37 °C, 150 rpm, ultrasound combined with dilute alkali cooking pretreatment AnSBBR, 30 °C, 7 g-COD/L, pH 8, OLR 24 kg-COD/m3/day, 3 h cycle

Wheat straw

Whey cheese + glycerin

Rice straw Palm oil mill effluent

Fruit and vegetable waste Corn stover hydrolyzate

CSTR, 55 °C, TS 6%, 120 rpm, HRT 3 days UASFF, 20 g-COD/L, HRT 7 h, 57 °C, pH 5 to 5.5 Batch, 55 °C, 250 rpm, pH 5.5 to 6.75 Batch, 55 °C, pH 7

Sugarcane molasses

AFBR, 25 g-COD/L, HRT 6 h

Cassava wastewater

Batch, 10 g-COD/L, 30 °C, pH 5.5

Food waste

Grass silage

Batch, 10.8 g-COD/L 35 °C, pH 7.5, C/N 9.27 ABR, 10% TS, pH 7.5, 55 °C Batch, pH 5 to 6, 70 °C

Cheese whey

Batch, 30 °C, pH 5.5

Rice crop waste

Maximum production 13.9 L-H2/ kg-bagasse 133.9 mL-H2/h 657 mL-H2/g— CODremoved 1.98 NL-H2/L 133.6 mL-H2/ g-TS

1.4 mol-H2/ mol-substrate 129.0 mol-H2/m3/ day 5.4 mol-H2/ kg-COD 63.60 mL/g-­VSadded 0.95 L-H2/g-­CODremoved 10.39 L-H2/day 27.19 NmL-­ H2/g-VS 802.4 mL-H2/L 3.07 mol-H2/ mol-glucose ≈1 L-H2/(Lh) 0.49 mol-H2/ mol-glucose 56.66 mL-H2/g-SV 157.25 mL-H2/g-­VSadded 40.04 mL-H2/ VSremoved 16.0 mL-H2/g-VS 4.04 mol-H2/ mol-substrate 129.33 mmol-H2/ (L day)

References Tawfik et al. (2022)

Battista et al. (2016) Zhu et al. (2023)

Lovato et al. (2018)

Chen et al. (2022) Zainal et al. (2022) Abubackar et al. (2019b) Zhang et al. (2015) Chaves et al. (2021) Amorim et al. (2018) Luo et al. (2022) Sattar et al. (2016) Pakarinen et al. (2008) Ramos and Silva (2018)

(continued)

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Table 6.3 (continued) Agriculture waste Vegetable waste

Operating conditions Batch, 28 °C, 120 rpm, pH 6

Lactate wastewater

Batch, 45 °C, pH 8.5

Sugarcane vinasse

Batch, 55 °C, 100 rpm

Oyster shells + food waste

Batch, 35 °C

Batch, 40 °C, pH 6.5 Food waste + cattle manure + corn silage + chicken manure + olive pomace Molasses wastewater + sewage Batch, 17.3 g-COD/L, sludge 35 °C, pH 5.5

Sugarcane vinasse + whey cheese

AFBR, 55 °C, TDH 8 h

Wine vinasse + sewage sludge Batch, 54.04 g-COD/L, 55 °C, pH 5.5

Wine vinasse + sewage sludge + poultry manure

Batch, 50.86 g-COD/L, 55 °C, pH 5.5

Sewage sludge + grass residue Batch, 10 g/L, 37 °C Food waste

Batch, 15 g-VS/L, pH 6.5, 100 rpm, 37 °C

Maximum production 1.22 L-H2

References Kumar and Mohan (2018) 0.85 mol-H2/ Ziara et al. mol-lactate (2019) 2.41 mmol-H2/g-­- Piffer et al. CODappl (2021) 8.4 mL-H2/g-­ Shi et al. VS/h (2021) 88.2 mL-H2/g-VS 50.4 mL-H2/g-VS Shen et al. (2022) 45.8 mL-H2/g-­ COD 35.8 mL-H2/g-­VSremoved 1411.2 mL-H2/ (L day) a 24.05 mL-H2/g-­CODappl 1.41 L-H2/(L day) 43.25 mL-H2/g-­VSadded b 620 mL-H2/ (L day) 22.34 mL-H2/g-­CODadded 27.10 mL-H2/g-­VSadded b 70 mL-H2/(L day) 45.6 mL-H2/g-­VSadded 75.3 mL-H2/g-VS

Lee et al. (2014)

Ramos and Silva (2018) Tena et al. (2020)

Sillero et al. (2022)

Yang and Wang (2019) Pu et al. (2019)

TS total solids, COD chemical oxygen demand, VS volatile solids, OLR organic loading rate, HRT hydraulic retention times, C/N carbon/nitrogen ratio, AnSBBR anaerobic biofilm batch sequencing reactor, CSTR continuous stirred-tank reactor, ABR anaerobic bioreactor, UASFF upflow anaerobic sludge fixed-film, AFBR anaerobic fluidized bed reactors a Converted from mmol to mL from data available in the article and the ideal gas Eq. (PV = nRT) b Calculated with article data

The additional and efficient substrate pretreatment directly influences dark fermentation in the case of lignocellulosic agricultural residues. A thorough analysis of the characteristics of the substrates, their components, and inhibitory substances is necessary to select the appropriate pretreatment and to improve the reactor performance (Prabakar et al. 2018).

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Babu et al. (2022) emphasize that pretreatment techniques must be economical and not harmful to the environment besides removing lignin, minimizing the loss of carbohydrates, and avoiding the formation of toxic substances. Prabakar et  al. (2018) point out the sonolysis, microwave, acid, alkali, thermal or heat shock, enzymatic process, or combinations between them as the most applied to improve the hydrogen production from agroindustry substrates. Previous studies tested different pretreatments on sugarcane bagasse to improve hydrogen production. Peroxyformic treatment acid (Bu et  al. 2021); laccase enzyme (Rabelo et  al. 2022); hydrothermal, hydrothermal  +  oligomer hydrolysis and acid pretreatments (Sá et  al. 2020); and autoclaving, acidification/autoclaving, and alkalization/autoclaving (Tawfik et al. 2022) resulted in 103.9 mL-H2/gbagasseinitial (94.1  mL/L/h, and 1083  mL/L), 166.8  mL-H2/L (3.2  mL/L/h), 228  mL-H2/g-­ carbohydrate (7.39  mL/g-carbohydrate/h), 231.4  mL-H2/g-carbohydrate (9.64  mL/g-­carbohydrate/h) and 265  mL-H2/g-carbohydrate (11.3  mL/gcarbohydrate/h), 4.7  L-H2/kg-bagasse (53.6  mL/h), 8.5  L-H2/kg-bagasse (105.9 mL/h), and 13.9 L-H2/kg-bagasse (133.9 mL/h and 657 mL/g-CODremoved), respectively. Olive pomace, a semisolid residue from olive oil production, was evaluated by ultrasonic pretreatment, basic pretreatment, and the addition of calcium carbonate. In all cases, occurred an improvement in the hydrogen production concerning the untreated residue (0.54  NL-H2/L). The basic (1.98  NL-H2/L) and carbonate (1.09 NL-H2/L) pretreatments showed the best results (Battista et al. 2016). Zhu et al. (2023) investigated the dark fermentation of wheat straw preceded by enzymatic saccharification using various pretreatments (lyophilization, hydrothermal pretreatment, and ultrasound combined with dilute alkali post-cooking). Raw wheat straw yielded 23.9  mL-H2/g-TS.  Ultrasound combined with dilute alkali cooking achieved 59.1% lignin removal and a maximum yield of 133.6 mL-H2/g­TS. Lyophilization and hydrothermal pretreatments resulted in 83.7 and 120.2 mL-­ H2/g-TS, respectively. Hydrogen production via anaerobic digestion using agricultural residues can encompass bench-scale reactors operated in batch or continuous mode. Verified reactor configurations include continuous-flow anaerobic reactors, anaerobic baffled reactors (ABR), expanded granular sludge bed (EGSB), continuous stirred-tank reactors (CSTR), sequencing batch biofilm reactors (SBBR), and anaerobic fluidized bioreactors (AFBR) (Chaves et al. 2021). Anaerobic fluidized bed reactors (AFBR) promote better mass transfer between substrates and microorganisms, besides high biomass adhesion to the support material. It enables the application of high organic loading rate (OLR) and low hydraulic retention times (HRT) associated with elevated yields. Sugarcane molasses, a by-­ product of the sugar and ethanol agroindustry rich in simple carbohydrates, when digested in AFBR (HRT = 6 h and OLR = 4.2 g-COD/L/h), yielded 3.07 mol-H2/ mol-glucose (Chaves et al. 2021). Fermentation in expanded granular sludge bed (HRT = 1 h and OLR = 360 kg-sucrose/m3/day), upflow anaerobic fixed structured bed reactors (HRT = 2 h and OLR = 120 g-COD/L/day), and anaerobic structured bed reactor and acidogenic (HRT = 4 h and OLR = 60 g/L/day) resulted in yields of

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0.25 mol-H2/mol-hexose (Freitas et al. 2020), 0.3 mol-H2/mol-carbohydrates (Vilela et al. 2019), and 1.18 mol-H2/mol-carbohydrates (Oliveira et al. 2020), respectively. The temperature of the fermentation medium affects the growth, diversity, and enzymatic activities of microorganisms and the transformation of complex organic matter into simpler compounds, influencing the hydrolysis of substrates (Silva et al. 2021). Given the high dependence on the type of substrate, the ideal range to produce hydrogen through dark fermentation is inconclusive, with many divergences regarding this. In general, thermophilic temperatures provide a faster hydrolysis rate. However, operation in the mesophilic range is steadier and consumes less energy (Chen et al. 2022). Lovato et  al. (2018), using an AnSBBR (anaerobic biofilm batch sequencing reactor), evaluated the mixture of dairy industry effluent (cheese whey—75%) with biodiesel production effluent (glycerin—25%) at mesophilic temperatures of 20, 25, 30, and 35 °C. Productivity increased up to 30 °C resulting in 129.0 mol-H2/m3/ day and 5.4 mol-H2/kg-COD. At 35 °C, the production decreased due to the increase in biomass in the medium. The biodigestion of rice straw was evaluated in a CSTR reactor at 37 and 55 °C with 3%, 6%, and 12% total solids content. The residue was naturally dried, ground, sieved, and mixed with anaerobic digestion sludge. The mixture was pretreated with acid to prevent hydrogen consumption and methane formation. The thermophilic condition resulted in higher hydrogen production (0.46 to 63.60 mL/g-VSadded) compared to the mesophilic (0.19 to 2.13 mL/g-VSadded) for the three concentrations of solids. The highest value of 63.60 mL/g-VSadded occurred with 6% total solids and an abundance of hydrolytic bacteria (Ruminiclostridium 54.24%). Increasing the solids content to 12% favored the switch from hydrogen production to methane (Chen et al. 2022). Chen et al. (2022) clarify that total solids content can affect the microorganism’s ability to assimilate substrates, altering the metabolic pathways and microbial communities, besides operational costs. Furthermore, the enzymatic activity is greater at higher temperatures, favoring biohydrogen production. Zainal et  al. (2022) investigated the effect of temperature (37 to 70  °C) and hydraulic retention time (3 to 9 h) on hydrogen production from palm oil mill effluent (POME). The authors used an upflow anaerobic sludge fixed-film bioreactor (UASFF) and observed that the production rate increased between 37 and 56.8 °C but decreased from 56.8 to 70 °C. The best results of 0.95 L-H2/g-CODremoved and 10.39 L-H2/day occurred at 57 °C and HRT of 7 h. Lignin and cellulose substrate composition at higher temperatures had relevance for the superior performance of the reactor. Abubackar et al. (2019a, b) analyzed mesophilic and thermophilic dry dark fermentation (with total solids content higher than 10%) of fruit and vegetable residues. The residue percentage composition was radish (5.71), pepper (5.06), pomegranate (7.02), pear (3.33), apple (4.66), pumpkin (2.06), mandarin (1.68), tomato (7.45), onion (6.20), potato (5.48), peach (12.90), lemon (2.28), eggplant (11.34), carrot (8.68), orange (2.59), cucumber (6.70), cabbage (4.19), and grape (2.68). Autoclaving was applied in waste pretreatment, improving mesophilic

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hydrogen production by 51% (23.53  NmL-H2/g-VS) and thermophilic by 39% (27.19 NmL-H2/g-VS). The authors mention that autoclave pretreatment offers the advantages of unrequired chemical products and preserving nutrients contained in the residues. In addition, a thermophilic environment causes a greater inhibition of hydrogen-consuming microorganisms but requests more energy expenditure. After undergoing acidogenic fermentation of corn stover hydrolyzate at different temperatures, Zhang et  al. (2015) observed the following order of efficiency in hydrogen production: 55 > 70 > 37 °C ≈ 30 °C. The behavior was similar for two applied inoculums without pretreatment (activated sludge from a municipal treatment plant and granular sludge from an anaerobic bioreactor). The highest yields of 611.8  mL-H2/L with activated sludge and 802.4  mL-H2/L with granular sludge arose at 55 °C. The inoculum pretreatment to inhibit methanogenic archaea and favor hydrogen production is another factor that influences dark fermentation. Heat shock is a cheap and efficient alternative where high temperatures destroy non-spore-forming methanogenic microorganisms, increasing spore-forming species (Dahiya et al. 2021). Studying the anaerobic digestion of cassava wastewater, Amorim et al. (2018) tested heat (autoclave—120 °C, 1 atm, 30 min) and acetylene treatment (1% v/v of headspace) to the inoculum obtained in a municipal sewage treatment plant. Both methods prevented methane formation. Autoclave resulted in the maximum yield of 56.66 mL-H2/g-SV against 27.63 mL-H2/g-SV achieved with acetylene. Luo et al. (2022) analyzed various inoculum pretreatments (aeration, acid, alkali, heat, heat + CO2, free nitrous acid, 2-bromoethanesulfonate, and electric shock) in the dark fermentation of food waste. The sludge came from a sewage treatment plant, and the residue consisted of bread (35%), boiled cabbage (25%), cooked rice (25%), and boiled pork (15%). The inoculum treated with alkali (5  M NaOH— pH 10) resulted in the highest yield (157.25 mL-H2/g-VSadded). The maximum productivity (140.75 mL-H2/L/h) occurred in the heat treatment (100 °C for 1 h in a water bath) + CO2 (10 min sparging with CO2). The aeration technique achieved the worst performance. Thermal shock consists of exposing the microorganisms to high temperatures. Luo et al. (2022) observed the necessity of longer acclimation to sporulate bacteria, resulting in the lengthiest lag phase (20  h). This pretreatment engendered lower yields than those presented using acid, base, heat  +  CO2, FNA, and BES.  The CO2purge after heat shock reduced the acclimatization time in half and increased the hydrogen production rate by 88%. The authors related the results to the ability of CO2 to increase hydrogenase activity, decreasing the hydrogen partial pressure and inhibiting hydrogen-consuming bacteria. Dissolved CO2 also can provide alkalinity to the system by neutralizing organic acids. The type of inoculum also influences hydrogen production. Amorim et al. (2018) evaluated municipal sewage, textile industry wastewater, and bovine rumen as a source of microorganisms, all treated by thermal shock. The results showed a maximum of 109.43 mL-H2/g-SV for the textile industry inoculum. Pakarinen et  al. (2008) verified the hydrogen production potential from grass silage with two types of inoculums (dairy farm digester and digested sewage sludge

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from an effluent treatment plant). The dairy farm digester inoculum was the only one to produce hydrogen. The heat-treated inoculum resulted in a maximum yield of 16.0 mL-H2/g-VS at initial pH between 5 and 6 and a temperature of 70 °C. The fermentation medium pH affects the solubilization of organic matter, the microbial community, and the products formed. Different microorganisms involved in digestion require diverse ideal pH ranges. While the optimum pH for methanogenic archaea is between 6.5 and 7.5, H2-producing bacteria prefer a pH range from 5.5 to 6.5 (Braz Romão et al. 2018; Wainaina et al. 2019; Wu et al. 2021). However, the optimal pH for hydrogen production by dark fermentation, as well as for temperature, is specific for each substrate. Ziara et al. (2019) cite pH varying from 5 and 6 for food waste, pH values closer to neutrality for animal processing wastewater, and pH between 6.5 and 8.5 for lactate wastewater. Sattar et al. (2016) found values between 6 and 7 as the ideal pH range to produce hydrogen from the straw, husk, and rice bran and pH from 4 to 5.5 for rice residue. Grinding and sieving were used to increase the surface area and degree of polymerization. Verifying the effect of temperature on the fermentation of waste, the authors observed that biohydrogen production increased between 37 and 55 °C for all substrates except for rice waste. The average yield of rice crop residues was 30.37 mL-H2/VSremoved at 37 °C and 33.6 mL-H2/VSremoved at 55 °C, while rice straw showed the highest yield of 40.04 mL-H2/VSremoved in the thermophilic condition. Braz Romão et  al. (2018) evaluated the H2 production using cheese whey at pH  5.5 and 6.5, with higher productivity (129.33  mmol-H2/day/L) and yield (4.04  mol-H2/mol-substrate consumed) achieved at pH  5.5. Kumar and Mohan (2018) analyzed initial pH conditions between 4 and 10 for solid vegetable residues and reached a maximum of 1.22 L-H2 at pH 6. Hydrogen production with lactate wastewater (dairy effluents obtained from a cattle slaughterhouse) was investigated at different temperatures (35, 45, 50, and 55 °C) and initial pH of 4.5, 5.5, 6.5, 7.5, and 8.5. Fermentation resulted in a maximum yield of 0.85 mol-H2/mol-lactate at 45 °C and pH 8.5, without production at temperatures above 45 °C or pH below 6.5 (Ziara et al. 2019). Piffer et  al. (2021) evaluated three strategies to control the pH of sugarcane vinasse thermophilic fermentation: (1) addition of NaOH (50% m/V), (2) addition of NaOH (50% m/V)  +  NaHCO3 (0.1  g-NaHCO3/g-COD), and (3) addition of NaOH supplemented with sodium chloride (NaCl) to obtain an SO42−/Na ratio of approximately 2.0. The single use of NaOH generated initial and final pH of 6.35 and 5.33, respectively, with a maximum hydrogen yield of 2.41 mmol-H2/g-CODappl. For NaOH + NaCl, the H2 yield was 2.33 mmol-H2/g-CODappl, with higher initial pH of 6.35 and a final of 5.64, suggesting the buffering capacity of Na. Probably, Na dosage caused an insignificant impact on H2 production, explaining similar results for these cases. The addition of NaOH  +  NaHCO3 resulted in 1.41  mmol-H2/g-­CODappl, initial pH of 7.12, and final pH of 6.19, showing that despite final pH above 6.0, NaHCO3 harmed the fermentation yield. Some of the most economical methods to control the pH of dark fermentation of food waste are the addition of constituents to the reaction medium. Examples of these materials include the white mud from the ammonia-soda process, fly ash, and

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bottom ash from the combustion of residual forest biomass, eggshells, and oyster shells. The oyster shells adding in percentages of 6–12% improved the hydrogen production, reaching a maximum of 8.4 mL-H2/g-VS/h and 88.2 mL-H2/g-VS with 8% of the additive. However, an amount equal to or greater than 10% caused the process inhibition. Oyster shells comprise 80% to 95% of CaCO3 and Ca3(PO4)2, so the presence in excess can produce Ca2+ and CO2. A high concentration of CO2 in water can lead to the appearance of HCO3−, which generates acetic acid when reacting with H2. On the other hand, excessive Ca2+ can contribute to the formation of precipitates, decreasing the degradation rate of organic acids (Shi et al. 2021). Dark fermentation of a single substrate (mono-fermentation) generally suffers constrained by characteristics such as nutrient imbalance and the presence of inhibitory toxic compounds. The co-fermentation using different resources with complementary characteristics is a strategy to overcome those limitations and to improve hydrogen production efficiency (Babu et  al. 2022). Karki et  al. (2021) state that co-digestion promotes the mixing and dilution of toxic compounds, the balance of nutrients and pH, and the improvement of synergistic effects among existing microorganisms. Shen et al. (2022) analyzed the anaerobic co-digestion of food waste and cattle/ chicken manure digestate. The authors initially evaluated heat-pretreated food residue (85 °C) at different proportions of 45% cattle manure, 25% corn silage, 15% chicken manure, and 15% olive pomace. The second phase verified the effect of the initial pH (5.5, 6.0, and 6.5). The highest biohydrogen yield (50.4  mL/g-VS; 45.8 mL/g-COD) was obtained under pH 6.5, with bacteria to volatile solids ratio of 2:1 and digested seed to food residues ratio of 6:4. The researchers emphasize that elevated hydrogen production was possible given the adequacy of the ­carbon/nitrogen (C/N) proportion by promoting the mixing of substrates, reaching a final ratio indicated for dark fermentation (20 to 30). Food residues with high COD concentration were adapted to the C/N ratio with the addition of chicken manure (C/N = 8.22) and cow manure (C/N from 11 to 14). Supplementation of olive pomace and corn silage to manure resulted in a C/N proportion between 20 and 25. Lee et al. (2014) improved the performance of the acidogenic fermentation of sewage sludge with the addition of molasses. The H2 yield varied from zero (100% sludge) to 0.9  mL/g-VSremoved (80% sludge), 16.3  mL/g-VSremoved (60% sludge), 23.3 mL/g-VSremoved (40% sludge), and 35.8 mL/g-VSremoved (20% sludge). Ramos and Silva (2018) observed that the addition of 2 g-COD/L of cheese whey to the fermentation of vinasse (10 g-COD/L) caused an 82% increase in hydrogen yield (0.82  mmol-H2/g-COD) and elevated production rate by 117% (1.41  L-H2/ d/L). Tena et  al. (2020), using 25% vinasse and 75% sewage sludge, reached 43.25 mL/g-VSadded, increasing by 14 times the yield obtained from the digestion of 100% sewage sludge. Sillero et al. (2022) studied the co-digestion of vinasse (50%) and sewage sludge (50%) and achieved 9.66  mL-H2/g-CODadded (18.97  mL/g-­VSadded). After the addition of 10 g/L of poultry manure to the original vinasse and sludge mixture, hydrogen yield increased to 22.34  mL-H2/g-CODadded (27.10 mL-H2/g-VSadded).

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Substrate concentration is also a significant factor in hydrogen production from agro-waste, as it can influence metabolic pathways and microbial activity. Yang and Wang (2019) analyzed substrate concentrations for co-fermenting sewage sludge and grass residues in a 3:7 ratio based on volatile solids (SV). The sludge was sterilized at 121 °C for 30 min, and the grass residue was dried at 60 °C and ground to about 1  mm. The inoculum from an anaerobic digester was heated (100  °C for 15 min) to eliminate H2-consuming bacteria. Substrate concentrations ranged from 5 to 80 g/L. The maximum yield of 45.6 mL-H2/g-VSadded was reached at a concentration of 10 g/L. Sparse substrate concentrations imply a lack of carbon, affecting the activity of fermentative bacteria. Meanwhile, excessive concentrations can cause organic acid accumulation, a decrease in pH, and an increase in hydrogen partial pressure, restricting bacterial metabolism (Yang and Wang 2019). Pu et  al. (2019) studied food residues (rice, vegetables, and meat) preheated (100 °C for 30 min) at concentrations of 0, 7.5, 15, 22.5, 30, and 37.5 g-VS/L, providing the highest yield of 75.3  mL-H2/g-VS to 15  g-VS/L.  The inoculum was anaerobic sludge from a brewery without pretreatment. Substrate concentrations below 15 g-VS/L possibly provided insufficient organic matter, while higher levels modified the metabolic pathways from hydrogen fermentation to lactic acid fermentation, reducing pH, enzymatic activity, and yield. The research referenced here shows that dark fermentation of agricultural waste is a promising alternative for waste treatment. The method allows for achieving significant hydrogen yield and production rate. However, results can suffer substantial variation and depend on the compositional substrate characteristics and the reactional medium conditions, being improved with the appropriate operational adjustments.

