Renewable Energy Innovations E-Book
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- Herausgeber: John Wiley & Sons
- Kategorie: Fachliteratur
- Sprache: Englisch
RENEWABLE ENERGY INNOVATIONS This critical text, designed for microbiologists, biotechnologists, entrepreneurs, process engineers, chemical engineers, electrical engineers, physicists, and environmentalists, assesses the current knowledge about lab-scale and large-scale production of renewable and sustainable fuels, chemicals, and materials. Global warming is having a huge impact on the world's ecosystem. Glaciers have shrunk, ice on rivers and lakes is breaking up early, and plant and animal ranges have relocated. On a worldwide scale, the threat posed by climate change and pollution is obvious. A green and sustainable future necessitates using renewable resources to produce fuels, chemicals, and materials. This book investigates diverse bioprocesses that are crucial to everyday life, including the key concerns regarding the generation of biofuels, energy, and food securities, along with waste management. Commercial interest in biotechnological processes has risen to produce pharmaceuticals, health supplements, foodstuffs, biofuels, and chemicals using a biocatalyst such as enzymes, microorganisms, plant cells, or animal cells in a bioreactor. The sustainability of renewable biomass, replacement of depleted fossil fuels, and the mitigation of greenhouse gas emissions from the existing chemical and oil industries are the key benefits of switching to bioproducts. This book discusses bioprocessing to produce biofuels, biobased chemicals, bioproducts, and biomass biorefinery processes. This involves designing novel pretreatment and fractionation technologies for lignocellulose biomass into cellulose, hemicellulose, and lignin and the conversion of these streams into biofuels and biobased chemicals via biochemical and thermochemical routes. This book also covers the advancement of oleaginous microorganisms for biofuels and nutraceutical, biological wastewater treatment. Written and edited by authors from leading biotechnology research groups from across the world, this exciting new volume covers all of these technologies, including the basic concepts and the problems and solutions involved with the practical applications in the real world. Whether for the veteran engineer or scientist, student, manager, or another technician working in the field, this volume is essential for any library.
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Table of Contents
Cover
Table of Contents
Series Page
Title Page
Copyright Page
1 Microbial Fuel Cells – A Sustainable Approach to Utilize Industrial Effluents for Electricity Generation
Abbreviation
1.1 Introduction
1.2 History of Microbial Fuel Cell
1.3 Principle of Microbial Fuel Cell
1.4 Material Used in MFC System
1.5 Electrogenic Microorganisms
1.6 Electron Transport Mechanism in MFCs
1.7 Configuration of MFC
1.8 Applications of Microbial Fuel Cell
1.9 Future Perspectives
1.10 Conclusion
References
2 Nanotechnologies in the Renewable Energy Sector
2.1 Introduction
2.2 Fundamentals of Renewable Energy Sources
2.3 Storage of Energy in Electrical Devices
2.4 Nanotechnology in Energy Storage Devices
2.5 Nanomaterials for Rechargeable Batteries
2.6 Nanomaterials in Fuel Cells
2.7 Conclusion
2.8 Future Scope
References
3 Sustainable Approach in Utilizing Bioenergy Commonly for Industrial Zones by Limiting Overall Emission Footprint
3.1 Introduction
3.2 Co-Firing Plants in Small- and Medium-Scale Industries
3.3 Impact of Usage of Biogas for Steam Generation
3.4 Case Scenarios for Promoting Industrial Uptake
3.5 Conclusion
Acknowledgment
References
4 Recycling of Plastic Waste into Transportation Fuels and Value-Added Products
4.1 Introduction
4.2 Plastic Waste: A Global Challenge
4.3 Future Projection of the Waste Plastic
4.4 Plastic Waste Effect on Environment and Ecology
4.5 Plastic Waste Management
4.6 Parameters Affect the Pyrolysis Process
4.7 Value-Added Products from Plastic Waste Pyrolysis
4.8 Application in Transportation Sector
4.9 Conclusion
References
5 An Outlook on Oxygenated Fuel for Transportation
5.1 Introduction
5.2 Oxygenated Fuel
References
6 Greenhouse Gas (GHG) Emissions and Its Mitigation Technology in Transportation Sector
6.1 Introduction
6.2 Mitigation Technologies
6.3 Conclusion
References
7 Advanced Techniques for Bio-Methanol Production
7.1 Introduction
7.2 Scope of Biofuel
7.3 Types of Biofuels
7.4 Why Biomethanol
7.5 Methanol Properties
7.6 Source of Bio-Methanol
7.7 Production of Methanol
7.8 Gasification
7.9 Pyrolysis
7.10 Liquefaction
7.11 Syngas to Methanol
7.12 Biomethanol from MSW
