Waste to Renewable Biohydrogen: Advances in Theory and Experiments [1] 012821659X, 9780128216590

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Waste to Renewable Biohydrogen Volume 1: Advances in Theory and Experiments

Edited by Quanguo Zhang Key Laboratory of New Materials and Facilities for Rural Renewable Energy of Ministry of Agriculture and Rural Affairs, College of Mechanical and Electrical Engineering, Henan Agricultural University, Zhengzhou, Henan Province, China

Chao He Key Laboratory of New Materials and Facilities for Rural Renewable Energy of Ministry of Agriculture and Rural Affairs, College of Mechanical and Electrical Engineering, Henan Agricultural University, Zhengzhou, Henan Province, China

Jingzheng Ren Department of Industrial and Systems Engineering, The Hong Kong Polytechnic University, Hong Kong SAR, China

Michael Goodsite Institute for Mineral and Energy Resources, University of Adelaide, Adelaide, South Australia, Australia

Academic Press is an imprint of Elsevier 125 London Wall, London EC2Y 5AS, United Kingdom 525 B Street, Suite 1650, San Diego, CA 92101, United States 50 Hampshire Street, 5th Floor, Cambridge, MA 02139, United States The Boulevard, Langford Lane, Kidlington, Oxford OX5 1GB, United Kingdom Copyright Ó 2021 Elsevier Inc. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Details on how to seek permission, further information about the Publisher’s permissions policies and our arrangements with organizations such as the Copyright Clearance Center and the Copyright Licensing Agency, can be found at our website: www.elsevier.com/permissions. This book and the individual contributions contained in it are protected under copyright by the Publisher (other than as may be noted herein).

Notices Knowledge and best practice in this field are constantly changing. As new research and experience broaden our understanding, changes in research methods, professional practices, or medical treatment may become necessary. Practitioners and researchers must always rely on their own experience and knowledge in evaluating and using any information, methods, compounds, or experiments described herein. In using such information or methods they should be mindful of their own safety and the safety of others, including parties for whom they have a professional responsibility. To the fullest extent of the law, neither the Publisher nor the authors, contributors, or editors, assume any liability for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions, or ideas contained in the material herein. Library of Congress Cataloging-in-Publication Data A catalog record for this book is available from the Library of Congress British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library ISBN: 978-0-12-821659-0 For information on all Academic Press publications visit our website at https://www.elsevier.com/books-and-journals

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Contributors Chao He, Key Laboratory of New Materials and Facilities for Rural Renewable Energy of Ministry of Agriculture and Rural Affairs, College of Mechanical & Electrical Engineering, Henan Agricultural University, Zhengzhou, China; Henan International Joint Laboratory of Biomass Energy and Nanomaterials, Henan Agricultural University, Zhengzhou, China; Collaborative Innovation Center of Biomass Energy, Henan Province, Zhengzhou, China Jianjun Hu, Key Laboratory of New Materials and Facilities for Rural Renewable Energy of Ministry of Agriculture and Rural Affairs, College of Mechanical and Electrical Engineering, Henan Agricultural University, Zhengzhou, China Danping Jiang, Key Laboratory of New Materials and Facilities for Rural Renewable Energy of Ministry of Agriculture and Rural Affairs, College of Mechanical and Electrical Engineering, Henan Agricultural University, Zhengzhou, Henan, China Youzhou Jiao, Key Laboratory of New Materials and Facilities for Rural Renewable Energy of Ministry of Agriculture and Rural Affairs, College of Mechanical & Electrical engineering, Henan Agricultural University, Zhengzhou, China; Henan International Joint Laboratory of Biomass Energy and Nanomaterials, Henan Agricultural University, Zhengzhou, China; Collaborative Innovation Center of Biomass Energy, Zhengzhou, Henan Province, China Yanyan Jing, Key Laboratory of New Materials and Facilities for Rural Renewable Energy of Ministry of Agriculture and Rural Affairs, College of Mechanical and Electrical Engineering, Henan Agricultural University, Zhengzhou, Henan Province, China Gang Li, Key Laboratory of New Materials and Facilities for Rural Renewable Energy of Ministry of Agriculture and Rural Affairs, College of Mechanical and Electrical Engineering, Henan Agricultural University, Zhengzhou, China Panpan Li, Key Laboratory of New Materials and Facilities for Rural Renewable Energy of Ministry of Agriculture and Rural Affairs, College of Mechanical and Electrical Engineering, Henan Agricultural University, Zhengzhou, China; Henan International Joint Laboratory of Biomass Energy and Nanomaterials, Henan Agricultural University, Zhengzhou, China; Collaborative Innovation Center of Biomass Energy, Zhengzhou, Henan Province, China Zhiqiang Liu, School of Energy Science and Engineering, Central South University, Changsha, Hunan, China

xiii

xiv Contributors Chaoyang Lu, Key Laboratory of New Materials and Facilities for Rural Renewable Energy of Ministry of Agriculture and Rural Affairs, College of Mechanical and Electrical Engineering, Henan Agricultural University, Zhengzhou, Henan, China; Henan International Joint Laboratory of Biomass Energy and Nanomaterials, Henan Agricultural University, Zhengzhou, Henan, China; Collaborative Innovation Center of Biomass Energy, Zhengzhou, Henan, China Kebo Ma, School of Energy Science and Engineering, Central South University, Changsha, Hunan, China Sheng Yang, School of Energy Science and Engineering, Central South University, Changsha, Hunan, China Quanguo Zhang, Key Laboratory of New Materials and Facilities for Rural Renewable Energy of Ministry of Agriculture and Rural Affairs, College of Mechanical and Electrical Engineering, Henan Agricultural University, Zhengzhou, Henan Province, China Zhiping Zhang, Key Laboratory of New Materials and Facilities for Rural Renewable Energy (MOA of China), Henan Agricultural University, Zhengzhou, China Huan Zhang, Key Laboratory of New Materials and Facilities for Rural Renewable Energy of Ministry of Agriculture and Rural Affairs, College of Mechanical and Electrical Engineering, Henan Agricultural University, Zhengzhou, China Shuheng Zhao, Key Laboratory of New Materials and Facilities for Rural Renewable Energy of Ministry of Agriculture and Rural Affairs, College of Mechanical & Electrical Engineering, Henan Agricultural University, Zhengzhou, China; Henan International Joint Laboratory of Biomass Energy and Nanomaterials, Henan Agricultural University, Zhengzhou, China; Collaborative Innovation Center of Biomass Energy, Zhengzhou, Henan Province, China Shengnan Zhu, Key Laboratory of New Materials and Facilities for Rural Renewable Energy of Ministry of Agriculture and Rural Affairs, College of Mechanical and Electrical Engineering, Henan Agricultural University, Zhengzhou, Henan, China

Chapter 1

Sustainable waste management: valorization of waste for biohydrogen production Sheng Yang, Kebo Ma, Zhiqiang Liu School of Energy Science and Engineering, Central South University, Changsha, Hunan, China

1.1 Introduction Problems involving energy have always drawn much attention from various countries in the world. Energy is not only the material basis of human life, it also has a significant impact on the development of the economy. The effective development and use of energy resources have been ongoing throughout the whole process of the development of social civilization. In the 20th century, energy used by humans mainly focused on nonrenewable fossil fuels, including crude oil, natural gas, and coal. Up to now, 78% of the worldwide energy supply came from fossil fuels and nuclear energy, in which the source of energy with the highest consumption (30%) was petroleum (coal 25%, natural gas 17%, and nuclear energy 4%). But clearly, the distribution of energy is of high inhomogeneity and the reserves of fossil energy are limited. Lots of countries are going to run out of fossil energy (Henstra, 2006). According to the International Energy Agency, three kinds of fossil energy (crude oil, natural gas, and coal) are forecasted to be depleted in merely 40, 60, and 220 years, respectively, according to current trends. Especially in recent years, as countries around the world simultaneously move toward industrialization, the demand for energy in the world has increased at high speed (Hepbasli, 2008) and energy has gradually become the limiting factor of the development of society. Another serious problem facing people is environmental pollution, including the greenhouse effect, acid rain, and the ozone hole. Overexploitation of fossil energy produces lots of waste and causes groundwater pollution. Meanwhile, modern industry excessively burns coal, petroleum, and Waste to Renewable Biohydrogen. https://doi.org/10.1016/B978-0-12-821659-0.00008-3 Copyright © 2021 Elsevier Inc. All rights reserved.

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2 Waste to Renewable Biohydrogen

natural gas, discharging a lot of carbon dioxide (CO2) CO, SO2, smoke, oxynitride, and other hazardous substances. This phenomenon not only aggravates atmospheric contamination and the greenhouse effect, it results in acid rain and ozone depletion (Jebaraj and Iniyan, 2006; Hallenbeck and Ghosh, 2009; Balat and Kırtay, 2010; Levin and Chahine, 2010). Since the industrial revolution, people have discharged hundreds of millions of tons of toxic pollutants into the atmosphere. People have tried to develop environmentally friendly and economically applicable renewable energy, fundamentally changing the state of the energy mix (Nakata, 2004). Therefore, governments and scientists have focused on developing and using biomass, solar, ocean, hydrogen (H2), and geothermal energy, as well as other alternative energy sources. Lots of waste has been produced and discarded, which causes environmental pollution owing to rapid urbanization. Considering the lack of energy, waste has drawn much attention as a new energy resource. Generally, as an important part of the waste, biomass could generate a lot of energy to fulfill the partial energy requirement in our daily lives. Thus, this chapter focuses on waste to energy (WTE) and biohydrogen technology. First, the classification, harm, and treatment technology of waste are introduced systematically. Then, biomass energy and biohydrogen are introduced clearly as a reference to process waste biomass.

1.2 Current status of waste 1.2.1 Introduction to waste Waste usually occurs during the process of human survival and development; it has no value for preservation and use. Generally, waste can be classified according to its properties, states, constituents, sources, processing mode, and others. Based on sources, waste can be sorted into domestic, industrial, and agricultural waste. Domestic waste comes from human activities such as food residue (Nahman et al., 2012; Han et al., 2018; Zhuang et al., 2008). Industrial waste includes kinds of skimmed refuse, effluent, dust, and other solid waste generated in the industrial production process, such as blast furnace slag and industrial wastewater (Stenis, 2004; Raupp-Pereira et al., 2006; Al-Qaydi, 2006). Agricultural waste could be straw, the excrement of animals, and agricultural product waste (Padkho, 2012).

1.2.2 Harm of waste 1.2.2.1 Harm to cities A large hysteresis and long influence time are both features of city waste pollution. Lots of rubbish contaminates surroundings and extends the pollution field by other mediums. Meanwhile, it poses harm to the soil, atmosphere, water, and other natural resources (Jebaraj and Iniyan, 2006; Hallenbeck and Ghosh, 2009; Levin and Chahine, 2010; Balat and Kırtay, 2010).

Sustainable waste management: valorization Chapter | 1

3

a. Soil pollution Waste not only encroaches on the land area, it also pollutes the surface soil for long-term partners. Initially, hazardous materials in garbage penetrate the soil through the wash of rain and surface water (Yanxun et al., 2011). With the influential absorption of soil, hazardous materials exist chronically in soil, causing changes in structure and composition. In one respect, this reduces the capacity of soil to decompose and purify garbage. Moreover, the soil itself changes qualitatively and aggravates the living environment of microorganisms and plants. Second, the landfill pollutes soil in-depth (Regadı´o et al., 2012). Once polluted, the soil costs lots of money and time to clear and repair. Furthermore, hazardous heavy metal elements can barely be degraded in soil, which destroys the soil’s construction (Qishlaqi et al., 2009). Finally, the phenomenon of discarding garbage carelessly is more common in the suburbs because of the lack of effective management. Waste scattered in suburban farmland cannot be recovered in time and harms farmland over a long time, which pollutes the farm’s products. When polluted farm products are delivered to cities, they harm residents’ health. b. Atmospheric pollution Atmospheric pollution is mainly caused by incinerating garbage; the process produces hazardous gases and pungent smells (Mcdonald, 2012). First, physicochemical reactions among different substances occur during the long process. Ammonia (NH3), sulfuretted hydrogen (H2S), and other gases, which are colorless, irritating, and flammable, are generated when materials decay (Ramanathan and Feng, 2009). There are more than 100 kinds of organic volatile gases detected at the open dump. These gases may bring about respiratory disease and even cancer. Second, when garbage is burned, some poisonous gases are generated, such as carbon monoxide (CO), benzene compound, and dioxin. Dioxin, which is colorless, has the features of latency and carcinogenicity. It can cause many diseases, even severe skin disease, when people suction a lot. c. Water pollution According to the International Water Association, more than 25 million children aged under 5 years were fatally poisoned by drinking polluted water. Thus, the pollution of water resources and the harm caused by polluted water are issues that must be addressed (Hu and Cheng, 2013). In one respect, when a lot of garbage is stored irrationally on open ground, organic pollutants are generated by chemical reactions. In addition, with persistent rain, the heavy metal element in some garbage dissolves and seeps into surface water, causing water pollution. Moreover, a great amount of household waste is dumped into

4 Waste to Renewable Biohydrogen

rivers, lakes, and oceans, destroying the self-purification capacity of water. Water can dissolve hazardous substances in kitchen waste, which intensifies pollution. The pollution of rivers will affects the growth of microbes and spoils the water, which can make water itself emit a foul odor (Waste brine may harm marine life, 2019). Finally, because it moves, the polluted water flows to other water areas, expanding pollution’s coverage. Therefore, great financial and material resources are needed to control and govern pollution.

1.2.2.2 Harm to humans The scope of the pollution of households need to be controlled; people already live on polluted land (Horsman, 1982; Santos et al., 2005). In our daily lives, people will inevitably touch the ground, which offers the necessary conditions for harmful substances to enter the human body. If there are no effective measures to solve the problem of pollution, people will bear the adverse consequences of garbage pollution. In addition, garbage may lead to an outbreak of accidents. For long-time storage, certain substances in garbage cause chemical reactions, generating lots of H2S and CO, which are explosive when kept together. Various countries in the world are actively formulating measures to manage garbage strictly (Chen and Liu, 2013; Arun and Sivashanmugam, 2015; Warunasinghe and Yapa, 2016). To build a civilized, harmonious, and healthy social environment, residents should be educated to get rid of bad habits such as dumping waste at will (Brown, 2015).

1.3 Waste to energy technologies Energy sources made from biomass can meet one-fifth (Geert Bergsma, 2010) of the demands of primary energy across the world. Hence, it is a huge misuse to deal with biomass waste improperly. Methods for recycling organic waste include anaerobic digestion, burning, and gasification. Energy conversion technology offers an opportunity for organic waste to be transferred to renewable energy sources and counteracts handing and environmental costs (Milbrandt et al., 2018). Within the increasingly tough regulatory environment, it is important to deal with environmentally friendly biomass waste. The most widely used methods of waste recycling technology are waste burning to generate electricity and biogas power generation.

1.3.1 Waste burning generating electricity technology The most mature waste energy conversion technology is combustion. In 2012, 455 incineration plants came into service in Europe (Lausselet et al., 2016). China increased the number of incineration plants from 45 to 188 from 2004 to 2014 (Mian et al., 2016). In recent years, the number of incineration plants has significantly increased, decreasing the waste being composted. Waste

Sustainable waste management: valorization Chapter | 1

5

incineration not only has an considerable effect on managing the growing amount of garbage, it has an important role in supplementing traditional energy. Although it needs a lot of investment at the initial stage, waste to energy has some advantages, including the conservation of land resources, effective resource recovery, and low pollution (Cucchiella et al., 2017). Therefore, WTE has been a tendency in the development of the environmental protection industry. Some developed countries such as Japan, the United States, and Germany have had terminal technology to make garbage harmless, recyclable, and reducible. Compared with landfills, waste incineration technology can effectively reduce more than 90% of the volume of garbage without further decomposition. Furthermore, the ashes can be used to cover the ground. During incineration, all causative agents are burned. Putrescible organic matter, which could generate noxious gas, is completely oxidized. Meanwhile, the operation of incineration is reliable, ideal, clean, and stable. An enclosed production mode is not influenced by natural conditions. Compared with landfills, the floor space of an incineration plant is small and the site is easily chosen (Li et al., 2016). However, it also has some disadvantages, such as a high investment in engineering, high operating costs, and difficult management. The heat value of waste combustion has much more exact demands. Only when the heat value reaches a certain value can the waste be dealt with by incineration. With the increase in management standards and the development of technology, waste incineration plants have successfully reduce emissions of fetor and dioxin (Monni, 2012; Damgaard et al., 2010; Abd Kadir et al., 2013). In some densely populated and economically developed areas such as Beijing, Shanghai, Guangzhou, Wuhan, and other large and medium-sized cities, garbage incineration power plants have been built and put into use (Zhao et al., 2011c; Chen and Christensen, 2010).

1.3.2 Marsh gas power generation Marsh gas power generation is another type of waste energy conversion technology. Marsh gas can be used to generate heat directly and can be transferred into electric and thermal energy, and combined heat and power generation. It can also be upgraded to become biomethane, which could replace natural gas. Therefore, a marsh gas plant has two functions: it helps to manage waste and generates alternative energy sources. Marsh gas power generation has a bright future. In Europe, 13.4
106 tons of equivalent petroleum marsh gas and 52.3
106 MW biogas generation were generated in 2013, an increase of 10% compared with 2012 and by 28.8% compared with 2011 (EUROBSERV-ER, 2014). Anaerobic fermentation is a significant segment of energy recovery that can transfer biomass into bioenergy. A lot of marsh gas is generated in the anaerobic treatment of kitchen waste, organic wastewater at a high

6 Waste to Renewable Biohydrogen

concentration, and farm manure. Marsh gas with a methane content of up to 75% has a high heat value, which makes it a good fuel. Meanwhile, marsh gas power generation could reduce pollution and protect the environment, with a lot of economic and social value. Research is focusing on transferring sewage treatment into resource recovery facilities. The recycling of nutrients in wastewater can reduce the cost of wastewater treatment facilities, avoiding effects on the environment (Song et al., 2018). There are four treatment methods for dealing with organic wastewater: biological, chemical, and physicochemical treatment, and biochemical pretreatment. Biological treatment technology is one of the most important processes; it uses microorganisms to degrade contaminants in water as its nutrients. For biological treatment, anaerobic digestion is a proven technique and has been used to produce marsh gas. Because of the characteristics of waste and the conditions of the fermentation process, the average compositions of marsh gas are different. According to Leonzio (2016), marsh gas consists of methane (CH4) and CO2, in which the amount of methane is about 55%e75% and the amount of carbon dioxide is about 30%e45%. Physical, chemical, and biological technology can be used to deal with farm manure. Of these, aerobic composting and anaerobic digestion are the two most commonly used methods. Anaerobic digestion could recycle valuable secondary products via marsh gas generation during the process of dealing with farm manure. The farm manure has some advantages for marsh gas generation. It occurs in large quantities and has great buffer ability. All macroorganisms, spectator nutrient substances, and essential microorganisms can be supplied by farm manure. In addition, biogas plant can storage farm manure in the rainy season to limit nutrient loss. Hence, farm manure is already used as the main organic provider of marsh gas plants.

1.4 Biomass energy 1.4.1 Introduction to biomass energy Biomass energy has a significant role in renewable resources because of its numerous sources, low-level technical demand, low cost, and large profit (Reddy and Yang, 2005; Pan et al., 2009). Biomass refers to the kinds of organics generated by photosynthesis. It consists of core wood, agricultural and forest crops, agricultural and forestry residues, municipal solid waste, sanitary sewage, aquatic pollution, and so on. High-yielding energy crops such as sugar grass, sweet potato, cassava, Canna edulis Ker, Euphorbia tirucalli, and kelp widely attract attention as modern biomass resources. When solar energy is transformed into chemical energy, it will be stored in biomass. Biomass energy comes from photosynthesis directly or indirectly in green plants. It can be conventional solid, liquid, and gas fuel.

Sustainable waste management: valorization Chapter | 1

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1.4.2 Application of biomass energy The investigation and exploitation of biomass energy is the most popular issue across the world. After years of research, some distinctive development techniques now exist: (a) Biogas technology Biogas technology mainly uses anaerobic methods to deal with animal dung and organic wastewater at high concentrations, which develop early. Before the 1980s, developing countries such as China mainly focused on biogas digesters, generating biogas to provide cooking fuel by using crop straw and animal dung, whereas developed countries emphasized anaerobic technology (Weiland, 2010; Bacenetti et al., 2013; White et al., 2011; Shen et al., 2015; Bojesen et al., 2015; Venkatesh and Elmi, 2013; Kobayashi, 2010; Kumaran et al., 2016). Currently, Japan, Denmark, the Netherlands, Germany, France, the United States, and other developed countries universally use anaerobic methods to deal with animal dung. Some countries use this method to dispose of garbage and generate electricity. Finally, waste after fermenting is recycled as manure. (b) Biomass pyrolysis gasification In the 1970s, some developed countries such as America, Japan, Canada, and European communities started to investigate and exploit biomass pyrolysis gasification technology. Until the 1980s, 19 companies and institutions studied biomass pyrolysis gasification technology in the United States; 12 university laboratories in Canada also carried out relevant research. In addition, the Philippines, Malaysia, India, Indonesia, and other developing countries also performed this research. (c) Biomass power generation Biomass power generation has drawn much attention in developed countries. It mainly has three forms: biomass boiler direct combustion power generation, biomassecoal mixed combustion power generation, and biomass gasification power generation. In Austria, Denmark, Finland, France, Norway, Sweden, America, and other countries, the proportion of biomass energy in all energy consumption is rapidly growing. Finland is one of the most successful countries to use biomass to generate electricity in the European Union, and America takes the leading position in biomass power generation. (d) Biomass liquid fuel Liquid fuel, with biomass as a raw material, consists of ethyl alcohol (Sarkar et al., 2012), pyrolysis oil, vegetable oil, and others; it could replace gasoline and other oil fuel as a clean fuel. Brazil is the most distinctive country to exploit and apply ethanol fuel. In the mid-1970s, to avoid excess

8 Waste to Renewable Biohydrogen

dependence on imported oil, it implemented the biggest program to exploit ethyl alcohol in the world. Until 1991, ethanol production reached 1300 million liters. Among 98 billion cars, almost 40 billion used only ethyl alcohol as fuel. Other cars generally used ethanol-blended gasoline fuel with a 20% ethanol content. Hydrolysis technology has been well developed by improving the filtration rate, strengthening the hydrolysis process, perfecting the evaporation of hydrolysate, recovering heat, and culturing new strains. With the development of new technologies, hydrolyzed ethanol liquid fuel will be more competitive economically. (e) Other methods Besides these mature techniques, some technologies are being explored and investigated, such as biohydrogen production technology, biodiesel production, and cellulosic ethanol production technology. In these technologies, biohydrogen production technology draws much attention due to its product, H2 (Zhang et al., 2007; Percival Zhang et al., 2006; Pandey et al., 2001; Fan et al., 2008). H2 is a new type of clean energy source, without carbon, nitrogen, sulfur and other detrimental impurities (Fan et al., 2006b; Al-Alawi, 2007). When it is burned with oxygen, the product is only water. There is no nitric oxide, sulfide and cancerogenic substance, which could put an end to environmental pollution, generated during the process. Besides, H2 also has many applications: (a) serving as the intermediate vector of other primary energy (like nuclear energy, solar energy); (b) making up fuel cell with oxygen; (c) acting deoxidant of preservative; (d) being used as the fuel of the rocket engine. Because of these special properties and purposes, H2 draws much attention from researchers.

1.5 Technologies for biohydrogen 1.5.1 Hydrogen production organisms In the process of producing biological H2, some anaerobes are used as matrix. This method can produce H2 when degrading organic matter. There are two types of biohydrogen methods: anaerobic photosynthetic H2 production and anaerobic fermentation H2 production. The microorganism used in anaerobic photosynthetic H2 production is anaerobic phototrophic bacteria (and some algae); anaerobic heterotrophic bacteria are used in another method. Until now, H2-production microorganisms can be divided into two categories: (1) photosynthetic organisms, including algae (cyanobacteria and green algae) and photosynthetic bacteria; and (2) compatible and specific anaerobic H2-production bacteria, such as Escherichia coli, Enterobacter aerogenes, Clostridium butyricum, Clostridium perfringens, and Clostridium acetobutylicum. Fig. 1.1 and Table 1.1 list the species and H2 production capacity of some photosynthetic organisms and fermentative H2-production bacteria.

Sustainable waste management: valorization Chapter | 1

FIGURE 1.1 The hydrogen productive capability of algae and photosynthetic bacterium.

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10 Waste to Renewable Biohydrogen

TABLE 1.1 Hydrogen-productive capability and rate of fermentation bacteria.

Bacteria name

Carbon source

Hydrogen production rate/[mL H2/ (L medium $ h)]

Enterobacter aerogenes

Molasses

291.2

2.2e3.5 mol H2/(mol saccharose)

850

0.73 mol H2/(mol saccharose)

Wastewater Glucose Saccharose

1.89 mol H2/(mol saccharose)

Starch

27 mL H2/(L medium)

Cellulose

694.4

Glucose

6 mL H2/(L medium) 0.5e0.65 mol H2/(mol saccharose)

Glucose Clostridium beijerinckii

Hydrogen production

/

344.0 mL H2/(g COD)

Saccharose

379.4 mL H2/(g COD)

Starch

230.3 mL H2/(g COD)

Clostridium butyricum

Glucose

1150

1.9 mol H2/(mol saccharose)

Clostridium baratii

Glucose

/

22.2 mL H2/(g COD)

Fusobacterium

Glucose

/

1.45 mol H2/(mol saccharose)

Clostridium thermocellum

Cellulose

/

56.7 mL H2/(g COD)

Enterobacter cloacae

Glucose

1388.8

/

Compared with photohydrogen production, fermentative H2 production has the advantages of a high H2 production rate, no limitation of illumination time, a wide range of available organic matter, and dimple craft. Therefore, anaerobic fermentative H2 production is greatly promising.

1.5.2 Process of organic anaerobic biodegradation During anaerobic treatment, many kinds of microorganisms have a combined action and transfer macromolecular organic matter into H2, CH4, CO2, H2O, H2S, NH3, and others. In this process, metabolic processes of microorganisms

Sustainable waste management: valorization Chapter | 1

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FIGURE 1.2 Degradation course of organic substances. VFA, volatile fatty acid.

affect and interact with each other, forming a complex ecosystem. Since the 1970s, after a deep investigation into microorganisms and their metabolic processes, Zeikus (1979) suggested four phases of progress of anaerobic degradation and divided them into four typical stages (Fig. 1.2): i. Hydrolysis phase During the hydrolysis phase, insoluble polymers are transferred into simple soluble monomers or dimers. Macromolecular organisms have a huge relative molecular mass. It cannot penetrate the cytomembrane and cannot be used directly by the germ. Hence, it is decomposed into micromolecules by hydrolytic enzymes in the first phase. In this phase, carbohydrates, proteins, and lipids are broken down into glucose, amino acids, glycerin, and fatty acids. These micromolecular hydrolysates are water soluble and can cross the cell membrane and be used by germs. The hydrolysis phase belongs to enzymatic reactions and usually needs an extended period. Thus, it is considered as the rate-limiting step. ii. Fermentation (acidize) phase Fermentation is defined as the process by which organic compounds can be the electron donor and the electron acceptor at the same time. In this phase, the small molecule compound generated in the hydrolysis phase is transformed into simpler end-products, mainly volatile fatty acids (VFAs) in fermenting bacteria cells. Then, the end-products are secreted into the outside of the cells. Therefore, this phase could be called the acidize phase. It includes the anaerobic oxidation processes of amino acids, saccharides, higher fatty acids, and alcohol. Primary products in this phase consist of VFAs, alcohol, lactic acid, CO2, H2, NH3, sulfuretted (H2S), and others. Meanwhile, acidated bacteria also use parts of the material to compound new cellular material. This phase moves quickly and decreases the pH value of the feed liquid to get rid of the moldy smell.

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iii. Acetic acidegenerating phase In this phase, the end-products (VFA, alcohol, lactic acid, and others) produced in the fermentation phase are further transformed into acetic acid, H2, carbonic acid, and other new cellular materials, which include acetic acid and H2 from the middle products (with the action of H2-producing acetogenic bacteria). Acetic acid can also be formed by H2 and carbon dioxide (by the action of homotypic acetogen). iv. Methane-generating phase In this phase, acetic acid, H2, carbonic acid, formic acid, and methyl alcohol are transformed into CH4, CO2, and other new cellular materials. There are two transformations: one uses H2 to generate CH4 with CO2 existing; the other uses acetic acid to produce CH4.

1.5.3 Reactors of hydrogen fermentation Several kinds of reactors are used for H2 fermentation. Table 1.2 compares the efficiency of common biohydrogen reactors. According to the forms of bacterial growth, these reactors can be classified as suspension growth and attached growth reactors. The form of reactor may be a continuous stirred tank reactor (CSTR), upflow anaerobic sludge blanket (UASB), sequencing batch reactor, packed bed reactor (PBR), fixed bed reactor, fluid bed, biological filter, fermenter, and so on. The main performance parameters of reactors include the hydrogen production rate (HPR), maximum biological density (X), H2 yield, specific hydrogen productoin rate (SHPR), and others. Among the biohydrogen reactors, CSTR has the most extensive coverage in actual application, owing to its advantages of a high mass transfer rate between gas and liquid, less inhibition in microbial metabolism, and fewer byproducts. However, because of the limitation of its construction, microorganisms in CSTR are in suspension growth mode. Meanwhile, the holding volume is less and the reactor lacks stability. Compared with CSTR, microorganisms in UASB grow in attachment mode and leave out the equipment and energy consumption used in the process of stir. PBR is usually used to investigate the H2 production of pure strains. However, microbial species and different carriers have a big impact on the HPR of reactors. Industrial applications of pure strains, especially involving H2-producing cell separation, further drive up the use of packed bed, fixed bed, and other reactors. Each kind of reactor has its own merits and demerits. Table 1.3 compares the H2 production efficiency of continuous flow fermentation process biological H2 production reactors. The attached growth reactor has obvious advantages for H2 production because of the microorganism’s holding volume and other respects, compared with a suspension growth reactor. This is because

TABLE 1.2 Various substrates used for fermentation hydrogen production.

Substrate

Inoculum

Range studied

Optimal

SHPR (mol/ g-VSS.D)

Yield (mol-H2/ mol-substrate)

Xylose

Municipal sewage sludge

100e10 g/L

20 g/L

e

2.25

Lin and Cheng (2006)

Clostridium butyricum CGS5

5e40 g/L

20 g/L

e

e

Lo et al. (2008)

Enterobacter cloacae 11T-BT 08

e

e

0.71

2.0

Kumar and Das (2001)

Ruminococcus albus

e

e

e

2.52

Ntaikou et al. (2009b), (2010)

Digested sludge

1.1e320 g/L

2.1 g/L

e

3.1

Substrate (2008)

Seed sludge

0e300 g/L

e

0.23

2.1

Fang and Liu (2002)

E. cloacae 11T-BT 08

0e1 g/L

e

0.71

6.0

Kumar and Das (2000)

Thermoanaerobacter thermosaccharolyticum PSU-2

5.6e56 g/L

20 g/L

0.29

2.53

O-Thong et al. (2008)

C. butyricum CGS5

5e30 g/L

20 g/L

e

2.78

Lo et al. (2008)

Anaerobic sludge

5e60 g/L

20 g/L

e

2.2

Lin et al. (2008)

Thermococcus kodakarensis KODI

2e12.15 g/L

e

0.3

1.9

Hussy et al. (2005)

Sustainable waste management: valorization Chapter | 1

Municipal digester sludge

8e32 g/L

32 g/L

e

1.8

Lee et al. (2008)

13

Substrate concentration

Glucose

Sucrose

Starch

References

Continued

Substrate concentration Substrate

Inoculum

Range studied

Optimal

SHPR (mol/ g-VSS.D)

Yield (mol-H2/ mol-substrate)

Ryngas (CO)

Rubrivivax gelatinosus

0e0.57 mmol/L

0.15 mmol/L

0.79

0.96

Wolfrum and Watt (2002)

Rhodospirillum rubrum

0.01e0.14 mmol/L

0.14 mmol/L

0.74

0.98

Do et al. (2007)

R. rubrum

5e14 mL/min

e

0.41

0.89

Younesi et al. (2008)

Carboxydothermus hydrogenoformans

0.09e1.1 mmol/L

0.55 mmol/L

3.0

0.97

Zhao et al. (2011)

C. hydrogenoformans

0.66e0.75 mmol/L

0.66 mmol/L

1.06

1.00

Zhao et al. (2011)

R. gelatinosus CBS

0e1.0 mmol/L

0.15 mmol/L

0.87

1.00

Chang et al. (2002)

R. gelatinosus CBS

0e0.12 mmol/L

0.12 mmol/L

0.95

1.00

Maness et al. (2005)

Rice slurry

Anaerobic digester sludge

2.9e23.6 g-COD/L

5.9 g-COD/L

e

346

Fang et al. (2006)

Non-fat dry milk

Anaerobic digester sludge

0-96 g-COD/L

4.0 g-COD/L

e

0.005

Chen et al. (2006)

Food waste

Anaerobic digester sludge

0e32.3 g-COD/L

4.6 g-COD/L

e

101

Chen et al. (2006)

Anaerobic sludge

3.2e10.7 g-COD/L

6.4 g-COD/L

e

1.8

Shin et al. (2004)

CO

References

14 Waste to Renewable Biohydrogen

TABLE 1.2 Various substrates used for fermentation hydrogen production.dcont’d

Wheat straw

Mixed culture from cow dung

0e15 g/L

Corn stalk wastes

Mixed culture

5e15 g/L

Clostridium sp. X9

0.003

Fan et al. (2006b)

e

0.007

Zhang et al. (2007)

0e15 g/L

e

0.006

Zhang et al. (2007)

Mixed culture

e

e

0.005

Lee et al. (2008)

Mixed culture from cow dung

0e50 g/L

e

0.0003

Fan et al. (2006a)

15 g/L

20 g/L

Sustainable waste management: valorization Chapter | 1

Beer lees biomass

0.11

15

Substrate

Hydrogen production rate (mol/d)

SHPR (mol/ g-VSS.d)

X (gVSS/L)

Yield (molH2/molsubstrate)

Reactor

Inoculum

Growth pattern

Continuous stirred tank reactor

Sludge

Suspended

Glucose

0.04

e

e

1.98

Lin and Lay (2004)

Mixed microflora

Suspended

Sucrose

0.32

0.17

2.9

4.8

Lin and Lay (2004)

Rhodospirillum rubrum

Suspended

Syngas

0.90

0.41

2.2

0.89

Younesi et al. (2008)

Upflow anaerobic sludge blanket

Sewage sludge

Attachment

Sucrose

0.28

0.05

5.06

6.0

Chang and Lin (2004)

Sludge

Attachment

Solid waste and wastewater

0.30

0.15

2

1.98

AlzateGaviria et al. (2007)

Sequencing batch reactor

Seed sludge

Attachment

Sucrose

16.07

0.47

35.4

3.5

Wu et al. (2006)

Packed bed

Enterobacter aerogenes

Attachment

Glucose

0.25

0.09

3.02

3.02

Palazzi et al. (2000)

Fixed bed

Seed sludge

Attachment

Sucrose

1.32

0.10

15.8

e

Chang et al. (2002)

References

16 Waste to Renewable Biohydrogen

TABLE 1.3 Various reactors for fermentation of biohydrogen production.

Fluid bed

Attachment

Sucrose

15.09

0.46

35.4

2.67

Wu et al. (2003)

Mixed anaerobic cultures

Attachment

Cornstalk waste

2.36

0.10

21.5

0.007

Zhang et al. (2007)

Trickling biofilter reactor (TBR)

Seed sludge

Attachment

Glucose

1.05

0.76

0.72

1.1

Oh et al. (2004)

Anaerobic seed sludge

Attachment

Sucrose

1.92

0.05

24

2.0

Wu and Chang (2007)

Fermenter

Seed sludge

Attachment

Sucrose

e

0.23

1.8

2.1

Fang and Liu (2002)

Sustainable waste management: valorization Chapter | 1

Sewage sludge

17

18 Waste to Renewable Biohydrogen

an attached growth reactor is beneficial for the gathering and flocculation of microorganisms, improving microbial density and maximizing biomass. When the charging rate of a substrate is certain, the H2 production ability of the reactor will increase with an increase in the percent conversion of the fermentation substrate. There are two indexes for measuring the H2 production performance of different reactors: the H2 production ability and the H2 yield of the reactor. The H2 production ability of the reactor is affected by the metabolic characteristics of the bacterium itself, but also by the operating parameters and the microorganism’s holding volume.

1.5.4 Principle and classification of hydrogen fermentation During the process of anaerobic digestion, glucose form pyruvic acid by glycolysis. Adenosine triphosphate (ATP) and reduced nicotinamide adenine dinucleotide (NADH) are also compounded. Then, pyruvic acid is converted into acetyl-CoA, which can generate H2 and CO2, by C. butyricum and other anaerobic fermentation bacteria. Meanwhile, pyruvic acid can be converted to acetyl-CoA and formic acid, which can easily be transformed into H2 and CO2. Under different conditions, acetyl-CoA could be converted to acetic acid, butyric acid, and ethyl alcohol by different microorganisms. NADH is used to form butyric acid and acetic acid. The surplus is oxidized to NADþ and releases H2. In the process acetyl-CoA is converted into butyric acid and acetic acid, which offers energy for the microorganism’s activity, as ATP is produced. According to the different end fermentation product compositions, H2 fermentation usually can be divided into three types: (1) butyric acid-type H2 fermentation; (2) propionic acid-type H2 fermentation; and (3) ethyl alcoholtype H2 fermentation. (a) Butyric acid-type hydrogen fermentation According to much investigations, the fermentation of solublecarbohydrates (such as glucose, sucrose, lactose, and starch) centers on butyric acid-type H2 fermentation. During the fermentation process, the main end-products consist of butyric acid, acetic acid, H2, CO2, and a small quantity of propionic acid. Butyric acid-type H2 fermentation is carried out under the influence of Clostridium, such as C. butyricum and C. tyrobutyricum. The main reaction equations can be expressed as: C6 H12 O6 þ 2H2 /O2 CH3 COOH þ 2CO2 þ 4H2 C6 H12 O6 / CH3 CH2 CH2 COOH þ 2CO2 þ 2H2 In the process of butyric acid-type H2 fermentation, glucose is transformed into pyruvic acid by the glycolytic pathway (EmbdeneMeyerhofeParnas [EMP]). After decarboxylation, pyruvic acid forms a complex combined with ethoxy and thiamine pyrophosphatase. This complex transfers electron to ferredoxin, which is repeatedly oxidized by ferredoxin hydrogenase, generating molecular H2.

Sustainable waste management: valorization Chapter | 1

19

(b) Propionic acid-type hydrogen fermentation In the anaerobic treatment of sewage, the acid fermentation of nitrogenous organic compounds (such as yeast extract, gelatin, and meat extract) usually happens during propionic acid-type fermentation. During the process of anaerobic fermentation, carbohydrates that are difficult to degrade (such as cellulose) often have propionic acid-type fermentation, too. Propionic acid fermentation bacteria mainly have Propionibacterium. In addition, because Propionibacterium has no hydrogenase, no H2 is generated. In propionic acidtype fermentation, superfluous NADH þ Hþ, which is released in the acetic acid production process, is regenerated by combining the propionic acid production pathway. The molar yield ratio of propionic acid and acetic acid is 1, theoretically. Comparing propionic acid-type fermentation and butyric acid-type fermentation, the propionic acid production pathway is more beneficial to the oxidation of NADH þ Hþ and has stronger reducing power. Propionic acid-type fermentation has a low output of gas, even none, and its fermentation end-products are propionic acid and acetic acid. (c) Ethyl alcohol-type hydrogen fermentation Ethyl alcohol-type fermentation was discovered and named by Nanqi Ren. Classical ethyl alcohol-type fermentation is the process in which Saccharomyces make carbohydrates become pyruvic acid by EMP or the Entnere Doudoroff pathway, and pyruvic acid is transferred into acetaldehyde and finally ethyl alcohol. In this process, the fermentation products are only ethyl alcohol and CO2, without H2. By observing the biology in the acidogenic reactor, Ren et al. did not discover Saccharomyces and Zymomonas mobilis. During the experiment, a lot of H2 exists in the fermentation gas. Therefore, this type of fermentation is not a classical ethyl alcohol fermentation; it is called ethyl alcohol-type H2 fermentation. The main end-products are ethyl alcohol, acetic acid, H2, CO2, and a small quantity of butyric acid.

1.5.5 Research status of anaerobic fermentation biohydrogen Anaerobic fermentation biohydrogen technology focuses on optimizing technological parameters, investigating oligomers, and classifying H2-producing bacteria.

1.5.5.1 Biological characteristics of fermentation-producing acid microorganisms Different kinds of functional bacteria exist in the process of fermentationproducing acid. The composition of microorganisms determines the biogas

20 Waste to Renewable Biohydrogen

FIGURE 1.3 Microbial types of different substrates.

effects and operating efficiency of the system. Microorganisms consist of 18 genera (more than 50 species), including Alcaligenes, Bacteroides, Aerobacter, Bacillus, Clostridium, Escherichia, Klebsiella, Leptospira, Pediococcus, aberrant coliform bacilli, Neisseria, Proteus, Pseudomonas, Sarcina, Rhodopseudomonas, and Streptococcus. The number of obligate anaerobic acidproducing fermentation bacteria could reach 108e1012 per milliliter. Different substrates are used to degrade different microbial (Fig. 1.3).

1.5.5.2 Methods of fermentation-producing acid microorganisms In the process of using organic matter, different oxidation and reduction processes are used because of the differences among species. Hence, different metabolites are generated by different methods of fermentation. The formation of metabolites is mainly affected by the production process and REDOX coupling process of NADH/NADþ. According to the difference in metabolites, some fermentation methods of microorganisms are listed in Table 1.4. The process of fermentation-producing acid microorganisms is carried out under anaerobic conditions, and organic matter is taken as the donors and acceptors of electrons. Unlike the electron transport chain using oxygen and nitrate as electron accepters in the aerobic process, fermentation-producing acid microorganisms can transmit electrons and generate energy only by substrate-level phosphorylation. In this process, microorganisms need to grow and thrive under appropriate conditions, and the balance of oxidation and reduction processes needs to be kept.

Sustainable waste management: valorization Chapter | 1

21

TABLE 1.4 Main classic types of carbohydrate fermentation. Types

Metabolites

Typical microorganisms

Butyric acid fermentation

H2, CO2

Clostridium, C. butyricum

Propionic acid fermentation

Propionic acid, acetic acid, CO2

Butyrivibrio, Propionibacterium

Mixed acid fermentation

Lactic acid, acetic acid, formic acid, ethyl alcohol, CO2, H2

Veillonella, Escherichia, Proteus, Shigella

Lactic acid fermentation (homotype)

Lactic acid

Salmonella, Lactobacillus

Lactic acid fermentation (heterotype)

Lactic acid, ethyl alcohol, CO2

Streptococcus, Leuconostoc, Mesenteroides

Ethyl alcohol fermentation

Ethyl alcohol, CO2

Leuconostoc dextranicum, saccharomyces

Substrate-level phosphorylation refers to the action in which the formation of ATP is directly transferred from the phosphate group on metabolic intermediates (high-energy compound) to adenosine diphosphate (ADP). Generally, 1 mol ADP needs 31.8 kJ/mol to generate 1 mol ATP. Thus, the Gibbs free energy of a high-energy compound should be greater than 31.8 kJ/mol. Naturally, acetic acid could ferment and couple with other acids owing to its higher energy. The approach to metabolizing the complex carbohydrates of microorganisms is shown in Fig. 1.4. Complex carbohydrates are first transferred into glucose. Under anaerobic conditions, glucose generate pyruvic acid by EMP. Pyruvic acid is transformed into acetic acid, propionic acid, ethyl alcohol, lactic acid, and other products by hydrolytic fermentation again.

1.5.5.3 Investigation of anaerobic hydrogen substrates A significant factor influencing the results of anaerobic fermentation is the choice of appropriate materials as resources of organic compound oligomers generating H2, which is especially important on an industrial H2 production scale. The main standards for choosing waste consist of availability, cost, total carbohydrates, and biodegradability. The best carbon sources of microbial metabolic transformation are monosaccharides (glucose) and disaccharides (such as lactose or saccharose). The HPR is exhibited in Table 1.5.

22 Waste to Renewable Biohydrogen

FIGURE 1.4 Schematic diagram of complex carbohydrate fermentation pathway.

TABLE 1.5 Hydrogen production rate from pure carbohydrates by continuous fermentations.

Inoculum

Carbon source

Hydrogen production rate

Reactor

Hydraulic retention time (HRT) (h)

Clostridium acetobutylicum (Chin et al., 2003)

Glucose

2 mol/mol glucose

In batches

e

Mixed culture (Oh et al., 2004)

Glucose (13.7 g/L)

1.2 mol/mol glucose

Drip biofiltration

4e12

Mixed culture (Chen et al., 2001)

Sucrose (20 g COD/L)

3.47 mol/ mol sucrose

CSTR

8

Clostridium butyricum þ Enterobacter aerogenes (Yokoi et al., 1998)

Starch (2%)

2.5 mol/mol glucose

CSTR

2

Mixed culture (Hussy et al., 2003)

Wheat starch (10 g/L)

0.83 mol/ mol starch d

CSTR

12

CSTR, continuous stirred tank reactor.

Sustainable waste management: valorization Chapter | 1

23

According to this research, there is a wonderful effect in which a single carbon source produces H2. Considering the cost of biohydrogen systems, the cost of using a single substrate to producing H2 is high, which is not appropriate for use in a large-scale industrial application. An increasing number of investigators have used industrial organic waste and wastewater rich in organic matter as substrates of anaerobic fermentation to produce H2, such as olive oil plant wastewater (Ntaikou et al., 2009a) and dairy products (Kargi et al., 2012). These kinds of wastewater and waste have the advantages of wide sources and also low cost. During the process of waste material resource treatment, they can generate H2 and decrease the cost of H2 production. Investigations into H2 production focusing on wastewater and waste are listed in Table 1.6.

TABLE 1.6 Experiments in hydrogen production from wastewater and waste.

Temperature ( C)

Maximum hydrogen production rate

Reactor

Substrates

OLR

Membrane bioreactor (MBR) (Kim et al., 2011)

Tofu processing waste

129 g substrates/ L/d

60

1.87 mol H2/ mol hexose added

Fluidized bed reactor (FBR) (activated carbon carrier) (Wu et al., 2012)

Saccharose

48 g substrates/ L/d

40

3.76 mol H2/ mol sucrose added

Batch (Ghimire et al., 2015)

Potato and pumpkin waste

e

35

135.3 cm3 H2/VS

Upflow anaerobic sludge blanket (Vijayaraghavan and Ahmad, 2006)

Palm oil wastewater

59 g COD/dm3

35

73 dm3/d

Batch (Chu et al., 2013)

Beer wastewater

60 g COD/dm3

e

2 mol H2/ mol hexose

Packed bed reactor (Close and Hafez, 2010)

Rice distillery wastewater

e

55

272 L H2/kg COD

Sequencing batch reactor (Venkata Mohan et al., 2007)

Dairy wastewater

4.7 kg COD/m3d

28

0.156 m3 H2/kg COD

24 Waste to Renewable Biohydrogen

1.6 Environment and economy efficiency assessment for biohydrogen Biohydrogen technology is an environmentally friendly, promising method for producing renewable energy, whose large-scale applications could provide more economic, environmental, and social benefit. The industrialization of biohydrogen is one of the most important targets of researchers. How to evaluate biohydrogen technology from the aspects of the environment and the economy are the general concerns of researchers (Brattebø, 2005).

1.6.1 Assessment of environmental efficiency Generally, there are two methods for evaluating environmental efficiency: (a) Life cycle assessment (LCA) (Yang et al., 2020) An LCA focuses on the whole life cycle of a special product, including the extraction and processing of raw materials, and their production, transportation, use, and ultimate disposal. It evaluates the impact of resource and energy consumption on the environment, including waste discharge. It quantifies the impact and gains on environmental efficiency to produce the product. However, the energy analysis of ecosystem usually does not include solar energy and other natural resource energy inputs. The result cannot reflect the great effect and contribution to nature. (b) Data envelopment analysis (DEA) (Huppes and Ishikawa, 2005) DEA can be divided into four methods: reciprocal conversion, linear transformation of an undesirable output, hyperbolic output efficiency measure, and directional distance function. However, these four methods still belong to the measurement of the radial and output angles of DEA. Some researchers have also pointed out that the efficiency value measured by the DEA model is inexact or has deviations (Marchettini et al., 2003). When dealing with an undesirable output, the direction distance function will measure its form as radial and output angles, without thinking about relaxed problems of undesirable output. Hence, the reliability of the computational result is low. Meanwhile, different types of environmental efficiency cannot be added directly, like economic indicators. Thus, different environmental efficiencies should be assigned corresponding weight before integration. However, no consensus has been reached regarding the weighting method. Scheel (2001) disscussed kinds of approaches to deal with undesirable outputs in the framework of DEA and compared the resulting efficient frontiers. Nieuwlaar (2013) divided a pollution-type weighting method into three types: expert scoring, willingness to pay survey, and policy objective. The BASF model improved the common weighting method, dividing weight into societal weighting and scientific weighting factors. Societal weighting factors are

Sustainable waste management: valorization Chapter | 1

25

graded by experts and scientific weighting factors are computed by the ratio of enterprise emissions and industry corresponding pollutants mean level. Thereafter, various environmental impact weights are gained by multiplying these two factors.

1.6.2 Assessment of economic efficiency The economic efficiency in traditional economics refers to Pareto optimality, which means the minimum input with output being constant and the maximum useful output with input being constant. Appropriate economic indicators could represent the economic value of crafts, products, and services. World business council for sustainable development (WBCSD) takes the net sales and quantity product or service produced or sold as general economic indexes, while taking the value added as an alternative indicator. Eik (2002) developed and perfected an index system fitting waste recycling. United nations conference on trade and development (UNCTAD) (Integrating, 2003) thought the value added should be treated as the leading indicator because it is the only index that is controllable by the enterprise. All of these indicators are financial indicators with high availability. However, when facing a specific process system, factors to consider are much more complex. Two methods compute the economic value of products or services: costebenefit analysis (CBA) and life cycle costing (LCC). LCC can compute market-related costs and benefits in the whole life cycle, whereas CBA includes environmental external economic costs, besides market-related costs and benefits. However, the quantization method of environmental external economic costs is still immature. As we know, all of the wealth created by humans and nature has value. Natural resources, products, labor services, science, and technology information need suitable units to measure their own real value and evaluate their contributions. But energy cannot be used to measure the value of nature and economy. The constitutive relations of humans, natural, the environment, and the economy cannot be expressed. Thus, it is hard to analyze the ecological economic system.

1.7 Conclusion As the city expands and the quality of life improves, an increasing amount of waste is hauled away to the corners of the city. It not only affects the townscape, it also pollutes the environment, with adverse impacts on humans. In this chapter, different kinds of waste and their impacts on people’s lives were introduced, especially its harm to cities and humans. Considering the resources for recycling, the conversion technology of waste energy was introduced in Section 1.2. As mentioned, waste burning generating electricity technology and marsh gas power generation are two main methods for reusing waste, which usually can meet one-fifth of the demands for primary energy across the world.

26 Waste to Renewable Biohydrogen

As for the whole waste, biomass takes up a large proportion, for which recycling has a significant role in protecting the environment and saving energy. Generally, biomass will be used to produce H2, because H2 is a clear and efficient resource. In Section 1.4, biomass energy was introduced, including its concepts, sources, and applications. In particular, in Section 1.5, biohydrogen, which could be one of the most important ways to use biomass, was introduced in detail. H2 production organisms, the process of organic biodegradation, H2 fermentation, and reactors were illustrated. In the end, there are two methods for evaluating efficiency according to the environmental and economic aspects explained in Section 1.6, which provided some ideas for measuring the economic and environmental efficiency of biohydrogen technologies.

References Abd Kadir, S.A.S., Yin, C., Rosli Sulaiman, M., Chen, X., El-Harbawi, M., 2013. Incineration of municipal solid waste in Malaysia: salient issues, policies and waste-to-energy initiatives. Renew. Sustain. Energy Rev. 24, 181e186. Al-Alawi, M., 2007. In: Sheffield, J.W., Sheffield, C ¸ . (Eds.), Biohydrogen Production by Anaerobic Biological Fermentation of Agriculture Waste. Springer Netherlands, Dordrecht, pp. 177e185. Al-Qaydi, S., 2006. Industrial solid waste disposal in Dubai, UAE: a study in economic geography. Cities 23, 140e148. Alzate-Gaviria, L.M., Sebastian, P.J., Pe´rez-Herna´ndez, A., Eapen, D., 2007. Comparison of two anaerobic systems for hydrogen production from the organic fraction of municipal solid waste and synthetic wastewater. Int. J. Hydrog. Energy 32, 3141e3146. Arun, C., Sivashanmugam, P., 2015. Identification and optimization of parameters for the semicontinuous production of garbage enzyme from pre-consumer organic waste by green RPHPLC method. Waste Manag. 44, 28e33. Bacenetti, J., Negri, M., Fiala, M., Gonza´lez-Garcı´a, S., 2013. Anaerobic digestion of different feedstocks: impact on energetic and environmental balances of biogas process. Sci. Total Environ. 463e464, 541e551. Balat, H., Kırtay, E., 2010. Hydrogen from biomass e present scenario and future prospects. Int. J. Hydrog. Energy 35, 7416e7426. Bojesen, M., Boerboom, L., Skov-Petersen, H., 2015. Towards a sustainable capacity expansion of the Danish biogas sector. Land Use Pol. 42, 264e277. Brattebø, H., 2005. Toward a methods framework for eco-efficiency analysis? J. Ind. Ecol. 9, 9e11. Brown, D.P., 2015. Garbage: how population, landmass, and development interact with culture in the production of waste, Resources. Conserv. Recycl. 98, 41e54. Chang, F., Lin, C., 2004. Biohydrogen production using an up-flow anaerobic sludge blanket reactor. Int. J. Hydrog. Energy 29, 33e39. Chang, J., Lee, K., Lin, P., 2002. Biohydrogen production with fixed-bed bioreactors. Int. J. Hydrog. Energy 27, 1167e1174. Chen, D., Christensen, T., 2010. Life-cycle assessment (EASEWASTE) of two municipal solid waste incineration technologies in China. Waste Manag. Res. 28, 508e519.

Sustainable waste management: valorization Chapter | 1

27

Chen, C., Liu, T., 2013. Fill the gap: developing management strategies to control garbage pollution from fishing vessels. Mar. Policy 40, 34e40. Chen, C., Lin, C., Chang, J., 2001. Kinetics of hydrogen production with continuous anaerobic cultures utilizing sucrose as the limiting substrate. Appl. Microbiol. Biotechnol. 57, 56e64. Chen, W., Chen, S., Kumar Khanal, S., Sung, S., 2006. Kinetic study of biological hydrogen production by anaerobic fermentation. Int. J. Hydrog. Energy 31, 2170e2178. Chin, H., Chen, Z., Chou, C., 2003. Fedbatch operation using Clostridium acetobutylicum suspension culture as biocatalyst for enhancing hydrogen production. Biotechnol. Prog. 19, 383e388. Chu, C., Tung, L., Lin, C., 2013. Effect of substrate concentration and pH on biohydrogen production kinetics from food industry wastewater by mixed culture. Int. J. Hydrog. Energy 38, 15849e15855. Close, G.N.H.E., Hafez, H., 2010. Waste-to-energy using a novel integrated biological process. In: Fourteenth International Water Technology Conference. IWTC 14, Cairo, Egypt. Cucchiella, F., D Adamo, I., Gastaldi, M., 2017. Sustainable waste management: waste to energy plant as an alternative to landfill. Energy Convers. Manag. 131, 18e31. Damgaard, A., Riber, C., Fruergaard, T., Hulgaard, T., Christensen, T.H., 2010. Life-cycleassessment of the historical development of air pollution control and energy recovery in waste incineration. Waste Manag. 30, 1244e1250. Do, Y.S., Smeenk, J., Broer, K.M., Kisting, C.J., Brown, R., Heindel, T.J., Bobik, T.A., DiSpirito, A.A., 2007. Growth of Rhodospirillum rubrum on synthesis gas: conversion of CO to H2 and poly-b-hydroxyalkanoate. Biotechnol. Bioeng. 97, 279e286. Eik, H.N.A., 2002. Microbial Biotechnology: Fundamentals of Applied Microbiology, New York and Basingstoke Copyright. EUROBSERV-ER, 2014. Fan, Y., Zhang, G., Guo, X., Xing, Y., Fan, M., 2006a. Biohydrogen-production from beer lees biomass by cow dung compost. Biomass Bioenergy 30, 493e496. Fan, Y., Zhang, Y., Zhang, S., Hou, H., Ren, B., 2006b. Efficient conversion of wheat straw wastes into biohydrogen gas by cow dung compost. Bioresour. Technol. 97, 500e505. Fan, Y., Xing, Y., Ma, H., Pan, C., Hou, H., 2008. Enhanced cellulose-hydrogen production from corn stalk by lesser panda manure. Int. J. Hydrog. Energy 33, 6058e6065. Fang, H.H.P., Liu, H., 2002. Effect of pH on hydrogen production from glucose by a mixed culture. Bioresour. Technol. 82, 87e93. Fang, H.H.P., Li, C., Zhang, T., 2006. Acidophilic biohydrogen production from rice slurry. Int. J. Hydrog. Energy 31, 683e692. Zeikus, J., 1979. Microbial Populations in Digesters, Anaerobic Digestion. Applied Science Publisher, pp. 66e89. Geert Bergsma, B.K.B.S., 2010. BUBE: Better Use of Biomass for Energy Background Report to the Position Paper of IEA REDT and IEA Bioenergy. IEA RETD IEA Bioenergy. Ghimire, A., Frunzo, L., Pontoni, L., D’Antonio, G., Lens, P.N.L., Esposito, G., Pirozzi, F., 2015. Dark fermentation of complex waste biomass for biohydrogen production by pretreated thermophilic anaerobic digestate. J. Environ. Manag. 152, 43e48. Hallenbeck, P.C., Ghosh, D., 2009. Advances in fermentative biohydrogen production: the way forward? Trends Biotechnol. 27, 287e297. Han, Z., Liu, Y., Zhong, M., Shi, G., Li, Q., Zeng, D., Zhang, Y., Fei, Y., Xie, Y., 2018. Influencing factors of domestic waste characteristics in rural areas of developing countries. Waste Manag. 72, 45e54.

28 Waste to Renewable Biohydrogen Henstra, A., 2006. CO Metabolism of Carboxydothermus Hydrogenoformans and Archaeoglobus Fulgidus. Hepbasli, A., 2008. A key review on exergetic analysis and assessment of renewable energy resources for a sustainable future. Renew. Sustain. Energy Rev. 12, 593e661. Horsman, P.V., 1982. The amount of garbage pollution from merchant ships. Mar. Pollut. Bull. 13, 167e169. Hu, Y., Cheng, H., 2013. Water pollution during China’s industrial transition. Environ. Dev. 8, 57e73. Huppes, G., Ishikawa, M., 2005. Eco-efficiency and its xsTerminology. J. Ind. Ecol. 9, 43e46. Hussy, I., Hawkes, F.R., Dinsdale, R., Hawkes, D.L., 2003. Continuous fermentative hydrogen production from a wheat starch co-product by mixed microflora. Biotechnol. Bioeng. 84, 619e626. Hussy, I., Hawkes, F.R., Dinsdale, R., Hawkes, D.L., 2005. Continuous fermentative hydrogen production from sucrose and sugarbeet. Int. J. Hydrog. Energy 30, 471e483. Integrating Environmental and Financial Performance at the Enterprise Level: A Methodology for Standardizing Eco-Efficiency Indicators, 2003. United Nations Publication. Jebaraj, S., Iniyan, S., 2006. A review of energy models. Renew. Sustain. Energy Rev. 10, 281e311. Kargi, F., Eren, N.S., Ozmihci, S., 2012. Hydrogen gas production from cheese whey powder (CWP) solution by thermophilic dark fermentation. Int. J. Hydrog. Energy 37, 2260e2266. Kim, M., Lee, D., Kim, D., 2011. Continuous hydrogen production from tofu processing waste using anaerobic mixed microflora under thermophilic conditions. Int. J. Hydrog. Energy 36, 8712e8718. Kobayashi, T., 2010. Applications and New Developments of Biogas Technology in Japan, pp. 35e58. Kumar, N., Das, D., 2000. Enhancement of hydrogen production by Enterobacter cloacae IIT-BT 08. Process Biochem. 35, 589e593. Kumar, N., Das, D., 2001. Continuous hydrogen production by immobilized Enterobacter cloacae IIT-BT 08 using lignocellulosic materials as solid matrices. Enzyme Microb. Technol. 29, 280e287. Kumaran, P., Hephzibah, D., Sivasankari, R., Saifuddin, N., Shamsuddin, A.H., 2016. A review on industrial scale anaerobic digestion systems deployment in Malaysia: opportunities and challenges. Renew. Sustain. Energy Rev. 56, 929e940. Lausselet, C., Cherubini, F., Del Alamo Serrano, G., Becidan, M., Strømman, A.H., 2016. Lifecycle assessment of a Waste-to-Energy plant in central Norway: current situation and effects of changes in waste fraction composition. Waste Manag. 58, 191e201. Lee, K., Hsu, Y., Lo, Y., Lin, P., Lin, C., Chang, J., 2008. Exploring optimal environmental factors for fermentative hydrogen production from starch using mixed anaerobic microflora. Int. J. Hydrog. Energy 33, 1565e1572. Leonzio, G., 2016. Upgrading of biogas to bio-methane with chemical absorption process: simulation and environmental impact. J. Clean. Prod. 131, 364e375. Levin, D.B., Chahine, R., 2010. Challenges for renewable hydrogen production from biomass. Int. J. Hydrog. Energy 35, 4962e4969. Li, X., Zhang, C., Li, Y., Zhi, Q., 2016. The status of municipal solid waste incineration (MSWI) in China and its clean development. Energy Proced. 104, 498e503. Lin, C., Cheng, C., 2006. Fermentative hydrogen production from xylose using anaerobic mixed microflora. Int. J. Hydrog. Energy 31, 832e840.