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Chapter 7

Biomethane Production as an Alternative for the Valorization of Agricultural Residues: A Review on Main Substrates Used as Renewable Energy Sources Georgia Nayane Silva Belo Gois, Amanda Santana Peiter, Norma Candida dos Santos Amorim, and Eduardo Lucena Cavalcante de Amorim Abstract Biomethane is one of the most promising gases among renewable energy sources. It is a fuel that can be applied to turbines, boilers, domestic stoves, and internal combustion engines to generate heat or electricity. One of the ways to obtain this gas is through biological technologies, such as anaerobic digestion reactors, that can convert agricultural residues like vinasse, swine effluent, and animal manure into biomethane, preventing their inappropriate disposal in the environment. Several studies show that co-digestion, the association of more than one type of waste, can be advantageous for obtaining this gas due to the greater availability of nutrients and diversification of microbial communities. However, obtaining biomethane and using it as a sustainable energy source still has challenges that range from improving the biological process to choosing the most efficient conversion technology. This chapter aims to present the main types and characteristics of agricultural wastes used as substrates and highlight some important factors that can influence the efficiency of biomethane production in anaerobic reactors. Keywords Biomethane · Agricultural waste · Agro-industrial residues · Renewable energy

Georgia Nayane Silva Belo Gois · E. L. C. de Amorim (*) Environmental Control Laboratory, Technology Center, Federal University of Alagoas, Maceió, Brazil e-mail: [email protected] A. S. Peiter Renewable Energy Center, Center of Agrarian Sciences, Federal University of Alagoas, Rio Largo, Brazil N. C. dos Santos Amorim Federal Institute of Alagoas, Satuba, Brazil © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024 P. Singh (ed.), Emerging Trends and Techniques in Biofuel Production from Agricultural Waste, Clean Energy Production Technologies, https://doi.org/10.1007/978-981-99-8244-8_7

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7.1 Introduction In a sustainable society, wastewater and waste treatments are strategies for pollution control, seeking other benefits through energy recovery and the production of value-­ added materials. The treatment of effluents containing high easily degradable organic matter, such as agricultural residues, can result in a positive net energy balance. Energy sources potentially available in the agricultural sector are plant biomass and animal residues, such as crop wastes, animal manure, and agro-industrial effluents like vinasse, cassava wastewater, and dairy wastewater (Pattnaik et al. 2019; Guo et al. 2021). However, most agricultural waste is deposited in landfills or incinerated, promoting adverse consequences for the environment (Obi et al. 2016). Biological treatments of agricultural waste are attractive because they can provide bioenergy or chemical compounds with associated added value and simultaneously achieve pollution control and recovery of by-products. The choice of bioprocess depends on technical and economic feasibility, operational simplicity, social demand, and political priority (Angenent et al. 2004). The main bioprocesses to generate bioenergy or biochemical compounds while treating agricultural residues are methanogenic anaerobic digestion, biological hydrogen production, microbial fuel cells, and fermentation. Anaerobic digestion is a process that occurs in the absence of oxygen by the action of microorganisms that degrade organic matter, producing biogas as a by-product of economic value (Silva et al. 2013). Biogas is a mixture of gases generated during the natural decomposition of organic material through biological processes. Its value is associated with the presence of methane gas, which gives it an approximate calorific value of 5200 kcal/ Nm3 and makes it attractive for applications such as heating and electricity generation, transport, or injection into the natural gas network (Ferreira et al. 2019; Khan et al. 2021). Biogas is mainly composed of methane (CH4) at 45–75%, CO2 between 20–55%, and small amounts of other gaseous compounds (impurities) such as hydrogen sulfide (H2S), nitrogen (N2), hydrogen (H2) and oxygen (O2) (Rasapoor et  al. 2020; Atelge et al. 2021). Classified as impurities, the gases CO2, H2S, and NH3, when in high concentrations, harm the quality of biogas. CO2, for example, reduces the calorific value, while H2S gives off an unpleasant odor and makes biogas corrosive to metallic materials (De Farias Silva et al. 2019; Li et al. 2019; Cremonez et al. 2021). Biomethane production happens when these contaminants are removed by purification processes, increasing energy density and improving the efficiency of biogas use (Mulu et al. 2021). In addition to biogas, the liquid effluent resulting from the anaerobic digestion process can be used as a biofertilizer, making the process an attractive option in the treatment of this type of waste, which has increased worldwide over the years following population growth (Awogbemi and Von Kallon 2022).

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7.2 Anaerobic Digestion Phases Anaerobic digestion encompasses a set of reactions occurring simultaneously through microbial action and comprises five main steps (Fig.  7.1): hydrolysis, acidogenesis, acetogenesis, sulfetogenesis, and methanogenesis (McCarty 1964). Hydrolysis is the phase where the conversion of complex organic materials (polymers) into simpler substances (sugars, amino acids, and peptides) occurs. Hydrolytic fermentative bacteria excrete exoenzymes, enabling the transformation of the particulate matter into dissolved constituents. Among the bacteria with hydrolytic capacity, the genera Clostridium, Micrococcus, Staphylococcus, Bacteroides, Butyvibrio, Bacillus, Acetivibrio, and Eubacterium can be mentioned (Ordaz-Díaz and Bailón-Salas 2020; Kumar Khanal et al. 2021). In a second phase, called acidogenesis, most microorganisms ferment sugars, amino acids, and fatty acids, producing organic acids (mainly acetic, propionic, and butyric acids), alcohols (ethanol), ketones (acetone), carbon dioxide, and hydrogen. The production of acids promotes a decrease in the pH of the medium (Ordaz-Díaz and Bailón-Salas 2020; Li et al. 2019).

Fig. 7.1  Steps of the anaerobic digestion process. (Source: Adapted from De Farias Silva et al. 2019)

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Acetogenesis promotes the oxidation of acidogenesis products yielding a substrate suitable for methanogenic bacteria. In this phase, bacteria act as intermediaries in the acidogenesis and methanogenesis processes, forming hydrogen and carbon dioxide, with a pH decrease caused by acetic and propionic acid generation. In the fourth step, methanogenesis, methanogenic microorganisms consume the H+ ions in the solution and convert hydrogen and carbon dioxide into methane (Lyu et al. 2018; Li et al. 2019). When the substrate has the presence of sulfate in its composition, a fifth phase called sulfetogenesis occurs, where sulfate-reducing bacteria (SRB) act by reducing sulfate to sulfide, competing with methanogenic archaea for H2 and organic matter (Lyu et al. 2018).

7.3 Biomethane Production from Agricultural Wastes The amount of biomethane produced depends on the composition of the materials involved in the anaerobic process. Numerous organic and inorganic compounds form biomass structures, with carbohydrates, proteins, and lipids as the main organic components. This composition varies significantly for each type of substrate (Rasapoor et  al. 2020). A simplified bibliometric analysis encompassing 1000 works between 2019 and 2023 on the production of biomethane from agricultural waste shows that some of the most studied materials with energy purposes are manure (chicken, swine, cattle, dairy and pig), straw, crop residues and food waste (Fig. 7.2). Table 7.1 presents some research aimed at the production of methane from the anaerobic digestion of agricultural residues. Fernandes and De Oliveira (2006) studied a two-stage system using a compartmentalized reactor (ABR) followed by a

Fig. 7.2  Simplified bibliometric analysis on biomethane production from agricultural waste

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Table 7.1  Methane production from agricultural residues Residue (substrate) Pig farming wastewater

Swine manure and sweet potato (SP) or cassava wastewater (CW)

Cow manure (CM) with grass silage (GS), sugar beet tops (SBT) and oat straw (OS)

Fish waste silage (FWS) and cow manure (CM) Sun dried sugar beet pulp and cow manure Vinasse and molasses

Manipueira (cassava processing wastewater) Vinasse Manipueira with addition of cassava waste

Biodigester type Compartment reactor (ABR) and UASB reactor

Results ABR: 0.068 m3-CH4/ kg-Total CODremoved UASB: 0.053 m3-CH4/ kg-Total CODremoved System: 0.078 m3-CH4/ kg-Total CODremoved Semi-continuous Biogas yield digesters SP: 901 LN/kg-VSadded CW: 883 LN/kg-VSadded CH4 SP: 590.5 LN/kg-VSadded CW: 546.8 LN/kg-VSadded Continuously stirred CM-GS: 268 L-CH4/ tank reactors kg-VSadded (CSTR) CM-SBT: 229 L-CH4/ kg-VSadded CM-OS: 213 L-CH4/ kg-VSadded Semi-continuous 0.400 L-CH4/g-VS stirred tank reactors Semi-continuous 315 mL-CH4/g-VSadded reactor 0.245 m3-CH4/ Upflow anaerobic sludge blanket kg-CODremoved (UASB) Fixed bed anaerobic 0.430 ± 0.150 Lmethane/g-­ reactor COD Bench scale batch 541.4 L-CH4/kg-VS reactor 259 mL-CH4/g-CODremoved Upflow Anaerobic Sludge Blanket (UASB)

References Fernandes and De Oliveira (2006)

Villa et al. (2020)

Lehtomäki et al. (2007)

Solli et al. (2014) Gómez-Quiroga et al. (2022) Santana Junior et al. (2019) Oliveira et al. (2017) Kiyuna et al. (2017) Chavadej et al. (2019)

UASB reactor to treat swine wastewater. ABR reactor was operated with hydraulic retention times (HRT) between 56 and 18 h, and from 13 to 4 h for the UASB reactor. The total COD ranged from 7557 to 11,640 mg/L, and methane content was above 70% for both reactors. The highest specific methane yield of 0.068 m3-CH4/ kg-CODtotal-removed occurred in ABR with an OLR of 5.05  kg-CODtotal (m3/day). UASB reached a maximum of 0.053 m3-CH4/kg-CODtotal-removed at 2.84 kg-CODtotal (m3/day). Some studies indicate that the use of pig manure as a substrate in the mono-­ digestion process difficulted the process due to the presence of nitrogen concerning available organic carbon (Wang et  al. 2012; Yin et  al. 2015). The high nitrogen content can generate an elevated level of toxic ammonia. Thus, materials rich in

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organic carbon need to be added to swine manure to provide the necessary organic carbon to improve methane production (Ojediran et al. 2021). Villa et al. (2020) used semi-continuous reactors to analyze the co-digestion of swine manure (SM), sweet potato (SP), and cassava wastewater (CW) in different proportions. Initially, the authors tested a batch reactor with C/N ratios of 10/1, 13/1, 17/1, and 22/1. Based on the results of the first stage, the C/N ratio of 10/1 showed greater reductions of volatile solids and specific biogas productions. In a second step, the authors concluded that co-digestion of swine manure with sweet potato and cassava wastewater resulted in increased methane yields of 31.5% and 21.8% (SP: 590.5 ± 23.9 LN/kg-VSadded; CW: 546.8 ± 14.9 LN/kg-VSadded) compared to single digester (SM: 449.5 ± 23.0 LN/kgVSadded). Anaerobic digestion of cattle farming residues has also been widely adopted in co-digestion with other agricultural waste. Lehtomäki et al. (2007) analyzed the co-­ digestion of cow manure with different residues from plant production (grass, beet husk, and oat straw—grass silage, sugar beet tops, and oat straw) in continuously stirred tank bench-scale reactors (CSTRs). The highest specific methane yields were 268, 229, and 213 L-CH4/kg-VSadded when adding 30% of grass, beet husk, and oat straw to cow dung, respectively. Co-digestion with 30% plant material promoted an increase in methane production from 16% to 65% concerning manure mono-­ digestion. The addition of 40% of plant material resulted in a decrease in specific methane yield (4–12%). Solli et  al. (2014) evaluated the co-digestion of cow manure (CM) with fish waste silage (FWS) in increasing volumes (3%, 6%, 13%, 16%, and 19%). The highest methane production of 0,400 L-CH4/g-VS was obtained when adding 16% of FWS, corresponding to twice the methane production obtained from CM mono-digestion. Gómez-Quiroga et al. (2022) observed the effect of HRT (30–3 days) and OLR (2–24 g-VS/Lreactor/day) in semi-continuous reactors on sugar co-digestion sun-dried sugar beet with cow manure. The highest methane yield was 315 mL-CH4/g-VSadded, obtained in the 5-day and OLR of 12.47 g-VS/Lreactor/day. The results demonstrated the possibility of obtaining great efficiency and stability in the co-digestion of agro-­ industrial residues and cattle manure in short HRTs. Vinasse is a residue from sugarcane processing quite studied for bio-methane production. This wastewater has application as a biofertilizer in the cultivation of sugarcane, supplying the needs of the soil with some minerals such as potassium, nitrogen, and phosphorus, being an alternative to synthetic fertilizers, mainly to the supply of potassium (Ferraz Júnior et  al. 2016; Janke et  al. 2016). However, an incorrect and indiscriminate application can result in damage to the soil and groundwater due to the high organic load and low vinasse pH (Fuess and Garcia 2014). Thus, anaerobic digestion is an alternative for the correct disposal of vinasse, reducing its polluting load and producing bioenergy. However, the interruption of industrial operation during the off-season period requires a new start of the reactors at each harvest, hindering the viability of using vinasse for bio-methane production on a real scale. Some authors have already

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reported difficulties in resuming sugarcane from full-scale reactors in the anaerobic treatment of vinasse of each crop (Souza et al. 1992; Aguiar et al. 2011). The use of sugarcane molasses, a by-product of the sugar refining process, during the off-season period is an option to ensure continuous bio-methane production. Santana Junior et al. (2019) used a two-stage UASB reactor (R1 and R2) operated at thermophilic temperature to treat molasses. The highest methane yield was 0.245 m3-CH4/kg-CODremoved in reactor R2 (using vinasse as substrate) with OLR between 0.15 and 3.50 kg/m3/day. When fed with molasses, yields were 0.056 and 0.090  m3-CH4/kg-CODremoved (OLR of 7.1–7.5  kg/m3/day in R1) in R1 and R2, respectively. The authors observed a 58% increase in energy production for the two-­ stage system compared to the single stage. Another concern about anaerobic digestion of vinasse is the use of sulfuric acid by sugarcane distilleries to avoid microbial contamination and yeast flocculation in fermentation vessels (Barth et al. 2014). This procedure can entail sulfate concentrations up to 9 g/L in vinasse (Kiyuna et al. 2017), which potentially inhibits the development of anaerobic microbial populations responsible for bio-methane production, such as methanogenic Archaea. Kiyuna et al. (2017) evaluated the influence of sulfate on the anaerobic digestion of vinasse using batch reactors under thermophilic conditions. The authors adopted three COD/sulfate ratios (12.0, 10.0, and 7.5) to analyze COD removal and bio-­ methane production. The system achieved COD removals above 80%, indicating that interference of sulfetogenesis was negligible to the degradation of organic matter. The authors observed a reduction in bio-methane production of 35% for the COD/sulfate of 7.5 (351.5  L-CH4/kg-VS) concerning the ratio of 12.0 (541.4 L-CH4/kg-VS). Oliveira et al. (2017) used an anaerobic fluidized bed reactor (AFBR) fed with cassava to produce hydrogen in the acidogenic phase. Later, a fixed bed reactor (FBR) was fed with RALF effluent to produce methane in the methanogenic phase. Expanded clay and shells of sururu (Mytella falcata) were used as support material in AFBR and FBR, respectively. The highest hydrogen yield was 1.91 mol-H2/mol-­ glucose in the HRT of 2 h, and the highest methane yield was 0.430 ± 0.150 L-methane/ g-COD in the HRT of 12  h. The authors also observed that the shells of sururu neutralized the pH in the fixed bed reactor efficiently. Chavadej et al. (2019) analyzed UASB reactors to produce biohydrogen and bio-­ methane in separate phases. The systems were operated at a thermophilic temperature (55 °C) using different concentrations of cassava residues. The concentration of 1200  mg/L resulted in the best biogas compositions: 42.3% H2, 55% CO2, and 2.70% CH4 for the acidogenic reactor, and 70.5% CH4, 28% CO2, and 1.5% H2 for the methanogenic reactor. The maximum biohydrogen and bio-methane yields were 15  mL-H2/g-CODremoved and 259  mL-CH4/g-CODremoved, displaying augmentations of 45.2% and 150% in H2 and CH4 production, respectively, compared to the system without the addition of cassava residue.

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7.4 Substrate Pre-treatment Most agricultural waste used in anaerobic digestion is of animal origin, especially from swine and cattle farming (Filho et al. 2018). According to Avaci et al. (2013), animal manure has already undergone a digestion process in the animal’s intestine, which would facilitate treatment. In the case of vegetable waste, the lignin presence hinders the anaerobic digestion process since it is a compound difficult to digest, despite the high fermentation potential. The high lignocellulosic structure resistance to hydrolysis causes operational system instability and restrains biodegradability (Yang et al. 2015). Thus, it is necessary to adopt some pre-treatment of this type of waste so that the microorganisms involved in the process can decompose the biomass more efficiently and quickly, increasing the methane contents in the biogas composition at the end of the process (Tian et al. 2018). The methods of substrates pre-treatment for anaerobic digestion can be classified as mechanical, thermal, chemical, enzymatic, or combinations of these. Mechanical pre-treatments are ultrasound, high pressure, grinding, and extrusion. They aim to reduce the size of waste particles, increasing their solubility and the contact surface with the microorganisms. This type of pre-treatment is generally adopted when the waste has large particles, such as food-industry, agricultural, and household organic residues (Appels et al. 2008; Carlsson et al. 2012). Thermal pre-treatments employ extreme temperatures and high pressures, seeking to avoid evaporation. In this case, the objective is the solubilization or degradation of components with a high molecular weight into simpler substances that can be decomposed more easily. Freezing cycles (from −10 to −80 °C) and thawing are also adopted as a pre-heat treatment in search of greater solubilization and reduction in the size of the waste particles (Wang et  al. 1999; Montusiewicz et  al. 2010; Carlsson et al. 2012). The chemical pre-treatment aims to destroy the cell wall and membrane present in the waste by the addition of acids or bases, increasing its solubilization. Before the start of the operation, it is necessary to neutralize the substrate pH to promote methane production. The pre-treatment combining chemical and thermal techniques is an advantageous option that employs lower temperatures (Appels et  al. 2008; Carlsson et al. 2012). Oxidation of substrates, another form of chemical pre-treatment, can be carried out using oxygen or air, at high temperatures and pressures, or ozone. Despite the efficiency of substrate solubilization, oxidation can be unfeasible due to high energy costs (Appels et al. 2008; Carlsson et al. 2012). Enzymatic pre-treatment aims to hydrolyze organic waste, facilitating the action of microorganisms (Pinheiro 2021). The requirement to adopt a substrate pre-treatment constrains the use of plant residues in the anaerobic digestion process. In general, its disposal in the soil is a more accessible alternative with a low environmental impact, unlike animal waste. Plant residues provide nutrients and help maintain soil moisture, besides protecting against erosion (Ramalho Filho and Beek 1995).

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However, the co-digestion of plant waste with other types of residues can overcome the need for pre-treatment. This technique associates two or more substrates to accelerate the anaerobic digestion of complex compounds, increasing biogas production from 25% to 400% compared to mono-digestion of the same substrates (Siddique and Wahid 2018). The co-digestion strategy can bring advantages such as reduction of toxic compound concentration, better loading of the biodegradable substrate, improved digestion rate, and increased biogas production (Cook et  al. 2017; Neshat et al. 2017; Bedoić et al. 2019).

7.5 Conclusions The anaerobic digestion process is a suitable alternative for biomethane production using different types of waste. The foremost agricultural residues studied as substrates are leftovers, crop residues, agro-industrial effluents, and animal manure such as swine and cattle. Animal composts are largely applied in anaerobic reactors since it is a material that has already gone through a digestion process in the animal’s intestine, which would facilitate the treatment. Despite the high fermentation potential of vegetal wastes, lignin is a plant constituent that hampers the anaerobic digestion process, requiring the adoption of pre-­ treatment techniques, which restricts its use. However, the co-digestion of materials of plant origin with other types of residues is a promising alternative for biomethane production. Co-digestion is an efficient and economical alternative, replacing the need to adopt substrate pre-treatments and overcoming the obstacles of mono-­ digestion. Another strategy that can result in elevated energy gain is separate acidogenic and methanogenic phases in different reactors, producing bio-hydrogen and biomethane separately. Therefore, this chapter presented a waste and wastewater variety from the agricultural sector commonly unused or inappropriately discarded in the environment. The treatment of agricultural residue by anaerobic digestion can generate value-­ added products such as biogas and natural biofertilizer to enrich soils lacking in organic matter. Anaerobic digestion presents economic advantages, reducing costs with the gas purchase and waste transport, and environmental benefits, avoiding the disposal of pollutants and generating a renewable energy source.

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Chapter 8

Biofuel Production from Agricultural Residue: An Effective and Sustainable Approach for Management of Agro-waste Swati Sachdev

Abstract Agriculture intensification for production of more food to feed an increasing global population, as a consequence, generates a large volume of agricultural waste. The agro-waste, which is biochemically composed of cellulose, lignin, and hemicellulose, is frequently burned or buried in the soil. These disposal methods result in the release of noxious compounds into the environment that agitates the problem of pollution, human health issues, and global warming. To overcome such drawbacks, some agro-wastes are utilized for roof thatching, soil mulching, and making products like papers, matchsticks, and others. Nevertheless, these approaches cannot entirely solve the problem of agricultural residue generation. However, the conversion of plant biomass into biofuel could facilitate the reduction of residue comprehensively along with the generation of value-added products. The production of biofuel can be mediated by the action of certain microorganisms and enzymes. The efficient utilization of such microbes and/or enzymes could facilitate sustainable management of agro-waste with the generation of renewable bioenergy and economic benefits. Keywords Bioenergy · Economic benefits · Global warming · Lignocellulose · Value-added products

S. Sachdev (*) Department of Liberal Education, Era University, Lucknow, Uttar Pradesh, India e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024 P. Singh (ed.), Emerging Trends and Techniques in Biofuel Production from Agricultural Waste, Clean Energy Production Technologies, https://doi.org/10.1007/978-981-99-8244-8_8

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8.1 Introduction The continuously growing human population and escalating industrial development have increased the demand for food and energy. In the past 100 years, the global population has increased fourfold and the annual energy generation by 21 times (Pryshliak and Tokarchuk 2020). Thus, to ensure food and energy security, the burden on agricultural lands and fossil fuel has been intensified. As a consequence, it has led to the generation of tons of agro-waste and the depletion of reserves of traditional energy resources. The agro-waste produced is often disposed of unsustainably in landfills or by burning, which generates harmful gases, eventually causing air pollution (Yevich and Logan 2003; Afolalu et al. 2021). In India, in 2017, wheat residue alone accounted for 29% of the total crop residue generated and 26% of the total crop residue burned. A similar trend, if continued, the crop residue emission will increase by 45% by the year 2050 (Tiwari et al. 2021). Moreover, the excessive use of fossil fuel as a primary energy source to fulfill the global energy demand has diminished the fuel reserve size and increased greenhouse gas (GHGs) concentration in the atmosphere (Panpatte and Jhala 2019). Increased levels of GHGs have aggravated the issue of global warming and climate change (Chandra et al. 2012; Panpatte and Jhala 2019). To overcome the problem of agro-waste disposal, resolve the issue of energy crisis, and mitigate climate change in a sustainable manner, utilization of agricultural waste for biofuel generation is an effective and eco-friendly alternative (Milano et al. 2022). Biofuels are fuels that are derived directly or indirectly from biomass. Biomass is a renewable resource that traps solar energy through photosynthesis and converts it into chemical energy. Thus, biomass shows extensive potential to generate biofuels. There are four generations of biofuel production depending upon the feedstock used for their production. The first generation of biofuel production is based on food crops and utilizes sugars, starch, and vegetable oils. However, the use of food crops for biofuel generation increases pressure on land as well as on water resources for the production of more edible crops, resulting in food shortage, monoculture cropping, and noneconomical production (Panpatte and Jhala 2019; Mehmood et  al. 2021). The second generation of biofuel production depends upon the utilization of agro-based biomass, like nonedible crops, forest biomass, and grasses, and agro-­ waste, including plant residues, agro-industry waste, and wood chips, which are mainly composed of lignocellulosic (lignin (7–25% of dry matter), cellulose (30–60% of dry matter), and hemicellulose (14–40% of dry matter)) materials (Robak and Balcerek 2018; Tiwari et al. 2021). This method facilitates the utilization of huge amounts of agricultural waste sustainably, improves economic development, and does not induce pressure on agricultural lands. Third-generation biofuel is obtained from algae having more than 50% of oil content, whereas fourth-­ generation biofuel involves the use of genetically modified algae (Panpatte and Jhala 2019; Mehmood et  al. 2021). The major limitation linked with algal-based third- and fourth-generation biofuel production is a high economic investment and

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environmental as well as a health risk, respectively (Panpatte and Jhala 2019; Abdullah et al. 2019). The production of a second-generation biofuel is an effective approach for producing biofuel and utilizes locally available agro-waste. The agro-waste generated by a nation can be employed to derive biofuels such as biogas, bioethanol, and biodiesel (Sarangi and Nayak 2021), which not only reduces the volume of the agricultural solid waste but also alleviates environmental pollution, generates cheap and renewable energy, and facilitates economy development in rural areas (Anwar et al. 2018; Boro et al. 2022; Hoang et al. 2023). As per the estimate of the International Energy Agency and World Bioenergy Association, biomass-based energy accounted for 72.3% share of the total renewable energy utilized all over the world in 2016. Moreover, the generation of energy from biomass has been recorded to be elevated from 42.8  EJ in 2000 to 56.5  EJ in 2016 (Uthandi et  al. 2022). Thus, the recent chapter aims to focus on the production of various biofuels from agricultural waste and provide information regarding benefits and new advances achieved in the field of biofuel production and application.

8.2 Agro-waste for Biofuel Production Agricultural waste and agro-based industry by-products are low-cost feedstock commonly utilized for the production of biofuels (Fig. 8.1). It has been anticipated that nearly 4 billion tons of agro-residue is generated annually and 75% of which is contributed by cereal crops (Sarangi and Nayak 2021). Agro-waste includes the waste generated as a result of farming activities that include crop cultivation, horticulture, dairy farming, animal husbandry, market gardens, and forestry (El-Ramady et al. 2022). It has been estimated that globally nearly 30% of the agricultural material produced end up as waste (El-Ramady et al. 2022). Crop straw, stover and husk, seed hulls, shells, sawdust, bagasse, meat, dairy waste products, and wood chips are major agro-wastes that are generated in huge quantities and could be used to produce value-added products including biofuels, agro-composites, nanocellulose, compost, biochar, and others (Afolalu et al. 2021; El-Ramady et al. 2022). Generally, agricultural waste has been categorized into four categories, i.e., crop residue, agro-­ industrial waste, livestock waste, and fruit and vegetable wastes based on their production technologies (Demirbas et al. 2011; Pattanaik et al. 2019). Crop residues include the waste generated directly from crop cultivation such as wheat, corn, and rice straw (Afolalu et al. 2021). These are the cheapest and abundantly available forms of agro-waste that can be easily converted into biofuel. Agro-industrial waste includes by-products and/or waste generated from food processing industries such as poultry waste, bagasse, molasses, fruit and vegetable peel, meat, animal fat, de-­ oiled seed cakes, and starch residue (Afolalu et al. 2021). This type of waste is also utilized for biofuel generation. For instance, bagasse which is obtained in huge quantities from the sugar industries is used to produce bioethanol. The waste generated from livestock manure is utilized as a suitable substrate for biofuel production,

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Fig. 8.1  Use of different agro-waste for the production of biofuel

particularly biogas (Seglah et al. 2022). Unprocessed waste of fruits and vegetables is also an agro-waste that could be used for biofuel generation. Like other agro-­ wastes, a huge quantity of fruit and vegetable waste is generated annually. In India, it has been reported that nearly 5.6  million tons of fruit and vegetable wastes is produced every year (Afolalu et al. 2021).

8.3 Types of Biofuels The fuels which are derived from biomass such as plants, algae, and waste generated from agriculture, industrial, domestic, and commercial sectors are called biofuels (Panpatte and Jhala 2019). Biofuels can be in the form of solids, liquids, and gas. They have the potential to replace conventional fuel sources due to their renewable nature (Basumatary et al. 2018; Afolalu et al. 2021). Biofuels are synthesized from agro-waste by using approaches like fermentation, anaerobic digestion, pyrolysis, combustion, and gasification (Koupaie et al. 2019). Various types of biofuels can be produced using biomass, in particular biogas, biomethanol, bioethanol, and biodiesel.

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8.3.1 Biodiesel It is one of the most important biofuels. Biodiesel has gained attention all around the world owing to its characteristics of biodegradability, nontoxicity, carbon neutrality, and renewable nature (Basumatary et al. 2018; Milano et al. 2022). Production of biodiesel was initiated in the early 1990s, and since then, it is increasing steadily (Balat and Balat 2009). Biodiesel is an alternative solution to petroleum diesel, which is produced via the transesterification of oils and/or fats (Demirbas 2002, 2009a). Transesterification of agro-waste includes the conversion of branched triglycerides into simpler and smaller straight chain esters (Narnoliya et al. 2018). In the process of transesterification, methanol is used as a solvent to abridge the saponification reaction (Rajendran et  al. 2022). Biodiesel has slightly low power and torque and higher fuel consumption than diesel #2 (Demirbas 2009a). However, biodiesel has better aromatic content, lubricity, flash point, and biodegradability than conventional diesel fuel (Demirbas 2009b). Biodiesel shows an improved combustion capacity due to the presence of oxygen (10–11%), which results in low emission of particulate matter, oxides of sulfur, carbon monoxides, and hydrocarbon but high emission of nitrogen oxide (Demirbas 2005, 2009a; Demirbas et al. 2011; Mehmood et al. 2018; Raman et al. 2019; Kanakdande and Khobragade 2020; Milano et al. 2022). Thus, biodiesel is blended with conventional diesel to reduce notorious emissions. The reduction in emissions increases with an increase in the amount of biodiesel in the blend (Demirbas et al. 2011). Moreover, the biodiesel-­ diesel fuel blend improves engine torque, brake power, thermal brake efficiency, and fuel efficiency (Dharma et al. 2017; Milano et al. 2022). Direct use of biodiesel in conventional diesel engines is avoided due to its high viscosity and low oxidative stability, which results in the corrosion of fuel tanks, pipes, and injectors, that is why it is blended with diesel (Mehmood et al. 2018; Milano et al. 2022). Biodiesel can be blended with fossil-based diesel in any amount and used in diesel engines without any modification (Demirbas et  al. 2011; Kanakdande and Khobragade 2020). Biodiesel can be used as an additive in small amounts in low-sulfur-­ containing diesel, which improves its lost lubricity due to the elimination of sulfur content (Dorado et al. 2003; Demirbas 2009a). Production of biodiesel from nonedible oilseed crops and waste cooking oil has gained momentum in recent years to reduce dependency on oil-rich edible crops, land use for oil crop cultivation, and water used for irrigation, which otherwise incur environmental as well as economic burden and abridge availability of food grade materials (Kanakdande and Khobragade 2020; Azadbakht et  al. 2021; Rajendran et  al. 2022). The waste oil generated from post-processing industries and fast food restaurants could be utilized for manufacturing biodiesel (Milano et al. 2022). Biodiesel can also be synthesized by using microorganisms that have high lipid content, and for the growth of such microbes, agro-waste is used as a substrate and source of nutrition (Narnoliya et al. 2018).

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8.3.2 Bioethanol Bioethanol or ethyl alcohol (C2H5OH) is an excellent renewable liquid biofuel, which shows compatibility with modern internal combustion engines due to the high octane number. Bioethanol has an octane number of 108 that prevents engine knocking and early ignition and therefore has a high antiknock value (Aditiya et al. 2016). Bioethanol has 68% less energy content than petrol but high oxygen content that generates less toxic emissions (Aditiya et al. 2016). It alleviates carbon dioxide emission by 80% compared to petrol; thus, it is considered an eco-friendly fuel (Aditiya et al. 2016). Bioethanol used in vehicles to run engines is often blended with petrol as per the standard (Aditiya et  al. 2016; Bušić et  al. 2018). As per European Union (EU) quality standard EN 228, 5% bioethanol is blended with petrol and used in existing engines without any modification. However, modification in engines can allow the use of 85% of bioethanol (E85) (Demirbas 2009a). Bioethanol is produced via fermentation of simple sugars, which is mediated by enzymatic digestion. Microorganisms are used in the process of bioethanol production, which facilitates digestion or fermentation (Kour et al. 2019). Plant residues, particularly rice, wheat, and corn straw, are suitable substrates for the production of bioethanol due to lignocellulosic content (Swain et  al. 2019). The cellulose and hemicellulose portion of lignocellulose can easily be hydrolyzed into soluble sugars which can be fermented to produce bioethanol (Binod et al. 2010). The process of bioethanol production is affected by several factors such as high lignin content, degree of polymerization, crystalline structure of cellulose, moisture content, and available surface area (Swain et al. 2019). Therefore, before hydrolysis and fermentation, pre-treatment of agro-waste is performed (Swain et al. 2019). The process of bioethanol production includes multiple steps (Fig. 8.2). Initially, agro-waste used as feedstock is pre-treated and then undergoes hydrolysis in the presence of microbial enzymes. The pre-treatment process involves various methods that are classified as physical (milling, grinding, irradiation), physicochemical (steam explosion, supercritical fluid pre-treatment), chemical (treatment with dilute acid or alkali), biological (microbial, enzymatic), and green solvent-based processes (Brodeur et al. 2011; Swain et al. 2019; Awogbemi and Von Kallon 2022). The second step of hydrolysis facilitates the conversion of complex carbohydrates into simpler forms such as glucose and pentose, using cellulolytic enzymes, which cleave polymers of cellulose and hemicellulose (Zhang and Lynd 2004; Swain et al. 2019). Further, the feedstock material is fermented in the presence of microorganisms, particularly yeast, which is subsequently followed by distillation and dehydration (Demirbas 2009a, 2009b; Kour et  al. 2019). The method selected for the pre-­ treatment of raw material is crucial as it facilitates an increase in bioethanol production (Kour et  al. 2019). For instance, rice straw pre-treated with different concentrations of NaOH (0.5%, 1.0%, 1.5%, and 2.0%) was reported to generate better sugar yield on treatment with 1.5% NaOH than other concentrations (Ashoor and Sukumaran 2020). Similarly, pre-treatment of rice straw with dilute sulfuric acid yielded 0.72  g/g of sugar during enzymatic hydrolysis, whereas

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Fig. 8.2  Steps involved in the production of bioethanol

steam-pre-­treated and steam-nontreated straw resulted in 0.60 g/g and 0.46 g/g of sugar yield, respectively (Abedinifar et al. 2009).

8.3.3 Biomethanol Biomethanol is a potential renewable biofuel, which can be generated from agro-­ waste. Biomethanol is considered superior to bioethanol because of the higher specific energy yield (Demirbas 2008). Liquid biomethanol exhibits several benefits over other fuels. It is easy to store and can easily be transported at room temperature (Gautam et al. 2020). Moreover, it has high a volumetric energy density and high octane number as compared to gasoline (Kumabe et al. 2008; Gautam et al. 2020). Biomethanol from biomass can be produced via two approaches: thermochemical conversion and biochemical method (Gautam et  al. 2020). The thermochemical method operates in two steps. The first step involves the conversion of biomass into

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syngas (a mixture of hydrogen and carbon monoxide) on thermal decomposition (high temperature and pressure) under oxygen-deficient conditions (gasification) (Sarangi et al. 2020). The syngas in the next step is catalytically processed to generate biomethanol (Gautam et al. 2020). The biochemical process of methanol synthesis involves the production of biogas (methane) from biomass through anaerobic digestion. The methane is then converted into methanol by methanotrophs. These microorganisms perform the conversion of methane into methanol under ambient temperature and pressure conditions in the rate-limiting step of methane oxidation in the presence of an enzymatic catalyst, methane monooxygenase (MMO) (Gautam et al. 2020). In the biochemical process of methanol production, the enzyme methanol dehydrogenase (MDH), an inhibitor of MMO, is also used to prevent further oxidation (Gautam et al. 2020). The commercial bioconversion of agro-­waste into biomethanol involves four steps, viz., pre-treatment, biogas production via anaerobic digestion, biogas purification, and methanol production. Pre-treatment is performed to break down the recalcitrant lignin and make it susceptible to biodegradation. Pre-treatment is followed by anaerobic digestion which takes place in a two-stage anaerobic digester to stabilize the process and increase biogas production. The biogas obtained is treated to remove gases like hydrogen sulfide generated as a side product, to eliminate their inhibitory, poisonous, and corrosive effect. The hydrogen sulfide is converted into elemental sulfur or sulfate by biological oxidation using biofilters containing bacteria like Thiobacillus and Sulfurimonas. Finally, the clean biogas is added to a bioreactor (trickle filter or fluidized bioreactor) as a substrate for methanotrophs to produce methanol (Gautam et al. 2020).

8.3.4 Biogas Biogas is an attractive alternative biofuel that is generated from waste organic materials. It contains 65–70% of methane gas and 30–45% carbon dioxide along with traces of other gases like hydrogen, nitrogen, and hydrogen sulfide (Azadbakht et al. 2021). The composition of the gas depends on the substrate used as feedstock and the conditions of anaerobic digestion (Neshat et al. 2017). The calorific value of biogas is 21–24 MJ/m3 (Azadbakht et al. 2021). Biogas can be produced from biomass through anaerobic fermentation/digestion, also known as bio-methanation (Azadbakht et al. 2021; Tiwari et al. 2021; Devi et al. 2022). Anaerobic fermentation is a complex process, which involves the action of facultative and anaerobic microorganisms such as acidogens, methanogens, and hydrolytic organisms in the absence of oxygen (Neshat et al. 2017). Anaerobic fermentation facilitates the conversion of complex organic material into a simpler form by recruiting various stages, i.e., hydrolysis, acidogenesis (also known as fermentation), and methanogenesis (Hagos et al. 2017; Neshat et al. 2017) (Fig. 8.3). The first step of anaerobic fermentation, i.e., hydrolysis, involves the conversion of complex substances like protein, nucleic acids, polysaccharides, and fats into amino acids, purines, pyrimidines, fatty acid, and monosaccharides. Acidogenesis or fermentation stage is subsequently

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Fig. 8.3  Steps involved in biogas production through anaerobic digestion

followed, resulting in the production of carbon dioxide, hydrogen, acetate, methanol, and others, eventually leading to the final stage of methane gas production (methanogenesis), catalyzed by the action of methanogens (Neshat et al. 2017). Biogas production through agro-waste has several ecological benefits (Neshat et al. 2017). Biogas is used for electricity and heat cogeneration, and the digestate produced is applied as a fertilizer (Bolzonella et  al. 2020). Moreover, anaerobic digestion facilitates the reduction of volume, odor, and putrescible organic matter of waste that otherwise contributes to GHG levels in the atmosphere (Bolzonella et al. 2020). The production of biogas from agro-waste has one major drawback. Agro-­ wastes such as corn stover, straw, and others are comprised of lignocellulosic material, which biodegrades very slowly and thus reduces the biogas production capacity (Bolzonella et al. 2020; Azadbakht et al. 2021; Tamang et al. 2023). Only 40–50% of the substrate is utilized for biogas production; the rest remains in the digester in unused form and affects the efficiency of the process (Bolzonella et  al. 2020). Besides, the digestate produced as an end product is stabilized partially which could result in odor and leakage on field application (Bolzonella et  al. 2020). The

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challenge posed by the low biodegradability of feedstock is resolved through pretreatment of the agro-waste. The pre-treatment improves the biodegradability of biorecalcitrant lignocellulosic waste by increasing its porosity and specific surface for microbes performing anaerobic digestion (Bolzonella et  al. 2020). Moreover, pre-treatment of agro-waste optimizes biogas production and enhances the stabilization of organic substrate generated at the end of the digestion (Bolzonella et al. 2020). Biogas production from agro-waste such as lignocellulose co-digested with other biodegradable materials (livestock manure, sewage sludge) could enhance the capacity of the anaerobic digestion process (Hagos et al. 2017; Tiwari et al. 2021). Lignocellulosic waste has high carbon content but low nitrogen content, resulting in high C/N ratio i.e., it has >50 C/N ratio, which eventually slower down the biodegradation (Tiwari et al. 2021). This reduces the efficiency of the digester to generate methane/biogas. The addition of another organic substrate that is rich in nitrogen such as livestock manure to the lignocellulosic feedstock could maintain the optimum C/N ratio, thereby improving the anaerobic digestion process and increasing biogas yield (Tyagi et  al. 2018; Tiwari et  al. 2021). The anaerobic co-digestion method also reduces the cost of biogas production from agro-waste, which generally remains high when lignocellulosic waste is pre-treated to enhance biodegradation (Neshat et al. 2017).

8.4 Technological Advancement to Improve Biofuel Production 8.4.1 Direct Interspecies Electron Transfer (DIET) This method has emerged as a solution for the challenges posed by the conventional anaerobic digestion process of biogas production (Gahlot et al. 2020; Tiwari et al. 2021). The application of DIET increases biogas production compared to microbe-­ amended anaerobic digestion and non-amended anaerobic digestion method (Zhang et  al. 2020). DIET process includes the transfer of a free electron between syntrophic microbes (necessary to overcome the energy barrier and facilitate catabolism of complex organic materials), without requiring an electron carrier or redox mediator, i.e., indirect interspecies electron transfer (IIET), which are involved in conventional anaerobic digestion process (Gahlot et al. 2020; Tiwari et al. 2021). Thus, the application of the DIET technique in the anaerobic digestion process is an alternative to IIET (Baek et al. 2018). The process of DIET takes place via three basic mechanisms, i.e., abiotic conductive materials like carbon-based materials, conductive pili, and membrane-bound electron transport proteins (Baek et al. 2018; Gahlot et al. 2020). The process of DIET mediated by iron oxide minerals as conductive material for cell-to-cell electron transfer was demonstrated by Kato et al. (2012). Analogously, the amendment of granular activated carbon and granular biochar to the anaerobic fermentation process involving the digestion of lignocellulosic

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waste with sewage sludge under thermophilic conditions increased biogas production efficiency and process stability (Tiwari et al. 2021).

8.4.2 Synthetic Biology Aided Production of Biofuel from Agro-waste To enhance the production of biofuel, there is a need to develop technology that improves the efficiency of the processes. For instance, the production of bio-ethanol through fermentation, where complex sugars are catabolized to simple sugars, could be increased by using genetically engineered microorganisms having better catabolic activity (Narnoliya et al. 2018). This can be achieved through the application of systemic biology. Systemic biology includes engineering and biology in a single stream. Systemic biology deals with the study of omics, i.e., genomic, proteomic, transcriptomic, and metabolomics, which facilitate to derive the valuable information on genes and enzymes that could be manipulated to engineer organisms or enzymes with desired characteristics (Narnoliya et al. 2018). In particular, for the production of biodiesel from yeast, recruitment of system biology can aid in identifying the pathways and enzymes that could enhance the oil content, and via the aid of genetic engineering, such pathways and enzymes could be altered (Narnoliya et al. 2018). The yeast Saccharomyces cerevisiae is well-known to mediate the production process of bioethanol from agro-waste. However, the efficiency of the yeast reduces with the production of compounds and altered conditions that could hamper their growth. However, these issues can be overcome by using systemic biology approaches (Madhavan et al. 2019).

8.5 Conclusion and Future Prospects Agro-waste generation and its disposal are great challenges worldwide. Burning of crop residues to dispose of waste is unsustainable and causes environmental pollution. Conversion of agro-waste into biofuel serves multiple benefits along with the sustainable management of waste. Biomass can be converted into liquids, solids, as well as gaseous biofuels by using approaches like fermentation, anaerobic digestion, gasification, pyrolysis, and combustion. The biofuels such as biogas, bioethanol, and others synthesized from agro-waste have enormous potential to be used as an alternative fuel. However, the conversion of lignocellulosic wastes into biofuels presents challenges due to their recalcitrant nature. To overcome such problems, waste is pre-treated before biofuel production, which incurs high-cost inputs. Many technological advancements have been attained to improve the efficiency of process generating biofuels, but, still, more research is needed to reduce the cost and increase

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the rate of biofuel production. This achievement would facilitate the substitution of conventional fossil fuels with renewable and less polluting biofuels.

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Chapter 9

Production and Characterization of Bio-alcohols from Agricultural Wastes Dharitri Borah, Baldev Edachery, Jayashree Rout, and Thajuddin Nooruddin

Abstract With the implementation of modern innovative technologies in agriculture, productivity is raised with profuse waste generation globally. Most often, huge agricultural wastes are burnt (stubble burning) and release harmful emissions into the air. It causes concern to the public and animal health, productivity (land and water), and economic loss. Bio-alcohols from the fermentation of agricultural waste do not compete with food, support other energy resources, and contribute to a circular economy and employment generation, together with clean energy. At present, most countries allow blending of bio-alcohols with gasoline for low emissions, energy security, saving foreign exchange, and socioeconomic upliftment with employment generation. Commercially, bio-alcohol production for biofuel is dependent on substrates like cellulose content/fermentable carbohydrates, microorganisms for fermentation, pre-treatment processes, inhibitory/toxic compounds (furfural, ferulic, phenolic compounds), growth medium, fermentation mode (fedbatch/continuous), engine performance (spark ignition/compression ignition), etc. Therefore, it is worthwhile to study the different aspects of bio-alcohol generation from agricultural wastes for sustainable, economically viable, clean bioenergy production. Keywords Agricultural waste · Bioenergy · Bio-alcohol blends · Fermentation · Engine performance D. Borah (*) Department of Environmental Science, Arunachal University of Studies, Namsai, Arunachal Pradesh, India B. Edachery Research and Development, Sreedhareeyam Farmherbs India Pvt. Ltd., Ernakulam, Kerala, India J. Rout Department of Ecology and Environmental Science, Assam University, Silchar, Assam, India T. Nooruddin Department of Microbiology, Bharathidasan University, Tiruchirappalli, Tamil Nadu, India © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024 P. Singh (ed.), Emerging Trends and Techniques in Biofuel Production from Agricultural Waste, Clean Energy Production Technologies, https://doi.org/10.1007/978-981-99-8244-8_9

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9.1 Introduction Agriculture is the only sector providing food of 24 million tons globally. However, agriculture is a potent source of greenhouse gases (21%) like CH4, N2O, CO, etc. with a notable impact pertaining to environment. The augmented agricultural production for requirement of the global population has resulted into the remarkable generation (production/processing/consumption/harvesting/livestock/aquaculture) of worldwide “agricultural solid wastes” (Adejumo and Adebiyi 2020). Agricultural wastes (AW) are the nonproduct production/processing outputs of products of which economic value for beneficial use is lower than the collection/transportation/ processing cost. Many countries are associated with rapid population growth/economic progress together with an increase in AW (Koul et al. 2022). China is the biggest producer of AW, followed by India generating huge amounts of paddy straw (130 million tonnes) composed of fodder.

9.1.1 Sources of Agricultural Wastes and Worldwide Production The annual global production of “biomass waste” is 140 Gt (Tripathi et al. 2019). This discarded biomass (leaves, stalks, roots, seed shells/nutshells, and fruit peels) has the negative impact on the environment. At least 3287 Mt of fresh weight of AW is generated from different countries, viz., China (716 Mt), the USA (682 Mt), India (605  Mt), Europe (580  Mt), Brazil (451  Mt), Argentina (148  Mt), and Canada (105  Mt). The UN’s Food and Agriculture Organization (FAO) has projected an increase of 13% of agricultural land use by the year 2030. By 2050, the global cereal will be increased by 0.9% with higher (60%) agricultural activity compared to 2007. The greater cereal crops are projected to be from developing countries. According to waste balance of the countries, China is the prime producer of waste after biomass processing of walnut shells (~40%), followed by India (~5%). At least 20% of rice husk remains unused in countries like India, Brazil, the USA, China, and Indonesia (Sokolova et al. 2018). For EU28 (2010–2016), agricultural waste and by-products (18.4  billion tonnes) are contributed by the sectors, viz., vegetable (~44%), animal (~31%), cereal (~22%), and fruits (~2%). The world’s population is likely to increase to 9 billion (2050) to 11 billion (2100) as predicted (Koop and van Leeuwen 2017; Koul et al. 2022). The sources of AW are crop residues (leaf litter, seed pods, stalks, stems, straws, husks), livestock wastes (urine, dung, wash water, residual milk), poultry wastes (spilled feed, feathers, droppings), agro-industrial wastes (bagasse, molasses, peels), pulps (orange, apple, mango, guava), etc. High population density with industrialization was responsible for the animal sector in developed countries. The higher agricultural wastes and by-products generated from cereal, fruit, and vegetable are from the countries with high land area and favorable climatic conditions (Bedoić et  al. 2019). The AW is predominantly of

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cellulose (30–50%), followed by lignin and hemicellulose. The global issue is the burning/burying of AW causing pollution to air, water, and soil. Also, the application of AW feedstocks for bio-alcohols reduces the substrate cost. Rice abundantly grown in Asian countries is a major source of cellulose and a low-cost substrate for bio-alcohol with low emission (Vivek et al. 2019).

9.1.2 Classification of Agricultural Wastes Agricultural solid wastes have been broadly classified into animal production (damaged feeders, animal carcasses, watering trough), food and meat processing (feathers, bones, hoofs, animal carcasses), crop production (husks, crop residues), on-farm medical (vaccine wrappers/containers, syringes, needles), horticultural production (prunings/grass cuttings), industrial agricultural (wood processing/paper), and other wastes (pesticide, insecticide, herbicide) generated through agriculture (Adejumo and Adebiyi 2020). The “agro-industrial wastes” are categorized into “agricultural residues” and “industrial residues” (Sadh et al. 2018). The “agricultural residues” are composed of field residues (stem, stalk, leaves, seed pods) and process residues (husks, seeds, roots, bagasse, molasses). Agricultural wastes can also be classified into crop residue (rice/wheat/barley/oat straw, corn stover), industrial processing waste (rice bran, bagasse, de-oiled seed cakes, rice husk, orange peel), livestock waste (cattle manure, swine manure, animal fat), and food waste (mango, apple, cabbage, tomato) obtained from production and processing (Pattanaik et al. 2019). The prime AW biomass produced is the rice husk (48%) and bagasse (34%) (Duque-­ Acevedo et al. 2022).

9.1.3 Composition of Agricultural Wastes The chemical composition varies with the nature of AW. The AW is mostly composed of lignocelluloses. Mostly, the crop residues contain cellulose (30–50%) followed by hemicellulose (20–38%) with lignin of 7–21% (Pattanaik et  al. 2019). Bagasse contains hemicellulose (56.7%), followed by cellulose (30.2%) and lignin (13.4%). Maximum cellulose is found in corn stalks (61.2%) followed by cotton stalks (58.5%), sawdust (45.1%), sunflower stalks (42.1%), oat straw (39.4%), rice straw (39.2%), soya stalk (34.5%), barley straw (33.8%), and wheat straw of 32.9% (Sadh et al. 2018). Likewise, lignin content is highest in rice straw (36.1%), sawdust (24.2%), cotton stalk (21.5%), soya stalks (19.8%), oat straw (17.5%), barley straw (13.8%), sunflower straw/sugarcane bagasse (13.4%), etc. In “agro-industrial wastes,” the total solid is comprised of >80%. The ultimate analysis of AW presents maximum carbon in barley straw (49.4%), followed by oat straw (48.8%), wheat straw (41.7–46.7%), corn stover (35.2–45.6%), and rice straw (34–41.5%) (Pattanaik et  al. 2019). The sulfur content varies from 0.1% to 0.13%. In crop residue, the

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proximate analysis presents maximum fixed carbon in barley straw (19.79%), followed by oat straw (19.53%), wheat straw (17.3%), corn stover (16.9%), and rice straw (14.5%).