Sustainable waste management: valorization Chapter | 1

29

Lin, C.Y., Lay, C.H., 2004. Carbon/nitrogen-ratio effect on fermentative hydrogen production by mixed microflora. Int. J. Hydrog. Energy 29, 41e45. Lin, C., Chang, C., Hung, C., 2008. Fermentative hydrogen production from starch using natural mixed cultures. Int. J. Hydrog. Energy 33, 2445e2453. Lo, Y., Chen, W., Hung, C., Chen, S., Chang, J., 2008. Dark H2 fermentation from sucrose and xylose using H2-producing indigenous bacteria: feasibility and kinetic studies. Water Res. 42, 827e842. Maness, P., Huang, J., Smolinski, S., Tek, V., Vanzin, G., 2005. Energy generation from the CO oxidation-hydrogen production pathway in Rubrivivax gelatinosus. Appl. Environ. Microbiol. 71, 2870e2874. Marchettini, N., Panzieri, M., Niccolucci, V., Bastianoni, S., Borsa, S., 2003. Sustainability indicators for environmental performance and sustainability assessment of the productions of four fine Italian wines. Int. J. Sustain. Dev. World Ecol. 10, 275e282. Mcdonald, K., 2012. 11 - Air Pollution in the Urban Atmosphere: Sources and Consequences, Metropolitan Sustainability. Woodhead Publishing, pp. 231e259. Mian, M.M., Zeng, X., Bin Nasry, A.A.N., Al-Hamadani, S., 2016. Municipal solid waste management in China: a comparative analysis. J. Mater. Cycles Waste 19. Milbrandt, A., Seiple, T., Heimiller, D., Skaggs, R., Coleman, A., 2018. Wet waste-to-energy resources in the United States, Resources. Conserv. Recycl. 137, 32e47. Monni, S., 2012. From landfilling to waste incineration: implications on GHG emissions of different actors. Int. J. Greenh. Gas Con. 8, 82e89. Nahman, A., de Lange, W., Oelofse, S., Godfrey, L., 2012. The costs of household food waste in South Africa. Waste Manag. 32, 2147e2153. Nakata, T., 2004. Energy-economic models and the environment. Prog. Energy Combust. Sci. 30, 417e475. Ntaikou, I., Kourmentza, C., Koutrouli, E.C., Stamatelatou, K., Zampraka, A., Kornaros, M., Lyberatos, G., 2009a. Exploitation of olive oil mill wastewater for combined biohydrogen and biopolymers production. Bioresour. Technol. 100, 3724e3730. Nieuwlaar, E., 2013. Life cycle assessment and energy systems. In: Reference Module in Earth Systems and Environmental Sciences. https://doi.org/10.1016/B978-0-12-409548-9.01334-8. Ntaikou, I., Gavala, H.N., Lyberatos, G., 2009b. Modeling of fermentative hydrogen production from the bacterium Ruminococcus albus: definition of metabolism and kinetics during growth on glucose. Int. J. Hydrog. Energy 34, 3697e3709. Ntaikou, I., Gavala, H.N., Lyberatos, G., 2010. Application of a modified Anaerobic Digestion Model 1 version for fermentative hydrogen production from sweet sorghum extract by Ruminococcus albus. Int. J. Hydrog. Energy 35, 3423e3432. Oh, Y., Kim, S.H., Kim, M., Park, S., 2004. Thermophilic biohydrogen production from glucose with trickling biofilter. Biotechnol. Bioeng. 88, 690e698. O-Thong, S., Prasertsan, P., Karakashev, D., Angelidaki, I., 2008. Thermophilic fermentative hydrogen production by the newly isolated Thermoanaerobacterium thermosaccharolyticum PSU-2. Int. J. Hydrog. Energy 33, 1204e1214. Padkho, N., 2012. A new design recycle agricultural waste materials for profitable use rice straw and maize husk in wall. Proced. Eng. 32, 1113e1118. Palazzi, E., Fabiano, B., Perego, P., 2000. Process development of continuous hydrogen production by Enterobacter aerogenes in a packed column reactor. Bioprocess Eng. 22, 205e213. Pan, C., Zhang, M., Fan, Y., Xing, Y., Hou, H., 2009. Production of cellulosic ethanol and hydrogen from solid-state enzymatic treated cornstalk: a two-stage process. J. Agric. Food Chem. 57, 2732e2738.

30 Waste to Renewable Biohydrogen Pandey, A., Soccol, C.R., Rodriguez-Leon, J.A., Singh Nee Nigam, P., 2001. Solid State Fermentation in Biotechnology: Fundamentals and Applications. Percival Zhang, Y.H., Himmel, M.E., Mielenz, J.R., 2006. Outlook for cellulase improvement: screening and selection strategies. Biotechnol. Adv. 24, 452e481. Qishlaqi, A., Moore, F., Forghani, G., 2009. Characterization of metal pollution in soils under two landuse patterns in the Angouran region, NW Iran; a study based on multivariate data analysis. J. Hazard Mater. 172, 374e384. Ramanathan, V., Feng, Y., 2009. Air pollution, greenhouse gases and climate change: global and regional perspectives. Atmos. Environ. 43, 37e50. Raupp-Pereira, F., Hotza, D., Segada˜es, A.M., Labrincha, J.A., 2006. Ceramic formulations prepared with industrial wastes and natural sub-products. Ceram. Int. 32, 173e179. Reddy, N., Yang, Y., 2005. Biofibers from agricultural byproducts for industrial applications. Trends Biotechnol. 23, 22e27. Regadı´o, M., Ruiz, A.I., de Soto, I.S., Rodriguez Rastrero, M., Sa´nchez, N., Gismera, M.J., Sevilla, M.T., Da Silva, P., Rodrı´guez Procopio, J., Cuevas, J., 2012. Pollution profiles and physicochemical parameters in old uncontrolled landfills. Waste Manag. 32, 482e497. Santos, I.R., Friedrich, A.C., Barretto, F.P., 2005. Overseas garbage pollution on beaches of northeast Brazil. Mar. Pollut. Bull. 50, 783e786. Sarkar, N., Ghosh, S.K., Bannerjee, S., Aikat, K., 2012. Bioethanol production from agricultural wastes: an overview. Renew. Energy 37, 19e27. Scheel, H., 2001. Undesirable outputs in efficiency valuations. Eur. J. Oper. Res. 132, 400e410. Shen, Y., Linville, J.L., Urgun-Demirtas, M., Mintz, M.M., Snyder, S.W., 2015. An overview of biogas production and utilization at full-scale wastewater treatment plants (WWTPs) in the United States: challenges and opportunities towards energy-neutral WWTPs. Renew. Sustain. Energy Rev. 50, 346e362. Shin, H., Youn, J., Kim, S., 2004. Hydrogen production from food waste in anaerobic mesophilic and thermophilic acidogenesis. Int. J. Hydrog. Energy 29, 1355e1363. Song, X., Luo, W., Hai, F.I., Price, W.E., Guo, W., Ngo, H.H., Nghiem, L.D., 2018. Resource recovery from wastewater by anaerobic membrane bioreactors: opportunities and challenges. Bioresour. Technol. 270, 669e677. Stenis, J., 2004. Environmental optimization in fractionating industrial wastes using cost-benefit analysis. Resour. Conserv. Recycl. 41, 147e164. The Effect of Substrate Concentration on Biohydrogen Production by Using Kinetic Models, Science in China(Series B:Chemistry), 2008. Venkata Mohan, S., Lalit Babu, V., Sarma, P.N., 2007. Anaerobic biohydrogen production from dairy wastewater treatment in sequencing batch reactor (AnSBR): effect of organic loading rate. Enzyme Microb. Technol. 41, 506e515. Venkatesh, G., Elmi, R.A., 2013. Economiceenvironmental analysis of handling biogas from sewage sludge digesters in WWTPs (wastewater treatment plants) for energy recovery: case study of Bekkelaget WWTP in Oslo (Norway). Energy 58, 220e235. Vijayaraghavan, K., Ahmad, D., 2006. Biohydrogen generation from palm oil mill effluent using anaerobic contact filter. Int. J. Hydrog. Energy 31, 1284e1291. Warunasinghe, W.A.A.I., Yapa, P.I., 2016. A survey on household solid waste management (SWM) with special reference to a Peri-urban area (Kottawa) in Colombo. Proced. Food Sci. 6, 257e260. Waste brine may harm marine life. New. Sci. 241, 2019, 4. Weiland, P., 2010. Biogas production: current state and perspectives. Appl. Microbiol. Biotechnol. 85, 849e860.

Sustainable waste management: valorization Chapter | 1

31

White, A.J., Kirk, D.W., Graydon, J.W., 2011. Analysis of small-scale biogas utilization systems on Ontario cattle farms. Renew. Energy 36, 1019e1025. Wolfrum, E.J., Watt, A.S., 2002. Bioreactor design studies for a hydrogen-producing bacterium. Appl. Biochem. Biotechol. 98, 611e625. Wu, K., Chang, J., 2007. Batch and continuous fermentative production of hydrogen with anaerobic sludge entrapped in a composite polymeric matrix. Process Biochem. 42, 279e284. Wu, S., Lin, C., Chang, J., 2003. Hydrogen production with immobilized sewage sludge in threephase fluidized-bed bioreactors. Biotechnol. Prog. 19, 828e832. Wu, S., Hung, C., Lin, C., Chen, H., Lee, A., Chang, J., 2006. Fermentative hydrogen production and bacterial community structure in high-rate anaerobic bioreactors containing siliconeimmobilized and self-flocculated sludge. Biotechnol. Bioeng. 93, 934e946. Wu, S., Chu, C., Shen, Y., 2012. Effect of calcium ions on biohydrogen production performance in a fluidized bed bioreactor with activated carbon-immobilized cells. Int. J. Hydrog. Energy 37, 15496e15502. Yang, S., Ma, K., Liu, Z., Ren, J., Man, Y., 2020. Chapter 5 - Development and Applicability of Life Cycle Impact Assessment Methodologies, Life Cycle Sustainability Assessment for Decision-Making. Elsevier, pp. 95e124. Yanxun, S., Yani, W., Hui, Q., Yuan, F., 2011. Analysis of the groundwater and soil pollution by oil leakage. Proced. Environ. Sci. 11, 939e944. 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, 143e147. Younesi, H., Najafpour, G., Ku Ismail, K.S., Mohamed, A.R., Kamaruddin, A.H., 2008. Biohydrogen production in a continuous stirred tank bioreactor from synthesis gas by anaerobic photosynthetic bacterium: Rhodopirillum rubrum. Bioresour. Technol. 99, 2612e2619. Zhang, M., Fan, Y., Xing, Y., Pan, C., Zhang, G., Lay, J., 2007. Enhanced biohydrogen production from cornstalk wastes with acidification pretreatment by mixed anaerobic cultures. Biomass Bioenergy 31, 250e254. Zhang, Z., Tay, J., Show, K., Yan, R., Tee Liang, D., Lee, D., Jiang, W., 2007. Biohydrogen production in a granular activated carbon anaerobic fluidized bed reactor. Int. J. Hydrog. Energy 32, 185e191. Zhao, Y., Cimpoia, R., Liu, Z., Guiot, S.R., 2011a. Kinetics of CO conversion into H2 by Carboxydothermus hydrogenoformans. Appl. Microbiol. Biotechnol. 91, 1677. Zhao, Y., Cimpoia, R., Liu, Z., Guiot, S.R., 2011b. Orthogonal optimization of Carboxydothermus hydrogenoformans culture medium for hydrogen production from carbon monoxide by biological water-gas shift reaction. Int. J. Hydrog. Energy 36, 10655e10665. Zhao, Y., Christensen, T.H., Lu, W., Wu, H., Wang, H., 2011c. Environmental impact assessment of solid waste management in Beijing City, China. Waste Manag. 31, 793e799. Zhuang, Y., Wu, S., Wang, Y., Wu, W., Chen, Y., 2008. Source separation of household waste: a case study in China. Waste Manag. 28, 2022e2030.

Chapter 2

Waste to biohydrogen: potential and feasibility Youzhou Jiao1, 2, 3 1 Key Laboratory of New Materials and Facilities for Rural Renewable Energy of Ministry of Agriculture and Rural Affairs, College of Mechanical & Electrical engineering, Henan Agricultural University, Zhengzhou, China; 2Henan International Joint Laboratory of Biomass Energy and Nanomaterials, Henan Agricultural University, Zhengzhou, China; 3Collaborative Innovation Center of Biomass Energy, Zhengzhou, Henan Province, China

2.1 Introduction Natural environmental pollution and the energy crisis are two important problems affecting sustainable development. The world’s energy demand is growing exponentially, fossil fuel reserves are dwindling, and the use of fossil fuels has had serious negative impacts on the environment and caused climate change and global warming. Hydrogen is 2.75 times higher than hydrocarbon fuel owing to its high calorific value and an energy value of 122 kJ/g (Kapdan and Kargi, 2006). Converting waste into hydrogen not only saves on fossil fuels, but also reduces the emission of carbon dioxide. More importantly, it can reduce the accumulation of waste and promote environmental improvement. It is considered one of the most promising alternatives to substitute fossil fuels. It has been reported that 50 million tons of hydrogen are traded globally each year with an increase rate of nearly 10% (Winter, 2005). Most commercial hydrogen comes from fossil fuels (natural gas, heavy oil and coal, etc.). The hydrogen production from fossil fuels is mainly through steam conversion, partial oxidation, cracking, and PSA (Pressure Swing Adsorption) recovery (Winter, 2005; Kapdan and Kargi, 2006). However, these technologies are energy-intensive that can be performed only at high temperatures. The method of biological hydrogen production has the advantages of mild reaction conditions, a wide range of raw materials, less consumption, and no pollution. It is considered a viable alternative to hydrogen production. Many researchers have been working on this approach. Biological hydrogen production technology meets the requirements of sustainable development and also can reuse the various types of waste, so it has been widely developed in recent years. Biological hydrogen production Waste to Renewable Biohydrogen. https://doi.org/10.1016/B978-0-12-821659-0.00006-X Copyright © 2021 Elsevier Inc. All rights reserved.

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34 Waste to Renewable Biohydrogen

technology can utilize all kinds of biomass which rich in carbohydrates to achieve biological hydrogen production through anaerobic and photosynthetic microorganisms. Biomass is an important renewable raw material that is rich in resources and the fourth largest energy type in the world (Luo et al., 2016). The main criteria of selecting waste materials to obtain biological hydrogen production are availability, cost, carbohydrate content, and biodegradability. Many types of agricultural and food industry waste contain starch and cellulose. Starch can be hydrolyzed by acid or enzyme, which converts carbohydrates into organic acids and then into hydrogen. Cellulose generally needs to be pretreated for biological hydrogen production. Some dairy industry and olive mill by-products, baker’s yeast, and brewery wastewater contain biodegradable carbohydrates and nontoxic industrial wastewater, which can be used as a raw material to produce biohydrogen. The wastewater may need to be pretreated to remove undesirable ingredients and obtain the nutrient balance for biological hydrogen production. Carbohydrate-rich wastewater from the food industry may be further treated to convert the carbohydrate into organic acids, which are then converted to hydrogen by appropriate biological processes. Waste residue from wastewater treatment plants contains large amounts of carbohydrates and proteins that can be used for energy production, such as methane or hydrogen. Anaerobic digestion of surplus sludge can be achieved in two steps. In the first step (acid production stage), organic matter is converted to organic acids, which is used in the second step to produce hydrogen. The waste is abundant, inexpensive, renewable, and highly biodegradable. The production of hydrogen from various renewable sources is also known as green technology. Biological hydrogen production technology can convert energy stored in these types of waste into hydrogen through the digestion of photosynthetic bacteria and dark fermentation bacteria (Hua et al., 2018; Guo, 2010). The combination of clean energy production and the use of waste materials makes the biohydrogen to be a novel and promising alternative of fossil fuels for meeting the growing needs of energy. Using this technology to turn all kinds of waste into hydrogen also has great advantages in environmental protection and sustainable energy development. There have been many studies on hydrogen production technology of agricultural production waste, industrial waste and municipal organic waste.This chapter discusses the properties of these wastes and their feasibility and potential for hydrogen production.

2.2 Hydrogen production potential by agricultural and forestry waste Almost all countries around the world are interested in finding new, clean, and renewable energy supplies. For the past few decades, the research efforts have focused on bioethanol and biodiesel. The first-generation biofuels which are

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made from food crops such as corn, sugarcane, and palm oil are recognized as promising alternatives to alleviate the world’s dependence on gasoline or diesel. However, they may indirectly lead to higher food prices. Therefore, the production of second-generation biofuels by converting various types of agricultural waste into biofuels is essential in the process of moving toward renewable energy. Biological hydrogen production is currently in the laboratory stage. Considering that agricultural waste is composed of a complex matrix and can be biodegraded by a complex microbial ecosystem, dark fermentation is a key technology to produce hydrogen from crop residues, livestock waste, and food waste. Many studies have used monosaccharides such as glucose sucrose as model substrates to investigate hydrogen production during dark fermentation. In contrast, fewer studies have chosen solid substrates. Organic materials that are potentially used as substrates for sustainable biohydrogen production are not only abundant but also easy to be used, cheap, and biodegradable. Agricultural waste meets these requirements. For example, straw, fruit tree branches, and fallen leaves are the cheapest organic types of waste in the process of biological transformation (Mtui, 2009). Three main types of animal manure have been distinguished: urine waste (that is livestock or poultry manure or liquid manure), solid manure or farm manure and wastewater and feed for collected farm water. All agricultural crops are biodegradable, so different methods can be biotransformed into biohydrogen during the anaerobic digestion process, which has great potential.

2.2.1 Straw biomass Straw is biomass produced by photosynthesis. Straw resources are rich, mainly including rice, corn, and wheat straw. The primary agricultural sector has assessed the annual production of lignocellulosic biomass at 200 billion tons worldwide (Ren et al., 2009). Straw constitutes the main organic waste resources in rural areas. The element composition of straw is C, H, 0, N, S, P, and so on. The material composition mainly consists of cellulose, starch, fat, and protein. From the perspective of the chemical composition, that of straw basically represents all biomass. From the perspective of theory, the research on hydrogen production by straw fermentation reflects the characteristics of hydrogen production by most biomass fermentation. The realization of hydrogen production by straw anaerobic fermentation is the development from the relatively simple sugar of raw materials to more complex biological hydrogen production from raw materials, which will greatly promote the research process of hydrogen production by anaerobic fermentation and provide the basic data, a theoretical basis and research methods for the realization of hydrogen production by biomass fermentation. Cellulose can also be used as the raw material for biological hydrogen production, but because the most microorganisms can not decompose cellulose directly and the yield from cellulose is relatively low. Therefore, the technical

36 Waste to Renewable Biohydrogen

bottleneck of hydrogen production by straw fermentation is the hydrolysis of lignocellulose in straw. Therefore, the research of straw pretreatment technology has become more and more important in the process of producing hydrogen from agricultural waste straw. Straw waste should be ground before fermentation and separated mechanically or chemically to increase the cellulose and hemicellulose content. Some of this cellulose and hemicellulose can be hydrolyzed into carbohydrates, which can then be treated to produce organic acids and hydrogen.

2.2.2 Livestock and poultry dung Feces are the biomass that remains after food is digested and absorbed. Manure discharged from large and medium-sized livestock and poultry farms has become one of the important sources of pollution, and livestock and poultry manure pollution has become the second largest source of pollution in rural areas after pollution from papermaking wastewater. Manure can cause air and water pollution if it is not properly managed or properly handled. On the one hand, nutrient leaching (mainly nitrogen and phosphorus) and pathogenic pollution can cause direct surface water damage; on the other hand, manure can release CO2 equivalents and CH4 that exacerbate the greenhouse effect (Holm-Nielsen et al., 2009). Livestock and poultry manure contains a large number of microorganisms that can be used for fermentation to produce hydrogen, organic substances (cellulose, hemicellulose, protein, etc.) that are not digested and absorbed, and nutrients such as N and P that are necessary for the growth and metabolism of microorganisms. Nutrients required for the growth of oxygen- and hydrogen-producing microorganisms, such as using them as raw materials for hydrogen production, not only obtain clean energy hydrogen but also realize the recycling of waste, which has positive practical significance in alleviating the energy crisis and reducing environmental pollution. The use of anaerobic microorganisms to treat livestock and poultry manure to obtain biogas while removing organic pollutants is a relatively mature technology. However, the use of livestock and poultry manure for anaerobic fermentation to produce hydrogen was developed only lately and is still in the laboratory research stage. However, the use of livestock manure resources and the fermentation technology of biohydrogen production have developed rapidly and combined organically. Some scholars have made progress in researching hydrogen production from livestock and poultry manure. Table 2.1 shows that the higher the hydrogen yield can be obtained at the higher temperature under the same substrate condition. When the cow dung and urine are used as fermentation substrates, the high-temperature pretreatment of the substrate can increase the hydrogen production. The use of livestock manure and manure-like biomass can effectively obtains the hydrogen.

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TABLE 2.1 Estimated H2 production yields of livestock manure-like biomass.

Substrate

Pretreatment

Maximum assessed production (yield mL H2/g VS)(VS: volatile solid)

Cow dung and urine

e

18

75

Yokoyama et al. (2007)

Cow dung and urine

e

29

60

Yokoyama et al. (2007)

Cow dung and urine

e

0.7

37

Yokoyama et al. (2007)

Cow dung

High temperature

65

52

Tang et al. (2008)

Cow manure wastewater

e

53

45

Tang et al. (2008)

Temperature (
C)

References

2.2.3 Forest deciduous biomass In addition to straw and livestock manure, many types of agricultural waste are available. For example, the garden stumps and forest deciduous biomass are mainly treated by composting, landfilling, and incineration, that caused the environmental pollution and waste of resources. Therefore, more appropriate processing methods are needed. The chemical composition of dried leaves is cellulose, lignin and protein. The use of garden residues and forest deciduous biomass for photosynthetic bacterial hydrogen production not only eliminates wasted resources and mitigates environmental pollution, it generates clean renewable energy. Some experiments have proved that using the arbor can be as substrate, and the amount of hydrogen produced without adding mixed enzymes and adding mixed enzymes has been studied. The results showed that the best hydrogen production was detected in the system with a feed/inoculum of 1.16. The hydrogen yield of the leaves without enzyme pretreatment was 12 cm3/g VS when the substrate was used as a substrate, and the hydrogen output of 40 cm3/g VS when the leaves were treated without a substrate. In addition, methane production is almost negligible in the pretreatment system (8 cm3/g VS) (Palkova´ et al., 2016). The researchers used sycamore leaves to produce hydrogen through simultaneous saccharification and fermentation and determined that the optimal conditions were an initial pH of 6.18 at 35.59
C and the inoculation amount of

38 Waste to Renewable Biohydrogen

26.29% (v/v). The predicted maximum hydrogen production was 65.03 mL H2/ gTS (Li et al., 2017). This shows that garden foliage and forest deciduous biomass can effectively produce hydrogen. This section mainly discusses the hydrogen production capacity of the straw, livestock and poultry manure and garden residues. These wastes are not only abundant but also easy to use, cheap, and biodegradable. They can reach a certain amount of hydrogen production. However, further research is needed to better understand the effects of various single or mixed substrate compositions on the performance of biological hydrogen production. Moreover, in addition to the influence of the substrate during the course of the fermentation experiment, it also depends on the operating conditions and key operating parameters. These parameters affect not only the hydrogen content in the fermentation process but also the types of by-products. According to current research, the rates of hydrogen production from agricultural waste and hydrogen production are both low. Therefore, a large amount of research is needed to make hydrogen from various types of agricultural waste to improve hydrogen production technology from agricultural waste. On the other hand, more efficient processing techniques and optimized reaction conditions need to be developed to improve the efficiency of reaction.

2.3 Hydrogen production potential from industrial waste 2.3.1 Industrial waste Industrial wastewater is one of the main sources of water pollution. It mainly refers to wastewater, sewage and waste liquid produced in industrial production, which contains industrial production materials, intermediate products and products that are lost with water, and pollutants generated during production. If industrial wastewater is not treated, it will cause a variety of environmental problems, the degree of impact of which is high (Cheng et al., 2018; Pereira et al., 2017). For example, industrial wastewater directly flowing into rivers and lakes pollutes surface water; if it is more toxic, it will cause death or even the extinction of aquatic plants and animals. Industrial wastewater may also penetrate into groundwater, pollute groundwater, contaminate crops, or threaten human survival. Sewage treatment is a fundamental guarantee for protecting China’s water resources, solving the problem of water scarcity, and protecting the environment. Using some industrial wastewater as raw materials for hydrogen production not only provides abundant hydrogen energy (a 47% increase in hydrogen emissions from existing methods). It also greatly saves the cost of treating industrial wastewater. Therefore, the use of industrial wastewater for hydrogen production has great potential. Wastewater from the sugar industry, food processing industry, paper mills, rice wineries, breweries, chemical products, starch factories, palm oil factories, beverage factories, and pharmaceutical industry are used as substrates for fermentation. The hydrogen yield of industrial wastewater under different working conditions is shown in Table 2.2.

TABLE 2.2 Hydrogen yield of different types of industrial wastewater under different operating conditions.

T (
C)

Mixed anaerobic sludge

5.5

55

34

2.14 mol/mol-hexose

Yu et al. (2002)

Paper soy protein processing wastewater

Waste sludge

6.7

35

1.83e2.4

25.67 L/d

(Zhu, 2013)

Cassava sewage

Pig sewage treatment sludge

5.0

28

4

1.91 mol H2/mol glucose

Amorim et al. (2014)

Paper mill effluent

Paper mill mire

5.0

35

2.217

1.22 mmol/g COD initial

Farghaly et al. (2015)

Molasses sewage

Enterobacter aerogenes

30

40

6.02 mm/g sugar

Kumar et al. (2016)

Pulp wastewater

Anaerobic mud

5.0

37

5

55.4 mL/g-COD

Vaez et al. (2017)

Beverage sewage

Starter culture

5.5

37

20

3.76 mol H2/mol-sucrose

Sivagurunathan and Chiu-Yue (2019)

Milk product waste

Biomass from fermentation

3.7e4.3

24e30

8.12e15.44

2.56 mol H2/mol saccharides

Silva et al. (2019)

Nutrient solution

Rice distillery sewage

COD, chemical oxygen demand.

Hydrogen yield

References

Waste to biohydrogen: potential and feasibility Chapter | 2

pH

Reactant concentration (g COD/l)

Types of industrial sewage

39

40 Waste to Renewable Biohydrogen

This shows that many factors affect the potential of biological hydrogen production from wastewater, such as pH, temperature, hydraulic retention time (HRT), organic load factor, the synthesis of nutrients, the volatile fatty acid (VFA) concentration, and wastewater as a fermentation substrate. pH is an important parameter affecting hydrogen production efficiency. A decrease in pH will eventually affect the growth of bacteria and metabolites. A pH range of 4.5e9 is considered effective for biological hydrogen production (Stavropoulos et al., 2016). Temperature has a major role because substrate degradation, hydrogen production, microbial growth, and by-products are interdependent (Perna et al., 2013). The different temperature ranges of anaerobic fermentation are normal temperature (15e30
C), intermediate temperature (30e49
C), thermophilic (50e64
C), superheat (65e80
C), and extreme heat (>80
C). The HRT or fermentation time is a parameter that affects hydrogen production and evaluates the efficiency of gas production. It is one of the main operating factors restricting the methanogenesis process of acid fermentation. A longer HRT results in metabolic activity shifting from the acid-producing to the methanogenic phase, which ultimately inhibits hydrogen production. However, shorter HRTs inhibit the effects of methanogens (Hawkes et al., 2007). The shorter the HRT, the slower the growth of slow-growing microorganisms (that is the methanogens), and the easier it is to wash them away. The organic loading rate (OLR) has an important effect on biological hydrogen production. The total conversion of carbohydrates in the reactor is inversely proportional to the OLR, indicating that the organic content in the reactor exceeds the standard and affects the performance of the reactor. At lower glucose uptake rates, hydrogen production is highest. When the organic matrix is overloaded, the hydrogen production value is lower. The effectiveness of nutrients is necessary for the optimal growth of microorganisms. Carbon, nitrogen, vitamins, and trace metals help maintain microbial growth. Nitrogen is an important source of plant growth and promotes hydrogen production. Organic salts do not participate in the generation of hydrogen (Yokoi et al., 2001), and the optimal phosphate content will increase the overall hydrogen production capacity, because an increase in phosphate content changes the reducing agent that produces hydrogen in the cell. If the VFA concentration increases, the overall hydrogen production is cut back. The final product of metabolism affects the amount of hydrogen produced by fermentation. The main metabolites are the small molecular acids. The amount of hydrogen production depends on the type of metabolite, which is an important factor in analyzing the total hydrogen production (Lee et al., 2002). Organic-rich wastewater can be used as a substrate for efficient hydrogen production because it reduces the overall treatment costs. Industrial wastewater contains a large amount of degradable organics, which can maintain a balance between wastewater use and recycling (Sivagurunathan et al., 2017). Converting industrial wastewater into biohydrogen involves mainly fermentation technologies, including dark, light, and darkelight coupled. According to the composition of the terminal fermentation products, hydrogenproducing fermentation mechanisms are divided into three categories: butyric,

Waste to biohydrogen: potential and feasibility Chapter | 2

41

propionic, and ethanolic fermentation. In recent years, some comprehensive strategies have been proposed to improve biological hydrogen production by the dark fermentation of industrial wastewater. It is feasible to use the acid-rich residue of the fermentation waste liquid as an organic-rich substrate for subsequent bioenergy production, especially in the form of a two-stage integrated fermentation process. There are several secondary processes such as methanogenesis (methane recovery), acidogenic fermentation (hydrogen recovery), photobiological process (hydrogen recovery) (Nagarajan et al., 2017), microbial electrolytic cells (hydrogen recovery) (Lu et al., 2016), anaerobic nutrition restriction method (bioplastic production), heterotrophic microalgae culture (lipid recovery), microbial fuel cell and microbial electrolytic cell (bioelectric recovery), and a primary combination of fermented biological hydrogen production. The use of multistage indicates that the dark fermentation process has great potential to produce biohydrogen with industrial wastewater as a renewable substrate.

2.3.2 Paper sludge Sludge is the by-product of wastewater treatment in the papermaking process. For every ton of recycled paper produced, 700 kg of sludge with a water content of 65% can be produced (Willie et al., 2017). The output is 5e10 times that of a municipal sewage treatment plant of the same size. Its composition is complex. The biomass content is rich, and the organic matter content is 40e50% that composed of high molecular organic matter, such as cellulose, hemicellulose and lignin, as well as fillers, coagulants and nitrogen, phosphorus, potassium, calcium, magnesium, silicon, copper, iron, zinc, and other plant nutrients. In addition, it has a large water content and is difficult to handle. Random disposal or abuse on farmland without harmless treatment will pollute groundwater resources, endanger human health, and cause an ecological crisis. The treatment process of sludge includes composting, drying, pyrolysis, incineration and humid air oxidation. Although there are various methods for sludge treatment, owing to immature technology development and high investment, they are still unsatisfactory and have limitations in actual operation. However, papermaking sludge can be used as a substrate, and hydrogen production technologies such as light fermentation, dark fermentation, continuous dark fermentation and light fermentation can be used to treat waste as well as obtain the hydrogen. Using the papermaking sludge for biological hydrogen production mainly refers to two methods of light and dark fermentation. Both methods convert organic matter into products such as biological hydrogen and carbon dioxide with microbial functions under different conditions. Photofermentation is a biological process in which photosynthetic bacteria occur. Photosynthetic nonsulfur (PNS) bacteria use organic acids or VFAs as substrates and carbon dioxide as by-products to produce hydrogen. Carbon sources, glucose, and so on can also be used for hydrogen production by PNS bacteria (Argun and

42 Waste to Renewable Biohydrogen

Kargi, 2011). However, control of the operating conditions of light fermentation hydrogen production cannot be ignored. In addition to sufficient light and an anaerobic environment, the pH value, temperature, and content of some metal elements are important considerations, and these elements are necessary for nitrate enzymes to produce H2. To obtain a higher hydrogen yield, the optimal range of some key parameters is pH 6.8e7.5, the temperature is 31e36
C, the light intensity is 6e10 Klux, and the VFA concentration is 1800e2500 mg/L. The evaluation of fermentation performance of photofermentation bacteria includes two aspects of hydrogen production and light efficiency. The optimal H2 yield is 80% and light efficiency is between 0.2% and 9.3%. Increasing the efficiency of light conversion to hydrogen is the main research direction of the future. However, the feasibility and specific performance of hydrogen production from papermaking sludge by light fermentation need further study. Dark fermentation refers to bacteria that use nitrogenase or hydrogenase to degrade carbohydrates (mainly glucose) under dark and hypoxic conditions to generate hydrogen, accompanied by VFAs and CO2 (Argun and Kargi, 2011). Butyric acid fermentation is usually accompanied by acetic acid fermentation. When both reactions are present, the theoretical yield of hydrogen is 2.5 mol (Krupp and Widmann, 2009). The challenge of dark fermentation is caused by hydrogen-consuming bacteria (HCB), which have a significant effect on hydrogen produced by a mixed culture. Therefore, it is necessary to pretreat the hydrogen-producing bacteria to inhibit the activity of HCB and increase their H2 production (Wong et al., 2014). The dark fermentation process is affected by factors such as the pretreatment method, inoculum, substrate, and reactor type, as well as nitrogen, phosphorus, sulfur, iron, temperature, pH, and other factors. In the process of hydrogen production by light and dark fermentation of papermaking sludge, the pretreatment method before dark fermentation usually includes acid hydrolysis, which can also be carried out with the biological hydrolysis step, followed by light fermentation to produce hydrogen, or acid hydrolysis. After the process, light fermentation is performed directly during dark fermentation and photosynthesis. Increasing the temperature can increase hydrogen production, and the pH value is controlled to be 4.5e6.5 and above 7 (Nikolaidis and Poullikkas, 2017). The theoretical total amount of H2 produced by two-step fermentation is considerable, but owing to the production of VFA compounds and the use of some raw materials, the actual yield is still far below the ideal value. The development status of the biological hydrogen production process by using paper sludge is still limited, and it is in the preliminary test stage. This is particularly evident in the research status of light fermentation. Because the source of papermaking sludge is usually papermaking wastewater, which contains a large amount of organic matter, research on photofermentation hydrogen papermaking sludge still has its accessibility and overall performance value. Current research is more focused on how to optimize operating conditions to increase total hydrogen production and the reaction rate. To

Waste to biohydrogen: potential and feasibility Chapter | 2

43

improve the total yield of hydrogen, synergetic fermentation, continuous dark fermentation, and light fermentation were proposed. Combined fermentation is a promising method for hydrogen production from sludge because it can simultaneously process other waste and achieve hydrogen recovery. In short, with the country’s increasingly stringent pollutant discharge standards and the rapid development of sewage treatment technology, the output of sludge will become increasingly larger. The use of papermaking sludge to convert to biohydrogen has broad application prospects.

2.4 Hydrogen production potential by domestic waste 2.4.1 Domestic sewage Domestic sewage is wastewater that is removed from the daily life of households, hotels, restaurants, schools, and shopping malls. It has a wide range of sources and a huge amount. With the rapid development of economy and the increase in residents’ living standards, there is more and more sewage discharge to be treated. This kind of sewage is characterized by a large amount of organic matter (such as protein, starch, fat, and urea), pathogenic microorganisms, and suspended matter. The main purpose of wastewater treatment is to remove organic matter and nutrients, not to recycle them. The selection of the best treatment process mainly depends on the concentration of pollutants and the nature of the wastewater. This is called the intensity of the wastewater. Wastewater with a chemical oxygen demand (COD) greater than 2000 mg/L is defined as medium to high intensity, and COD less than 2000 mg/L is defined as low-intensity wastewater. Biomass is one of the largest potential sources of energy. It is extracted from organic materials and natural resources and can be converted into high-energy gases such as methane and hydrogen by anaerobic digestion (Mehrpooya et al., 2018). Generally, high-intensity wastewater is used, but low-intensity wastewater is not widely used because of its poor performance. Nevertheless, anaerobic systems have been developed and successfully applied to the treatment of low-intensity wastewater such as domestic sewage. Research will increasingly focus on the fermentation of domestic sewage to produce hydrogen, because hydrogen has the characteristics of high energy density, recyclability, and freedom from pollution, and it is considered the most ideal alternative to fossil fuels (Batista et al., 2015). Domestic wastewater is a relatively diluted resource stream, so the low metabolic capacity of anaerobic bacteria leads to the low efficiency of anaerobic process. The most widely used domestic anaerobic wastewater treatment fields are high-efficiency systems and membrane biological reactions such as an anaerobic baffled reactor, anaerobic filter, and upflow anaerobic sludge, upflow anaerobic sludge blanket, and expanded granular sludge bed. McCarty et al. (2011) evaluated the potential benefits of anaerobic wastewater treatment. Compared with traditional anaerobic sludge digestion

44 Waste to Renewable Biohydrogen

systems, energy production greatly exceeds the energy required for plant operation. Shoener et al. (2014) explored the potential of the anaerobic treatment of domestic sewage and the economy of energy consumption. Anaerobic fermentation has huge application prospects. However, because domestic sewage often contains high concentrations of ammonia, in an alkaline environment (pH 9.5), the initial ammonia level will cause a decrease in maximum specific hydrogen yield. The total amount of ammonia is an important parameter in the fermentation process. When the ammonia ion concentration is changed from When 0e50 mmol/L (0e900 mg/L) is increased, hydrogen production is promoted, but as the ammonia ion concentration is further increased to 500 mmol/L (9000 mg/L), hydrogen production is suppressed (Wang et al., 2018). Therefore, pretreatment of domestic wastewater with a high ammonia nitrogen concentration and controlling its concentration level before hydrogen fermentation are main directions in research.

2.4.2 Municipal organic solid waste Photo fermentation of municipal solid waste to produce hydrogen is also affected by many factors. Nitrogenase is an important enzyme when photofermentative bacteria produce hydrogen, oxygen, ammonia, and high. Both nitrogen and carbon ratios inhibit the activity of the enzyme. Therefore, this process requires anaerobic conditions and control of the ammonia concentration. When ammonium salts are present, the hydrogen yield is lower, but if protein is used as the nitrogen source, the production can enhanced hydrogen (Oh et al., 2004). Light intensity is a parameter that affects the performance of light-fermenting bacteria. Increasing the light intensity can promote hydrogen production and increase the yield, but it reduces the light conversion efficiency. Chen and Chang (2006) added clay and silica gel support to the reactor; the hydrogen yield increased by 50.9e67.2%, and the hydrogen yield increased by 32.5e37.2%. In addition, different organic acids as substrates were affected. The description of hydrogen yield and acid yield rate in the literature is shown in Table 2.3. Lactic acid as a carbon source had the highest conversion efficiency (Fascetti and Todini, 1995).

2.5 Feasibility of waste to biohydrogen 2.5.1 Feasibility of technology Hydrogen is a clean fuel that has an important role in reducing greenhouse gas. However, about 80% of current demand for hydrogen comes from the restructuring of fossil fuels (Dincer and Acar, 2015). A variety of renewable carbohydrates are used as hydrogen substrates, such as various types of industrial and agricultural waste and organic wastewater, which effectively

TABLE 2.3 Yield and rate of biological hydrogen production by photofermentation of organic acids. Organic acid

Butyrate

Acetate

Rate of biological hydrogen

References

Microorganism

Light intensity

Rhodopseudomonas palustris

480 mmol photons/m2 s

14.8

0.1

2.2 mL/h

Barbosa et al. (2001)

Butyrate

680 mmol photons/m2 s

8.4

0.3

7.6 mL/h

Barbosa et al. (2001)

R. palustris

480 mmol photons/m s

12.6

0.5

9.1 mL/h

Barbosa et al. (2001)

Rhodopseudomonas

680 mmol photons/m s

9.6

0.4

10.7 mL/h

Barbosa et al. (2001)

R. palustris

2500 lux

60e70

1.6 mL/h

Oh et al. (2004)

0.88 mL/h

Fang et al. (2005)

2 2

2

Rhodopseudomonas capsulata

200 W/m

76.5

R. capsulata

4170 lux

32.6 2

4.2

67.6

1.28 mL/h

Fang et al. (2005)

1.1 mL/h

Barbosa et al. (2001)

6.6

1.1 mL/h

Barbosa et al. (2001)

5 mL H2/L h

Koku et al. (2002)

25.2 mL/h

Barbosa et al. (2001)

R. capsulata

200 W/m

R. palustris

480 mmol photons/m s

36

Rhodopseudomonas

680 mmol photons/m s

2 2

2

Shi and Yu (2005)

Rhodopseudomonas sphaeroides

150e250 W/m

35e45

Rhodopseudomonas

680 mmol photons/m2 s

72.8

0.3

0.9

Waste to biohydrogen: potential and feasibility Chapter | 2

Lactate

Light conversion

Transfer efficiency (%)

45

46 Waste to Renewable Biohydrogen

combine energy output, waste reuse, and pollution control so as to realize waste resource and reduce the cost of hydrogen production. Technologies of hydrogen production from biomass mainly include dark fermentation, light fermentation, darkelight coproduction, and thermochemistry (Kapdan and Kargi, 2006). The main biological processes for hydrogen production can be divided into three types: hydrogen production by light fermentation, hydrogen production by dark fermentation in the stage of acid production by the anaerobic digestion of solid organic waste, and combined production by two stages of dark and light fermentation. There are different methods for the types of waste, as shown in Table 2.4. The production of hydrogen by anaerobic fermentation is accomplished by the physiological metabolism of hydrogen-producing bacteria. Organic oxidation of NADH and Hþ can generally be with acetic acid, butyric acid, and ethanol fermentation, such as phase I. They achieve NAD regeneration, but when slow oxidation occurs in the formation process to avoid the accumulation of NADH and Hþ, and the cells release H2 in a balanced way, while maintaining the reduction of electrons during oxidation to ensure that the metabolic process goes smoothly. Hydrogen production by dark fermentation can quickly use a variety of organic compounds as substrates to produce hydrogen by fermentation, but the production of VFAs and ethanol inhibits the hydrogen production effect, and the COD removal rate becomes low, so the hydrogen production liquid requires further treatment (Wadjeam et al., 2019). Comparing with dark fermentation, hydrogen production by light fermentation has a higher theoretical hydrogen production and COD removal rate, but hydrogen production by photosynthetic organisms is still affected by the low activity of hydrogenase (nitrogenase) and the photoinhibition of the photosynthetic bacteria feed liquid at a high concentration. The photo contact efficiency of microorganisms and the inhibition of residual acid metabolites also restrict the biohydrogen conversion effect. A darkelight combined production method makes dark fermentation and light fermentation complementary and further improves the hydrogen production effect. Therefore, the development of efficient hydrogen-producing strain breeding and manufacturing, hydrogenproducing enzyme activity, hydrogen-producing kinetics, and reactor development is still the focus of research.

2.5.2 Efficiency of hydrogen production Increasing attention has been paid to the energy recovery of waste by biohydrogen production technology. Many researchers have explored the conversion of various types of waste into biohydrogen. Regarding waste with different characteristics, organic solid waste such as starch and cellulose usually goes through dark fermentation to produce hydrogen to obtain a higher degradation effect and hydrogen production. The high content of cellulose, hemicellulose and lignin from agricultural production waste can be obtained

TABLE 2.4 Comparison of different biological hydrogen production technologies. Disadvantages

Outlook

Photofermentation

A variety of waste resources can be used. Almost all transformation of matrix can be realized. H2 can be extracted from waste liquor of dark fermentation.

Photobiochemical reactor is required. Low efficiency of nitrogenase in hydrogen production. Low photosynthetic conversion efficiency. Large surface area.

Metabolic engineering improved strain performance. Hydrogenase was used to replace nitrogenase. Research on mutants. Breakthroughs in materials science and technology.

Dark fermentation

A variety of waste resources can be used. Reactor is easy to operate without sterilization. Higher gas yield can be obtained by immobilized mixed culture.

A variety of waste resources can be used. Reactor is easy to operate without sterilization. Higher gas yield can be obtained by immobilized mixed culture.

Metabolic engineering improvement of metabolic limiting factors. Two-step hydrogen system produces more energy and reduces chemical oxygen demand.

Dark photofermentation

A variety of waste resources can be used. The dark fermentation inhibitor (volatile fatty acid) was further converted to hydrogen. Higher hydrogen production can be obtained by a continuous process

Bacteria control or sterilization is required. Temperature and biomass control of reaction conditions. Darkelight conditions convert to control complexity.

Characterization and quantification of properties of transition substrates. Strict control of reaction conditions. Continuous process control and reactor design.

Thermochemical

Applicable to solid waste, especially plastic waste. Lower greenhouse gas emissions.

High-temperature and high-pressure conditions. You need a lot of catalysts. Product separation is complex.

Reaction conditions and reactor optimization. Environmental protection and economic catalyst research and development. Control the pollution of by-products.

47

Advantages

Waste to biohydrogen: potential and feasibility Chapter | 2

Methods

48 Waste to Renewable Biohydrogen

by biomass gasification. Organic wastewater with good rheological properties and phototransmissibility is a sustainable and environmentally friendly technology for hydrogen production that uses the metabolic energy of photosynthetic hydrogen-producing bacteria. Table 2.5 shows the research status of hydrogen production from various types of waste (the TS is means the total solid; the “POME” means the palm oil mill effluent). Organic waste has great potential as dark, light, and integrated darkelight fermentation to produce hydrogen substrates. The commercialization of waste into hydrogen requires a higher concentration of substrates, which is much higher than the current stage of experimental exploration. Even with this highload digestion, the estimated cost of hydrogen production is about $13.19/kg (Acar and Dincer, 2019). The production of hydrogen by fermentation is not limited to key operating parameters such as pH and temperature. The development of advanced technologies such as immobilization and the application of nanotechnology have also promoted the production of hydrogen by fermentation. Immobilized inoculants can effectively provide better stability for the biological hydrogen production process when a wide range of waste or wastewater is subjected to substrate action. In addition, the type and amount of culture, reactor design and other factors have different effects on hydrogen production efficiency, which requires further research.

2.6 Concluding remarks and prospects The greenhouse effect caused by the large amount of carbon dioxide emissions has led to an increase in extreme weather and global warming. Among various renewable energy sources, hydrogen is considered an attractive alternative. There are many ways to convert waste into biohydrogen. For different waste materials, the gasification technology can treat almost all waste except liquid organic wastewater. Agricultural and industrial waste can be converted to biohydrogen by dark and light fermentation techniques of microorganisms. However, plastic waste cannot be degraded by fermentation technology, but it can be treated by pyrolysis and gasification. On the other hand, dark fermentation can also accept a variety of waste, including different wastewaters, food waste and household waste. usually, the hydrogen production rate is higher. In addition, a simple reactor configuration is an important advantage of dark fermentation technology. In the combination of dark and light fermentation, waste products and by-products obtained after dark fermentation are used as the starting materials of light fermentation. It is essential to adjust the concentration, pH value, nutrient composition, and concentration of VFAs in dark fermentative medium before light fermentation to improve hydrogen production. Therefore, the development of an efficient hydrogen production system and the establishment and optimization of optimal hydrogen production conditions are conducive to the improvement of hydrogen yield.

Waste Solid waste

Organic wastewater

Substrate

Inoculum

Temperature


pH

Mode

Hydrogen yield

References

Rice straw

Bacillus cereus (KR809374)

35 C

7

Batch

28 mL H2/g TS

He et al. (2014)

Wheat straw

Anaerobic sludge

37
C

5.5

Batch

5.2e10.5 mL H2/g TS

Que´me´neur et al. (2012)

Cornstalk

Cow manure

35
C

6

Batch

69.6e93.4 mL H2/g TS

Wu et al. (2013)

Cow dung

Anaerobic sludge

35
C

5.5

CSTR

165  25.16 mL H2/g

Wadjeam et al. (2019)

Palm oil mill effluent

Immobilized Clostridium

37
C

5.5

Batch

5.35 LH2/L-POME

Singh et al. (2013)

Paperboard mill wastewater

Anaerobic sludge

e

e

Batch

1.73 mol H2/mol glucose

Dinesh et al. (2019)

Waste to biohydrogen: potential and feasibility Chapter | 2

TABLE 2.5 Yield of waste to biohydrogen.

49

50 Waste to Renewable Biohydrogen

References Acar, C., Dincer, I., 2019. Review and evaluation of hydrogen production options for better environment. J. Clean. Prod. 218, 835e849. https://doi.org/10.1016/j.jclepro.2019.02.046. Amorim, N.C.S., Alves, I., Martins, J.S., Amorim, E.L.C., 2014. Biohydrogen production from cassava Wastewater in an anaerobic fluidized bed reactor. Braz. J. Chem. Eng. 31 (3), 603e612. https://doi.org/10.1590/0104-6632. Argun, H., Kargi, F., 2011. Bio-hydrogen production by different operational modes of dark and photo-fermentation: an overview. Int. J. Hydrogen Energy 36, 7443e7459. http://doi:10.1016/ j.ijhydene.2011.03.116. Barbosa, M.J., Rocha, J.M.S., Tramper, J., Wijffels, R.H., 2001. Acetate as a carbon source for hydrogen production by photosynthetic bacteria. J. Biotechnol. 85, 25e33. https://doi.org/ 10.1016/S0168-1656(00)00368-0. Batista, A.P., Ambrosano, L., Graca, S., Sousa, C., Marques, P., Ribeiro, B., Botrel, E.P., Neto, P.C., Gouveia, L., 2015. Combining urban wastewater treatment with biohydrogen production - an integrated microalgae-based approach. Bioresour. Technol. 184, 230e235. https://doi.org/10.1016/j.biortech.2014.10.064. Chen, C.Y., Chang, J.S., 2006. Enhancing phototropic hydrogen production by solid-carrier assisted fermentation and internal optical-fiber illumination. Process Biochem. 41, 2041e2049. https://doi.org/10.1016/j.procbio.2006.05.005. Cheng, D.L., Ngo, H.H., Guo, W.S., Chang, S.W., Nguyen, D.D., Kumar, S.M., Du, B., Wei, Q., Wei, D., 2018. Problematic effects of antibiotics on anaerobic treatment of swine wastewater. Bioresour. Technol. J. 263, 642e653. https://doi.org/10.1016/j.biortech.2018.05.010. Dincer, I., Acar, C., 2015. Review and evaluation of hydrogen production methods for better sustainability. Int. J. Hydrogen Energy 40 (34), 11094e11111. https://doi.org/10.1016/ j.ijhydene.2014.12.035. Dinesh, G.H., Nguyen, D.D., Ravindran, B., Chang, S.W., Vo, D.V.N., Bach, Q.V., Tran, H.N., Basu, M.J., Mohanrasu, K., Murugan, R.S., Swetha, T.A., 2019. Simultaneous biohydrogen (H2) and bioplastic (poly-b-hydroxybutyrate-PHB) productions under dark, photo, and subsequent dark and photo fermentation utilizing various wastes. Int. J. Hydrogen Energy 45 (10), 5840e5853. https://doi.org/10.1016/j.ijhydene.2019.09.036. Fang, H.H.P., Liu, H., Zhang, T., 2005. Phototrophic hydrogen production from acetate and butyrate in wastewater. Int. J. Hydrogen Energy 30, 785e793. https://doi:10.1016/j.ijhydene. 2004.12.010. Farghaly, A., Tawfik, A., Danial, A., 2015. Inoculation of paperboard mill sludge versus mixed culture bacteria for hydrogen production from paperboard mill wastewater. Environ. Sci. Pollut. Res. 23 (4), 3834e3846. http://doi:10.1007/s11356-015-5652-7. Fascetti, E., Todini, O., 1995. Rhodobacter sphaeroides RV cultivation and hydrogen production in a one- and two-stage chemostat. Applied Microbiology and Biotechnology 44, 300e305. https://doi.org/10.1007/BF00169920. Guo, X., 2010. Hydrogen production from agricultural waste by dark fermentation: a review. Int. J. Hydrogen Energy 35, 10660e11067. http://doi:10.1016/j.ijhydene.2010.03.008. Hawkes, F.R., Hussy, I., Kyazze, G., Dinsdale, R., Hawkes, D.L., 2007. Continuous dark fermentative hydrogen production by mesophilic microflora: principles and progress. Int. J. Hydrogen Energy 32, 172e184. http://doi:10.1016/j.ijhydene.2006.08.014. He, L.L., Huang, H., Lei, Z.F., Liu, C.G., Zhang, Z.Y., 2014. Enhanced hydrogen production from anaerobic fermentation of rice straw pretreated by hydrothermal technology. Bioresour. Technol. 171, 145e151. https://doi.org/10.1016/j.biortech.2014.08.049.

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Holm-Nielsen, J., AlSeadi, T., Oleskowicz-Popiel, P., 2009. The future of anaerobic digestion and biogas utilization. Bioresour. Technol. 100 (22), 5478e5484. http://doi:10.1016/j.biortech. 2008.12.046. Hua, W., Xu, J.J., Sheng, L., Liu, X., Lu, Y., Li, W., 2018. A review on bio-hydrogen production technology. Int. Energy Res. 42, 3442e3453. http://DOI: 10.1002/er.4044. Kapdan, I.K., Kargi, F., 2006. Bio-hydrogen production from waste materials. Enzym. Microb. Technol. 38 (5), 569e582. https://doi.org/10.1016/j.enzmictec.2005.09.015. Koku, H., Eroglu, I., Gunduz, U., Yucel, M., Turker, L., 2002. Aspects of metabolism of hydrogen production by Rhodobacter sphaeroides. Int. J. Hydrogen Energy 27, 1315e1329. https:// doi.org/10.1016/S0360-3199(02)00127-1. Krupp, M., Widmann, R., 2009. Biohydrogen production by dark fermentation: experiences of continuous operation in large lab scale. Int. J. Hydrogen Energy 34, 4509e16. http://doi:10. 1016/j.ijhydene.2008.10.043. Kumar, G., Mudhoo, A., Sivagurunathan, P., Nagarajan, D., Ghimire, A., Lay, C.-H., Chang, J.S., 2016. Recent insights into the cell immobilization technology applied for dark fermentative hydrogen production. Bioresour. Technol. 219, 725e737. https://doi.org/10.1016/ j.biortech.2016.08.065. Lee, Y.J., Miyahara, T., Noike, T., 2002. Effect of pH on microbial hydrogen fermentation. J. Chem. Technol. Biotechnol. 77 (6), 694e698. http://doi:10.1002/jctb.623. Li, Y.M., Zhang, Z.P., Jing, Y.Y., Ge, X.M., Wang, Y., Lu, C.Y., Zhou, X.H., Zhang, Q.G., 2017. Statistical optimization of simultaneous saccharification fermentative hydrogen production from Platanus orientalis leaves by photosynthetic bacteria HAU-M1. Int. J. Hydrogen Energy 42 (9), 5804e5811. https://doi.org/10.1016/j.ijhydene.2016.11.182. Luo, W., Liao, C.H., Chen, H.J., Zhu, Y.Z., 2016. Research progress in hydrogen production from biomass via supercritical water gasification. Nat. Gas Chem. Indust. 41 (1), 84-90. McCarty, P.L., Bae, J., Kim, J., 2011. Domestic wastewater treatment as a net energy producer-can this be achieved Environ. Sci. Technol. 45, 7100e7106. https://doi.org/10.1021/es2014264. Mehrpooya, M., Khalili, M., Sharifzadeh, M.M.M., 2018. Model development and energy and exergy analysis of the biomass gasification process (based on the various biomass sources). Renew. Sustain. Energy Rev. 91, 869e887. https://doi.org/10.1016/j.rser.2018.04.076. Mtui, G.Y.S., 2009. Recent advances in pretreatment of lignocellulosic wastes and production of value added products. Afr. J. Biotechnol. 8 (8), 1398e1415. http://doi:10.4314/ajb.v8i8.60134. Nagarajan, D., Lee, D.J., Kondo, A., Chang, J.S., 2017. Recent insights into biohydrogen production by microalgaeefrom biophotolysis to dark fermentation. Bioresour. Technol. 227, 373e387. https://doi.org/10.1016/j.biortech.2016.12.104. Nikolaidis, P., Poullikkas, A., 2017. A comparative overview of hydrogen production processes. Renew. Sustain. Energy Rev. 67, 597e611. https://doi.org/10.1016/j.rser.2016.09.044. Oh, Y.K., Scol, E.H., Kim, M.S., Park, S., 2004. Photoproduction of hydrogen from acetate by a chemoheterotrophic bacterium Rhodopseudomonas palustris P4. Int. J. Hydrogen Energy 29, 1115e1121. https://doi:10.1016/j.ijhydene.2003.11.008. Palkova´, V., Lazor, M., Smolinska´, M., Taka´ova´, A., Hutnan, M., Bodı´k, I., Ryba, J., Ga´l, M., emlika, L., Pangallo, D., Mackuak, T., 2016. Enhanced hydrogen bioproduction from birdcherry leaves using enzyme mixture(Article). Monatshefte fur Chemie 147, 201e206. http://doi:10.1007/s00706-015-1572-y. Pereira, E.L., Borges, A.C., Heleno, F.F., Costa, T.H.C., Mounteer, A.H., 2017. Factors influencing anaerobic biodegradation of biodiesel industry wastewater. Water Air Soil Pollut. 228. http:// doi:10.1007/s11270-017-3395-4.

52 Waste to Renewable Biohydrogen Perna, V., Castello, E., Wenzel, J., Zampol, C., Lima, D.M.F., Borzaconni, L., et al., 2013. Hydrogen production in an upflow anaerobic packed bed reactor used to treat cheese whey. Int. J. Hydrogen Energy 38, 54e62. https://doi.org/10.1016/j.ijhydene.2012.10.022. Que´me´neur, M., Bittel, M., Trably, E., Dumas, C., Fourage, L., Ravot, G., Steyer, J.P., Carre`re, H., 2012. Effect of enzyme addition on fermentative hydrogen production from wheat straw. Int. J. Hydrogen Energy 37, 10639e10647. https://doi.org/10.1016/j.ijhydene.2012.04.083. Ren, N., Wang, A., Cao, G., Xu, J., Gao, L., 2009. Bioconversion of lignocellulosic biomass to hydrogen: potential and challenges. Biotechnol. Adv. 27 (6), 1051e1060. http://doi:10.1016/j. biotechadv.2009.05.007. Shi, X.Y., Yu, H.Q., 2005. Response surface analysis on the effect of cell concentration and light intensity on hydrogen production by Rhodopseudomonas capsulate. Process Biochem. 40, 2475e2481. Shoener, B.D., Bradley, I.M., Cusick, R.D., Guest, J.S., 2014. Energy positive domestic wastewater treatment: the roles of anaerobic and phototrophic technologies. Environ. Sci. Processes Impacts 16, 1204e1222. In: https://doi:10.1016/j.procbio.2004.09.010. Silva, A.N. da, Maceˆdo, W.V., Sakamoto, I.K., Pereyra, D. de L.A.D., Mendes, C.O., Maintinguer, S.I., CaffaroFilho, R.A., Damianovic, M.H.Z., Varesche, M.B.A., Amorim, E.L.C. de, 2019. Biohydrogen production from dairy industry wastewater in an anaerobic fluidized-bed reactor. Biomass Bioenergy 120, 257e264. https://doi.org/10.1016/ j.biombioe.2018.11.025. Singh, L., Wahid, Z.A., Siddiqui, M.F., Ahmad, A., Rahim, M.H.A., Sakinah, M., 2013. Biohydrogen production from palm oil mill effluent using immobilized Clostridium butyricum EB6 in polyethylene glycol. Process Biochem. 48, 294e298. https://doi.org/10.1016/ j.procbio.2012.12.007. Sivagurunathan, P., Kumar, G., Mudhoo, A., Rene, E.R., Saratale, G.D., Kobayashi, T., Xu, K., Kim, S.H., Kim, D.H., 2017. Fermentative hydrogen production using lignocellulose biomass: an overview of pre-treatment methods, inhibitor effects and detoxification experiences. Renew. Sustain. Energy Rev. 77, 28e42. https://doi.org/10.1016/j.rser.2017.03.091. Sivagurunathan, P., Chiu-Yue, L., 2019. Biohydrogen production from beverage wastewater using selectively enriched mixed culture. Waste Biomass Valorization 1e10. https://doi.org/ 10.1007/s12649-019-00606-z. Stavropoulos, K.P., Kopsahelis, A., Zafiri, C., Kornaros, M., 2016. Effect of pH on Continuous Biohydrogen Production from End-of-Life Dairy Products (EoL-DPs) via Dark Fermentation. Waste and Biomass Valorization 7, 753e764. https://doi.org/10.1007/s12649-016-9548-7. Tang, G.L., Huang, J., Sun, Z.J., Tang, Q.Q., Yan, C.H., Liu, G.Q., 2008. Biohydrogen production from cattle wastewater by enriched anaerobic mixed consortia: Influence of fermentation temperature and pH. Journal of Bioscience and Bioengineering 106 (1), 80e87. https:// doi.org/10.1263/jbb.106.80. Vaez, E., Taherdanak, M., Zilouei, H., 2017. Dark hydrogen fermentation from paper mill effluent (PME): the influence of substrate concentration and hydrolysis. Environ. Energy Econ. Res. 1 (2), 163e170. http://doi:10.22097/eeer.2017.47243. Wadjeam, P., Reungsang, A., Imai, T., Plangklang, P., 2019. Co-digestion of cassava starch wastewater with buffalo dung for bio-hydrogen production. Int. J. Hydrogen Energy 44 (29), 14694e14706. https://doi.org/10.1016/j.ijhydene.2019.04.138. Wang, D., Duan, Y., Yang, Q., Liu, Y., Ni, B.-J., Wang, Q., Zeng, G., Li, X., Yuan, Z., 2018. Free ammonia enhances dark fermentative hydrogen production from waste activated sludge. Water Res. 133, 272e281. https://doi.org/10.1016/j.watres.2018.01.051.

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Willie, J., et al., 2017. Anaerobic treatment of pulp and paper mill. EffluentAppita 60 (2), 101e105. https://doi.org/10.1016/j.matpr.2019.09.011. Winter, C.J., 2005. Into the hydrogen energy economy-milestones. Int. J. Hydrogen Energy 30, 681e685. https://doi:10.1016/j.ijhydene.2004.12.011. Wong, Y.M., Wu, T.Y., Juan, J.C., 2014. A review of sustainable hydrogen production using seed sludge via dark fermentation. Renew. Sustain. Energy Rev. 34, 471e482. https://doi.org/ 10.1016/j.rser.2014.03.008. Wu, J.N., Ein-Mozaffari, F., Upreti, S., 2013. Effect of ozone pretreatment on hydrogen production from barley straw. Bioresour. Technol. 144, 344e349. https://doi.org/10.1016/j.biortech.2013.07.001. Yokoi, H., Aratake, T., Hirose, J., et al., 2001. Simultaneous production of hydrogen and bioflocculant by Enterobacter sp. BY-29. World J. Microb. Biot. 17, 609e613. https://doi.org/ 10.1023/A:1012463508364. Yokoyama, H., Waki, M., Moriya, N., Yasuda, T., Tanaka, Y., Haga, K., 2007. Effect of fermentation temperature on hydrogen production from cow waste slurry by using anaerobic microflora within the slurry. Appl. Microbiol. Biotechnol. 74, 474e483. https://doi.org/ 10.1007/s00253-006-0647-4. Yu, H., Zhua, Z., Hu, W., Zhang, H., 2002. Hydrogen production from rice winery wastewater in an upflow anaerobic reactor by using mixed anaerobic cultures. Int. J. Hydrogen Energy 27, 1359e1365. https://doi.org/10.1016/S0360-3199(02)000733. Zhu, G.F., et al., 2013. Simultaneous production of bio-hydrogen and methane from soybean protein processing wastewater treatment using anaerobic baffled reactor (ABR). Desalination Water Treat. 53, 2675e2685. https://doi.org/10.1080/19443994.2013.868836.

Chapter 3

Waste to biohydrogen: progress, challenges, and prospects Quanguo Zhang Key Laboratory of New Materials and Facilities for Rural Renewable Energy of Ministry of Agriculture and Rural Affairs, College of Mechanical and Electrical Engineering, Henan Agricultural University, Zhengzhou, Henan Province, China

3.1 Introduction In activities of production, people produce some organic articles or substances that have lost their original use or value or have not lost those but have been abandoned. These articles or substances are called organic waste, including agricultural organic waste (mainly including crop straw and vines, livestock and poultry manure, aquatic waste, etc.), industrial organic waste (mainly including high-concentration organic waste water, organic waste residue, etc.), and municipal organic waste (mainly including garden waste, municipal sludge, the animal contents of slaughterhouses, kitchen waste, etc.) (Dhanya et al., 2020). Organic waste contains a large number of hydrocarboncontaining organic substances, regarded as a potential resource rather than a pollution waste (Srivastava et al., 2020). It is a new concept of resource and ecological harmony. Compared with conventional incineration and other treatment methods, it can be used as raw materials to produce new renewable energy, which has the advantages of a clean process and recycling of hydrocarbon resources (Wainaina et al., 2020). Hydrogen produced by biomass gasification and microbial catalytic dehydrogenation is called biohydrogen; it is an important way to obtain hydrogen from nature (Rajesh Banu et al., 2020). Hydrogen production from biomass is a low-energy consuming, economic and promising method of hydrogen production (da Silva Veras et al., 2017; Kataoka et al., 1997). Main methods of biohydrogen production involve photosynthetic bacteria using organic waste to produce hydrogen, algae and cyanobacteria photolyzing water to produce hydrogen, and anaerobic fermentation bacteria using organic waste to produce hydrogen (Hallenbeck and Benemann, 2002; Show et al, 2011, 2012). However, the incompleteness Waste to Renewable Biohydrogen. https://doi.org/10.1016/B978-0-12-821659-0.00002-2 Copyright © 2021 Elsevier Inc. All rights reserved.