9.1.4 Biofuels from Agricultural Wastes AWs are converted into biofuel by biochemical or thermochemical conversions. Biochemical conversion by microorganisms and enzymes is preferred when AW is rich in cellulose/hemicellulose/moisture/C:N (Pattanaik et al. 2019). The microorganisms break down the AW into amino acids, sugars, and fatty acids (short chain) for the generation of biofuels like biogas (anaerobic digestion), biohydrogen (dark fermentation), bioethanol (fermentation), biobutanol (ABE fermentation), and biodiesel. The lignin-rich AW with C:N of 0.30 is subjected to thermochemical conversions. The thermochemical conversions involve pyrolysis (syngas, bio-oil, char), gasification (syngas), and torrefaction (bio-coal). In Northwestern part of India, a huge amount of paddy straw (parali) is burnt. This stubble burning produces substantial air pollution creating plant, animal, and public health concerns (Koul et al. 2022). The AW rich in lignocellulose can be efficiently used in biofuel generation (biodiesel, bioethanol, biobutanol, biomethanol, biohydrogen) as a support to the fossil fuel-derived bioenergy. Biofuels have been generated from AW like rice straw, potato waste, sawdust, corn stalks, sweet potato waste, sugar beet bagasse, etc. (Duhan et al. 2013; Kumar et al. 2016; Sadh et al. 2018). Bio-alcohols are derived from the carbohydrate fraction. The hydrolysate of AW residues is rich in carbohydrate/sugar (Raita et al. 2021). The hydrolysate of rice straw is composed of glucose (52.3 g/L) and xylose (7.7 g/L). Similarly, the hydrolysate of bagasse is composed of more glucose (50.7  g/L) than xylose (15.2  g/L). Bio-alcohols present suitable properties and are promising substitutes for nonrenewable “fossil fuels,” which can be applied in different engines. Presently, many of the vehicles are run with 10–15% alcohol blending popularly with ethanol. Also, biofuel engines are designed for more concentrated ethanol (93%)/E85 (85% ethanol with 15% water) blends (Khuong et al. 2017). Alcohols (ethanol/methanol/butanol) are used extensively as liquid fuel in “internal combustion engines” derived from biological/chemical processes (Rana and Parul 2018). Therefore, it is worthwhile to study the generation of bio-alcohols from different AW for their application as a biofuel. Appertaining to the efficient conversion of AW into bio-alcohol, different pre-treatment, hydrolysis, fermentation, and physicochemical factors for the processes are discussed. Improvement in production by modern technologies like nanomaterial and genetic improvements is discussed contingent with the properties of bio-alcohols as fuel blend.

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9.2 Ethanol from Agricultural Waste Crop-based AWs are usually significant among the feedstocks for bioethanol production. AW presents potential for generating biofuels. Major “crop wastes” include corn stover, cornstalk, sugarcane bagasse, cassava peels, potato peels, sugarcane leaves, and rice straw (Table 9.1).

9.2.1 Raw Materials Presently, rice, wheat, and corn straws and bagasse are the four major AW feedstocks pertaining to bioethanol generation. Considering the input-output ratio, availability, and low-cost/higher ethanol yields, lignocellulosic AWs act as a promising option for bioethanol (Saini et al. 2015). Maize, wheat, rice, and sugarcane are the four agricultural crops with maximum production as well as the area under cultivation (Irfan et al. 2014). “Corn stover” is the leftover residue after harvesting corn kernel and comprises stalks, leaves, cobs, and husks. Annually, wheat straw is generated (1–3  t/acre) under intensive farming. Rice straw is embodied with stems, blades/sheaths (leaf), and panicle left after threshing. The rice straw production in Asia is ~668 of 731 million tons of global production. Bagasse is generated in distillery industry pertaining to sugarcane processing. Approximately 205  billion litres of bioethanol/year are credible to rice straw, and this is the highest among maize/wheat/rice/sugarcane.

9.2.2 Pre-treatment Pre-treatment is important for processing the “lignocellulosic biomass” into bioethanol. The constituents of “lignocellulosic biomass” are the matrix of hemicellulose, lignin, and cellulose. The compact matrix is difficult to be acted upon by the enzymes/microbes for degradation and hydrolysis (Sarkar et al. 2012). Pre-treatment helps in the solubilization and separation of the constituents and allows access to further chemical or biological reactions. It increases the porosity of the biomass, surface area, hydrolysis susceptibility, and monomeric sugar and decreases the “crystalline” nature (Mosier et  al. 2005). The pre-treatment methods are of four categories: physical, chemical, physiochemical, and biological.

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Table 9.1  Feedstock (AW) used for bioethanol production Feedstock Liquefied cassava starch Sugarcane leaves

Alfalfa fibers Banana leaves

Corn stover Rice straw Banana ‘pseudo stem’ Wheat straw Sugarcane bagasse Rice straw Rye stillage Barley straw Corn stover Corn stover Wheat straw Wheat straw

Microorganisms S. cerevisiae Zymomonas mobilis Trichoderma reesei S. cerevisiae ‘NRRL-Y-132’ Kluyveromyces fragilis ‘NCIM 3358’ Candida shehatae‘FPL-702’

Ethanol Method/treatments yield (g/L) 0.24–0.34 Monoculture or mixed culture fermentation with yeasts SSF 20–35

SHF/SSF with/without “liquid hot water” pre-treatment Anaerobic fermentation (coculture)

References Amutha and Gunasekaran (2000) Krishna et al. (2001)

5–6.4/9.6– Sreenath et al. 18 (2001) 22

Reddy et al. (2010)

CBP

7.0

Jin et al. (2012)

Batch SSCF

28.6

Suriyachai et al. (2013) Ingale et al. (2014)

Clostridium thermocellum ‘CT2’ C. thermosaccharolyticum ‘HG8’ Clostridium Phytofermentans ‘ATCC 700394’ S. cerevisiae, C. tropicalis, S. stipitis A. ellipticus A. fumigatus S. cerevisiae NCIM 3570 S. cerevisiae, Z. mobilis

Batch fermentation

68.2%

S. cerevisiae

Fermentation

37

S. cerevisiae P. stipitis NCIM 349 S. cerevisiae

Fermentation

3.32

Fermentation

16

S. cerevisiae

SSF

50

S. cerevisiae

SSF

28.73

S. cerevisiae

Batch fermentation

3.6

S. cerevisiae

SHF

43.1

Angel yeast

SHF

15.42

17.1 SSF (cellulases from fungi and fermentation by yeast cells)

Tsegaye et al. (2019) Bittencourt et al. (2019) Nandal et al. (2020) Mikulski and Kłosowski (2018) Duque et al. (2020) Fírvida et al. (2021) Hamdy et al. (2021) Ziaei-Rad et al. (2021) Xian et al. (2022) (continued)

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Table 9.1 (continued) Feedstock Rice straw

Microorganisms S. cerevisiae

Rice straw

Mucor indicus

Sugarcane bagasse Sugarcane bagasse Barley straw

S. cerevisiae S. cerevisiae Yeast

Ethanol yield (g/L) References 5.9 Chuetor et al. (2022) SSF (phosphoric acid and 44.2 Molaverdi et al. (2022) N-methylmorpholine-N-­ oxide-pretreated straw) Fed batch and 77.51 Shen et al. enzyme-SSCF (2022) SSF 19.9 Khongchamnan et al. (2022) SSCF 38 Díaz et al. (2022) Method/treatments Batch fermentation

SSF solid-state fermentation, SHF separated hydrolysis and fermentation, CBP consolidated bioprocessing, SSCF simultaneous saccharification and cofermentation

9.2.2.1 Physical Pre-treatment Mechanical processing is the primary step for ethanol generation from AW. This mainly involves AW’s “size reduction” by wet milling, dry milling, compression milling, vibratory ball milling, grinding/chipping, etc. (Pattanaik et al. 2019). The “size reduction” decreases the “crystalline nature” of cellulose and increases the “surface area” for downstream processes. Extrusion is another mechanical method. Industrially, it provides enzyme access to the cellulosic matter (Lee et al. 2009). The microwave radiations weaken the bondage, disrupt the structure, and increase the surface area for enzymes (Hu and Wen 2008). Sonication or ultrasonic sound wave is another pre-treatment method disturbing the structure of lignocellulosic biomass. Both microwave and ultrasonic techniques are accompanying “chemical pre-­ treatment” methods (Binod et al. 2010; Subhedar and Gogate 2016). In “pyrolysis,” the AW is heated >300 °C to generate H2, CO, and residual char. The “residual char” is subjected to leaching with water/mild acid, which further converts glucose into bioethanol (Das et al. 2004; Sarkar et al. 2012). These methods depolymerize the “lignocellulosic matrix” rather than delignification (Zabed et al. 2016). 9.2.2.2 Physiochemical Pre-treatment Many “physiochemical methods” such as steam explosion, subcritical water, supercritical CO2, acid treatment, alkali treatment, and ammonia fiber explosion (AFEX) are found to be effective for the pre-treatment of lignocellulosic AW (Chang and Holtzapple 2000; Sun and Cheng 2002; Mosier et al. 2005; Sipos et al. 2010). These methods are substantially more effective than physical methods of pre-treatment. The chemical agents used are acids/alkali, ozone, and peroxide together with organic solvents. Steam explosion (high pressure) is a pre-treatment method in which “lignocellulosic matrix” expands and is fractionated into alcohol/levulinic

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acid/xylitol. Liquid hot water/subcritical water treatment (temperature, 170 to 230 °C; pressure, 5 bar) is an efficient technique for treating different kinds of AW, viz., wheat straw, corncobs/stover, and bagasse (Laser et  al. 2002; Mosier et  al. 2005). Ammonia fiber expansion (AFEX) pre-treatment uses high temperature/ pressure with the combination of liquid ammonia/steam explosion (Balat et  al. 2008). This system allows “enzymatic breakdown” of polymers. AFEX increased the “enzymatic saccharification” of corn stover with a glucose yield of 98% (Teymouri et al. 2004). CO2 explosion is just as similar to that of steam and ammonia explosion techniques. However, CO2 explosion presents higher yield, is more cost-effective than ammonia explosion, and does not form inhibitors (Hamelinck et al. 2005; Prasad et al. 2007). 9.2.2.3 Chemical Pre-treatment Chemical pre-treatment methods involve dilute acid (HCl/H2SO4/HNO3/H3PO4), alkali, ammonia, organic solvents, SO2, CO2, etc. The yield is high, instant, and easy in operational. However, acid pre-treatment produces inhibitors for fermentative microorganisms like acetic acid, furfural, 5-hydroxymethylfurfural, etc. Alkali treatment (hydroxides of Na, K, Ca, and NH4+) disrupts the cell wall, swells cellulose, dissolves hemicelluloses/lignin/silica, and hydrolyzes uronic acid/acetic esters. Alkaline pre-treatment requires lower temperatures/pressures than other pre-­ treatments (Mosier et al. 2005). In wet oxidation, the feedstock material is treated with water and air/oxygen at temperatures >120 °C (Martín et al. 2007). Organic solvent/organosolv (methanol/ethanol/acetic acid/performic acid/peracetic acid/ acetone) pulping processes are alternative methods for the “delignification” of lignocellulosic AW. 9.2.2.4 Biological Pre-treatment Degradation of the lignocellulosic complex is plausible by brown/white/soft rot fungi. Biological pre-treatment renders the degradation pertaining to lignin/hemicellulose. The “white rot fungi” is considered to be the most competent microorganism. The “brown rot” attacks cellulose. White/soft rots attack cellulose together with lignin (Prasad et al. 2007). Bio-delignification generally needs long continuance pertaining to lower hydrolysis rate (Sun and Cheng 2002). Reduction in the cellulose content by Aspergillus terreus was ~55%, while delignification was found to be ~92% (Singh et al. 2008). Reduced chemicals, lesser energy, lignin specificity, and eco-friendly nature are the important advantages of biological pre-treatment.

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9.2.3 Hydrolysis The lignocellulosic AW is hydrolyzed to produce sugar monomers. Hydrolysis is essential for AW-based ethanol generation as per the effective break of sugars. Hydrolysis is accomplished either by acid (dilute/concentrated) or enzymes (Lynd et al. 2002). Enzymatic hydrolysis of pre-treated AW involves enzymatic reactions that convert cellulose into glucose and hemicellulose into pentoses (xylose/arabinose) and hexoses (glucose/galactose/mannose). The conversion of cellulose/hemicellulose is catalyzed by specific cellulase and hemicellulase enzymes, respectively. The enzymatic hydrolysis is usually accomplished at mild conditions (pH 4.8 and temperature 45–50 °C) (Cheng and Timilsina 2011). Pertinent to commercialization, the economic production of “cellulolytic enzymes” with a reduction in the “enzyme-to-biomass” ratio for hydrolysis is required. Acetivibrio, Trichoderma reesei, Bacillus, Thermomonospora, Bacteroides, Clostridium, Erwinia, Cellulomonas, Ruminococcus, etc. produce cellulase enzyme. Many fungi, viz., Trichoderma, Fusarium, Penicillium, Phanerochaete, Schizophyllum, and Humicola sp., also have been reported (Sun and Cheng 2002; Rabinovich et al. 2002). Substrate concentration, cellulose enzyme loading, surfactant addition, temperature, pH, and mixing rate are the main factors of enzymatic hydrolysis of lignocellulosic material (Sun and Cheng 2002; Börjesson et al. 2007; Taherzadeh and Karimi 2007). In ethanol generation from AW, cellulase adds to the major cost. Hence, a potential pre-­ treatment is required to decrease “cellulose crystallinity” and to remove “lignin” to the maximum extent (Eggman and Elander 2005). Surfactants adsorb lignin and modify the cellulose surface. Hence, the surfactant prevents the enzyme from unproductive binding with lignin and lowers enzyme loading (Eriksson et al. 2002).

9.2.4 Fermentation The hydrolysis yields hexose/pentose sugars and is converted to bioethanol by fermentation. Fermentation is accomplished by batch, semicontinuous, and continuous methods. Often, hydrolysis together with fermentation is integrated to produce more economical bioethanol. Different approaches used are simultaneous saccharification and fermentation (SSF), simultaneous saccharification and cofermentation (SSCF), consolidated bioprocessing (CBP)/direct microbial conversion (DMC), and separate or sequential hydrolysis and fermentation (SHF) (Pattanaik et  al. 2019). Simultaneous optimization of process conditions for fermentation with “enzymatic hydrolysis” is the major limitation of the SSF (Hamelinck et al. 2005). Lower yield in SHF may be due to the occurrence of toxic compounds inhibiting the growth and activity of fermenting organisms (Buaban et al. 2010). A microorganism that can ferment pentoses together with hexose sugars efficiently is the key to the success of every industrial-scale production of bioethanol. For commercial and cost-effective ethanol production, the microorganisms must possess maximum

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ethanol yield with extensive substrate utilization and productivity. Microorganisms reported for fermentation of AW are S. cerevisiae, Escherichia coli, Zymomonas mobilis, Pachysolen tannophilus, Candida shehatae, Mucor indicus, etc. (Bjerre et  al. 1996; Balat et  al. 2008; Talebnia et  al. 2010; Sanchez and Cardona 2008; Moniruzzaman 1995; Girio et al. 2010; Sukumaran et al. 2010). S. cerevisiae is a very ideal organism for ethanol production with high rate. However, it can only ferment the hexose sugars. The concurrent fermentation of hexoses/pentoses occurs in SSCF. The suitable microorganisms reported for SSCF are coculture of C. shehatae and S. cerevisiae (Sanchez and Cardona 2008). The CBP or DMC is the most cost-­ effective method which avoids the usage of individual enzymes for hydrolysis/fermentation. Microorganisms produce cellulase, hydrolyze the biomass, and produce ethanol in a common reactor. However, this method is not much attractive as per the poor yield and longer time of fermentation.

9.2.5 Factors Affecting Bioethanol Production The important factors for bioethanol generation are pH, temperature, fermentation time, feedstock concentration, inoculum size, agitation rate, etc. (Zabed et al. 2014). The optimum temperature testified for ethanol generation is 20–35  °C (Liu and Shen 2008). Enzyme activity is hindered at high temperatures pertaining to the denaturation of enzymes. High temperature may affect the transport system leading to the saturation of solvent in the cells of fermenting organisms, thus building up toxins, and causing death. Thus, at such high temperatures, a sudden decline in ethanol production occurs pertaining to the growth inhibition or death of microorganisms (Lin et al. 2012). At the same time, a slow growth rate at lower temperatures decreases ethanol production (Torija et al. 2003). In general, a moderately acidic medium (pH 4–5) enhances ethanol production pertaining to favorable cell permeability for easy passage of essential nutrients in the fermentation medium (Zabed et al. 2014). The low pH prevents the fermentation medium from bacterial attack. A rise in “feedstock concentration” generally favors ethanol production; however, prolonged exposure to high concentrations of feedstock decreases ethanol production (Lin et al. 2012; Triwahyuni et al. 2015). A sufficient time period has to be set for complete microorganism growth, leading to efficient fermentation. The fermentation for short duration results in insufficient growth and for a long time as the ethanol in the broth inhibits the fermentative microorganisms’ growth (Zabed et  al. 2014). A higher rate of agitation leads to higher production of ethanol. The reported “agitation rate” for optimum growth together with the activity of yeast cells is 150–200 rpm. Excess agitation may affect metabolic activities.

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9.2.6 Nanotechnology in Bioethanol Production Industrially, the use of innovative and modern technologies would be more sustainable for economically viable bioethanol generation. Nanoparticles or nanomaterials are eco-friendly, renewable, cost-effective, and sustainable and can enhance the production process at various stages. Different nanocatalysts, nanomaterials, nanoparticles, and nanocomposites are used in various stages of bioethanol production (Mahapatra and Pradhan 2022). The use of nanoparticles in pre-treatment/fermentation process increases the production and the rate of reaction (Chaturvedi et  al. 2012). Nanoparticles linked with enzymes (nano-biocatalyst) are used for the improvement of the pre-treatment process. These nanocatalyst/nanomaterials are reusable, which makes them more cost-effective and eco-friendlier. Metal nanoparticles like nickel, cobalt, iron, manganese, silica, magnetic nanoparticles, carbon nanotubes, nanoparticle sheets, zinc nanosheets, etc. are widely used (Chaturvedi et al. 2012; Rai et al. 2018). Presently, nanofilters are used for the effective separation of sugar molecules, which can be used for bioethanol production (Mahapatra and Pradhan 2022).

9.3 Biobutanol from Agricultural Wastes Biobutanol (C-4) is derived biochemically at fermentation from carbohydrates of AW (Table 9.2). Butanol is highly acceptable in different engines with blends in technical/environmental aspects. Different lignocellulosic AWs like rice/wheat/barley straw, sorghum bagasse, corn stover/cobs/fiber, potato/banana/orange peel waste, and pineapple waste are applied for the generation of biobutanol (Amiri 2020). Biobutanol has advantages over bioethanol like efficient blending with gasoline/diesel in more concentrations without vehicle retrofitting, close energy content/ octane number to gasoline, more fuel economy, less evaporative, low water solubility/vapor pressure, and high biodegradability (Niemistö et al. 2013). However, lignocellulosic AWs are difficult to convert into biobutanol as compared to bioethanol pertaining to recalcitrant degradation properties and chemical compositions (Cao et al. 2016). Hence, lignocellulosic AW requires pre-treatments and hydrolysis for efficient conversion into biobutanol. Biobutanol from AW residues (bagasse/corn stover/straw) have an advantage for easy upstream processing for converting into fermentable sugars (Niemistö et al. 2013).

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158 Table 9.2  Solvent production from different substrates Product Substrate Biobutanol Sweet potato residue

Microorganism Clostridium acetobutylicum CICC 8012

Biobutanol AW

C. beijerinckii BA101 C. acetobutylicum strain ABE1201

Biobutanol Sweet sorghum bagasse hydrolysate

Biobutanol Bagasse

Biobutanol Rice straw

Biobutanol Rice straw

Biobutanol Bagasse

Biobutanol Potato waste Biobutanol Steam-­ exploded corn straw Biobutanol Wheat straw Biobutanol Cassava stems

Composition Cellulose, 40.42%; residual sugar content (oligosaccharide or/ pentose), 13.01% Starch: 96.4 g/L

Cellulose, 23.5%; hemicellulose, 32.6%; lignin, 21.5%; ash, 2%; glucose, 37.8 g/L; fructose, 8.3 g/L; xylose, 7.1 g/L; arabinose, 1.5 g/L Pseudomonas sp. Cellulose, 39.72%; CL3/Clostridium hemicellulose, 26.96%; others, sp. TCW1 33.2% Pseudomonas sp. Cellulose, 35.17%; CL3/Clostridium hemicellulose, 24.37%; others, sp. TCW1 3.50% C. sporogenes Cellulose, 47.57%; BE01 hemicellulose, 15.75%; lignin, 8.66%; hydrolysate with glucose, 39.02 g/L; xylose,11.35 g/L; arabinose, 1.71 g/L C. beijerinckii Total sugar, 25 g/L; xylose, 14 g/L; glucose, 11 g/L C. Glucose: 20–80% acetobutylicum C. Glucose acetobutylicum C. acetobutylicum ATCC824 Clostridium sp.

Yield 7.96 g/L

References Jin et al. (2022)

13.7 g/L

Jesse et al. (2002) Cai et al. (2013)

12.3 g/L

2.29 g/L

Cheng et al. (2012)

2.92 g/L

Cheng et al. (2012)

~6 g/L

Gottumukkala et al. (2013)

1.23 g/L/ day

Narayanasamy et al. (2019)

9.9 g/L

Kheyrandish et al. (2015) Zhang et al. (2018)

9.88 g/L

Glucose, 13.25 g/L; xylose, 4.07 g/L

7.05 g/L

Wang et al. (2013)

Glucose, 29.94 g/L; maltose, 3.54 g/L; xylose, 2.30 g/L

~12 g/L

Saekhow et al. (2020) (continued)

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Table 9.2 (continued) Product Substrate Biobutanol Rice straw

Microorganism C. acetobutylicum NCIM 2337

Composition Glucose, 23.29 g/L; reducing sugars, 31.67 g/L; total sugars, 39.88 g/L Total reducing sugars, 53.1 g/L; glucose, 21.3 g/L; xylose, 17.4 g/L; arabinose, 10.6 g/L –

C. acetobutylicum CICC 8012

–

13.42 g/L

C. beijerinckii BA101 C. beijerinckii P260 C. beijerinckii P260

–

37.01 g/L Lépiz-Aguilar et al. (2013) 20 g/L Qureshi et al. (2007) 0.21 g/L/h Qureshi et al. (2021)

Biobutanol Wheat bran C. beijerinckii ATCC 55025

ABE ABE

ABE ABE ABE

Cassava waste Sweet potato residue (SPR) Cassava flour Wheat straw Sweet sorghum bagasse

Clostridium sp.

Glucose: 62 g/L Glucose, 34.32 g/L; xylose, 17.52 g/L; arabinose, 2.02 g/L

Yield 13.5 g/L

References Ranjan et al. (2013)

8.8 g/L

Liu et al. (2010)

10.5 g/L

Johnravindar et al. (2019)

ABE acetone-butanol-ethanol

9.3.1 Pre-treatment The pre-treatment of lignocellulosic AW should be capable of separating lignin and hemicellulose in cellulosic microfibrils. Also, it must increase the sugar yield, prevent excessive sugar loss, and be cost-effective (Mahalingam et al. 2022). The pre-­ treatment is important for the breakdown of AW lignocellulose into fermentable sugar molecules. The pre-treatment method generally involves physical [mechanical milling (wet, dry, ball)/microwave/ultrasonic], chemical (acid/alkali/organosolvent/ozonolysis/ionic liquid), physiochemical (steam explosion/subcritical water/ ammonia fiber explosion/supercritical CO2), and biological pre-treatments (microbial delignification). In mechanical intrusion (single/twin screw extruders), the biomass is heated above 300 °C under shear mixing to break down the crystallinity of cellulose (Vivek et  al. 2019). The milling (ball/two-roll/hammer/colloid/disk) reduces the feedstock up to 0.2 mm. The electromagnetic radiation used in physical pre-treatment weakens the lignocellulosic components in the AW. This is an auxiliary treatment with chemical pre-treatment. Microwaves enhance the hydrolysis twofold to threefold as presented in rice straw/sugar cane bagasse (Pattanaik et al. 2019). Among different pre-treatment methods (acid/alkali/hot water/milling/defatting/microwave/steam explosion/others), the enzymatic method (>75  times) is highly applied for pre-treatments, which is followed by acid treatment (>40 times)

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pertaining to biobutanol production (Birgen et  al. 2019). Acids like HCl/H2SO4/ peroxyacetic acids are useful in hydrolyzing cellulose/hemicellulose while pre-­ treating with alkali (NaOH/KOH). The by-product corn fiber from corn processing industries was pre-treated with H2SO4 (0.5%) at 121 °C for 1 h. However, this process requires removing inhibitors prior to fermentation and is considered disadvantageous economically (Qureshi and Ezeji 2008). Wheat straw (86 g) was ground to fine particles (1.27 mm sieve) and added to 1-L dilute sulfuric acid (10 mL conc. H2SO4 in 990 mL dH2O). The mixture was autoclaved at 121 °C for 1 h (Qureshi et al. 2007). The pre-treatment of sweet potato residue was carried out by diluted H2SO4 of 0.9 L (Jin et al. 2022). Other parameters like time and temperature were optimized by response surface methodology (RSM). Ionic liquids (large cation/ small anions) are used to dissolve biomass with different hardness. Other treatments involve oxidative pre-treatment, steam explosion, liquid hot water, wet oxidation, etc. (Vivek et al. 2019). Steam explosions, alkaline pre-treatment, ammonium fiber explosion, autohydrolysis, acid (dilute H2SO4), ethanol organosolv, acetone organosolv, and phosphoric treatments are useful for the butanol production (Amiri 2020). Cellulose can be broken down by alkali like NaOH/Ca(OH)2 or ammonia while removing lignin and hemicellulose (Cheng et  al. 2012). The microwave-assisted NaOH pre-treatments (140 W, 30 min) of cassava waste resulted into 459 mg/g of reducing sugars (Saekhow et al. 2020). Pre-treatments by acid/alkali are effective, however not eco-friendly. Instead, organosolv and ozonolysis are the preferred chemical pre-treatments for removing lignin (Pattanaik et al. 2019). Steam explosion in high temperature/pressure is useful in separation of the fibers in AW. Biological pre-treatment involves microbial (Irpex lacteus and Phanerochaete chrysosporium) delignification/decomposition. Although the most successful pre-­ treatments are acid/alkali and enzymatic, it reduces the fermentation efficiency due to the release of inhibitory chemicals like acetic acid, formic acid, and levulinic acid (Goyal and Khanna 2019). The inhibitor generation is substrate-specific (Qureshi and Ezeji 2008). However, the inhibitors might be removed by charcoal adsorption, evaporation, XAD resin, and lime treatment.

9.3.2 Hydrolysis Hydrolysis converts the pre-treated AW with cellulose/hemicellulose into monomeric forms. Acidic hydrolysis (diluted acid-0.5–1.5%) is performed mostly targeting hemicellulose for a short duration at high temperature/pressure. The two-stage hydrolysis is preferred for cellulose degradation. A low temperature (M30 decreased NOx emissions. Alcohol (methanol/ethanol)-diesel blend decreased CO, THC, and smoke opacity (Sayin 2010). Smoke opacity varied with blends of M10 (52%), M5 (57%), E10 (59%), E5 (61%), and D100 (65%). BSFC increases with an increase in methanol/ethanol blend with a decrease in LHV. BTE decreased to its minimum at M10 (22.2%).

9.7 Conclusion and Future Prospect Lignocellulosic AW is an ample and sustainable natural resource for bio-alcohol production. Each year, a large portion of agricultural residues is disposed of as waste. The options for the disposal of these agricultural wastes are limited by the great bulk of the material, slow degradation in the soil, harboring of rice stem diseases, and high mineral content. To attain food security, livestock/crop production has to be increased, which contributes to more AW generation. Preferably, cellulose-/hemicellulose-rich AWs are biochemically converted by potential microorganisms into bio-alcohols. However, biochemical conversion/fermentation for biofuel has several limitations like expensive feedstocks, low solvent productivity, and solvent separation methods. Moreover, the availability of AW is seasonal and inconsistent in yield. Strain improvement pertaining to efficient substrate utilization and more required solvent (bio-alcohol) production with resistance to inhibitory effects during fermentation is required. Application of “nanomaterials” as a modern technology can further improve bio-alcohol production. The abundant AW arises due to the improper management and strategies for sustainable agriculture/food/ health security by proper utilization with valorization (Koul et al. 2022). Hence, a sustainable and circular model is required for adequate management of AW generated in agricultural field (Duque-Acevedo et  al. 2022). The bio-alcohols blended with gasoline reduce fossil fuel consumption and pollutant exhaust and save foreign exchange. The use of AW has a huge environmental benefit, as it is the most potent route to produce fuel sustainably with the least environmental impact.

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Chapter 10

Technological Advancement for Biohydrogen Production from Agricultural Waste Anudeb Ghosh, Apurba Koley, Saradashree Pal, Nitu Gupta, Binoy Kumar Show, Gaurav Nahar, and Srinivasan Balachandran Abstract The recent interest in the production of biohydrogen (bio-H2) from biomass in laboratory scale has enhanced, while there is a need for subsequent technical advancements in the associated biological processes to make it economically viable. H2 is considered as one of the most competitive substitutes for fossil fuels where biological processes are reflected as the most eco-friendly alternatives for meeting future H2 demands. The bio-H2 from agricultural waste is especially advantageous since these biomass is readily available, biodegradable, inexpensive, and renewable. Such wastes are composed of complex lignocellulosic substrates that can be biologically degraded by the complex microbial consortia where dark fermentation coupled with other biological processes like photofermentation and microbial electrolysis cell under various operating conditions has been proved to be a key technology for H2 production from various agricultural wastes. This study emphasizes on different technological advancements in terms of pre-treatment of biomasses for lignin removal, reactor design optimization, and hybridization of different techniques for H2 production from agri-wastes with a special focus on the role of nanoparticles and biotechnological advancements for process stabilization and enhancement of H2 production. The study has revealed that despite the proven efficiency of the various approaches, a detailed and in-depth research is needed for understanding the cellulosic H2 generation process at a molecular level.

A. Ghosh · A. Koley · S. Pal · B. K. Show · S. Balachandran (*) Bioenergy Laboratory, Department of Environmental Studies, Institute of Science, Visva-Bharati (A Central University), Santiniketan, India e-mail: [email protected] N. Gupta Department of Environmental Science, Tezpur University, Tezpur, Assam, India G. Nahar Defiant Renewables Pvt Ltd, Chinchwad, Pune, India © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024 P. Singh (ed.), Emerging Trends and Techniques in Biofuel Production from Agricultural Waste, Clean Energy Production Technologies, https://doi.org/10.1007/978-981-99-8244-8_10

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Keywords  Biohydrogen · Photo-fermentation · Microbial electrolysis · Waste to wealth · Agriculture waste management

10.1 Introduction With sharp increase in population and fast development, the volume of wastes and the consumption of energy are increasing significantly around the globe (Zacharia et al. 2020). In developing countries, with rapid industrialization, the agricultural activities have increased considerably where agricultural wastes remain a large pool of unexploited biomass resources. As the world faced concerns such as climate change and the exhaustion of nonrenewable resources, engineers and scientists focused on green energy. The process of methane (CH4) generation from organic leftovers has been commercialized already. The synthesis of biological hydrogen (bio-H2) from unused biomass has proven to be a novel and challenging strategy for satisfying the growing need of eco-friendly power. The concepts of “Waste to Wealth” and “Take, Make, and Dispose” have expanded rapidly in recent years. Due to the growing scientific and commercial interest, ecological concerns, depletion of nonrenewable resources, and public perception, there are no viable biotechnological methods to convert crude cellulosic waste into biofuels, chemicals, and industrial products. The development of refining concepts is accelerated. Agricultural waste is a catch-all phrase for solid and liquid wastes produced by processing of the farm product harvests as well as by livestock and poultry breeders and rural people (Hu 2021). Agricultural trash and leftovers such as stover, chaff, cobs debris, peel-offs, and bagasse are produced when commercially important crop products are harvested where the leftover plant fiber waste, which are essentially made of hemicellulose, cellulose, and lignin are produced over time through photosynthesis process. Liquid wastes with high organic content, such as from poultry and other livestock manure, constitute a major part of this type of wastes. Several literatures have discussed the advantages and disadvantages of using biological agricultural wastes as feedstocks for biohydrogen generation (Zheng et  al. 2022; Chandrasekhar et  al. 2020; Sharma et al. 2022; Karimi-Maleh et al. 2023). The practice of agricultural leftovers as bio-H2 feedstock is known as an efficient waste disposal technology with recognized capability of preventing environmental damage and delivering renewable energy (Zheng et al. 2022). If their complex and diverse molecular structures can be addressed through adequate transformation into competitive products, agricultural waste is a possible resource for the creation of high-value compounds. Therefore, there is a need to develop state-of-the-art nonpolluting and low-cost conversion processes. In addition, expanding the range of agricultural residue conversion technologies as well as the high-quality final product portfolio should enable the transition to sustainable agricultural residue biorefinery concepts (Gontard et  al. 2018). Agricultural residues have a complicated structure of carbohydrate polymers composed of cellulose (40%), hemicellulose (25%), and lignin (15%). The pre-treatment techniques, namely physical, chemical, and biological, are essential to break down the

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recalcitrant character of lignocellulosic biomass in order to increase its accessibility for the production of biogas, thereby enhancing the effective and complete utilization of wastes (Kavitha et al. 2020; De Pretto et al. 2018). Biohydrogen (H2) has recently attracted global attention as an important energy carrier due to their diverse viable uses. There are some popular methods for H2 production, for example, steam methane reformation and electrolysis of water, but these methods come with limitations of significant energy consumption and release of carbon dioxide (CO2) gases (Wang et al. 2014; Kechagiopoulos et al. 2017). Now, we are at a junction where we need alternate production approach which needs less energy and emits less GHGs. Production of fermentative bio-H2 is a biological method that has gained recent attention because of its eco-friendly features when compared to other chemical as well as physical generation approaches. This approach is well applied to a wide variety of raw materials such as crop residues and industrial waste/wastewater rich in organic content. Production of bio-H2 from organic waste is of great importance, not only as a waste treatment process but also as a clean energy source (Show et al. 2012). Since there are fewer environmental risks associated with production of bio-H2 through biological methods, the release of pollutants is minimal, the energy input is low, the cost of production is manageable, and the operating conditions are relatively benign, bio-H2 production using biological methods has been previously acknowledged as a feasible option for bio-H2 production. Dark fermentation, photofermentation, and microbial electrolytic cells are the most studied biological approaches for H2 generation (Lee et al. 2022; Balachandar et al. 2020; Mahidhara et al. 2019). Dark fermentation process has a lot of potential due to its higher rates of H2 production and lower costs (Sarangi and Nanda 2020). Bio-H2 is less energy-intensive and less technically risky than thermochemical conversion (Rahman et  al. 2015) where dark fermentation (DF) is a promising method of generation (Arimi et  al. 2015). Several methods have been devised to increase enzyme production, efficiency, yield, and biohydrogen generation, but the economic viability of these approaches is still debatable (Cipolatti et al. 2016). Due to their inimitable features, nanomaterials have proven efficiency in improving biomass to biohydrogen conversion (Kumar et al. 2019c; Pugazhendhi et al. 2019; Fani et al. 2018). The individual stages of biohydrogen generation technology can possibly be catalyzed with high electroconductivity, surface area, and surface-to-­ volume (S/V) ratio (Taherdanak et  al. 2015). Nanomaterials made of iron (Fe), nickel (Ni), copper (Cu), gold (Au), silver (Ag), and titanium (Ti) increase biohydrogen generation via fermentation process (dark and/or photo) (Taherdanak et al. 2016; Lin et al. 2016a, b). Hydrogen-consuming bacteria (HCB) and the assembly of reduced products (e.g., solvents) lead to poor hydrogen yield and unstable production rate by biological techniques (Singh and Wahid 2015). Advantages of magnetic nanoparticles (NPs) include their ability to boost hydrogen generation by bacteria and their simple control release qualities because of their significantly small size, large total surface area, and strong reactivity. Both progressive and adverse effects of NP addition on H2 generation during AD process have been documented in various studies. In their study, Mullai et al. observed how Ni NPs affected glucose’s ability to ferment into

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hydrogen gas. The H2 production for glucose doped with Ni NPs was found 22.7% greater compared to the controlled experiment (Mullai et al. 2013). Another effective way of stabilizing and enhancing H2 generation is the hybridization of various processes for biomass to bio-H2 conversion (Gebreslassie et al. 2021). Researchers are exploring ways to scale up bio-H2 production for meeting the world’s increasing energy consumptions. Zhang et al. (2020) assessed the potential of using large-scale AD to produce bio-H2 from agricultural waste. The study found that large-scale anaerobic digestion could effectively enhance the production substantially reducing the cost of bio-H2 production. Traditional biogas has limited economic value and is not suitable for waste streams with high lignocellulose content (Koley et al. 2023), as it has lower conversion rates. The only practical use for the byproduct of the anaerobic digestion (AD) process in agriculture is as a renewable fertiliser (Bolzonella et al. 2018b), but this still presents potential sanitary and environmental risks due to limited land disposal options. This review focuses on the sustainable use of agricultural residues with the aim of contributing toward the advances of advanced and holistic approaches that support the eco-efficient transformation pathways and intelligent management strategies for agricultural residues via recent progress in the generation of bio-H2 through the process of dark fermentation (DF) and anaerobic digestion (AD) exploiting the agricultural residues (Gontard et al. 2018). This review attempts to summarize the recent technological advancements in pre-treatment, nanotechnology, immobilization, and hybridization for enhancing bio-H2 production from agricultural residues.

10.2 Lignocellulosic Content of Different Agricultural Wastes Biomass from plants is a complex mixture of lignin, cellulose, and hemicelluloses, all of which play an important role in the generation of bioenergy. Lignin in particular has a very complex structure and is quite resistant to degradation, making it one of the key components of biomass. The presence of lignin prevents the breakdown of fermentable organic compounds (hemicelluloses and cellulose) to their simplest sugars, which would otherwise fuel the development and function of bacteria, and results in the creation of volatile organic compounds (volatile fatty acids) and methane (Sinha et  al. 2021; Koley et  al. 2022; Show et  al. 2022). Biotechnologically significant, bacterial delignification of plant biomass has several advantages over fungal delignification due to bacteria’s significant growth efficiency, product flexibility, low-space prerequisite for cultivation, appropriate genetic temperament, and vulnerability to genetic influence (Banerjee et  al. 2017). Plants have their own unique combination of carbohydrate (50% cellulose and 20% hemicelluloses) and noncarbohydrate (primarily 25% lignin and rest of proteins) components that prevents it from being used by microorganisms (biomass recalcitrance) Banerjee et al. 2023. (Table 10.1).

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Table 10.1  Lignocellulosic ingredients in different agricultural waste biomass Cellulose content (%) 31–31 34.9

Hemicellulose content (%) 17–22 17

Lignin content (%) 17–20 –

References Mund et al. (2021) Kumar et al. (2020)

Biomass Pineapple waste Common Lantana Wastes from fruit and vegetable processing Switch grass

Group Tree Shrub Herb and shrub Herb

26.9

15.3

12

Edwiges et al. (2018)

45.9

24.0

22.3

Palm nut shell Shells of groundnut Bermuda grass

Tree Herb

24.5 25–30

22.9 25–30

33.5 30–40

de Lima Brossi et al. (2016) Chan et al. (2015) Howard et al. (2003)

Herb

25

35.7

6.4

Sugarcane top Bamboo

Herb Tree

29.85 39.80

18.85 19.49

25.69 20.81

Hazelnut shell Bamboo stem Birch Eucalyptus Empty fruit bunch Giant reed Meadow grass Pinewood Poplar Sawdust waste Spruce Willow sawdust

Tree Tree Tree Tree Tree

25.2 43.04 40.1 52.07 34.9

28.2 22.13 17.5 24.51 26.64

42.1 27.14 24.2 25.2 31.1

Herb Herb Tree Tree – Tree Tree

41.5 41.28 38.2 46.0 31.5 24.7 35.6

20.5 28.14 24.1 16.7 26.1 10.2 21.5

18.4 30.14 34.4 26.6 24.9 35.0 28.7

Maize straw Barley straw Rye straw Corn straw Rice straw Wheat straw Sorghum straw

Herb Herb Herb Herb Herb Herb Herb

38.33 31–45 33–35 49.3 35.8 30 26.93

29.76 27–38 27–30 28.8 21.5 50 32.57

3.82 14–19 16–19 7.5 24.4 15 10.16

Rice husk Cornstalk

Herb Herb

35 34.45

17 27.55

26 21.81

Reshamwala et al. (1995) Sindhu et al. (2011) Rabemanolontsoa and Saka (2013) Brosse et al. (2010) Chen et al. (2016) Luo et al. (2019) Xu et al. (2017) Zawawi et al. (2018) Jiang et al. (2016) Tsapekos et al. (2018) Salehian et al. (2013) Luo et al. (2019) Ali et al. (2017) Gao et al. (2013) Alexandropoulou et al. (2017) Khatri et al. (2015) Saini et al. (2015) Sánchez (2009) Song et al. (2014) Imman et al. (2015) Howard et al. (2003) Hernández-Beltrán and Hernández-Escoto (2018) Heng et al. (2017) Ma et al. (2016) (continued)

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Table 10.1 (continued)

Biomass Sugarcane bagasse Corn stover Cotton stalk Rice husks Sunflower stalk

Group Herb

Cellulose Hemicellulose content (%) content (%) 30 35

Lignin content (%) 18

References Sarkar et al. (2012)

Herb Herb Herb Herb

36.3 41.6 36 34

17.2 23.3 26 29.7

Saha et al. (2016) Yuan et al. (2016) Cabrera et al. (2014) Monlau et al. (2013)

31.4 23.6 12 20.8

10.3 Biohydrogen (Bio-H2) Generation Pathways from Agricultural Wastes Bio-H2 can be generated from various resources by means of a variety of biological approaches, which include fossil fuels like coal, petroleum, as well as organic wastes (e.g., plant and animal residues, fruit and vegetable processing, agricultural waste) and wastewater discharges from the industries (e.g., sugar, palm oil, and beverage industrial discharges). Because of its high organic content, hydrogen generation through biological processes is a feasible method for recovering energy from agricultural waste. Bio-photolysis, microbial electrolysis cell, and fermentation processes (such as dark and light fermentation) (Table  10.2) are only a few examples of the many biological technologies that may be used to generate biohydrogen (Oceguera-Contreras et al. 2019; Wang et al. 2021). Hydrogen generation by dark fermentation is gaining popularity due to its reduced energy usage, higher output, and faster rate of production (Saravanan et al. 2021). This section discusses the various pathways for the generation of H2 through microbial processes.

10.3.1 H2 Production by Photofermentation In photofermentation (PF), the purple non-sulfur photosynthetic bacteria (PNS) reduce the ferrodoxins (Fd) and produce ATP under the anaerobic environments, in the presence of solar energy (Liu et al. 2008; Hallenbeck and Ghosh 2009). Under anaerobic conditions, the PNS bacterium obtains electrons from organic molecules, such as organic acid, rather than via water-splitting processes, as in microalgae and cyanobacteria. Figure 10.1a depicts a schematic illustration of this photofermentation process. Species like Rhodospirillum rubrum, Rhodopseudomonas palustris, Rhodobacter sphaeroides, and Rhodobacter capsulatus show H2-producing capability through the process of photofermentation (Thulasisingh et al. 2023; Ozturk et al. 2006).

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Table 10.2  Process advantages of bio-photolysis, photofermentation, and dark fermentation Sl. no. Process 1 Bio-photolysis

2

Photofermentation

3

Dark fermentation

Advantages Can be accomplished by using solar energy Does not require organic substrates Can produce high-purity hydrogen Can be integrated with other processes, such as CO2 fixation

Challenges Low light conversion efficiency (Miura 1995) Hydrogen and oxygen cannot be produced simultaneously (Show et al. 2018) Product removal cost is high (impermeable hydrogen bioreactor) (Holladay et al. 2009) Can be accomplished Low photochemical by using solar energy efficiency Can produce hydrogen (Abo-Hashesh et al. 2013) and other valuable products, such as  – Relative lower organic acids and hydrogen alcohols productivity (Xia Can be integrated with et al. 2013) other processes, such  – Nitrogenase as wastewater requires high treatment energy for the Can operate at ambient process temperature and pressure Relatively poor Suitable for a variety of agricultural biomass yield (Keskin and Hallenbeck 2012) Can be operated at ambient temperature  – Metabolic and pressure product Can produce hydrogen inhabitation (Sun and other value-added et al. 2019a) products, such as  – Lack of organic acids and researches on alcohols continuous Has a lower footprint fermentation compared to photofermentation Is independent of solar energy Presents very high efficiency compared to photofermentation

Process optimization for hydrogen enhancement Simultaneous separation of oxygen for removing the adverse effect to the hydrogenase (Aslam et al. 2018; Kapdan and Kargi 2006) Optimization of co-culture (Laurinavichene et al. 2008)

Batch cycled arrangement (Machado et al. 2018) Recombined DNA techniques (Kars et al. 2009) Immobilization of microbes (Ren et al. 2009) Addition of chemicals, such as Ni2+, EDTA, DMSO (Budiman and Wu 2018) Cultivation of hybrid microbial consortia (Zagrodnik and Laniecki 2017; Shen et al. 2018) Additions of metal monomers, metal ions, and metal oxides (Hwang et al. 2019) Nanoparticles (Pugazhendhi et al. 2019) Membrane reactor (Ren et al. 2018)

(continued)

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Table 10.2 (continued) Sl. no. Process 4 Microbial electrolytic cell (MEC)

Advantages H2 yield is comparatively high Can be operated at high pressure with lower energy consumption Suppressed O2 production Material cost comparatively low Use of wide range of organic compounds as substrate (Osman et al. 2020)

Challenges External power supply is required for the process Electrodes (anode) need catalyst Risks of H2 consumption at anode Sensitivity of anode to acidic pH The use of saline electrolytes can increase the risks of corrosion (Dixit et al. 2023)

Process optimization for hydrogen enhancement Co-culture (Hasibar et al. 2020) Inhibition of methanogens, development of novel cathode catalyst (Cheng et al. 2022)

10.3.2 H2 Production by Dark Fermentation (DF) The DF is characterized by the conversion of organic substrates to H2 through different catalytic pathways under anaerobic conditions as shown in Fig. 10.1b. The glycolysis of glucose (metabolic oxidation of substrates) by the microorganisms provides the energy required for the generation of H2 through proton (H+) and electron (e−) neutralization process. During DF, complex metabolic metabolites like volatile fatty acids (VFAs) are created. The distribution of metabolic products changes greatly with microbe species, substrate oxidation, and ambient factors such as pH, partial pressure of H2, and nutritional status (de la Cueva et al. 2018, Kumari and Das 2017). The oxidation of nicotinamide adenine dinucleotide (NAD+) to nicotinamide adenine dinucleotide (NADH) is one example of a substrate phosphorylation and energy-yielding process that results in ATP. The redox equivalents are used to decrease the intermediate metabolites produced in the pyruvate pathway, which in turn results in the production of lactate, carbon dioxide, and ethanol (Ergal et al. 2018). Another fermentation pathway involves the conversion of pyruvate to acetyl coenzyme A (acetyl-CoA), which is then followed by the production of ATPs and acetate as well as an additional redox equivalent, carbon dioxide (CO2), and formate (the formate pathway) (Buckel and Thauer 2013; Schafer et al. 1993). The molecular H2 generation can be described by Eqs. 10.1–10.3:

C6 H12 O6 + 2 NAD + → 2CH 3 COCOOH + 2 NADH + 2H + (10.1)



2 NADH + H + + 2Fd 2 + → 2Fd + + NAD + + 2H + (10.2)



2Fd + + 2H + → 2Fd 2 + + 2H 2 (10.3)

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Fig. 10.1  Pathways for biohydrogen production (a) through bio-photolysis, (b) through photofermentation, and (c) through dark fermentation

Under anaerobic conditions, hydrogenase catalyzes these hydrogen-generating processes.

10.3.3 H2 Production by Microbial Electrolysis Cell (MEC) In microbial cells, enzymes like hydrogenase assists in transforming the hydrogen ions (H+) generated into H2 gas using electrons provided by reduced ferredoxin (Sarangi et al. 2022). A microbial electrolysis cell (MEC) is a bioelectrochemical process in which electrogenic bacteria oxidize organic molecules at the anode, resulting in the evolution of H2 at the cathode using external energy. It works

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similarly to how a microbial fuel cell works—in that it converts microorganisms into usable energy. The full system functions as a combination of bacterial electrolysis of organic materials and electrochemically aided augmentation of external voltage to generate H2 as shown in Fig. 10.1c. Despite the high H2 evolution rate (up to 192 m3 H2/m3-day) in mesophilic dark fermentation, the H2 yield is low (Lee et al. 2022). H2 generation is slow in MECs, but they are perfect for increasing H2 yield from carboxylate accumulated during dark fermentation, for which MEC bio-H2 relies heavily on enhancing anode kinetic. However, critical MEC restrictions must be overcome for this for commercialization. In order to construct and run large-scale MECs, first, we need a better knowledge of the kinetics in biofilm anode, which includes factors like inoculation and acclimation methods, anode surface area per volume of MECs, organic loading rate, specific (or volumetric) H2 generation rate, and so on. Second, greater research into anode biofilms, cathode, and separator improvements is needed to ensure the dependability and stability of large-scale MEC systems. There is a dearth of data about the upkeep of anode biofilms and cathodes in industrial-sized MECs. For an effective presentation of MECs, a single-chamber design is preferable because the dual-chamber arrangement requires frequent cleaning or replacement of the separator. When high solid organic waste and wastewater, which can commonly cause separator fouling or clogging, are utilized as the feedstock to MECs, the benefits of using a single MEC are amplified. Third, pilot studies should be used for process optimization and manual preparation for MEC operation and maintenance (O & M) in large-scale MECs. Combining MECs with dark fermentation boosts bio-H2 production. That’s because MECs may utilize the substrate’s unused energy to recover more H2, up to the thermodynamic limit of 4 mol of H2 per mole of glucose in the dark fermentation process. Using the assistance of acidogenic bacteria, volatile fatty acids (VFA) are generated during the dark fermentation process by converting complex organic matter into H2. Electrogenic bacteria can leverage the synthesis of VFAs in MECs as a feedstock for making bio-H2. H2 yields from substrates with high degradation potential are increased as a result of such an integration procedure. When compared to integrated process approaches, the production rate and overall process efficiency achieved through the utilization of MECs alone are much lower. Furthermore, MECs enhance H2 production through dark fermentation, increasing the overall process efficiency (Wang et al. 2011; Chookaew et al. 2014a, b; Tran and Nguyen 2022; Magdalena et al. 2023). While the transition from dark fermentation to MECs has improved H2 generation, a few stumbling blocks have been identified which include cell biomass, pH, and reactor architecture. Another promising technology that has evolved during the recent years is microbial fuel cell (MFC). An advantage of MFC over MEC is highlighted by its efficiency in producing H2 and electricity at the same time which discards the requirement of external energy input during the process. The hybridization of MFC with dark fermentation has been discussed under Sect. 10.4.5 of this chapter.