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of substrate conversion and the instability of biohydrogen production have been main obstacles in the practical application of biohydrogen technology. In recent years, some methods have been put forward to overcome these shortcomings, such as screening strains that can produce hydrogen efficiently and designing reactors with high efficiency and energy savings (Boodhun et al., 2017; Guo et al., 2010; Jung et al., 2011). Fermentative bacteria can produce hydrogen gas continuously in anaerobic wastewater treatment (Kumar et al., 2017; Tao et al., 2007). In addition to hydrogen, these bacteria can produce some by-products to meet their metabolic needs and further growth. These by-products include organic acids, alcohol, and acetone, which can be converted into electrical energy, biodegradable plastics, and fibers (Hallenbeck, 2005; Khan et al., 2016). Therefore, hydrogen production by fermentation seems to be more feasible, and significant progress is being made in practical applications (Das and Veziroglu, 2008; Hawkes et al., 2007; Kraemer and Bagley, 2007). Conventionally, continuous biohydrogen production reactors have been widely used in the biohydrogen production of fermentation bacteria, including dark fermentation, light fermentation, and darkelight combined hydrogen production (Bartacek et al., 2010; Davila-Vazquez et al., 2008; Gomes et al., 2015; Venkata Mohan and Prathima Devi, 2012). Characteristics of reactors for hydrogen production by dark fermentation are their simple structure, convenient operation, and even mixing, so that the reactors can be operated under the changing conditions of substrate, pH value, and hydraulic retention time (Kapdan and Kargi, 2006; Wang and Wan, 2009). A reactor for hydrogen production by photofermentation needs to provide light to meet the growth and metabolism of photofermenting bacteria. The design and operation of the reactor are a little more complicated. How to use natural light reasonably is also an important factor of this reactor (Lu et al., 2016; Zhang et al., 2017). In addition, the darkelight combined hydrogen production reactor needs to couple two ways of fermentation for hydrogen production to obtain the best hydrogen production effect, which still needs further research (Chen et al., 2008; Redwood and Macaskie, 2006).

3.2 Progress of waste to biohydrogen 3.2.1 Development of waste pretreatment technology To convert waste into biohydrogen, a series of pretreatment is needed, and the pretreatment methods for different kinds of waste are also different. The pretreatment methods are mainly divided into three kinds: physical, chemical, and biological. (1) The physical method includes the mechanical method, steam explosion method, cooking method, microwave method, freezing method, and so forth. The mechanical method includes grinding, extraction, and so on. The main purposes of physical pretreatment are to reduce the particle

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size of the material, increase the specific surface area, and then improve the accessibility of subsequent treatment. Generally, the pretreatment effect is better when combined with other chemical methods. Steam blasting is a widely used physical pretreatment method. Li et al. studied the effect of heat pretreatment (55e160
C) on the anaerobic fermentation degradation characteristics of medium-temperature kitchen waste (Li and Jin, 2015). The results showed that heat pretreatment could strengthen the two-phase anaerobic digestion of kitchen waste, and the best temperature of heat pretreatment was 90e120
C. (2) The chemical method mainly includes acid pretreatment, alkali pretreatment, organic solvent pretreatment, and oxidant and other catalyst pretreatment. The main function of chemical pretreatment is to degrade unusable organic components in the materials. According to the different components of the materials, a variety of chemical pretreatment can be used selectively for a better treatment effect. Banerji et al. studied the degradation effect of dilute acid treatment on sweet sorghum bagasse (Banerji et al., 2013). The results showed that sweet sorghum bagasse after dilute acid treatment had higher reducing sugar release and less inhibiting compounds. (3) The biological method refers to the use of microorganisms and their metabolized enzymes to decompose materials. It has a role in removing stubborn and useless organics, reducing the degree of polymerization, and then obtaining the final product. This kind of microorganism mainly includes white rot fungus, brown rot fungus, and soft rot fungus. Zhao et al. used white rot fungus and Phanerochaete chrysosporium to improve the enzymatic saccharification and hydrogen production of corn straw (Zhao et al., 2012).

3.2.2 Progress in hydrogen production technology Biohydrogen production technology is the process of catalyzing hydrogen production by microorganisms through light energy or fermentation and taking organic compounds in nature as substrate at normal temperature and in a normal-pressure aqueous solution. Compared with conventional hydrogen production methods such as the chemical or electrochemical method, which need a high-temperature or pressure environment, it has the following characteristics: (1) The reaction conditions are mild. Hydrogen production is derived from the metabolism of hydrogen-producing microorganisms, which do not need to provide high temperature and pressure. It can be carried out in a near-neutral environment, with low energy consumption. It is suitable for establishing small-scale hydrogen production workshops in areas rich in biomass or waste resources. The savings in transportation links reduce the cost of hydrogen production to a certain extent. (2) A variety of renewable

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carbohydrates can be used as substrates for hydrogen production, such as various types of industrial and agricultural waste and organic wastewater, which can effectively combine energy output, waste reuse, and pollution control, and reduce the cost of hydrogen production while realizing the use of waste resources. The use and development of agricultural and forestry waste biomass resources and energy crops can significantly improve the output of bioenergy. (3) There are various hydrogen production processes, including direct and indirect photolysis of water by green algae and cyanobacteria, hydrogen production by the fermentation of organic matter in the dark environment of anaerobic bacteria, and hydrogen production by the metabolism of organic matter by photosynthetic bacteria under light. There are three kinds of biohydrogen production technology: photosynthetic biohydrogen production, anaerobic dark fermentation for biohydrogen production, and light and dark fermentation combined for hydrogen production. (1) Photosynthetic hydrogen production Under anaerobic conditions, cyanobacteria and green algae decompose water through photosynthesis to produce hydrogen and oxygen, which is a way for photosynthetic organisms to produce hydrogen. In this photosynthetic system, there are two independent but coordinated photosynthetic centers: photosystem II (PS II), which receives solar energy to decompose water to generate Hþ, electrons, and O2, and photosystem I (PS I), which generates a reductant to fix CO2.The electrons produced by PS II are carried by ferriredox protein through PS II and PS I to hydrogenase, and Hþ forms H2 under certain conditions under the catalysis of hydrogenase (Ramachandran and Menon, 1998). Hydrogenase is the key factor of hydrogen production in all organisms. Green plants cannot produce hydrogen because they do not have hydrogenase, which is an important difference between algae and green plants in the process of photosynthesis. Therefore, in addition to the formation of hydrogen, the photosynthetic law and research conclusions regarding green plants can be used to analyze the algae metabolism process. Benemann studied the mixed hydrogen production pathway of green algae. Green algae were cultured in an open pond to store carbohydrates (biomass of green algae) in CO2, and then the cultured green algae were transferred into a dark and airtight anaerobic fermentation vessel for hydrogen production (Benemann et al., 1973). Belkin et al. isolated Chromatium sp. Miami pbs1071 and found that it is the fastest marine photosynthetic microalgae they had ever seen, with a doubling time of only 1.75 h. The study found that it could not use carbohydrates, but it could use a variety of other carbon and nitrogen sources for growth and reproduction (Belkin and Padan, 1978). Sasikala et al. studied the growth stage of Rhodobacter sphaeroides O.U.001, the pH value of hydrogen production matrix, and the relationship between glutamic acid content and the hydrogen production rate. The results showed that the static stage of bacterial growth was favorable for hydrogen production, and the pH value and glutamic acid content had a

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great influence on the hydrogen production rate and hydrogen production (Sasikala et al., 1995). At the same time, the researchers studied the relationships among light intensity, cell growth rate, and hydrogen production. The results showed that the growth and hydrogen production of cells were not inhibited by high light intensity, which was different from that of green algae. Many studies showed that the main obstacle to continuous hydrogen production is the simultaneous production of H2 and O2 by algae. Hydrogenproducing enzymes are extremely sensitive to oxygen, while the activity of hydrogen absorbing enzymes is not affected by O2. Gaffron et al. found that green algae may have higher hydrogen production efficiency than cyanobacteria, because the nitrogen enzymes of cyanobacteria need the participation of energy carrier adenosine triphosphate to work (Gaffron and Rubin, 1942). There are many advantages in producing hydrogen from photodegradation water: only water is the raw material, the solar energy conversion efficiency is about 10 times higher than trees and crops, there are two photosynthetic systems, and so on, but there are also many disadvantages, such as the inability to use organic matter, the inability to use organic waste, the need for light, the need to overcome the inhibition effect of oxygen, the low efficiency of light conversion, the maximum theoretical conversion efficiency of 10%, and the complex photosynthetic system. The free energy needed to be overcome for hydrogen production is higher, which affects the development of photolysis water biohydrogen production technology. The production of hydrogen by photosynthetic bacteria is the production of hydrogen through the decomposition of organic matter by photosynthetic microorganisms under certain light conditions. It is generally believed that the production of hydrogen by photosynthetic bacteria has a bright future. According to the estimate of the US Solar Energy Research Center, if the conversion rate of light energy can reach 10%, it can compete with other energy sources. Compared with other biohydrogen production technologies, photosynthetic hydrogen production contains only photosynthetic pigment system I, and does not produce O2. It has a simple technology and can use solar energy. The energy use rate is high and the theoretical efficiency of light conversion can reach 100%. The earliest report on the production of hydrogen by photosynthesis began with the phenomenon of PSB (Photosynthetic Bacteria) releasing hydrogen in the dark, observed by Nakamura in 1937 (Weaver et al., 1980). In 1949, Gest and Kamen reported the hydrogen production of Rhodospirillum under light conditions, and also found the photosynthetic nitrogen fixation of Rhodospirillum (Gest and Kamen, 1949). However, because of the limitation of light conversion efficiency and hydrogen production pathway, no further research has been carried out. In 1973, the energy crisis in the United States led to the application of biohydrogen production. Research in photosynthetic hydrogen production at home and abroad includes hydrogen production mechanisms, hydrogen production process conditions, hydrogen production bacteria, the hydrogen production process, hydrogen production

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enzyme, and light conversion efficiency and reactors. Singh et al. screened photosynthetic bacteria producing hydrogen at high temperature. Four strains of photosynthetic bacteria were isolated from three kinds of aquatic plants (Singh and Srivastava, 1991). According to cell morphology and staining analysis, they were identified as Rhodopseudomonas sp. and recorded as BH1e4, respectively. The results showed that BH1 and BH4 strains had good hydrogen production effects under high temperature in equatorial India. The State Key Laboratory of Microbial Technology of Shandong University also carried out a series of research on photosynthetic bacteria of hydrogen production (Su and Chun, 2002). Acetic acid, the main degradation product of organic wastewater, was selected as the only hydrogen donor. Under the conditions of a natural ecological environment, purple nonsulfur bacteria culture medium, purple sulfur bacteria culture medium, and green sulfur bacteria culture medium were used to screen photosynthetic bacteria of hydrogen production from different water environments. Starting from factors affecting the solar energy conversion efficiency, the morphological characteristics of 15 strains of photosynthetic bacteria were studied, focusing on determining the optimum growth temperature, photosynthetic pigment composition, use of sulfide, and salt tolerance. Minnan Long et al. of Xiamen University studied the physical and chemical properties and primary structure of soluble hydrogenase of photosynthetic bacteria (Long et al., 2007). Shuhua Ma and Xiaodong Zhang of the Institute of Chemistry of the Chinese Academy of Sciences studied the mechanism, structure, and relationship between the structure and function of electron transfer of the photosynthetic reaction center of Rhodopseudomonas (Zhang et al., 2000). (2) Hydrogen production by anaerobic dark fermentation Anaerobic dark fermentation produces hydrogen by degrading organic matter by anaerobic microorganisms under dark conditions. Under the action of nitrilase or hydrogenase, many anaerobic microorganisms can decompose a variety of substrates to obtain hydrogen. These substrates include: formic acid, pyruvic acid, Co, various short chain fatty acids and other organic compounds, sulfides, starch cellulose, and other sugars. These substances exist widely in high-concentration organic wastewater and human and animal excrement in industrial and agricultural production. Using this waste to produce hydrogen not only obtains energy, it also protects the environment. The conversion efficiency of anaerobic microorganisms to organic matter in wastewater is still low. Scientists have studied the process of hydrogen production by the anaerobic fermentation of organics, and have done more work in strain selection, acclimation, and reactor structures. Bagai et al. studied the effect of nitrogen sources on hydrogen production when three strains of anaerobic fermentation bacteria were continuously mixed for hydrogen production (Bagai and Madamwar, 1998). The intermittent addition of a nitrogen source to the hydrogen producing matrix was the necessary condition to ensure cell

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activity, and the regular addition of a nitrogen source prolonged hydrogen production. Singh et al. fixed Rhodobacter sphaeroides with agar and used hydrogen from the waste aquatic products of a tofu processing factory (Singh et al., 1994). The maximum hydrogen production rate was 2.1 L/h min. Singh et al. screened photosynthetic bacteria with a high temperature for hydrogen production (Singh and Srivastava, 1991). Tanisho et al. studied the process conditions of hydrogen production by Enterobacter aerogenes. The constant discharge of CO2 in the liquid phase promoted hydrogen production, and the pH value of hydrogen production matrix had a significant impact on hydrogen production. When the pH value was 7, the bacteria grew fastest (Tanisho et al., 1987). Kumar et al. conducted a hydrogen production experiment by fixing Enterobacter cloacae with sawdust (Kumar and Das, 2001). When the dilution rate was 0.93/h, the hydrogen production rate was 44 mmol/h. Sasikala et al. studied the hydrogen production of Rhodococcus using the wastewater from a lactic acid fermentation plant (Sasikala et al., 1991). The results showed that the wastewater from the lactic acid fermentation plant was a good substrate for hydrogen production. Rousset et al. found that hydrogen was produced when Plectonema boryanum was transferred from a nitrogen-containing aerobic medium to microoxygen or an anaerobic nitrogen-free medium (Rousset et al., 1998). Banerjee et al. showed that the mixed nitrogen source of NH4Cl and KNO3 could promote the hydrogen production of Azolla anabaena (Banerjee et al., 1989). The Harbin Institute of Technology carried out research on anaerobic hydrogen production technology (Ren et al, 2006, 2011). With organic wastewater as a raw material, hydrogen was produced by acid production and the fermentation of an acclimated anaerobic microbial community. A comprehensive process integrating biohydrogen production and high-concentration organic wastewater treatment was formed, and stage research results were obtained. The results showed that it was feasible to produce hydrogen from organic wastewater by anaerobic fermentation using the acid-producing phase of a two-phase anaerobic treatment process. Anaerobic dark fermentation for hydrogen production combines the biohydrogen production process with the treatment of high-concentration organic wastewater, which can effectively treat organic wastewater and recover a large amount of hydrogen, with good economic and environmental benefits. Although anaerobic bacteria can decompose sugars to produce hydrogen and organic acids, the decomposition of substrate is incomplete, and the organic acids cannot be decomposed further to produce hydrogen, so the hydrogen yield is low. (3) Hydrogen production by light and dark fermentation The technology of combined light and dark fermentation hydrogen production has many advantages over one method alone. This technology includes the combined production of hydrogen by photosynthetic organisms and dark fermentation organisms, the two-stage combined production of hydrogen by

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dark and light fermentation, and the multistage combined production of hydrogen. The combination of the two fermentation methods can increase hydrogen production. Hydrogen production by photosynthetic and dark fermenting organisms is a technology that combines photosynthetic organisms such as algae, cyanobacteria, photosynthetic bacteria, and dark fermenting bacteria. Its chemical equation is: C6H12O6 þ 6H2O / 12H2 þ 6CO2. This technology can improve the conversion efficiency of light energy and the use efficiency of substrate as well as reduce the toxicity of volatile fatty acids to bacteria, so as to increase hydrogen production, and it is possible to achieve the complete degradation of organic matter and sustained and efficient hydrogen production. However, growth, the optimal pH value of hydrogen production, and the demand for light of the two kinds of bacteria in the combined hydrogen production technology are different, which limits the development and application of the technology to a certain extent. The two-stage combined biohydrogen production technology of dark and light fermentation is a biohydrogen production technology that couples dark and light fermentation. The end products of dark fermentation are mostly small organic acids and alcohols such as acetic acid, ethanol, and butyric acid, which can be used by photosynthetic bacteria. The combination of the two fermentation methods can greatly improve the use efficiency of the substrate, increase hydrogen production, and realize the efficient degradation of organic matter. However, it is a difficult problem to select a light fermentation strain that can use the end products of the dark fermentation liquid phase, and it is also an important factor to restrict the cumulative hydrogen production of combined hydrogen production technology. Multistage combined hydrogen production technology is an attempt to realize large-scale industrial production; it is based on two-stage combined hydrogen production technology, adding the enzyme hydrolysis process to improve the application scope and use efficiency of substrate. The development of light and dark fermentation combined hydrogen production technology is a contentious and difficult point at home and abroad. It is a necessary stage of large-scale and continuous production and a key factor in promoting the development of biohydrogen production technology.

3.3 Challenges of waste to biohydrogen 3.3.1 Challenges of waste pretreatment technology Physical pretreatment is relatively simple, and the treatment effect of solid materials is obvious. However, the disadvantages are that it cannot degrade organic matter that cannot be used, and the treatment cost is relatively high. Although some pretreatment methods, such as microwave, gamma ray, and electron ray, can remove some resistant organics to a certain extent, they cause some available organics to be lost. Thus, the cost is greatly increased, the economy is poor, and the applications are limited.

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The chemical method is mainly used to treat materials through acid-based solution, ion solution, and other methods that can effectively remove some organic substances with strong resistance. However, after chemical treatment, the substrate needs to be separated from the solution or solvent before it can be used for microbial fermentation. To reduce environmental pollution, the waste liquid can be discharged only after the subsequent treatment, and chemical reagents such as concentrated acid have a strong corrosive effect on the reaction vessel. These processes will significantly increase the cost of pretreatment. Biological pretreatment has the advantages of low energy consumption, mild reaction conditions, environmental friendliness, and no inhibitors. However, the treatment process takes a long time, and the treatment effect is general. The selection and cultivation of microorganisms are also the key factors of biological pretreatment. These are the bottleneck of the developing this method.

3.3.2 Challenges of biohydrogen production technology Photosynthetic hydrogen production technology can use a variety of waste resources as the hydrogen production substrate, even the tail liquor of anaerobic dark fermentation for hydrogen production. In addition, almost all of the substrate can be transformed. However, the design and operation of the reactor for the production of hydrogen from photosynthetic organisms are complex, additional light sources are needed, and the photosynthetic conversion efficiency is not high. In addition, the screening and culture of photosynthetic bacteria have always been the focus in studies on hydrogen production by light fermentation. There is still no simple and effective separation and screening scheme for efficient hydrogen-producing bacteria in existing research. Most selected bacteria used in the research were existing bacteria, and the hydrogenproducing effect and mechanism under different substrate environment were studied. In fact, research on the bacterial separation and screening program has a decisive role in hydrogen production, so research in this area is particularly critical. The hydrogen production technology of anaerobic dark fermentation can use a variety of waste resources as the hydrogen production substrate, generally using mixed flora. The reactor is simple and easy to operate, and it does not need sterilization or other treatment. Using the immobilized mixed culture technology, high hydrogen production can be obtained. Although anaerobic activated sludge is rich in microbial colonies, if anaerobic activated sludge is used as a bacterial strain for hydrogen production, the material is complex as is the microbial environment. Simple and effective measures should be taken to treat the sludge so that the bacteria can be quickly separated and screened and the methanogenic bacteria in the activated sludge can be killed. In this way, hydrogen-producing bacteria can continue to survive and

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enter the stage of growth and metabolism, and generate hydrogen continuously in the dark fermentation system. Therefore, the study of effective sludge pretreatment measures is important, whereas existing sludge pretreatment measures are relatively simple and the screening effect of bacteria is not ideal. In addition, there are other shortcomings in the hydrogen production technology of anaerobic dark fermentation: there are many by-products that are not easy to separate, the chemical oxygen demand removal rate is low, and different types of reactors have large differences in hydrogen production performance. The combination of light and dark fermentation is recognized as the most potential hydrogen production technology to increase the efficiency of substrate use, increase hydrogen production, and use organic substrate deeply. The effective combination of the two methods has also become a hot topic. However, combine this hydrogen production technology, we need to remove the obstacle between the two independent hydrogen production technologies. The research is still limited, and it is still not simple and effective to combine the two fermentation hydrogen production technologies to achieve stable and sustainable hydrogen production. Three kinds of hydrogen production technologies have advantages and disadvantages. However, in addition to the stability and efficiency of hydrogen production, cost is also one of the most important factors restricting the development of hydrogen production technology. From the screening and cultivation of bacteria, to the design, construction, and maintenance of fermentation equipment, and to the maintenance and automatic control of fermentation conditions, these processes will increase the cost. How to do well in each step while controlling the cost is also a big problem that must be solved in the development of biohydrogen production technology.

3.4 Prospects of waste to biohydrogen The world’s energy demand is almost entirely dependent on carbon-containing fossil fuels such as oil, coal, and natural gas. These fossil fuels have been converted from plant biomass for millions of years. With the rapid development of the economy, fossil fuel resources are also consumed rapidly and petroleum resources will be exhausted over decades. Another persistent problem of fossil fuels is that greenhouse gases and other substances released after combustion are important causes of global warming and climate change. Compared with the existing energy sources, hydrogen energy has many advantages: it is renewable, there are no greenhouse gas emissions, it has a high energy density, it can be converted into electric energy through fuel cells, and it produces only water when it is burned. Therefore, as a kind of clean, efficient, renewable, and sustainable alternative energy, hydrogen energy is regarded as the most potential clean energy in the 21st century, which is the development direction of strategic energy for humans. There has been fierce

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competition among countries in the commercialization of hydrogen transport all over the world, such as in Iceland, China, Germany, Japan, and the United States. However, there are still many problems in large-scale application, and it remains necessary to carry out all-around research on hydrogen energy production technology in the future. The technology of hydrogen production by microorganisms has become a research focus in the world, and researchers have paid extensive attention to small-scale hydrogen production technology. Regarding research into the mechanisms of hydrogen production, it includes hydrogen binding and hydrogen-producing enzymes. In the research of catalysis technology, it includes photocatalysis, x-ray diffraction, and photosensitivity. For engineering application research, it includes raw materials and output. For experimental device research, it is mainly about materials (alloy and steel), mechanical efficiency, and other technical aspects. Small-scale hydrogen production is an ideal process for hydrogen production, which can be used directly and supplied to other places. The output of biohydrogen production depends not only on its own characteristics and production cost, but also on its integration with supporting energy facilities. There are still some difficulties in transforming the fossil fuelebased energy system to the biohydrogen-based energy system, and it is also difficult to realize it directly in the short term. To promote biohydrogen production in the near future, research should be carried out according to these aspects: (1) It is necessary to use waste or cheap raw materials widely or improve the process of hydrogen production. In the selection of raw materials for hydrogen production, it is necessary to ensure that the cost of raw materials collection or purchase is low and easy to handle. It is necessary to conduct more in-depth research on the pretreatment process of raw materials to reduce pollution and improve the organic matter extraction rate of raw materials. In the process of hydrogen production, the main parameters that affect the effect of hydrogen production need more in-depth study and optimization, and optimization of its control process to make it simple and effective. (2) It is necessary to improve the use ratio of microbial strains to various fermentation substrates continuously. As a laborer in the process of hydrogen production, the screening and cultivation of hydrogenproducing microorganisms have a direct impact on the hydrogen production effect. Further breeding is needed to obtain strains that can effectively use the substrate, to achieve the purpose of stable and efficient hydrogen production. (3) It is necessary to use a variety of mixed flora to use fermentation substrates better and also increase hydrogen production. On the basis of a single strain, a mixed strain with a high substrate use rate should be selected by a proportion study. We should study multistage fermentation technology, such as light and dark fermentation coupling hydrogen

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production technology, to take advantage of the synergy between strains, further realize the maximum use of substrate, and effectively improve hydrogen production. (4) The bioreactor should be continuously improved. Biohydrogen production needs to be carried out in the bioreactor, so the design of the bioreactor has an important role in the realization of industrial production of biohydrogen technology. To realize the industrial production of hydrogen production from biomass, the technology of continuous fermentation, immobilization of microorganism, parameter control in fermentation process, multistage fermentation coupling technology, tail liquid recovery technology, and intelligent control technology of the whole reactor need to be studied further. (5) The process of hydrogen production should be standardized. The formation and industrialization of the technology need a reasonable implementation standard to measure the effect of the transformation of biohydrogen production technology into achievements. Therefore, it is necessary to establish a reasonable technical index to evaluate the effect of biohydrogen production while developing biohydrogen production technology. It is necessary to establish corresponding standards for hydrogen production capacity, hydrogen production rate, tail liquid recycling efficiency, and other aspects of biohydrogen production, which is an essential step for transforming technology into achievements.

3.5 Perspective Hydrogen is one of the most ideal energy materials. Biohydrogen production technology can transform waste into hydrogen, and it is an important way to obtain hydrogen from nature. The technology of biohydrogen production is immature and needs to be studied further before large-scale application. Therefore, biohydrogen production has not yet been industrialized, and a large number of studies have reached only the pilot scale. On the basis of existing research, more in-depth research is needed on the high-efficiency pretreatment technology of waste, the screening of strains with a high hydrogen production rate, the rational design of a hydrogen production process, the development of a high-efficiency hydrogen production process, and the stability and continuity of biological hydrogen production.

References Bagai, R., Madamwar, D., 1998. Prolonged evolution of photohydrogen by intermittent supply of nitrogen using a combined system of Phormidium valderianum, Halobacterium halobium, and Escherichia coli. Int. J. Hydrog. Energy 23 (7), 545e550. https://doi.org/10.1016/s03603199(97)00107-9.

Waste to biohydrogen: progress, challenges, and prospects Chapter | 3

67

Banerjee, M., Kumar, A., Kumar, H.D., 1989. Factors regulating nitrogenase activity and hydrogen evolution in Azolla-anabaena symbiosis. Int. J. Hydrog. Energy 14 (12), 871e879. https:// doi.org/10.1016/0360-3199(89)90074-8. Banerji, A., Balakrishnan, M., Kishore, V.V.N., 2013. Low severity dilute-acid hydrolysis of sweet sorghum bagasse. Appl. Energy 104 (APR.), 197e206. https://doi.org/10.1016/ j.apenergy.2012.11.012. Bartacek, J., Zabranska, J., Lens, P.N.L., 2010. Developments and constraints in fermentative hydrogen production. Biofuels Bioprod. Biorefining 1 (3), 201e214. https://doi.org/10.1002/ bbb.17. Belkin, S., Padan, E., 1978. Hydrogen metabolism in the facultative anoxygenic cyanobacteria (blue-green algae) Oscillatoria limnetica and Aphanothece halophytica. Arch. Microbiol. 116 (1), 109e111. https://doi.org/10.1007/BF00408741. Benemann, J.R., Berenson, J.A., Kaplan, N.O., Kamen, M.D., 1973. Hydrogen evolution by a chloroplast-ferredoxin-hydrogenase system. Proc. Natl. Acad. Sci. U S A 70 (8), 2317e2320. https://doi.org/10.1073/pnas.70.8.2317. Boodhun, B.S.F., Mudhoo, A., Kumar, G., Kim, S.H., Lin, C.Y., 2017. Research perspectives on constraints, prospects and opportunities in biohydrogen production. Int. J. Hydrog. Energy 42 (45), 27471e27481. https://doi.org/10.1016/j.ijhydene.2017.04.077. Chen, C.Y., Yang, M.H., Yeh, K.L., Liu, C.H., Chang, J.S., 2008. Biohydrogen production using sequential two-stage dark and photo fermentation processes. Int. J. Hydrog. Energy 33 (18), 4755e4762. https://doi.org/10.1016/j.ijhydene.2008.06.055. da Silva Veras, T., Mozer, T.S., da Costa Rubim Messeder dos Santos, D., da Silva Ce´sar, A., 2017. Hydrogen: trends, production and characterization of the main process worldwide. Int. J. Hydrog. Energy 42 (4), 2018e2033. https://doi.org/10.1016/j.ijhydene.2016.08.219. Das, D., Veziroglu, T.N., 2008. Advances in biological hydrogen production processes. Int. J. Hydrog. Energy 33 (21), 6046e6057. https://doi.org/10.1016/j.ijhydene.2008.07.098. Davila-Vazquez, G., Arriaga, S., Alatriste-Mondrago´n, F., De Leo´n-Rodrı´guez, A., RosalesColunga, L.M., Razo-Flores, E., 2008. Fermentative biohydrogen production: trends and perspectives. Rev. Environ. Sci. Biotechnol. 7 (1), 27e45. https://doi.org/10.1007/s11157007-9122-7. Dhanya, B.S., Mishra, A., Chandel, A.K., et al., 2020. Development of sustainable approaches for converting the organic waste to bioenergy. Sci. Total Environ. 723, 138109. https://doi.org/ 10.1016/j.scitotenv.2020.138109. Gaffron, H., Rubin, J., 1942. Fermentative and photochemical production of hydrogen in algae. J. Gen. Physiol. 26 (2), 219e240. https://doi.org/10.1085/jgp.26.2.219. Gest, H., Kamen, M.D., 1949. Photoproduction of molecular hydrogen by Rhodospirillum rubrum. Science 109 (2840), 558e559. https://doi.org/10.1126/science.109.2840.558. Gomes, S.D., Fuess, L.T., Penteado, E.D., Lucas, S.D.M., Gotardo, J.T., Zaiat, M., 2015. The application of an innovative continuous multiple tube reactor as a strategy to control the specific organic loading rate for biohydrogen production by dark fermentation. Bioresour. Technol. 197, 201e207. https://doi.org/10.1016/j.biortech.2015.08.077. Guo, X.M., Trably, E., Latrille, E., Carrre, H., Steyer, J.P., 2010. Hydrogen production from agricultural waste by dark fermentation: a review. Int. J. Hydrog. Energy 35 (19), 10660e10673. https://doi.org/10.1016/j.ijhydene.2010.03.008. Hallenbeck, P.C., 2005. Fundamentals of the fermentative production of hydrogen. Water Sci. Technol. 52 (1e2), 21e29. https://doi.org/10.2166/wst.2005.0494.

68 Waste to Renewable Biohydrogen Hallenbeck, P.C., Benemann, J.R., 2002. Biological hydrogen production; Fundamentals and limiting processes. Int. J. Hydrog. Energy 27 (11e12), 1185e1193. https://doi.org/10.1016/ S0360-3199(02)00131-3. Hawkes, F.R., Hussy, I., Kyazze, G., Dinsdale, R., Hawkes, D.L., 2007. Continuous dark fermentative hydrogen production by mesophilic microflora: principles and progress. Int. J. Hydrog. Energy 32 (2), 172e184. https://doi.org/10.1016/j.ijhydene.2006.08.014. Jung, K.W., Kim, D.H., Kim, S.H., Shin, H.S., 2011. Bioreactor design for continuous dark fermentative hydrogen production. Bioresour. Technol. 102 (18), 8612e8620. https://doi.org/ 10.1016/j.biortech.2011.03.056. Kapdan, I.K., Kargi, F., 2006. Bio-hydrogen production from waste materials. Enzym. Microb. Technol. 38 (5), 569e582. https://doi.org/10.1016/j.enzmictec.2005.09.015. Kataoka, N., Miya, A., Kiriyama, K., 1997. Studies on hydrogen production by continuous culture system of hydrogen-producing anaerobic bacteria. Water Sci. Technol. 36 (6e7), 41e47. https://doi.org/10.1016/S0273-1223(97)00505-2. Khan, M.A., Ngo, H.H., Guo, W.S., Liu, Y.W., Zhou, J.L., Zhang, J., Liang, S., Ni, B.J., Zhang, X.B., Wang, J., 2016. Comparing the value of bioproducts from different stages of anaerobic membrane bioreactors. Bioresour. Technol. 816e825. https://doi.org/10.1016/ j.biortech.2016.05.013. Kraemer, J.T., Bagley, D.M., 2007. Improving the yield from fermentative hydrogen production. Biotechnol. Lett. 29 (5), 685e695. https://doi.org/10.1007/s10529-006-9299-9. Kumar, N., Das, D., 2001. Continuous hydrogen production by immobilized Enterobacter cloacae IIT-BT 08 using lignocellulosic materials as solid matrices. Enzym. Microb. Technol. 29 (4e5), 280e287. https://doi.org/10.1016/S0141-0229(01)00394-5. Kumar, G., Sivagurunathan, P., Sen, B., Mudhoo, A., Davila-Vazquez, G., Wang, G., Kim, S.H., 2017. Research and development perspectives of lignocellulose-based biohydrogen production. Int. Biodeterior. Biodegrad. 119, 225e238. https://doi.org/10.1016/j.ibiod.2016.10.030. Li, Y., Jin, Y., 2015. Effects of thermal pretreatment on acidification phase during two-phase batch anaerobic digestion of kitchen waste. Renew. Energy 77, 550e557. https://doi.org/10.1016/ j.renene.2014.12.056. Long, M., Liu, J., Chen, Z., Bleijlevens, B., Roseboom, W., Albracht, S.P.J., 2007. Characterization of a HoxEFUYH type of [NiFe] hydrogenase from Allochromatium vinosum and some EPR and IR properties of the hydrogenase module. J. Biol. Inorg. Chem. 12 (1), 62e78. https:// doi.org/10.1007/s00775-006-0162-1. Lu, C., Zhang, Z., Ge, X., Wang, Y., Zhou, X., You, X., Liu, H., Zhang, Q., 2016. Bio-hydrogen production from apple waste by photosynthetic bacteria HAU-M1. Int. J. Hydrog. Energy 41 (31), 13399e13407. https://doi.org/10.1016/j.ijhydene.2016.06.101. Rajesh Banu, J., Kavitha, S., Yukesh Kannah, R., Bhosale, R.R., Kumar, G., 2020. Industrial wastewater to biohydrogen: possibilities towards successful biorefinery route. Bioresour. Technol. 298, 122378. https://doi.org/10.1016/j.biortech.2019.122378. Ramachandran, R., Menon, R.K., 1998. An overview of industrial uses of hydrogen. Int. J. Hydrog. Energy 23 (7), 593e598. https://doi.org/10.1016/s0360-3199(97)00112-2. Redwood, M.D., Macaskie, L.E., 2006. A two-stage, two-organism process for biohydrogen from glucose. Int. J. Hydrog. Energy 31 (11), 1514e1521. https://doi.org/10.1016/ j.ijhydene.2006.06.018. Ren, N., Li, J., Li, B., Wang, Y., Liu, S., 2006. Biohydrogen production from molasses by anaerobic fermentation with a pilot-scale bioreactor system. Int. J. Hydrog. Energy 31 (15), 2147e2157. https://doi.org/10.1016/j.ijhydene.2006.02.011.

Waste to biohydrogen: progress, challenges, and prospects Chapter | 3

69

Ren, N., Guo, W., Liu, B., Cao, G., Ding, J., 2011. Biological hydrogen production by dark fermentation: challenges and prospects towards scaled-up production. Curr. Opin. Biotechnol. 22 (3), 365e370. https://doi.org/10.1016/j.copbio.2011.04.022. Rousset, M., Montet, Y., Guigliarelli, B., Forget, N., Asso, M., Bertrand, P., FontecillaCamps, J.C., Hatchikian, E.C., 1998. [3Fe-4S] to [4Fe-4S] cluster conversion in Desulfovibrio fructosovorans [NiFe] hydrogenase by site-directed mutagenesis. Proc. Natl. Acad. Sci. U S A 95, 11625e11630. https://doi.org/10.1073/pnas.95.20.11625. Sasikala, K., Ramana, C.V., Subrahmanyam, M., 1991. Photoproduction of hydrogen from wastewater of a lactic-acid fermentation plant by a purple nonsulfur photosynthetic bacterium, Rhodobacter sphaeroides O.U.001. Indian J. Exp. Biol. 29, 74e75. Sasikala, C.H., Ramana, C.H.V., Rao, P.R., 1995. Regulation of simultaneous hydrogen photoproduction during growth by pH and glutamate in Rhodobacter sphaeroides O.U. 001. Int. J. Hydrog. Energy 20 (2), 123e126. https://doi.org/10.1016/0360-3199(94)E0009-N. Show, K.Y., Lee, D.J., Chang, J.S., 2011. Bioreactor and process design for biohydrogen production. Bioresour. Technol. 102 (18), 8524e8533. https://doi.org/10.1016/j.biortech.2011.04.055. Show, K.Y., Lee, D.J., Tay, J.H., Lin, C.Y., Chang, J.S., 2012. Biohydrogen production: current perspectives and the way forward. Int. J. Hydrog. Energy 37 (20), 15616e15631. https:// doi.org/10.1016/j.ijhydene.2012.04.109. Singh, S.P., Srivastava, S.C., 1991. Isolation of non-sulphur photosynthetic bacterial strains efficient in hydrogen production at elevated temperatures. Int. J. Hydrog. Energy 16 (6), 403e405. https://doi.org/10.1016/0360-3199(91)90139-A. Singh, S.P., Srivastava, S.C., Pandey, K.D., 1994. Hydrogen production by Rhodopseudomonas at the expense of vegetable starch, sugarcane juice and whey. Int. J. Hydrogen Energy 19 (5), 437e440. https://doi.org/10.1016/0360-3199(94)90020-5. Srivastava, R.K., Shetti, N.P., Reddy, K.R., Aminabhavi, T.M., 2020. Sustainable energy from waste organic matters via efficient microbial processes. Sci. Total Environ. 722, 137927. https://doi.org/10.1016/j.scitotenv.2020.137927. Su, Y., Chun, Z., 2002. High effective screening of hydrogen e producing photosynthetic bacteria. J. Shangdong Univ. 37, 353e358. Tanisho, S., Suzuki, Y., Wakao, N., 1987. Fermentative hydrogen evolution by Enterobacter aerogenes strain E.82005. Int. J. Hydrogen Energy 12 (9), 623e627. https://doi.org/10.1016/ 0360-3199(87)90003-6. Tao, Y., Chen, Y., Wu, Y., He, Y., Zhou, Z., 2007. High hydrogen yield from a two-step process of dark- and photo-fermentation of sucrose. Int. J. Hydrog. Energy 32 (2), 200e206. https:// doi.org/10.1016/j.ijhydene.2006.06.034. Venkata Mohan, S., Prathima Devi, M., 2012. Fatty acid rich effluent from acidogenic biohydrogen reactor as substrate for lipid accumulation in heterotrophic microalgae with simultaneous treatment. Bioresour. Technol. 123, 627e635. https://doi.org/10.1016/j.biortech.2012.07.004. Wainaina, S., Awasthi, M.K., Sarsaiya, S., Chen, H., Singh, E., Kumar, A., Ravindran, B., Awasthi, S.K., Liu, T., Duan, Y., Kumar, S., Zhang, Z., Taherzadeh, M.J., 2020. Resource recovery and circular economy from organic solid waste using aerobic and anaerobic digestion technologies. Bioresour. Technol. 301, 122778. https://doi.org/10.1016/j.biortech.2020.122778. Wang, J., Wan, W., 2009. Factors influencing fermentative hydrogen production: a review. Int. J. Hydrogen Energy 34 (2), 799e811. https://doi.org/10.1016/j.ijhydene.2008.11.015. Weaver, P.F., Lien, S., Seibert, M., 1980. Photobiological production of hydrogen. Sol. Energy 24 (1), 3e45. https://doi.org/10.1016/0038-092X(80)90018-3.

70 Waste to Renewable Biohydrogen Zhang, X., Ma, S., Xu, H., 2000. The theoretical studies on the machanism of the primary electron transfer in the mutant photosynthetic reaction center. ACTA Chim. Sin. 58 (12), 1576e1581. Zhang, Z., Zhou, X., Hu, J., Zhang, T., Zhu, S., Zhang, Q., 2017. Photo-bioreactor structure and light-heat-mass transfer properties in photo-fermentative bio-hydrogen production system: a mini review. Int. J. Hydrog. Energy 42 (17), 12143e12152. https://doi.org/10.1016/ j.ijhydene.2017.03.111. Zhao, L., Cao, G.L., Wang, A.J., Ren, H.Y., Dong, D., Liu, Z.N., Guan, X.Y., Xu, C.J., Ren, N.Q., 2012. Fungal pretreatment of cornstalk with Phanerochaete chrysosporium for enhancing enzymatic saccharification and hydrogen production. Bioresour. Technol. 114, 365e369. https://doi.org/10.1016/j.biortech.2012.03.076.

Chapter 4

Comparisons of biohydrogen production technologies and processes Jianjun Hu Key Laboratory of New Materials and Facilities for Rural Renewable Energy of Ministry of Agriculture and Rural Affairs, College of Mechanical and Electrical Engineering, Henan Agricultural University, Zhengzhou, China

4.1 Introduction Energy is the driving force for the development of the global society. Fossil energy has made a tremendous contribution to the rapid development of industrialization in the world, but it has also caused a lot of problems such as environmental pollution, wasted resources, ecological destruction, and the crisis of human health. With the increase in the proportion of resource-based industries, the rapid development of social economy (Chung et al., 2014) and the increasing demand for energy, global climate change and environmental pollution have become increasingly serious (Forsberg, 2007). These phenomena alert scientists to research on renewable energy. Researchers are seeking a new energy source that does not depend on nonrenewable resources. Hydrogen energy is an ideal alternative energy source because it is the type of energy with the highest density among all known energy sources (Inagaki et al., 2007). It has strong compatibility, it is easy to realize energy conversion, and it will not cause environmental pollution and changes in the greenhouse effect. However, from the current fossil energy economy to a hydrogen energy economy, there are still many technical challenges in the production, storage, transmission, and use of hydrogen. Climate change and the depletion of fossil fuels are the main reasons leading to the development of hydrogen production technology (Lang et al., 2011; Ranke and Schodel, 2004). With the joint promotion of scientific and technological progress and ecological protection requirements, the global energy supply is changing toward cleaner, lower-carbon renewable energy (Ren et al., 2009). Among all kinds of renewable energy, hydrogen energy is considered to be the most promising because of its many advantages. Hydrogen fuel is a promising new Waste to Renewable Biohydrogen. https://doi.org/10.1016/B978-0-12-821659-0.00010-1 Copyright © 2021 Elsevier Inc. All rights reserved.

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energy source to replace traditional fossil fuels because it has the potential to eliminate all environmental problems caused by fossil fuels. As an energy carrier, hydrogen does not involve carbon in the transfer of chemical energy. It can greatly reduce carbon dioxide emissions and is significant in environmental protection (Karthic and Joseph, 2012). Petrochemical, fuel cell, and other industries have a large amount of hydrogen demand now, or they will. Hydrogen energy has been recognized as a promising future energy source owing to its reproducibility and because only water is produced after combustion. Hydrogen is the most abundant element in nature, and its properties are active, all in the form of compounds. Water covers 70% of the earth’s surface area, with a total volume of 1.37 billion cubic meters. Hydrogen accounts for one-ninth of the mass of water molecules, so it is said that the reserves of hydrogen energy on the earth are very large and can reach 1.4
1017 tons. Hydrogen energy has many advantages as an energy source: (1) It does not contain carbon, and the product after combustion is only water, which does not produce carbon dioxide and other greenhouse gases, and does not cause environmental pollution; (2) The calorific value of hydrogen is high; its calorific value can reach 122 kJ/g, which is three times that of gasoline and five times that of coal; (3) Hydrogen resources are abundant and can be obtained through various methods such as liquid petroleum gas reforming, electrolyzed water, and biological hydrogen production; (4) Hydrogen has many uses and can be widely employed in clinical medicine, the petrochemical industry, the electronics industry, food, aerospace, and so on; and (5) Hydrogen is easy to transport. Compared with traditional energy sources such as petroleum and coal, hydrogen can be stored and transported by liquefaction and solidification, and can be transported over long distances by means of pipelines, tanks, and so forth. However, hydrogen is a secondary energy source that cannot be directly separated in nature. To obtain hydrogen, it must be produced by the decomposition of other substances. Hydrogen can be produced in many ways, including electrolyzed water, the thermal catalytic reforming of fossil energy, and biological methods (Aasadnia and Mehrpooya, 2018). The industrial production of hydrogen mainly comes from the reforming of electrolyzed water and the steam reforming of methane. However, these methods not only need to consume a large amount of primary energy, they also cause serious environmental pollution, so there is an urgent need to find an efficient, clean, and low-cost hydrogen production method. In recent years, biological hydrogen production has become an emerging hydrogen production method that has gradually attracted people’s attention, mainly including direct biological decomposition hydrogen production, indirect biological decomposition hydrogen production, light fermentation hydrogen production, and dark

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fermentation hydrogen production. Biological hydrogen production can use industrial and agricultural waste and urban domestic sewage to produce clean hydrogen energy; thus, it has become the best way to alleviate environmental pollution and produce clean and renewable energy (Ghimire et al., 2015). Hydrogen production by the catalytic reforming of petroleum gas uses petroleum, coal, natural gas, and so forth as raw materials to produce H2, CO, CH4, and C2H4. This method is currently the most mature hydrogen production method, accounting for about 96% of the current hydrogen production ratio. The main problem with this method is that by-products such as ethylene and ethane are produced at high temperatures. These hydrocarbons can cause catalyst deactivation. The researchers found that the oxidation steam reforming method can be used to suppress the accumulation of hydrocarbons such as ethylene and ethane in the reforming process, and the stability of the catalyst can be improved by reacting the oxygen of the reactant with the hydrocarbon carbon. However, this method consumes a large amount of nonrenewable fossil energy and it needs to provide a high temperature of more than 1000 C during the hydrogen production process (Sousa et al., 2013). Electrolyzed water can directly separate water into hydrogen and oxygen, but this technology requires high energy consumption (50e60 kWh/kg H2). Scientists observed electrolytic water for the first time in 1789, and this technology was continuously improved and widely used. Hydrogen production from electrolyzed water mainly includes three types of hydrogen production: from alkaline electrolytic cells, from polymer film electrolysis cells, and from solid oxide electrolysis cells. The alkaline electrolyzer hydrogen production method has a long research time and mature technology, but its efficiency is lower than the other two methods of electrolyzed water (Ursua et al., 2012). In 1966, the hydrogen production method of the polymer film electrolyzer developed by General Electric Company used ion exchange technology. This electrolyzer does not require an electrolyte, only pure water, high safety, chemical stability, hard work, and high efficiency. The gas separation is good, but the use of high-cost precious metals such as platinum at the electrode makes it difficult to put it into industrial production (Rahim et al., 2016). The solid oxide electrolyzer hydrogen production method has been developed since 1972. It has high efficiency and the total efficiency can reach more than 90% using waste heat; moreover, the manufacturing cost is low. It is the current research hot spot of electrolytic water hydrogen production. Biological hydrogen production is the conversion of organic matter or water into hydrogen during its own metabolism by hydrogen-producing microorganisms through light or fermentation. Biological hydrogen production mainly includes four methods: dark fermentation hydrogen production, light fermentation hydrogen production, darkelight combined hydrogen production, and photolysis water production (Manish and Banerjee, 2008). Biological hydrogen production does not rely on traditional petroleum fossil energy and uses industrial and agricultural waste as hydrogen production substrates. As it

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eliminates waste, it produces clean renewable energy. Biological hydrogen production has the advantages of a wide range of available substrates, mild hydrogen production conditions, and a fast hydrogen production rate. At the same time, the problems of a high hydrogen production cost, low light energy conversion efficiency, and low substrate conversion rate still need to be resolved (Nikolaidis and Poullikkas, 2017). Researchers have invested a lot of work in selecting high-efficiency hydrogen-producing strains, designing highefficiency hydrogen-producing reactors, optimizing of hydrogen production processes, evolving mixed colonies, removing reaction inhibitors, and stabilizing continuous hydrogen production (AlZahrani and Dincer, 2017). Compared with the mature electrochemical hydrogen production method, biological hydrogen production has many advantages: (1) It does not rely on nonrenewable resources. Biological hydrogen production uses industrial and agricultural waste or organic wastewater as a substrate for hydrogen production. While it eliminates waste, it produces clean and renewable hydrogen energy. The development of large-scale biological hydrogen production will have a significant important role in promoting the development and use of industrial and agricultural waste resources and energy crops, and it will produce objective economic profits. (2) The reaction conditions for biological hydrogen production are mild. Biological hydrogen production is the use of organic matter by hydrogen-producing microorganisms to produce hydrogen gas during their own metabolism. The reaction process is safe, reliable, and stable. It is convenient to construct industrial hydrogen production devices of different scales according to the distribution of raw materials, turn waste into treasure on-site, and reduce the cost of hydrogen production. (3) Biohydrogen production methods are diverse. Biological hydrogen production mainly includes green algae and cyanobacteria that use light energy to produce hydrogen by the photolysis of water. Light fermentation bacteria degrade organic matter to produce hydrogen under the action of light energy, and dark fermentation bacteria degrade organic matter to produce hydrogen without relying on light sources. Because of the many characteristics of biological hydrogen production, this chapter mainly describes four biological hydrogen production methods, including the hydrogen production mechanism and their influential factors. Through an analysis and comparison of the advantages and disadvantages of the four types of hydrogen production technology, it describes the limitations of the biological hydrogen production methods at the emergence stage and the beautiful vision of biological hydrogen production technology (Kannah et al., 2019).

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4.2 Biological hydrogen production technology and process 4.2.1 Hydrogen production by photohydrolysis The hydrogen production route of green algae and cyanobacteria belongs to hydrogen production by photolysis water (Argun and Kargi, 2010a). Under anaerobic lighting conditions, water is produced by the decomposition of water through photosynthesis to produce hydrogen and oxygen, so it is usually called the hydrogen production route of photolysis water. The reaction mechanism of this process is similar to the photosynthesis mechanism of plants, but the hydrogen release process is quite different. Due to the low nutrients required for the growth of these two microorganisms, only air (carbon dioxide and nitrogen are used as carbon and nitrogen sources), water (electrons and protons), simple inorganic salts and light can directly pass through the photolysis of water to convert solar energy into hydrogen can (Cheng et al., 2019; Eker and Sarp, 2017; Guo et al., 2020). For many years, hydrogen production by photolysis has attracted people’s attention as a promising biological hydrogen production route (Hu et al., 2016).

4.2.1.1 Hydrogen production by green algae Chlorella is currently the only eukaryotic microbe found to produce oxygen through photosynthesis and to have a hydrogen production pathway (Happe et al., 2002). In 1939, Gafforn first reported that Scenedesmus obliquus in Chlorophyta can produce hydrogen during metabolism. In 1942, Gafforn and Rubin discovered that S. obliquus could absorb hydrogen and fix CO2 under anaerobic conditions while generating hydrogen under light conditions, but the duration was short. Since then, many studies have reported that green algae have hydrogen production characteristics, such as Chlamydomonas reinhardtii (Maione and Gibbs, 1986), Spirulina platensis (Llama et al., 1979), Chlorella fiscal, S. obliquus (Kessler, 1973), and Dunaliella salina. These green algae can use sunlight and water in the natural world to produce hydrogen. The hydrogenase activity in green algae is more than 100 times that of cyanobacteria and light-fermenting bacteria, and the solar energy conversion efficiency is about 10 times higher than that of crops and trees. Green algae hydrogen production does not require a large amount of adenosine triphosphate (ATP), and it produces hydrogen only under the catalysis of reversible hydrogenase (Kapdan et al., 2009; Kargi and Arikan, 2013). It has the characteristics of high catalytic efficiency and clean production. It can realize the self-collection of light energy, the spontaneous accumulation of energy, and directed rapid conversion (Kotkondawar et al., 2019).

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Green algae photolysis water produces hydrogen and oxygen. The reaction process is: 2H2 O þ Light energy/2H2 þ O2

(4.1)

Chlorella contains two photosynthetic systems, PSI and PSII, which are located on the thylakoid membrane. The role of PSI is mainly to generate a reducing agent to reduce CO2. The function of PSII is to cleave water and release oxygen. The hydrogen production mechanism of green algae is shown in Fig. 4.1. First, the light-harvesting pigment on the thylakoid membrane is used to absorb light energy. The absorbed light energy is quickly transferred to the reaction center of PSII (P680); then, the water is decomposed into Hþ and O2, releasing electrons. Oxygen enters the mitochondria through the chloroplast membrane and is consumed by mitochondrial respiration, while fixing CO2. Protons are pumped to the substrate by ATP synthase to ensure a proton gradient inside and outside the membrane. In order of increasing redox potential, electrons pass through a series of electron transport chains such as plastid quinone and cytochrome on the thylakoid membrane to the optical system PSI (P700) and sexual center (Florin et al., 2001). Under the catalysis of hydrogenase, protons in the matrix and electrons from the membrane combine to generate hydrogen gas; the hydrogen production process lasts only a few seconds to a few minutes (Naterer et al., 2015; Phanduang et al., 2019). The presence of oxygen molecules strongly inhibits the activity of hydrogenase. When the oxygen partial pressure reaches 2%, the hydrogenase will lose its vitality and affects the hydrogen production rate and hydrogen production efficiency (Ghirardi et al., 1997).The reason is that oxygen is close to [Fe] hydrogenase or [NiFe]. The catalytic site of the hydrogenase, which prevents hydrogen from binding to the H2 channel, resulting in inactivation of the

FIGURE 4.1 The mechanism of bio-hydrogen production by green algae. ATP, adenosine triphosphate; ADP, Adenosine Diphosphate; FNR, Ferredoxin -NADP Reductase; PQ, Plastoquinone; PS, photosynthetic system.

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hydrogenase. Many researchers are committed to increasing the tolerance of hydrogenase to oxygen through different methods to extend the hydrogen production time and increase hydrogen production.

4.2.1.2 Hydrogen production by cyanobacteria Cyanobacteria are a type of simple prokaryotic organism that can produce oxygen through photosynthesis. They have various forms such as single cells, filaments, and colonies. They are widely grown in fresh water, seawater, and soil in nature, and can survive in extreme environments such as hot springs, barren soil, salt lakes, weathered crusts or rock surfaces, and plant trunks. They are known as “pioneer creature”s. The nitrogen-fixing cyanobacteria Anabaena cylindrical B-629 with heteromorphic cells was used earlier for photosynthetic hydrogen-producing microorganisms (Pinto et al., 2002). The reaction process of cyanobacteria for the photolysis of water is: 12H2 O þ 6CO2 þ Light energy/C6 H12 O6 þ 6O2

(4.2)

C6 H12 O6 þ 12H2 O þ Light energy/12H2 þ 6CO2

(4.3)

Cyanobacteria used to research hydrogen release mainly include filamentous nonalien cyanobacteria, single-cell nonnitrogen-fixing cyanobacteria, marine cyanobacteria, and filamentous alien cyanobacteria (Sagnak and Kargi, 2011). Research on the hydrogen production of heterocytic cyanobacteria such as Nostoc and Anabaena is more in-depth. Hydrogenase-catalyzed and nitrogenase-catalyzed hydrogen production are two processes of hydrogen production by cyanobacteria, and hydrogen-absorbing enzymes, reversible hydrogenases (bidirectional hydrogenases), and nitrogenases are important enzymes in the process of hydrogen metabolism. Among them, nitrogenase catalyzes the release of hydrogen by nitrogen fixation; the generated hydrogen can be oxidized by the hydrogen-absorbing enzyme, whereas the reversible hydrogenase can both absorb and release hydrogen. Cyanobacteria conduct biological hydrogen production under the joint action of these three enzymes. The hydrogen release process of cyanobacteria is similar to that of green algae (Fig. 4.1). First, light energy is absorbed by the light-harvesting pigment on the thylakoid membrane; then, it is quickly transferred to the reaction center of PSII, decomposing water into Hþ and O2 and releasing electrons. At this time, mitochondria consume oxygen entering them through the chloroplast membrane by breathing and fix CO2. The high-energy electrons produced by PSII then enter the plastid quinone, pass through a series of electron transporters mainly composed of PSI and cytochrome complex on the thylakoid membrane, and then are transferred to ferredoxin (Fd), and further reduce NADPþ to generate NADPH. In the process of hydrogen production by green algae, electrons may not be transferred to NADPþ after being transferred to

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Fd, but are transferred to Hþ and reduced to H2. At the same time, protons in the thylakoid enter the matrix through the proton channel (CF0) (Su et al., 2010; Yang et al., 2015). Cyanobacteria include two types of cells: “vegetative cells” and “heterocysts.” Cyanobacteria nitrogen fixation produces hydrogen. Heteromorphous cyanobacteria produce hydrogen mainly through nitrogen fixation. They can be divided into vegetative cells and heteromorphic cells. Vegetative cells contain PSI and PSII, which can perform CO2 reduction and H2O photolysis, release O2, and produce reducing substances. The generated reducing substances can be transported to the heteromorphic cells through the thick-walled channels, which are used for nitrogen fixation and hydrogen production of the heteromorphic cells. Under nitrogen-deficient conditions, cyanobacteria filaments are alien cells, which are specialized cells formed by the thickening of common cells through cell walls. O2 can be effectively prevented from entering by the thickened cell wall, providing a local hypoxic or anaerobic environment for heteromorphic cells, which is conducive to hydrogen production. When normal vegetative cells are grown under anaerobic conditions, the nitrogenase system in the heteromorphic cells can produce nitrogenase and fix nitrogen. Alien cells do not have PSII and contain only PSI, so it is not possible to fix the photolysis of oxygen and CO2 in water; thus, the alien cells can be maintained in an anaerobic or anoxic environment. The energy of nitrogenase provides photosynthetic phosphorylation from heteromorphic cells to ensure the smooth progress of nitrogen fixation and hydrogen production. Under the combined action of heteromorphic cells and vegetative cells, most algae release hydrogen through nitrogen fixation catalysis, and release hydrogen and oxygen through photolysis of water, which is the process of nitrogen fixation and hydrogen release (Argun and Kargi, 2010a). Under the joint action of alien cells and vegetative cells, photolysis water releases H2 and O2, which is the process of nitrogen fixation and hydrogen release. The hydrogen production of single-cell cyanobacteria without alien cells is mainly catalyzed by nitrogenases (Hu et al., 2017). Most cyanobacteria without alien cells lose their protective ability against oxygen owing to the absence of alien cells and can release H2 only under alternating light and dark conditions. Under light conditions, cells fix CO2 to store polysaccharides and release O2; under dark anaerobic conditions, the stored polysaccharides are degraded to release electrons, making nitrogen fixation and hydrogen production smooth. At the same time, some cyanobacteria can also produce hydrogen under the catalysis of hydrogenase (Zou et al., 2018). For example, the nonshaped cytosolic nitrogen-fixing cyanobacteria, Oscillatoria limnetica, can use glycogen accumulated during daytime photosynthesis to hydrolyze to produce hydrogen under anaerobic light conditions.

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4.2.2 Hydrogen production by dark fermentation Dark fermentation biological hydrogen production is the use of anaerobic fermentation hydrogen-producing bacteria under anaerobic conditions through dark fermentation to decompose organic matter into hydrogen. This process does not require a light energy supply. The ethanol-type fermentation of fermentation hydrogen-producing bacteria mainly produces H2, which can be divided into facultative dark fermentation hydrogen-producing bacteria according to different electron acceptors (in the case of cytochrome as an electron donor, hydrogen is produced by methanol cracking, such as Escherichia coli (Argun and Onaran, 2016; Azwar et al., 2014), obligate dark fermentation hydrogen-producing bacteria (without a cytochrome-type electron donor, producing H2 through pyruvate-type two-carbon units or pyruvate, such as Clostridium butyrate) (Belokopytov et al., 2009) and special types of hydrogen-producing bacteria (the transition type of anaerobic and obligate anaerobic, metabolized to produce H2 without sulfur source, such as Vibrio desulfuricans) (Cai et al., 2018). Bacteria that can use organic wastewater for dark fermentation mainly include Bacillus, Clostridium butyricum, Lactobacillus, Enterobacter, and other obligate anaerobic bacteria, anaerobic bacteria and a small amount of aerobic bacteria. Table 4.1 lists fermentation hydrogen-producing bacteria reported at home and abroad (Chen et al., 2005; Karube et al., 1976; Kerby et al., 1995; Lee et al., 2008; Minnan et al., 2005; Oh et al., 2002; Wang et al., 2007).

4.2.2.1 Dark fermentation type Owing to the different species of bacteria, there are different ways to produce hydrogen by dark fermentation, and the final end product composition will also be different (Cheng et al., 2011). According to the composition of the terminal fermentation product, dark fermentation can be divided into three types: propionic acid, butyric acid, and ethanol. Common fermentation types of carbohydrates are shown in Table 4.2. 4.2.2.1.1 Hydrogen production by propionic acid type fermentation When using dark fermentation for wastewater treatment, nitrogen-containing organic compounds (such as meat extract, yeast extract, and gelatin) and hard-to-degrade carbohydrates (such as cellulose) often use propionic acidtype fermentation (Dipasquale et al., 2014). Propionic acidetype fermentation requires the joint action of ferredoxin oxidoreductase and ferredoxin hydrogenase. The end products of fermentation are acetic acid and propionic acid. The biggest feature is that there are fewer gas products. The reaction process is shown in Fig. 4.2.

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TABLE 4.1 Hydrogen-producing yield and rate of fermentative bacteria. Serial number

Hydrogen production ability (mol H2/mol [substrate])

Ethanoligenens harbinense

B.R3

2.43 mol/mol (glucose)

E. harbinense

B49

2.34 mol/mol (glucose)

Enterobacter aerogenes

E.82005

17 mmol H2/g dry cell h (sucrose)

Rhodopseudomonas palustris

P4

2.76 mol/mol (glucose)

Enterobacter cloacae

IIT-BT08

29.63 mmol H2/g dry cell h (sucrose)

Klebsiella oxytoca

HPI

1.0 mol/mol (glucose)

Clostridium thermocellum

YS

56.7 ml H2/g COD (cellulose)

Citrobacter sp.

Y19

2.49 mol/mol (glucose)

Citrobacter intermedius

Y19

9.5 mmol H2/g dry cell h

Citrobacter pasteurianum

DSM525

22.166 mlH2/g COD (glucose)

Citrobacter butyricum

CGS5

2.78 mol/mol (sucrose)

C. butyricum

LMG77-11

189.6 ml H2/g COD (glucose)

C. butyricum

IF013949

19 (glucose)

Enterobacter aerogenes

HU-101

0.5e0.65 (glucose)

E. aerogenes

HO-39

0.73 (glucose)

E. aerogenes

E.82005

2.2e3.5 (glucose)

Bacterial species

4.2.2.1.2 Hydrogen production by butyric acid fermentation The microorganisms that mainly produce hydrogen by butyric acid fermentation are Clostridia, including C. butyricum, Vibrio butyricum, and C. butyrate (Marone et al., 2017). Glucose, sucrose. and other soluble carbohydrates are the main substrates for butyric acidetype fermentation; the main fermentation end products are acetic acid, a small amount of propionic acid, butyric acid, carbon

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TABLE 4.2 Common types of carbohydrate fermentation. Fermentation type

Primary end product

Representative microorganism

Propionic acid fermentation

Acetic acid, propionic acid, fewer gas products

Propionic bacterium, Veillonella

Butyric acid fermentation

Acetic acid, butyric acid, hydrogen, carbon dioxide, acetic acid

Clostridium

Ethanol fermentation

Ethanol, acetic acid, hydrogen, carbon dioxide, butyric acid

Ethanol type B49

Mixed acid fermentation

Lactic acid, lactic acid, ethanol, formic acid, hydrogen, carbon dioxide

Escherichia, Proteus, Salmonella, Shigella

FIGURE 4.2 Route of propionic acid fermentation. EMP, glycolytic pathway.

dioxide, and hydrogen. The molar ratio of butyric acid to acetic acid at the end product of butyric acid fermentation is 2:1. The main reaction of butyric acid fermentation is: C6 H12 O6 þ 2H2 O/2CH3 CH2 COOH þ 2CO2 þ 4H2

(4.4)

C6 H12 O6 / CH3 CH2 COOH þ 2CO2 þ 2H2

(4.5)

4.2.2.1.3 Hydrogen production by ethanol fermentation The main end products of ethanol-type fermentation are ethanol, acetic acid, a small amount of butyric acid, carbon dioxide, and hydrogen (Menia et al., 2019). According to the analysis of its metabolic mechanism, ethanol-type fermentation microorganisms are the glycolysis of glucose-type carbohydrates to produce pyruvate, which is then converted into acetaldehyde under the joint action of ammonium pyrophosphate sulfate and pyruvate decarboxylase, emitting carbon dioxide. With hydrogen, acetaldehyde is finally degraded into ethanol under the action of alcohol dehydrogenase; its fermentation pathway is shown in Fig. 4.3.