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Arvanitoyannis and Varzakas (2008) highlighted the importance of anaerobic digestion (AD), dark fermentation (DF), and co-digestion in the biological conversion of agricultural residues to a sustainable energy source. The process generates methane (CH4) and hydrogen (H2), two fuel gases that may be utilized alone or in combination to make a clean fuel transition for bio-hythane (Anu et  al. 2019). Improvements in energy recovery and decreases in atmospheric emissions are two side benefits of bio-hythane research and development (Bolzonella et al. 2018a, b, Si et al. 2016). Bio-hythane’s composition and properties have given it a wide range of potential applications. Bio-hythane’s high-energy potential makes it superior to other waste-to-value conversion methods. Biomass fermentation yields hydrogen gas (H2) and methane (CH4) gas (bio-­ hythane) via a renewable and low-impact process. A sufficient amount of bio-­ hythane can only be produced through the use of biologically justifiable means for the generation of hydrogen and methane. Cavinato et al. (2012), Liu et al. (2018), Kumar et al. (2019a, b, c), and Si et al. (2016) all agree that the use of AD is among the most effective methods for the production of bio-hythane from organic waste.. Table 10.3 discusses the bio-hythane generation from different agricultural wastes using different reactors under varied operating conditions.

10.4 Enhancement of Biohydrogen Production 10.4.1 Pre-treatment During bio-H2 production, the hydrolysis step is the bottleneck that slows down output overall. Factors that affect substrate degradation include particle size, material age, feedstock mix, and so on (Indran et al. 2021). Lignocellulose is found in complex organic molecules and is resistant to assault by most microbial enzymes. Due to their high nutritional content, lignocellulosic materials may be processed and utilized as substrates for biogas generation. The breakdown potential of a wide variety of complicated solid substrates can be increased by pre-treatment (Ariunbaatar et al. 2014). In order to degrade the complex lignocellulosic materials, different types of pre-­ treatment are required, which include (1) physical, (2) chemical, and (3) biological, among which the efficacy and ease of biological pre-treatment have made it more popular than alternative approaches (Sammani et al. 2021). Different methods provide a wide variety of yield and products because they each employ their own unique strategy for dismantling the cell wall’s intricate structure. However, the pre-­ treatment of biomass prior to microbial degradation has a notable impact on boosting biogas output, and in the following paragraphs, we’ll take a look back at where we are in terms of understanding pre-treatment methods.

Oil processing waste substrates

Type of waste Agri-based processing waste substrates

Palm oil mill effluent (POME)

POME (palm oil mill effluent)

Corn silage and cattail Mixture of ensiled sorghum and cow manure Sweet sorghum

Wheat bran

Sugarcane syrup

Substrate Cassava residue

37

NS

CSTR systems

CSTR systems

55 Two-stage reactor Anaerobic Sludge blanket reactor (ASBR) with UASB – 60

37

UASB reactor

5.3 (first stage), 10.4 L/kg 7.5 (second stage) NS 55C 73 mL g 1 COD NS 21.9/gVS

Antonopoulou et al. (2008)

Corneli et al. (2016) Nkemka et al. (2015) Dareioti and Kornaros (2015)

Nualsri et al. (2016)

References Chavadej et al. (2019)

364.3/gVS

Suksong et al. (2015)

342 mL g 1 Seengenyoung COD et al. (2019)

78 L/kg

243 L/ kgVS 328 L/ kgVS 0.90/L LRd

2.25 L/day

17.5 L/day

8.9 L/kgVS

CH4 259 mL/ gm COD

Yield H2 15 mL H2/ gm COD

59.4 L/ kgVS 5.5 (first stage), 2.14/L LRd 8 (second stage)

NS

Operating environment Reactor type temperature (°C) pH 5.5 Continuous two-stage 55 upflow anaerobic sludge blanket (UASB) reactor 37 4.5–6.1 (first Integrated Continuous stage), 7–8 stirred tank reactor (CSTR) (second stage) with UASB reactor NS

Table 10.3  Production of bio-hythane (H2 and CH4) using different anaerobic reactors from agricultural wastes

186 A. Ghosh et al.

Brewery processing waste substrates

Serum bottles

Two-stage reactors: sludge blanket reactor with UASB reactors CSTR system

Vinasse

Tequila vinasse (glucose adapted)

Ethanol stillage

Two-stage anaerobic fermenter Two-stage reactors: CSTR with UASB

Palm oil mill effluent (POME) Agave bagasse

57.4 mL/ gmVS

35

344 L/ kgVS

258 mL/ gmVS

14.8 mL/ gmVS

48 L/kgVS

274 mL/ gmVS

105 mL/g

5.5 (first stage), 7.5 (second stage) 5.5 (first stage), 7.2 (second stage) 5.5 (first stage), 6.8–7.5 (second stage) NS

35 (first stage), 23–25 (second stage) 35

35

240.62/ gVS 225 mL/g

16.26/gVS

NS

55

Luo et al. (2011)

Buitron et al. (2014)

Mamimin et al. (2019) Corona and Razo-Flores (2018) Fu et al. (2017)

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10.4.1.1 Physical Pre-treatment In most cases, the physical method is the one that is utilized in order to adjust the surface area, particle size, biomass crystallinity index, and degree of polymerization of biomass (Jędrzejczyk et  al. 2019). Mechanical techniques primarily involve chopping, grinding, and milling where size reduction is considered as the fundamental step. There is a necessity for modifying the biomass structure by breaking the crystalline nature of the cellulose and increasing the surface area of the substrate for better microbial degradation. Schell and Harwood (1994) reported that reduction of size also helps to deal with the problem of mass heat transmission throughout the pre-treatment process. Ball milling technique is advantageous over other techniques for its mild condition and lower energy input (Günerken et al. 2016). Smaller particle sizes (0.380, 0.250, and 0.180 mm) were found to have a favorable impact on biofuel kinetic generation and yield in the study. Extrusion is a procedure that combines the integration of heat and machine-­ driven approaches, established by rotating a screw within a sealed container. As the feedstock, screw, and barrel rotate at high speeds, they generate a significant shearing force that raises the temperature and pressure in the extruder. Single-screw and twin-screw extruders are the two primary varieties. Products with no sugar degradation, high continuous output, and improved monitoring and control are just some of the benefits of extrusion pre-treatment (Zheng and Rehmann, 2014). Other advantages include lower costs and greater adaptability to change. Some researchers have found that irradiation can be an effective substitute for conventional biomass preparation methods. This irradiation method is more accessible and effective, thanks to its high energy efficiency, low energy need, simple operation, and great selectivity (Kassim et  al. 2016; Chen et  al. 2011). For this method, we use high-energy radiations to break down the biomass’s chemical bonds. Changes in cellulose crystallinity, depolymerization of lignocellulose, and hemicellulose hydrolysis may occur as a result of exposure to certain types of radiations (Chaturvedi and Verma 2013; Chen et  al. 2012a). Irradiation’s efficacy is determined mostly by the nature of the biomass being treated, the duration of its exposure to radiation, and the radiation’s frequency (Saini et al. 2015). Irradiation process mechanics differ depending on methods. Microwaves, gamma rays, electron beam, and ultrasonication are the four most used forms of radiation treatment. In Table 10.4, we have compiled some key statistics regarding these techniques. Irradiation pre-treatment methods have increased biomass digestibility (Chen et al. 2012b; Hassan et al. 2018; Zabed et al. 2019). The lignin’s chemical bonds are broken as ultrasonication generates oxidizing radicals that target the lignocellulose matrix. Cavitation bubbles form as a result, growing larger and more unstable until high temperature and pressure necessary for pre-treatment are reached (Shirkavand et al. 2016). According to research by Hassan et al. (2018), combining microwave and ultrasonication had a significant impact on the pre-treatment process, leading to improved hydrolysis and a higher sugar yield. Though gamma irradiation reports are scarce, what little there is suggests that the process reduces lignin and increases

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Table 10.4  Various irradiance pre-treatment methods on biomass with yield Irradiance Microwave

Operating parameters Varied temperatures (100–180 °C)

Yield Observations 15.8 ml/g of H2 Yield increased by 1.9-fold with highest yield at 160 °C H2 content Reduced energy Iron oxide consumption nanoparticles increased by used as additives 1.5% v/v 60–90% of Yield and Ultrasonication Characteristics sugar crystallinity of features of sugars increased biomass without any changes in chemical structure Electron beam Added with NS Crystallinity ionic liquids decreased with increase in irradiation dose Electron beam High ion beams 7.23 mg/ml of Enzymatic sugar hydrolysis was accelerated when compared to untreated biomass Combined with 2–9 g/l of total Variation in Microwave cellulose structure irradiance ionic liquids sugar concentration with steep rise in crystallinity index

References Yin et al. (2019)

Zaidi et al., (2019)

Zhang et al. (2017)

Jusri et al. (2019)

Xu et al. (2019)

Luengnaruemitchai and Anupapwisetkul (2020)

cellulose (Kassim et al. 2016). Different irradiance pre-treatment on biomass has been discussed in Table 10.4. 10.4.1.2 Chemical Pre-treatment Pre-treatment using alkali increases the porosity of high lignin content biomass through the alkaline hydrolysis of ester bonds between molecules which crosslinks lignin with hemicellulose. Previous studies presented various alkaline pre-­treatments with sodium hydroxide (NaOH), ammonia (NH3), and calcium hydroxide (Ca(OH)2) (Kim et  al. 2016). NaOH, a commonly used alkali, inhibits enlargement that increases the inner surface areas, substantially lowering the grade of aggregation and crystallinity, unscrambling lignin from the biomass, and recreating chemical assemblies of lignin (Yan et al. 2020; Show et al. 2023b). When compared to lignocellulosic wastes with elevated lignin levels, the lower lignin biomasses are more preferred when alkali-based pre-treatment is considered. For promoting the operation of alkali pre-treatment, researches have been focused

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on utilizing the delignification and carbohydrate stabilization (Xu et al. 2016). A wide variety of chemicals are used for alkali-based pre-treatment, which includes O2, H2O2, anthraquinone, and surfactants (Table  10.5). Exo-glucanase and β-glucosidase activities were reduced by 58.6% and 40.6%, respectively, following NaOH (10 wt%) pre-treatment of the substrates at 70 C for 2.5 h with the addition of 10 wt% poly(ethylene glycol) diglycidyl ether (PEGDE) (Lai et al. 2017). This resulted in a 46.4% increase in overall fermentable sugar production. It has been suggested in many literatures that ozonolysis, which has strong reactive properties but low selectivity of the substrate, might be an effective oxidative pre-treatment of lignocellulosic biomass. Binder et al. (1980) showed that straws Table 10.5 Changes in lignin structure of different agricultural wastes due to chemical pre-treatment Type of waste Rice straw

Pre-­ treatment Diluted acid

Pine

Diluted acid

Spurce

Diluted acid Diluted acid

Mixed wood sawdust Poplar Spurce Larch

Switch grass Wheat straw

Corn stover Corn stover

Additives Boric acid

4-Hydroxybenzoic acid, vanillic acid, syringic acid Bisulfite 2-Naphthol, 2-naphthol-7-sulfonate

Diluted acid Auto-­ hydrolysis Acid/alkali

Ascorbic acid

Alkali

H2O2

Alkali

O2

Alkali

Anthraquinone (AQ)

Alkali

Sodium lignosulfonate and AQ

Dimethyl-­ phloroglucinol Poly(ethylene glycol) diglycidyl ether (PEGDE)

Changes in lignin bonding Decreased aromatic C-C stretching and increased aliphatic C-H stretching in the methyl and phenol hydroxyl groups Decreased the amount of phenolics with a low molecular weight Sulfonation of lignin

References Chiranjeevi et al. (2018)

Zhai et al. (2018) Shuai et al. (2010) Lai et al. (2018)

Decreased S/G ratio; β-O-4, β-β, and β-5; increased aliphatic and phenolic hydroxyl groups Surface lignin content Shimada et al. decrease was amplified (1997) Decreased molecular weight Pielhop et al. (2016) Lai et al. Non-condensed phenolic (2020), Lai hydroxyl groups decreased et al. (2017) while the condensed phenolic hydroxyl groups increased Enhanced lignin solubility Gupta and Lee by fragmenting the molecule (2010) Geng et al. Combined with aliphatic side chains and electron-rich (2014) aromatic and olefinic moieties Bifurcation in the aryl-ether Li et al. (2012) bonds Increase in lignin solubility Xu et al. (2015)

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from wheat processing may be delignified by 60% utilizing ozone gas as early as the 1980s. As a result, glucose concentrations (>75%) were increased, while lignin content was decreased relative to untreated wheat. Recent experiments with ozonolysis pre-treatment of Chaetomorpha linum (a type of macroalgae) showed higher yields of ethanol, i.e., 41 g from 31 g of ethanol/100 g glucan, showing promising new uses for this material (Schultz-Jensen et al. 2013). Wood leftovers, grasses, straws, fruit pulps, sugarcane bagasse, and microalgae are only some of the different forms of biodegradable materials that have been investigated comprehensively for delignification through ozonolysis (Travaini et al. 2014). The mechanism of the reaction of ozone and lignin is currently the subject of debate. In a nutshell, ozonolysis depends on the strong oxidizing potential of ozone gas (O3), which, when combined with water, produces highly reactive hydroxyl radicals (OH+) that boost the gas’s reactivity with various macromolecules (Appels et al. 2012). Although many methods of process intensification have been shown to be effective in increasing H2 production—including pre-treatment, process optimization, and co-fermentation—the addition of additives has gained a lot of interest in DF for its low complexity and affordability (Yang and Wang 2018). Metal additives are among the most frequently used types of supplemental additives. Trace metals have been discovered to have a major role in the fermentation process under anaerobic conditions, particularly for hydrogenase activity (Sun et al. 2007). It has been determined that the metal addition to fermentation media has the following positive effects: (1) aid for intracellular electron transport and (2) provision of critical nutrients for bacterial development. 10.4.1.3 Biological Pre-treatment When opposed to physical and chemical pre-treatment procedures, biological pre-­ treatment is seen as a more eco-friendly and effective option that requires less energy to complete. Treatment using enzymes, bacteria, or fungi is among the most widely used biological methods. Enzyme therapy employs hydrolytic and ligninolytic enzymes in their crude, pure, or partially purified forms of enzymatic hydrolysis of cellulose (Sidana and Farooq 2014). Several combinations of oxidative and hydrolytic classes of enzymes have been utilized to alter lignocellulose breakdown. This decomposition mechanism is selective for lignin, which increases the saccharification ratio of hemicellulose and cellulose enzymatic hydrolysis (Saha et al. 2016). In addition to the minimal loss of carbohydrates during anaerobic digestion, the maximal elimination of lignin is also one of the key reasons for preferring biological pre-treatment. Enzymes are essentially biocatalysts; hence, enzymatic pre-treatment is a sort of biological pre-­ treatment. Table  10.6 summarizes the various microorganisms used in biological pre-treatment with their effect in breaking down the lignin and cellulose structures. Agricultural waste can be broken down by enzymes such laccases, xylanases, and cellulases, which can break down the lignin, hemicellulose, and cellulose present. Bio-H2 can be produced by bacteria by the fermentation of sugars with five or

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Table 10.6  Advantages of different biological pre-treatment approaches involved in pre-treatment of lignocellulosic biomass Microorganism Punctualaria sp. TUFC20056 Dictyopanus sp. Exidiopsis sublivida Irpex lacteus Fungal consortium P. ostreatus/P. pulmonarius P. chrysosporium Fungal consortium Ceriporiopsis subvermispora Ceriporiopsis subvermispora Fungal consortium Soft-rot fungus

White-rot fungus

Trametes orientalis (white rot) and Fomitopsis pinicola (brown rot)

Substrate Bamboo culms Bamboo culms Bamboo culms Cornstalks

Changes in overall process 53% of lignin removal

References Suhara et al. (2012) 27% lignin removal Suhara et al. (2012) 30% lignin removal Suhara et al. (2012) 82% of hydrolysis yield after Du et al. 28 days (2011) Straw Seven times increase in the rate Taha et al. of hydrolysis (2015) Sawdust Twenty times increase in the rate Castoldi et al. of hydrolysis (2014) Rice husk Potumarthi et al. (2013) Corn stover 43.8% lignin removal/sevenfold Song et al. increase in hydrolysis (2013) Minimal cellulose loss Cianchett et al. Wheat straw (2014) Corn stover Twofold to threefold increase in Wan and Li reducing sugar yield (2011) Complete elimination of the use Dhiman et al. Plant biomass of hazardous chemicals (2015) Wood Thinning of secondary cell wall Sánchez (2009) through breakdown of non-­ phenolic structures Wan and Li Wood Removal of lignin through (2012) oxidation of individual molecules Corn cobs Increased glucose yield of 83% Wang et al. substantially decreasing process (2017) time

six carbons, such as glucose, arabinose, xylose, or mannose (Srivastava et al. 2017). Recent studies (Ravindran et al. 2018) show that laccase can speed up the oxidation of phenols, anilines, and aromatic thiols in lignocellulosic substrates. The enzyme’s copper ion is distinct from that of phenoloxidase, from which it was derived. Elbeshbishy et al. (2017) found that treatment promoted both microbial growth and anaerobic digestion. The benefits of biological pre-treatment of lignocellulosic substances include low-energy consumption, moderate reaction conditions, environmental friendliness, and the absence of inhibitors. Feedstocks that have been fungal pre-treated prior to physical or thermochemical pre-treatment can effectively shorten the pre-treatment time, lessen the demanding requirements of thermochemical treatment, and reduce the use of toxic chemicals and energy (Sindhu et al. 2016). The current enzyme treatment technology has the drawback of immaturity, as microbial pre-treatment is time-consuming and inefficient. Low treatment efficacy

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is also a barrier to the growth of this strategy because oxidase treatment efficacy is chemical media-dependent (Bian et al. 2019). Researchers found that removing lignin from lignocellulosic biomass with a ligninolytic enzyme could be as effective as removing it with a fungal pre-treatment (Zabed et al. 2019). According to experts, the cost of enzymatic lignin removal is comparable to that of more conventional thermochemical processes. By altering its structure, these enzymes increased the rate of cellulose hydrolysis (Asgher et  al. 2013). Enzyme concentration, enzyme adsorption, product inhibition, heat inactivation, and poor lignin binding are only some of the parameters that might affect hydrolysis independent of the enzyme itself (Sindhu et al. 2016). The structure of cellulose has a major impact on the rate of enzyme hydrolysis. Hydrolysis is influenced by cellulose’s structural features, such as its polymerization level, crystallization arrangement, surface area accessibility, particle size, and the presence of hemicelluloses and lignin (Binod et al. 2011). When it comes to pre-treatment of microalgal biomass, it has been suggested that hydrolytic enzymes may be useful in hydrolyzing biopolymers, particularly for decreasing the thick cell walls. CH4 gas (Vanegas et al. 2015), bio-H2 gas, and bioethanol are just a few of the many products for which enzyme pre-treatment of microalgae has been studied (Kim et al. 2016). One or more enzymes may be used in combination during the pre-treatment procedure. Enzyme cocktails could be generated either from isolated enzyme from bacteria and fungus or from pure enzymes. According to research, the product yield from pre-treated biomass with a single enzyme was greater than that from untreated biomass (Vanegas et al. 2015). The many benefits of microorganism-based biological pre-treatment over chemical pre-treatment, such as reduced energy use, lower environmental impact, lower manufacturing costs, and fewer inhibitors, have prompted intensive study in recent years (Sindhu et al. 2016). Biomass pre-treatment using brown, white, and soft-rot fungus has been used because these microorganisms are effective in breaking down lignin, hemicelluloses, and a little amount of cellulose (Sánchez 2009). When it comes to delignifying wood, white-rot fungi are recognized for their specialized lingo-lytic systems (Wan and Li 2012). Using oxidation of individual lignin molecules, certain white-rot fungi have been found to be successful in completely delignifying wood (Wan and Li 2012). In contrast, until recently (Zabed et  al. 2019), lignin degradation by soft-rot fungi was regarded to be a slow and inadequate process. Soft-rot fungi, as indicated before, can help remove lignin in angiosperm wood and promote thinning of the outermost layer of cells, as discovered by Sánchez (2009). The soft-rot fungus was shown to break down non-phenolic structures, and as a result, they require a substrate with a low concentration of lignin. The basidiomycetes, commonly known as brown-rot fungus, are in charge of the major changes to cellulose and hemicelluloses and the small changes to lignin concentration (Rouches et al. 2016). Therefore, lignin is the primary target of the fungal attack. Recently, it has been shown that a fungal-chemical and fungal-fungal synergistic therapy can reduce process time and enzyme quantity while simultaneously increasing cellulose digestion. Synergistic fungal treatment improved lignin extraction

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efficiency, according to a recent study, with white-rot fungus aiding in the structural modification and reconstruction of lignin and brown-rot fungus aiding in the disintegration of guaiacyl units. Synergistic fungal pre-treatment led to an improvement in lignin oil quality (You et al. 2019). Bacteria have a higher metabolic activity and a faster growth rate than fungus; hence, their application in biological pre-treatment holds promise for shortening the duration of treatment. Bacteria are classified according to their ability to alter, solubilize, or decompose lignin. Streptomycetes, Actinomycetes, Nocardia, and Eubacteria are only a few of the species used as examples here. After 7  days of incubation, a bacterial pre-treatment study showed that Cupriavidus basilensis B-8 successfully removed 41.5% of the lignin and 37.7% of the carbon. After being incubated with the bacteria, kraft lignin was more easily depolymerized into smaller fragments (Shi et al. 2017). Pre-treatment of microalgae often involves the use of hydrolytic bacteria. Pre-­ treatment of biomass frequently involves the use of bacteria with algicidal capabilities (Chen et  al. 2013). Chlorella sp. was pre-treated with Bacillus licheniformis bacteria in an anaerobic digestion study to improve biogas. Sixty hours of microbial pre-treatment increased methane production by 22.7%, according to the study (He et al. 2016). Limitations in developing highly specialized products are a major challenge with bacterial pre-treatment of microalgal biomass. The subsequent bioconversion and downstream recovery operations will be hindered by the low specificity product (Zabed et  al. 2019). However, the problem could seem very different depending on the hydrolytic bacteria used, the amount of bacteria employed, and the consequence sought in the subsequent procedure. Pre-treatment of Chlamydomonas reinhardtii biomass with Clostridium butyricum is an example of related research. During the treatment process, H2 and a number of by-products, including as acetic acid, propionate, and butyrate, are created (Kim et  al. 2016). Regardless, a rate of H2 generation that is orders of magnitude higher than that of other anaerobic fermentative bacteria was achieved. Future large-scale studies, as well as merging biological pre-treatment with biorefinery to develop a sustainable bioprocess, will help improve the pre-treatment method.

10.4.2 Use of Nanoparticles and Metal Monomers to Enhance the Yield of Biohydrogen Metal monomers like Fe0 and Ni0 were found to increase H2 generation during DF. The consequences of these extra metal monomers can be broken down into two categories below: increased H2 generation occurs because it (1) impacts the activity of the biocatalyst directly and (2) changes the complicated metabolic processes occurring during DF.  The addition of different metal monomers boosted the H2 yield by a factor of 10% to 110% relative to the control test without metal addition, depending on the specific parameters used.

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Iron metal monomers are the most promising type of metal monomer because they suppress hydrogenase activity at a low cost and with high efficiency (Yang 2018). The fermentation solution’s oxidative-reductive potential (ORP) can be lowered by adding zero-valent iron, making it thermodynamically more favorable for bacterial growth. Due to their unique surface size and quantum size impact, nanoscale zero-valent metal monomers, such as iron, nickel, or gold nanoparticles (NPs), began to attract attention. To boost H2 generation, adding iron or nickel nanoparticles will speed up electron transport between ferredoxin and hydrogenase. Additionally, the anaerobic corrosion process may oxidize the zero-valent Fe or Ni nanoparticles into metal ions, such as Fe2+ or Ni2+, which may have similar beneficial effects on BHP as the addition of metal ions Fe2+ or Ni2+ does during fermentation. One of the most common supplements utilized to boost catalyst performance during the DF is metal ion. Because of its essential role in the structures of hydrogenase and ferredoxin, the iron ion is widely used despite being relatively inexpensive compared to other metal ions. It appears that nickel ion plays a similar role to that of iron ions in stimulating hydrogenase activity. Numerous hydrogenases, including those that absorb nickel, have been characterized (Zhang et  al. 1984). Zhang et al. (1983) reported that Ni2+ supplementation resulted in a direct increase in hydrogenase activity. Many possibilities suggest that an increase in nickel availability in a cell might boost hydrogen evolution by altering the activity of the biocatalyst or the production of other proteins. It has been demonstrated that metal irons such as Fe2+/Fe3+ and Ni2+ stimulate both biomass growth (cell division) and H2 production during the DF. Hybrid compositions, such as Fe-Ni or Ni-Mg-Al (hydrotalcite), were found to be superior to the addition of a single ion in boosting H2 generation. Their addition was found to boost H2 production by 70–80%. Table 10.7 displays the results of the addition of several nanoparticles and metal monomers.

10.4.3 Enhancement in the Production of Biohydrogen Through Biotechnological Approach 10.4.3.1 Genetic and Metabolic Engineering Approach Instead of producing H2, microorganisms have evolved to effectively use the substrates that are now accessible for growth and survival. To create efficient biocatalysts for H2 generation, more attention has been given to redesigning microorganisms’ metabolic pathways to increase their capacity to produce H2 (Oh et  al. 2011). A potential method to increase H production from carbon sources is to genetically modify the enzymes responsible for H2 production through gene overexpression, gene insertion, and gene knockout. Genetically altering a heterologous or homologous gene, developing engineered metabolic processes, combining strains, and

Glucose Glucose

Glucose

Wastewater Organic fraction of market waste Sucrose Sludge Dewatered sludge Grass

Hexose

Sugarcane juice Starch

Glucose

Glucose

Palm oil mill effluent

Ag (NPs) Ni0

Ni (NPs)

Ni (NPs) Fe0

Cu (NPs)

Fe (NPs) Ni + Fe (NPs)

Ni (NPs)

Ni (NPs) + BC

CoO (NPs)

Fe0 Fe0 Fe0 Fe (NPs)

Substrate Sucrose

Metals Au (NPs)

Clostridium butyricum Clostridium butyricum Anaerobic sludge

Batch CSTR Batch Batch

Anaerobic sludge Anaerobic sludge Anaerobic sludge Clostridium butyricum Clostridium acetobutylicum Anaerobic sludge Anaerobic sludge

Batch

Batch

Batch

Batch Batch

Batch

Batch Batch

Batch

Batch Batch

Reactor type Batch

Anaerobic sludge Anaerobic sludge

Anaerobic sludge

Mixed consortia Anaerobic sludge

Microorganism Mixed consortia

37

35

35

30 37

30

30 37 37 37

55 30

33

37 37

Temperature (°C) 35

Table 10.7  Biohydrogen production with synergistic effects of adding of nanoparticles and metal ions

Yang and Wang (2018) Khan et al. (2013) Zhang and Shen (2007) Sun et al. (2019a)

1.7 mol mol−1

Sun et al. 2019a Mishra et al. (2018)

238 L/kg TSS 0.5 μmol mg−1 h−1

212 L/kg TSS

1.15 mol mol−1 250 L/kg TSS

Camacho et al. (2018) Zhang et al. (2015b) Yu et al. (2015) Yu et al. (2014)

References Pugazhendhi et al. (2019) Zhao et al. (2013) Zhang and Shen (2007) Pugazhendhi et al. (2019) Elreedy et al. (2017) Patel et al. (2014)

1.2 mol mol−1 650 ml/L day 26 mL/g-dry grass 65 mL/g-dry grass

24.7 L/kg TSS 102 L/kg TSS

2.54 mol mol−1

2.48 mol mol−1 57 mL/g-dry grass

Yield 4.47 mol mol−1

196 A. Ghosh et al.

Anaerobic sludge

Glucose

Glucose

Glucose

Potato starch Glucose Sucrose Glucose Glucose

Sucrose Glucose

Glucose

FeSO4

FeSO4

FeSO4

FeSO4 FeSO4 FeCl2 FeCl2 FeCl3

Ni2+ Ni2+

NiCl2

Anaerobic sludge

Clostridium butyricum Clostridium butyricum Anaerobic sludge Heat-treated sludge Anaerobic sludge Anaerobic sludge Enterobacter aerogenes Cow dung Mixed consortia

Batch

Cyanobacteria

Batch

Batch Batch

Batch Batch Batch Batch Batch

Batch

Batch

Batch

Batch Batch Batch

Batch

Bacillus anthracis Anaerobic sludge Anaerobic sludge

Mixed consortia

NiO (NPs) NiO (NPs) Fe2O3/NiO (NPs) Metal ion addition FeCl3 BG110 media

Complex dairy wastewater Palm oil mill effluent Glucose and starch Distillery water

NiO (NPs)

35

35 35

30 35 37 37 30

30

37

35

30

37 35 37

37 Mishra et al. (2018) Engliman et al. (2017) Gadhe et al. (2015)

25 μmol mg−1 h−1 2.1 mol mol−1 19 μmol mg−1 h−1

(continued)

Gou et al. (2015) Wang and Wan (2008a, b) Wang and Wan (2008a, b)

2.1 mol mol−1 2.4 mol mol−1 289 ml

Vi et al. (2017) Mullai et al. (2013) Lee et al. (2001) Dhar et al. (2012) Karthic et al. (2012)

Alshiyab et al. (2008)

226 ml 2.6 mol mol−1 132 ml 216 ml 1.7 mol mol−1

408 ml

0.06 μmol mg−1 h−1 Taikhao and Phunpruch (2017) 302 ml Wang and Wan (2008b) 2.4 mol mol−1 Chong et al. (2009)

Gadhe et al. (2015)

13 μmol mg−1 h−1

10  Technological Advancement for Biohydrogen Production from Agricultural Waste 197

Clostridium butyricum Clostridium butyricum Clostridium acetobutylicum Heat-treated sludge

Glucose

Glucose

Glucose

Sucrose

MgCl2

CaCl2

NaCl

Ni-Mg-Al (hydrotalcite) Ni-Fe

Glucose

Mixed consortia Anaerobic sludge

Glucose Sucrose

MgCl2 Na2CO3

Clostridium butyricum

Anaerobic sludge

Synthetic wastewater

NiCl2

Microorganism

Substrate

Metals

Table 10.7 (continued)

Upflow anaerobic sludge blanket Anaerobic continuous stirred tank reactor

Batch

Batch

Fed batch Upflow anaerobic sludge blanket Batch

Batch

Reactor type

30

37

30

30

30

35 37

Temperature (°C) 34

Alshiyab et al. (2008) Le and Nitisoravut (2015) Karadag and Puhakka 2010

2.7 mol mol−1 3.4 mol mol−1 300 ml

Alshiyab et al. (2008)

Alshiyab et al. (2008)

Srikanth and Mohan (2012) Calli et al. (2006) Xiaolong et al. (2006)

References

82 ml

209 ml

1.75 ml 40 ml

1120 ml

Yield

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isolating novel strains with improved or mutant populations can all increase metabolic H2 production (Goyal et al. 2016). The key enzymes, hydrogenase and nitrogenase, play crucial roles in the metabolic process of purple non-sulfur bacteria by converting protons into H2. Hydrogenase aids the oxidation of H2 to protons, recycles electrons and ATP as well as nitrogenase, and generates H2 amid nitrogen-deficient environments (Koku et al. 2002; Mathews and Wang 2009; Brentner et  al. 2010). Kaji et  al. (1999) documented that overexpression of the hydA gene raised the production of H2 to 1.7 times that of Clostridium paraputrificum M-21’s parent organism. Additionally, overexpression of the hydA gene accelerated NADH’s oxidation to NAD, inhibiting the formation of lactic acid. Overall, the production of bioH2 from agricultural waste can be significantly improved by genetic and metabolic engineering, leading it to be a potential renewable energy source. 10.4.3.2 Eco-biotechnological Approach Eco-biotechnology strives to combine the approach of environmental biotechnology with the objectives of industrial biotechnology by working with methods utilizing consortia and ecological selection principles. It focuses on designing the ecosystem via competition and natural selection rather than utilizing a genetic or metabolic engineering approach (Varrone et al. 2011). It relies on facilitating ecophysiological activities and interactions, minimizing by-product inhibition, using of unprocessed substrates, applying an optimized eco-biotechnological approach, and achieving high productivity using microbial consortia which boosts the bio-­ production of H2 (Ergal et al. 2022). An eco-biotechnological method was used to choose enriched activated sludge that can successfully convert crude glycerol into bio-H2 and ethanol by utilizing a mixed culture of Klebsiella, Cupriavidus, and Escherichia coli/Shigella. This results in up to 0.66 ± 0.06 mol/mol H2 which has nearly five times increase in the production of H2 (Varrone et al. 2011). 10.4.3.3 Bioaugmentation and Co-culture Approach To improve H2 output without the utilization of exogenous enzymes, options include a co-culture strategy to aid in hydrolyzing a range of complicated substrates, such as cellulose and molasses into simple sugars. Co-culture strategies enable the coexistence of even among geographically dispersed, separated microorganisms from various sources for the bio-production, i.e., H2 with 99.99% purity by simultaneously using the substrate and end products without the addition of reducing agents (Laxman Pachapur et al. 2015). Patel et al. reported two bacterial co-cultures of the H2 production by 3 mol/mol of glucose using the two co-cultures composed of Bacillus cereus EGU43, Klebsiella sp. HPC793, and Enterobacter cloacae HPC123. The reactor was scaled up to 16 times, and the increased H2 generation resulted in a 7.44-L evolution. It made up

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58.2% of the total amount of biogas (Patel et al. 2014). According to Ozmihci et al., co-cultures of Clostridium pasteurianum-NRRL B-598 and Clostridium butyricum-­ NRRL 1024 yield the H2 up to 109 ml H2 g TS-1 with a substrate maximum loading rate of 1.38 g/day (Ozmihci and Kargi 2011). The fundamental idea behind bioaugmentation is that some microbes are more adept than others at creating H2 from particular substrates (Mohd Johari et al. 2021; Yang et al. 2019). It is possible to boost the overall output of H2 from the waste material by adding these bacteria to a mixed culture (Anjum et al. 2023; Rathi et al. 2022). For example, different strains of the bacterium Clostridium have shown a special aptitude for generating H2 from agricultural waste, such as cornstalks, sugarcane bagasse, and rice straw. A mixed culture can benefit from the addition of these strains to maximize H2 generation (Usman et al. 2021). Medina-Morales et al. (2021) reported Clostridium acetobutylicum bioaugmented with bovine ruminal fluid (BRF) and the pre-treatment corncob could be used to concurrently hydrolyze cellulose and boost the production of bio-H2. Three thermochemical processes were used to pre-treat the corncob: autohydrolysis H2O at 190 °C, 2% NaOH at 140 °C, and 2% NaOCl at 140 °C, H2SO4 at 160 °C, and hence the mixed culture hydrolyzing the pre-treated corncob yielding up to 575 mL of H2.

10.4.4 Reactor Design When dealing with tiny amounts in laboratory-scale activities, reactor systems in batch mode have the benefits of simple operating mode and the option of various parameter evaluations simultaneously. Most of the published research on biohydrogen production from organic fraction of solid waste appears to employ batch reactor systems (Chu and Wang 2017). However, the implementation of new solid waste disposal techniques has become an important issue, particularly in developing nations, where open burning and speculative disposal of crop wastes have become major problems; trends toward continuous systems have increased in order to eliminate wastes in huge quantities (Zahedi et  al. 2013). The primary objective of the unremitting process is to concurrently decompose the waste substrates while maintaining a highly active microbial community. While CSTRs and UASB reactors are often utilized for biohydrogen generation from wastewater, their drawback of significant solid deposits that should be removed from the reactors makes them incompatible for bio-H2 production from solid/agricultural wastes. Therefore, innovative configurations have been devised in recent years for increasing biohydrogen generation from agricultural wastes (Ndayisenga et  al. 2021). These include the (a) anaerobic baffled reactor (ABR), (b) the anaerobic sequencing batch reactor (ASBR), (c) the dry fermentation system, and (d) the hybrid system. Bio-H2 is commonly produced using the ABR where the acidogenesis and methanogenesis processes can be kept distinct in an ABR system (Elsamadony and Tawfik 2015). This quality allows for the contained growth of microorganisms that produce bio-H2. Table  10.8 shows the many feedstocks

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utilized for biohydrogen generation in ABR systems, including wheat starch (Jürgensen et al. 2015) and soybean (Zhu et al. 2012). Agricultural waste CSTR systems are notoriously difficult to implement because of issues including waste buildup and clogged pumps or pipelines. The ASBR is a useful option for producing bio-H2 from solid waste that avoids this drawback (Kim et  al. 2010). The Table 10.8  Influence of reactor design in H2 yield from different substrates Type of reactor Hybrid fixed bed

Downflow bed bioreactor Upflow bed bioreactor

Biofilm bioreactor Biofilm bioreactor

Biofilm bioreactor

HCSTR (horizontal continuous stirred tank reactors)

ABR ABR ASBR ASBR

Type of Maximum H2 Optimal design fermentation Substrate yield Dark Glucose 32.3 mL H2/g Integrated chlorinated glucose polyethylene fixed bed and Fe-modified zeolite Dark Sucrose and 2.0 mol H2/mol Recycled urea low-density converted sucrose polyethylene bed Submerged tubular ultrafiltration membrane module Silica gel sheet as the carrier Light guide plate modified with SiO2-chitosan medium as the carrier Annular optical fiber as the carrier

References Zhao et al. (2021)

del Pilar AnzolaRojas et al. (2016) Buitron et al. (2014)

Dark

Glucose

2.0 mol H2/mol glucose

Photo

Acetate

Photo

Glucose

2.52 ± 0.13 mol H2/mol acetate 1.11 times higher than that of traditional carrier

Fu et al. (2017) Zhang et al. (2017)

Photo

Glucose-­ based synthetic wastewater Molasses

0.34 mmol H2/ mmol glucose

Zhang et al. (2017)

Production increased from 43 to 62 l/day

Ri et al. (2017)

Wheat starch Soya bean

1.2 L H2/l day

Jürgensen et al. (2015) Zhu et al. (2012) Kumar and Lin (2014) Wang et al. (2006)

Photo Generating circular vortex by dividing the radial flows into axial flows at the bottom of the reactor NS Mesophilic dark NS Mesophilic dark NS Mesophilic dark NS Mesophilic dark

De-oiled Jatropha Pineapple waste

3 L H2/l/day 1.48 l H2/l/day 754 ml H2/l/day

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original intent of the anaerobic sludge blanket reactor (ASBR) was to process trash with a significant solid content in order to generate methane. The system is continuous, with a bigger capacity for substrate loading from the feed compartment, and it requires four sequential stages: (a) feed, (b) react, (c) settle, and (d) decant. In addition, removal of digestate from the reactor system, including recovery of inoculum for reuse, is considerably more practicable. In the end, biodegradable and treated wastes are separated out after the bio-H2 production process in a reaction compartment. This system’s ability to regulate organic chemicals and its large loading capacity are two of its most appealing features (Kumar and Lin 2014). Recent years have seen a small number of studies focused on this technique, as it is widely employed for biogas generation. De-oiled Jatropha waste was employed in a hydrogen fermentation system by Kumar and Lin (2014), yielding 1.48  l H2/L/day. Dry fermentation is a cutting-edge method for converting solid waste into biohydrogen. When the solid content is over 20%, dry fermentation is utilized. It has been argued that this method is superior to wet digesting systems, which produce less than 10% solid waste (Keskin et al. 2019). Wet anaerobic digestion systems require more capacity in the digesters to handle waste since the substrate and inoculum are diluted. The dry fermentation method has several benefits, such as using less energy than a wet system because there is no mixing involved and producing less digestate, which is inversely related to the threat of microbial contamination. This process is environmentally benign since it recycles materials and generates bioenergy at the same time. Because of how little water is needed to operate the system, less space in the digester is required.

10.4.5 Hybridization Because of its abundance and low cost, agricultural waste has been recognized as a favorable feedstock for bio-H2 generation through fermentation. Combining multiple fermentative reactors, with further degradation stages for stabilization of feedstock and boosting conversion of energy, is helpful since the bulk of the organic content of agricultural residues remains semi-degraded in case of single-stage systems. Numerous second-stage therapy strategies have been proposed in the scientific literature. The characteristics of the agricultural waste being processed should guide the choice of second-stage technology. The lower efficiency and energy conversion values are the primary obstacle to the fermentation of agricultural residues. Since we are already familiar with the features of existing reactor configurations, it is more efficient to make improvements to current designs or to integrate systems rather than to develop a new reactor configuration from scratch. Anaerobic digestion in two-phase systems occurs in two separate reactors. This technology has the potential to increase productivity and process stability, leading to a reduced stabilization time for waste. These setups attenuate the first-stage organic loading rate to keep the second-stage feed rate more stable. This method has been around since

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Fig. 10.2  The possible hybrid reactor systems for biohydrogen production from solid wastes. (a) dark fermentation and methane production, (b) dark fermentation and photofermentation, (c) dark fermentation and microbial electrolysis cell, and (d) dark fermentation and microbial fuel cell

1978 for producing biogas, but it has just been used for producing bio-H2 in the last 5 years (Pisutpaisal et al. 2014). To increase bio-H2 output from agricultural biomass, hybrid systems have become increasingly popular in the current years (Dong et al. 2011; Rathi et al. 2022). However, these coupled systems have their own advantages and disadvantages. When dark fermentation is coupled with methanogenesis in separate steps, the overall energy efficiency and effluent stabilization are increased, but the H2 yield is decreased for the composite structure of the wastes. Although dark fermentation allows complete conversion of VFA and agricultural residues, when the dark fermentation process is followed by photofermentation, an additional light energy is essential with a strict requirement of sterile working conditions. As demonstrated in Fig.  10.2, the hybridization of dark fermentation with microbial electrolysis cell requires additional external energy for running the anode and cathode system. Although microbial fuel cell has an additional advantage of simultaneous H2 and electricity generation, oxygen is required to be fed at the anode continuously which can be a major disadvantage affecting system stabilization (Keskin et al. 2019).

10.4.6 Others In Table 10.9, a summary of bio-H2 production with synergistic effects is compared. When the evolution rate of H2 is low, immobilization of microbes is one of the most often used strategies for avoiding substrate washout during continual operation. The following are benefits of bacterial or cell biocatalyst immobilization: (a) resistance to varying operating variables such as temperature, pH, and inhibitory intermediate

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Table 10.9 Bio-H2 production with coactive effects of adding immobilization agents and metals Sl no. Additives 1 Urethane foam

2 3 4

5

6 7

8 9 a

Reactor Temperature Yield type (°C) (mol mol−1) References Batch 60 13 mmol Tanisho l−1 h−1 and Ishiwata (1995) Biochar food Not studied Batch 35 1475a Muri et al. Waste (2018) Fe Potato Not studied Batch 38 298b Yokoi et al. (NPs) + CAB waste (2002) Gel Glucose Enterobacter Batch 30 1.77 Jamali aerogenes et al. (2016) PF Glucose Not studied CSTR 37 0.6 Sunyoto et al. (2017) Sponge Starch Enterobacter CSTR 40 3.03 Zhang et al. aerogenes (2015a, b) Foam + Fe Molasses Enterobacter CSTR 37 3.5 Sekoai and aerogenes Daramola (2018) Fe2++ BC Glucose Not studied Batch 35 234b Satar et al. (2017) Ni Glucose Clostridium Batch 35 238b Sun et al. (NPs) + BC butyricum (2019a) Substrate Microbe Glucose Not studied

ml l−1 h−1 ml g−1

b

accumulation, (b) increased catalyst activities, and (c) increased stability in overall process (Sivagurunathan et  al. 2018). Table  10.9 summarizes the performance of numerous microbial immobilizer additions during DF (Holladay et al. 2009). The application of immobilization clearly improves bio-H2 production on various levels. Several studies have reported that immobilizing provisions like biochar (BC) have a favorable thermodynamic as well as redox potential, which increases hydrogenase-­ catalyzed H2 generation (Sun et al. 2019b).

10.5 Challenges and Future Perspectives Energy and fuels made from lignocellulosic and microalgal biomass are renewable alternatives. The process’s economic feasibility still has to be enhanced, and pre-­ treatment technologies must be fine-tuned for different biomass kinds. With numerous advantages of biological pre-treatment methods instead of more traditional chemical pre-treatment strategies, there are also many obstacles that must be

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overcome before this can be done on a commercial scale. These include the changes in reactor configurations for reducing the heat generation, the cost of production of a system for enzymatic breakdown of carbohydrate, and the identification of efficacious microbes for the hydrolysis of lignin using unique molecular methods. The barriers and challenges have been depicted in Fig. 10.3. In general, the yield of H2 molecules and the substrate budget are the two most significant limitations for the technologies involving fermentation. The energy recovery percentage from the organic agricultural residues in form of bio-H2 is less than 15%, which poses the greatest obstacle in fermentative H2 production (Logan 2008). As a result, it is not unexpected that significant efforts are focused on greatly boosting the H2 yield. In addition, several integrated techniques, such as the two-­stage fermentation method (acidogenic and photobiological or acidogenic and methanogenic techniques) or the implementation of microbial fuel cells (MFCs), are now under research (De Vrije and Claassen 2003; Logan and Regan 2006; Ueno et al. 2001). Instability in H2 production is another difficulty posed by the H2 fermentation process. The instability of H2 generation may be attributable to the metabolic alteration of H2-generating bacteria, which needs to be mitigated through detailed and diversified research of these microbes. A fundamental procedural need for higher H2 yields from the fermentation processes is the constant removal of H2 from the fermentation broth to maintain low H2 partial pressures. The notion of waste management has evolved from “appropriate final disposal” to “zero waste by total recycling” as we enter a new era that places a premium on resource circulation and sustainability. The UN’s proposed SDGs make it abundantly apparent that efforts should be made to promote inexpensive and clean energy in order to guarantee a sustainable terrestrial ecosystem. In response to the United Nations’ recommendation, the European Union (EU) has unveiled the European Green Deal that includes the “clean energy” as well as “eliminating pollution” strategies for promoting resource efficiency through the transition toward a cleaner and sustainable economy. Renewable energy is a viable substitute to conventional energy sources for power generation and could help us reach our sustainability goals. Responsible production and consumption have gained traction as a way to guarantee environmental sustainability as the United Nations and the European Union support the required steps to establish a circular economy. Here, we carefully examined what sort of feedstock, pre-treatment, operational constraints, kinetics/ modeling, and bacterial growth and richness are needed to implement an AD process for treating agricultural waste. For all intents and purposes, methane gas, liquid fertilizers, and organic-rich digestate produced through anaerobic co-digestion (show et al. 2023a) might replace traditional methods of treating agricultural waste and WAS. Though advancements in reactor design are necessary, designers and researchers must take into consideration that rusticity, robustness, liability, ease of operation, and maintenance are also highly sought after. Whatever the case may be, effective resource usage is seen as a crucial component in creating a true circular economy. When incorporating the idea of sustainable development into practice, it is also

Fig. 10.3  Barriers and challenges in Bio-H2 production

206 A. Ghosh et al.

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important to think about the necessary investments for site acquirement, construction of facility structures, and operation and management of the system. To bring about the predicted circular economy, supplemental measures such as feedstock collection, transportation of post-fermentation resources for interdisciplinary applications, and contamination prevention and mitigation are crucial. Additionally, the incorporation of nanotechnology in different production modes or stages has the potential to significantly improve the technology’s cost-benefit ratio for producing bio-H2. Based on the available literature, nanomaterials may play an important part for making this process more stable so that we can extract a large yield of bio-H2 at a realistic scale. Since this field is only getting started, further investigation is required to fill in the knowledge gap and make it useful for real-world applications and long-term economic viability. Last but not least, one should not discount the importance of public acceptability because public involvement can be a huge help in moving toward a sustainable circular bio-economy.

10.6 Conclusion Bio-H2 production from cellulosic-based biomass like agricultural waste has been hailed as one of the most sustainable and feasible alternatives which still need thorough investigations for its applicability on a large scale for its continuing realworld implementations. Various progresses have been made for improving the biohydrogen-­based production technology in terms of pre-treatment, reactor design optimization, biotechnological routes, and process integration/hybridization. One promising approach for renewable fuel generation with improved energy recovery and organic mass valorization is the DF of agricultural remains for the generation of biohydrogen. Complex polymer forms of the agricultural biomass make efficient microbial bioconversion for biofuel production more difficult. However, various pre-treatment technologies have made it possible for easy and faster degradation of these complex polymers into available monomers. However, the use of nanomaterials in the bio-H2 production process from cellulose-rich biomass is expected to be able to circumvent the current constraints associated with different biological methods of producing hydrogen. The biochemical and molecular processes by which nanomaterials affect the cellulose bio-H2 generation process remain to be fully investigated. More comprehensive and value-added utilization of fermentative bio-H2 generation may be possible by the combination of biohydrogen-producing processes through improved biological methods (e.g., DF, PF, MEC, or MFC). These combined technologies may prove useful, as they may be implemented over much longer time frames and so speed up the widespread adoption of bio-H2.