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FIGURE 4.3 The route of ethanol fermentation.

4.2.2.2 Hydrogen production mechanism of dark fermentation There are two main hydrogen production pathways for dark fermentation hydrogen-producing microorganisms: the direct hydrogen production mechanism and the NADH/NADþ balance regulation mechanism for oxygen production. 4.2.2.2.1 Direct hydrogen production mechanism Microorganisms capable of producing molecular hydrogen all have hydrogenases. Research on hydrogenases in light-fermentation hydrogen-producing microorganisms have made great achievements, whereas studies on hydrogenases in dark fermentation microorganisms are relatively weak (Mishra et al., 2016). The production of molecular hydrogen is closely related to the electron carrier Fd in hydrogenase. Enterobacteria, Clostridium, and other fermentative hydrogen-producing microorganisms all contain 4Fe and 8Fe Fd. It is apparent that the hydrogen production process of bacteria fermentation is carried out in an environment containing iron. Fd is closely related to photosynthesis; it is ubiquitous in algae, bacteria, and higher plants and can be isolated from Pichia pastoris. However, in Clostridia, it acts as an electron donor for hydrogenase in the H2 release process and becomes an electron acceptor for pyruvate-Fd-oxidoreductase in the formation of acetyl CoA (Ozgur et al., 2010a). The direct hydrogen production process of hydrogen-producing bacteria can be divided into two ways, both of which occur in the process of pyruvate decarboxylation. The first is the formation of formic acid after the decarboxylation of pyruvate, after which formic acid is converted to CO2 and H2 to varying degrees. The second is pyruvate decarboxylation by pyruvate dehydrogenase that forms a thiamine pyrophosphateeenzyme complex. In this process, electrons are transferred to Fd, and the reduced Fd is the hydrogenase is reoxidized to produce H2. 4.2.2.2.2 NADþ/NADH balance regulates the mechanism of hydrogen production NADþ is oxidized codehydrogenase I; NADH is reduced codehydrogenase I, also known as nicotinamide adenine dinucleotide, which is produced by citric acid during bacterial respiration and the glycolysis cycle.

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The metabolic process of acid-producing and hydrogen-producing fermentation bacteria is based on substrate-level phosphorylation. Therefore, in the process of oxidative decomposition, organic matter is not oxidized by the electron transport system, but NADþ accepts hydrogen ions to form NADHþHþ. However, the number of NADþ in the acid-producing hydrogenproducing microbial cells is limited, so it must be completed by redox including other organic compounds produced by pyruvate, namely the dark fermentation process, as shown in Fig. 4.4. NADHþHþ produced by the glycolysis pathway of organic matter can be oxidized into NADþ by coupling with fermentation processes such as butyric acid, propionic acid, lactic acid, or ethanol, which ensures the amount of NADþ in the system, and thus the NADH/NADþ balance. The normal progress of the reaction will be affected by the accumulation of NADH/NADþ in the microorganism. The microbial organism will adopt some control mechanisms to this effect. Under the action of hydrogenase, the amount of NADþ is increased by releasing H2, so that the reaction can continue; or the output of the liquid phase ends such as butyric acid, propionic acid, lactic acid, and ethanol can be increased, to increase the content of NADþ or reduce the rate of glycolysis pathway through the feedback inhibition of NADHþHþ (Ren et al., 2011; Yang et al., 2010). The chemical equation for NADH/NADþ balance adjustment hydrogen production is: NADH þ Hþ /NADþ þ H2

(4.6)

þ

NADH/NAD is oxidized by the release of H2 under the action of hydrogenase. From the Gibbs free energy in this formula, it can be seen that the process of NADH/NADþ releasing H2 is greatly affected by the pH value. The decrease in value decreases, and it responds to energy consumption. Although

FIGURE 4.4 Fermentation hydrogen production pathways of carbohydrates by microorganisms.

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the process of NADH conversion to H2 cannot proceed spontaneously, under the action of NADH-Fd reductase, under special conditions with acetyl-CoA as an activator, the reaction can proceed (Zhang et al., 2020).

4.2.2.3 Influencing factors of hydrogen production by dark fermentation The amount of hydrogen produced in the process of dark fermentation hydrogen production, the activity of hydrogen-producing bacteria, the metabolic pathway and type, and the rate of hydrogen production will be affected by various tests and environmental factors, such as the concentration and selection of fermentation substrate and trace elements, strains, and dark fermentation conditions (Xia et al., 2015). 4.2.2.3.1 Strains The choice of dark fermentation hydrogen-producing bacteria will affect the hydrogen production efficiency and the choice of fermentation substrate (Sim et al., 2005; Sunjin et al., 2013). The harsh culture conditions of single microorganisms for hydrogen production and easily contaminated bacteria increase the difficulty of the actual test process and cause greater troubles; the use of animal manure compost or activated sludge reduces the cost of hydrogen production and avoids concerns about the contamination of pure bacteria. The conditions of the dark fermentation of mixed strains for hydrogen production are easy to operate and are not strict. Synergy between the strains makes it more promising for practical use, but some pretreatment measures are required. 4.2.2.3.2 Fermentation substrate The range of substrates that can be used by dark fermentation hydrogen production technology is wide, especially for various organic-rich sewage. It has a degree of sewage treatment and obtains clean hydrogen energy if it can achieve industrial production. Its application will bring good environmental and economic benefits. 4.2.2.3.3 Fermentation temperature Temperature is an important factor affecting the growth and reproduction of microorganisms. The enzymatic reaction of microbial metabolism requires a particular temperature range to proceed normally, which is also required for microbial growth. When the temperature is too high, the microbial population will accelerate the decline, which is not conducive to continued hydrogen production metabolism. When the temperature is low, microbial cell activity

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is reduced, growth and metabolic activity are not strong, the delay period of the fermentation process is long, and the hydrogen production cycle is also extended. 4.2.2.3.4 pH value The pH value of the fermentation broth mainly affects the metabolic pathway of hydrogen production by bacterial dark fermentation, the oxidationreduction potential, the hydrogen production type, bacterial enzyme activity (including nitrogenase and hydrogen production enzymes that are closely related to hydrogen production by dark fermentation), and the final substrate. The degree of use, for instance, is a key nonbiological factor for dark fermentation biological hydrogen production. 4.2.2.3.5 Inorganic nutrients Various inorganic elements required for the growth and metabolism of microorganisms are indispensable nutrients. These inorganic elements have a variety of physiological roles in the growth and metabolism of darkfermenting hydrogen-producing bacteria, such as promoting or suppressing enzyme activity, maintaining the stability of cell metabolism, and promoting cell growth.

4.2.3 Hydrogen production by light fermentation Hydrogen production by photosynthetic organisms refers to the process of small molecules of organic matter releasing hydrogen through the metabolism of photosynthetic bacteria under anaerobic light conditions (Argun and Kargi, 2010c). Research on the biological hydrogen production of photosynthetic bacteria began early in the past century. In 1931, Stephenson and others first confirmed that photosynthetic bacteria contain hydrogen-producing enzymes (hydrogenase). Hydrogenase can catalyze the production of hydrogen; the redox reaction is a reversible reaction. In 1937, Nakamura and others first reported the phenomenon of hydrogen production by photosynthetic bacteria in a dark anaerobic environment. In the middle of the past century, technology related to the cultivation and production of photosynthetic bacteria continued to develop. Since then, photosynthetic bacteria have been widely used in aquaculture and sewage treatment. Photosynthetic bacteria hydrogen production under light conditions was reported in 1949. Gest and Kamen first discovered that Rhodospirillum rubrum in photosynthetic bacteria can produce hydrogen gas under anaerobic light conditions. Photosynthesis was also found in experiments. The bacteria themselves have the function of biological nitrogen fixation, thus opening the door to research into microbial photosynthetic hydrogen production (Argun and Kargi, 2011). Since 2000, research into the production of hydrogen by photosynthetic bacteria has attracted increasing

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attention from researchers. This technology is widely regarded as one of the most feasible technologies to solve the future energy shortage (Argun et al., 2008).

4.2.3.1 Characteristics and classification of photosynthetic bacteria Like cyanobacteria, photosynthetic bacteria are relatively ancient microorganisms. They are widely distributed in various water bodies and environments in nature. They are prokaryotic microorganisms capable of anabolizing light energy. Photosynthetic bacteria are mostly distributed in the water environment; the suitable growth temperature is 15e40 C. Photosynthetic bacteria contain more than 60% of the cell’s dry matter in the cell body. The cell contains a variety of pigments, the vitamins are also rich, and biotin, folic acid, pantothenic acid, and other content are high. However, photosynthetic bacteria are different from algae. Photosynthetic bacterial cells contain only PSI, usually using organic matter or sulfide as hydrogen donors, by decomposing organic compounds for heterotrophic metabolism and growth and reproduction (Iniguez Monroy et al., 2013). Photosynthetic bacteria that can produce photosynthesis without generating oxygen in nature are mainly purple phototrophic bacteria. Violet photosynthetic bacteria contain a large amount of carotenoids and bacteriochlorophylls, which can carry out photosynthesis. Some purple photosynthetic bacteria use sulfate and sulfide as electron donors to grow in an autotrophic form (Jaapar et al., 2009). Violet photosynthetic bacteria contain different types of carotenoids, and their culture liquids have different colors such as red, purple, and yellowish brown. They are called purple sulfur bacteria. Another important branch of purple photosynthetic bacteria is classified as purple nonsulfur bacteria because they cannot metabolize sulfides to produce electron donors and cannot fix CO2 to form cells. Purple nonsulfur bacteria are diverse and varied photosynthetic bacteria that can grow in aerobic, anaerobic, illuminated, nonilluminated, and other environments; they rely on organic matter in the water body for heterotrophic growth (Mishra et al., 2016). 4.2.3.2 Hydrogen production mechanism by light fermentation Hydrogen production by photofermentation bacteria is the process of anaerobic electron transfer in the PS that provides energy for phosphorylation to produce ATP; organic matter provides a reducing power through degradation and is completed under the conditions of nitrogenase catalysis. Light-fermenting bacteria can use small-molecule end products fermented by organic waste such as from agriculture or restaurants, and some light-fermenting bacteria can also use large-molecule sugars as substrates (Ozmihci and Kargi, 2010a). Using the PS to absorb solar energy, the photofermentation bacteria completely

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oxidize the organic substrate into hydrogen and carbon dioxide. Therefore, the photofermentation hydrogen production capacity is close to the theoretical value. The mechanism of hydrogen production by light fermentation is shown in Fig. 4.5. Organic substrates are oxidized to carbon dioxide and biomass by light fermentation bacteria. The generated electrons are transferred to the PS through ubiquinone and activated by light energy in the PS. The electrons are repeatedly activated and generate a proton gradient through the circulation of the photosynthetic electron transfer chain. The ATP produced by the proton gradient is used to transfer electrons from the photosynthetic electron transport chain to Fd oxidoreductase. Then, hydrogen is generated by N2ase catalysis. Nitrogenase is a key enzyme that catalyzes the production of hydrogen by light fermentation. Nitrogenase is composed of two proteins: one contains iron, called ferritin, and the other contains iron and molybdenum, called molybdenum ferritin. Among them, ferritin is mainly used as an electron carrier to transfer electrons to molybdenum ferritin; molybdenum ferritin contains catalytic reaction sites, and the catalytic reaction proceeds. When molybdenum ferritin and ferritin exist at the same time, nitrogenase has the role of nitrogen fixation. Its important function is to reduce molecular nitrogen to ammonia (Eq. 4.7). In the absence of nitrogen, nitrogenase catalyzes the production of hydrogen, and there is no feedback suppression (Eq. 4.8) (Sagnak and Kargi, 2011). In this process, the consumption of ATP will not limit the progress of the reaction, because a single electron can be repeatedly activated through the photosynthetic electron transfer chain, maintaining the Hþ gradient, thereby maintaining ATP levels: N2 þ 8Hþ þ 8e þ 16ATP/2NH3 þ H2 þ 16ADP

(4.7)

8Hþ þ 8e þ 16ATP/4H2 þ 16ADP

(4.8)

FIGURE 4.5 Mechanism of H2 production by photofermentation bacteria. ADP, Adenosine Diphosphate; ATP, adenosine triphosphate; OR, oxidoreductase; PS, photosynthetic system; UQ, ubiquinone.

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Hydrogenase is another key enzyme that affects the hydrogen production process of photofermentative bacteria (Gogotov, 1986; Vignais et al., 1985). Basically, this kind of enzyme is found in all photofermentative bacteria. According to the structure or type of metal contained, hydrogenase can be divided into Fe hydrogenase, NiFe hydrogenase, NiFeSe hydrogenase, and hydrogenase with no metal. According to the different characteristics of hydrogenase catalytic reaction, it can be divided into hydrogenase catalyzing hydrogen absorption and hydrogenase catalyzing hydrogen production. The hydrogenase of photofermentation bacteria has no major role in the hydrogen production process. The roles of hydrogenase are to absorb hydrogen released by nitrogenase during nitrogen fixation or hydrogen production and recover energy consumed by hydrogen production. Both light-fixing bacteria nitrogen fixation and hydrogen production need to consume a large amount of ATP, and hydrogen absorption can recover and compensate some ATP as well as provide proton Hþ (Eq. 4.9), which reflects the process. When the substrate of photofermentation bacteria is exhausted, the absorption of hydrogen is mainly catalyzed by hydrogenase: 2Hþ þ 2e/H2

(4.9)

4.2.3.3 Influencing factors of hydrogen production by light fermentation Many factors affect the hydrogen production of light fermentation. In addition to the types of hydrogen-producing microorganisms and substrates (hydrogen donors), there are light, key enzymes related to hydrogen metabolism, bacterial age, inoculation concentration, carbon-to-nitrogen ratio, pH, and temperature. 4.2.3.3.1 Effect of light on hydrogen production by light fermentation Light is a necessary condition for hydrogen production by photofermentation. Light conversion efficiency is the ratio of the heat of combustion of photosynthetic bacteria to produce hydrogen and the light energy absorbed by photosynthetic bacteria. The properties of the light source, light intensity, light mode, and so on all affect the active light source properties of photofermentation hydrogen production on hydrogen production, mainly owing to the nature of photosynthetic hydrogen-producing microorganisms to absorb light of a specific wavelength. Compared with the absorption spectrum of photosynthetic bacteria, it can be seen from the solar spectrum that it generally uses sunlight only in the 400e950 nm band. Therefore, selecting a light source that matches the spectral characteristics of the photosynthetic hydrogenproducing microorganism can significantly improve the light conversion efficiency of the hydrogen production process.

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Another light factor affecting the hydrogen production performance of light fermentation is light intensity. With the increase in light intensity, the speed and amount of hydrogen produced by light fermentation will increase, but the light conversion efficiency will decrease. There may be two reasons for the reduction in light conversion efficiency: one may be that high light intensity increases nitrogenase activity and ATP energy levels, but when the light intensity exceeds the limit, the photosynthetic organs absorb more energy than is required for photosynthesis. This may cause excessive excitation of PSI, reducing photosynthetic efficiency and inhibiting hydrogen production. Second, it is possible that the light intensity also affects the absorption of substrates (such as hydrogen donors such as organic acids) by photosynthetic bacteria. The efficiency of photo-fermentation hydrogen production can be improved by adjusting different lighting methods. In addition, the use of increased lighting area, high-speed stirring technology, and research and development of photosynthetic reactors can all improve the utilization of light energy. Regulating environmental factors to improve the efficiency of light conversion is an important method, but from the analysis of hydrogen production mechanisms, transforming the photosynthetic mechanism is the fundamental way to solve this problem. The use of genetic engineering to transform photosynthetic mechanisms to improve photosynthetic bacteria photoconversion efficiency will become an important research direction for future biological hydrogen production (Barbosa et al., 2001; Basak and Das, 2007; Kim et al., 2004). 4.2.3.3.2 Effect of key enzymes on hydrogen production by light fermentation As mentioned, the main enzymes directly related to hydrogen production and hydrogen absorption by photosynthetic bacteria are nitrogenase and hydrogenase. Nitrogenase is a key enzyme for catalyzing photosynthetic hydrogen release. The level of nitrogenase activity is affected by O2, NHþ 4, nitrogen source concentration, and so forth, which directly affect photosynthetic hydrogen release activity. Three types of hydrogenases in photosynthetic bacteria have been identified: iron hydrogenase, nickel iron hydrogenase, and nickel iron selenase. Among them, iron hydrogenase mainly catalyzes hydrogen production, and nickel iron hydrogenase catalyzes hydrogen absorption. Photosynthetic bacteria are mainly hydrogen-absorbing enzymes, which are the opposite of the hydrogen-producing properties of nitrogenases. They use hydrogen to reduce carbon dioxide and other substances. When the activity of hydrogen-absorbing enzymes is limited, they can increase the hydrogen production of photosynthetic bacteria (Zhang et al., 2017).

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4.2.3.3.3 Other factors Like dark fermentation for hydrogen production, the performance of light fermentation for hydrogen production is affected by factors such as ambient temperature, pH, inoculum age, and inoculation volume. The optimal temperature range for photosynthetic bacteria growth and hydrogen production is 30e35 C and the optimal pH value for growth and hydrogen production is about 7.0 because the nutritional status of the bacteria is closely related to the composition of metabolic enzymes in the body and the age of the inoculum. The level of hydrogen release activity to photosynthesis. Generally speaking, the higher the biomass, the higher the amount of hydrogen produced. However, excess biomass will have a negative impact on hydrogen production.

4.2.4 Coupling hydrogen production technology of fermentation bacteria by darkelight method Lightedark coupled fermentation hydrogen production has the advantages and complementary synergy of anaerobic dark fermentation hydrogen-producing bacteria and light fermentation hydrogen-producing bacteria (Argun and Kargi, 2010b). The hydrogen production system composed of both is called lightedark fermentation coupled biological hydrogen production technology, including the darkelight fermentation bacteria two-step method and the mixed-culture hydrogen production method. Light fermentation and dark fermentation coupled hydrogen production technology have many advantages over using a single method of hydrogen production. Combining the two fermentation methods alternately complements each other and can increase the production of hydrogen (Argun and Kargi, 2010c).

4.2.4.1 Darkelight fermentation two-step biological hydrogen production Two-step fermentation is a hydrogen production technology that goes through dark fermentation and then light fermentation. This is a new method of hydrogen production. It has many advantages over hydrogen production using only one method, which can effectively increase the production of hydrogen. The fermentation broth after dark fermentation is rich in organic acids that can be used for light fermentation, which can eliminate the inhibitory effect of organic acids on hydrogen production by dark fermentation. Moreover, the use of organic acids by photosynthetic bacteria in light fermentation can reduce the chemical oxygen demand value of wastewater. The two bacteria have a role in their respective environments. The first step is the fermentation of dark fermentation bacteria to produce hydrogen, while producing a large amount of soluble small molecule organic metabolites; and the second step is the light fermentation bacteria, which rely on light energy to use these small molecules to metabolize H2 (Argun et al., 2009).

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When dark fermentation and light fermentation are combined to produce hydrogen, the theoretical maximum hydrogen production of 1 mol glucose is 12 mol H2. However, if the dark fermentation broth is directly used for light fermentation to produce hydrogen, there are some problems, such as a high ammonia nitrogen concentration and high volatile acid concentration., This will reduce the efficiency of hydrogen production by light fermentation, so before applying dark fermentation broth to hydrogen production by light fermentation, reasonable measures should be taken to keep the concentration of these two substances within a certain concentration range (generally TVFA [Total Volatile Fatty Acid] Fe2þ > Ni nanoparticles. The effects of more trace elements (Zn, Co, Cu, Mn, Al, B, Se, Mo, and W) on hydrogen production from fruit and vegetable waste were reported by Keskin et al. (2018). The result showed that adding trace elements improved the hydrogen yield by two- to threefold. The researchers also found that the optimum addition dose of the trace elements depended on the type of inoculum and substrate. Dark fermentative hydrogen production can be enhanced by the addition of a low concentration of sodium (Naþ); on the contrary, it would be inhibited when the concentration was more than 2g/L because a greater proportion of the ATP generated during dark fermentation was used by the hydrogen production bacteria of Clostridium butyricum for cell maintenance rather than for cell synthesis (Lee et al., 2012). Lin et al. (2016) evaluated the effect of adding ferric oxide nanoparticles (FONPs) to dark fermentative hydrogen production, the hydrogen yields were

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increased by 17.0%e63.1% with 200 mg/L FONPs added owing to the enhanced activities of hydrogenase and electron transfer of hydrogen production bacteria Enterobacter aerogenes. The presence of calcium peroxide (CaO2) in the dark fermentative hydrogen production system of WAS accelerated the breakage and death of sludge cells, improving the biodegradability of released substances, and providing more biodegradable organics for subsequent reactions. With the concentration of CaO2 increased from 0.05 to 0.25 g CaO2/g VSS, the highest hydrogen yield increased from 0.77 to 10.55 mL/g VSS. Although CaO2 inhibited all tested microorganisms, its inhibition of hydrogen-consuming bacteria was far greater than that for hydrolysis bacteria and hydrogen-producing bacteria (Wang et al., 2019b). In addition, metal elements such as sodium, potassium, calcium, magnesium, and iron released from biomass combustion ash provided a buffering capacity and inorganic nutrients for the function of hydrogen-forming bacteria. The addition of fly ash and bottom ash in the dark fermentation process of FW effectively enhanced hydrogen production (Alavi-Borazjani et al., 2019).

6.5 Use of dark fermentation tail liquid At the termination of the dark fermentative hydrogen production process, many soluble metabolites remained in the fermentation broth, such as acetic acid, butyric acid, and ethanol, which cannot be used by bacteria for further hydrogen production. These cause environmental pollution if discharged directly. There are operations to improve the efficiency of substrate use and obtain different products from the tail liquid. Approaches to using fermentation effluent include: (1) combined with photofermentative hydrogen production, because the small molecular acids produced during dark fermentation can be used by photosynthetic bacteria to produce hydrogen (Li et al., 2020); (2) combined with methane production, in which dark fermentation acts as a pretreatment step of two-stage hydrogen and methane production so that metabolites in the tail liquid can be used by methanogens to produce methane (Garritano et al., 2018); (3) combined with microbial electrochemical technology, which was realized by extracting protons and electrons from dark fermentation wastewater for hydrogen production in a microbial electrochemical cell (Jia et al., 2020); and (4) at the end of dark fermentative hydrogen production with duckweed and others as substrate; the small molecular acids, nitrogen, phosphorus, and other resources in the tail liquid can be used to culture algae for further lipid production (Mu et al., 2020).

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6.6 Perspectives The ultimate goal of hydrogen production is to realize industrial application. However, industrialization is still far off owing to the low hydrogen productivity and unstable operation conditions of bioreactors using dark fermentation from waste. Proper pretreatment methods, well-structured bioreactors, efficient anaerobic bacterial strains, reasonable operations, and scientific management are approaches to improving dark fermentative hydrogen production from waste.

References Abdeshahian, P., Al-Shorgani, N.K.N., Salih, N.K.M., Shukor, H., Kadier, A., Hamid, A.A., Kalil, M.S., 2014. The production of biohydrogen by a novel strain Clostridium sp. YM1 in dark fermentation process. Int. J. Hydrogen Energy. https://doi.org/10.1016/ j.ijhydene.2014.05.081. Alavi-Borazjani, S.A., Capela, I., Tarelho, L.A.C., 2019. Dark fermentative hydrogen production from food waste: effect of biomass ash supplementation. Int. J. Hydrogen Energy. https:// doi.org/10.1016/j.ijhydene.2019.08.091. Alibardi, L., Cossu, R., 2016. Effects of carbohydrate, protein and lipid content of organic waste on hydrogen production and fermentation products. Waste Manag. https://doi.org/10.1016/ j.wasman.2015.07.049. Argun, H., Kargi, F., 2011. Bio-hydrogen production by different operational modes of dark and photo-fermentation: an overview. Int. J. Hydrogen Energy. https://doi.org/10.1016/ j.ijhydene.2011.03.116. Cakr, A., Ozmihci, S., Kargi, F., 2010. Comparison of bio-hydrogen production from hydrolyzed wheat starch by mesophilic and thermophilic dark fermentation. Int. J. Hydrogen Energy. https://doi.org/10.1016/j.ijhydene.2010.09.029. Cappelletti, B.M., Reginatto, V., Amante, E.R., Antoˆnio, R.V., 2011. Fermentative production of hydrogen from cassava processing wastewater by Clostridium acetobutylicum. Renew. Energy. https://doi.org/10.1016/j.renene.2011.05.015. Chen, J., Xu, W., Wu, X., E, J., Lu, N., Wang, T., Zuo, H., 2019. System development and environmental performance analysis of a pilot scale microbial electrolysis cell for hydrogen production using urban wastewater. Energy Convers. Manag. https://doi.org/10.1016/ j.enconman.2019.04.060. Chu, Y., Wei, Y., Yuan, X., Shi, X., 2011. Bioconversion of wheat stalk to hydrogen by dark fermentation: effect of different mixed microflora on hydrogen yield and cellulose solubilisation. Bioresour. Technol. https://doi.org/10.1016/j.biortech.2010.11.092. Cui, M., Shen, J., 2012. Effects of acid and alkaline pretreatments on the biohydrogen production from grass by anaerobic dark fermentation. Int. J. Hydrogen Energy. https://doi.org/10.1016/ j.ijhydene.2011.02.078. De Gioannis, G., Friargiu, M., Massi, E., Muntoni, A., Polettini, A., Pomi, R., Spiga, D., 2014. Biohydrogen production from dark fermentation of cheese whey: influence of pH. Int. J. Hydrogen Energy. https://doi.org/10.1016/j.ijhydene.2014.10.046. Garritano, A.N., Faber, M. de O., De Sa`, L.R.V., Ferreira-Leita˜o, V.S., 2018. Palm oil mill effluent (POME) as raw material for biohydrogen and methane production via dark fermentation. Renew. Sustain. Energy Rev. https://doi.org/10.1016/j.rser.2018.04.031.

Advances in dark fermentation Chapter | 6

135

Guo, X.M., Trably, E., Latrille, E., Carrre, H., Steyer, J.P., 2010. Hydrogen production from agricultural waste by dark fermentation: a review. Int. J. Hydrogen Energy. https://doi.org/ 10.1016/j.ijhydene.2010.03.008. Hay, J.X.W., Wu, T.Y., Juan, J.C., Jahim, J.Md., 2013. Biohydrogen production through photo fermentation or dark fermentation using waste as a substrate: overview, economics, and future prospects of hydrogen usage. Biofuels Bioprod. Biorefining. https://doi.org/10.1002/bbb.1403. Huang, J., Feng, H., Huang, L., Ying, X., Shen, D., Chen, T., Shen, X., Zhou, Y., Xu, Y., 2020. Continuous hydrogen production from food waste by anaerobic digestion (AD) coupled single-chamber microbial electrolysis cell (MEC) under negative pressure. Waste Manag. https://doi.org/10.1016/j.wasman.2019.12.015. Jia, X., Li, M., Zhu, J., Jiang, Y., Wang, Y., Wang, Y., 2019. Enhancement split-phase hydrogen production from food waste during dark fermentation: protein substances degradation and transformation during hydrothermal pre-treatments. Int. J. Hydrogen Energy. https://doi.org/ 10.1016/j.ijhydene.2018.12.199. Jia, X., Li, M., Wang, Y., Wu, Y., Zhu, L., Wang, X., Zhao, Y., 2020. Enhancement of hydrogen production and energy recovery through electro-fermentation from the dark fermentation effluent of food waste. Environ. Sci. Ecotechnol. https://doi.org/10.1016/j.ese.2019.100006. Jiang, D., Ge, X., Zhang, T., Liu, H., Zhang, Q., 2016. Photo-fermentative hydrogen production from enzymatic hydrolysate of corn stalk pith with a photosynthetic consortium. Int. J. Hydrogen Energy. https://doi.org/10.1016/j.ijhydene.2016.07.129. Kargi, F., Eren, N.S., Ozmihci, S., 2012. Bio-hydrogen production from cheese whey powder (CWP) solution: comparison of thermophilic and mesophilic dark fermentations. Int. J. Hydrogen Energy. https://doi.org/10.1016/j.ijhydene.2012.02.162. Keskin, T., Arslan, K., Nalakth Abubackar, H., Vural, C., Eroglu, D., Karaalp, D., Yanik, J., Ozdemir, G., Azbar, N., 2018. Determining the effect of trace elements on biohydrogen production from fruit and vegetable wastes. Int. J. Hydrogen Energy. https://doi.org/10.1016/ j.ijhydene.2018.01.028. Kim, D.H., Kim, S.H., Jung, K.W., Kim, M.S., Shin, H.S., 2011. Effect of initial pH independent of operational pH on hydrogen fermentation of food waste. Bioresour. Technol. https://doi.org/ 10.1016/j.biortech.2011.03.030. Lee, M.J., Kim, T.H., Min, B., Hwang, S.J., 2012. Sodium (Naþ) concentration effects on metabolic pathway and estimation of ATP use in dark fermentation hydrogen production through stoichiometric analysis. J. Environ. Manage. https://doi.org/10.1016/ j.jenvman.2012.04.027. Lee, D.J., Wang, Y., Zhang, Z., Lee, D.J., Zhou, X., Jing, Y., Jiang, D., Hu, J., He, C., 2017. Photofermentative hydrogen production from crop residue: a mini review. Bioresour. Technol. https://doi.org/10.1016/j.biortech.2017.01.008. Li, Z., Chen, Z., Ye, H., Wang, Y., Luo, W., Chang, J.S., Li, Q., He, N., 2018. Anaerobic codigestion of sewage sludge and food waste for hydrogen and VFA production with microbial community analysis. Waste Manag. https://doi.org/10.1016/j.wasman.2018.06.046. Li, Y., Zhang, Z., Zhu, S., Zhang, H., Zhang, Y., Zhang, T., Zhang, Q., 2018. Comparison of biohydrogen production yield capacity between asynchronous and simultaneous saccharification and fermentation processes from agricultural residue by mixed anaerobic cultures. Bioresour. Technol. https://doi.org/10.1016/j.biortech.2017.09.053. Li, Y., Zhang, Z., Zhang, Q., Tahir, N., Jing, Y., Xia, C., Zhu, S., Zhang, X., 2020. Enhancement of bio-hydrogen yield and pH stability in photo fermentation process using dark fermentation effluent as succedaneum. Bioresour. Technol. https://doi.org/10.1016/j.biortech.2019.122504.

136 Waste to Renewable Biohydrogen Lin, R., Cheng, J., Ding, L., Song, W., Liu, M., Zhou, J., Cen, K., 2016. Enhanced dark hydrogen fermentation by addition of ferric oxide nanoparticles using Enterobacter aerogenes. Bioresour. Technol. https://doi.org/10.1016/j.biortech.2016.02.009. Liu, C.Z., Cheng, X.Y., 2010. Improved hydrogen production via thermophilic fermentation of corn stover by microwave-assisted acid pretreatment. Int. J. Hydrogen Energy. https://doi.org/ 10.1016/j.ijhydene.2010.06.025. Liu, X., He, D., Wu, Y., Xu, Q., Wang, D., Yang, Q., Liu, Y., Ni, B.J., Wang, Q., Li, X., 2020. Freezing in the presence of nitrite pretreatment enhances hydrogen production from dark fermentation of waste activated sludge. J. Clean. Prod. https://doi.org/10.1016/ j.jclepro.2019.119305. Łukajtis, R., Hołowacz, I., Kucharska, K., Glinka, M., Rybarczyk, P., Przyjazny, A., Kaminski, M., 2018. Hydrogen production from biomass using dark fermentation. Renew. Sustain. Energy Rev. https://doi.org/10.1016/j.rser.2018.04.043. Margareta, W., Nagarajan, D., Chang, J.S., Lee, D.J., 2020. Dark fermentative hydrogen production using macroalgae (Ulva sp.) as the renewable feedstock. Appl. Energy. https://doi.org/ 10.1016/j.apenergy.2020.114574. Montiel Corona, V., Razo-Flores, E., 2018. Continuous hydrogen and methane production from Agave tequilana bagasse hydrolysate by sequential process to maximize energy recovery efficiency. Bioresour. Technol. https://doi.org/10.1016/j.biortech.2017.10.032. Mu, D., Liu, H., Lin, W., Shukla, P., Luo, J., 2020. Simultaneous biohydrogen production from dark fermentation of duckweed and waste utilization for microalgal lipid production. Bioresour. Technol. https://doi.org/10.1016/j.biortech.2020.122879. Ortigueira, J., Martins, L., Pacheco, M., Silva, C., Moura, P., 2019. Improving the non-sterile food waste bioconversion to hydrogen by microwave pretreatment and bioaugmentation with Clostridium butyricum. Waste Manag. https://doi.org/10.1016/j.wasman.2019.03.021. Pattra, S., Sangyoka, S., Boonmee, M., Reungsang, A., 2008. Bio-hydrogen production from the fermentation of sugarcane bagasse hydrolysate by Clostridium butyricum. Int. J. Hydrogen Energy. https://doi.org/10.1016/j.ijhydene.2008.05.008. Rafieenia, R., Girotto, F., Peng, W., Cossu, R., Pivato, A., Raga, R., Lavagnolo, M.C., 2017. Effect of aerobic pre-treatment on hydrogen and methane production in a two-stage anaerobic digestion process using food waste with different compositions. Waste Manag. https://doi.org/ 10.1016/j.wasman.2016.10.028. Ramos, C., Buitro´n, G., Moreno-Andrade, I., Chamy, R., 2012. Effect of the initial total solids concentration and initial pH on the bio-hydrogen production from cafeteria food waste. Int. J. Hydrogen Energy. https://doi.org/10.1016/j.ijhydene.2012.06.051. Salem, A.H., Brunstermann, R., Mietzel, T., Widmann, R., 2018. Effect of pre-treatment and hydraulic retention time on biohydrogen production from organic wastes. Int. J. Hydrogen Energy. https://doi.org/10.1016/j.ijhydene.2018.01.114. Sarkar, N., Ghosh, S.K., Bannerjee, S., Aikat, K., 2012. Bioethanol production from agricultural wastes: an overview. Renew. Energy. https://doi.org/10.1016/j.renene.2011.06.045. Sivagurunathan, P., Sen, B., Lin, C.Y., 2015. High-rate fermentative hydrogen production from beverage wastewater. Appl. Energy. https://doi.org/10.1016/j.apenergy.2015.01.136. Stanislaus, M.S., Zhang, N., Yuan, Y., Zheng, H., Zhao, C., Hu, X., Zhu, Q., Yang, Y., 2018. Improvement of biohydrogen production by optimization of pretreatment method and substrate to inoculum ratio from microalgal biomass and digested sludge. Renew. Energy. https:// doi.org/10.1016/j.renene.2018.05.022.

Advances in dark fermentation Chapter | 6

137

Taherdanak, M., Zilouei, H., Karimi, K., 2016. The effects of Fe0 and Ni0 nanoparticles versus Fe2þ and Ni2þ ions on dark hydrogen fermentation. Int. J. Hydrogen Energy. https://doi.org/ 10.1016/j.ijhydene.2015.11.110. Tepari, E.A., Nakhla, G., Haroun, B.M., Hafez, H., 2020. Co-fermentation of carbohydrates and proteins for biohydrogen production: statistical optimization using Response Surface Methodology. Int. J. Hydrogen Energy. https://doi.org/10.1016/j.ijhydene.2019.11.160. Veluchamy, C., Kalamdhad, A.S., 2017. Enhancement of hydrolysis of lignocellulose waste pulp and paper mill sludge through different heating processes on thermal pretreatment. J. Clean. Prod. https://doi.org/10.1016/j.jclepro.2017.09.040. Wang, J., Yin, Y., 2018. Fermentative hydrogen production using various biomass-based materials as feedstock. Renew. Sustain. Energy Rev. https://doi.org/10.1016/j.rser.2018.04.033. Wang, D., He, D., Liu, X., Xu, Q., Yang, Q., Li, X., Liu, Y., Wang, Q., Ni, B.J., Li, H., 2019a. The underlying mechanism of calcium peroxide pretreatment enhancing methane production from anaerobic digestion of waste activated sludge. Water Res. https://doi.org/10.1016/ j.watres.2019.114934. Wang, D., Zhang, D., Xu, Q., Liu, Y., Wang, Q., Ni, B.J., Yang, Q., Li, X., Yang, F., 2019b. Calcium peroxide promotes hydrogen production from dark fermentation of waste activated sludge. Chem. Eng. J. https://doi.org/10.1016/j.cej.2018.07.192. Wicher, E., Seifert, K., Zagrodnik, R., Pietrzyk, B., Laniecki, M., 2013. Hydrogen gas production from distillery wastewater by dark fermentation. Int. J. Hydrogen Energy. https://doi.org/ 10.1016/j.ijhydene.2013.04.008. Wu, Y., Wang, D., Liu, X., Xu, Q., Chen, Y., Yang, Q., Li, H., Ni, B., 2019. Effect of poly aluminum chloride on dark fermentative hydrogen accumulation from waste activated sludge. Water Res. https://doi.org/10.1016/j.watres.2019.01.016. Xu, Q., Li, X., Ding, R., Wang, D., Liu, Y., Wang, Q., Zhao, J., Chen, F., Zeng, G., Yang, Q., Li, H., 2017. Understanding and mitigating the toxicity of cadmium to the anaerobic fermentation of waste activated sludge. Water Res. https://doi.org/10.1016/ j.watres.2017.07.067. Yang, G., Wang, J., 2018a. Various additives for improving dark fermentative hydrogen production: a review. Renew. Sustain. Energy Rev. https://doi.org/10.1016/j.rser.2018.07.029. Yang, G., Wang, J., 2018b. Pretreatment of grass waste using combined ionizing radiation-acid treatment for enhancing fermentative hydrogen production. Bioresour. Technol. https:// doi.org/10.1016/j.biortech.2018.01.105. Yang, G., Wang, J., 2019. Biohydrogen production by co-fermentation of sewage sludge and grass residue: effect of various substrate concentrations. Fuel. https://doi.org/10.1016/ j.fuel.2018.10.026. Yang, G., Hu, Y., Wang, J., 2019. Biohydrogen production from co-fermentation of fallen leaves and sewage sludge. Bioresour. Technol. https://doi.org/10.1016/j.biortech.2019.121342. Yin, Y., Wang, J., 2019. Hydrogen production and energy recovery from macroalgae Saccharina japonica by different pretreatment methods. Renew. Energy. https://doi.org/ 10.1016/j.renene.2019.03.139. Ziara, R.M.M., Miller, D.N., Subbiah, J., Dvorak, B.I., 2019. Lactate wastewater dark fermentation: the effect of temperature and initial pH on biohydrogen production and microbial community. Int. J. Hydrogen Energy. https://doi.org/10.1016/j.ijhydene.2018.11.045.

Chapter 7

Thermochemical processes for biohydrogen production Shuheng Zhao1, 2, 3 1 Key Laboratory of New Materials and Facilities for Rural Renewable Energy of Ministry of Agriculture and Rural Affairs, College of Mechanical & Electrical Engineering, Henan Agricultural University, Zhengzhou, China; 2Henan International Joint Laboratory of Biomass Energy and Nanomaterials, Henan Agricultural University, Zhengzhou, China; 3Collaborative Innovation Center of Biomass Energy, Zhengzhou, Henan Province, China

7.1 Introduction Energy is the most basic element for maintaining and developing socioeconomic development, human life, and material civilization. All human daily life and activities of production are inseparable from energy. With the continuous development of modern civilization, energy consumption has also increased. People are facing an extremely severe energy situation. As nonrenewable resources such as traditional fossil energy are decreasing and serious environmental problems are caused in the process of development and use, countries around the world are trying their best to adjust their energy structures and control the use of fossil fuels such as coal, oil, and natural gas (Bauen et al., 2009; Kumar and Sarkar, 2011; Patel et al., 2016; Patel and Kumar, 2016; Sarkar and Kumar, 2010). Therefore, all countries in the world attach great importance to the development and use of renewable energy. Many countries regard the development of renewable energy as an important part of their energy strategies, put forward clear goals for renewable energy, and have formulated laws and regulations that encourage the development of renewable energy policies. Among the many energy sources explored by humans, hydrogen has potential because it has characteristics that other energy sources do not have, such as: (1) Hydrogen is rich in resources: Hydrogen on earth mainly exists in the form of compounds such as water (H2O), methane (CH4), ammonia (NH3), and hydrocarbons (CnHm). Water is the main resource of the

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(2)

(3)

(4)

(5)

earth. Over 70% of the earth’s surface is covered by water. Even on land, there is abundant surface water and groundwater. Rich sources of hydrogen: Hydrogen energy can be obtained from various primary energy sources (fossil fuels) or from renewable energy sources (such as solar energy, wind energy, and biomass energy) or secondary energy sources (electricity). Hydrogen energy is the cleanest and most environmentally friendly energy source: Using low-temperature fuel cells, hydrogen is converted into electricity and water by electrochemical reactions. There are no CO2 and NOX emissions and no pollution. Hydrogen has storability: Hydrogen energy can be easily stored on a large scale, and the time instability of renewable energy can be compensated for by hydrogen energy; that is, renewable energy is stored in the form of hydrogen energy. High calorific value of hydrogen: The calorific value of hydrogen is 142,351 kJ/kg, which is 2.6 times that of gasoline, 3.9 times that of ethanol, and 4.5 times that of coke.

Because hydrogen energy is nontoxic, and high-quality hydrogen has high calorific value, good performance, and no pollution of in the combustion products, it is regarded as the most environmentally friendly energy source. Global energy resource shortages and environmental pollution issues are the preferred form of energy. According to the Global Demand for Pure Hydrogen report (Fig. 7.1) on the International Energy Agency website, the global demand for hydrogen energy is increasing annually, so technology for producing hydrogen from biomass and its waste has great development prospects.

7.2 Hydrogen production technology Because of the good development prospects of hydrogen energy, the development of hydrogen production technology is also rapid. Common hydrogen production technologies include fossil energy hydrogen production technology (natural gas, coal, and methanol hydrogen production technology), water electrolysis (Resende, 2014), and hydrogen, solar hydrogen, and biomass hydrogen production technology (Chaubey et al., 2013) (microbial hydrogen production technology and biomass thermochemical conversion hydrogen production technology) (C¸a glar and Demirbas¸, 2002; Yan et al., 2006). Among them, hydrogen produced by water electrolysis has little environmental pollution but high energy consumption, so there are obstacles on the economic level (Bartels et al., 2010); Although the production of hydrogen from fossil energy causes a large amount of carbon emissions when hydrogen is obtained, there are restrictions on the environmental level. Hydrogen production from biomass is a hydrogen production method based on biomass produced by

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FIGURE 7.1 Global demand for pure hydrogen, 1975e2018.

photosynthesis with the help of chemical or biological methods (Akgu¨l and Kruse, 2012). It can use waste organic matter remaining in pulp and paper, biorefinery, and agricultural production as raw materials. It has the advantages of energy savings and cleanliness, but large-scale industrialization still has some problems. Here we will briefly introduce these technologies.

7.2.1 Hydrogen production technology from fossil energy Fossil energy hydrogen production has the advantages of large-scale production and good economics. It is also the most common hydrogen production route in the world. Fossil energy mainly includes primary energy such as natural gas, coal, and petroleum, and secondary energy carriers derived from its conversion. Natural gas is a high-quality, efficient, and clean type of energy and chemical raw material. Natural gas produces hydrogen production, which takes about 50% of current global hydrogen production. Its technology includes steam reforming to produce hydrogen, partial oxidation to produce hydrogen, and natural reforming to produce hydrogen, in addition to cracking hydrogen production, for which the current industry mainly employs steam reforming. The steam reforming of natural gas needs to be carried out at a high temperature of 800e900
C, and the hydrogen content in the reaction gas can reach 75%.

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Coal is the most abundant substance in all fossil fuels, and its chemical composition is also the most complex. Although the efficiency of coal to produce hydrogen is not as efficient as natural gas to produce hydrogen, the global reserves of coal are far greater than natural gas (Chiesa et al., 2005). Coal hydrogen production technology can be divided into direct and indirect hydrogen production. The direct hydrogen production of coal includes the coking of coal and the gasification of coal. Indirect hydrogen production refers to the conversion of coal to an intermediate product, and then the intermediate product further conversion produces hydrogen. If the raw material methanol is produced from coal, methanol hydrogen production belongs to the coal indirect hydrogen production route. If it comes from natural gas, it is the indirect hydrogen production route of natural gas. This route can solve transportation and storage problems in the application of hydrogen energy. The transportation and storage of hydrogen cannot meet the requirements of commercialization in terms of technology and cost, but the transportation and storage of methanol have matured. The routes of methanol reforming hydrogen production technology include steam reforming hydrogen production, partial oxidation hydrogen production, autothermal reforming hydrogen production, and cracking hydrogen production. The technical principles of hydrogen production from methanol are similar to hydrogen production from natural gas, but because the raw materials of hydrogen production change from gaseous to liquid, the process flow of the two is different. At the same time, the reaction temperature of methanol steam reforming to produce hydrogen is much lower than the temperature of natural gas to produce hydrogen. The temperature range is 200e300
C and the process conditions are relatively mild.

7.2.2 Hydrogen production technology by water electrolysis Water electrolysis technology is relatively mature and the equipment is complete and systematic (Fig. 7.2). The production of hydrogen by electrolyzing water accounts for about 4% of total hydrogen production (Mazloomi and Gomes, 2012). There are three main types of electrolyzers in water electrolysis hydrogen production process technology: alkaline electrolytic cells, polymer electrolytic cells, and solid oxide electrolytic cells. Among them, alkaline electrolytic cells are the earliest commercially available electrolytic cell technologies. The efficient is low (70% w 80%), but it is still widely used in large-scale hydrogen production because of its easy operation and low price. In the process of water electrolysis hydrogen production, a large amount of electricity is needed. Because electrical energy is a secondary energy source, the economics of hydrogen production by this technology are poor, and its large-scale application is also limited to a certain extent.

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FIGURE 7.2 Water electrolysis.

7.2.3 Solar hydrogen production technology Solar energy is a renewable energy and also a low-carbon energy. Since Fujishima and Honda published a research report on hydrogen production from water electrolysis on n-type semiconductor TiO2 electrodes in Nature in 1972 (Fujishima and Honda, 1972), a new era of research on solar hydrogen production began. There are two main ways to produce hydrogen by using solar energy to decompose water: photocatalytic decomposition of water to produce hydrogen (Fig. 7.3) and solar photoelectrochemical decomposition of water to produce hydrogen (Konstandopoulos et al., 2015; Song et al., 2016). The photoelectrochemical cell is composed of a photoanode and a counterelectrode. The photoanode (semiconductor material) absorbs solar energy and is excited to generate electron-hole pairs. The electrons flow to the counterelectrode through an external circuit. Protons in water receive electrons from the counterelectrode to generate hydrogen (Huang et al., 2006; de Lasa et al., 2011). Because the structure of the photoelectrochemical cell is complicated, it must be biased, and the conversion efficiency is low, so it is difficult to apply it on a large scale. The photocatalytic decomposition of water to produce hydrogen uses photocatalytic materials in water to absorb sunlight energy and effectively passes them to water molecules, so that water undergoes photolysis to generate hydrogen. Because most photocatalysts can be excited only under ultraviolet light, the efficiency of photocatalytic water decomposition with photocatalysts is only about 2% and the cost of photocatalysts is relatively high, which is difficult to apply on a large scale.

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FIGURE 7.3 Solar hydrogen production. From Zhang, K., Kim, J.K., Park, B., Qian, S., Jin, B., Sheng, X., Zeng, H., Shin, H., Oh, S.H., Lee, C.-L., Park, J.H., 2017. Defect-induced epitaxial growth for efficient solar hydrogen production. Nano Lett. 17, 6676e6683. https://doi.org/10.1021/ acs.nanolett.7b02622.

7.2.4 Biomass hydrogen production technology Domestic and foreign research on hydrogen production from biomass and other types of waste focus on two aspects: hydrogen production by biological methods and hydrogen production by thermochemical conversion. Biological hydrogen production is the conversion of hydrogen production by biological pathways, such as direct biophotolysis, indirect biophotolysis, photofermentation, the wateregas transfer reaction of photosynthetic heterotrophic bacteria to synthesize hydrogen, dark fermentation, and microbial fuel cells (Das and Veziroglu, 2008; Gavala et al., 2006; Okamoto et al., 2000; Zhou et al., 2013). Microbial hydrogen production is the conversion of energy stored in organic compounds in nature into hydrogen through the action of hydrogenproducing bacteria. The raw materials used for the hydrogen production by the microbial method can be agricultural and forestry waste (stalks and wood chips), municipal solid waste, and sewage sludge (Kumar et al., 2018). These types of solid waste are abundant and inexpensive. However, the reaction conditions of microbial oxygen production are difficult to control, the cycle is long, and efficiency is low. The thermochemical conversion of hydrogen is based on solid waste as a raw material to produce hydrogen by thermophysical and chemical methods, such as biomass gasification to produce hydrogen, supercritical conversion to produce hydrogen, and pyrolysis to produce hydrogen. The general process of biomass thermochemical conversion to hydrogen production is shown in Fig. 7.4.

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FIGURE 7.4 Hydrogen production process by thermochemical conversion of biomass. PSA, pressure swing adsorption.

Thermochemical hydrogen production can be made directly from biomass and other waste, or it can be converted into easily storable intermediate products (such as methanol and ethanol) and then reformed to produce hydrogen. The direct preparation method and device are relatively simple, and the method of passing intermediate products can reduce the cost of transporting raw materials. Among them, thermochemical hydrogen production is easier to achieve industrialization, and it is a hot spot of current research. In addition, owing to the many types of waste, including agricultural, forestry, industrial (such as wastewater and sludge), and municipal, different types of waste need to be treated differently in accordance with their characteristics (Fig. 7.4).

7.3 Thermochemical conversion hydrogen production technology The technology of thermochemical conversion hydrogen production from waste converts waste into hydrogen-rich gas by a thermochemical method and then obtains pure hydrogen by gas separation. Among various renewable energy hydrogen production technologies, thermochemical conversion hydrogen production is more suitable for large-scale hydrogen production systems. Raw materials for this technology have a wide range of applications, and many

146 Waste to Renewable Biohydrogen

related technologies and engineering experiences can be used for reference; thus, there are great development prospects. The most widely used thermochemical conversion hydrogen production technology is for agricultural or forestry biomass materials. It can be divided into pyrolysis hydrogen production technology, gasification hydrogen production technology, and supercritical water gasification hydrogen production technology (Resende, 2014).

7.3.1 Pyrolysis 7.3.1.1 Pyrolysis mechanism Biomass pyrolysis to produce hydrogen is a basic chemical reaction process. It is indirectly heated under isolation from air to cause thermal cracking. Volatile substances occupying 70%e75% of the mass of the raw materials are precipitated and transformed into a gaseous state. The gas phase products include H2, CO, CO2, CH4, and other noncondensable gases and some macromolecular hydrocarbons that can be condensed into tar at low temperatures. The process of hydrogen production from biomass pyrolysis is shown in Fig. 7.5. It goes through two steps: (1) Pyrolysis of biomass yields gas, liquid, and solid three-phase products; and (2) The gas or bio-oil produced by pyrolysis is used to reform hydrogen. In the first step, continuous high temperature promotes the production of viscous and unstable tar. Because it is difficult for gasification to take place at a low temperature and carbon deposits are easily formed at a high temperature during gasification processing, it is important to adjust the reaction temperature and pyrolysis residence time. However, hydrogen production remains low in this way, so it is necessary to improve the hydrogen production effect through reforming. Pyrolytic process is the core of biomass thermochemical conversion. According to different operating conditions, it can be divided into

FIGURE 7.5 Process flow of hydrogen production from biomass pyrolysis.

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slow pyrolysis, fast pyrolysis, and flash pyrolysis (Bridgwater, 2003; Jahirul, 2012). Slow pyrolysis has been known for a long time; its operating temperature is generally 550e950K. During slow pyrolysis, biomass produces solid char with a low gas yield. Rapid pyrolysis is the process of the pyrolysis of biomass under normal pressure and 850e1250K. Depending on the raw materials, the yield of fast pyrolysis products will be different. The yield of biooil is about 60%e75%, the yield of solid carbon is about 15%e25%, and the yield of cracked gas is about 10%e20%; rapid pyrolysis should have the following characteristics: a. The heating and heat transfer rate is fast, so the pyrolysis raw material particles are small; b. The temperature of the pyrolysis reaction should be strictly controlled; c. The residence time of the gas in the reactor is short, generally less than 2 s; and d. Pyrolysis gas can be quickly cooled to separate bio-oil. The operating temperature of flash pyrolysis is 1050e1300K. This method is often used to refine bio-oil. Among these methods, the most common method is rapid pyrolysis. Pyrolysis is an endothermic reaction; the reaction equation is: Biomass þ Energy/H2 þ CO þ CH4 þ Other

(7.1)

Methane and other hydrocarbons can be converted into H2 and CO by steam reforming: CH4 þ H2 O/CO þ 3H2

(7.2)

A water vapor shift reaction is used to improve the hydrogen yield: CO þ H2 O/CO2 þ H2

(7.3)

In the second step described, hydrogen is produced by reforming the gas or bio-oil produced by pyrolysis. Many reforming technologies will produce hydrogen from biomass pyrolysis. Common technologies include steam reforming, aqueous reforming, autothermal reforming, and chemical looping reforming. These techniques are briefly described next (Kaur et al., 2019): Steam reforming removes the pyrolyzed biomass residual carbon out of the system and then subjects the pyrolysis product to a second high-temperature treatment. Under the combined action of the catalyst and water vapor, the heavy hydrocarbons of a relatively large molecular weight are cracked into hydrogen, methane, and so on. With the aim of increasing the hydrogen content in the gas, the secondary cracked gas is then catalyzed to convert carbon monoxide and methane into hydrogen. In addition, pressure swing adsorption or membrane separation technology is used to obtain high-purity hydrogen.

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Aqueous phase reforming is a process in which the pyrolysis products are converted into hydrogen, carbon monoxide, and alkanes in the liquid phase using a catalyst. Compared with steam reforming, water phase reforming has the following advantages: (1) The reaction temperature and pressure are easily reached and suitable for the water gas reaction, and they avoid the decomposition and carbonization of carbohydrates. (2) The carbon monoxide volume fraction in the product is low and is suitable for fuel cells. (3) Water phase reforming does not require the gasification of water and carbohydrates, and thus avoids high energy consumption. Autothermal reforming is based on steam reforming, during which an appropriate amount of oxygen is passed into the reaction system to oxidize the semicoke precursors adsorbed on the catalyst surface to avoid carbon deposits and coking. The heat of the system can be changed by adjusting the ratio of oxygen to the material to achieve a self-heating system without an external heat supply. Autothermal reforming couples exothermic and endothermic reactions and reduces energy consumption compared with steam reforming. Autothermal reforming is concentrated in the production of hydrogen from methanol, ethanol, and methane. It is similar to steamecarbon dioxide mixed reforming, adsorption enhanced reforming, and so forth. Chemical looping reforming uses metal oxides as an oxygen carrier to replace water vapor or pure oxygen required by traditional processes, and directly converts fuel into high-purity synthesis gas or carbon dioxide and water. The reduced metal oxides are re-oxidized in the air reactor to complete the in-situ separation of oxygen and nitrogen. Chemical looping reforming is a new and efficient hydrogen production process. In the process of biomass pyrolysis, a special pyrolysisemicrowave catalytic pyrolysis technology has gradually been developed. Biomass microwave pyrolysis depends on microwave-specific dielectric heating methods. Dielectric heating refers to the interaction between charged particles and electromagnetic radiation in a material, which causes intense collisions and friction between molecules to generate heat, and thus to heat an object. Unlike traditional heating methods during pyrolysis, which are from the outside to the inside, microwaves are a volumetric heating method from the inside to the outside, which can heat deep inside the biomass raw material. In addition, microwave heating has the potential to control reaction conditions easily with rapid selective heating, a low reaction temperature, and low energy requirements. Compared with traditional heating methods, microwave heating method can improve the yield and quality of pyrolytic products, reduce the generation of dangerous products, and minimize the emission of pollutants. These make the technology more environmentally friendly during pyrolysis.

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FIGURE 7-6 Bubbling fluidized bed reactor.

7.3.1.2 Pyrolysis reactor There are four main types of biomass pyrolysis reactors (Resende, 2014) (Fig. 7.6): 1. Bubbling fluidized bed reactor: As shown in Fig. 7.6, the important features of bubbling fluidized bed are: a. It provides good mixing and uniform conditions throughout the bed. b. It is efficient with a high degree of temperature control. c. The system is scalable. d. It features a short residence. 2. Circulating fluidized bed reactor: The construction of a circulating fluidized bed reactor is similar to a bubbling fluidized bed reactor, as shown in Fig. 7.7. The elutriation process carries both sand and char particles outside the bed. The reactor is connected to the cyclone, which separates char and sand from the main gas stream. The separated char is combusted to generate energy, which heats the sand. The hot sand is then recirculated back into the reactor. The features of circulating fluidized bed reactors are: a. It maintains good temperature control and uniform conditions. b. It is easily scalable. c. It is used only for commercial applicable because of the control requirements. 3. Auger reactor: It is the most popular pyrolysis reactor because of its basic construction, as shown in Fig. 7.8. In this reactor, the biomass is fed continuously to rotating augers filled with preheated sand. When the biomass is mixed with the preheated sand, the auger rotation moves the

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Gas/aerosols

To cyclone / condenser

Cyclone

Bed particles

Biomass feed

Fluidizing agent FIGURE 7.7 Circulating fluidized bed reactor.

FIGURE 7.8 Auger reactor.

product along the auger axis. When it reaches the end of the reactor, gases and volatiles exit from the top; combined char and sand are collected at the bottom. Because of the auger design, vapors take much longer time to exit compared with the fluidized bed type. This increases the possibility of secondary reactions and increases the yield of char.

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4. Ablative reactors: In ablative reactors, heat transfer takes place by solidesolid contact. Solid biomass such as entire wood rods is heated by direct contact with a hot metallic surface. The main significance of solidto-solid contact is a high heat transfer rate; however, the limited surface area of contact makes large scale-up difficult. Thus, ablative reactors are recommended only for small-scale applications.

7.3.2 Gasification Biomass gasification is also a kind of thermochemical conversion of biomass. It refers to biomass under high temperature (500e1400
C) and pressure (1.01e33 bar) with a gasification agent such as air or water vapor (Hosseini and Wahid, 2016; Nikolaidis and Poullikkas, 2017), taking place of converting hydrocarbons into hydrogen-containing combustible gases. Compared with pyrolysis, the temperature of biomass gasification process is higher and has the following advantages: (1) The process flow and equipment are relatively simple and there is more engineering experience in coal chemical industry from which to learn from. (2) It makes full use of heat generated by partial oxidation to crack biomass and decompose water vapor, and the energy conversion efficiency is high. (3) It has wide raw material adaptability. (4) It is suitable for large-scale continuous production. The process flow is shown in Fig. 7.9. Biomass gasification produces the reaction: Biomass þ O2 ðH2 OÞ/CO; CO2 ; H2 ; CH4 þ Cn Hm þ Tar þ Carbon

(7.4)

In the gasification, the composition of the gas product is related to the type of gasifier and raw materials. In the gasification process, the gasifier can be O2,

FIGURE 7.9 Process flow of hydrogen production from biomass gasification.

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air, and water vapor, or a mixture of these (Barelli et al., 2008; Sucipta et al., 2007). Because different gases are used, the chemical composition, fuel gas composition, and tar content are also different: (1) Air gasification: It is the most widely used gasification technology. It has high gasification efficiency and does not require additional oxygen, but N2 is mixed in the air, which makes it difficult to purify H2 in the future. (2) Oxygen gasification: The calorific value of the gasification products is high, but during gasification, the reactor temperature is high and there are safety issues. (3) Water vapor gasification: The gasification products generate syngas (H2, CO, CO2, CH4, and CnHm), bio-oil, and bio-char. In this process, the H2 yield is large. Biomass gasification hydrogen uses a circulating fluidized bed or a bubbling fluidized bed as a gasification reactor, and nickel-based catalysts or cheaper dolomite or limestone are used as tar cracking catalysts. Thermal cracking of tar requires a high reaction temperature, generally 1000e1200
C. Considering the fire resistance of the material and the carbon black that is decomposed at a high temperature, which is difficult to separate, the catalytic cracking method is often used in actual applications. The use of a catalyst can greatly reduce the tar cracking temperature (750e900
C) and can improve cracking efficiency, so the tar cracking rate can reach more than 99% in a short time. Moreover, in the process of using the catalyst, considering the mechanical strength and service life of the catalyst, the gasification of the biomass and the catalytic reaction are generally set in different reactors. During the biomass gasification process, because the composition of the gasification product and its yield are affected by a variety of factors, such as the gasification temperature, type of gasification agent, water vaporebiomass molar ratio, catalyst type (Vamvuka, 2011; de Lasa et al., 2011), reactor type, raw material type, and so on, with the aim of obtaining different products and improving conversion efficiency, a variety of forms for gasification hydrogen production have been developed, including highelow temperature catalytic gasification, chemical looping gasification, and other technologies (Basu, 2013). Biomass chemical looping gasification (BCLG) is developed from chemical looping combustion. By rationally controlling the oxygen supply of the oxygen carrier, the gasification medium (CO2/H2O) is appropriately introduced into the fuel reactor. Biomass or semicoke is converted to synthesis gas or hydrogen-rich gas. BCLG has advantages over traditional gasification: the introduction of oxygen carriers can eliminate air separation equipment and reduce system investment. Oxygen carriers can catalytically convert gasified tars while supplying heat to the gasification reaction. Moreover, the reactor is divided into a pyrolysis area and a gasification area. In addition, the introduction of water vapor at different locations can effectively adjust the

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hydrogenecarbon molar ratio of the synthesis gas. It is also possible to consider the use of the high water content of the biomass to adjust its carbonehydrogen ratio.

7.3.3 Supercritical water gasification The biggest difference between biomass supercritical water gasification hydrogen production technology and biomass pyrolysis or gasification hydrogen production technology is related to the different reaction conditions and reaction products. Supercritical water gasification can be considered a special hydrogenation method by gasification. This technology was first proposed by Modell in the United States in 1977 (Modell, 1977). It is a method of mixing biomass raw materials coupling with a proportion of water, and placing them under supercritical conditions at 22e35 MPa and 450e650
C to generate hydrogen (Fiori et al., 2012; Akgu¨l and Kruse, 2012). The process flow of hydrogen production by supercritical water gasification with a higher gas content and residual carbon is shown in Fig. 7.10. At the supercritical state, water has a low dielectric constant, small viscosity and high diffusion coefficient. Thus, the system has good diffusion transfer performance, which can reduce mass transfer resistance and dissolve most organic components and gases, and makes the convention of biomass near 100%. The processes include a wateregas shift reaction (7.3), steam reforming reaction (7.5), and methanation reaction (7.6), (7.7). CHn Om þ ð1  mÞ H2 O/ðn=2 þ 1  mÞ H2 þ CO

(7.5)

CO þ 3H2 /CH4 þ H2 O

(7.6)

CO2 þ 4H2 /CH4 þ 2H2 O

(7.7)

Research on hydrogen production from biomass supercritical water gasification focuses on the effects of different operating conditions (temperature, pressure, reactant concentration, residence time, catalyst, and so on) on

FIGURE 7.10

Process flow of hydrogen production by supercritical water gasification.

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different types of biomass and their mechanisms. For examples, Gutie´rrez Ortiz et al. (2015) studied the effect of temperature on the reaction. A supercritical water gasification experiment was carried out on glycerol under the conditions of 500
C, 24 MPa, 5% by mass, and 1 L/h per mol when the temperature was increased to 550, 600, 700, and 800
C, the hydrogen yield increased to 2.43, 3.27, 5.70, and 6.52 mol/mol, respectively. Nanda et al. (2015) used fructose as a model compound of fruits or vegetables and carried out an experimental analysis. At 550
C, 60 s, and 4% mass fraction, the carbon gasification rate was 23%. As the temperature increased to 600, 650, and 700
C, the carbon gasification rate increased to 41%, 67%, and 88%, respectively. Compared with traditional hydrogen production, biomass thermochemical conversion hydrogen production has a high operating cost, which is not beneficial for commercial use. However, with continuous improvements in gasification and pyrolysis technology, an in-depth study of the mechanism of supercritical water biomass gasification, and improvements in the economics of the entire process, thermochemical conversion hydrogen technology would be able to compete with traditional hydrogen production. The production of biomass hydrogen will inevitably move toward commercialization.

7.4 Hydrogen production technology by thermochemical conversion of waste In daily production and living activities, various types of waste are unavoidable, such as straw waste and processing by-products of various crops in agricultural production activities, wood chips and fallen leaves in forestry production, and industrial waste such as wastewater and sludge (Amidon et al., 2008; Chong et al., 2009; Demirbas¸, 2001; Reddy and Yang, 2005). Although there are many types of waste, not all types are suitable for thermochemical conversion to produce hydrogen. Choosing a suitable hydrogen production route can make the waste value higher and effectively reduce the cost of waste treatment (Psomopoulos et al., 2009). In the use of various types of waste, kitchen waste, livestock and poultry manure, and so on are suitable as raw materials for biological hydrogen production, whereas straw, wood chips and nut shells, and so forth are more suitable as raw materials for hydrogen production by thermochemical conversion. To best use waste, this chapter first classifies the waste and then reviews technologies applicable to the thermochemical conversion of waste to produce hydrogen (Fig. 7.11).

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FIGURE 7.11 Common waste.

7.4.1 Agricultural and forestry waste 7.4.1.1 Composition and classification of agricultural and forestry waste The main components of agricultural and forestry waste are biomass, which is mainly composed by cellulose, hemicellulose, lignin, starch, protein, and hydrocarbons (Cao et al., 2017). Forest trees and herbaceous crops mainly composed of cellulose, hemicellulose, and lignin. Grains contain more starch, and sludge and livestock manure contain more protein and lipids. In short, the composition of different types of waste varied greatly. From the perspective of energy use, biomass waste consisting of cellulose and hemicellulose has great potential for use with the technology of thermochemical conversion for hydrogen production. Therefore, knowledge of the composition of biomass is beneficial for selecting a conversion method. 7.4.1.1.1 Representative composition (Carrier et al., 2011) a. Cellulose: It is a polysaccharide composed of D-glucose through bglucoside bonds. Its molecular formula is represented by (C6H12O5)n, where n is the degree of polymerization. Cellulose has a crystalline structure; it is a white substance that is insoluble in water and is highly resistant to acids and alkalis.

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b. Hemicellulose: Heteromeric polymers are composed of several different types of monosaccharides. These sugars are five- and six-carbon sugars, including xylose, arabinose, and galactose. c. Lignin: This is a compound made of phenylpropane and its derivatives as a structural unit and is three-dimensionally combined. From the perspective of chemical structure, it has the characteristics of both phenol and sugar, and the polymer structure formed is complicated. d. Starch: Like cellulose, it is a compound formed by the polymerization of D-glucose molecules. Its molecular formula is (C6H10O5)n, which is the most common storage form of carbohydrates in cells and nutrients stored in plants. e. Protein: Protein is an important substance that constitutes the cytoplasm, accounting for more than 60% of the total dry mass of cells. Proteins are polymer compounds made from highly polymerized amino acids. The properties of proteins vary with the type, ratio, and degree of polymerization of the amino acids they contain. 7.4.1.1.2 Classification and composition analysis Table 7.1 classifies representative biomass.

TABLE 7.1 Representative biomass classification. Types of waste

Description

Grain, wheat, and potato straw

Crop waste such as rice, sorghum, corn, wheat, barley, oats, and potatoes

Legume crop stalks

Soybean, broad bean, pea, and other legume crop waste

Oil crop straw

Crop waste such as rapeseed, peanuts, castor, and sunflower

Horticulture and other crop straws

Crop waste such as vegetables, flowers, herbs, and cotton

By-products during processing

By-products from postharvest processing of crops such as rice bran, wheat bran, bagasse, and beet residue

Production waste

Fallen leaves, dead branches, felling residues, dead wood, etc.

Processing residue

Husk, stone core, bark, sawdust, sawdust, etc.

Livestock manure

Livestock, poultry, manure, etc.

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7.4.1.2 Progress in hydrogen production from agricultural and forestry waste by thermochemical conversion In the previous classification, except for animal and poultry manure and urine containing more protein and lipids, waste is mostly rich in cellulose, hemicellulose, and lignin, which are suitable as raw materials for thermochemical conversion for hydrogen. In this section, we use common agricultural and forestry wastes as examples to describe the progress in the thermochemical conversion of agricultural and forestry waste to produce hydrogen. The key to hydrogen production from biomass by thermochemistry is how to produce hydrogen efficiently with low energy consumption. There is much research on the technology of thermochemical conversion of agricultural and forestry waste to produce hydrogen; some of this work is listed in Table 7.2.

TABLE 7.2 Research progress in thermochemical conversion of agricultural and forestry waste to produce hydrogen. Raw material

Processing conditions and results

References

Eucalyptus, pine

The effects of pyrolysis temperature on the pyrolysis process of eucalyptus were studied at 450e550
C. The results showed that concentrations of CO, CO2, CH4, and C2H6 in the gas products increased with the temperature. However, when the pyrolysis temperature of pine wood was used as the raw material, the concentration of CO, CO2, CH4, and C2H6 decreased as the pyrolysis temperature increased from 700
C to 900
C.

Garcia-Perez et al. (2008), Lv et al. (2003)

Hazelnut shells, waste tea leaves, spruce fir

When the temperature rose from 700 to 950 K, the hydrogen concentration in the hydrogen-rich gas obtained by pyrolyzing hazelnut shells, waste tea leaves, and spruce fir increased from 36.8% to 43.5%, 41.0% to 53.9%, and 40% to 51.5%, respectively.

Demirbas (2009)

Continued

158 Waste to Renewable Biohydrogen

TABLE 7.2 Research progress in thermochemical conversion of agricultural and forestry waste to produce hydrogen.dcont’d Raw material

Processing conditions and results

References

Apricot kernels

When the heating rate was 40
C/min, the hydrogen-rich gas yield was 17.8 mol%, and when the heating rate was 15
C/min, the hydrogen-rich gas yield was 22.4 mol%.

Savova et al. (2001)

Pine sawdust

The effect of the gasification medium on gasification results was studied. Under the same conditions, when the gasification medium was air, a low calorific value gas was generated, with a calorific value of 4w7 MJ/m3 and an H2 content of 8%e14%. When the medium was water vapor, it produced medium calorific value gas with a calorific value of 10e16 MJ/m3, and the content of H2 was 30%e60%.

Delgado et al. (1997)

Pine sawdust

Pine sawdust was used as the raw material. The catalysts were dolomite and nickelbased catalysts. When the other conditions were maintained, the hydrogen production rate and potential hydrogen production rate increased with an increase in temperature, but when the temperature exceeded 800
C, the hydrogen production rate and potential hydrogen production rate slowly changes with an increase in temperature.

Lu et al. (2003)

North Florida pine

In the thermochemical conversion of biomass-based steam gasification to produce hydrogen-rich syngas, the results showed that the highest hydrogen production rate was 51%.

Dascomb et al. (2013)

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Because there are many types of agricultural waste and the composition of biomass are different, it is difficult to study the thermochemical hydrogen production method for each biomass individually. Nevertheless, the main components of biomass are the same: cellulose (30%e60%), hemicellulose (20%e35%), lignin (15%e30%), extracts, and minerals. Among the three components, hemicellulose has the worst thermal stability and is mainly pyrolyzed at 220e315
C (Yang et al., 2007). Cellulose pyrolysis has a higher initial temperature and a narrower pyrolysis temperature range of 310e390
C; The structure of lignin is complex, the pyrolysis rate is slow, the temperature interval is large, and the weight loss of pyrolysis is in the range of 200e550
C. During the pyrolysis of cellulose and hemicellulose, volatiles are produced and a small amount of coke is produced; the main product of pyrolysis of lignin is coke. However, different components and chemical structures of biomass make the mechanisms, paths, and rates of pyrolysis and gasification different, and the resulting products content different as well. Research showed that the thermal conversion characteristics of biomass are related to the thermal characteristics of the three components, and the thermal conversions of the three components are independent of each other under certain conditions. For examples, Qu et al. (2011) studied the pyrolysis of cellulose, hemicellulose, and lignin in a tubular reactor (350e650
C). The results showed that the concentration of H2 increased sharply above 550
C during the pyrolysis of cellulose. For the hemicellulose pyrolysis process, when the temperature is below 500
C, the concentration of H2 is relatively low; as the temperature rises to 550
C, the concentration of H2 increases rapidly and reaches the maximum. Tiantian (2017) carried out a biomass water vaporization experiment at 920e1220
C on a fixed suction bed. The biomass components of cellulose, hemicellulose, lignin, and three kinds of actual biomass were used as research objects. The characterization coefficient was used to characterize the composition of biomass, and the effects of temperature and biochemical components on hydrogen production characteristics were investigated. Simultaneous simulations of biomass gasification were performed using Aspen Plus. The results show that (1) in the temperature range of 920e1220
C, the hydrogenation characteristics of the gasification of cellulose and hemicellulose were similar, but they were significantly different from lignin; (2) biomass with a high lignin characterization coefficient can produce a larger hydrogen production rate and higher H2 volume fraction, which is more suitable as a raw material for gasification hydrogen production; (3) the component characterization coefficient is used to fit the gasification gas components of the actual biomass. The fitted results have a linear correlation with the experimental results, so the fitted results can be used to estimate the gas components of a particular biomass; and (4) among the three components, the hydrogen production rate of lignin is the highest, and the hydrogen production rate of cellulose and hemicellulose is low. The actual hydrogen production rate of biomass is between lignin and hemicellulose.

160 Waste to Renewable Biohydrogen

7.4.2 Municipal solid waste 7.4.2.1 Characteristics and classification of municipal solid waste Municipal solid waste refers to solid waste generated by urban residents in their daily lives or activities. Its main components include kitchen waste, waste paper, waste plastic, waste fabric, scrap metal, scrap glass, and scrap furniture (Arena, 2012; Yan et al., 2019). With the rapid economic development of various countries in the world and the acceleration of urbanization, the number of cities and the scale of cities have continued to expand, which has led to a significant increase in the total amount of urban garbage. Moreover, the composition of urban garbage is complex and its nature is changeable, which is affected by many factors. Therefore, the composition of municipal solid waste generated in different countries and cities varies. Municipal solid waste, which is a mixture of multiple substances, has no specific internal structure and therefore does not have specific material properties (Elbaba and Williams, 2012; Mastellone et al., 2010; McKay, 2002). The physical properties of municipal solid waste change with the nature and proportion of its constituents. The material composition of urban domestic waste is divided into four categories: organic, inorganic, recyclable, and other garbage. Treatment and disposal methods of municipal solid waste include sanitary landfill, biodegradation (anaerobic fermentation and aerobic composting), heat treatment (preparation of waste-derived fuel, incineration power generation, pyrolysis, gasification, etc.), and comprehensive resource treatment. Among them, sanitary landfill, composting and incineration power generation are common urban domestic waste disposal methods (Fig. 7.12).

FIGURE 7.12 Ways to dispose of municipal waste.

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These treatment methods have a low use rate of garbage and are likely to cause environmental pollution. Therefore, the classification and utilization of different garbage can make high-value use.

7.4.2.2 Progress in hydrogen production from municipal solid waste by thermochemical conversion The components of municipal solid waste generally change with the time, season, and region; most are organic components. The technology of the thermal chemical conversion of municipal solid waste to produce hydrogen is a new type of waste treatment technology. It has good pollution control and a significant volume reduction effect. By studying the pyrolysis and gasification characteristics of organic components, we can understand the process of garbage in pyrolysis and gasification, especially of the pyrolysis characteristics of single-component waste (such as plastic, wood chips, and paper). Compared with traditional waste incineration, advantages of thermochemical conversion include improved energy conversion efficiency, generated value-added products, and controlled pollutant emissions. The intermediate products of thermochemical conversion can be widely used, from high-quality fuels to fine chemicals. Lower operating temperatures could reduce the risk for alkali volatilization, scaling, slagging, and bed agglomeration (Arena, 2012). In addition, thermochemical conversion systems for gasification and pyrolysis are often equipped with product cooling and collection devices to improve emissions control of organic and inorganic pollutants (Young, 2010). Although there are some advantages, the thermochemical conversion of municipal solid waste is still controversial owing to potential negative environmental impacts such as the production of heavy metals and dioxins. Many scholars have performed research on the pyrolysis and gasification characteristics of municipal solid waste (Table 7.3). In addition, some scholars studied the effects of catalysts, heating methods, reaction temperature, pyrolysis gasification time, and other conditions on the thermochemical conversion of municipal solid waste to produce hydrogen. Because those processes are complicated, the specific reaction mechanism needs further exploration and research. 7.4.3 Industrial waste 7.4.3.1 Characteristics and classification of industrial waste Industrial waste refers to various waste liquids, dust, and other types of solid waste discharged into the environment during the production process of industrial enterprises (Fig. 7.13). According to its state, it can be divided into solid, liquid, and gas waste. Industrial waste has the characteristics of a huge quantity, large variety, complex composition, and difficult disposal. The storage of industrial waste occupies a large amount of land and easily contaminates soil

162 Waste to Renewable Biohydrogen

TABLE 7.3 Research progress on thermochemical conversion of municipal solid waste for hydrogen production. Raw material

Processing conditions and results

References

Polyvinyl chloride (PVC) pipe

Pyrolysis experiments were conducted using PVC pipes as materials. The results show that there are three weight loss stages in the pyrolysis of PVC pipes. The corresponding temperature ranges are 220e400
C, 400e550
C, and 550e980
C. The weight loss share accounts for 80%. In addition, the increase in the heating rate has an impact on the high-temperature decomposition of carboncontaining compounds and inorganic additives in the third stage.

Jin et al. (2001)

Plastic, kitchen waste, tree branches

Pyrolysis experiments were performed on plastic, kitchen waste, and branches in a fixed-bed reactor. The results show that the particle size of the pyrolysis sample had a significant effect on the pyrolysis products and composition. The smaller the particles, the higher the gas production. The higher the concentration of H2 and CO in the composition, the lower the tar and semicoke production.

Luo et al. (2010)

Plastic

A type of seawater and plastic gasification experiment was studied. The effects of different operating conditions (temperature, time, raw material concentration, and pressure) on gasification performance were discussed. The results of supercritical water gasification experiments showed that increasing the temperature and time promoted cracking and free radical reactions, improved gasification efficiency, reduced raw material concentrations, improved the gasification level of the plant raw materials, and improved gasification efficiency.

Bai et al. (2020)

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TABLE 7.3 Research progress on thermochemical conversion of municipal solid waste for hydrogen production.dcont’d Raw material

Processing conditions and results

References

Municipal solid waste

Based on the thermos elect process, the municipal solid waste was gasified in a 3-t/d capacity pilot test facility. When the reaction temperature was 1200
C, the heat value of the generated syngas was 8.0e10.2 MJ/Nm3, of which CO and H2 concentration can reach 27e40 and 36e40 vol%, respectively

Kwak et al. (2006)

Municipal solid waste

In a two-stage gasification catalytic furnace, air was used to gasify municipal solid waste, and activated carbon was used as a tar cracking catalyst. When the equivalence ratio (ER) was 0.21 and the temperature of the gasifier was 750e800
C, the calorific value of the obtained gas reached 8.44 MJ/Nm3.

Kim et al. (2011)

Municipal solid waste

In the spouted bed, air was used as a gasifier to gasify municipal solid waste. The effects of excess air coefficient and secondary air volume on the gasification process were investigated. The experimental results showed that the high calorific value (higher heating value) of gas products could reach 2.40e5.05 MJ/Nm3, the tar content was 11.3e20.76 g/Nm3, and the gas production composition was CO: 14.79e 18.51 vol%, H2: 7.06e9.66 vol%.

Thamavithya and Dutta (2008)

Municipal solid waste

A rotary furnace water vapor was used to gasify municipal solid waste. The gasification temperature was 850e1050
C. The H2 content in the obtained gas product was 42.69%e66.02%, the CO content was 17.86%e18.16%, and the gas yield was 81.3%e89.0%

Galvagno et al. (2006)

Continued

164 Waste to Renewable Biohydrogen

TABLE 7.3 Research progress on thermochemical conversion of municipal solid waste for hydrogen production.dcont’d Raw material

Processing conditions and results

References

Municipal solid waste

An experimental study was conducted on the preparation of high calorific value hydrogen-rich gas by steam vaporizing organic components of municipal solid waste using calcined dolomite as a catalyst in a down-suction fixedbed gasification furnace. The results showed that at a gasification temperature of 750e950
C, when the mass ratio of steam and waste materials was 0.57e1.28, the hydrogen content in the obtained gas reached 53.22%, the hydrogen production rate reached 7.13e 46.52 mol/kg, and the gas yield was 0.74e1.92 m3/kg.

He et al. (2009)

Municipal solid waste

An experimental study was performed on catalytic water vaporization of municipal solid waste in a vertically connected twin bed reactor. The experimental results showed that when nanoNiLaFe/g-Al2O3 was used as the catalyst, the tar removal rate reached 99%. The higher the catalytic temperature, the smaller the particle size of the municipal solid waste raw materials, and the higher the quality of the obtained gas products; S/M and the best value of C/M (the ratio of catalyst to the amount of municipal solid waste) were 1.33 and 0.5 when the content of H2 in the gas product reached 50% or more.

Li et al. (2012)

and water bodies by leaching. Powdery waste flies about in the wind, polluting the atmosphere, and some also emits odors and poisonous gases, which affects the growth of organisms and endangers human health. With the development of industrial production, the quantity and type of industrial waste are constantly increasing. Therefore, how to use economical and

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165

FIGURE 7.13 Industrial waste.

effective methods to maximize industrial waste recycling is an environmental and economic problem that urgently needs to be solved (Chaubey et al., 2013). Among the many technologies for processing industrial waste, thermochemical conversion hydrogen production is a type of treatment that converts some industrial waste into clean and environmentally friendly hydrogen energy for storage and use, and has broad development space. For common industrial waste, researchers use waste tires, papermaking black liquor, sludge, and other types of wastes as raw materials for thermochemical conversion to produce hydrogen (Akbari et al., 2018; Demirbas¸, 2002; Eriksson and Harvey, 2004; Naqvi et al., 2010).

7.4.3.2 Progress in hydrogen production from industrial waste by thermochemical conversion We will use sludge as an example of industrial waste for analysis. Sludge is a by-product of the sewage treatment process. Because of its large output, its treatment has become a hot topic. Sludge as a hydrogen production matrix has advantages: (1) it has a wide range of sludge sources; (2) it has a variety of sludge hydrogen production methods; and (3) sludge hydrogen production technology has considerable potential for hydrogen production. As a hydrogen production raw material, researchers have carried out a series of experiments on the thermal chemical conversion hydrogen production of sludge. Table 7.4 lists some research on the thermochemical conversion of sludge and other industrial waste to produce hydrogen. 7.4.4 Hydrogen production from other types of waste and multiple waste Some other types of waste, such as algae, are also considered raw materials for hydrogen production by thermochemical conversion (Ghatora et al., 2016; Voloshin et al., 2016; Williams and Laurens, 2010). In fact, the

Raw material

Processing conditions and results

References

Sludge

Sludge was subjected to steam vaporization treatment. The hydrogen yield increased with an increase in the reactor temperature. Under the same gasification conditions, sludge was more prone to produce hydrogen than paper residue and kitchen waste. In addition, hydrogen gas produced by the vaporization of sewage sludge was about three times the hydrogen gas produced by the gasification of air. At 1000
C, the yield of hydrogen was 0.076 ggas/gsample

Nipattummakul et al. (2010)

Sludge

Used traditional heating and microwave heating to maximize sludge pyrolysis biofuel production to obtain a maximum of 38% H2 and 66% H2 and CO

Domı´nguez et al. (2006)

Sludge

The potential of hydrogen production from sludge was studied using the down-draft gasification method. Experimental research on a pilot scale (5 kW) downdraft gasifier yielded 10%e11% (v/v) hydrogen

Midilli et al. (2002)

Sludge

A throat-type down-suction gasifier was used to gasify the sludge, combined with uncertainty analysis: 8%e12% H2 composition was finally obtained.

Dogru et al. (2002)

Waste tire

Thermogravimetric analysis of tires under different atmospheres (air, oxygen, and hydrogen diluted in nitrogen) using different heating rates. The researchers focused on effects of different parameters on combustion and gasification process

Castaldi (2007), Castaldi and Weiss (2007)

Waste tire

Gasified crushed rubber tires using steam in a fluidized bed reactor in range 627e787
C. Results showed that the gas produced was rich in olefins.

Pattabhi Raman et al. (1981)

Waste tire

The thermal decomposition of automobile tire samples under different steam contents at different temperatures was studied. Results showed that H2 and CO were the main components of the generated gas mixture, and aliphatic hydrocarbons and alkylbenzenes were petroleum products. With the increase of water volume and temperature, the main components of H2 and CO increase, and the residue gradually decreases.

Ogasawara et al. (1987)

166 Waste to Renewable Biohydrogen

TABLE 7.4 Research on thermochemical conversion of industrial waste to produce hydrogen.

In a laboratory-scale rotary kiln, three types of waste chemical products were obtained through steam gasification: tires, poplar, and garbage-derived fuels were compared under the same conditions. The tires had lower gas production and more solid residues. However, synthesis gas from tires had the highest hydrogen content (about 52 vol%), the highest yields of methane, ethylene, and ethane, and the lowest yields of oxygenates. In addition, tire syngas had higher heating values than other research waste.

Galvagno et al. (2009)

Waste tire

Tests were performed at a pyrolysis temperature of 500
C and a gasification temperature of 800
C. The results showed that higher gas and hydrogen production was obtained in pyrolysis and gasification than in pyrolysis alone.

Elbaba et al. (2010)

Black liquor

The reed pulp black liquid droplets and particles were pyrolyzed (N2 atmosphere) at different temperatures (530, 580, 630, 680, 730, and 780
C). The proportions of CO2, CH4, and CnHm in the gas-phase products varied with the operating temperature. The ratio of H2 and CO increased with the increase in operating temperature; the gasification test of the reed pulp papermaking black liquor with a solid content of 36% at different temperatures (530, 580, and 630
C) and the proportions of the components of the gas-phase products at three bed temperatures had consistent patterns with time: before equilibrium was reached, the proportion of H2 increased, the proportion of CO2, CH4, and CO decreased, and CnHm was almost unchanged. The proportion of each component after equilibrium was reached (from high to low) was: H2 (53%), CO2 (22%), CO (12%), CH4 (11%), and CnHm (2%).

Bai et al. (2020)

Black liquor

The technical and economic feasibility of supercritical water gasification of integrated black liquor in a pulp mill was studied. The process simulation was performed using Aspen Plus software. The results showed that compared with stainless steel, the chromium-nickel alloy reactor was more advantageous in terms of cogeneration and hydrogen. Production costs were lower.

¨ zdenkc¸i et al. (2019) O

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Tires, poplar, waste-derived fuel

167

168 Waste to Renewable Biohydrogen

thermochemical conversion of waste to produce hydrogen is not just the conversion of a single raw material; many researchers have studied the mechanism of hydrogen production by the joint action of a variety of wastes. Compared with a single raw material to produce hydrogen, there is a synergy in the joint action of a variety of raw materials, such as improvement in the energy conversion rate, improvement in the yield of syngas, and so on. Some of those studies are listed in Tables 7.5.

TABLE 7.5 Research in the thermochemical conversion of other types of waste to produce hydrogen. Raw material

Processing conditions and results

References

Cyanobacteria

The effects of particle size and residence time on gas yield and composition were studied in a fixed bed using water vapor as a gasification agent and biomass charcoal obtained after pyrolysis of cyanobacteria as raw materials. The results showed that solid residence time was more important than particle size for gas yield and biomass char conversion. Appropriate particle size and longer residence time were beneficial to increase gas yield and biomass char conversion.

Yan et al. (2010)

Microalgae

Gasification of spirulina into synthesis gas composed of H2, CO2, CO, and CH4 at 850e1000
C. Results showed that temperature had a key role in improving the conversion of hydrogen and carbon.

Hirano et al. (1998)

Chlorella vulgaris

Gasification of chlorella in the presence of an Ni catalyst at 350
C showed that the catalyst had a positive effect on improving conversion.

Raheem et al. (2017)

Microalgae

The gasification potential of microalgae was studied. Results showed that the ratio of H2/CO was largest when the ER was 0.3.

Adnan et al. (2017)

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TABLE 7.5 Research in the thermochemical conversion of other types of waste to produce hydrogen.dcont’d Raw material

Processing conditions and results

References

Algae

In the presence of 10% Fe2O3e90% CeO2 and red mud, algae biomass was used for steam gasification. This catalyst improved the tar reforming reaction and water-gas shift reaction (WGSR). Among various algae raw materials, the highest hydrogen yield was 413e1036 cc/g.

Duman et al. (2014)

Algae

Algae biomass was pyrolyzed in a fixed bed reactor at 1 atm and 500
C for 1 h to produce tritium biochar, which produced 5.93 wt% gas, 46.68% wt% oilewater, and 44.67 wt% solid residue; the gaseous product contained 45.7 mol% H2, 44.05 mol% CH4, and 10.25 mol% wt CO.

Ibrahim et al. (2020)

Microalgae

The supercritical water gasification of microalgae with an Ni catalyst was studied to produce hydrogen. With the increase in the catalyst molar ratio, the yield of H2 increased from 2.195.61 to 5.61 mmol/g.

Xie et al. (2019)

Black liquor, wheat straw

The synergistic effect of cogasification of black liquor and wheat straw in supercritical water was studied. The results showed that the H2 yield of cogasification of black liquor and wheat straw increased from 12.29 to 46.02 mol/kg at 500
C.

Cao et al. (2019)

Waste tire, palm core shell

Palm core shell was catalytically vaporized with waste tires. The results show that at 800
C, 30% of waste tires had a steam/raw material ratio of 4 kg/kg, hydrogen 66.15 vol%; and the total synthesis gas content (83.8 vol%) was the highest.

Suzana et al. (2013)

Microalgae, sludge

Microalgae cultured from struvite containing waste Chlorella from a wastewater treatment plant was converted into solid biofuel. By applying 5 wt% H,C mixed

Sztancs et al. (2020)

Continued

170 Waste to Renewable Biohydrogen

TABLE 7.5 Research in the thermochemical conversion of other types of waste to produce hydrogen.dcont’d Raw material

Processing conditions and results

References

concentration and reduced volatile matter content (24.61 wt%), the resulting high hydrogen, methane yield, and carbon conversion were 19.49, 2.98 mol/kg, and 82.31%, respectively. Polyvinyl chloride (PVC), coal, plastic

Research in PVC pyrolysis is introduced, including copyrolysis of PVC with biomassecoal and other plastics, catalytic dechlorination of raw material PVC, and subcritical and supercritical hydrothermal treatment of chlorine-containing crude oil.

Yu et al. (2016)

Horticultural waste, sludge

Cogasification with water vapor at different temperatures is described, as well as research into product distribution and gas synergy in the process of cogasification. The results showed that as the mass ratio increased, the H2 content in the blend increased and the yield of syngas decreased. At higher temperatures, the synergy was more pronounced.

Hu et al. (2020)

7.5 Conclusion Hydrogen energy is expected to have an important role in the upcoming global market. Hydrogen production from waste has a good protective effect on the environment and broad development prospects. In many hydrogen production technologies, thermochemistry is undoubtedly the key point to achieving large-scale production. Therefore, many researchers have studied the thermochemical conversion of waste (agricultural and forestry waste, urban domestic waste, industrial waste, and so on) to produce hydrogen. The main thermochemical pathways of hydrogen production are pyrolysis, gasification, and supercritical water gasification. The performance of hydrogen production is determined by many factors; thus, the mechanism of thermochemical conversion to hydrogen production has not been fully defined. The technology of thermochemical hydrogen production needs further research.

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References Adnan, M.A., Susanto, H., Binous, H., Muraza, O., Hossain, M.M., 2017. Feed compositions and gasification potential of several biomasses including a microalgae: a thermodynamic modeling approach. Int. J. Hydrogen Energy 17009e17019. https://doi.org/10.1016/ j.ijhydene.2017.05.187. Akbari, M., Oyedun, A.O., Kumar, A., 2018. Ammonia production from black liquor gasification and co-gasification with pulp and waste sludges: a techno-economic assessment. Energy 151, 133e143. https://doi.org/10.1016/j.energy.2018.03.056. Akgu¨l, G., Kruse, A., 2012. Influence of salts on the subcritical water-gas shift reaction. J. Supercrit. Fluids 66, 207e214. https://doi.org/10.1016/j.supflu.2011.10.009. Amidon, T., Wood, C., Shupe, A., Wang, Y., Graves, M., Liu, S., 2008. Biorefinery: conversion of woody biomass to chemicals, energy and materials. J. Biobased Mater. Bioenergy 2, 100e120. https://doi.org/10.1166/jbmb.2008.302. Arena, U., 2012. Process and technological aspects of municipal solid waste gasification. A review. Waste Manag. 625e639. https://doi.org/10.1016/j.wasman.2011.09.025. Bai, B., Liu, Y., Meng, X., Liu, C., Zhang, H., Zhang, W., Jin, H., 2020. Experimental investigation on gasification characteristics of polycarbonate (PC) microplastics in supercritical water. J. Energy Inst. 93, 624e633. https://doi.org/10.1016/j.joei.2019.06.003. Barelli, L., Bidini, G., Gallorini, F., Servili, S., 2008. Hydrogen production through sorptionenhanced steam methane reforming and membrane technology: a review. Energy 33, 554e570. https://doi.org/10.1016/j.energy.2007.10.018. Bartels, J.R., Pate, M.B., Olson, N.K., 2010. An economic survey of hydrogen production from conventional and alternative energy sources. Int. J. Hydrogen Energy 35, 8371e8384. https:// doi.org/10.1016/j.ijhydene.2010.04.035. Dedication. In: Basu, P. (Ed.), 2013. Biomass Gasification, Pyrolysis and Torrefaction, second ed. Academic Press, Boston. https://doi.org/10.1016/B978-0-12-396488-5.00021-6. p. v. Bauen, A., Berndes, G., Junginger, H.M., Londo, M., Vuille, F., 2009. Bioenergy - a sustainable and reliable energy source - a review of status and prospects. IEA Bioenergy ExCo 6. Bridgwater, A.V., 2003. Renewable fuels and chemicals by thermal processing of biomass. Chem. Eng. J. 91, 87e102. https://doi.org/10.1016/S1385-8947(02)00142-0. C¸a glar, A., Demirbas¸, A., 2002. Conversion of cotton cocoon shell to hydrogen rich gaseous products by pyrolysis. Energy Convers. Manag. 43, 489e497. https://doi.org/10.1016/S01968904(01)00037-1. Cao, C., Zhang, Y., Li, L., Wei, W., Wang, G., Bian, C., 2019. Supercritical water gasification of black liquor with wheat straw as the supplementary energy resource. Int. J. Hydrogen Energy 15737e15745. https://doi.org/10.1016/j.ijhydene.2018.10.006. Cao, L., Zhang, C., Chen, H., Tsang, D.C.W., Luo, G., Zhang, S., Chen, J., 2017. Hydrothermal liquefaction of agricultural and forestry wastes: state-of-the-art review and future prospects. Bioresour. Technol. 245, 1184e1193. https://doi.org/10.1016/j.biortech.2017.08.196. Carrier, M., Loppinet-Serani, A., Denux, D., Lasnier, J.-M., Ham-Pichavant, F., Cansell, F., Aymonier, C., 2011. Thermogravimetric analysis as a new method to determine the lignocellulosic composition of biomass. Biomass Bioenergy 35, 298e307. https://doi.org/10.1016/ j.biombioe.2010.08.067. Castaldi, M., 2007. An investigation into the mechanisms for styrene-butadiene copolymer (SBR) conversion in combustion and gasification environments. Int. J. Green Energy 45e63. https:// doi.org/10.1080/15435070601015478.

172 Waste to Renewable Biohydrogen Castaldi, M., Weiss, B., 2007. Beneficial use of waste tires: an integrated gasification and combustion process design via thermo-gravimetric analysis (TGA) of styreneebutadiene rubber (SBR) and PolyIsoprene (IR). Environ. Eng. Sci. 1160e1178. https://doi.org/10.1089/ ees.2007.0111. Chaubey, R., Sahu, S., James, O.O., Maity, S., 2013. A review on development of industrial processes and emerging techniques for production of hydrogen from renewable and sustainable sources. Renew. Sustain. Energy Rev. 23, 443e462. https://doi.org/10.1016/ j.rser.2013.02.019. Chiesa, P., Consonni, S., Kreutz, T., Williams, ], [Robert, 2005. Co-production of hydrogen, electricity and CO2 from coal with commercially ready technology. Part A: performance and emissions. Int. J. Hydrogen Energy 30, 747e767. https://doi.org/10.1016/ j.ijhydene.2004.08.002. Chong, M.-L., Sabaratnam, V., Shirai, Y., Hassan, M.A., 2009. Biohydrogen production from biomass and industrial wastes by dark fermentation. Int. J. Hydrogen Energy 34, 3277e3287. https://doi.org/10.1016/j.ijhydene.2009.02.010. Das, D., Veziroglu, T.N., 2008. Advances in biological hydrogen production processes. Int. J. Hydrogen Energy 33, 6046e6057. https://doi.org/10.1016/j.ijhydene.2008.07.098. Dascomb, J., Krothapalli, A., Fakhrai, R., 2013. Thermal conversion efficiency of producing hydrogen enriched syngas from biomass steam gasification. Int. J. Hydrogen Energy 11790e11798. https://doi.org/10.1016/j.ijhydene.2013.07.022. de Lasa, H., Salaices, E., Mazumder, J., Lucky, R., 2011. Catalytic steam gasification of biomass: catalysts, thermodynamics and kinetics. Chem. Rev. 111, 5404e5433. https://doi.org/10.1021/ cr200024w. Delgado, J., Aznar, M.P., Corella, J., 1997. Biomass gasification with steam in fluidized bed: effectiveness of CaO, MgO, and CaOMgO for hot raw gas cleaning. Ind. Eng. Chem. Res. 1535e1543. https://doi.org/10.1021/ie960273w. Demirbas, A., 2009. Hydrogen-rich gases from biomass via pyrolysis and air-steam gasification. Energy Sources, Part A Recover. Util. Environ. Eff. 1728e1736. https://doi.org/10.1080/ 15567030802459693. Demirbas¸, A., 2002. Pyrolysis and steam gasification processes of black liquor. Energy Convers. Manag. 43, 877e884. https://doi.org/10.1016/S0196-8904(01)00087-5. Demirbas¸, A., 2001. Biomass resource facilities and biomass conversion processing for fuels and chemicals. Energy Convers. Manag. 42, 1357e1378. https://doi.org/10.1016/S0196-8904(00) 00137-0. Dogru, M., Midilli, A., Howarth, C.R., 2002. Gasification of sewage sludge using a throated downdraft gasifier and uncertainty analysis. Fuel Process. Technol. 55e82. https://doi.org/ 10.1016/S0378-3820(01)00234-X. Domı´nguez, A., Mene´ndez, J.A., Inguanzo, M., Pı´s, J.J., 2006. Production of bio-fuels by high temperature pyrolysis of sewage sludge using conventional and microwave heating. Bioresour. Technol. 1185e1193. https://doi.org/10.1016/j.biortech.2005.05.011. Duman, G., Uddin, M.A., Yanik, J., 2014. Hydrogen production from algal biomass via steam gasification. Bioresour. Technol. 24e30. https://doi.org/10.1016/j.biortech.2014.04.096. Elbaba, I.F., Williams, P.T., 2012. Two stage pyrolysis-catalytic gasification of waste tyres: influence of process parameters. Appl. Catal. B Environ. 125, 136e143. https://doi.org/10.1016/ j.apcatb.2012.05.020. Elbaba, I.F., Wu, C., Williams, P.T., 2010. Catalytic pyrolysis-gasification of waste tire and tire elastomers for hydrogen production. Energy Fuels 3928e3935. https://doi.org/10.1021/ ef100317b.

Thermochemical processes for biohydrogen production Chapter | 7

173

Eriksson, H., Harvey, S., 2004. Black liquor gasificationdconsequences for both industry and society. Energy 29, 581e612. https://doi.org/10.1016/j.energy.2003.09.005. Fujishima, A., Honda, K., 1972. Electrochemical photolysis of water at a semiconductor electrode. Nature 238, 37e38. https://doi.org/10.1038/238037a0. Fiori, L., Valbusa, M., Castello, D., 2012. Supercritical water gasification of biomass for H2 production: process design. Bioresour. Technol. 121, 139e147. https://doi.org/10.1016/ j.biortech.2012.06.116. Galvagno, S., Casciaro, G., Casu, S., Martino, M., Mingazzini, C., Russo, A., Portofino, S., 2009. Steam gasification of tyre waste, poplar, and refuse-derived fuel: a comparative analysis. Waste Manag. 678e689. https://doi.org/10.1016/j.wasman.2008.06.003. Galvagno, S., Casu, S., Casciaro, G., Martino, M., Russo, A., Portofino, S., 2006. Steam gasification of refuse-derived fuel (RDF): influence of process temperature on yield and product composition. Energy Fuels 2284e2288. https://doi.org/10.1021/ef060239m. Garcia-Perez, M., Wang, X.S., Shen, J., Rhodes, M.J., Tian, F., Lee, W.-J., Wu, H., Li, C.-Z., 2008. Fast pyrolysis of oil mallee woody biomass: effect of temperature on the yield and quality of pyrolysis products. Ind. Eng. Chem. Res. 1846e1854. https://doi.org/10.1021/ie071497p. Gavala, H.N., Skiadas, I.V., Ahring, B.K., 2006. Biological hydrogen production in suspended and attached growth anaerobic reactor systems. Int. J. Hydrogen Energy 31, 1164e1175. https:// doi.org/10.1016/j.ijhydene.2005.09.009. Ghatora, S., Kumar, M., Vaezi, M., Kumar, A., Bressler, D., 2016. Monitoring sugar release during pipeline hydro-transport of wheat straw. Biomass Bioenergy 93, 144e149. https://doi.org/ 10.1016/j.biombioe.2016.07.007. Gutie´rrez Ortiz, F.J., Campanario, F.J., Aguilera, P.G., Ollero, P., 2015. Hydrogen production from supercritical water reforming of glycerol over Ni/Al2O3eSiO2 catalyst. Energy 634e642. https://doi.org/10.1016/j.energy.2015.03.046. He, M.Y., Hu, Z.Q., Xiao, B., Liu, S.M., Guo, X.J., Luo, S.Y., 2009. Study on hydrogen-rich gas production from municipal solid waste (MSW) by catalytic gasification. Environ. Eng. 02, 97e101. https://doi.org/10.13205/j.hjgc.2009.02.007 (In Chinese). Hirano, A., Hon-Nami, K., Kunito, S., Hada, M., Ogushi, Y., 1998. Temperature effect on continuous gasification of microalgal biomass: theoretical yield of methanol production and its energy balance. Catal. Today 399e404. https://doi.org/10.1016/S0920-5861(98)00275-2. Hosseini, S.E., Wahid, M.A., 2016. Hydrogen production from renewable and sustainable energy resources: promising green energy carrier for clean development. Renew. Sustain. Energy Rev. 57, 850e866. https://doi.org/10.1016/j.rser.2015.12.112. Hu, Q., Dai, Y., Wang, C.-H., 2020. Steam co-gasification of horticultural waste and sewage sludge: product distribution, synergistic analysis and optimization. Bioresour. Technol. 301, 122780. https://doi.org/10.1016/j.biortech.2020.122780. Huang, J.Z., Xu, Z., Li, H.L., Kang, G.H., Wang, W.J., 2006. Progress in study of hydrogen production by solar energy. Acta Energiae Solaris Sinica 27 (9), 947e954. https://doi.org/ 10.3321/j.issn:0254-0096.2006.09.018. Ibrahim, A.F.M., Dandamudi, K.P.R., Deng, S., Lin, J.Y.S., 2020. Pyrolysis of hydrothermal liquefaction algal biochar for hydrogen production in a membrane reactor. Fuel 265, 116935. https://doi.org/10.1016/j.fuel.2019.116935. Jahirul, M.I., 2012. Biofuels production through biomass pyrolysis da technological review. Energies 5, 4952e5001. https://doi.org/10.3390/en5124952. Jin, yu qi, Yan, jian hua, Chi, Y., Li, xiao dong, Cen, ke fa, 2001. Study on the pyrolysis kinetics of PVC. J. Fuel Chem. 381e384. https://doi.org/10.3969/j.issn.0253-2409.2001.04.022.

174 Waste to Renewable Biohydrogen Kaur, R., Gera, P., Jha, M., Bhaskar, T., 2019. Thermochemical Route for Biohydrogen Production, pp. 187e218. https://doi.org/10.1016/B978-0-444-64203-5.00008-3. Kim, J.-W., Mun, T.-Y., Kim, J.-O., Kim, J.-S., 2011. Air gasification of mixed plastic wastes using a two-stage gasifier for the production of producer gas with low tar and a high caloric value. Fuel 2266e2272. https://doi.org/10.1016/j.fuel.2011.02.021. Konstandopoulos, A.G., Pagkoura, C., Dimitrakis, D.A., Lorentzou, S., Karagiannakis, G.P., 2015. Solar hydrogen production. In: Fang, Z., Smith Jr., R.L., Qi, X. (Eds.), Production of Hydrogen from Renewable Resources. Springer, Netherlands, Dordrecht, pp. 283e311. https://doi.org/10.1007/978-94-017-7330-0_10. Kumar, A., Sarkar, S., 2011. Chapter 21 - biohydrogen production from bio-oil. In: Pandey, A., Larroche, C., Ricke, S.C., Dussap, C.-G., Gnansounou, E. (Eds.), Biofuels. Academic Press, Amsterdam, pp. 481e497. https://doi.org/10.1016/B978-0-12-385099-7.00022-X. Kumar, M., Olajire Oyedun, A., Kumar, A., 2018. A review on the current status of various hydrothermal technologies on biomass feedstock. Renew. Sustain. Energy Rev. 1742e1770. https://doi.org/10.1016/j.rser.2017.05.270. Kwak, T.-H., Maken, S., Lee, S., Park, J.-W., Min, B., Yoo, Y.D., 2006. Environmental Aspects of Gasification of Korean Municipal Solid Waste in a Pilot Plant. Fuel, pp. 2012e2017. https:// doi.org/10.1016/j.fuel.2006.03.012. Li, J., Liao, S., Dan, W., Jia, K., Zhou, X., 2012. Experimental study on catalytic steam gasification of municipal solid waste for bioenergy production in a combined fixed bed reactor. Biomass Bioenergy 174e180. https://doi.org/10.1016/j.biombioe.2012.08.026. Lu, P.M., Xiong, Z.H., Zhang, J., Fu, Y., Chen, Y., 2003. Study on catalytic hydrogenation of biomass to produce hydrogen-rich gas. Environ. Pollut. Treat. Technol. Equip. 31e34. https:// doi.org/10.3969/j.issn.1673-9108.2003.11.007 (In Chinese). Luo, S., Xiao, B., Hu, Z., Liu, S., 2010. Effect of particle size on pyrolysis of single-component municipal solid waste in fixed bed reactor. Int. J. Hydrogen Energy 93e97. https://doi.org/ 10.1016/j.ijhydene.2009.10.048. Lv, P., Chang, J., Xiong, Z., Huang, H., Wu, C., Chen, Y., Zhu, J., 2003. Biomass airsteam gasification in a fluidized bed to produce hydrogen-rich gas. Energy Fuels 677e682. https:// doi.org/10.1021/ef020181l. Mastellone, M.L., Zaccariello, L., Arena, U., 2010. Co-gasification of coal, plastic waste and wood in a bubbling fluidized bed reactor. Fuel 89, 2991e3000. https://doi.org/10.1016/ j.fuel.2010.05.019. Mazloomi, K., Gomes, C., 2012. Hydrogen as an energy carrier: prospects and challenges. Renew. Sustain. Energy Rev. 3024e3033. https://doi.org/10.1016/j.rser.2012.02.028. McKay, G., 2002. Dioxin characterisation, formation and minimisation during municipal solid waste (MSW) incineration: review. Chem. Eng. J. 86, 343e368. https://doi.org/10.1016/ S1385-8947(01)00228-5. Midilli, A., Dogru, M., Akay, G., Howarth, C.R., 2002. Hydrogen production from sewage sludge via a fixed bed gasifier product gas. Int. J. Hydrogen Energy 1035e1041. https://doi.org/ 10.1016/S0360-3199(02)00011-3. Modell, M., 1977. Reforming of glucose and wood at the critical conditions of water. Am. Soc. Mech. Eng. 99. Nanda, S., Reddy, S.N., Hunter, H.N., Dalai, A.K., Kozinski, J.A., 2015. Supercritical water gasification of fructose as a model compound for waste fruits and vegetables. J. Supercrit. Fluids 112e121. https://doi.org/10.1016/j.supflu.2015.05.009.

Thermochemical processes for biohydrogen production Chapter | 7

175

Naqvi, M., Yan, J., Dahlquist, E., 2010. Black liquor gasification integrated in pulp and paper mills: a critical review. Bioresour. Technol. 101, 8001e8015. https://doi.org/10.1016/ j.biortech.2010.05.013. Nikolaidis, P., Poullikkas, A., 2017. A comparative overview of hydrogen production processes. Renew. Sustain. Energy Rev. 67, 597e611. https://doi.org/10.1016/j.rser.2016.09.044. Nipattummakul, N., Ahmed, I.I., Kerdsuwan, S., Gupta, A.K., 2010. Hydrogen and syngas production from sewage sludge via steam gasification. Int. J. Hydrogen Energy 11738e11745. https://doi.org/10.1016/j.ijhydene.2010.08.032. Ogasawara, S., Kuroda, M., Wakao, N., 1987. Preparation of activated carbon by thermal decomposition of used automotive tires. Ind. Eng. Chem. Res. 2552e2556. https://doi.org/ 10.1021/ie00072a030. Okamoto, M., Miyahara, T., Mizuno, O., Noike, T., 2000. Biological hydrogen potential of materials characteristic of the organic fraction of municipal solid wastes. Water Sci. Technol. 41, 25e32. ¨ zdenkc¸i, K., De Blasio, C., Sarwar, G., Melin, K., Koskinen, J., Alopaeus, V., 2019. TechnoO economic feasibility of supercritical water gasification of black liquor. Energy 116284. https:// doi.org/10.1016/j.energy.2019.116284. Patel, M., Kumar, A., 2016. Production of renewable diesel through the hydroprocessing of lignocellulosic biomass-derived bio-oil: a review. Renew. Sustain. Energy Rev. 58, 1293e1307. https://doi.org/10.1016/j.rser.2015.12.146. Patel, M., Zhang, X., Kumar, A., 2016. Techno-economic and life cycle assessment on lignocellulosic biomass thermochemical conversion technologies: a review. Renew. Sustain. Energy Rev. 53, 1486e1499. https://doi.org/10.1016/j.rser.2015.09.070. Pattabhi Raman, K., Walawender, W.P., Fan, L.T., 1981. Gasification of waste tires in a fluid bed reactor. Conserv. Recycl. 79e88. https://doi.org/10.1016/0361-3658(81)90036-9. Psomopoulos, C.S., Bourka, A., Themelis, N.J., 2009. Waste-to-energy: a review of the status and benefits in USA. Waste Manag. 29, 1718e1724. https://doi.org/10.1016/ j.wasman.2008.11.020. Qu, T., Guo, W., Shen, L., Xiao, J., Zhao, K., 2011. Experimental study of biomass pyrolysis based on three major components: hemicellulose, cellulose, and lignin. Ind. Eng. Chem. Res. 10424e10433. https://doi.org/10.1021/ie1025453. Raheem, A., Dupont, V., Channa, A.Q., Zhao, X., Vuppaladadiyam, A.K., Taufiq-Yap, Y.-H., Zhao, M., Harun, R., 2017. Parametric characterization of air gasification of Chlorella vulgaris biomass. Energy Fuels 2959e2969. https://doi.org/10.1021/acs.energyfuels.6b03468. Reddy, N., Yang, Y., 2005. Biofibers from agricultural byproducts for industrial applications. Trends Biotechnol. 23, 22e27. https://doi.org/10.1016/j.tibtech.2004.11.002. Resende, F.L.P., 2014. Chapter 1 - reactor configurations and design parameters for thermochemical conversion of biomass into fuels, energy, and chemicals. In: Shi, F. (Ed.), Reactor and Process Design in Sustainable Energy Technology. Elsevier, Amsterdam, pp. 1e25. https://doi.org/10.1016/B978-0-444-59566-9.00001-6. Sarkar, S., Kumar, A., 2010. Biohydrogen production from forest and agricultural residues for upgrading of bitumen from oil sands. Energy 35, 582e591. https://doi.org/10.1016/ j.energy.2009.10.029. Savova, D., Apak, E., Ekinci, E., Yardim, F., Petrov, N., Budinova, T., Razvigorova, M., Minkova, V., 2001. Biomass conversion to carbon adsorbents and gas. Biomass Bioenergy 133e142. https://doi.org/10.1016/S0961-9534(01)00027-7.

176 Waste to Renewable Biohydrogen Song, R., Luo, B., Jing, D., 2016. Efficient photothermal catalytic hydrogen production over nonplasmonic Pt metal supported on TiO2. In: Dong, C.-L. (Ed.), Solar Hydrogen and Nanotechnology XI. SPIE, pp. 4e17. https://doi.org/10.1117/12.2239178. Sucipta, M., Kimijima, S., Suzuki, K., 2007. Performance analysis of the SOFCeMGT hybrid system with gasified biomass fuel. J. Power Sources 174, 124e135. https://doi.org/10.1016/ j.jpowsour.2007.08.102. Suzana, Y., Moghadam, R., Shoaibi, A., Melati, M., Khan, Z., Lim, M., Ghani, W., 2013. Hydrogen Production from Catalytic Steam Co-gasification of Waste Tire and Palm Kernel Shell in Pilot Scale Fluidized Bed Gasifier. https://doi.org/10.1109/SECON.2011.5752896. Sztancs, G., Juhasz, L., Nagy, B.J., Nemeth, A., Selim, A., Andre, A., Toth, A.J., Mizsey, P., Fozer, D., 2020. Co-Hydrothermal gasification of Chlorella vulgaris and hydrochar: the effects of waste-to-solid biofuel production and blending concentration on biogas generation. Bioresour. Technol. 302, 122793. https://doi.org/10.1016/j.biortech.2020.122793. Thamavithya, M., Dutta, A., 2008. An investigation of MSW gasification in a spout-fluid bed reactor. Fuel Process. Technol. 949e957. https://doi.org/10.1016/j.fuproc.2008.03.003. Tiantian, 2017. Study on the Influence of Biomass Composition on Gasification Hydrogen Production Rate. thesis (In Chinese). Vamvuka, D., 2011. Bio-oil, solid and gaseous biofuels from biomass pyrolysis processes-an overview. Int. J. Energy Res. 35, 835e862. https://doi.org/10.1002/er.1804. Voloshin, R.A., Rodionova, M.V., Zharmukhamedov, S.K., Veziroglu, N., Allakhverdiev, S.I., 2016. Review: biofuel production from plant and algal biomass. Int. J. Hydrogen Energy 41, 17257e17273. https://doi.org/10.1016/j.ijhydene.2016.07.084. Williams, P.J., le, B., Laurens, L.M.L., 2010. Microalgae as biodiesel & biomass feedstocks: review & analysis of the biochemistry,energetics & economics. Energy Environ. Sci. 3, 554e590. https://doi.org/10.1039/B924978H. Xie, L.-F., Duan, P.-G., Jiao, J.-L., Xu, Y.-P., 2019. Hydrothermal gasification of microalgae over nickel catalysts for production of hydrogen-rich fuel gas: effect of zeolite supports. Int. J. Hydrogen Energy 5114e5124. https://doi.org/10.1016/j.ijhydene.2018.09.175. Yan, F., Zhang, L., Hu, Z., Cheng, G., Jiang, C., Zhang, Y., Xu, T., He, P., Luo, S., Xiao, B., 2010. Hydrogen-rich gas production by steam gasification of char derived from cyanobacterial blooms (CDCB) in a fixed-bed reactor: influence of particle size and residence time on gas yield and syngas composition. Int. J. Hydrogen Energy 10212e10217. https://doi.org/10.1016/ j.ijhydene.2010.07.113. Yan, M., Su, H., Hantoko, D., Kanchanatip, E., Hamid, F.B.S., Zhang, S., Wang, G., Xu, Z., 2019. Experimental study on the energy conversion of food waste via supercritical water gasification: improvement of hydrogen production. Int. J. Hydrogen Energy 44, 4664e4673. https:// doi.org/10.1016/j.ijhydene.2018.12.193. Yan, Q., Guo, L., Lu, Y., 2006. Thermodynamic analysis of hydrogen production from biomass gasification in supercritical water. Energy Convers. Manag. 47, 1515e1528. https://doi.org/ 10.1016/j.enconman.2005.08.004. Yang, H., Yan, R., Chen, H., Lee, D.H., Zheng, C., 2007. Characteristics of hemicellulose, cellulose and lignin pyrolysis. Fuel 86, 1781e1788. https://doi.org/10.1016/j.fuel.2006.12.013. Young, G.C., 2010. MSW processes to energy with high-value products and specialty by-products. Munic. Solid Waste Energy Convers. Process. https://doi.org/10.1002/9780470608616.ch10. Yu, J., Sun, L., Ma, C., Qiao, Y., Yao, H., 2016. Thermal degradation of PVC: a review. Waste Manag. 48, 300e314. https://doi.org/10.1016/j.wasman.2015.11.041.

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Zhang, K., Kim, J.K., Park, B., Qian, S., Jin, B., Sheng, X., Zeng, H., Shin, H., Oh, S.H., Lee, C.-L., Park, J.H., 2017. Defect-induced epitaxial growth for efficient solar hydrogen production. Nano Lett. 17, 6676e6683. https://doi.org/10.1021/acs.nanolett.7b02622. Zhou, P., Elbeshbishy, E., Nakhla, G., 2013. Optimization of biological hydrogen production for anaerobic co-digestion of food waste and wastewater biosolids. Bioresour. Technol. 130, 710e718. https://doi.org/10.1016/j.biortech.2012.12.069.

Further reading IEA, 2019. The Future of Hydrogen. https://www.iea.org/reports/the-future-of-hydrogen (All rights reserved).

Chapter 8

Photosynthetic hydrogen production bacteria breeding technologies Panpan Li1, 2, 3 1 Key Laboratory of New Materials and Facilities for Rural Renewable Energy of Ministry of Agriculture and Rural Affairs, College of Mechanical and Electrical Engineering, Henan Agricultural University, Zhengzhou, China; 2Henan International Joint Laboratory of Biomass Energy and Nanomaterials, Henan Agricultural University, Zhengzhou, China; 3Collaborative Innovation Center of Biomass Energy, Zhengzhou, Henan Province, China

8.1 Introduction Research into renewable energy has become one of the major hot topics in the world, attracting the attention of governments and scientists in various countries. Green energy such as hydrogen energy, biodiesel, biogas, and other technologies has continuously improved through the deep processing of biomass. Among them, hydrogen can achieve zero emissions owing to its high calorific value of combustion and no pollution. Therefore, hydrogen is considered the most ideal alternative energy of fossil fuels (Zhang et al., 2017a,b). There are two ways to produce hydrogen: conventional and biological hydrogen production. Conventional hydrogen production methods mainly include water electrolysis, the transformation of fossil fuels and other hydrogen-containing substances, and chemical methods. In the process of hydrogen production by chemical conversion, the cost of environmental pollution is inestimable; the production is also based on the consumption of mineral energy. Thus, chemical hydrogen production has not been able to meet the requirements of environmental protection and sustainable development (Zhang et al., 2017a,b). Compared with chemical methods, biological hydrogen production is more friendly to the environment. The raw materials used in biohydrogen production are industrial and agricultural waste, which have the advantages of abundant sources and the reuse of waste. Therefore, biological hydrogen production is a promising method for hydrogen production and a focus of interest in the field of renewable energy research (Zhang et al., 2015; Liu, 2007). Waste to Renewable Biohydrogen. https://doi.org/10.1016/B978-0-12-821659-0.00005-8 Copyright © 2021 Elsevier Inc. All rights reserved.

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Biological hydrogen production methods mainly consist of the photolysis of water, dark fermentation, and photosynthetic fermentation.

8.1.1 Hydrogen production by photolysis of water Cyanobacteria and green algae can decompose aquatic hydrogen under light and anaerobic conditions to produce hydrogen. The advantages of hydrogen production by photolysis of water have two aspects. First, water is used as the raw material. Second, the solar energy conversion efficiency is about 10 times higher than that of plants. Meanwhile, disadvantages are outstanding. In the process of water photolysis, organic matter cannot be used and the complicated photosynthetic system makes it difficult to overcome the high free energy when producing hydrogen. Owing to the release of oxygen during the reaction process, there are serious technical obstacles in the direct photolysis of aquatic hydrogen, resulting in the low efficiency of hydrogen production, which limits the application in large-scale industry (Greenbmua, 1988; Hallenbeek and Benemann, 2002). In the process of the indirect photolysis of water, the concentration of biomass requires a huge amount of energy. Moreover, it is still in the initial stages (Benemann, 1998; Melies and Happe, 2001; Zhang et al., 2002).

8.1.2 Hydrogen production by dark fermentation Hydrogen production by dark fermentation relies on bacteria to decompose organic products to produce hydrogen under dark and anaerobic conditions. Hydrogen production condition is not restricted by light. Anaerobic fermentation can be widely used in the treatment of various organic raw materials and a high concentration of organic liquid waste. However, the amount of hydrogen production is still low, mainly because pyruvate fermentation is mostly used for the synthesis of cell materials rather than for the formation of hydrogen. On the other hand, the produced H2 can be catalyzed by the hydrogen absorption enzyme. Therefore, the technology of hydrogen production by anaerobic dark fermentation needs to be further improved through metabolic engineering and other methods (Khanal et al., 2004; Wu et al., 2004).

8.1.3 Hydrogen production by photosynthetic fermentation Photosynthetic bacteria can produce hydrogen under light and anaerobic conditions, with the advantage that it is able to use a variety of small molecule organic compounds. The theoretical light conversion efficiency is 100%. With only one photosynthetic system, the free energy required to produce hydrogen is smaller. Hydrogen production by photosynthetic bacteria is catalyzed by nitrogenase, and it has been proved that photosynthetic bacteria can use a variety of organic acids, sugars, amino acids, sulfides, and agricultural processing waste as substrates for continuous culture (Hallenbeck and

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181

Benemann, 2002; Li, 2010). Breeding of highly efficient photosynthetic hydrogen-producing bacteria and improving the efficiency of light conversion have become the main problems in photosynthetic hydrogen production technology. Photosynthetic bacteria (photosynthesis bacteria) are a kind of hydrosphere microorganism. They are widely distributed in oceans, lakes, rivers, paddy fields, sludge, soil, and other anaerobic places, carrying out noneoxygen producing photosynthesis to obtain their own nutrients. Two kinds of microbes can produce hydrogen by photosynthesis: microalgae and photosynthetic bacteria. Photosynthetic bacteria belong to photosynthetic heterotrophic microorganisms. There are many studies on Rhodospirillum rubrum, Rhodopseudomonas sphaeroides, Rhodopseudomonas rubrum, Rhodopseudomonas capsularis, Rhodobacter sphaeroides, and Ectothiorhodospiraceae vacuolata (Zhou et al., 2006).

8.2 Photosynthetic hydrogen production bacteria Photosynthetic hydrogen production bacteria contain photosynthetic system I (PSI) of the photosynthetic system. Electron donors or hydrogen donors are organics or reduced sulfide, which mainly rely on the decomposition of organics to produce hydrogen. Three enzymes are involved in hydrogen metabolism in photosynthetic bacteria: nitrogenase, hydrogenase, and reversible hydrogenase. The major enzyme that catalyzes the production of hydrogen by photosynthetic bacteria has been proved to be nitrogenase (Zhou et al., 2006). Photosynthetic bacteria have an important role in the circulation of natural elements because of functions such as carbon fixation, nitrogen fixation, nitrogen removal, and sulfur oxides (Zhang, 2008). Studies have shown that photosynthetic bacteria are nontoxic and nutrient-rich and contain a large number of proteins, coenzyme Q, and other amino acids (Ke, 1997; He et al., 2000). Poly-b-hydroxybutyrate (PHB), glycogen, and other special structures exist in the cells of photosynthetic bacteria. Under light conditions, CO2 can be reduced to organic matter, and nitrogen in the atmosphere can be fixed by the photosynthetic hydrogen production bacteria (Loach, 2000). Photosynthetic bacteria belong to gram-negative bacteria, and their forms are diverse (mainly spherical, rod-shaped, spiral-shaped, and ovoid). Most of the cells rely on flagella to move. They mainly propagate by binary division, and a few bacteria propagates by bud or trisection (Liu et al., 1991). Photosynthetic bacteria contain chlorophyll and carotenoids, and their suspensions would appear in different colors (magenta, red, orange-brown, or green). Current studies show that more than 20 strains of seven genera related to hydrogen production, including Clostridium, Rhodospirillum, Rhodopseudomonas, Trdiumbutyricum, Chromatium, Ectothiorhodospira, and Rhodomicrobium. Among them, more than 10 strains of seven species have been studied deeply in hydrogen production, such as R. sphaeroides, Rhodopseudomonas palustris, and R. capsularis (Zhu, 2013).

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8.2.1 Pure cultured photosynthetic hydrogen production bacteria Photosynthetic hydrogen production bacteria are abundant in marshes, lake channel sediments, sewage, and sewage treatment plants, especially in an environment with a high biodegradable organic matter content. Researchers have carried out a lot of work on isolating the strain. In 1942, Gest and Kamen (Gest and Kamen, 1949) found that Rh. rubrum could produce H2 under light and anaerobic condition with glutamate or aspartic acid as nitrogen source and organic acids as substrates. Rh. rubrum is a species in the genus Rhodophyllum. The cell size is 0.8
1.0 mm  7
10 mm, and the width of a spiral circle is 1.5e2.5 mm. Under anaerobic conditions, the liquid culture suspension is initially light pink; later, it is deep purple-red without brown. Cells under aerobic conditions appear colorless to pale pink. They can grow in a mineral salt medium with simple organic substrates supplemented with biotin. The optimum pH is 6.8e7.0. The optimum temperature is 30e35 C. R. pyogenes is a facultative photosynthetic anaerobic bacterium. It has characteristics and morphology similar to those of Pseudomonas capsulatum. Each strain of R. pyogenes grows rapidly under the light and anaerobic conditions with a size of 1.1
1.2  1.6
1.7 nm and a single polar flagellum. R. pyogenes is brown and red. On the RCVBN medium, the colony is round, smooth, slightly protruding, shiny, and nonsticky with neat edges. Under dark aerobic conditions, R. pyogenes strain is dark red with red in the center of the colony and milky white around it. All three strains of R. pyogenes could produce H2 through photosynthesis (Wu et al., 1984). More than 60 species in 22 genera of four families have been isolated, including purple nonsulfur bacteria, red sulfur bacteria, green sulfur bacteria, and slithery sulfur bacteria. Pure strains are preferred in theoretical research on hydrogen production by photosynthetic bacteria. However, large-scale hydrogen production by a single strain is difficult because many biological processes must be performed by at least two or more microorganisms (Yang et al., 2003). More attention has been paid to the mixed culture and fermentation of mixed microorganisms.