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References Abo-Hashesh M, Desaunay N, Hallenbeck PC (2013) High yield single stage conversion of glucose to hydrogen by photofermentation with continuous cultures of Rhodobacter capsulatus JP91. Bioresour Technol 128:513–517 Alexandropoulou M, Antonopoulou G, Fragkou E, Ntaikou I, Lyberatos G (2017) Fungal pretreatment of willow sawdust and its combination with alkaline treatment for enhancing biogas production. J Environ Manag 203:704–713 Ali SS, Abomohra AEF, Sun J (2017) Effective bio-pretreatment of sawdust waste with a novel microbial consortium for enhanced biomethanation. Bioresour Technol 238:425–432 Alshiyab H, Kalil MS, Hamid AA, Yusoff WMW (2008) Effects of salt addition on hydrogen production by C. acetobutylicum. Pak J Biol Sci 11:2193–2200 Anjum S, Aslam S, Hussain N, Bilal M, Boczkaj G, Smułek W et  al (2023) Bioreactors and biophoton-­driven biohydrogen production strategies. Int J Hydrog Energy Antonopoulou G, Gavala HN, Skiadas IV, Angelopoulos K, Lyberatos G (2008) Biofuels generation from sweet sorghum: fermentative hydrogen production and anaerobic digestion of the remaining biomass. Bioresour Technol 99:110–119 Anu R, Meena A, Banu JR, Kannah RY, Yogalakshmi KN, Kumar G (2019) Biohythane production from food processing wastes – challenges and perspectives. Bioresour Technol 122449. https:// doi.org/10.1016/j.biortech.2019.122449 Appels L, Impe JV, Dewil R (2012) Oxidizing agents and organic solvents as pretreatment for anaerobic digestion. In: Mudhoo A (ed) Biogas production: pretreatment methods in anaerobic digestion. Wiley, New York, pp 199–214. https://doi.org/10.1002/9781118404089 Arimi MM, Knodel J, Kiprop A, Namango SS, Zhang Y, Geißen SU (2015) Strategies for improvement of biohydrogen production from organic-rich wastewater: a review. Biomass Bioenergy 75:101–118 Ariunbaatar J, Panico A, Esposito G, Pirozzi F, Lens PN (2014) Pretreatment methods to enhance anaerobic digestion of organic solid waste. Appl Energy 123:143–156 Arvanitoyannis IS, Varzakas TH (2008) Fruit/fruit juice waste management: treatment methods and potential uses of treated waste. Waste Manage Food Industries 2:569–628 Asgher M, Ahmad Z, Iqbal HMN (2013) Alkali and enzymatic delignification of sugarcane bagasse to expose cellulose polymers for saccharification and bio-ethanol production. Ind Crop Prod 44:488–495 Aslam M, Ahmad R, Yasin M, Khan AL, Shahid MK, Hossain S, Khan Z, Jamil F, Rafiq S, Bilad MR et al (2018) Anaerobic membrane bioreactors for biohydrogen production: recent developments, challenges and perspectives. Bioresour Technol 269:452–464 Balachandar G, Varanasi JL, Singh V, Singh H, Das D (2020) Biological hydrogen production via dark fermentation: a holistic approach from lab-scale to pilot-scale. Int J Hydrog Energy 45(8):5202–5215 Banerjee S, Maiti TK, Roy RN (2017) Protease production by thermo-alkaliphilic novel gut isolate Kitasatospora cheerisanensis GAP 12.4 from Gryllotalpa africana. Biocatal Biotransformation 35(3):168–176 Banerjee S, Gupta N, Pramanik K, Gope M, GhoshThakur R, Karmakar A, Gogoi N, Hoque RR, Mandal NC, Balachandran S (2023) Microbes and microbial strategies in carcinogenic polycyclic aromatic hydrocarbons remediation: a systematic review. Environ Sci Pollut Res. https:// doi.org/10.1007/s11356-023-31140-0 Bian H, Dong M, Chen L, Zhou X, Ni S, Fang G, Dai H (2019) Comparison of mixed enzymatic pretreatment and post-treatment for enhancing the cellulose nanofibrillation efficiency. Bioresour Technol 293:122171 Binder A, Pelloni L, Fiechter A (1980) Delignification of straw with ozone to enhance biodegradability. Eur J Appl Microbiol Biotechnol 11:1–5. https://doi.org/10.1007/BF00514070

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Chapter 11

Recycling of Agricultural Waste for Biohydrogen Production Zeenat Arif and Pradeep Kumar

Abstract Rapid deteriorations of the natural environment and the energy crisis are prime concerns for sustainable development. Hydrogen being the promising candidate and research highlight is considered because it possesses high energy content and is the cleaner form of energy. In this context, biohydrogen production from biological process (fermentation) is an environmentally friendly alternative and creates a path for utilization of agricultural waste. Being abundant in nature, utilization of agricultural waste for biohydrogen production is very advantageous since they are cheap and highly biodegradable, but their limitation lies in lower productivity. Many conducted researches focused their work on improving biohydrogen production efficiency. Hence, this chapter highlights the improving routes and recent advances for its production from agricultural waste. In extend to it, key factors and operational parameter pretreatment method, substrate resource, and fermentation conditions (pH, partial pressure, temperature, etc.) are discussed along with challenges to facilitate further research and future prospects in this domain. Keywords Agricultural waste · Biohydrogen · Energy · Productivity

11.1

Introduction

In current scenario, emission of greenhouse gas is a great threat and prime concern across the countries. Main causes responsible for emissions include fossil fuel and waste combustion. Excluding greenhouse gas, other toxic gas emissions such as CO, CO2, NO2, SO2, and hydrocarbons are also produced during combustion process along with particulate matter (PM) mainly PM 10 and PM 2.5 which are Z. Arif (*) Harcourt Butler Technical University, Kanpur, Uttar Pradesh, India P. Kumar Indian Institute of Technology (BHU), Varanasi, Uttar Pradesh, India © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024 P. Singh (ed.), Emerging Trends and Techniques in Biofuel Production from Agricultural Waste, Clean Energy Production Technologies, https://doi.org/10.1007/978-981-99-8244-8_11

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dangerous to human health during combustion (Panin et al. 2021). Excessive consumption of fossil fuel for energy results in depletion of fossil fuel reserves draws attention of researcher towards sustainable renewable source as an alternative to augment the energy supply freedom without creating threat to environment and could. Major sources of renewable energy are depicted in Fig. 11.1. Among existing renewable energy resources, biofuel draws attention toward itself as they are widely in transport sectors (Ventura et al. 2021). Renewable energy is superior in comparison to fossil fuel in terms of economics viability and is efficient enough to overcome the burden arises from energy dependency and environmental protection. Walsh et al. (2017) highlighted hydrogen, biofuels, and natural gas as leading ecologically prudent energy origins in the foreseeable time. Innovation and research in the field of bioenergy utilizing the concept of conversion of waste to energy is an inevitable alternative for reducing environmental pollution and maintains energy security as well. To overcome the above issues, biohydrogen is an alternative source for clean energy carrier that could significantly reduce emission. It is recognized more because of its specific properties including clean renewable source of energy with high energy content and is not a contributor for the accumulation of greenhouse gases (GHGs) (Singh et al. 2022). H2 produces only water during combustion with liberation of high amount of energy and possesses highest specific energy content among all other conventional fuels, making it a potential source of renewable energy

Fig. 11.1  Source of renewable energy

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(Ventura et al. 2021). Being considered a part of zero carbon emission, hydrogen exhibits good working efficiency with fuel cells compared to existing internal combustion engines. It is also regarded as versatile energy resource as it can be converted to different other energy forms such as heat and electricity (Singh et  al. 2015). Apart from its application in energy sector, it is a raw material of different manufacturing industries, including fertilizers, used in the synthesis of different chemicals, food preparation, and petroleum refineries (Trchounian et al. 2017). Currently, carbon-intensive processes contribute to 96% of hydrogen, and 48% contribution was obtained from steam reforming of natural gas, whereas petroleum fractionation and coal gasification account to 30% and 18%, respectively, and the remaining was obtained from electrolysis and other renewable resources (Chai et al. 2021). As per reports of the Hydrogen Council, 70 million ton of hydrogen is available to meet the demand for the existing applications; however, hydrogen obtained from fossil fuel sources results in approximately 500  Mt of CO2 emissions. But through decarbonization of hydrogen production with carbon capture and storage (CCS) integration or the use of clean energy sources (referred to as green hydrogen), it can effectively reduce annual carbon dioxide emissions by nearly 440 million tonnes in 2050 (Pudukudy et al. 2014). In the past decade, biomass-based feedstocks become the topic of attention for the generation of bioenergy as they are of low cost and have low-carbon emission. Biomass acts as a stimulus for economic growth in least developed to developing countries via energy production. Biomass-based feedstock is an inexpensive alternative compared to water electrolysis for hydrogen generation, because in electrolysis process 80% of the production costs come from electricity cost (Chai et  al. 2021). Being green source of energy, still there are several critical challenges that persist in the biohydrogen production from biomass feedstocks including requirement of high temperature for biomass waste valorization via thermochemical conversion routes (pyrolysis and gasification). In addition, physicochemical properties and morphological irregularity in different biomass feedstocks also play a crucial factor in conversion efficiency and products (Dou et al. 2019). The chapter highlights the different biomass feedstock, conversion efficiency, and techniques available for production of biohydrogen along with their advantages and disadvantages.

11.2 Biohydrogen: Supply, Demand, and Outlook Hydrogen regarded as the highest energy density fuel (~118.2 kJ/g) (Kapdan and Kargi 2006) has more benefits compared to any other fuels. Hydrogen production from renewable sustainable source is referred to as a clean energy carrier because during combustion water formation creates an attractive energy source (Hosseini et  al. 2015). Biohydrogen carries the potential to reduce the dependency on the conventional fossil fuels, thereby reducing greenhouse gas emissions from both sectors (industrial and transportation). Figure 11.2 shows energy content of different fuel (Sampath et al. 2020).

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Fig. 11.2  Energy content of different fuels

According to the analysis of the Economic Research Institute in 2019 for ASEAN and East Asia, it is predicted that hydrogen demand and supply in the East Asia Summit are to be well-proportioned by the year 2040. It was also anticipated that hydrogen production from conventional fossil fuels will going to shift toward renewable sources, like solar, biomass, wind, hydro, and geothermal. There will be an increase in the supply potential from renewable source with increase in the advancement of technology for the respective hydrogen production. The evaluation of production in terms of economical aspect plays a crucial factor in determining the supply and demand aspect of hydrogen production. As per Prabakar et al. (2018), the cost of hydrogen production from steam-reforming process is thrice than the cost of natural gas, whereas from electrolysis it accounts for USD 28/million BTU. Thus, it becomes necessary to develop the waste-based hydrogen to meet the requisite ever-rising energy demand in a sustainable manner. Hosseini et al. (2015) reported the overall efficiency of various thermochemical processes of hydrogen and hydrogen prices, and results show the highest overall efficiency of approximately 75% was obtained using steam methane reforming with a cost of hydrogen as USD 5–8/GJ and it is three times less than that produced from direct gasification of biomass (Preethi et  al. 2019). Hence, economic barrier and limitations of the technological aspects for both biochemical and thermochemical conversions need to be analyzed for commercialization of biohydrogen production. It can be achieved through establishing and managing the systematic supply chain to optimize and integrate biomass for biohydrogen production.

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11.3 Agro-waste-to-Biohydrogen Production: Waste to Energy Advancement in waste-to-energy technologies such as incineration, gasification, and anaerobic digestion is becoming the thematic area of research over the past decades, depending on the different physicochemical characterization of the waste. Huge quantity of waste (food waste, agricultural residuals, sewage sludge) is produced per year (it was estimated around 140 Gt annual generation of biomass globally) which contains significant proportion of carbon-based renewable organic compound. Efficient utilization of these wastes is attracting researchers to produce biohydrogen. Production of hydrogen from waste and wastewater by fermentation, gasification, and microbial electrolysis cell technologies is developed successfully (Nikolaidis and Poullikkas 2017; Zhang and Angelidaki 2014). In order to enhance the production yield, investigations are being carried out to optimize the operational parameters, reactor configurations, and development of efficient microorganisms. With increasing environmental issues, the focus is not only over efficiency improvement in the developed technology but also to analyze the impacts of the proposed technology on environment (Tian et al. 2019). Life cycle assessment (LCA) as one of the scientific methodology is used to analyse the environmental impacts by considering all the materials, energy in the inlet and outlet streams including. Implementation of LCA on waste-to-hydrogen technologies can be out in different literatures, and most of them focus on inhibitors in dark fermentation (Elbeshbishy et al. 2017), sludge fermentation (Wong et al. 2014), biomass hydrothermal gasification (Rodriguez Correa and Kruse 2018), MEC reactor configuration (Kadier et al. 2016), and cathode materials and catalysts (Tian et al. 2019).

11.4 Biohydrogen Production Pathways Thermochemical and biochemical conversion routes are two broad categories for biohydrogen production as shown in Fig.  11.3. High-temperature operations are required in former case, and product quality is greatly affected by feedstock type and condition where in the later case the factors responsible are physical conditions of the living organisms and catalysts used. However, both pathways provide sustainable approach compared to conventional route. Irrespective of upstream process, in both cases, biohydrogen produced is separated by the same downstream methods such as absorption, adsorption, membrane separation, and cryogenics separation (Jiménez-Llanos et al. 2020). Figure 11.2 shows different production pathways.

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Fig. 11.3  Biohydrogen production pathways

11.4.1 Thermochemical Process Thermochemical process is a nonbiological process for biohydrogen production. It involves biomass heating; gasification and pyrolysis are the two most common examples of thermochemical process and produce “syngas”: H2-rich stream (a mixture of H2 and CO). In gasification, biomass undergoes partial oxidation when heated to a temperature above 1000 K in the presence of oxygen environment and/ or steam yields a gas and char product, whereas decomposition of biomass in the absence of air in the temperature range 650–800  K (1–5  bar) yields a gas, solid charcoal, and liquid oils (Kumar et al. 2020). Table 11.1 enlists different organic biomass used for biohydrogen production through pyrolysis and gasification technique.

11.4.2 Biological Route Much significant attention is given by research society for biohydrogen from different biological routes such as anaerobic, photofermentation, and microbial electrolysis cell (MEC)/electro-fermentation in recent years. In context to energy efficiency and practical application ability, each of the defined process has its own advantages and disadvantages. Biocatalyst or inoculum is a concern of major subject for this process as this directly affects hydrogen production process.

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Table 11.1  List of different organic biomass used for biohydrogen production through pyrolysis and gasification technique Biomass type Sugarcane bagasse

Olive pomace

Palm kernel shell

Reactor Operational condition Hastelloy-type 953 K Horizontal Cylindrical reactor Fixed bed (two 500 to 700 °C stages)

High-pressure reactor

600 to 900 °C at 0.1 to 4.0 MPa

Chicken manure Fluidized bed reactor

600 °C in the presence of activated charcoal (6 wt%) 900 °C at 0.6 g/min steam flow rate 700 to 1046 °C

Raw sewage sludge Pine cones

Fixed bed reactor Fixed bed reactor (downdraft) Lignocellulosic Packed bed reactor

120 to 150 °C in the presence of char and oxygen (mass flux: 16–120 g/m2s)

Yield Approx. 45.3%

References Al Arni (2018)

315.3 mL of hydrogen production/g of biomass 40.82 g of hydrogen production/kg of biomass 25.2 mol/kg of mass

Duman and Yanik (2017)

56.2%

Feng et al. (2018) Aydin et al. (2019)

H2 molar ratio— 17.28% and 21.39% 30–40 g of hydrogen production/kg of biomass

Matamba et al. (2020)

Cao et al. (2016)

Jaganathan et al. (2019)

Photofermentation and biophotolysis come under photobiological route for hydrogen production. Major advantage of this is the utilization of abundantly available source called solar radiation and advanced technique/rector for efficiently converting solar energy to moderate hydrogen yields. However, the process requires the design of advanced reactors for efficient conversion of solar radiation to produce moderate hydrogen yields. In fermentation processes, hydrogen is produced by utilizing free carbon sources and is therefore widely used in converting organic wastes (agricultural or industrial effluents) to desirable products. Table 11.2 enlists different organic biomass used for biohydrogen production through different biological pathways (Sampath et  al. 2020). Figure  11.4 shows mechanism of different biological route for hydrogen production (Sivaramakrishnan et al. 2021).

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Table 11.2  List different organic biomass used for biohydrogen production through different biological pathways Substrate Bread waste

Corncob

Bacteria R. palustris

Rhodospirillum rubrum, R. capsulatus, and R. palustris Potato Rhodospirillum residue rubrum, R. capsulatus, and R. palustris Para clostridium, Dark fermentation Enterococcus, Sporanaerobacter, effluent and Clostridium sensu_stricto_1 Corn stalk Rhodospirillum rubrum, R. capsulatus, and R. palustris Alfalfa HAU-M1

Brewery wastewater (BW)

Operating condition pH = 6.8 T = 25–28 °C Intensity = 40 W/m2 pH = 6 T = 30 °C Intensity = 4000/7000 lux

Yield 3.1 mol of hydrogen/mol of glucose

References Adessi et al. (2018)

pH = 5–9 T = 30 °C Intensity = 3000 lux

642 ± 22 mL H2

Hu et al. (2020)

pH = 6.5 T = 30 °C Intensity = 3000 lux

1287.06 mL H2/g TOC

Li et al. (2020)

pH = 6

23.96 mL/h of H2 production

Guo et al. (2020)

84.7 mL H2/g Zhang TS et al. (2020)

55.81 mL/g pH = 6.90, cellulase loading = 0.13 g/g, substrate concentration = 31.23 g/mL 90% PPME + 10% BW 0.69 mol H2/L medium

Lu et al. (2020)

Hay et al. (2017)

11.5 Potential Feedstock for Biohydrogen Production Agricultural and industrial wastes as substrates can be effectively utilized in dark fermentation process as they are rich in starch content with low percentage of undesirable compounds. Abundant and easy availability facilitate starch wastes, a potential source for hydrogen generation. Also, production from starch wastes serves a dual benefit in reference to waste reduction and energy generation (Das and Basak 2021). Continuous increase in different landscaping shrub waste, derived from city afforestation, can also serve as efficient feedstock for energy production. Yue et al. (2021) evaluated and compared the performance of eight different kinds of shrub landscaping wastes as substrate by photofermentation. The results concluded Buxus megistophylla as the most suitable substrate among different others and produces hydrogen yield of 73.82  ±  0.06  mL/g TS under optimized condition at pH  6.98, substrate concentration at 24.49 g/L, light intensity of 3000 Lux, and temperature of 29.78 °C.

Fig. 11.4  Biological pathway and mechanism for hydrogen production

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Rao and Basak (2022) reported utilization of cheese whey by Enterobacter aerogenes via dark photofermentation in a double-walled cylindrical bioreactor gives maximum and cumulative yield as 2.43 ± 0.12 mol/mol lactose and 3270 ± 143.5 mL, respectively, at concentration of 105-mM lactose L−1. The increasing demand for palm oil in the near future opens a pathway to treat palm oil bass and its effluent as feedstock for production of sustainable biohydrogen by either of existing techniques as discussed in above section. However, proper pretreatment is needed for effective generation of gas due to the presence of complex structure in oil palm biomass such as the lignocellulosic composition. According to report of Ong et al. (2021), hydrogen production rates achieved through biological route were up to 52  L-H2/L-­medium/h for solid palm and 6  L-H2/L-medium/h for liquid palm oil industrial waste. Table 11.3 shows biohydrogen yield against different feedstock.

11.5.1 Pretreatment of Feedstock Lignocellulosic biomass and agriculture residues being recalcitrant in nature do easily degrade. Hence, to ensure the presence of biodegradable carbon substrates, it becomes essential to carry out pretreatment of biomass before adopting any of the available techniques for production. Broad classification of pretreatment technologies is physical (milling and grinding), chemical (use of chemicals like acid, alkali, ionic liquids for hydrolysis to enhance the fermentation process), physiochemical (includes steam explosion, ammonia fiber expansion, and CO2 explosion), and Table 11.3  Biohydrogen yield against different feedstock (Han et  al. 2015; Silva et  al. 2018; Syahrial et al. 2015; Vi et al. 2017; Veeravalli et al. 2019) Feedstock Reactor Sugarcane bagasse Batch reactor

Culture Clostridium

Corn stover

Mixed mesophilic

Sugar beet juice Switchgrass

Continuous reactor Continuous reactor Continuous reactor

Carbohydrate-rich algal Lactose

Mixed mesophilic Mixed microbial culture

Sucrose Cashew apple bagasse Sweet potato

Microbial mesophilic

Dark fermentation Dark fermentation

Enterobacter aerogenes strain HO-39 Enterobacter aerogenes strain HO-39 Clostridium roseum ATCC 17797 Microorganism present in sludge

Yield 1.73 mol hydrogen/mol of hexose 3.00 mol hydrogen/mol of hexose 1.90 mol hydrogen/mol of hexose 99.8665.60 mL/g total volatile solids 2.68 mol/mol of hexose 37.8 mol mol–1 109.4 mLg–1 1.89 mL H2 g−1 cashew apple bagasse 138 mL g−1H2 starch

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biological processes (use of bacteria and algae to increase the accessibility of carbohydrate sugars). Any of employed methods has its own advantage and disadvantage like physical techniques suffers from high energy consumption, similarly in chemical techniques is the phenolic compounds formation which results in increase of downstream processing cost, physiochemical process there is a scope of incomplete disruption of lignin-carbohydrate whereas the biological process suffers from slow rate of degradation even though they are energy efficient and eco-friendly in nature (Veeravalli et al. 2019).

11.6 Factors Affecting the Production Yield 11.6.1 Substrates Apart from different conventional substrates such as organic acids (butyric, lactic, malic, propionic, pyruvic, etc.) and sugars (glucose, maltose, and fructose), there are other sources which can be regarded as good substrate for generation of hydrogen including agricultural effluents and food and dairy industry wastes as they have the potential to be used as carbon source. Among different mentioned substrates, high production was achieved in using organic acids. The variation in yield w.r.t to different substrate is attributed to the presence of different oxidation state, variation in metabolic pathway, etc. The production rate is influenced by substrate instead of cellular growth. For example, alteration in iron concentration, cofactor in enzymes of photosynthetic bacteria, changes the hydrogenase activity and process of transfer of electron in bacteria, and the production rate increases with an increase in Fe2+ concentration, but beyond certain limit, it plays a negative role due to the kts toxic effect. Similarly, molybdenum concentration, a cofactor for nitrogenase, influences the hydrogen production.

11.6.2 Light Light intensity also influences the production rate of hydrogen production as bacteria absorb light because it contains chlorophyll and carotenoid pigments. Production rate is a linear function of light intensity which is linearly proportional to the till saturation point.

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11.6.3 pH Conditions Bacteria are very sensitive to the change in pH. Change in pH may change their metabolic activity in reference to proton translocation or substrate degradation rate, thus increasing the time period of the lag phase. pH fluctuations also bring changes in the intracellular and extracellular reactions. The optimum level of pH was found be in the range of 5 to 5.5 for biohydrogen production by most researchers (Sarangi and Nanda 2020).

11.6.4 Process Temperature Different ranges of bacteria are available for hydrogen generation by dark fermentation route. These include mesophilic, thermophilic, and extreme thermophilic range and hyperthermophilic range. Hydrogen production through dark fermentation route is favorable in the temperature range of 35–55 °C. Biohydrogen production was twice times more under high thermophilic conditions than in mesophilic conditions (Sarangi and Nanda 2020).

11.6.5 Hydrogen Partial Pressure Other than pH, partial pressure of H2 is considered a crucial parameter while exploring generation of biohydrogen. According to the principle of Le Chatlier’s, the forward reaction will be inhibited on accumulation of hydrogen gets accumulated or in other words it can be concluded that higher the partial pressure of hydrogen greater will be the negative impact on generation of hydrogen. Investigations (Nagarajan et al. 2019).

11.7 Waste-to-Hydrogen Energy Production: Challenges and Future Scope Biological approach for hydrogen generation is gaining interest from the last few years. It proves to be a promising method since it utilizes feedstock consisted of different organic wastes originated from different sectors such as industrial and municipal including agricultural where disposal of solid waste is a major issue. In reference to utilizing the concept of waste to valuable energy, the process is economically viable when compared with other energy-generating methods. Yet, the percentage of studies is very less where the economic feasibility for commercial biohydrogen production is mentioned. According to Lee (2016), forecasted energy

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cost for biohydrogen per kg will be sustained at 2.5$ and can effectively compete with the cost of fossil fuel in the near future. Experimental studies concluded better performance was achieved via photofermentation route than dark fermentation but from cost point of view later was relatively pricier. Although the researcher’s finding has pushed up in the forward direction the H2 production but shifting the economy from fossil fuel toward H2 energy-based, still efforts are needed to overcome drawbacks and limitation existing in production pathway by optimizing different production processes. Different limitations observed in biological process for hydrogen generation are as follows:

11.7.1 Biophotolysis • • • • •

High cost attributed to expensive photobioreactor Requirement of large surface area Formation of explosive gas mixer Productivity is very low with low conversion efficiency Solar energy utilization