8.2.2 Mixed culture photosynthetic hydrogen production bacteria The mixed culture technology of photosynthetic hydrogen production bacteria increases the hydrogen production significantly and also degrades the large organic molecules into CO2 and H2O (Yang and Qu, 2003). It is essential to screen mixed cultured photosynthetic hydrogen production bacteria with high efficiency to ensure a high capacity of organic decomposition and hydrogen production.

8.2.2.1 Screening of mixed cultured hydrogen-producing photosynthetic bacteria Researchers in Henan Agricultural University have done a lot of work on isolating hydrogen-producing photosynthetic bacteria (You, 2005). The complete

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technological routes of strain isolation included sampling, enrichment, isolation, pure culture, preliminary screening (single-strain hydrogen production test), preliminary identification of dominant strains, and rescreening (compound strain hydrogen production test). A total of 24 samples were obtained from six sites in four seasons. According to different requirements of enrichment and isolation, the 24 samples were cultivated on anaerobic enrichment medium (You, 2005). The enriched suspension was isolated on the medium plate twice when its color turned from black or gray to red, pink, lime green, or brown. Until the pure strain was observed under the microscope, a single colony was chosen for cultivation to obtain a pure liquid strain suspension in vitro. After preliminary color observation, a staining test, and a substrate test, the pure bacteria obtained contain 11 strains of purple nonsulfur bacteria (denoted as F1eF11), 13 strains of purple sulfur bacteria (denoted as S1eS13), six strains of green sulfur bacteria (denoted as L1eL6), and three strains of slithering green sulfur bacteria (denoted as H1, H2, and H3). Thirty-three photosynthetic bacteria were tested for the use capacity of small molecule organic acids, pig manure, and glucose. Among the photosynthetic bacteria isolated, 18 strains were capable of producing H2. To screen photosynthetic bacteria with a strong hydrogen production capacity further, the 18 hydrogen-producing strains were tested for their hydrogen production capacity using acetic acid, propionic acid, and butyric acid as substrate, from which the efficient hydrogen-producing bacteria could be screened. The results showed that seven strains (F3, F5, F7, F11, L6, S7, and S9) were screened to produce hydrogen-using acetic acid, propionic acid, and butyric acid. Table 8.1 shows that the accumulative hydrogen production of the three organic acids by the seven photosynthetic bacteria obtained from the initial screening varied greatly. The total H2 production amount of L6 is only 43% of F7. However, considering its strong ability to use acetic acid, strain L6 is kept to construct highly efficient hydrogen-producing bacteria (You, 2005).

8.2.2.2 Natural microbes of Rhodospira Zhang has obtained the natural microbes of Rhodospira from the activated sludge of the Zhengzhou sewage treatment plant. The optimal hydrogen TABLE 8.1 Hydrogen production of photosynthetic bacteria using butyric acid. Strain

F3

F5

F7

F11

L6

S7

S9

H2 volume/mL

13.1

23.7

22.6

11.2

9.7

25.1

24.2

From You, X.F., 2005. Screening of Photosynthetic Hydrogen-Producing Bacteria and Study on Hydrogen-Producing Factors from Pig Waste Water. Zhengzhou Henan agricultural university.

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production process conditions were 32e40 C, pH 5e8, and inoculation at 5%e15%. The addition of organic nitrogen source greatly increased hydrogen production. The maximum hydrogen production of natural microbes of Rhodospira under optimal conditions was 1.62 L/L with 1% glucose (Zhang et al., 2005).

8.3 Growth characteristics of photosynthetic hydrogen production bacteria 8.3.1 Single-factor analysis of growth characteristics 8.3.1.1 Effect of spectrum Zhang conducted a comparative study on the effects of different light sources on the growth of photosynthetic bacteria by using blue light (400e520 nm), green light (550e570 nm), yellow light (about 590 nm), red light (600e700 nm), white light-emitting diode (LED) multicolor mixed spectral band light, and incandescent light (continuous spectrum) as the light sources during the hydrogen-producing process (Zhang et al., 2010). After cultivation in the enrichment medium for 24 h, the absorption spectrum of mixed photosynthetic hydrogen-producing bacteria was studied (Zhang et al., 2010). There were three absorption peaks at 383, 490, and 590 nm and two absorption peaks at 800 and 850 nm, which indicated that microbes could absorb infrared light while absorbing visible light. The absorption spectra of the mixed microbes may be the result of the combined action of the absorption spectra of various single strains. Strains Fl, F5, F7, and F11 had similar absorption characteristics, with the maximum absorption peaks at 375 and 590 nm, S7 and S9 at 380 and 490 nm, and L6 at 590 nm (You, 2005). The results showed that these seven strains had their own characteristics in the mixed microbes. The absorption spectrum of photosynthetic bacteria is mainly affected by the components of chlorophyll-a and carotenoids; the absorption peaks of chlorophyll-a are 800e810 nm and 850e890 nm, and the absorption peaks of carotenoids are 400e600 nm (Zhu et al., 1991; Wilson and Bradley, 1997; Miller and Varel, 2002; Yang et al., 2002). Based on the absorption spectrum of photosynthetic hydrogen production bacteria, Zhang chose yellow light (590 nm), blue light (400e520 nm), green light (520e570 nm), red light (620e700 nm), white LED light, and a common incandescent lamp for a further comparison experiment. The growth curves of the mixed microbes under different lights were studied (Zhang et al., 2010). The results showed that the growth curves were similar under the yellow, green, red, and blue light sources. The microbes grew slowly under each light source from 24 to 48 h. At 48e96 h, the microbes entered the logarithmic growth stage, the cell metabolism were vigorous, the bacteria multiplied in large numbers, and the number of bacteria increased rapidly. During the

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experiment, the liquid suspension changed from brown to dark red. The growth rate of microbes at 96e120 h slowed. After 120 h, the microbes entered the decay period, the total number of cells decreased significantly, the color of the liquid suspension quickly became lighter and finally white, and a large number of brown-red bacterial precipitation appeared at the bottom of the bottle. Under the white LED and incandescent light source, the lag phase of the microbes was longer. The logarithmic growth period, stable period, and decay period began at 72, 120, and 168 h, respectively (Zhang et al., 2010).

8.3.1.2 Effects of different nutrient elements Zhu studied the effects of different nutrient elements on the growth of photosynthetic bacteria, including carbon sources, acetic acid concentration, nitrogen sources, and nitrogen source concentration (Zhu, 2013). 8.3.1.2.1 Carbon sources The effects of three alkyd acids (acetic acid, lactic acid, and butyric acid) on the growth of photosynthetic bacteria were analyzed. The results are shown in Fig. 8.1 (Zhu, 2013). The metabolic pathways of photosynthetic hydrogen-producing mixed bacteria are diverse, so the use pathways of small-molecule acids in different species are also different. Fig. 8.1 shows that mixed microbes can use lactic acid, acetic acid, and butyric acid as carbon sources for growth. In the 96-h cultivation process, the maximum optical density (OD) of a sample measured at a wavelength of 600 nm of microbes using lactic acid, acetic acid,

FIGURE 8.1 The impact of different carbon sources on the growth of photosynthetic bacteria (Zhu, 2013). OD, optical density.

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and butyric acid reached 1.2, 2.2, and 2.39, respectively. Fig. 8.1 also shows that the medium with lactic acid as the carbon source had no significant influence on the growth of mixed microbes, the growth curve did not change much, and the overall growth of bacteria was slow. After 96 h of cultivation, the OD value was only 1.2, indicating that lactic acid is not an effective carbon source for photosynthetic bacteria. As can be seen in Fig. 8.1, acetic acid had a certain influence on the adaptability of mixed microbes, making it stay in the lag phase for a long time. However, after that, the bacteria grew actively, and the growth rate was basically unchanged after 48 h. Fig. 8.1 also shows that in the hydrogen-producing environment where the carbon source was butyric acid, the mixed microbes had no obvious lag phase after inoculation. The bacteria quickly adapted to the new environment and began to show exponential growth, and the OD value reached the maximum at the stable period. This indicates that butyric acid can effectively provide a viable carbon source for photosynthetic mixed bacteria (Zhu, 2013). However, whether butyric acid can effectively serve as a hydrogen donor and its effect on hydrogen production remains to be verified. 8.3.1.2.2 Acetic acid concentration Acetic acid is a common carbon source in the process of microbial metabolism and it is the end product of the microbial anaerobic fermentation process. Therefore, the effects of different acetic acid concentrations on the growth of photosynthetic hydrogen-producing microorganisms were analyzed and the concentrations were set to 2, 3, 4, 5, 6, and 7 g/L, respectively. The results showed that under the environment of a higher concentration of acetic acid, the amount of microbes was higher: that is, the higher the concentration of acetic acid, the better the growth of photosynthetic bacteria. When the acetic acid concentration was 2w4 g/L, the substrate concentration could still support the growth and metabolic activities of mixed bacteria in the early growth stage, but within 72 h, the substrate was almost exhausted and the cell growth basically stopped. When the acetic acid concentration was 5w6 g/L, the amount of microbes was higher and the growth period lasted longer. It also shows that there was no need to increase the acetic acid concentration to 7 g/L, because there was no obvious increase in the amount of microbes (Zhu, 2013). 8.3.1.2.3 Nitrogen source The nitrogen source is an essential material for the growth of photosynthetic microorganisms. Its main function is to synthesize nitrogen-containing substances in cells, but it is not used as an energy source. Nitrogen sources commonly used by microorganisms include proteins, nitrates, molecular nitrogen, and other substances. Photosynthetic bacteria have a strong selectivity in the absorption and use of nitrogen sources. Some ammonium salts can be directly used by microorganisms, whereas nitrate can be used only after reducing to NHþ 4.

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FIGURE 8.2 Growth of photosynthetic bacteria with different nitrogen sources (Zhu, 2013). OD, optical density.

Different strains in photosynthetic hydrogen-producing mixed microbes have different use pathways and efficiencies of different nitrogen sources, and they have strong selectivity for nitrogen sources during the growth process. Four substances ([NH4]2SO4, NaNO3, glutamine, and peptone) were selected as nitrogen sources to analyze the effects of different nitrogen sources on the growth characteristics of bacteria in the process of hydrogen production. The results are shown in Fig. 8.2 (Zhu, 2013). As shown in Fig. 8.2, the growth of photosynthetic bacteria is a relatively standard S-shaped curve with peptone as nitrogen source, and the boundary between the lag phase and logarithmic period is relatively clear. Because peptone cannot provide sufficient nitrogen source for growth, there is a long lag phase from 0 to 24 h, after which the overall growth is also slow. With ammonium sulfate as the nitrogen source, the photosynthetic bacteria quickly adapts to the growth environment, with a short lag phase and a long logarithmic period, showing an overall growth trend. Photosynthetic bacteria in a sodium nitrate environment grows faster in the initial stage, but the logarithmic period is shorter, whereas in the cultivation of glutamine as nitrogen source, the logarithmic phase is longer after lag phase, which indicates that the overall growth is good. When the nitrogen source is ammonium sulfate, photosynthetic bacteria are superior to other groups at any stage of growth and have the best growth conditions. After cultivation for 72 h, the OD660 value of the bacteria reaches 2.83. This is mainly because NHþ 4 of ammonium salts can be directly used by

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microbes without conversion, and thus it is more conducive to growth. Other nitrogen sources such as sodium nitrate and glutamine need to be further converted into NHþ 4 to be absorbed and used by cells. Photosynthetic bacteria grew slowly in the peptone group (Zhu, 2013). This is mainly because the nitrogen fixation efficiency of photosynthetic bacteria is lower than the growth rate, and the supplement of nitrogen is insufficient, resulting in a slow growth rate. 8.3.1.2.4 Ammonium salt concentrations To study on the effects of different (NH4)2SO4 concentrations on the growth of photosynthetic bacteria during hydrogen production, the concentrations of (NH4)2SO4 were set to 0, 0.5, 1, 1.5, 2, and 2.5 g/L. The results showed that under the condition of no nitrogen source, photosynthetic bacteria hardly grew, indicating that a nitrogen source is an essential substance for photosynthetic bacteria to grow and metabolize. When the concentration of (NH4)2SO4 was 0w1 g/L, the bacteria had a normal metabolism and good growth conditions. At the concentration of 1 g/L, the growth rate was highest. When the concentration of (NH4)2SO4 exceeded 1 g/L, the nitrogen source showed a strong inhibitory effect on the growth of the bacteria, and the bacteria hardly grew. This is mainly because the high concentration of (NH4)2SO4 might increase the cell osmotic pressure, leading to cell rupture and death (Zhu, 2013).

8.3.2 Multifactor analysis of growth characteristics Zhu explored appropriate bacterial growth conditions under various factors using photosynthetic hydrogen-producing microorganisms constructed by the laboratory of Henan Agricultural University to improve the amount of hydrogen production and the rate of hydrogen production of photosynthetic hydrogen-producing bacteria (Zhu, 2013). The OD value was selected as the single index of analysis and evaluation. Based on the results of the single-factor experiment, the temperature, light intensity, inoculum ratio, and pH value are four main parameters that have a great influence on the growth of photosynthetic hydrogen production bacteria. Orthogonal experiments were conducted on temperature (25, 30, and 35 C), light intensity (500, 1500, and 2500 lx), pH (6, 7, and 9), and inoculation ratio (10%, 30%, and 50%). An orthogonal table of L9 was selected. The OD (660 nm) value at the beginning of each experiment was 0.53, and the OD (660 nm) was measured after 72 h of cultivation (Zhou, 2004).

8.3.2.1 Range analysis of orthogonal experiments The results showed that the light intensity was the most important factor that affected microbial growth, followed by the inoculation ratio, pH value, and temperature (Zhu, 2013). The light intensity had the largest influence on the growth of photosynthetic bacteria, whereas the pH value and inoculation ratio influenced the growth of photosynthetic bacteria and the temperature had a relatively small influence on the growth of photosynthetic bacteria.

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8.3.2.2 Variance analysis According to the formula, the sum of the deviation square of each column and the sum of total deviations were calculated; the results are as follows. The deviation square of each column is calculated as (Zhu, 2013): T¼

n X

xi ¼ 4:67 þ 4:91 þ 4:90 ¼ 14:48

i¼1

CT ¼ S1 ¼

T 2 14:482 ¼ ¼ 23:30 n 9

3  1X 1 K1j2
CT ¼ 4:672 þ 4:192 þ 4:902
23:30 ¼ 0:009 3 j¼1 3

S2 ¼

3  1X 1 K2j2
CT ¼ 3:522 þ 5:522 þ 5:442
23:30 ¼ 0:87 3 j¼1 3

S3 ¼

3  1X 1 K3j2
CT ¼ 5:582 þ 5:622 þ 3:282
23:30 ¼ 1:19 3 j¼1 3

S4 ¼

3  1X 1 K4j2
CT ¼ 4:102 þ 5:932 þ 4:452
23:30 ¼ 0:63 3 j¼1 3

The total deviation sum of squares is: QT ¼

n X

x2i ¼ 1:132 þ 2:422 þ 1:122 þ 1:342 þ 1:112 þ 2:462 þ 1:052

i¼1

þ 1:992 þ 1:862 ¼ 26:03 ST ¼ QT
CT ¼ 25:719
23:30 ¼ 2:73 The total deviation within the group is: SE ¼ ST


4 X

Si ¼ 2:419
ð0:009 þ 0:87 þ 1:19 þ 0:63Þ ¼ 0:031

i¼1

Where the total degree of freedom is dfT ¼ n
1 ¼ 9
1 ¼ 8; and the factor degree of freedom is dfi ¼ m
1 ¼ 3
1 ¼ 2: Fi ¼ Si =Serror The results of variance analysis show that the inoculum ratio, light intensity, and pH value have significant effects on the growth of photosynthetic hydrogen-producing microorganisms. The pH value is the most significant impact factor. When the temperature is 25e35 C, its influence on microorganisms is not obvious. The best growth conditions are 30 C, inoculum ratio 10%, 1500 lx, and pH 7 (Zhu, 2013).

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8.4 Continuous culture system and device for photosynthetic hydrogen production bacteria Continuous culture, also called open culture, is relative to a batch culture or closed culture. Continuous culture is a cultivation method that uses effective measures to keep microorganisms growing vigorously in a specific environment. Specifically, when the microorganisms are cultured in a single batch to the later stage of the exponential phase, on the one hand, the fresh medium and the sterile air are continuously flowed in at a certain speed; on the other hand, the cultures are continuously flowed out at the same flow rate in the manner of overflow. Then, the cultures in the container can reach dynamic equilibrium. The microorganisms in the container can be in an equilibrium growth state and a constant growth rate in the exponential phase for a long time, so that a continuous growth system is constructed.

8.4.1 Continuous culture device of photosynthetic hydrogen production reactor Yang designed a continuous culture system of photosynthetic bacteria and developed a continuous cultivation device suitable for hydrogen-producing reactors of photosynthetic microorganisms (Yang, 2011).

8.4.1.1 Overall design The single unit of the system consists of medium storage tank, constant flow pump, reaction tank, lighting, seed liquid outlet (feeding box), and other parts (Yang, 2011). The incubator uses a glass box with dimensions of 100, 30, and 70 cm. The box can be opened from the bottom and side. The diameter of the box is 10 cm. It is equipped with pipes and valves. The light bands surround the box and provide the solar light source. The incubator adopts a side tangential feeding method. The reaction solution flows upward in the reactor, and the lateral outlet at the bottom is controlled by the valve to flow out. The effective volume of the single tank is 200 L. Multiple tanks can be operated in parallel according to production requirements. This device consists of six parallelepiped box-shaped glass incubators with a volume of 200 L in parallel, with a total volume of 1200 L (Yang, 2011). 8.4.1.2 Light system and culture medium delivery The light source is mainly provided by a light strip and sunlight surrounding the box. According to different wavelength ranges, blue light (460e465 nm), yellow light (about 590 nm), red light (650e790 nm), green light (550e568 nm), white light (three primary color combination wavelengths of 450, 540, and 510 nm), and infrared light (900 nm) were used to observe the growth characteristics of the bacteria (Yang, 2011). Under yellow light, bacteria grew fastest and had the highest absorption and use rate of the band

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around 590 nm. The experimental system used a bright LED band (yellow light). The system is made of glass, which increases light transmittance and can effectively use the solar light source. To ensure the stability of the operating parameters such as the inoculation ratio at the inlet of the reaction solution incubator, the flow rate of the medium liquid must be accurately controlled. The system uses two groups of six incubators. Each group has three incubators and one set of liquid metering pump. The metering pump transports the liquid culture medium so that it can be mixed in the pipeline before the inlet into the reactor and flow into the three incubators at a uniform speed.

8.4.1.3 Operation process control During the operation of the system, the temperature should be maintained at about 30 C. The incubator should be placed in an environment with a temperature of 30  1 C. The culture medium should be preheated and fed into the pump. 8.4.1.4 Operation of continuous photosynthetic hydrogen production device Microbes used in the operation experiment are photosynthetic hydrogenproducing bacteria constructed by the Ministry of Agriculture’s Key Laboratory of Renewable Energy, Henan Agricultural University. The whole process includes continuous cultivation, inoculation, hydrogen-producing fermentation, gas collection, and residual liquid collection of photosynthetic bacteria production strains (Fig. 8.3). A continuous photosynthetic hydrogen production test device was developed by Henan Agricultural University. It consists of an incubator unit, a feeding box unit, a reactor unit, a solar photovoltaic conversion, and an LED auxiliary lighting unit, heat exchange unit, solar concentrator unit, automatic

FIGURE 8.3 Process flowchart (Yang, 2011).

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control unit, and hydrogen metering and hydrogen storage unit (Yang, 2011). To determine the stability of production strains during continuous photosynthetic hydrogen production, the change in the OD660 value of the strains (liquid suspension at the exit of the incubator) was measured during continuous operation at about 30 C. The results showed that during continuous operation of the device, absorbance of photosynthetic bacteria was between 0.8 and 1.2, which basically meets the requirements of the hydrogen production stage. The pH value of photosynthetic bacteria was maintained between 7 and 7.5, which is relatively stable. In the continuous photosynthetic hydrogen production process, the stability of bacteria cultivated in the incubator could meet the requirements of the hydrogen production stage (Yang, 2011).

8.4.1.5 Features of the device This device consists of six parallelepiped box-shaped glass incubators with a volume of 200 L in parallel, with a total volume of 1200 L. It is placed on the iron frame, and rubber pads are laid on the iron frame to prevent the glass from being unevenly stressed and cracking. The single box adopts the method of tangential liquid feeding at the top and lateral liquid discharging at the bottom. When the solar light source is sufficient, it is not necessary to turn on the auxiliary LED light source for cultivation. The LED light sources are placed on the sides of a single incubator for light supplement. The liquid medium is delivered by a constant-flow pump. The continuous culture system of the photosynthetic microorganisms has the following characteristics: (1) Sunlight is the main form of dependable light source in the evolution of photosynthetic bacteria. The use of cheap and clean solar energy can effectively reduce the operating costs of hydrogen produced by photosynthetic bacteria and dependence on fossil fuel energy. The auxiliary light source is an LED cold light, which saves a lot of energy compared with ordinary incandescent light sources. (2) A reasonable incubator structure and material are used. When designing an incubator for the cultivation of photosynthetic hydrogen production microbes, the first consideration is the large amount of cultured bacteria. Faced with such a large amount of cultures, it is necessary to find a material that can withstand huge pressure if a single incubator is used. This kind of material usually does not have light transmission, which reduces the use of solar light sources and increases the artificial light source. The pressure of the glass incubator should be considered. This device is used to provide bacteria continuously for a large-scale photosynthetic biological hydrogen production reactor. If a serial method is adopted, once a problem occurs in a single link, the whole device cannot work. Therefore, the device uses six small incubators made of glass to

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provide bacteria to the reactor in parallel. In addition, there is a 5-cm water seal on the top of each incubator to increase the tightness of the incubator. (3) The glass at the top of the incubator can be disassembled for easy cleaning. Because photosynthetic bacteria exhibit different intensities of phototaxis during the growth, reproduction, and photosynthesis periods, they receive light by photoreceptors and perform phototaxis by moving organs. This phototaxis often causes photosynthetic pigments to concentrate around the light supply point. It causes pigment adsorption and pigment precipitation. If it is not cleaned in time, it will affect the cultivation of bacteria and affect the entire hydrogen production process. (4) The material and liquid transportation is controlled by a constant flow pump, and the flow is stable, which ensures the continuous supplement of the liquid cultures.

8.4.2 Anaerobic baffled reactoretype photosynthetic hydrogen production device Artificial light sources are mostly used for photofermentative bacteria, but they are basically thermal radiation sources, which have high energy consumption and can easily cause local thermal effects and light saturation effects on the near-light surface. In the design of large reactors, sufficient lighting conditions need to be considered, but the consumption of conventional energy must also be reduced. The anaerobic baffled reactor (ABR)-type photosynthetic hydrogen production device was designed by Wei of Henan Agricultural University. The total volume is 10.56 m3 and the effective volume is 7.8113 m3 (Wei, 2016).

8.4.2.1 Overall design The core processing technology of the device is raw material pretreatment plus ABR. The baffles are used to separate the reaction device into different monomers. The monomers can be individually lighted, which realizes the dark interval time required for photosynthetic bacteria during hydrogen production. There is no need to design a special stirring device because of effective selfstirring. The photosynthetic fermentation unit adopts a baffled structure and consists of eight compartments, four of which are a structural unit; two units are placed side by side. A plate heat exchanger is designed and installed at the bottom of the reactor to ensure the temperature requirements of the system. The overall structure of the reactor is made of 6-mm steel plate. Each format is individually designed with temperature detection equipment and has a gas collection device. The anticorrosive paint is painted inside the reactor to reduce the corrosion effect of the liquid on the wall (Wei, 2016).

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8.4.2.2 Light source Using sunlight as the main light source and LED as the auxiliary light source, the high-efficiency light collection and transmission system were designed. The high-efficiency solar energy transmission device adopts an advanced end fiber, which can realize multipoint light distribution in the reactor according to different paths of light propagation. A low-LED cold light source is used as an auxiliary light source to supplement for the instability and periodicity of the solar light source, and the LED lights are powered by solar photovoltaic cells. Through the efficient combination of sunlight, multipoint distribution of the built-in light source, and the combination of internal lighting of the LED auxiliary light source, the light conditions required by the bacteria during operation process are met to achieve efficient hydrogen production by photosynthetic microorganisms. 8.4.2.3 Operation process control Because of the large volume of the combined hydrogen production device, to achieve continuous and stable hydrogen production in the cold season, the system is equipped with a solar collector to provide a heat source for the hydrogen production reactor to ensure the optimal growth temperature of microorganisms and improve the efficiency of the heat exchange system. At the same time, the electric auxiliary heating device is installed and the temperature is automatically controlled to ensure a continuously and stable hydrogen-producing reactor.

8.5 Hydrogen production of photosynthetic bacteria Many elements affect the hydrogen production of photosynthetic microorganisms, including light conditions, strain characteristics, inoculation concentration, cultivation process, pH value, temperature, hydrogen donor, nitrogen source, and enzyme activities related to hydrogen metabolism (Zhou et al., 2006). Hydrogen release in the metabolism of photosynthetic bacteria is catalyzed by nitrogenase with energy provided by the photosynthetic phosphorylation process and the reducing power provided by the degradation of organics. Therefore, all factors related to the hydrogen production process can regulate photosynthetic hydrogen release. In addition to environmental factors such as light intensity, temperature, and pH value, the physiological state of the strains, the composition of the nutrients, and other biological factors are important elements that affect hydrogen production activity. Among them, light is the main factor (Yang et al., 2003).

8.5.1 Effect of culture conditions on hydrogen production Zhang discussed the influence of factors on the efficient hydrogen production process of photosynthetic bacteria, such as light intensity, temperature, pH value, inoculation ratio, air, and nitrogen source.

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The effects of light intensity, temperature, and pH value on the hydrogen production of photosynthetic bacteria are significant. The optimal light intensity is 2000e6000 lx, the suitable temperature is 28e34 C, the optimal initial pH value is 5e8, and the inoculation ratio is 10%e100%. The addition of nitrogen source has no significant effect on hydrogen production. However, in the glutamic acid group, the average hydrogen production rate in the stable H2 production stage is slightly higher than for other groups. The presence of O2 in the reaction flask will seriously affect hydrogen production (Zhang et al., 2006). Based on the absorption spectrum of photosynthetic hydrogen production bacteria, Zhang chose blue light (400e520 nm), green light (520e570 nm), yellow light (590 nm), red light (620e700 nm), white LED light, and a common incandescent lamp for a further comparison experiment. Zhang chose different light sources including blue light (400e520 nm), green light (550e570 nm), yellow light (about 590 nm), red light (600e700 nm), and white LED (multicolor mixed spectral band) to study on the effects on photosynthetic hydrogen production with an incandescent lamp (continuous spectrum) as control (Zhang et al., 2010). The results showed that mixed photosynthetic hydrogen-producing bacteria had better absorption and use of light at the absorption peak. The group with the yellow light source was the most prominent one, and the amount of hydrogen production was stable and largest. Except for the red light group, the average hydrogen production rate of photosynthetic bacteria increased to different extents compared with the incandescent lamp group. The average hydrogen production rate increased 1.73 times under the yellow light, then 1.22 times in the blue light group, both 1.12 times in green and white LED illumination groups. The average hydrogen production rate under red light was only 0.98 times that of control (Zhang et al., 2010). This is mainly because mixed photosynthetic hydrogenproducing bacteria have no obvious absorption peak at 620e700 nm, which leads to low use efficiency in this band.

8.5.2 Effect of nutrients on hydrogen production Many researchers have studied the effect of substrate on hydrogen production by photofermentation (Lu et al., 2018). Zhu studied the effects of different carbon sources, acetic acid concentration, nitrogen source, and nitrogen source concentrations on photosynthetic hydrogen production (Zhu, 2013).

8.5.2.1 Effects of different carbon sources Small molecular acids can be used as both carbon sources and hydrogen donors for photosynthetic hydrogen production bacteria. Photosynthetic bacteria of different species have different efficiencies in the use of carbon sources. The effects of three alkyd acids (acetic acid, lactic acid, and butyric acid) on photosynthetic hydrogen production were analyzed. The results showed that photosynthetic hydrogen production bacteria effectively used acetic acid and

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butyric acid for hydrogen production, and the total hydrogen production reached 563 and 985 mL, respectively. With lactic acid as the substrate, the total hydrogen production was only 108 mL (Zhu, 2013). The activity of bacteria to produce H2 from lactic acid was low. This result had a positive correlation with the growth curve of microbes. Photosynthetic hydrogen production bacteria grew vigorously and the hydrogen production increased accordingly.

8.5.2.2 Effects of different acetic acid concentrations Acetic acid is a common carbon source in the process of microbial metabolism; it is the end product of the microbial anaerobic fermentation process. Therefore, the effects of different acetic acid concentrations on the hydrogen production of photosynthetic hydrogen-producing microorganisms were analyzed. The concentrations were set to 2, 3, 4, 5, 6, and 7 g/L. When the acetic acid concentration was 3 g/L, the total amount of hydrogen production was the largest and the hydrogen production rate was also significantly higher than that under other concentrations. When the concentration of acetic acid exceeded 3 g/L, the hydrogen production began to decrease. When the acetic acid concentration was 7 g/L, the amount of hydrogen production declined severely and the hydrogen production phenomenon was hardly observed (Zhu, 2013). During the process of metabolism, some acidic substances may be generated. Too much acidic substances could lower the pH value of the solution, which is not conducive to the growth of bacteria. Therefore, the optimal concentration of acetic acid is 3 g/L for hydrogen production by photosynthetic hydrogen-producing bacteria. 8.5.2.3 Effects of different nitrogen sources Photosynthetic bacteria can produce hydrogen because of the catalysis of nitrogenase. The activity of nitrogenase directly affects the hydrogen production of photosynthetic bacteria. NHþ 4 has a strong inhibitory effect on the nitrogenase of photosynthetic bacteria, making the hydrogen production capacity of the bacteria decline. The organic nitrogen source needs to be decomposed into NHþ 4 by the bacteria, so the inhibitory effect on nitrogenase is weak. The inorganic nitrogen source can be directly used by the bacteria so that it will directly affect the activity of nitrogenase and the hydrogen production. In general, organic nitrogen glutamine is commonly used as a nitrogen source during the photosynthetic hydrogen production process. To explore the effects of nitrogen sources on photosynthetic hydrogen production, (NH4)2SO4, NaNO3, glutamine, and peptone were chosen to be the substrates. The results showed that the highest hydrogen production was 400 mL in the glutamine group, followed by the ammonium sulfate group at 380 mL, and then the ammonium nitrate group at 340 mL. Hydrogen was the least in the peptone group, which is consistent with its growth curve trend (Zhu, 2013).

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This is mainly because the nitrogen source is insufficient, the growth and the hydrogen production of photosynthetic bacteria are both slow. There is no obvious difference in total hydrogen production in the ammonium sulfate, sodium nitrate, and glutamine groups, and the inorganic nitrogen source did not significantly inhibit the hydrogen production of photosynthetic bacteria. There are interactions among different species of the mixed bacteria. Different use pathways may eliminate the inhibition of inorganic nitrogen on hydrogen production. Related studies showed that the inhibition of nitrogen source does not have a critical effect on photosynthetic hydrogen production. Whether the inorganic nitrogen source has an inhibitory effect on photosynthetic hydrogen production may also be related to C/N in the culture medium.

8.5.2.4 Effect of different nitrogen source concentrations To study on the effects of different (NH4)2SO4 concentrations on the hydrogen production of photosynthetic bacteria, the concentration of (NH4)2SO4 was set to 0, 0.5, 1, 1.5, and 2 g/L. The results show that when the (NH4)2SO4 concentration was 0.5e1 g/L, the hydrogen production amount was large and the hydrogen production phenomenon was obvious. When the nitrogen source concentration was 1 g/L, photosynthetic hydrogen-producing bacteria were more active in metabolism, the growth and the hydrogen-producing ability were strong and had the largest hydrogen production amount. Moreover, the total hydrogen production decreased significantly with an increase in (NH4)2SO4 concentration when it exceeded 1.5 g/L (Zhu, 2013). This may be due to excessive NHþ 4 in a free state existing in the solution; nitrogenase activity is inhibited by NHþ 4 , which ultimately leads to a decrease in hydrogen production. The optimal concentration of (NH4)2SO4 is 1 g/L in the photosynthetic hydrogen production process.

8.6 Conclusion Screening and breeding of photosynthetic hydrogen production bacteria is a key point of stable and continuous H2 production. Hydrogen production by mixed photosynthetic bacteria is a coordinated metabolic action among multiple species. Compared with hydrogen production by pure bacteria, mixed bacteria have more advantages in the substrate use rate and hydrogen production efficiency. Many elements such as temperature, inoculation ratio, illumination, and pH value can significantly affect the growth of photosynthetic bacteria and photosynthetic H2 production. The effect of pH on hydrogen production is similar in all hydrogen-producing microorganisms. Although different strains are selective according to light intensity and temperature, screening of hydrogen-producing strains with the same light and temperature demands for growth and hydrogen production can greatly simplify the H2 production process. Meanwhile, the inoculation ratio and strain cultivation directly affect the physiology, growth state, and metabolite activity of

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the strains. Photosynthetic hydrogen production bacteria can use small molecules such as acetic acid, butyric acid, and lactic acid as a carbon source and hydrogen-producing matrix. The nutrients including carbon sources and nitrogen sources, and their concentrations could significantly affect the growth and H2 production of photosynthetic bacteria. The continuous culture system and device of the photosynthetic microorganisms is an important guarantee for effective photosynthetic H2 production.

References Benemann, J.R., 1998. Processes analysis and economics of biophotolysis of water. Photoproduction of Hydrogen 10, 2e28. Gest, H., Kamen, M.D., 1949. Photoproduction of molecular hydrogen by Rhodospirillum rubrum. Science 109 (2840). Greenbaum, E., 1988. Energetic efficiency of hydrogen photoevolution by algal water splitting. Biophys. J. 54 (2), 365e368. Hallenbeck, P.C., Benemann, J.R., 2002. Biological hydrogen production: fermentations and limiting processes. Int. J. Hydrogen Energy 27 (1), 1184e1193. He, Z., Wang, X., Sun, X., Ma, J., 2000. Research progress of photosynthetic bacteria. J. Hebei Vocat. Tech. Norm. Univ. 14 (1), 69e72. Ke, S., 1997. Advances in research and application of photosynthetic bacteria. Chin. J. Sci. 06.02 (2), 33e36. Khanal, S.K., Chen, W.H., Li, L., Sung, S., 2004. Biological hydrogen production: effects of pH and intermediate products. Int. J. Hydrogen Energy 29, 1123e1131. Li, Y.L., 2010. Study on colony characteristics of photosynthetic bacteria. Agric. Technol. Equip. 22, 3e6. Liu, J., 2007. Study on Reduction of Ammonium by Aerobic Nitrate from Microorganisms. Sichuan university, Chengdu. Liu, R., Diao, H., Liang, F., Zhao, D., et al., 1991. Photosynthetic Bacteria and Their Applications. China Agricultural Science and Technology Press, Beijing, pp. 163e166. Loach, P.A., 2000. Supramolecular complexes in photosynthetic bacteria (comment). Proc. Natl. Acad. Sci. U S A 97 (10), 506e508. Lu, C.Y., Zhang, Z.P., Zhou, X.H., Hu, J.J., Ge, X.M., Xia, C.X., Zhao, J., Wang, Y., Jing, Y.Y., Zhang, Q.G., 2018. Effect of substrate concentration on hydrogen production by photofermentation in the pilot-scale baffled bioreactor. Bioresour. Technol. 247, 1173e1176. Melis, A., Happe, T., 2001. Hydrogen production. Green algae as a source of energy. Plant Physiol. 127 (3), 740e748. Miller, D.N., Varel, V.H., 2002. An invitro study of manure composition on the biochemical origins, composition, and accumulation of odorous compounds in cattle feedlots. Anim. Sci. 80, 2214e2222. Wei, B., 2016. Design and Operation Research of Biomass Dark-Light Combined Biological Hydrogen Production Unit Based on Solar Energy. Henan agricultural university, Zhengzhou. Wilson, N.G., Bradley, G., 1997. A study of a bacterial immobilization substratum for use in the bioremediation of crude oil in a saltwater system. Appl. Microbiol. 23, 524e530. Wu, X., Yang, Q., Liu, W., Yu, G., 2004. Research progress and application of photosynthetic bacteria. J. Agric. Sci. Technol. China 6 (2), 34e38.

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Wu, Y.Q., Yu, J.L., Song, H.Y., 1984. Isolation, identification and classification of Pseudomonas spheroids. Microbiol. China 01, 17e20. Yang, J.H., 2011. Continuous Culture System and Equipment for Producing Hydrogen Strains by Photosynthetic Microorganisms. Henan Agricultural University, Zhengzhou. Yang, S.P., Zhao, C.G., Li, J., Kang, C., Qu, Y.B., 2002. Study on efficient breeding of hydrogenproducing photosynthetic bacteria. J. Shandong Univ. 37 (4), 353e358. Yang, S.P., Qu, Y.B., 2003. Hydrogen production by photosynthetic bacteria. Mod. Chem. Ind. 23 (9), 17e21. Yang, S.P., Zhao, C.G., Qu, Y.B., Qian, X.M., 2003. Progress in the research on hydrogen production by photosynthetic bacteria. Acta Hydrobiol. Sin. 27 (1), 85e91. You, X.F., 2005. Screening of Photosynthetic Hydrogen-Producing Bacteria and Study on Hydrogen-Producing Factors from Pig Waste Water. Zhengzhou Henan agricultural university. Zhang, Q.G., An, J., Wang, Y., Yang, Q., Li, G., 2010. Effects of visible spectrum on hydrogen production and growth characteristics of hybrid photosynthetic bacteria. Acta Energiae Solaris Sin. 31 (03), 391e395. Zhang, L., Happe, T., Melies, A., 2002. Biochemical and morphological characterization of sulfurdeprived and H2 producing Chlamydomonas reinhardtii (green alge). Planta 214, 552e561. Zhang, Q.G., Hu, J.J., Lee, D.J., Lee, Y.J., 2017a. Sludge treatment: current research trends. Bioresour. Technol. 243, 1159e1172. Zhang, Q.G., Lei, T.Z., You, X.F., Yang, Q.F., Yuan, Y., Zhang, J., 2005. Experimental study on factors affecting hydrogen production of natural mixed helicobacter oryzae. Acta Energiae Solaris Sin. 26 (2), 248e251. Zhang, Q.G., Wang, S.L., You, X.F., 2006. Effects of the influencing factors of photosynthetic bacteria group on hydrogen production. Trans. Chin. Soc. Agric. Eng. 22 (10), 182e185. Zhang, Q.G., Wang, Y., Zhang, Z.P., Lee, D.J., Zhou, X.H., Jing, Y.Y., Ge, X.M., Jiang, D.P., He, C., 2017b. Photo-fermentative hydrogen production from crop residue: a mini review. Bioresour. Technol. 229, 222e230. Zhang, Y., 2008. Study on Physiological and Biochemical Characteristics of Photosynthetic Engineering Bacteria and Reaction Kinetics of Biological Treatment. Hebei university of science and technology, Shijiazhuang. Zhang, Z.P., Wang, Y., Hu, J.J., Wu, Q.L., Zhang, Q.G., 2015. Influence of mixing method and hydraulic retention time on hydrogen production through photo-fermentation with mixed strains. Int. J. Hydrogen Energy 40 (20), 6521e6529. Zhou, D., 2004. Course in Microbiology. Higher Education Press, Beijing. Zhou, R.Y., You, X.F., Zhang, Q.G., 2006. Advances in hydrogen production by photosynthetic microorganisms. China Biogas 02, 31e34. Zhu, Y., 2013. Study on Microflora Characteristics of Hydrogen Production by Photosynthetic Organisms. Henan Agricultural University, Zhengzhou. Zhu, Z., Yu, J., Lin, Z., Li, K., 1991. Research and Application of Photosynthetic Bacteria. Shanghai Jiao Tong University Press, Shanghai.

Chapter 9

Photosynthetic biological hydrogen production reactors, systems, and process optimization Chaoyang Lu1, 2, 3 1 Key Laboratory of New Materials and Facilities for Rural Renewable Energy of Ministry of Agriculture and Rural Affairs, College of Mechanical and Electrical Engineering, Henan Agricultural University, Zhengzhou, Henan, China; 2Henan International Joint Laboratory of Biomass Energy and Nanomaterials, Henan Agricultural University, Zhengzhou, Henan, China; 3 Collaborative Innovation Center of Biomass Energy, Zhengzhou, Henan, China

9.1 Introduction Hydrogen energy economy is an assumption of economic structure with hydrogen energy as the energy medium. Solar energy, wind energy, water energy, and so on are transformed into electric energy, and then electric energy is used to electrolyze water to produce hydrogen. Finally, hydrogen is used cleanly and efficiently by combustion or power generation. Biohydrogen production is a hydrogen production method in which hydrogen-producing microorganisms degrade domestic waste, organic wastewater, waste biomass, and so forth. Photo-fermentation hydrogen production has the advantages of a stable hydrogen production rate, a high hydrogen concentration, and the degradation of volatile fatty acids. A bioreactor is a device or system that supports a bioactive environment. A photobioreactor can be defined as a culture system. To complete a lightdependent biological process, light must pass through the transparent walls of the reactor to reach the cultured cells. A successful photobioreactor must ensure the design is simple, material and production costs are cheap, light use is high, and temperature can be controlled. Many technological parameters affect the performance of photobioreactors, such as light, the biomass concentration, the method of mixing substrates, cell shear, temperature, and the mass transfer rate.

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This study discusses different types of photosynthetic hydrogen production, the influence of different factors on photosynthetic hydrogen production, and optimization of continuous-flow photosynthetic biological hydrogen production.

9.2 Reactor type 9.2.1 Baffled reactor A baffled reactor can increase the agitation of a fermentation broth and increase the reaction time of the substrate in the reactor, improving the hydrogen production performance and energy conversion rate. Zhang et al. (2015) studied the biohydrogen performance of five different bioreactors with diverse mixing methods by using two types of reactors: batch and static batch. For the baffle plate and counterflow baffle continuous bioreactor, mixing was achieved with the fermentation medium flowing through the baffle plate in the baffle plate, and low-energy light-emitting diode (LED) lamps were built into the baffle plate. Repeated experiments with different hydraulic retention times were performed to test the capacity of hydrogen production. It was found that magnetic stirring bioreactors were more likely to damage the structure of bacteria than were conventional bioreactors, leading to an increase in pH, so magnetic stirring was not suitable for the photo-fermentation biohydrogen production (PFHP) system. According to the experimental results, the hydrogen production rate of the continuous bioreactor was higher than that of the intermittent bioreactor, the hydrogen production yield in baffle photo-fermentation bioreactor was highest, and the hydrogen production rate of the batch bioreactor was stable.

9.2.2 Triangle flask A triangle flask is a commonly used bioreactor in a laboratory. It has the advantages of a small size, high controllability, and low cost. Basar Uyar et al. (2007) studied biohydrogen production with a 4.1-mL rubber conical glass tube. They found that photobioreactors were completely filled with culture medium without argon blowing. Most photobioreactors had headspace and the anaerobic environment was made of flushing argon. The bioreactor can be connected to a computer to detect and record continuous hydrogen production. The research results found that infrared light had a vital role in hydrogen synthesis. The hydrogen-producing ability of bacteria could be developed when the wavelength of light was 600e800 nm.

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9.2.3 Tubular A tubular reactor is also a common photosynthetic hydrogen production reactor. It has the advantages of uniform light transmittance and uniform reaction conditions. A tubular photobioreactor is the most common type of bioreactor used in photo-fermentation hydrogen production. Because of its sufficient light permeability and large surface volume ratio, its surface can capture maximal light energy. However, there are many shortcomings, such as the small diameter and working volume, large footprint, large flow resistance, and energy input in the tube; in addition, it is difficult to control temperature, there is a high material cost, and there is low light conversion efficiency. Although the design of the tubular reactor is diverse, the main effect of the specific design on the light state is the difference in photon flux density incident on the surface of the reactor. In most designs, the shape of the light gradient in the tube is similar. In terms of liquid mixing methods, most designs are similar. The way to scale up is to connect many tubes through manifolds. The tube reactor should theoretically show better efficiency because the average lightedark period is shorter (Show et al., 2012). Modigell modified a tubular reactor to make it a modular outdoor photobioreactor. In outdoor experiments, the hydrogen production yield of lactic acid reached 2 L/m2 h and the light conversion efficiency was 2% (Kapdan and Kargi, 2006). In addition to the depth of the photobioreactor, the height of the panel or the length of the tube of the tubular photobioreactor may be a parameter that limits amplification. The plate height (or tube length) determines the maximum travel distance of hydrogen bubbles during cultivation: that is, the hydrogen bubbles formed at the bottom (or inlet) of the photobioreactor must pass through the medium all the way up to the gas collection system. The longer the generated hydrogen bubbles stay in the photobioreactor, the easier it is for bacteria to absorb and use hydrogen bubbles through the absorption of hydrogenase, resulting in a decrease in hydrogen yield (Uyar, 2016). Wang et al. (2019) used lignocellulosic biomass of paulownia to study the hydrogen production potential of cellulose. They used a tubular multicycle bioreactor to produce biohydrogen, dark reaction, and photoreaction synergistically using a mixed flora of photosynthetic and anaerobic bacteria. The volume ratio of the reaction zone was 1:4. The photoreaction device was composed of five parallel glass tubes with a length and diameter of 2.0and 0.05 m, the total volume of the photoreaction device was 16 L, and yellow LED fiber-optic lighting was used. The reaction rate reflected the raw material processing capacity of the bioreactor. The entire process of hydrogen production in the reactor was stable, the minimum value was 0.91 L/h, the maximum value was 1.06 L/h, and the fluctuation of gas production was small.

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Tredici et al. (1998) used three different types of photobioreactors: a polyvinyl chloride (PVC) spiral tube reactor; a near-horizontal tube reactor; and a near-horizontal plate (the last two were made of polymethyl methacrylate and organic glass) for cyanobacteria plateau culture experiments. The spiral tubular photobioreactor consisted of three 49-m-long transparent PVC tubes (inner diameter: 3 cm, wall thickness: 0.5 cm), wrapped around a rigid vertical structure. Bubbles injected at the bottom of the pipe rose along the length of the reactor and escaped through the upper end of the pipe, which were connected to a deaerator with a capacity of about 20 L. The nearhorizontal tube reactor consisted of five 6-m-long plexiglass tubes (inner diameter: 3.4 cm, wall thickness: 0.3 cm), which were placed side by side with no intertube space. The flat plate reactor was a rectangular room with a height of 0.54 m, width of 0.40 m, and thickness of 0.025 m. The top was open and it was a flat reactor made of plexiglass flakes of 0.6-cm-thick material. Using Arthrospira platensis M2 for culture in outdoor tubular bioreactors and flatmounted bioreactors, under the strict control of the temperature, concentration, and pH of the two reactors, the culture in the tubular bioreactor had higher productivity and a higher growth rate. The ideal bioreactor will maximize volumetric productivity and light use efficiency. Fresnel lenses and optical fibers are used in experiments, but they are too complicated to achieve mass production and commercial applications. In Das’s work (Das et al., 2001), taking microalgae as an example, the biomass produced in large ponds was higher than that produced in tubular photobioreactors. However, the amount of hydrogen produced in the tubular photobioreactor was higher. Gas retention was a major problem for immobilizing entire cell systems because it reduced the working volume of the bioreactor. Compared with tubular bioreactors, cone and diamond bioreactors performed better owing to reduced gas holdup. Using a diamond-shaped bioreactor, the gas content of the tubular reactor was reduced by 67%. Tamburic et al. (2011) used a tubular photobioreactor with good light penetrability and a large surface-to-volume ratio to get maximal hydrogen production by testing dissolved oxygen, optical density, temperature, and agitation during the anaerobic photosynthetic hydrogen production of cyanobacteria. The results showed that the stirring speed and light intensity had significant effects on the growth of the culture, and the hydrogen production was increased by upgrading the photobioreactor. Tubular reactors consist of one or more transparent tubes of the same or different size. The structure can be a single cylinder, a parallel cylinder, or a sine tube. Compared with flat reactors, tubular reactors have a higher surface volume ratio. In addition, tubular reactors improve hydrogen production and solideliquid separation because of the high mass transfer rates between the liquid and gas phases. However, there are many shortcomings, such as that the diameter and working volume are small, the footprint is large, the flow resistance and energy input in the tube are large, the temperature is difficult to

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control, the material cost is high, and light conversion efficiency is low (Zhang et al., 2017b). Adessi et al. (Adessi and De Philippis, 2014) studied hydrogen production by purple nonsulfur bacteria. They found that the longer the pipe of tubular bioreactor, the longer the bubble stayed in the reactor and the more hydrogen was absorbed by the cells, so the hydrogen production capacity was reduced in theory. Adessi et al. (2012) used Chlorophyll a fluorescence as a detection tool to study the hydrogen-producing ability of cultured bacteria in a 50-L tubular bioreactor. The photobioreactor consisted of 10 parallel heat-resistant glass tubes (length: 2 m, inner diameter: 4.85 cm), which were connected by PVC U-shaped elbows and watertight flanges. The tube was placed in a constanttemperature stainless-steel container. The tube was washed with circulated 50 L 1% sodium hypochlorite solution for 12 h; then, the reactor was washed twice with sterile deionized water. The hydrogen yield was highest in outdoor experiments using purple non-sulfur (PNS) bacteria in the tubular bioreactor. Zhang et al. (2017c) think that the tubular reactor may be the first photobioreactor. It was also the simplest reactor type developed for photofermentation biohydrogen production. The surface volume ratio of tubular reactor is bigger than others, which makes light energy irradiation in the bioreactor. The column reactor is also an advanced tubular reactor, consisting of several reactors connected in series or parallel. Molina et al. (2001) cultivated microalgae with a tubular photobioreactor. The photobioreactor used a gas lift device to circulate the culture. This circulation method has no moving parts, which reduces the possibility of pollution and avoids damage to mechanical air pumps. This design method combines battery growth related to external radiation, oxygen accumulation in the solar loop, oxygen removal in gas lifts, and the fluid dynamics of gas lift systems effectively. These factors have a significant impact on the flow rate through the solar receiver. Javanmardian and Palsson (1992) designed a cylindrical photobioreactor consisting of six parts: a light source, a light transmission system, a reactor, a gas exchange unit, an ultrafiltration unit, and an online sensing detection device. A mixture of nitrogen, oxygen, and carbon dioxide acted as a gas exchange module. The pH values, dissolved oxygen, and dissolved oxygen concentrations in the inlet and outlet streams were continuously measured and entered into a computer that stored the data. The online ultrafiltration device was used to dialyze the medium at a higher flow rate. Waste or secretions can be selectively separated and exchanged with fresh medium when this device is used. The culture volume of the reactor was 0.6 L and the total volume of the photobioreactor system was 1 L. The light radiators in the cylindrical bioreactor were arranged as concentric vertical cylinders. Light entered the reactor through fiber-optic cables and the reactor was capable of cultivating highdensity cultures.

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Miro´n et al. (2000) studied bubble columns and airlift photobioreactors. They found that the gas permeability of bubble columns and airlift deicers was affected by the inflation rate, gas holdup, liquid velocity mixing, and turbulence. The oxygen produced by photosynthesis also needed to be supplemented. Because too much decomposition of oxygen can inhibit photosynthesis, the fluid dynamics and mass transfer parameters of three types of air-stirred reactors, including bubble tower, split-cylinder, airlift deicing, and concentric diversion tube airlift containers, were studied. Except for research purposes, bubble columns and airlift reactors are not used as photobioreactors, and existing correlations are used to predict the gas content and pressure in bubble columns. In contrast, existing nonmechanical correlations perform poorly in predicting the behavior of airlift bioreactors. Camacho Rubio et al. (1999) established a predictive model of the axial concentration distributions of dissolved oxygen and carbon dioxide in a tubular photobioreactor for microalgal culture. The length of the solar receiver tube, photosynthesis rate, flow rate, mixing degree, and gaseliquid transmission quality were designed in the model. This work involved the main aspects of the design of a tubular photobioreactor, including the accumulation and removal of oxygen from photosynthesis, the high use of expensive carbon dioxide, and the effect of liquid velocity on the concentration distribution of these gases in a solar tube. A model for predicting the distribution of oxygen and carbon dioxide in the gas and liquid phases was established. Perez-Mora et al. (2016) used airlifted tubular photobioreactors to study Staphylococcus bovis, a eukaryotic photosynthetic microorganism that requires light, water, and inorganic nutrients for growth. The reactor consisted of 12 transparent glass tubes (1.0 cm inside diameter) with a slope of 2% (1.15) to facilitate the flow of liquid. It was connected to a silicone hose with the same inside diameter. There were three inlets at the top of the deaerator. Lee et al. (2011) used synthetic wastewater and anaerobic hydrogen fermentation wastewater as feed water to construct a laboratory-scale series of photobioreactors consisting of a three-column reactor. The reactor worked continuously, and several parameters affecting photohydrogen production were studied. This series of photobioreactors consisted of three main vertical column reactors. Each column reactor had a height of 68 cm and diameter of 8 cm and was equipped with a magnetic stirrer. The working volume of each column reactor was 2.5 L and four lamps were arranged around each column reactor. The light intensity measured on the surface of the column reactor varied between 4 and 7 Klux. Sasi et al. (2011) studied the growth kinetics and fat production yield of common Chlorella using carbon dioxide as the sole carbon source with a cyclic photobioreactor. Results showed that owing to the high photosynthetic active radiation flux, Chlorella vulgaris showed an exponential growth pattern. Effective light distribution throughout the reactor, effective gas mass transfer, and proper mixing are important factors that should be considered when designing a photobioreactor for microalgae growth.

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9.2.4 Flat-type reactor The plate reactor has a large light-receiving surface, which can keep the uniformity of light, temperature, and other conditions in the reactor stable. Compared with other photobioreactors, flat-type photobioreactors have the advantages of being more economical, and compact in structure, they have a short light path and high ratio of illuminated area to culture volume, as well as a simple structure. They are more economically feasible in large-scale hydrogen production. The pH values, different carbon sources, and different lighting conditions are important factors affecting the efficiency of photobioreactors. In photobioreactors, argon is commonly used for mixing and providing anaerobic conditions, and the cost is low. In a gas-phase stirred photobioreactor, continuous argon injection suppresses the growth of Pseudomonas spp. owing to CO2 loss, whereas recycling provides a better culture growth environment. Degen et al. developed a new type of flat airlift photobioreactor (Kapdan and Kargi, 2006). Berberoglu et al. (2008) constructed a flat-type photo and bioreactor with acrylic as the main raw material. The reactor was made of a 6-mm-thick acrylic plate with a total volume of 1.35 L. The temperature of the reactor was controlled at 30 C. The exhaust pipe was made of stainless steel, the diameter of which was 4.76 mm with a wall thickness of 0.71 mm, and it was equipped with a sampling port. A diaphragm valve was set on the side of the reactor. The reaction solution could be sampled with a syringe, a magnetic stirring rod, and gas ejector for liquid mixing in the photobioreactor with a magnetic stirrer. The researchers obtained experimental results with the two-stage operation of a flat-plate photobioreactor with three different media. Li et al. (2009) designed a novel external-circulation flat-plate photobioreactor for the anaerobic photo-fermentation of salicylic acid ZX-5. The reactor (with a length, width and height of 4, 24, and 30 cm, respectively) was composed of a stainless-steel frame and a 5-mm glass plate, and the irradiation area was 720 cm2. With the experimental conditions of a reaction temperature of 30 C, oxido-reducing potential (ORP) feedback control unit, and batch feeding, higher hydrogen production efficiency was obtained. Gilbert et al. (2011) developed a flat-plate bioreactor, which can solve the problem of shaking and stirring, and improve the light penetration. Compared with the vertical plate reactor, spiral tube reactor, airlift reactor and bubble column reactor, the mixing time of the plate swing reactor was shorter (17 s). Therefore, the plate shaker reactor has potential for large-scale hydrogen production outdoors. Zhang et al. (2017b) compared the performance of three different photobioreactors with hydrolyzed corn cob and found that the baffle reactor based on the flat reactor design had the highest hydrogen production yield (589.21 mmol/L), and substrate conversion efficiency (40.48%) of it was higher than bath and tube reactors.

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Tsygankov et al. (1994) used a multicontrol glass as an immobilized substrate to construct a photobioreactor. The reactor was a rectangular glass container containing a porous glass plate. The maximum hydrogen evolution rate of porous glass was 1.3 mL/h/mL. The glass surface was electrically modified to enhance the adsorption capacity of bacteria. In the photobioreactor, the hydrogen production rate was most stable when the light intensity was 40 W/m2 and the succinate feed rate was 30. Zhang et al. (1999) used thermophilic cyanobacteria to evaluate the fixation capacity of flat-plate photobioreactors for carbon dioxide. The reactor consisted of three to five layers of transparent acrylic plastic plates. These plastic plates were placed vertically and parallel, and the optical path was 0.015 m. The height of the reactor was 0.8 m, the length was 1 m, and the working volume was 9 L. An acrylic plastic water jacket was installed on one side of the reactor to maintain the temperature. How to cultivate carbon dioxideeresistant microalgae in a closed photobioreactor is the research direction of many scholars. Sierra et al. (2008) introduced the characteristics of a flat-type photobioreactor with a width of 0.07 m, a height of 1.5 m, and a length of 2.5 m. They studied varying the gas holdup, mass transfer, mixing, and heat transfer with the aeration rate. When the power was 53 W/m3, the mass transfer rate was high enough to avoid excessive accumulation of dissolved oxygen in the flat-type photobioreactor. Flat-plate bioreactors require less of a power supply than tube-type bioreactors to achieve sufficient mass transfer, mixing, and heat transfer capabilities.

9.3 Systems and process optimization 9.3.1 Effect of hydraulic retention time on continuous hydrogen production 9.3.1.1 Effect of hydraulic retention time on characteristics of gas The effect of the hydraulic retention time on the hydrogen production rate of the four series reaction chambers of a continuous streamer fermentation biological hydrogen production unit is shown in Fig. 9.1 (Lu et al., 2020b; Zhang et al., 2017a). As the hydraulic retention time decreased from 72 to 24 h, the hydrogen production rate of reaction chamber 1 was reduced from 181.25 to 70.54 mol/m3/d, and the hydrogen production rate of reaction chamber 2 rapidly increased from 49.55 mol/m3/d at 72 h to 133.48 mol/m3/d at 48 h, and then dropped to 118.30 mol/m3/d at 24 h. The hydrogen production rate of reaction chamber 3 increased from 16.96 to 133.04 mol/m3/d, and the hydrogen production rate of reaction chamber 4 increased from 8.93 to 96.88 mol/m3/d. The hydrogen production rate of the photosynthetic biological hydrogen production unit increased from 64.29 to 104.91 mol/m3/d, and the feed rate of the hydrogen-producing medium and photosynthetic

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FIGURE 9.1 Effect of hydraulic retention time on hydrogen production rate.

hydrogen-producing bacteria in photo-fermentation biological hydrogen production was slower at a hydraulic retention time of 72 h. The photosynthetic hydrogen-producing bacteria had a sufficient hydraulic retention time in the reaction chamber 1 to degrade the substrate, grow, and produce hydrogen, which resulted in a higher hydrogen production rate in reaction chamber 1. With the shorter hydraulic retention time, the feed rate of the hydrogen-producing medium and photosynthetic hydrogen-producing bacteria was continuously improved and a large amount of hydrogen-producing substrates was rapidly pumped into the photosynthetic biological hydrogen production device. This provided nutritional requirements for growth and the hydrogen production of photosynthetic hydrogen-producing bacteria, which ensured that the overall hydrogen production rate of the photosynthetic biological hydrogen production device rose rapidly. At the same time, photosynthetic hydrogen-producing bacteria did not have enough time to grow and produce hydrogen in reaction chamber 1, so the highest peak of hydrogen production moved from reaction chamber 1 to reaction chambers 2 and 3. The effect of the hydraulic retention time on the hydrogen concentration of the four series reaction chambers of a continuous streamer fermentation biological hydrogen production unit is shown in Fig. 9.2. When the hydraulic retention time was reduced from 72 to 24 h, the hydrogen concentration in reaction chamber 1 of the photosynthetic biological hydrogen production device showed a continuous downward trend from 49.47  0.37% to 43.44  0.84%; chamber 2 increased from 40.27  2.15% to 49.15  0.68%

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FIGURE 9.2 Effect of hydraulic retention time on hydrogen content.

and then decreased to 46.39  1.34%. The hydrogen concentration in chambers 3 and 4 showed an upward trend, rising from 29.25  2.41% and 25.04  5.51% at 72 h to 46.98  2.11% and 44.5  1.42% at 24 h, respectively. The high hydrogen concentration indicates that a short hydraulic retention time can provide a suitable environment for photosynthetic bacteria. Similar results were reported in Marzieh Badiei’s study (Badiei et al., 2011).

9.3.1.2 Effect of hydraulic retention time on characteristics of fermentation broth The effect of the hydraulic retention time on the pH value of the four series reaction chambers of a continuous streamer fermentation biological hydrogen production unit is shown in Fig. 9.3. When the hydraulic retention time decreased from 72 to 24 h, the pH value of reaction chamber 1 increased from 4.37  0.01 to 5.52  0.02, the pH value of reaction chamber 2 increased from 4.61  0.09 to 5.29  0.01, and the pH values of reaction chambers 3 and 4 showed a slow downward trend, from 5.40  0.03 and 6.25  0.16 to 5.03  0.01 and 5.83  0.01, respectively. This is because the hydrogenproducing microorganism first degraded glucose into soluble volatile fatty acids in the process of hydrogen production, and the accumulation of volatile fatty acids caused the pH of the reaction solution to decrease continuously. As the hydraulic retention time decreased from 72 to 24 h, the rate at which photosynthetic bacteria and hydrogen-producing medium were pumped into the biological hydrogen production device continued to increase. The photosynthetic hydrogen-producing bacteria quickly passed reaction chamber 1 to

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FIGURE 9.3 Effect of hydraulic retention time on pH.

the rear reaction chamber, which led to the rise in the pH of the reaction solutions in reaction chambers 1 and 2 and the decrease in the pH in reaction chambers 3 an 4. When the hydraulic retention time was 24 h, the pH value of the continuous streamer fermentation biological hydrogen production device showed a continuous downward trend from reaction chamber 1 to reaction chamber 3, and the pH values of reaction chambers 3 to 4 showed an upward trend. Zhang et al. reported similar results (Zhang et al., 2015). This may be because with the depletion of glucose by the hydrogen-producing microorganisms and the accumulation of volatile fatty acids, the hydrogen-producing microorganisms began to use the volatile fatty acids in the reaction solution for hydrogen production, which caused the pH of the reaction solution to rise slowly (Lu et al., 2020a, 2016). The effect of hydraulic retention time on the oxidation-reduction potential of the four series reaction chambers of a continuous streamer fermentation biological hydrogen production unit is shown in Fig. 9.4. It can be seen from the figure that when the hydraulic retention time decreases from 72 to 24 h, the oxidationreduction potential of the reaction chamber 1 of the photosynthetic biological hydrogen production device shows a rising trend, from 474.43  25.01 mV to 404.14  6.52 mV. The oxidation-reduction potential of reaction chamber 2 decreased from 356.57  14.29 mV at 72 h to 456.43  24.38 mV at 48 h, then slowly rose to 436.43  14.27 mV at 24 h. The redox potentials of 3 and 4 reaction chambers showed a downward trend, from 178.57  12.16 mV and 112.86  6.52 mV to 503.14  50.61 mV and 481  42.52 mV, respectively. Reduction potential is an important parameter to characterize

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FIGURE 9.4 Effect of hydraulic retention time on oxidation-reduction potential.

biochemical reactions, which reflects the gain and loss of electrons in the reaction solution. During the fermentation hydrogen production, the accumulation of NADH electrons in the hydrogen production reaction solution continuously reduces the reduction potential, which is conducive to maintaining the activity of dehydrogenase and forming a microenvironment that is beneficial to the hydrogen production by microorganisms. The effect of hydraulic retention time on the biomass of the four series reaction chambers of a continuous streamer fermentation biological hydrogen production unit is shown in Fig. 9.5. When the hydraulic retention time decreased from 72 to 24 h, the biomass of photo-fermentative hydrogenproducing microorganisms in reaction chamber 1 showed a continuous downward trend from 2.64  0.05 to 2.2  0.02 g volatile suspended solids (VSS) /L, reaction chambers 2 and 3 showed a parabolic trend, and reaction chamber 4 showed an upward trend, rising from 2.01  0.01 to 2.44  0.004 g VSS/L. This is because, with the shorter hydraulic retention time, the pumping rate of photosynthetic hydrogen-producing bacteria and medium continued to increase and the photosynthetic hydrogen-producing bacteria in the reaction chamber 1 flowed into the subsequent reaction chamber before entering the logarithmic growth period, which led to a decrease in the biomass in reaction chamber 1. The trend of the curve of the effect of hydraulic retention time on biomass is basically the same as the curve of the effect the rate of hydrogen production. This shows that photosynthetic hydrogen-producing microorganisms are closely related to the rate of hydrogen production, in a are positive relationship.

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FIGURE 9.5 Effect of hydraulic retention time on biomass concentration.

When the hydraulic retention time decreased from 72 to 24 h, the reducing sugar concentrations of the reaction liquids in the four reaction chambers of the photosynthetic biological hydrogen production unit all showed an upward trend. Chamber 1 had the highest reducing sugar concentration in the reaction solution, followed by reaction chambers 2 and 3, and finally reaction chamber 4, with a reducing sugar concentration of 0. This is because, as the substrate flows through reaction chambers 1e4 of the photosynthetic biological hydrogen production device, photosynthetic bacteria continue to use the substrate in the reaction solution for growth and hydrogen production, causing the reducing sugar to decrease. The reducing sugar concentration of the reaction solution in reaction chamber 2 had a greater decline rate than the reducing sugar concentration in reaction chamber 1. The decrease value was 47.57%e59.47%. The reducing sugar concentration in reaction chamber 2 was only 28.9%e46.3% of the initial substrate concentration. This indicates that the substrate was rapidly degraded by bacteria after entering the photosynthetic biological hydrogen production device, rapidly increasing the amount of hydrogen-producing microorganisms in the reaction chamber.

9.3.2 Effects of substrate concentration on continuous biohydrogen production 9.3.2.1 Effects of substrate concentration on characteristics of biohydrogen gas The effect of a low substrate concentration on hydrogen production by photofermentation is reflected in the restrictive aspect, and the effect of a high

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substrate concentration on hydrogen production by photo-fermentation is reflected in the inhibitory aspect. When the bacteria are under the most suitable substrate concentration conditions, the bacteria can obtain the best hydrogenproducing activity. However, as the substrate concentration deviates from the optimal value, it will cause a decrease in the hydrogen production rate (La Licata et al., 2011). Different optimal substrate concentrations reported in the literature may be caused by factors such as the strain, temperature, and hydraulic retention time. Fig. 9.6 shows the effect of the substrate concentration on the hydrogen production rate of four series reaction chambers of a continuous photofermentation biological hydrogen production bioreactor (Lu et al., 2018, 2019). When the substrate concentration is 10 g/L, chamber 3 has the maximal hydrogen production rate, at 133.12  17.77 mol/m3/d. The hydrogen production rates of chamber 2 and 4 are 118.16  11.58 and 97.09  11.34 mol/ m3/d, respectively. Chamber 1 has the minimum hydrogen production rate, at 70.44  5.71 mol/m3/d. At that time, the hydrogen production rate of the bioreactor is 104.7  4.72 mol/m3/d, when the substrate concentration increased from 10 to 20 g/L. The hydrogen production rate of the four chambers of the bioreactor showed a continuously increasing trend. When the substrate concentration is 20 g/L, the hydrogen production rate of the photo bioreactor is 148.65  4.19 mol/m3/d; chamber 3 has a maximal hydrogen production rate of 202.64  8.83 mol/m3/d and chamber 1 has a minimal hydrogen production rate of 88.52  2.4 mol/m3/d. As the substrate

FIGURE 9.6 Effect of substrate concentration on hydrogen production rate.

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concentration continued to increase to 25 g/L, hydrogen production in the four chambers of the bioreactor showed a downward trend. The results show that within the range of substrate concentration in this experiment, the substrate concentration can greatly affect the hydrogen production rate of the continuous photo-fermentation biological hydrogen production bioreactor, and as the substrate concentration increases, the hydrogen production rate will first increase and then decrease. The reason for the increase in the hydrogen production rate is that when the substrate concentration increases, photosynthetic bacteria can obtain more nutrients for growth and hydrogen production. However, as the substrate concentration exceeds the optimal value, an excessively high substrate concentration will inhibit the hydrogen-producing activity of photosynthetic bacteria. Substances such as volatile fatty acids also will be generated during the hydrogen-producing process, which will cause the pH value in the broth to destroy the hydrogen production environment. Fig. 9.7 shows the effect of the substrate concentration on the hydrogen concentration in the four chambers of the photosynthetic biological hydrogen production bioreactor. The hydrogen production concentration of the bioreactor is basically maintained at 42.19  0.94% to 49.71  0.27%. When the substrate concentration increased from 10 to 20 g/L, the hydrogen concentration in the four chambers of the bioreactor showed an increasing trend. When the substrate concentration was 10 g/L, chamber 1 had a minimal hydrogen concentration, 43.44  0.84%, and the maximal hydrogen

FIGURE 9.7 Effect of substrate concentration on hydrogen content.

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concentration is 46.98  2.11% in reaction chamber 3. In the process of photofermentation for which HAU-M1 bacteria use glucose to produce hydrogen, it degrades glucose into intermediate metabolites such as acetic acid and butyric acid. When the metabolite of photosynthetic bacteria is acetic acid, the hydrogen concentration is higher. When the substrate concentration is 20 g/L, the hydrogen concentration in the bioreactor is higher than other substrate concentrations. This may be caused by an increase in the concentration of the broth of the bioreactor. When the metabolite of photosynthetic bacteria is butyric acid, the ratio of carbon dioxide and hydrogen changes and causes an increase in hydrogen concentration.

9.3.2.2 Effects of substrate concentration on characteristics of fermentation broth Different substrate concentrations can directly affect the changes in pH in the photosynthetic biological hydrogen production bioreactor. Changes in pH directly affect the hydrogenase activity and then involve the metabolism process. Changes in pH also can affect the growth and reproduction rate of different types of bacteria. Because of these factors, the substrate concentration can affect hydrogen production in photo-fermentation. Fig. 9.8 shows the effect of substrate concentration on the pH of the broth in the four chambers of a photosynthetic biological hydrogen production bioreactor. When the substrate concentration increased from 10 to 25 g/L, the pH values of the four series chambers of the bioreactor all showed a continuous downward trend. This may be due to volatile fatty acids. After the broth

FIGURE 9.8 Effect of substrate concentration on pH values.

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enters the bioreactor, the bacteria will degrade the glucose in the broth to produce hydrogen, volatile organic acids, and other metabolites. The accumulation of volatile fatty acids affects the drop in the pH of the broth. With the increase in the substrate concentration in the broth, the photobacteria can use more substrates to produce more volatile fatty acids, resulting in a further decrease in the pH value of the broth. When the substrate concentration is 10 g/L, the pH value in chambers 1e3 of the bioreactor showed a downward trend, from 5.52  0.02 to 5.03  0.01, and the pH value in chamber 4 showed an upward trend, rising to 5.83  0.01. The reason is that in the early stage of the hydrogen production process by photobacteria, a large amount of volatile fatty acids were produced by photosynthetic bacteria, causing the pH of the broth to decrease continuously. At the later stage of the process, the photobacteria can use the volatile fatty acids in the broth to produce hydrogen, so the pH of the broth rises again. The oxidation-reduction potential is an important indicator for judging the suitability of a hydrogen production environment for anaerobic fermentation. During the process of photosynthetic fermentation, the accumulation of NADH electrons in the broth and the dynamic balance change of NADH/NAD will cause the oxidation-reduction potential of the fermentation broth to decrease continuously and maintain a certain range suitable for hydrogen production, so that the environment of broth will be conducive to photofermentation hydrogen production (Li et al., 2008). Fig. 9.9 shows the effect of substrate concentration on the oxidationreduction potential of the continuous streamer fermentation biological

FIGURE 9.9 Effect of substrate concentration on oxidation-reduction potential.

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hydrogen production bioreactor. When the substrate concentration increased from 10 to 20 g/L, oxidation-reduction potentials of the four reaction chambers of the bioreactor showed a downward trend. As the substrate concentration increased to 25 g, the oxidation-reduction potential of four chambers showed a continuous upward trend. When the substrate concentration was 10 g/L, the lowest oxidation-reduction potential was 503.14  50.61 mV in chamber 3 and the highest oxidation-reduction potential was 404.14  6.52 mV. When the substrate concentration was 20 g/L, the lowest oxidation-reduction potential of reaction chamber 3 was 534.29  2.56 mV. This shows that the photosynthetic biological hydrogen production device is a better environment for photosynthetic fermentation. The trend in the effect of substrate concentration on the amount of bacteria remained approximately the same as the trend of the effect of substrate concentration on the rate of hydrogen production. The close relationship shows a positive correlation. Fig. 9.10 shows the effect of substrate concentration on biomass by continuous photo-fermentation. When the substrate concentration of the bioreactor increased from 10 to 25 g/L, the biomass of the four series chambers of the continuous photo-fermentation biological hydrogen production bioreactor first increased and then decreased. When the substrate concentration was 10 g/L, the minimal microbial biomass was 2.20  0.02 g VSS/L in chamber 1 and the maximal biomass was 2.53  0.02 g VSS/L in chamber 3. When the substrate concentration was 20 g/L, the minimal biomass was 2.36  0.001 g VSS/L in chamber 1 and the maximal biomass was

FIGURE 9.10 Effect of substrate concentration on biomass concentration.

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2.63  0.19 g VSS/L in chamber 3. This is because, as the substrate concentration increased, photobacteria used more substrate to increase the biomass in the broth. When the substrate concentration increased from 10 to 25 g/L, the reducing sugar concentrations in the broth of the four chambers of the bioreactor all showed a continuous increasing trend. When the substrate concentration was 25 g/L, the reducing sugar concentration in the broth of reaction chamber 4 was 6.71  0.12 g/L. A large amount of substrate was lost from the bioreactor, which caused much wasted resources. Therefore, photosynthetic hydrogen production should use a lower substrate concentration from the perspective of energy conservation when the hydrogen production rate of the bioreactor is not affected.

9.3.2.3 Effect of organic loading rate on biological hydrogen production The organic load rate reflects the concentration of organic matter in a unit volume of reaction liquid and per unit time directly, and is an important influencing factor that affects the hydrogen production rate. When the organic loading rate is lower than the optimal value, the broth cannot provide enough nutrients for photosynthetic hydrogen-producing bacteria growth and hydrogen production, which limits the increase in the hydrogen production rate. When the organic loading rate is higher than the optimal value, higher substrate concentrations in the broth can cause excessive osmotic pressure for hydrogen-producing microorganism cells, leading to cell death (Reungsang et al., 2013). In addition, the higher feed rate will also cause a certain shear force to the hydrogen-producing microorganisms in the bioreactor, which is not conducive to the growth of microorganisms and hydrogen production (Zhang et al., 2015). The experimental results of the effect of the organic load factor on the hydrogen production of the continuous streamer fermentation biological hydrogen production unit are shown in Table 9.1. Table 9.1 shows that when the substrate concentration was 10 g/L, as the hydraulic retention period decreased from 72 to 24 h, the organic load rate increased from 3.3 to 10 g/L/d and hydrogen production rate increased from 64.13  4.58 to 104.7  4.72 mol/m3/d, but hydrogen production rate decreased from 19.43  1.39 to 10.47  0.47 mmol/g. Zhang et al. studied the effect of hydraulic retention time on hydrogen production by HAU-M1 photosynthetic bacteria in a baffle-type photosynthetic fermentation hydrogen production bioreactor (Zhang et al., 2015). The optimal hydraulic retention time was 24 h and the hydrogen production rate was 185.71 mol/m3/d (Zhang et al., 2015). When the hydraulic retention period was 24 h, as the substrate concentration increased from 10 to 25 g/L, the organic loading rate increased from 10 to 25 g/L/d. The hydrogen production rate increased from 104.7  4.72 to 148.65  4.19 mol/m3/d and then decreased to 128.64  4.17 mol/m3/d.

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TABLE 9.1 Effect of organic loading rate on hydrogen production.

Trial

Hydraulic retention time (h)

Substrate concentrate (g/L)

Organic loading rate (g/L/d)

Hydrogen production rate (Mol/m3/d)

Hydrogen yield (mmol/g)

1

72

10

3.3

64.13  4.58

19.43  1.39

2

48

10

5

83.48  5.84

16.70  1.17

3

24

10

10

104.7  4.72

10.47  0.47

4

24

15

15

137.69  2.89

9.18  0.19

5

24

20

20

148.65  4.19

7.43  0.21

6

24

25

25

128.64  4.17

5.15  0.17

The hydrogen production rate was 10.47  0.47 mol/m3/d and then decreased to 5.15  0.17 mmol/g. The experimental results show that the organic load factor has a great influence on the continuous hydrogen production of the baffle-type photosynthetic biological hydrogen production unit. Only a suitable organic load rate can make the hydrogen production unit achieve the maximum hydrogen production rate (Fig. 9.11) (Lin et al., 2011).

FIGURE 9.11 Effect of organic loading rate on hydrogen production rate and hydrogen yield.

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9.4 Conclusions and perspectives Photo-fermentation biohydrogen production is an important biohydrogen production method. Photo-fermentation biohydrogen production is comprehensively influenced by reactor and process parameters. Therefore, in this chapter, first, all kinds of reactors were reviewed. Second, the effects of the substrate concentration, hydraulic retention time, and organic loading rate on photo-fermentation biohydrogen production were evaluated. An optimal bioreactor structure can increase photosynthetic biological hydrogen production, and optimized process parameters will further increase photosynthetic biological hydrogen production.

References Adessi, A., De Philippis, R., 2014. Photobioreactor design and illumination systems for H-2 production with anoxygenic photosynthetic bacteria: a review. Int. J. Hydrogen Energy 39, 3127e3141. Adessi, A., Torzillo, G., Baccetti, E., De Philippis, R., 2012. Sustained outdoor H-2 production with Rhodopseudomonas palustris cultures in a 50 L tubular photobioreactor. Int. J. Hydrogen Energy 37, 8840e8849. Badiei, M., Jahim, J.M., Anuar, N., Rozaimah, S., Abdullah, S., 2011. Effect of hydraulic retention time on biohydrogen production from palm oil mill effluent in anaerobic sequencing batch reactor. Int. J. Hydrogen Energy 36, 5912e5919. Berberoglu, H., Jay, J., Pilon, L., 2008. Effect of nutrient media on photobiological hydrogen production by Anabaena variabilis ATCC 29413. Int. J. Hydrogen Energy 33, 1172e1184. Camacho Rubio, F., Acie´n Ferna´ndez, F.G., Sa´nchez Pe´rez, J.A., Garcı´a Camacho, F., Molina Grima, E., 1999. Prediction of dissolved oxygen and carbon dioxide concentration profiles in tubular photobioreactors for microalgal culture. Biotechnol. Bioeng 62, 71e86. Das, D., Veziroǧlu, T.N., 2001. Hydrogen production by biological processes: a survey of literature. Int. J. Hydrog. Energy 26, 13e28. Gilbert, J.J., Ray, S., Das, D., 2011. Hydrogen production using Rhodobacter sphaeroides (OU 001) in a flat panel rocking photobioreactor. Int. J. Hydrogen Energy 36, 3434e3441. Javanmardian, M., Palsson, B., 1992. Design and operation of an algal photobioreactor system. Adv. Space Res. 12 (5), 231e235. Kapdan, I.K., Kargi, F., 2006. Bio-hydrogen production from waste materials. Enzyme Microb. Technol. 38, 569e582. Lee, C.M., Hung, G.J., Yang, C.F., 2011. Hydrogen production by Rhodopseudomonas palustris WP 3-5 in a serial photobioreactor fed with hydrogen fermentation effluent. Bioresour. Technol. 102, 8350e8356. Li, J.Z., Ren, N.Q., Li, B.K., Qin, Z., He, J.G., 2008. Anaerobic biohydrogen production from monosaccharides by a mixed microbial community culture. Bioresour. Technol. 99, 6528e6537. Li, X., Wang, Y.H., Zhang, S.L., Chu, J., Zhang, M., Huang, M.Z., et al., 2009. Enhancement of phototrophic hydrogen production by Rhodobacter sphaeroides ZX-5 using a novel strategy shaking and extra-light supplementation approach. Int. J. Hydrogen Energy 34, 9677e9685.

222 Waste to Renewable Biohydrogen La Licata, B., Sagnelli, F., Boulanger, A., Lanzini, A., Leone, P., Zitella, P., et al., 2011. Biohydrogen production from organic wastes in a pilot plant reactor and its use in a SOFC. Int. J. Hydrogen Energy 36, 7861e7865. Lin, P.J., Chang, J.S., Yang, L.H., Lin, C.Y., Wu, S.Y., Lee, K.S., 2011. Enhancing the performance of pilot-scale fermentative hydrogen production by proper combinations of HRT and substrate concentration. Int. J. Hydrogen Energy 36, 14289e14294. Liu, C.F., Sun, R.C., Qin, M.H., Zhang, A.P., Ren, J.L., Ye, J., et al., 2008. Succinoylation of sugarcane bagasse under ultrasound irradiation. Bioresour. Technol. 99, 1465e1473. Lu, C.Y., Tahir, N., Li, W.Z., Zhang, Z.P., Jiang, D.P., Guo, S.Y., Wang, J., Wang, K.X., Zhang, Q.G., 2020. Enhanced buffer capacity of fermentation broth and biohydrogen production from corn stalk with Na2HPO4/NaH2PO4. Bioresour. Technol. 313. Lu, C.Y., Wang, Y., Lee, D.J., Zhang, Q.G., Zhang, H., Tahir, N., Jing, Y.Y., Liu, H., Zhang, K., 2019. Biohydrogen production in pilot-scale fermenter: Effects of hydraulic retention time and substrate concentration. J. Clean. Prod. 229, 751e760. Lu, C.Y., Zhang, Z.P., Ge, X.M., Wang, Y., Zhou, X.H., You, X.F., Liu, H.L., Zhang, Q.G., 2016. Bio-hydrogen production from apple waste by photosynthetic bacteria HAU-M1. Int. J. Hydrog. Energy 41 (31), 13399e13407. Lu, C.Y., Zhang, H., Zhang, Q.G., Chu, C.Y., Tahir, N., Ge, X.M., Jing, Y.Y., Hu, J.J., Li, Y.M., Zhang, Y., Zhang, T., 2020. An automated control system for pilot-scale biohydrogen production: Design, operation and validation. Int. J. Hydrog. Energy 45 (6), 3795e3806. Lu, C.Y., Zhang, Z.P., Zhou, X.H., Hu, J.J., Ge, X.M., Xia, C.X., Zhao, J., Wang, Y., Jing, Y.Y., Li, Y.M., Zhang, Q.G., 2018. Effect of substrate concentration on hydrogen production by photo-fermentation in the pilot-scale baffled bioreactor. Bioresour. Technol 247, 1173e1176. Miro´n, A.S., Camacho, F.G., Go´mez, A.C., Grima, E.M., Chisti, Y., 2000. Bubble-column and airlift photobioreactors for algal culture. AIChE J. 46 (9), 1872e1887. Molina, E., Ferna´ndez, J., Acie´n, F.G., Chisti, Y., 2001. Tubular photobioreactor design for algal cultures. J. Biotechnol. 92 (2). Perez-Mora, L.S., Matsudo, M.C., Cezare-Gomes, E.A., Carvalho, J.C.M., 2016. An investigation into producing Botryococcus braunii in a tubular photobioreactor. J. Chem. Technol. Biotechnol. 91, 3053e3060. Reungsang, A., Sittijunda, S., O-thong, S., 2013. Bio-hydrogen production from glycerol by immobilized Enterobacter aerogenes ATCC 13048 on heat-treated UASB granules as affected by organic loading rate. Int. J. Hydrogen Energy 38, 6970e6979. Sasi, D., Mitra, P., Vigueras, A., Hill, G.A., 2011. Growth kinetics and lipid production using Chlorella vulgaris in a circulating loop photobioreactor. J. Chem. Technol. Biotechnol. 86, 875e880. Show, K.Y., Lee, D.J., Tay, J.H., Lin, C.Y., Chang, J.S., 2012. Biohydrogen production: current perspectives and the way forward. Int. J. Hydrogen Energy 37, 15616e15631. Sierra, E., Acien, F.G., Fernandez, J.M., Garcia, J.L., Gonzalez, C., Molina, E., 2008. Characterization of a flat plate photobioreactor for the production of microalgae. Chem. Eng. J. 138, 136e147. Tamburic, B., Zemichael, F.W., Maitland, G.C., Hellgardt, K., 2011. Parameters affecting the growth and hydrogen production of the green alga Chlamydomonas reinhardtii. Int. J. Hydrogen Energy 36, 7872e7876. Tredici, M.R., Zlttelli, G.C., 1998. Efficiency of sunlight utilization: Tubular versus flat photobioreactors. Biotechnol. Bioeng. 57, 187e197.

Photosynthetic biological hydrogen production reactors Chapter | 9

223

Tsygankov, A.A., Hirata, Y., Miyake, M., Asada, Y., Miyake, J., 1994. Photobioreactor with photosynthetic bacteria immobilized on porous glass for hydrogen photoproduction. J. Ferment. Bioeng. 77 (5), 575e578. Uyar, B., 2016. Bioreactor design for photofermentative hydrogen production. Bioproc. Biosyst. Eng. 39, 1331e1340. Uyar, B., Eroglu, I., Yucel, M., Gunduz, U., Turker, L., 2007. Effect of light intensity, wavelength and illumination protocol on hydrogen production in photobioreactors. Int. J. Hydrogen Energy 32, 4670e4677. Wang, Y., Joshee, N., Cao, W.X., Wu, Q.L., Tahir, N., 2019. Continuous hydrogen production by dark and photo co-fermentation using a tubular multi-cycle bio-reactor with Paulownia biomass. Cellulose 26, 8429e8438. Zhang, Z.P., Wang, Y., Hu, J.J., Wu, Q.L., Zhang, Q.G., 2015. Influence of mixing method and hydraulic retention time on hydrogen production through photo-fermentation with mixed strains. Int. J. Hydrogen Energy 40, 6521e6529. Zhang, K., Kurano, N., Miyachi, S., 1999. Outdoor culture of a cyanobacterium with a vertical flat-plate photobioreactor: effects on productivity of the reactor orientation, distance setting between the plates, and culture temperature. Appl. Microbiol. Biotechnol. 52 (6), 781e786. Zhang, Q., Lu, C., Lee, D.J., Lee, Y.J., Zhang, Z., Zhou, X., et al., 2017a. Photo-fermentative hydrogen production in a 4m(3) baffled reactor: effects of hydraulic retention time. Bioresour. Technol. 239, 533e537. Zhang, Q.G., Wang, Y., Zhang, Z.P., Lee, D.J., Zhou, X.H., Jing, Y.Y., et al., 2017b. Photofermentative hydrogen production from crop residue: a mini review. Bioresour. Technol. 229, 222e230. Zhang, Z.P., Zhou, X.H., Hu, J.J., Zhang, T., Zhu, S.N., Zhang, Q.G., 2017c. Photobioreactor structure and light-heat-mass transfer properties in photo-fermentative bio-hydrogen production system: a mini review. Int. J. Hydrogen Energy 42, 12143e12152.

Chapter 10

Spectral coupling characteristics of photosynthetic biological hydrogen production system Yanyan Jing Key Laboratory of New Materials and Facilities for Rural Renewable Energy of Ministry of Agriculture and Rural Affairs, College of Mechanical and Electrical Engineering, Henan Agricultural University, Zhengzhou, Henan Province, China

10.1 Introduction With the rapid development of human society and the economy, the energy shortage has become a key factor restricting development. Owing to the nonrenewability of fossil energy and serious pollution to the environment, research and development into clean and renewable energy and its applications have been put on the agenda in various countries (Ajmi et al., 2015). Photosynthetic bacteria can make extensive use of the solar light band for photosynthesis, convert light energy into its own energy to carry out metabolic activities, and also release hydrogen. A wide range of substrates can be decomposed and consumed while producing hydrogen, including wastewater, biomass straw, and small molecule acids (Lu et al., 2016). Because the production of hydrogen by photosynthetic bacteria does not require the consumption of mineral resources, photosynthetic pigments are unique pigments of photosynthetic organisms and the key substances for converting light energy into chemical energy. Different species of photosynthetic bacteria contain different photosynthetic pigments, and the type and the quantity of photosynthetic pigments have significant effects on light capture. Photosynthetic bacteria are a type of prokaryote with a photosynthetic system. They have the characteristics of containing photosynthetic pigments: bacterial chlorophyll and carotenoids, photosynthetic growth under anaerobic light conditions, and no oxygen production during photosynthesis. They use solar energy to assimilate CO2 and fix molecular nitrogen. At the same time, photosynthetic bacteria use a variety of organic waste for photosynthetic Waste to Renewable Biohydrogen. https://doi.org/10.1016/B978-0-12-821659-0.00009-5 Copyright © 2021 Elsevier Inc. All rights reserved.

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hydrogen production under the catalysis of nitrogenase and hydrogenase (Benemann et al., 1987). Under anaerobic conditions, photosynthetic bacteria can perform photosynthetic autotrophy and photosynthetic heterotrophy metabolism. Photosynthetic bacteria consist of four families: Rhodospirillaceae (purple nonsulfur bacteria), Chromatiaceae (purple sulfur bacteria), Chlorobiaceae (green sulfur bacteria), and Chloroflexaceae (sliding filamentous green sulfur bacteria). All photosynthetic bacteria contain chlorophyll a or b and various carotenoids. With different types and numbers, the cells show different colors. Among them, carotenoids have a decisive role. This is because they can affect the wavelength of the absorption spectrum according to the composition and quantity (Wilson and Bradley, 1997; Miller and Varel, 2002; Kumazawa and Mitsui, 1981). Each species of photosynthetic bacteria has a specific absorption spectrum, which mainly depends on the type and amount of photosynthetic pigments it contains, and each type of photosynthetic pigment has its specific absorption peak. The growth and metabolism of photosynthetic bacteria are inseparable from light energy. Illumination has a significant effect on the production of bacterial chlorophyll and carotenoids of photosynthetic bacteria. There are two types of photosynthetic reactions in photosynthetic bacteria: photoreactions (reactions directly related to light) and dark reactions (reactions in the dark). For higher plants, cyanobacteria, and green algae with two photosynthetic systems, the dark reaction rate refers to the speed at which electrons pass through the two photosynthetic systems. Among them, the light reaction is a minority; most of the rest are dark reactions. The speed of the light reaction is much faster than the dark reaction. Under strong light, the light reaction proceeds quickly, and the dark reaction often cannot keep up. Because a complete photosynthetic reaction is a combination of light and dark reactions, photosynthesis cannot proceed until the dark reactions are completed. Ormerod et al. (1961) also pointed out that the limiting factor for light conversion efficiency under strong light is the dark reaction speed. Dark reaction speed is usually about 10 times slower than the rate of photons captured by pigments; as a result, 90% of photons captured by photosynthetic organs under strong light cannot be used for photosynthesis. Photons that can’t participate in photosynthesis are lost in the form of heat or fluorescence (Zhu et al., 1999; Shin et al., 2004; Philips and Mitsui, 1983). Various photosynthetic bacteria contain different photosynthetic pigments. Therefore, they cannot absorb light in all bands of sunlight, and can absorb only specific bands. Research into photometric effect and the absorption spectrum bands of photosynthetic bacteria only provide suitable light energy for its growth and metabolism and eliminate the light saturation effect, which is greatly significant for improving light conversion efficiency and hydrogen production.

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10.2 Absorption spectrum of photosynthetic hydrogenproducing bacteria 10.2.1 Morphological characteristics of photosynthetic bacteria The strains for photosynthetic biological hydrogen production were obtained by screening and cultivation samples from six locations: the Zhengzhou Sewage Treatment Plant, Zhengzhou Xin mu Big Pig Farm, Zhengzhou West Liu hu, Zhengzhou Suburban Tofu Processing Plant, Henan Academy of Agricultural Sciences, Experimental Field, and Jin shui he in Zhengzhou. The seven strains, including F1, F5, F7, F11, S7, S9, and L6, were selected as the dominant species for efficient hydrogen production (Zhang, 2006). The morphology of the seven strains of high-yield bacteria finally screened was observed through a high-power microscope, as shown in Fig. 10.1. The seven strains of highly efficient hydrogen-producing photosynthetic bacteria had different cell morphologies and belonged to different populations. Strains

FIGURE 10.1 Microscope photograph (magnification 1500) of highly efficient hydrogen production photosynthetic bacteria (You, 2005).

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F1, F5, F7, and F11 are purple nonsulfur bacteria that belong to Rhodospirillaceae, S7 and S9 are Chromatiaceae purple sulfur bacteria, and L6 is green sulfur bacteria Chlorobiaceae (An, 2009).

10.2.2 Absorption spectrum of mixed photosynthetic bacteria After culturing for 24 h under enriched culture conditions, the mixed photosynthetic hydrogen-producing bacteria group had an obvious absorption spectrum and the bacteria group had four absorption peaks near visible light at 380, 490, and 590 nm. In addition, there were obvious absorption peaks near 800 and 860 nm, indicating that the flora could also absorb infrared light.

10.2.3 Absorption spectrum of single strain The study found that F1, F5, F7, and F11 had similar absorption characteristics, with maximum absorption peaks at 375 and 590 nm, and S7 and S9 had maximum absorption peaks at 380 and 490 nm (You, 2005). The maximum absorption peak of L6 was 590 nm, and all seven strains had larger absorption peaks around 800 nm. The study found that when these seven single strains were mixed and cultured, the spectral test results showed that the maximum absorption peak characteristics of the single strain could still be expressed. The absorption spectrum of the mixed photosynthetic hydrogen-producing flora was the result of the combined effects of the absorption spectra of various single strains, whereas the seven dominant hydrogen-producing strains still exhibited their own characteristics in the mixed solution. Both purple and green photosynthetic bacteria contain a light energy ringtype electron transfer system composed of basically the same photosynthetic pigment and redox carrier, including bacteriochlorophyll, bacterial pheophytin, carotenoids, quinone, iron thio proteins, and cytochromes (Zhao, 2017). The strains had obvious absorption peaks near 800 and 865 nm, indicating that the photosynthetic hydrogen-producing strain contained chlorophyll. Carotenoids are auxiliary pigments that capture light energy and efficiently transfer the absorbed light energy to chlorophyll. The carotenoid absorption band was in the blue-violet light region of 400e550 nm (Wilson and Bradley, 1997; Miller and Varel, 2002; Kumazawa and Mitsui, 1981). The types of carotenoids contained in photosynthetic bacteria varied according to the species.

10.3 Spectral coupling characteristics for growth and hydrogen production of photosynthetic bacteria Pig manure wastewater is a mixture of pig manure, urine, washing and drinking water, and feed. It is usually a liquid containing 10% dry matter and has a high chemical oxygen demand (COD) value. The composition and content of chemical elements in pig manure are basically consistent with the

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growth needs of microorganisms, which contain not only essential elements such as C and N but also almost all nutrients needed for microbial growth composition, including trace elements and heavy metals (Zhang et al., 2007; Lo et al., 1994). Heavy metals such as Fe, Mn, and Mo in pig manure are much higher than those of most other heavy metals, which are important components needed by photosynthetic bacteria to synthesize hydrogenase during hydrogen production (Ni et al., 1999). Photosynthetic bacteria and most microorganisms have similar nutritional needs, so the composition of pig manure can also meet the growth and hydrogen production needs of photosynthetic bacteria. Animal manure as a raw material for hydrogen production by photosynthetic bacteria can save raw material costs and also open up new ways to treat animal manure (Xu et al., 1996; Lee et al., 2010). Light conversion efficiency is an important parameter for measuring the effect of light conversion in biological hydrogen production. The light conversion efficiency in biological hydrogen production is relatively low, on average between 1% and 8% (Yi git et al., 1999). The low light conversion rate is an important obstacle to the industrialization of biological hydrogen production. The development of a photobioreactor, the transmission mode, and the supply mode of light are important research areas to improve the efficiency of light conversion (Zhang et al., 2017). To solve the problems of the high cost of hydrogen produced by photosynthetic organisms and the low efficiency of solar light conversion, sunlight introduced into the reactor through a solar collector and fibers is used to replace artificial light sources completely, which enables photosynthetic biological hydrogen production to operate without consuming a large amount of conventional energy, effectively reducing the cost of photosynthetic biological hydrogen production (Boran et al., 2010; Zhang et al., 2005, 2006). To this end, pig manure wastewater treated with dark aerobic treatment for 4 days was used as the raw material, at a temperature of 30 C, pH 7.0, and an inoculation of 10%. The bandpass filters DTB400, DTB470, DTB540, DTB600, and DTB700 with a bandwidth of 100 nm were used to process the collected sunlight and study the growth characteristics and hydrogen production characteristics of photosynthetic bacteria in different wavelength bands (You, 2005). The study found that the four strains (F1, F7, F5, and F11) had similar growth characteristics and hydrogen production characteristics, which were similar to their absorption spectra (You, 2005). Owing to the maximum absorption peak at 390 nm, these strains grew faster near the wavelength of 400 nm. Another absorption peak of these strains was at 490 nm, so the photosynthetic strains also grew faster in the 470-nm spectrum band. Because optical fiber can transmit only visible light, the absorption peak of a single strain at 490 nm was smaller than the absorption peak at 390 nm, whereas energy at 490 nm in the visible light spectrum was higher than 390 nm, so the photosynthetic strain growth and hydrogen production

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difference were not large at the wavelengths of 400 and 470 nm. These several strains showed slow growth and low hydrogen production at 700 nm because the absorption spectrum curve shows a small absorption value at 700 nm, and energy at 700 nm in the visible light spectrum is also low, causing insufficient light energy provided to photosynthetic bacteria. The photosynthetic bacteria growth and hydrogen production capacity at 540 and 600 nm are somewhere in between. Photosynthetic bacteria growth and hydrogen production capacity with visible light were both slightly less than those with the 400-nm wavelength. Although the visible light contains two absorption peaks at 390 and 490 nm, and the light in each band can be absorbed by photosynthetic bacteria to varying degrees, a large proportion of the visible light cannot be absorbed efficiently by the bacteria, leading to the generation of a light saturation effect. Compared with the 400-nm wavelength, hydrogen production with visible light is inhibited to some extent. Strains S7 and S9 have similar growth characteristics and hydrogen production characteristics, which is similar to their absorption spectra. Strains S7 and S9 can grow and produce hydrogen under visible light without filtering, and both can grow faster and produce hydrogen more at 470 and 540 nm. However, the fastest growth and highest hydrogen production yield of strains S7 and S9 occur at the wavelength of 400 nm, because they have the highest absorption peak at 370 nm, and the filter with a center wavelength of 400 nm and a bandwidth of 100 nm covers this peak. Strain L6 grows faster at 600 nm and has larger hydrogen production. This is because the strain has an absorption peak at 600 nm, and the absorption value here is higher than that at 400 nm. Therefore, the absorption and hydrogen production characteristics at 600 nm are better than those at 400 nm. The absorption values at other wavelengths are higher than the absorption values of other strains. Therefore, the overall growth rate of this strain is faster than other strains. There is also a light saturation effect in the full range of visible light, so the optimal wavelength for growth and hydrogen production of strain L6 should be 600 nm.

10.4 Comparison of hydrogen production capacity under optimal spectrum Pig manure sewage was treated with dark aerobic treatment for 4 days and used as a raw material. The hydrogen production capacity was determined under at a temperature of 30 C, pH 7.0, and inoculation of 10% and the total COD of the pig manure sewage was 5000 mg L 1. To obtain the maximum hydrogen production for different strains, the wavelength light provided for strains F1, F5, F7, F11, S7, and S9 was at 400 nm, L6 was at 600 nm. Visible light transmitted through the optical fiber was provided to the mixed bacteria combining these several strains.

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2.5 Hydrogen production (L)

2 1.5 1 0.5 0 F1

F5

F7 F11 Strains

S7

S9

L6

Mixed strains

FIGURE 10.2 Study of hydrogen production of various bacteria (Zhang, 2006).

Fig. 10.2 shows that although the light used by each strain is in the optimal absorption band, the hydrogen production capacity is not as high as that of the mixed flora with visible light. This may be related to the types of substrates available for each single strain. Each single strain (F1, F5, F7, F11, S7, S9, and L6) can dispose of some limited substrate type for hydrogen production. The type of substrate that the mixed bacteria can use is more than that of the single strain, and the small molecule organic acids coming from pig degradation with light fermentation can also be comprehensively used. Therefore, photosynthetic hydrogen production with solar energy using pig manure sewages best for a mixed bacteria system composed of highly efficient hydrogen-producing bacteria and light with a wavelength of 380e780 nm transmitted through optical fibers, which can obtain the maximum hydrogen production and also remove and use more organic matter in the substrate.

10.5 Absorbance of mixed photosynthetic hydrogen production bacteria 10.5.1 Photometric effect on photosynthetic hydrogen production Based on the spectral coupling characteristics of photosynthetic bacteria, using corn straw as a raw material, through fine pulverization and enzymatic pretreatment, the photometric effect in photosynthetic hydrogen production was researched (Hu et al., 2014). For different illuminations, the relationship between hydrogen production and reaction time was varied. At the end of the photosynthetic hydrogen production, hydrogen production increased with an increase in illumination over 500e4000 lx, but it decreased with an increase in illumination of 4000e6000 lx. For an illumination of 2000, 4000, and 6000 lx,

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the difference in hydrogen production was small and the hydrogen production of the illumination at 6000 lx was the lowest. This indicates that strong illumination is not conducive to photosynthetic bacteria hydrogen production (Kondo et al., 2002). Reasons for this phenomenon are that the photosynthetic bacteria contain only the PSI photosynthetic system, which uses adenosine triphosphate, protons, and electrons to produce hydrogen through nitrogenase (Gou et al., 2013).When the illumination intensity exceeds a certain range, the photosynthetic bacteria absorb more energy than photosynthesis, which will cause excessive excitation of the PSI photosynthetic system and the number of highenergy electrons increase. However, the supply of electron donors generated by the Embden-Meyerhof-Parnas pathway is insufficient, which leads to optical suppression. Illumination at 6000 lx exceeds the light saturation point, so the phenomenon of hydrogen production decreases.

10.5.2 Photometric effect on optical energy conversion rate To reflect the effective use of light energy and optimize illuminance process parameters, the optical energy conversion rate is defined: the ratio of the combustion heat of hydrogen produced by photosynthetic bacteria to the input optical radiation energy within a certain reaction time (Zhu et al., 2011; Fan, 2011). The study found that no matter how the illumination changes (Kondo et al., 2002), the relationship between the optical energy conversion rate and the reaction time has the following trends: When the reaction time is within 24e72 h, the optical energy conversion rate increases with the extension of the reaction time; when the reaction time is between 72 and 168 h, the optical energy conversion rate decreases with the extension of the reaction time; and the maximum optical energy conversion rate appears around 72 h, which is consistent with the peak time of the hydrogen production rate. The effect of different illumination intensities on the optical energy conversion rate is significant. In terms of the maximum optical energy conversion rate, the optical energy conversion rate of photosynthetic bacteria hydrogen production is the highest at 500 lx, followed by illumination at 1000 lx, and the minimum optical energy conversion rate at 6000 lx is 8%. However, the amount of hydrogen produced at 500 lx is about 50% that produced at 2000 and 4000 lx. That is, if the illumination intensity is low (500 lx), the light source supply capacity is less than the photosynthetic bacteria’s growth and metabolic hydrogen production capacity, the photosynthetic bacteria’s effective use of illumination is higher, whereas the hydrogen production effect is poor at 500 lx illumination intensity. When the light intensity is 6000 lx, although the amount of hydrogen production is high, the maximum optical energy conversion rate is less than 10%, so the application value is not great. The maximum optical energy conversion rate of illumination at 2000 and

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4000 lx is respectively 25.3% and 13.3%. Although the maximum optical energy conversion rate of the latter is 52.6% of the former, the difference of hydrogen production is small between them. The illumination intensity of 2000 lx guarantees hydrogen production and also takes into account the optical energy conversion rate. It is the best for hydrogen production.

10.6 Conclusion (1) The same types of photosynthetic bacteria had similar absorption characteristics shown by the absorption spectra of living cells of seven strains hydrogen-producing bacteria. The maximum absorption peak of purple nonsulfur bacteria (F1, F5, F7, and F11) occur at 375 and 590 nm, purple sulfur bacteria S7 and S9 have a maximum absorption peak at 380 and 490 nm, whereas the maximum absorption peak of green sulfur bacteria L6 appear at 590 nm. (2) The same types of photosynthetic bacteria have similar growth characteristics and hydrogen production characteristics, and the strains grow faster and produce hydrogen more near the wavelength of its maximum absorption peak. Spectral coupling characteristics for the growth and hydrogen production of photosynthetic bacteria show that it is best to use mixed bacteria and light with a wavelength of 380e780 nm transmitted through optical fibers, which can obtain the maximum hydrogen production and also remove and use more the organic matter in the substrate. (3) For systems with an illuminance of 2000 and 4000 lx, hydrogen production is better than for other conditions. Although the maximum optical energy conversion rate of 13.3% for the illuminance of 4000 lx is only 52.6% of illuminance at 2000 lx, hydrogen production is small between them. The illumination intensity of 2000 lx guarantees hydrogen production and also takes into account the optical energy conversion rate. It is the best for hydrogen production.

References Ajmi, A.N., Hammoudeh, S., Nguyen, D.K., et al., 2015. On the relationships between CO2 emissions, energy consumption and income: the importance of time variation. Energy Econ. 49, 629e638. An, J., 2009. Effects of Light Source and Spectrum on Hydrogen Production Process of Photosynthetic Hydrogen-Producing Bacteria. Benemann, J.R., Tillett, D.M., Weissman, J.C., 1987. Microalgae biotechnology. Trends Biotechnol. 5 (2), 47e53. ¨ zgu¨r, E., Van Der Burg, J., et al., 2010. Biological hydrogen production by RhodoBoran, E., O bacter capsulatus in solar tubular photo bioreactor. J. Clean. Prod. 18, S29eS35. Fan, Z., 2011. Study on the Exergy Analysis of Photosynthetic Biological Continuous Hydrogen Production System.

234 Waste to Renewable Biohydrogen Gou, W.C., Deng, C.H., He, J.H., et al., 2013. Progress and problems of hydrogen production by photosynthetic bacteria. Kezaisheng Nengyuan/Renew. Energy Resour. 31 (9), 94e102. Hu, J., Zhou, X., Guo, J., Zhang, Z., Zhang, Q., 2014. Study on illumination effect of enzymatic hydrolysis of microstraw by photosynthetic bacteria in hydrogen production. Acta Energiae Solaris Sin. 35 (07), 1230e1236. Kondo, T., Arakawa, M., Wakayama, T., et al., 2002. Hydrogen production by combining two types of photosynthetic bacteria with different characteristics. Int. J. Hydrogen Energy 27, 1303e1308. Kumazawa, S., Mitsui, A., 1981. Characterization and optimization of hydrogen photoproduction by a saltwater blue-green alga, Oscillatoria sp. Miami BG7. I. Enhancement through limiting the supply of nitrogen nutrients. Int. J. Hydrogen Energy 6 (4), 339e348. Lee, H.S., Vermaas, W.F.J., Rittmann, B.E., 2010. Biological hydrogen production: prospects and challenges. Trends Biotechnol. 28 (5), 262e271. Lo, K.V., Liao, P.H., Gao, Y.C., 1994. Anaerobic treatment of swine wastewater using hybrid UASB reactors. Bioresour. Technol. 47 (2), 153e157. Lu, C., Zhang, Z., Ge, X., et al., 2016. Bio-hydrogen production from apple waste by photosynthetic bacteria HAU-M1. Int. J. Hydrogen Energy 41 (31), 13399e13407. Miller, D.N., Varel, V.H., 2002. An in vitro study of manure composition on the biochemical origins, composition, and accumulation of odorous compounds in cattle feedlots. J. Anim. Sci. 80 (9), 2214e2222. Ni, J.Q., Vinckier, C., Coenegrachts, J., et al., 1999. Effect of manure on ammonia emission from a fattening pig house with partly slatted floor. Livest. Prod. Sci. 59 (1), 25e31. Ormerod, J.G., Ormerod, K.S., Gest, H., 1961. Light-dependent utilization of organic compounds and photoproduction of molecular hydrogen by photosynthetic bacteria; relationships with nitrogen metabolism[J]. Arch. Biochem. Biophys. 94 (3), 449e463. Philips, E.J., Mitsui, A., 1983. Role of light intensity and temperature in the regulation of hydrogen photoproduction by the marine cyanobacterium Oscillatoria sp. strain Miami BG7. Appl. Environ. Microbiol. 45 (4), 1212e1220. Shin, H.S., Youn, J.H., Kim, S.H., 2004. Hydrogen production from food waste in anaerobic mesophilic and thermophilic acidogenesis. Int. J. Hydrogen Energy 29 (13), 1355e1363. Wilson, N.G., Bradley, G., 1997. A study of a bacterial immobilization substratum for use in the bioremediation of crude oil in a saltwater system. J. Appl. Microbiol. 83, 524e530. Xu, P., Qian, X.M., Wang, Y.X., Xu, Y.B., 1996. Modeling for waste water treatment by Rhodoseudomonas palustris Y6 immobilized on fiber in a columnar bioreactor. Appl. Microbiol. Biotechnol. 44 (5), 676e682. ¨ ., Gu¨ndu¨z, U., Tu¨rker, L., et al., 1999. Identification of by-products in hydrogen proYi git, D.O ducing bacteria; Rhodobacter sphaeroides OU 001 grown in the waste water of a sugar refinery. J. Biotechnol. 70 (1e3), 125e131. You, X., 2005. Screening of Photosynthetic Hydrogen-Producing Bacteria and Study on HydrogenProducing Factors from Pig Manure. Zhang, J., Zhang, Q., Yang, Q., Wang, Y., 2005. Effects of light intensity on photosynthetic hydrogen production by pseudomonas rhodopsin in pig manure. Trans. Chin. Soc. Agric. Eng. 09, 134e136. Zhang, J., Zhang, Q., Shi, Y., You, X., Liu, Z., 2006. Study on the hydrogen content of photosynthetic bacteria in pig waste water. J. Henan Agric. Univ. 02, 177e180. Zhang, Q., Shi, Y., Zhang, J., Yang, Q., Zhou, L., 2007. Effects of solar spectrum on the growth and hydrogen production of photosynthetic bacteria. Acta Energiae Solaris Sin. 10, 1135e1139.

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Zhang, Z., Zhou, X., Hu, J., et al., 2017. Photo-bioreactor structure and light-heat-mass transfer properties in photo-fermentative bio-hydrogen production system: a mini review. Int. J. Hydrogen Energy 42 (17), 12143e12152. Zhang, J., 2006. Study on Solar Photosynthetic Biological Hydrogen Production System and its Spectral Coupling Characteristics. Zhao, Q., 2017. Study on Photosynthetic Bacteria Fermentation Based on Cow Dung Slurry and Biogas Slurry and its Application. Zhu, H., Suzuki, T., Tsygankov, A.A., Asada, Y., Miyake, J., 1999. Hydrogen production from tofu wastewater by Rhodobacter sphaeroides immobilized in agar gels. Int. J. Hydrogen Energy 24 (4), 305e310. Zhu, X., Xie, X., Liao, Q., et al., 2011. Enhanced hydrogen production by Rhodopseudomonas palustris CQK 01 with ultra-sonication pretreatment in batch culture. Bioresour. Technol. 102 (18), 8696e8699.

Chapter 11

Photosynthetic thermal effect of biological hydrogen production system Chao He1, 2, 3 1 Key Laboratory of New Materials and Facilities for Rural Renewable Energy of Ministry of Agriculture and Rural Affairs, College of Mechanical & Electrical Engineering, Henan Agricultural University, Zhengzhou, China; 2Henan International Joint Laboratory of Biomass Energy and Nanomaterials, Henan Agricultural University, Zhengzhou, China; 3Collaborative Innovation Center of Biomass Energy, Henan Province, Zhengzhou, China

11.1 Introduction Physical changes, chemical reactions, and biological metabolic processes that occur in nature are usually accompanied by changes in energy, some of which are manifested in the form of thermal effects. The precise measurement and research of these thermal effects have become an important branch of physical chemistry-thermochemistry. With the development of modern science and technology, especially the rapid development of materials science and electronics, it has provided the necessary experimental conditions for the birth of “dynamic” thermochemistry. Therefore, high-sensitivity and highly automated microcalorimeters continue to emerge. A new branch of science that studies the dynamic process of enthalpy change and integrates thermochemistry and chemical kinetics-thermodynamics came into being at the beginning of this century (Liu et al., 1993). So-called thermodynamics is a branch of science based on calorimetry, chemical thermodynamics, and chemical kinetics; it studies the laws of process dynamics based on the exothermic (exothermic) rate of the changing process. Because the thermodynamic method has the nonspecific unique advantages of the solvent system, and the spectral properties and electrical properties of the reaction system with no restrictions, and the operation is simple and the conditions can be changed at any time to simulate the process. Therefore, it is becoming an effective research method in chemical reactions, biochemical processes, and chemical engineering, and has shown broad application prospects in many fields such as physical chemistry, biochemistry, organic chemistry, and inorganic chemistry. Waste to Renewable Biohydrogen. https://doi.org/10.1016/B978-0-12-821659-0.00012-5 Copyright © 2021 Elsevier Inc. All rights reserved.

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Biomass energy is a kind of clean and renewable energy that can be used on a large scale. Owing to increasingly serious energy and environmental problems, its development and use have attracted widespread attention. Pyrolysis is a biomass heat with high conversion efficiency. In the chemical conversion process, under different reaction conditions, the process can obtain gas-, liquid-, and solid-phase products of different qualities and quantities. At the same time, it is an important initial process that generally exists in thermochemical conversion processes such as gasification and combustion. Pyrolysis itself is an extremely complicated process. To describe fully the many chemical and physical processes involved in the pyrolysis process and understand their interrelationships, a lot of exploration is needed, which reflects the intrinsic nature of the pyrolysis chemical reaction. Studying the biomass pyrolysis kinetics and establishing a reliable biomass kinetic model will help avoid interference, enable a deeper understanding of the nature of the pyrolysis process, and lay a foundation for studying the true process of the overall biomass pyrolysis. The metabolic process of an organism is accompanied by a certain thermal effect. If it is detected with a microcalorimeter with sufficient sensitivity, it can provide a new method for studying the metabolic process and related characteristics of living cells. Using thermodynamics to analyze the thermal spectrum, we can obtain the thermodynamic and kinetic information of bacterial growth and metabolism. There are many research methods of thermodynamics. General calorimetry is an important method in thermodynamics research. The calorimeter has been used for microbial research for nearly a century. As early as 1911, Hill used calorimetry to study the effect of yeast cells on sucrose. However, in the past few decades, automation and high sensitivity were developed as a result of the development of modern experimental technology. The microcalorimetry instrument has laid the foundation for the calorimetric research at the cellular level. The calorimetric method used in life science research has many advantages, such as the extensiveness, nonspecificity, nondestructiveness, continuity, and quantitative (semiquantitative) nature of the research system (Wadso and Spink, 1976).

11.2 Research on microbial thermodynamic model 11.2.1 Bacterial exponential growth kinetics Exponential growth is an ideal, nonlimiting growth mode. Bacterial growth conforms to the Malthus equation. Most of the literature uses an exponential model to treat the thermal spectrum of bacterial growth (Holzel et al., 1994; Xie et al., 1992; Zhang et al., 1993). Under uniform liquid culture conditions, if the supply of nutrients and environmental conditions can meet the needs of all members of the microbial

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population, and the inhibitory effect of metabolites is negligible, the growth of the biological population is under unrestricted conditions proceeding (Boling et al., 1973). Mond first proposed a kinetic model for the exponential growth of bacteria under unrestricted nutritional conditions, which had been confirmed by subsequent analysis results, so it was accepted as the basic kinetic model for bacterial growth (Calvet and Part, 1963). The mathematical expression is shown in Eq. (11.1): Nt ¼ N0 ekðtt0 Þ

(11.1)

where N0 and Nt are the number of bacteria at time t0 and t, respectively, and k is the bacterial growth rate constant. For a certain species of bacteria, k is constant and the number of populations grows exponentially with time, so this equation is called the exponential growth equation, which is the Malthus equation. This is the simplest model of bacterial growth kinetics, which belongs to the deterministic model. The values of parameters N0 and Nt in the equation remain unchanged, and the population number can be determined in a given time.

11.2.2 Logistic equation of bacterial growth When microorganisms grow in a limited environment, for various reasons such as an insufficient supply of nutrients, limited living space or the inhibition of growth caused by the accumulation of metabolites, the specific growth rate of the microbial population will gradually decrease to zero or even become negative. In the past century, Belgian mathematicians derived the logistic equation (Boling et al., 1973) describing the microbial population proliferation under restrictive conditions (Eq. 11.2): dN ¼ mN  bN 2 dt

(11.2)

where m is the population growth rate constant, b is the population decay rate constant, bN 2 is negative, and N 2 has a higher order than N, so the total population will not increase infinitely, which is consistent with the experimentally measured thermogram. Combining the logistic model of bacterial growth and applying the assumption of thermal power ratio to the number of bacteria and the “heat flow method”, Professor Honglin Zhang and others reported the thermodynamic equation of bacterial growth. Integrating Eq. (11.2) gives: N¼

K  K  N0 kt 1þ e N0 

(11.3)

where N0 is bacterial growth initiation time and K ¼ m=b is the maximum number of bacteria under experimental conditions.

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K  N0 ¼ M; M denotes the maximum fold increase in the number of N0 bacteria under this test condition, which has a clear physical meaning. Eq. (11.3) becomes: Let

N¼

K 1 þ Mekt

(11.4)

Because PðtÞ is the exothermic power of bacteria at t, P0 is the exothermic power of a single bacterium. Then, Pm ¼ P0 K where Pm is the maximum heating power for bacterial growth. From Eqs. (11.4) and (11.5),   Pm  1 ¼ ln M  kt ln PðtÞ

(11.5)

(11.6)

Eq. (11.6) is a thermodynamic equation growth and meta  of bacterial Pm 1 to fit time t linearly to bolism, and it is a linear equation. Use ln PðtÞ obtain k and M. From M and Eq. (11.5), K and P can be obtained.

11.2.3 Bacterial linear growth kinetics model Under certain conditions, bacterial growth follows a linear equation, as shown in Eq. (11.7): dN ¼C dt

(11.7)

where N is the number of groups and t is time. From the bacterial linear growth kinetics model, combined with Eq. (11.1), the thermodynamic equation of bacterial linear growth can be obtained: Pt ¼ P 0 þ k m t In Eq. (11.8), km ¼ CW， C ¼

(11.8)

dN ， W is the exothermic power of a dt

single bacterium.

11.2.4 Nonideal growth thermodynamic model The classic exponential model describes the growth process of cells under unlimited ideal conditions, and the classic logistic model describes the process of cells growing in an “S” shape under ideal conditions. At this time, the inflection point of the growth curve should be at Nm =2. However, in some experiments, the measured bacterial growth curve is an irregular “S”

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type, which is a growth process under nonideal conditions. Its thermodynamic model (Yan et al., 1997; Tu and Zhou, 2003) is:   N kN 1  dNt Nm ¼ (11.9) N dt 1 N’m where N is the cell number at time t, Nm is the maximum number of cells during growth, and Nm’ is the number of cells that the nutrients in the medium can fully use. Tu Jian-bin studied the difference model of Eq. (11.9): 1axn

Xnþ1 ¼ Xn er1bxn

(11.10)

Among them: r > 0; a  b > 0. Considering that the heat production of microorganisms under nonideal conditions has the characteristics of time lag and changeability, the thermodynamic differential model of nonideal growth of bacteria is studied (Tu, 1998) as: Xnþ1 ¼ Xn ern

1  xnk 1  axnk

(11.11)

Among them: a ˛ ð0; 1Þ， rn > 0; k  o.

11.2.5 Metabolite inhibition model Batch culture is a traditional culture method used to study the growth of microorganisms (Liu et al., 1996). A small amount of microorganisms are inoculated into the medium. As the culture time increases, nutrients are gradually consumed and metabolites are accumulated, which will inhibit growth and reduce the growth rate. This process can be expressed by the formula: dNt=dt ¼ kNt ð1  aiÞ

(11.12)

Among them, l is the inhibitor concentration and a is a constant, and when a ¼ 0, Eq. (11.12) becomes an exponential model. Assuming that the rate of inhibitor increase is proportional to the rate of cell proliferation: di=dt ¼ b dNt=dt

(11.13)

where b is a constant. When t ¼ 0, i is also 0. Integrate Eq. (11.13) and substitute Eq. (11.10); then:   dP=dt ¼ k0 P 1  P=P (11.14) st

k0 ¼ kð1 þabN0 Þ; Nst ¼ ð1 þ abN0 Þ=ab. Subscript “st” indicates the stable period of microbial growth. Using the boundary conditions, t ¼ 0, P ¼ P0 are

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substituted into Eq. (11.14) to obtain the growth thermodynamic model of metabolite inhibition:     1 1  1 ¼ ln  1  k0 t (11.15) ln bPt bP0

11.3 Factors affecting photosynthetic heat effect of biological hydrogen production system 11.3.1 Initial temperature When the photosynthetic bacteria undergo hydrogen production experiments at different initial temperatures, the system temperature will increase to different degrees. At different initial temperatures before 12 h, the system temperature of photosynthetic bacteria hydrogen production increases to a large extent. The system temperature rises slowly at 12e20 h. From 20 h onward, it will remain basically inconvenient.

11.3.2 Light intensity Photosynthetic bacteria require appropriate light intensity for hydrogen production. The intensity of light affects the number of photons captured by photosynthetic bacteria, affects the formation of adenosine triphosphate and the proton gradient, and has an important role in the hydrogen production of photosynthetic bacteria.

11.3.3 Inoculation amount An appropriate inoculation amount is particularly important for the hydrogen production of photosynthetic bacteria. The concentration of bacteria is too low, the substrate cannot be fully decomposed and used, and the conversion efficiency of organic substances is low, which affects the efficient progress of the hydrogen production reaction and the regeneration of organic waste reuse. The concentration of bacteria is too high, and the amount of organic matter that can be used is relatively small. Photosynthetic bacteria start to compete for organic matter. Some of the photosynthetic bacteria in the reaction system do not function normally, which wastes bacteria and hydrogen production volume, and reduces hydrogen production efficiency.

11.3.4 Carbon source Photosynthetic bacteria can use glucose, sucrose, lactic acid, acetic acid, and so on as carbon sources to grow, and they can also use their original hydrogen

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donors to produce hydrogen. Different photosynthetic bacteria can use different carbon sources, even if the same population can grow. The carbon source and the carbon source as the donor of the hydrogen-producing electron are not necessarily the same.

11.3.5 Glucose concentration Photosynthetic bacteria must grow with glucose, fructose, malic acid, and other substances as carbon sources, and use them to provide hydrogenproducing hydrogen donors to make the hydrogen production reaction proceed smoothly. Glucose is the most commonly used carbon source in the hydrogen production reaction of photosynthetic bacteria. The effects of different glucose concentrations on the system temperature and heat production rate during hydrogen production by photosynthetic bacteria were studied experimentally.

11.3.6 Glucose access time Glucose is an important small molecule organic carbon source for the growth of photosynthetic bacteria. It is also an important donor of hydrogenproducing electrons. However, after the glucose is inserted into the medium, the solution immediately becomes acidic, and the degree is more serious. To give glucose as the hydrogen-producing substrate, photosynthetic bacteria have a better access time for hydrogen production. We studied the effect of different glucose access times on hydrogen production.

11.3.7 NHD 4 concentration The hydrogen production reaction of photosynthetic bacteria requires suitable nitrogen, especially during the growth of photosynthetic bacteria. Nitrogen is an important raw material for the synthesis of nitrogenase in the growth of photosynthetic bacteria. At the same time, the concentration of NHþ 4 has an effect on the activity of nitrogenase. When the concentration of NHþ 4 is too high, nitrogenase activity is hindered and hydrogen production is weakened.

11.4 Influence of thermal effect on hydrogen production 11.4.1 Influence on different initial temperatures on thermal effect hydrogen production Photosynthetic bacteria with a light intensity of 2000 lux, with an inoculum of 10%, pH 7, cultured for 48 h with an optical density (OD) of 0.4e0.6 and logarithmic growth period, were selected. A 30 g/L glucose solution was the hydrogen production matrix. The initial environmental temperatures were set to 24, 27, 30, and 33 C.

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The SWJ-c precision digital thermometer probe was inserted into the rubber plug of the adiabatic reaction bottle. Then, it was checked whether the probe touched the bottle wall, and the contact point was sealed to ensure that the measured temperature was the temperature of the reaction solution. The degree of heat release during the hydrogen production of photosynthetic bacteria was measured by the temperature change rate. Calculation of the temperature change rate is shown in Eq. (11.16): Temperature change rate ¼

Final temperature  initial temperature Time (11.16)

where the hydrogen production capacity is expressed by the hydrogen production volume and hydrogen production rate. The yield of hydrogen was measured by the drainage method. The content of hydrogen was measured by gas chromatography. A 6820 GC-14b gas chromatograph was used for gas chromatography with a thermal conductivity cell as a detector, a 5A molecular sieve packed column, high-purity nitrogen as the carrier gas, a column temperature of 80 C, a detector temperature of 150 C, an injection volume of 500 mL, and a standard gas of high-purity hydrogen with a content of H2 of 99.999%: y ¼ 10798X þ 139268 where y is the hydrogen content and X is the peak sealing area. Fig. 11.1 shows that when the initial temperature is 24 and 27 C, the hydrogen production of photosynthetic bacteria affected by thermal effect is greater than when it is not affected by the thermal effect. There is little difference in hydrogen production between these results before 48 h. After 48 h, the hydrogen production of the two systems increases rapidly, but the rate of increase of the system affected by the thermal effect is faster than that of the other system. With the extension of time, the increase rate of hydrogen production gradually decreases. The hydrogen yield of the system with the heat effect is 328 mL, and that of the system without the thermal effect is 262 mL at 24 C. At 27 C, the hydrogen production of the two systems of hydrogen production is 865 and 562 mL, respectively. When the temperature is 30 and 33 C, the trend of the influence of the thermal effect on hydrogen production is similar. Fig. 11.1C and D shows that the hydrogen production of the system affected by thermal effect is lower than that of the system without the thermal effect. Hydrogen production for the system affected by the thermal effect and that without the thermal effect at 30 C is 546 and 806 mL, respectively, and that at 33 C is 374 and 496 mL, respectively. Hydrogen production for the system with the thermal effect is the largest at the initial temperature of 27 C, followed by the system with the initial temperature of 30 C, and then the system with the initial temperature of 33 C; that with the initial temperature of 24 C is the smallest.

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(a) Initial temperature 24

(b) Initial temperature 27

(c) Initial temperature 33

(d) Initial temperature 30

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FIGURE 11.1 Effect of thermal effect on hydrogen production at different initial temperatures: (A) Initial temperature of 24 C; (B) Initial temperature of 27 C; (C) Initial temperature of 30 C; and (D) Initial temperature of 33 C.

Fig. 11.2 shows that the rate of gas production first increases and then decreases with the extension of time, and reaches the maximum at 72 h. The rate of hydrogen production reaches a maximum of 8.23, 21.88, 17.33, and 11.91 mL/h$L, respectively, at different initial temperatures. When the initial temperature is 24 and 27 C, the hydrogen production rate with the thermal effect is greater than that without the thermal effect. When the initial temperature is 24 C, the system basically stops hydrogen production at 120 h; when the initial temperature is 27 C, the hydrogen production rate of the system with a thermal effect lasts to 168 h. When the initial temperature is 30 and 33 C, the hydrogen production rate of the system with a thermal effect is lower than that of the system without a thermal effect. At two initial temperatures, the thermal effect on the hydrogen production rate has the same trend, but the change in the hydrogen production rate of the system with a thermal effect is smaller than that of the system without a thermal effect when the initial temperature at 33 C. The reason may be that when the initial temperature is high, there is a large amount of accumulated heat, and hydrogen production is not stable because the activity of the hydrogen-producing enzyme of photosynthetic bacteria is blocked.

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(a) Initial temperature 24

(b) Initial temperature 27

(c) Initial temperature 30

(d) Initial temperature 33

FIGURE 11.2 Effect of thermal effect on hydrogen production velocity at different initial temperatures: (A) Initial temperature of 24 C; (B) Initial temperature of 27 C; (C) Initial temperature of 30 C; and (D) Initial temperature of 33 C.

11.4.2 Effect of thermal effect on hydrogen production with different illuminations The light intensity of the experiment was set at 500, 1000, 2000, and 3000 lux; the rest conditions were set at 27 C; inoculum was 10%, pH was 7.0; the inoculum culture was selected for 48 h; the OD value of photosynthetic bacteria in the logarithmic growth period was 0.4e0.6; and a 30 g/L glucose solution was the hydrogen production substrate. The lux1010b digital illuminance meter was placed on the surface of the adiabatic reaction bottle. Symmetrical points of different directions were taken to measure the light intensity, and then the average value was taken. The calculated average is the light intensity. Fig. 11.3 shows that under different light intensities, hydrogen production in photosynthetic reaction stage increased with the extension of time and hydrogen production of the system with a thermal effect was greater than that of the system without a thermal effect. When the light intensity was 500 lux, the hydrogen production of the system with a thermal effect was larger than that of the system without a

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(a) Light intensity 500Lux

(c) Light intensity 2000Lux

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(b) Light intensity 1000Lux

(d) Light intensity 3000Lux

FIGURE 11.3 Effect of thermal effect on hydrogen production with different light intensities: (A) Light intensity 500 lux; (B) Light intensity 1000 lux; (C) Light intensity 2000 lux; (D) Light intensity 3000 lux.

thermal effect, but the difference between the two systems was not significant. Hydrogen production was low, 408 and 338 mL respectively. When the light intensity was 1000 lux, hydrogen production of the system with a thermal effect increased faster than that of the system without a thermal effect. Hydrogen production was high, 728 and 512 mL, respectively. When the light intensity was 2000 lux, the hydrogen production of both systems was large and the increase in hydrogen production was fast. The hydrogen production was 837 and 629 mL, respectively. When the light intensity was 3000 lux, the thermal effect on hydrogen production was similar to that of 2000 lux. Hydrogen production was 894 and 652 mL, respectively. The results show that a series of activities such as the metabolism of photosynthetic bacteria caused the accumulation of heat and a systemic rise in temperature, which contributed to the increase in hydrogen production. With the increase in light intensity, the hydrogen production of the system also increased under the influence of the thermal effect. Fig. 11.4 shows that the hydrogen production rate was small before 24 h, and then it increased continuously. The maximum hydrogen production rate generally occurred at 72e96 h; after 96 h, the hydrogen production rate began to decline until the end of hydrogen production. The hydrogen production rate of the system with a thermal effect was higher than that of the system without a thermal effect.

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(a) light intensity 500Lux

(c) light intensity 2000Lux

(b) light intensity 1000Lux

(d) light intensity 3000Lux

FIGURE 11.4 Thermal effect on hydrogen production velocity with different light intensities: (A) Light intensity of 500 lux; (B) Light intensity of 1000 lux; (C) Light intensity of 2000 lux; and (D) Light intensity of 3000 lux.

When the light intensity was 500 lux, the difference in hydrogen production rate between the system with a thermal effect and the one without a thermal effect was not significant: is 8.45 and 7.37 mL/h$L, respectively. When the light intensity was 1000 lux, the maximum hydrogen production rate of the system with a thermal effect appeared earlier and the duration of the high hydrogen production rate was longer than that of the system without a thermal effect. When the light intensity was 2000 lux, the system with a thermal effect had obvious advantages. The maximum hydrogen production rate was 22.32 mL/h$L. At 72e96 h, hydrogen production increased dramatically. When the light intensity was 3000 lux, the maximum hydrogen production rate of the two systems was 23.92 and 19.07 mL/h$L, respectively at 72 h, but the hydrogen production rate of the system with a thermal effect changed greatly.

11.4.3 Thermal effect on hydrogen production with different inoculations Photosynthetic bacteria in the logarithmic growth period were selected. The initial OD value was 0.48 and the inoculation amount was set at 5%, 10%, 20%, and 50%, according to the volume percentage. Other conditions were a temperature of 27 C, light intensity of 2000 lux, pH of 7.0, and glucose solution of 30 g/L, recorded during changes in hydrogen production.

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(a) Inoculation 5 %

(b) Inoculation 10 %

(c) Inoculation 20 %

(d) Inoculation 50 %

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FIGURE 11.5 Thermal effect on hydrogen production with different inoculations: (A) Inoculation of 5%; (B) Inoculation of 10%; (C) Inoculation of 20%; and (D) of Inoculation 50%.

Fig. 11.5 shows that the hydrogen production of the two systems increased with the extension of time. Except for 50% inoculation, the hydrogen production of the system with a thermal effect was greater than that of the system without a thermal effect. Hydrogen production with 5% inoculation was the least, at 419 and 326 mL, respectively. Owing to the small number of living bacteria, glucose could not be fully used. However, 10% and 20% inoculation was close. When inoculation was 10% and 20%, the hydrogen production of the system with a thermal effect was 808 and 848 mL, respectively; that of the system without a heat effect was 719 and 745 mL, respectively. At 50% inoculation, hydrogen production of I and II was 714 and 683 mL, respectively. The concentration in the reaction vessel was large and the color of the reaction solution was deep, so that the penetration rate of light was reduced, resulting in a decrease in the enzyme activity of photosynthetic bacteria and less hydrogen production. Fig. 11.6 shows that at inoculations of 5%, 10%, and 20%, the thermal effect on the hydrogen production rate was similar. The hydrogen production rate of the system affected by the thermal effect was higher than that of the system without a thermal effect, and the hydrogen production rate first increased and then decreased with the extension of time. When 5%, 10% and 20% were inoculated, the hydrogen production rate of the system affected by the heat effect increased more than that of the system without a thermal effect. The hydrogen production rate reached its maximum

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(a) Inoculation 5 %

(c) Inoculation 20 %

(b) Inoculation 10 %

(d) Inoculation 50 %

FIGURE 11.6 Effect of thermal effect on hydrogen production velocity with different inoculations; (A) Inoculation of 5%; (B) Inoculation of 10%; (C) Inoculation of 20%; and (D) Inoculation of 50%.

at 72 h, at 12.78 and 11.14 mL/h$L, respectively. When inoculation was 10%, the maximum hydrogen production rates of the system with and without a thermal effect were 19.28 and 17.14 mL/h$L, respectively, whereas the maximum hydrogen production rates of the system with and without a thermal effect accumulation were 18.50 and 15.82 mL/h$L at 72e96 h with 20% inoculation. The maximum hydrogen production rate of the system with a thermal effect lasted longer with 10% and 20% inoculation. When inoculated at 50%, the hydrogen production rate decreased after 48 h and the hydrogen production rate of the system with a thermal effect decreased more than that of the system without a thermal effect. The hydrogen production rate of the system without a thermal effect at 96 h was 3.68 mL/h$L, and that of the system with a thermal effect was almost 0. This may be because the bacterial concentration was higher, light permeability is blocked, and the physiological activity of photosynthetic bacteria was affected by the limited substrate, which had a competitive effect. The rate of gas production significantly increased. Glucose is first used by photosynthetic bacteria, and then small molecular acids are used. When glucose is decomposed in large quantities and small molecular acids cannot be fully used for a hydrogen production reaction, secondary hydrogen production may occur.

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11.4.4 Effect of on hydrogen production with different kinds of carbon The temperature was 27 C, the light intensity was 2000 lux, and the inoculation was 10%. Photosynthetic bacteria with an initial OD value of 0.43 were selected in the logarithmic growth period, and the carbon source was glucose, sucrose, lactic acid, and acetic acid. Fig. 11.7 shows that when photosynthetic bacteria used different kinds of carbon for hydrogen production, hydrogen production increased with time. Moreover, the system with a thermal effect had greater hydrogen production than that of the system without a thermal effect. When glucose was the carbon source, the yield of hydrogen was the largest. The hydrogen production of the system with or without a thermal effect was 865 and 572 mL, respectively, followed by sucrose at 766 and 458 mL, respectively; then acetic acid at 640 and 421 mL, respectively; and least for lactic acid at 551 and 393 mL, respectively. The accumulated heat of glucose was smaller and the temperature change rate was smaller than that of sucrose and lactic acid, whereas the hydrogen production of glucose was 1.129 times that of sucrose and 1.570 times that of lactic acid. The accumulated heat of acetic acid was the largest, whereas hydrogen production was larger only than lactic acid. The hydrogen production of photosynthetic bacteria had different degrees of use for different kinds

(a) Glucose

(b) Sucrose

(c) Lactic acid

(d) Acetic acid

FIGURE 11.7 Thermal effect on hydrogen production with different kinds of carbon: (A) Glucose; (B) Sucrose; (C) Lactic acid; and (D) Acetic acid.

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of carbon. It is not that the more heat accumulated, the greater the change in system temperatures. Different carbon sources have different effects on hydrogen production, and the specific reasons need to be studied further. Fig. 11.8 shows that the hydrogen production rate of the system with a thermal effect was greater than that of the system without a thermal effect, and the hydrogen production rate first increased and then decreased with the extension of time. When glucose was a carbon source, the rate of hydrogen production at 72 h was the largest at 21.88 mL/h$L, and the gas production was relatively concentrated at this time. In the system without a thermal effect, hydrogen production lasted relatively long but was not concentrated. Thus, the system with a heat effect was better when glucose was used as a carbon source for hydrogen production. The hydrogen production rate of the sucrose system was lower than that of glucose. The hydrogen production rate of the system with a thermal effect and that without a thermal effect were 12.78 and 9.66 mL/h$L, respectively. When lactic acid and acetic acid produced hydrogen, the trends of hydrogen production rate were similar. In the process of hydrogen production, the system with acetic acid as the carbon source had the most heat accumulated, whereas the hydrogen production rate of glucose was the highest among all kinds of carbon. Under different carbon source conditions, it is not that the stronger the thermal effect

(a) Glucose

(b) Sucrose

(c) Lactic acid

(d) Acetic acid

FIGURE 11.8 Thermal effect on hydrogen production velocity with different kinds of carbon: (A) Glucose; (B) Sucrose; (C) Lactic acid; and (D) Acetic acid.

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is, the stronger the hydrogen production is. It may be that for the photosynthetic hydrogen-producing bacteria selected by our research group, the carbon of growth and the carbon of hydrogen production were not the same, or substances that are good sources of growing carbon are not good sources of hydrogen.

11.4.5 Thermal effect on hydrogen production with different concentrations of glucose The temperature was set to 27 C, the light intensity was 2000 lux, the inoculation was 10%, and the pH was 7.0. The photosynthetic bacteria in the logarithmic growth period were cultured for 48 h and the initial OD value was 0.42. The glucose concentrations were 0.5%, 1.0%, 2.0%, 3.0%, and 4.0%. When the concentration of glucose was 0.5%, the color of the reaction solution gradually deepened from pink to dark red. There was no gas generation and the color change of the system with the thermal effect was faster than that of the system without a thermal effect. The relationship between the yield of hydrogen and the glucose concentration is shown in Fig. 11.9. The hydrogen production of the system with a thermal effect was higher than that of the system without a thermal effect. When the glucose concentration was 1.0%,

(a) Glucose concentration of 1.0%

(b) Glucose concentration of 2.0%

(c) Glucose concentration of 3.0%

(d) Glucose concentration of 4.0%

FIGURE 11.9 Effect of thermal effect on hydrogen production with different glucoses concentrations: (A) Glucose concentration of 1.0%; (B) Glucose concentration of 2.0%; (C) Glucose concentration of 3.0%; (D) Glucose concentration of 4.0%.

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the hydrogen production of the system with a thermal effect and that of the system without a thermal effect were 278 and 211 mL, respectively. The yield of hydrogen at 2.0%, 3.0% and 4.0% glucose was relatively large. Among them, when the glucose concentration was 4%, the hydrogen production was the largest, at 833 and 611 mL, respectively. The next, at 3.0% glucose, was 784 and 587 mL, respectively. The minimum hydrogen production at the concentration of 2.0% glucose was 671 and 525 mL, respectively. Comparison of the hydrogen production at different concentrations shows that the thermal effect of different glucose concentrations was conducive to the increase in hydrogen production. Fig. 11.10 shows that the effect of glucose concentration on hydrogen production rate was significant. Under various concentrations, the hydrogen production rate of the system with a thermal effect was higher than that of the system without a thermal effect. The rate of hydrogen production was the highest when the reaction lasted 72 h. When the concentration of glucose was 4.0%, the hydrogen production rate was the largest; the maximum hydrogen production rates of the system with a thermal effect and without a thermal effect were 20.71 and 13.86 mL/h$L, respectively. Under the influence of a thermal effect, when the concentration of glucose was 4.0%, the hydrogen production rate was the highest, followed by 3%, and

(a) Glucose concentration of 1.0%

(b) Glucose concentration of 2.0%

(c) Glucose concentration of 3.0%

(d) Glucose concentration of 4.0%

FIGURE 11.10 Thermal effect on hydrogen production velocity with different glucose concentrations: (A) Glucose concentration of 1.0%; (B) Glucose concentration of 2.0%; (C) Glucose concentration of 3.0%; (D) Glucose concentration of 4.0%.

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the lowest was 1%. The pH of the reaction solution with a 4.0% glucose concentration was less than 5.0 after 48 h, and the pH was low, which is not conducive to hydrogen production. When the glucose concentration was high, the acidification degree of the reaction solution was high and the reaction speed was fast.

11.4.6 Thermal effect on hydrogen production with glucose in reactor at different times The main parameters of the experiment were set to a temperature of 27 C, light intensity of 2000 lux, inoculation of 10%, and pH of 7.0. Photosynthetic bacteria with an initial OD value of 0.41 were cultured for 48 h in a logarithmic growth period. Glucose was set to 36, 48, and 60 h after photosynthetic bacteria were cultured. Fig. 11.11 shows that the hydrogen production of the system with a thermal effect was greater than that of the system without a thermal effect. The hydrogen production trend was similar with different times of glucose placement, indicating that the thermal effect was conducive to the increase in hydrogen production. Hydrogen production for the system with and without a thermal effect was 785 and 691 mL, respectively, when glucose was placed

(a) Put glucose after 36h

(b) Put glucose after 48h

(c) Put glucose after 60h

FIGURE 11.11 Effect of thermal effect on hydrogen production with glucose placed in reactor in different times: (A) Glucose after 36 h; (B) Glucose after 48 h; (C) Glucose after 60 h.

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36 h after photosynthetic bacteria inoculation; 706 and 567 mL, respectively, after 48 h of inoculation; and 645 and 541 mL, respectively, after 60 h of inoculation. In the presence of a thermal effect, hydrogen production was quite different owing to the different placement time of glucose. The hydrogen production of photosynthetic bacteria was the highest after 36 h of inoculation, followed by the placement of glucose at 36 h after photosynthetic bacteria inoculation, and then 60 h. When glucose was placed after 36 and 48 h, hydrogen production stopped at 144 h, whereas when glucose was placed after 60 h, the hydrogen production of the system continued to 168 h. This may be because the multiplication cycle of photosynthetic bacteria growth generally occurs at 48 h after photosynthetic bacteria inoculation, and during the multiplication cycle, photosynthetic bacteria can reproduce faster after the placement of glucose, adapt to the new environment earlier, improve the activity of enzymes, and improve hydrogen production. The hydrogen production rate with different glucose placement times is shown in Fig. 11.12. The hydrogen production rate of the system with a thermal effect was greater than that of the system without a thermal effect; the hydrogen production rate was high at 48e96 h and the duration of the high hydrogen production rate was long. The maximum hydrogen production rate of the two systems was 15.38 and 14.7 mL/h$L, respectively, when glucose was

(a) Put glucose after 36h

(b) Put glucose after 48h

(c) Put glucose after 60h

FIGURE 11.12 Thermal effect on hydrogen production velocity placing glucose in reactor at different times: (A) Glucose after 36 h; (B) Glucose after 48 h; and (C) Glucose after 60 h.

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placed 36 h after photosynthetic bacteria inoculation; 14.30 and 13.22 mL/h$L, respectively, after 48 h of inoculation; and 13.43 and 12.78 mL/h$L, respectively, after 60 h of inoculation.

11.4.7 Thermal effect on hydrogen production with different nitrogen concentrations The main parameters of the experiment were a temperature of 27 C, light intensity of 2000 lux, inoculation of 10%, and pH of 7.0; inoculants were cultured for 48 h; the OD value was 0.4e0.6; photosynthetic bacteria were in þ the logarithmic growth period; and the NH4 concentrations were 0.2, 0.4, 0.6, and 0.8 g/L. Fig. 11.13 shows that the yield of hydrogen increased with the prolongation þ of time. When the NH4 concentration was 0.2, 0.4, and 0.6 g/L, the hydrogen production of the system with a thermal effect was greater than that of the þ system without a thermal effect. It is opposite with an NH4 concentration of þ 0.8 g/L. When the NH4 concentration was 0.2 g/L, the hydrogen production of the system with and without a thermal effect was 614 and 530 mL, respecþ tively; it was 865 and 702 mL respectively with an NH4 concentration of þ 0.4 g/L, 832 and 660 mL, respectively, with an NH4 concentration of 0.6 g/L, þ and 460 and 478 mL, respectively, with an NH4 concentration of 0.8 g/L.

(a) NH4+ of 0.2g/L

(b) NH4+ of 0.4g/L

(c) NH4+ of 0.6g/L

(d) NH4+ of 0.8g/L

FIGURE 11.13 Thermal effect on hydrogen production with different nitrogen concentrations: þ þ þ (A) NHþ 4 at 0.2 g/L; (B) NH4 at 0.4 g/L; (C) NH4 at 0.6 g/L; and (D) NH4 at 0.8 g/L.

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(a) NH4+ of 0.2g/L

(b) NH4+ of 0.4g/L

(c) NH4+ of 0.6g/L

(d) NH4+ of 0.8g/L

FIGURE 11.14 Thermal effect on hydrogen production velocity with different nitrogen conþ þ þ centrations: (A) NHþ 4 at 0.2 g/L; (B) NH4 at 0.4 g/L; (C) NH4 at 0.6 g/L; and (D) NH4 at 0.8 g/L.

The order of hydrogen production of system affected by the thermal effect þ þ was: NHþ 4 concentration of 0.4 g/L > NH4 concentration of 0.6 g/L > NH4 þ concentration of 0.2 g/L > NH4 concentration of 0.8 g/L. The high NHþ 4 concentration was not suitable for hydrogen production. As shown in Fig. 11.14, the NHþ 4 concentration was 0.2 g/L. Before 120 h, the hydrogen production rate of the system with a thermal effect was higher than that of the system without a thermal effect. The hydrogen production rate decreased after 120 h and the hydrogen production rate of the system with a thermal effect was lower than that of the system without a thermal effect at þ 144 h. This may be because the concentration of NHþ 4 was too low. The NH4 of the system with a thermal effect was consumed after a period of reaction time. The activity of nitrogenase was weak, which led to a decrease in the hydrogen production rate. The maximum hydrogen production rates of the system that was affected and not affected by the thermal effect with an NHþ 4 concentration was 0.2 g/L was 13.61 and 11.61 mL/h$L, respectively. When the NHþ 4 concentration was 0.4 and 0.6 g/L, the hydrogen production rate of the system with a thermal effect was higher than that of the system without a thermal effect. The maximum hydrogen production rate of the system with an

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NHþ 4 concentration of 0.4 g/L was 21.88 and 19.28 mL/h$L, respectively, at 72 h, and that of the system with an NHþ 4 concentration of 0.6 g/L was 20.19 and 17.85 mL/h$L, respectively, at 96 h. when the NHþ 4 concentration was 0.8 g/L. Before 72 h, the hydrogen production rate of the system with a thermal effect was higher than that of the system without a thermal effect; it was the opposite after 72 h. This may be because when the concentration of NHþ 4 was relatively high, the system with the thermal effect had a higher temperature, which was conducive to growth and bad for hydrogen production. As a result, the rate of hydrogen production was greatly reduced, even smaller than that of the system without a thermal effect.

11.5 Conclusion The thermal effect of photosynthetic hydrogen production is related to the initial temperature, light intensity, amount of inoculation, carbon source, glucose concentration, glucose placement time, NHþ 4 concentration, and other factors. There are thermal effects on the hydrogen production of photosynthetic bacteria: (1) In the case of a low initial temperature, it can promote the hydrogenproducing ability of photosynthetic bacteria, but in the case of a high initial temperature, it is the opposite. (2) Light intensity can promote the hydrogen production of photosynthesis. With an increase in light intensity, the hydrogen production of the system with a thermal effect increases. (3) At an inoculation at 5%, 10%, and 20%, the heat effect can increase the hydrogen production of photosynthetic bacteria. When inoculated at 50%, the heat effect response can inhibit the hydrogen production of photosynthetic bacteria. (4) Glucose as a carbon source has the greatest effect on the hydrogen production capacity of photosynthetic bacteria, which is 865 mL. (5) The concentration of glucose was 0.5% and no gas was produced. When the glucose concentration was 1.0%, 2.0%, 3.0%, and 4.0%, the heat effect increased the hydrogen production of photosynthetic bacteria. (6) When glucose placement time is different, the hydrogen production of photosynthetic bacteria thermal effect is significantly different. When glucose is placed at 36 h after accessing photosynthetic bacteria, the hydrogen production of photosynthetic bacteria is the largest. (7) When the concentration of NHþ 4 is 0.2, 0.4, and 0.6 g/L, the effect of heat promotes the hydrogen production of photosynthetic bacteria, but it is opposite when the concentration is 0.8 g/L. When the concentration is 0.4 g/L, the gas production is largest at 865 mL.

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References Boling, E.A., et al., 1973. Bacterial identification by microcalorie-tr. Nature 241, 472. Calvet, E., Part, H., 1963. Recent Progress in Microcalorimetry. Pergamon Press, London, p. 132. Holzel, R., Motzkus, C., Lamprecht, I., 1994. Kinetic investigations of microbial metabolism by means of flow calorimeters. Thermochim. Acta 239, 17e32. Liu, J.-song, Zeng, X., Deng, Y., 1993. Progress in thermokinetics of chemical reactions. Chem. Bull. (4), 21e25. Liu, Y., Wang, C., et al., 1996. Study on cell dynamics Ⅳ.Thermodynamics of non-ideal growth of bacteria. Acta Phys. Chim. Sin. 12 (7), 659e663. Tu, J., 1998. Global attractivity of difference equation. Math. Econ. 15 (1,2), 100e105. Tu, J.B., Zhou, F., et al., 2003. Global attractivity of the thermodynamic difference model of non-ideal growth of bacteria. J. Changde Teachers Coll. (J. Nat. Sci.) (1), 3e5. Wadso, I., Spink, C., 1976. Biochem. Anal. 23, 1. Xie, W.H., Xie, C.L., Qu, S.S., et al., 1992. Measurement of multiplication rate of Bacillus sp. NTT61 growth and study on its thermodynamic properties. Themochimica Acta 195, 297e302. Yan, C., 1997. Research progress in microbial metabolic thermochemistry. J. Nat. 19 (5), 85e90. Zhang, H.-L., Sun, H.-tao, Liu, Y.-J., et al., 1993. J. Thermochimica Acta 216, 19.

Chapter 12

Scale-up and design of biohydrogen production reactor from laboratory scale to industrial scale Gang Li, Huan Zhang Key Laboratory of New Materials and Facilities for Rural Renewable Energy of Ministry of Agriculture and Rural Affairs, College of Mechanical and Electrical Engineering, Henan Agricultural University, Zhengzhou, China

12.1 Introduction The structure of the photobioreactor and the light source distribution and characteristics are the key factors in photo-fermentation hydrogen production. The flow form of fermentation liquid depends on the structure of the photobioreactor, which will affects contact between the substrate and the photosynthetic bacteria (PSB), resulting in differences in hydrogen production performance (Lu et al., 2019). During photo-fermentation hydrogen production, PSB capture energy from light to oxidize organic matter; then, electrons are generated as a drive force to conduct hydrogen production (Zhang et al., 2017). Light energy decreases on the light path through the fermentation medium when light penetrates into cell suspensions of the biohydrogen production system, and 90% of incident light energy is absorbed in a light path of 1.0 cm (Nakada et al., 1995). Hence, the distribution and density of light energy significantly affect the energy absorbed by PSB. In this chapter, a circumfluent cylindrical reactor and light source distribution are first investigated to improve the use of light energy in Section 12.2. The critical factors of the photoreactor for hydrogen production are discussed and some suggestions are suggested in Section 12.3. The requirements and key points of the design of large and medium-scale photoreactors are discussed and some suggestions are made in Section 12.4. The design of a photoreactor with an interior light source and multipoint light source distribution is discussed in Section 12.5. Waste to Renewable Biohydrogen. https://doi.org/10.1016/B978-0-12-821659-0.00001-0 Copyright © 2021 Elsevier Inc. All rights reserved.

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12.2 Circumfluent cylindrical reactor for hydrogen production by photosynthetic bacteria 12.2.1 Structure of circumfluent cylindrical reactor To solve the problems of a limited lighting surface and low light use efficiency with an external light source mode, setting the light source inside the reactor can improve the use of light because light from all sides of the light source can be used, which increases the light receiving area, and then heat from the light source can be used to maintain the temperature of the reactor. The circumfluent cylindrical reactor is mainly composed of the reactor body, reaction liquid mixing unit, temperature control unit, sunlight collection and transmission unit, and auxiliary light source unit; the working volume is 31.07 L. The circumfluent cylindrical reactor (including the light distribution pipe) is made of polymethyl methacrylate. The light distribution pipe is located inside the reactor, sealed with the upper and lower cover, and combined into a closed space. An artificial light source and sunlight imported by optical fiber are installed in light distribution pipe, and a filament lamp or light-emitting diode (LED) can be used as an artificial light source. The reactor and its structure are shown in Figs. 12.1 and 12.2.

FIGURE 12.1 Structure of circumfluent cylindrical reactor (Ruyan, 2007). 1 ¼ gas production outlet; 2 ¼ strain inoculation inlet; 3 ¼ biochemical parameter adjustment port; 4 ¼ bacterial fluid outlet; 5 ¼ sampling port; 6 ¼ reaction liquid circulation inlet; 7 ¼ bacteria liquid circulation outlet/raw material inlet; 8 ¼ light, temperature, and biochemical parameter measurement equipment outlet; 9 ¼ heat exchanger; 10 ¼ lighting, temperature, and biochemical parameter control equipment; 11 ¼ sunlight acquisition and transmission equipment; 12 ¼ auxiliary light source; 13 ¼ reactor tank; 14 ¼ circulation/feeding pump; 15 ¼ discharge port.

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FIGURE 12.2 Circumfluent cylindrical reactor for hydrogen production by photosynthetic bacteria. From Ruyan, Z., 2007. Study on the Circumfluence Cylindrical Photobioreactor for Photobioreactor Hydrogen Production and its Transmission of Energy. Zhenghzou:Hnan Agricultural University.

12.2.2 Operation characteristics of circumfluence cylindrical reactor for hydrogen production by photosynthetic bacteria The PSB growth medium (Ruyan, 2007) was 1000 mL distilled water, 1.5 g KH2PO4, 1 g (NH4)SO4, 0.2 g NaCl, 0.2 g MgSO4, 0.05 g CaCl2, 0.6 g K2HPO4, 3 g sodium acetate, 2 g yeast cream, 1 mL trace element, and 1 mL of growth factor, pH 7.0. The composition of trace elements was 5 mg FeCl3$6H2O, 0.05 mg CuSO4$6H2O, 0.05 mg MnCl2$4H2O, 1 mg ZnSO4$7H2O, 1 mg H3BO4, 0.5 mg CO(NO3)$6H2O, and 1000 mL distilled, filtered, and sterilized water. Growth factor was 0.001 mg vitamin B1, 0.1 mg niacin, 0.001 mg biotin, 10 mL distilled water, and 0.1 mg filtered and sterilized P aminobenzoic acid. PSB were cultured in an anaerobic environment with a 3000-lux filament lamp and a culture temperature of 30 C. Then a solid strain was obtained after centrifugation, and fixed with sodium alginate to get PSB immobilized particles, which were split into pieces 1 mm and cross-linked with 0.7% glutaraldehyde and put into the reactor. Pig manure was used as the substrate. It was first pretreated with aerobic fermentation in the dark for 4 days. Then, it was diluted with water and filtered with a 60-mesh sieve to remove particulate matter and then diluted to 5000 mg/L (chemical oxygen demand [COD]) with water.

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Operating conditions were: 2000 lux light intensity was, 31  2 C temperature, batch work, and working time of 120 h. The results of the batch experiment are shown in Table 12.1 and Fig. 12.3. The total yield of hydrogen production was 60.9 L at 120 h, the hydrogen production time with a higher yield lasted nearly 96 h, the average hydrogen production rate was 484.7 mL/L$d, and the maximum hydrogen production rate was 877.4 mL/L$d. From the change in the hydrogen production rate, the hydrogen production process first experienced rapid growth and then rapidly declined. From the beginning of hydrogen release, the hydrogen production rate reached a peak at 35 h; then it rapidly decreased owing to PSB activity and the consumption of substrates. In the initial stage, the anaerobic environment in the reactor gradually formed and PSB activity became more and more active, with the hydrogen-producing rate increasing accordingly. Along with the fermentation, the substrate concentration decreased accordingly and finally became the limiting factor for the hydrogen production process. Changes in the COD and pH of the reaction mixture in the batch experiment are shown in Figs. 12.4 and 12.5. Fig. 12.4 shows that the COD of the reaction solution gradually decreased with progress in hydrogen production, which corresponds to conversion of the substrate in the reaction solution. Over 18e60 h, the COD decreased rapidly; meanwhile, the corresponding hydrogen production rate was higher. At the end of the experiment, the COD was about 2000 mg/L (the initial COD of the substrate was 5130 mg/L), which means some organic matter in the substrate could not be degraded by PSB. In the batch experiment, the hydrogen production rate of COD was 171.4 mL/g COD$d and the use rate of the substrate was 68.4%. During hydrogen production, the pH of the solution also gradually increased owing to the conversion and use of organic acids in the substrate. After 60 h, the pH remained at about 6.7, indicating that available acidic substances were exhausted. During hydrogen production, the hydrogen yield and hydrogen production rate were influenced by some factors such as substrate, light sources, and temperature. Therefore, the hydrogen production yield from the substrate and the hydrogen production rate can be improved by optimizing the fermentation process.

12.3 Critical factor of photoreactor for hydrogen production 12.3.1 Anaerobic condition and illumination The anaerobic condition is a basic condition for electron chain transfer during the biochemical metabolism of PSB, which means the reactor must be cultured in a closed space. At the same time, a closed reactor should provide adequate light intensity to meet the need light energy of PSB to produce high-energy electrons.

time(h)

0

12

24

36

48

60

72

84

Yield (L)

0

4.3

13.2

26.8

37.4

45.5

52.1

57.5

Rate (mL/L$d)

0

277.4

574.1

877.4

683.9

522.6

425.8

348.4

96

108

120

60.1

60.7

60.9

167.7

38.7

12.9

From Ruyan, Z., 2007. Study on the Circumfluence Cylindrical Photobioreactor for Photobioreactor Hydrogen Production and its Transmission of Energy. Zhenghzou:Hnan Agricultural University.

Scale-up and design of biohydrogen production reactor Chapter | 12

TABLE 12.1 Total H2 produced and H2 generation rate in batch cultures process.

265

266 Waste to Renewable Biohydrogen

FIGURE 12.3 Hydrogen production ability of photobioreactor in batch cultures (Ruyan, 2007).

FIGURE 12.4 Substrate medium chemical oxygen demand (COD) in batch culture process (Ruyan, 2007).

FIGURE 12.5 Substrate medium pH in batch culture process (Ruyan, 2007).

Scale-up and design of biohydrogen production reactor Chapter | 12

267

12.3.2 Material of reactor and illumination To meet the requirements of anaerobic conditions and illumination, glass or plexiglass (polymethyl methacrylate) was used to produce a photoreactor, but the machining performance is poor and it is difficult to meet machine or strength requirements for large and medium-scale photoreactors. A material with good light transmittance, high strength, and machining performance is a basic prerequisite for a large-scale photoreactor construct.

12.3.3 Photosynthetic pigment adsorption and light absorption Phototaxis is a characteristic of PSB, which causes PSB to gather on the lighting surface. The pigment released from PSB and dead PSB deposited on the lighting surface will hinder light transfer through the lighting surface. At the same time, a large number of bacteria and substrate solution also cause light absorption and scattering, which causes the light intensity to decline rapidly when passing through the reaction solution, and directly limits the distance or diameter between the reactor walls.

12.3.4 Insulation and illumination Suitable temperature and illumination are the basic elements for PSB to produce hydrogen with high efficiency. A reactor structure based on the integration of a daylit surface and reactor wall cannot heat-preserve the wall. Environmental conditions in a natural state will have a great impact on the reactor. Some reactors adopt water bath heating or cooling to keep the solution temperature; this results in a high operation cost; meanwhile, water can also absorb light, which reduces the light intensity inside the reactor and the use of light energy.

12.3.5 Light source and temperature control Sunlight is the main light source for PSB under natural conditions. However, the periodicity and instability of sunlight limit the reactor’s continuous operation, resulting in limitations to sunlight applications in commercial hydrogen production. A thermal radiant light source widely used in the laboratory has high energy consumption and releases more heat, which will cause the local temperature to exceed the tolerance of PSB, especially when the light source is placed inside the reactor. Thus, the light source should choose a cool light source or low power light source in a large and medium-scale photoreactor design.

12.4 Design of large and medium-scale photoreactor 12.4.1 Interior light source An interior light source is an important way to solve the volume limitation and temperature control and improve the use of light energy in the reactor. When

268 Waste to Renewable Biohydrogen

external light source is chosen to provide light energy for PSB, the photoreactor must be made by some special material that can let light pass through, such as glass or plexiglass, which is a limiting factor, as described earlier. At same time, the diameter of the reactor or the distance of the reactor wall will be in be in the range of the optical path to meet the light intensity for hydrogen production. Therefore, it is the key limiting factor for large-scale reactor design. Higher strength and easy machining reactor materials can be selected to use an interior light source, which is a methods for large-scale photo-reactor design. Moreover, an interior light source can improve the use efficiency of light energy owing to the light spread around the solution, and it can avoid the conflict between the insulation and illumination. Of course, the thermal effect and light saturation effect should be attended to in the design.

12.4.2 Multipoint light source distribution model Multipoint light source distribution in the reactor can avoid the limitation of the optical path and local light saturation caused by one light source, and make light cover each space of the reactor.

12.4.3 Enhance mixing and mass transfer by improving the reactor structure This is an effective method for improving hydrogen production yield by stirring. Compared with other reactors, the photoreactor with an external light source cannot own an agitator in the reactor because of the short distance between two light sources. To avoid a dead zone in the reactor, the reactor structure should be improved to change the solution flow state and enhance the mass transfer in a large-scale photoreactor design.

12.4.4 Remove pigment from lighting surface Pigment deposited on the lighting surface should be removed automatically by a mechanical device, or the lighting surface should be easy to disassemble and clean.

12.4.5 Provide light by sunlight and an artificial cold light source Sunlight imported by optical fiber collected by a Fresnel lens leads to hydrogen production independence on fossil energy and reduces the product cost. An artificial cold light source with a special wavelength for PSB and low energy consumption can make up for the periodicity and instability of sunlight.

269

Scale-up and design of biohydrogen production reactor Chapter | 12

12.5 Design of photoreactor with interior light source and multipoint light source distribution 12.5.1 Operation mode of photoreactor with interior light source and multipoint light source distribution A photoreactor with an interior light source and multipoint light source distribution can use the sun to provide light, heat, and electricity for reactor work. Sunlight is imported by optical fiber focused by a Fresnel lens and cooled by air. An LED can be an auxiliary light source powered by photovoltaic panels and a battery. At the same time, a solar collector is used to provide hot water to keep the solution temperature steady. The operation mode of the photoreactor is shown in Fig. 12.6.

12.5.2 Design of sunlight collector and transmission unit A Fresnel lens is used to focus sunlight to improve the light density and optical fiber is used to import sunlight directly into the photoreactor. The sunlight collector and transmission unit are mainly composed of a Fresnel lens, cooling hood, and optical fiber. To get enough sunlight, an automatic tracking and positioning device are used in the sunlight collector. A structure diagram of a sunlight collector and transmission is shown in Fig. 12.7, a sunlight collector

fiber

tor

n

FIGURE 12.6 Operating mode of photoreactor with interior light source and multipoint light source distribution.

270 Waste to Renewable Biohydrogen f

2

1 1. Sun

2. Fresnel lens

3

4 3. Filter

4. Optical fiber

FIGURE 12.7 Schematic diagram of sunlight collector and transmission (Li, 2008).

FIGURE 12.8 Focused sunlight with Fresnel lens.

with a Fresnel lens is shown in Fig.12.8, a structure diagram of a sunlight collector with light cooling is shown in Fig.12.9, and a schematic diagram of the device is shown in Fig.12.10.

12.5.3 Measurement of optical path in solution of substrate for hydrogen production An optical path is the spreading distance to meet the minimum light intensity when definite luminance passes through the solution of substrate for PSB to produce hydrogen. It is the main reference for defining the distance between adjacent light sources. Light spreading is affected by the absorption and refraction of a solution, and the refraction and scattering of pigments and particulate matter. An optical path measuring device schematic diagram is shown in Fig. 12.11. The water tank is made of high-permeability glass, and a scale is

Scale-up and design of biohydrogen production reactor Chapter | 12

Fresnel Lens

271

Lens Heavy Tank

Concentrated Cones Transparent Heat Shield Dust Cover Sleeve Fiber Optic Cage Positioning Bolt Positioning Sleeve

FIGURE 12.9

Sunlight collector with dust-proofing and cooling (Li, 2008).

FIGURE 12.10 Sunlight collector and transmission (Li, 2008).

attached along the two long sides to measure the distance. Except the side near the artificial light source machine, all sides of the tank are blackened to shade light. Moreover, two movable pieces of black glass cover the tank, which can shade light from of tank when moving the glass to measure distance. In the experiment, an artificial light source machine with an incandescent lamp was chosen to provide the test light source. An underwater illuminometer (ZDS-10W-1D) was used to measure the change in light intensity in the

272 Waste to Renewable Biohydrogen Illuminometer Light Shading Source Cylinder

Dividing Searching Ruler Unit

Cover Plate Water Channel Visor

FIGURE 12.11 Optical path-measuring device schematic diagram.

FIGURE 12.12 Change in light spread in solution concentration.

solution at different distances beyond the tank side with the artificial light source machine. The sample for the test came from a continuous hydrogen production reactor whose substrate was 1% glucose, and the sample times were 24, 48, 72, 96, 120, 144, and 168 h. The characteristics of light spread in the solution during hydrogen production are shown in Fig. 12.12. The absorption and refraction of solution, and the refraction and scattering of pigments and particulate matter are the key factors that affect light spreading in solution. The ability of light to spread in solution decreases in the process of hydrogen production and tends to stabilize gradually from 72 to

Scale-up and design of biohydrogen production reactor Chapter | 12

273

FIGURE 12.13 Schematic for baffled reactor (Li, 2008).

120 h, but after 120 h, the ability of light to spread in solution begins to increase owing to the death of PSB. In the process of hydrogen production by PSB, bacteria concentration reaches a maximum at 72 h, which means the absorption and scattering ability of light in the solution at a maximum. At this time, the light just passes through 12 cm when the illuminance is reduced from 13,000 to 1000 lux. Thus, 12 cm can be considered the effective distance of visible light in the solution of hydrogen production to meet PSB growth and metabolism, which means the distance between two light sources in the reactor should be more than 24 cm.

12.5.4 Structure type of reactor Compared with a traditional bioreactor, a baffled reactor can meet the requirements of an anaerobic environment, bacterial retention, and reaction liquid mixing for hydrogen production by PSB because of the integrated push flow type and mixing flow type. Its structure is shown in Fig. 12.13. In the reactor structure, the distance between two baffles can be changed by adjusting the cross-section areas of the up-flow compartment and down-flow compartment, which increase the flow speed in the down-flow compartment and mix the solution. At the same time, the baffle separates the reactor into several independent compartments, which can set the light resource with different requirements. Based on the simulation of an anaerobic baffled reactor (ABR) structure and flow state, the cross-sectional area ratio of the up-flow compartment and down-flow compartment is 3:1, the width-height ratio is 1:2, and the angle of the baffle plate is 45 degrees toward the direction of water flow. The structure of the reactor is shown in Fig. 12.14. The schematic diagram of a photoreactor with an interior light source and multipoint light source distribution are shown in Figs. 12.15 and 12.16.

274 Waste to Renewable Biohydrogen

FIGURE 12.14 Schematic of photoreactor with interior light source and multipoint light sources distribution (Li, 2008).

Scale-up and design of biohydrogen production reactor Chapter | 12

275

FIGURE 12.15 Diagram of photoreactor (Li, 2008).

FIGURE 12.16 Photoreactor with interior light source and multipoint light source distribution (Li, 2008).

12.6 Conclusions In this chapter, critical factors affecting the design of a photo-fermentation hydrogen production reactor were discussed and some suggestions were made. Lighting is the critical influencing factor in photosynthetic hydrogen production reactor design. A PSB cannot produce hydrogen independent of light. Lighting limitations can be overcome by improving the reactor’s structure, which can help in designing reactors from the laboratory scale to the pilot or industrial scale.

276 Waste to Renewable Biohydrogen

References Li, G., 2008. Study on 5m3 Experimental System for Continuous Hydrogen Production by Photosynthetic Bacteria with Sunlight. Henan Agricultral University, Zhegnhzou. Lu, C., Zhang, H., Zhang, Q., Chu, C.Y., Tahir, N., Ge, X., et al., 2019. An automated control system for pilot-scale biohydrogen production: design, operation and validation. Int. J. Hydrogen Energy. https://doi.org/10.1016/j.ijhydene.2019.04.288. Nakada, E., Asada, Y., Arai, T., Miyake, J., 1995. Light penetration into cell suspensions of photosynthetic bacteria and relation to hydrogen production. J. Ferment. Bioeng. 80, 53e57. https://doi.org/10.1016/0922-338X(95)98176-L. Ruyan, Z., 2007. Study on the Circumfluence Cylindrical Photobioreactor for Photobioreactor Hydrogen Production and its Transmission of Energy. Hnan Agricultural University, Zhenghzou. Zhang, Z., Zhou, X., Hu, J., Zhang, T., Zhu, S., Zhang, Q., 2017. Photo-bioreactor structure and light-heat-mass transfer properties in photo-fermentative bio-hydrogen production system: a mini review. Int. J. Hydrogen Energy 42, 12143e12152. https://doi.org/10.1016/ j.ijhydene.2017.03.111.

Index Note: ‘Page numbers followed by “b” indicate boxes, those followed by “f” indicate figures and those followed by “t” indicate tables.’

A Ablative reactors, 151 Acetic acid concentration, 186 Acetic acid-generating phase, 12 Agricultural organic waste, 55 Air gasification, 152 Airlifted tubular reactor, 206 Alkaline electrolyzer hydrogen production method, 73 Alkali pretreatment, 115 Ammonium salt concentrations, 188 Anaerobic baffled reactor-type photosynthetic hydrogen production device, 193e194 Anaerobic dark fermentation, 60, 63e64 Anaerobic digestion, 6 Anaerobic fermentation, 5e6, 46, 180 fermentation-producing acid microorganisms biological characteristics, 19e20 carbohydrate fermentation, 21t complex carbohydrates, 21, 22f substrate-level phosphorylation, 21 substrates, 20f hydrogen substrates, 21e23 Aqueous phase reforming, 148 Atmospheric pollution, 3 Auger reactor, 149e150, 150f Azolla anabaena, 55e56

B Bacterial exponential growth kinetics, 238e239 Bacterial linear growth kinetics model, 240 Baffled reactor, 202, 273f Ball mill pretreatment process, 110e111 Batch culture, 241 Biogas technology, 7 Biohydrogen production, 179 algae and photosynthetic bacterium, 9f

comparison, 96e98, 97t conventional hydrogen production methods, 57e58 dark fermentation, 79e85, 180 darkelight method, 90e96 data envelopment analysis (DEA), 24 economic efficiency, 25 vs. electrochemical hydrogen production method, 74 environmental efficiency, 24e25 fermentation. See Fermentation hydrogen production organisms, 8e10 life cycle assessment (LCA), 24 light fermentation, 85e90 limitations, 98e99 organic anaerobic biodegradation, 10e12, 11f photohydrolysis cyanobacteria, 77e78 green algae, 75e77, 76f mechanism of action, 75 photosynthetic. See Photosynthetic biological hydrogen production photosynthetic fermentation, 180e181 pretreatment technology. See Waste pretreatment technology stability and continuity, 99 thermal effect. See Thermal effect thermochemical conversion. See Thermochemical conversion wastes agricultural and forestry waste, 34e38 domestic sewage, 43e44 forest deciduous biomass, 37e38 industrial waste, 38e41 livestock and poultry dung, 36 municipal organic solid waste, 44 paper sludge, 41e43 straw biomass, 35e36 water photolysis, 180

277

278 Index Biological pretreatment, 118e119 Biomass energy, 238 biogas technology, 7 high-yielding energy crops, 6 liquid fuel, 7 photosynthesis, 6 power generation, 7 pyrolysis gasification, 7 Biomass resources, 109 Bioreactor, 66, 201 Bubbling fluidized bed reactor, 149, 149f Butyric acid-type hydrogen fermentation, 18, 80e81

C Calcium peroxide, 132e133 Carbohydrate fermentation, 21t Carbohydrate-rich wastewater, 33e34 Catalysis technology, 64e66 Cellulose, 35e36, 126, 155 Chemical looping reforming, 148 Chemical oxygen demand (COD), 264 Chemical pretreatments, 113e116, 130e131 Chlorella, 75e77 Circulating fluidized bed reactor, 149, 150f Circumfluent cylindrical reactor batch culture chemical oxygen demand (COD), 264, 266f substrate medium pH, 266f total H2 produced and H2 generation rate, 265t hydrogen production, 263f light distribution pipe, 262 operation characteristics, 263e264 pig manure, 263 PSB growth medium, 263 structure, 262, 262f Coal hydrogen production technology, 142 Cofermentation, 131e132 Combustion, 4e5 Continuous hydrogen production, 55e56 hydraulic retention time biomass concentration, 212, 213f fermentation broth, 210e213 hydrogen concentration, 209e210, 210f hydrogen production rate, 208e209, 209f nutritional requirements, 208e209

oxidation-reduction potential, 211e212, 212f pH value, 210e211, 211f reducing sugar concentrations, 213 substrate concentration biomass concentration, 218, 218f fermentation broth, 216e219 hydrogen content, 215e216, 215f hydrogen production rate, 214e215, 214f oxidation-reduction potential, 217, 217f photo-fermentation, 213e214 pH values, 216e217, 216f Continuous stirred tank reactor (CSTR), 12 Conventional hydrogen production, 179 Costebenefit analysis (CBA), 25 Cyanobacteria, 77e78

D Dark fermentation biological hydrogen production, 41e42, 47t additives, 132e133 anaerobic fermentation, 180 biophotolysis, 123 butyric acid fermentation, 80e81 chemical pretreatments, 130e131 cofermentation, 131e132 degradation process, 124 direct hydrogen production mechanism, 82 ethanol fermentation, 79, 81, 82f facultative dark fermentation hydrogenproducing bacteria, 79 fermentation substrate, 84 fermentation temperature, 84e85 food waste (FW), 127 glycolysis, 124 hydrogenase, 124 inocula, 127e128 inorganic nutrients, 85 lignocellulosic wastes, 126e127 NAD+/NADH balance, 82e84 nicotinamide adenine dinucleotide (NADH) formation, 124 obligate dark fermentation hydrogenproducing bacteria, 79 operation pH, 128e129 pH value, 85 physical pretreatment, 130 physiochemical combined pretreatment, 131

Index principle, 124 process temperature, 129 propionic acid type fermentation, 79, 81f sewage sludge, 125 strains, 84 substrate, 125e127 tail liquid, 133 wastewater, 126 yield and rate, 80t Darkelight fermentation biomass, 91, 91f concentration range, 91 continuous reaction, 91e93 fed-batch fermentation, 91e93 mixed-culture, 93e96, 94f, 99 sequential batch reaction, 91e93 substrates, 92t Dark photofermentation, 47t Data envelopment analysis (DEA), 24 Dielectric heating, 148 Dilute acid pretreatment, 113e115 Direct hydrogen production, 82 Domestic sewage, 43e44 Domestic waste, 2 Double-strain experiment, 119

E Economic efficiency, 25 Electrochemical hydrogen production method, 74 Energy crisis, 33 Ethanol fermentation, 81, 82f Ethyl alcohol-type hydrogen fermentation, 19 External-circulation flat-plate photobioreactor, 207

279

fermentation-producing acid microorganisms biological characteristics, 19e20 carbohydrate fermentation, 21t complex carbohydrates, 21, 22f substrate-level phosphorylation, 21 substrates, 20f packed bed reactor (PBR), 12 principle and classification, 18e19 propionic acid-type hydrogen fermentation, 19 reactors, 12e18, 16te17t substrates used, 13te15t upflow anaerobic sludge blanket (UASB), 12 Ferric oxide nanoparticles (FONPs), 132e133 Filamentous aerobic nitrogen-fixing cyanobacteria, 78 Flat-type reactor, 207e208 Food waste (FW), 127 Forest deciduous biomass, 37e38 Fossil energy, 33, 71 hydrogen production, 141e142 sources, 123 Fossil fuel-based energy system, 64e66

G Garden residues, 38 Gasification, 151e153, 151f Global energy supply, 71e72 Glycolysis, 124 Green algae, 75e77, 76f Green energy, 179 Greenhouse effect, 1e2

F

H

Facultative dark fermentation hydrogenproducing bacteria, 79 Fed-batch fermentation, 91e93 Fermentation, 11 anaerobic fermentation, 19e23 anaerobic hydrogen substrates, 21e23 attached growth reactor, 12e18 bacteria, 10t, 55e56 butyric acid-type hydrogen fermentation, 18 continuous fermentations, 22t continuous stirred tank reactor (CSTR), 12 ethyl alcohol-type hydrogen fermentation, 19

Hemicellulose, 126, 156 Heterocysts, 78 Heteromorphous cyanobacteria, 78 High-temperature liquid water pretreatment, 116e117 Hydraulic retention time (HRT), 40, 208e213 Hydrogenase, 76e77, 88, 124 Hydrogen-consuming bacteria (HCB), 41e42 Hydrogen energy, 71 advantages, 71e72 characteristics, 139e140 economy, 201 fossil energy, 141e142

280 Index Hydrogen energy (Continued ) industrial production, 72e73 petroleum gas reforming, 73 Hydrogen production technology biomass, 144e145 fossil energy hydrogen production, 141e142 solar, 143 thermochemical conversion. See Thermochemical conversion water electrolysis, 142 Hydrolysis phase, anaerobic treatment, 11 Hydrolysis technology, 7e8

I Incineration, 5 Industrial waste, 2, 55, 165f Inocula, 127e128

L Life cycle assessment (LCA), 24 Life cycle costing (LCC), 25 Light and dark fermentation, 61, 64 Light fermentation anaerobic electron transfer, 86e87 environmental factors, 89 hydrogenase, 88e89 light conversion efficiency, 88 light effect, 88e89 light-fermenting bacteria, 86e87 light intensity, 89 nitrogenase, 87, 89 optimal pH value, 90 optimal temperature range, 90 organic substrates, 87 photosynthetic bacteria, 85e86 redox reaction, 85e86 Lignin, 156 Lignocellulosic biomass pretreatment, 110, 110f Lignocellulosic wastes, 126e127 Liquid fuel, 7 Livestock and poultry dung, 36, 37t Logistic equation, bacterial growth, 239e240

M Marsh gas power generation, 5e6 Mechanical crushing pretreatment, 110e111 Mechanical pulverization, 110e111 Metabolite inhibition model, 241e242

Methane-generating phase, anaerobic treatment, 12 Microbial hydrogen production, 144 Microwave pyrolysis, 148 Mixed-culture hydrogen production, 94f, 182e184 biochemical decomposition of glucose, 93, 94f chemical reaction, 94e95 complex organic matter, 94e95 substrates, 95t Mixed photosynthetic hydrogen production, 231e233 Multipoint light source distribution model, 268 Municipal organic waste, 44, 55

N Natural gas, 141 Near-horizontal tube reactor, 204 Nicotinamide adenine dinucleotide (NADH) formation, 124 Nitrogenase, 87, 89, 196 Nitrogen sources, hydrogen production, 55e56 Nonideal growth thermodynamic model, 240e241

O Obligate dark fermentation hydrogenproducing bacteria, 79 Optical path-measuring device, 270e273 Organic acids photofermentation, 45t Organic anaerobic biodegradation, 10e12, 11f Organic loading rate (OLR), 40 Organic waste, 55 Orthogonal experiment method, 113 Oscillatoria limnetica, 78 Oxidation pretreatment, 116 Oxidation steam reforming method, 73 Oxygen gasification, 152

P Packed bed reactor (PBR), 12 Papermaking sludge biological hydrogen production, 41e42 Paper sludge, 41e43 Peroxyacetic acid, 116 Petroleum gas reforming, 73

Index Photoelectrochemical cell, 143 Photofermentation, 47t Photo-fermentation hydrogen production, 201 Photohydrolysis cyanobacteria, 77e78 green algae, 75e77 mechanism of action, 75 Photometric effect optical energy conversion rate, 232e233 photosynthetic hydrogen production, 231e232 Photoreactor, 201, 204 anaerobic condition and illumination, 264 insulation and illumination, 267 interior light source, 267e273, 275f large and medium-scale, 267e268 light source and temperature control, 267 material, 267 mixing and mass transfer, 268 multipoint light source, 268e273, 275f optical path-measuring device, 270e273 pigment adsorption and light absorption, 267 structure type, 273 sunlight collector and transmission unit, 269e270 Photosynthetic bacteria, 86, 181 Photosynthetic biological hydrogen production, 109 cell morphology and staining analysis, 59e60 continuous hydrogen production hydraulic retention time, 208e213 substrate concentration, 213e220 dark reaction rate, 226 energy use rate, 59e60 green algae, 58e59 hydrogen production capacity, 230e231 hydrogen production matrix, 58e59 light reaction, 226 mixed photosynthetic hydrogen production, 231e233 organic loading rate, 219e220, 220f, 220t organic matter decomposition, 59e60 photoreactions, 226 photosynthetic bacteria growth and hydrogen production capacity, 230 light conversion efficiency, 229 mixed photosynthetic bacteria, 228

281

morphological characteristics, 227e228, 227f pig manure wastewater, 228e229 single strain, 228 spectral coupling characteristics, 228e230 photosynthetic system, 58e59 pigments, 225e226 reactor baffled reactor, 202 flat-type reactor, 207e208 triangle flask, 202 tubular reactor, 203e206 substrates, 225 water degradation, 58e59 Photosynthetic fermentation, 180e181 Photosynthetic hydrogen production bacteria acetic acid concentrations, 196 anaerobic baffled reactor-type, 193e194 carbon sources, 195e196 continuous culture system light system and culture medium delivery, 190e191 microorganisms, 190 operation process control, 191 overall design, 190 photosynthetic microorganisms, 192e193 process flowchart, 191, 191f culture conditions, 194e195 electron donors, 181 gram-negative bacteria, 181 growth characteristics, 184e189 acetic acid concentration, 186 ammonium salt concentrations, 188 carbon sources, 185e186, 185f multifactor analysis, 188e189 nitrogen source, 186e188 nutrient elements, 185e188 range analysis, 188 single-factor analysis, 184e189 spectrum effects, 184e185 variance analysis, 189 mixed culture, 182e184 natural elements circulation, 181 nitrogen sources, 196e197 nutrient effect, 195e197 pure cultured, 182 strains, 181 Photosynthetic nonsulfur (PNS) bacteria, 41e42 Photosynthetic systems, 58e59, 76e77

282 Index Phototaxis, 267 Physical pretreatment, 130 Physiochemical pretreatment, 116e118, 131 Pig manure wastewater, 228e229 Polymer film electrolyzer, 73 Polyvinyl chloride (PVC) spiral tube reactor, 204 Power generation, biomass energy, 7 Propionic acid-type hydrogen fermentation, 19, 79, 81f Protein, 156 Pulverization, 110e111 Pure cultured photosynthetic hydrogen production bacteria, 182 Purple nonsulfur bacteria, 86 Pyrolysis, 7, 238

R Radiation pretreatment, 110f, 111 Reactors, 149e151 Rhodospira, 183e184

S Scenedesmus obliquus, 75e77 Sequential batch reaction, 91e93 Sewage sludge (SS), 125 Simultaneous saccharification and fermentation (SSF), 126e127 Single-strain experiment, 118 Soil pollution, 3 Solar energy conversion, 180 Solar hydrogen production, 143, 144f Solid oxide electrolyzer hydrogen production method, 73 Starch, 156 Steam blast pretreatment, 56e57, 117e118 Steam reforming, 147 Straw biomass, 35e36, 109, 110f Sunlight collector and transmission unit, 269e270 Supercritical water gasification, 153e154, 153f Superfine crushing method, 112e113

T Thermal effect carbon source, 242e243 glucose access time, 243 glucose concentration, 243 hydrogen production

carbon source, 251e253 different illuminations, 246e248 different initial temperatures, 243e245 different times, 255e257 glucose concentrations, 253e255, 253fe254f inoculations, 248e250 nitrogen concentrations, 257e259 initial temperature, 242 inoculation amount, 242 light intensity, 242 microbial thermodynamic model, 238e242 bacterial exponential growth kinetics, 238e239 bacterial linear growth kinetics model, 240 logistic equation, 239e240 nonideal growth thermodynamic model, 240e241 NH4+ concentration, 243 Thermochemical conversion, 47t, 145f agricultural and forestry waste biomass, 159 cellulose, 155 composition and classification, 155e156 hemicellulose, 156 lignin, 156 protein, 156 representative biomass, 156t research progress, 157te158t, 159 starch, 156 gasification, 151e153, 151f industrial waste characteristics, 161e165 powdery waste, 161e165 research, 166te167t sludge, 165 municipal solid waste disposal methods, 160e161, 160f gasification and pyrolysis, 161 industrial waste, 165f physical properties, 160e161 research progress, 162te164t urban residents, 160 pyrolysis aqueous phase reforming, 148 biomass, 144e145, 146f chemical looping reforming, 148 endothermic reaction, 147 gasification, 146e147 microwave pyrolysis, 148

Index rapid pyrolysis, 146e147 reactors, 149e151 reforming technologies, 147 steam reforming, 147 water vapor shift reaction, 147 solid waste, 144e145 supercritical water gasification, 153e154 waste and multiple waste, 165e168, 168te170t Thermodynamics, 237 Triangle flask, 202 Tubular reactor airlifted, 206 Chlorella yield, 206 chlorophyll, 205 cylindrical photobioreactor, 205 design, 203 feed water, 206 lignocellulosic biomass, 203 microalgae, 204e205 near-horizontal plate, 204 near-horizontal tube reactor, 204 outdoor experiments, 203 polyvinyl chloride (PVC) spiral tube reactor, 204 purple nonsulfur bacteria, 205 shortcomings, 203 surface volume ratio, 205 tube length, 203 Two-stage combined biohydrogen production technology, 61

U Ultrafine pulverization and enzymolysis, 110e111 Upflow anaerobic sludge blanket (UASB), 12

V Vegetative cells, 78 Volatile fatty acid (VFA) concentration, 40 Volatile fatty acids (VFAs), 11e12

W Waste-activated sludge (WAS), 130 Waste incineration technology, 5 Waste management atmospheric pollution, 3 biomass energy, 6e8 combustion, 4e5

283

current status, 2e4 environmental pollution, 1e2 fossil energy, 1 harm cities, 2e4 humans, 4 incineration, 5 marsh gas power generation, 5e6 soil pollution, 3 water pollution, 3 Waste pretreatment technology alkali pretreatment, 115 biological method, 57, 63 biological pretreatment, 118e119 catalysis technology, 64e66 chemical method, 57, 63 chemical pretreatment, 113e116 dilute acid pretreatment, 113e115 direct and indirect photolysis, 57e58 energy demand, 64e66 fossil fuels, 64e66 high-temperature liquid water pretreatment, 116e117 hydrogen production anaerobic dark fermentation, 60, 63e64 bioreactor, 66 light and dark fermentation, 61, 64 mixed flora and fermentation substrates, 65 photosynthetic, 58, 63 raw materials collection, 65 lignocellulosic biomass pretreatment, 110, 110f oxidation pretreatment, 116 physical pretreatment, 56e57, 62, 110e113, 110f physicochemical pretreatment, 116e118 radiation pretreatment, 110f, 111 reaction conditions, 57e58 renewable wastewater, 57e58 steam blast pretreatment, 117e118 straw biomass energy conversion, 109, 110f superfine crushing, 112e113 Waste to biohydrogen production agricultural and forestry waste, 34e38 anaerobic fermentation, 46 biological processes, 44e46 biomass, 33e34 dark fermentation, 46

284 Index Waste to biohydrogen production (Continued ) darkelight combined production method, 46 domestic sewage, 43e44 domestic waste, 43e44 efficiency, 46e48 forest deciduous biomass, 37e38 industrial waste fermentation technologies, 40e41 hydraulic retention time (HRT), 40 operating conditions, 39t organic loading rate (OLR), 40 organic salts, 40 pH and temperature, 40 sewage treatment, 38 sources, 38

volatile fatty acid (VFA) concentration, 40 light fermentation, 46 livestock and poultry dung, 36 municipal organic solid waste, 44 organic acids photofermentation, 45t organic waste, 48 paper sludge, 41e43 renewable carbohydrates, 44e46 straw biomass, 35e36 wastewater, 33e34 Water electrolysis, 142, 143f Water photolysis, 180 Water pollution, 3 Water vapor gasification, 152 Water vapor shift reaction, 147