7.13 Energy Efficiency of a Process
7.14 Biological Conversion of Methanol
7.15 Anaerobic Digestion
7.16 Methanotrophic Bacteria
7.17 Production of Methanol from Methanotrophic Bacteria (Methanotrophs)
7.18 Large-Scale Production of Methanol from Waste Biomass
7.19 Challenges Associated with Methanol Production Using Methanotrophic Bacteria at the Industrial Level
7.20 Role of Ammonia-Oxidizing Bacteria (AOB)
7.21 Future Prospective and Conclusion
References
8 Biodiesel Production: Advance Techniques and Future Prospective
8.1 Introduction
8.2 Biodiesel and Its Properties
8.3 Synthesis of Biodiesel
8.4 Modern Methods for the Development of Prospects
8.5 Future Prospects and Policies
8.6 Conclusions
References
9 Biomass to Biofuel: Biomass Sources, Pretreatment Methods and Production Strategies
9.1 Introduction
9.2 Biomass Sources in India
9.3 Lignocellulosic Biomass
9.4 Biomass Pretreatment Methods
9.5 Biomass to Biofuel Conversion Technologies
9.6 Types of Biofuel
9.7 Conclusion
References
10 Opportunity and Challenges in Biofuel Productions through Solar Thermal Technologies
10.1 Introduction
10.2 Solar Pyrolysis of Biomass Feedstocks
10.3 Production of Bio-Oil by Solar Pyrolysis
10.4 Conclusions
References
11 Algae Biofuels: A Promising Fuel of the Transport Sector
11.1 Introduction
11.2 Biofuels in the Transport Sector
11.3 Modes of Biofuels in Practice
11.4 Algae Biofuel – A Promising Energy Source
11.5 Microalgae Growth Conditions
11.6 Harvesting of Algae
11.7 Biofuel Extraction Techniques from Microalgae
11.8 Algae Biofuel as a Transport Fuel
11.9 Conclusion
References
12 A Review of Chemical and Physical Parameters of Biodiesel vs. Diesel: Their Environmental and Economic Impact
12.1 Introduction
12.2 Historical Background
12.3 Current Status of Biodiesel
12.4 Sources of Biodiesel
12.5 Advantages of Biodiesel Over Diesel
12.6 Biodiesel as Safer and Cleaner Fuel
12.7 Major Negative Aspects to Use of Biodiesel
12.8 Chemical and Physical Properties of Biodiesel
12.9 Biodiesel Applications
12.10 Conclusion and Future Prospective
Acknowledgments
References
13 An Indian Viewpoint on Promoting Hydrogen-Powered Vehicles: Focussing on the Scope of Fuel Cells
List of Abbreviations
13.1 Introduction
13.2 Can Hydrogen Be the Way Forward?
13.3 The Inception of Fuel Cells (FCs) and PEMFCs in Particular
13.4 FCEVs v/s Existing Automobile Infrastructure in India
13.5 The Green Policy Push for Hydrogen and Associated Technologies in India
13.6 Pervasive Challenges of PEMFC Technology
13.7 Conclusion and Recommendations
Acknowledgments
References
14 Microalgae as Source of Bioenergy
14.1 Introduction
14.2 Microalgae Bioenergy Production Options
14.3 Conclusions
Acknowledgement
References
15 Hazards and Environmental Issues in Biodiesel Industry
15.1 Introduction
15.2 Life Cycle Analysis of Biodiesel
15.3 Life Cycle Analysis of Biodiesel
15.4 Future Risk and Opportunities
15.5 Future Risk and Opportunities
15.6 Conclusion
References
Index
Also of Interest
End User License Agreement
List of Tables
Chapter 4
Table 4.1 Proximate analysis of plastic [7].
Chapter 5
Table 5.1 Performance and emission characteristic of Butanol/Diesel blend un...
Chapter 6
Table 6.1 Power generation sources [33].
Table 6.2 Drag coefficient of different vehicle [39].
Chapter 7
Table 7.1 Potential fuels for automobiles [11].
Table 7.2 RDF physical and chemical composition (% wt.).
Chapter 8
Table 8.1 Comparison between properties of biodiesel from different sources [...
Table 8.2 Methods of biodiesel production.
Table 8.3 Advantages and disadvantages of different types of catalysts in tra...
Table 8.4 Novel biodiesel production technologies.
Table 8.5 Biofuel production ranking and major feedstocks [44].
Chapter 9
Table 9.1 Crops and its residue production in 2017-18.
Table 9.2 Production of animal wastes worldwide in 2015.
Table 9.3 Lignin, hemicelluloses and cellulose content in agro-biomass.
Chapter 10
Table 10.1 Projects for biomass power generation in various Indian states ti...
Table 10.2 Various biomass feedstock pyrolysis process using solar energy.
Table 10.3 Product distribution of various biomass feedstock.
Chapter 11
Table 11.1 Types of microalge.
Table 11.2 Physico-chemical properties of diesel, algae and other biodiesels...
Table 11.3 Use of algae biofuel in internal combustion engines.
Chapter 13
Table 13.1 The classification of various fuel cells [26–28].
Table 13.2 The key differences based on selected parameters (No performance d...
Chapter 14
Table 14.1 A list of oleaginous microalgae cultivated on various sources and...
Table 14.2 Carbohydrate content of different microalgal strains for bioethan...
Table 14.3 Biohydrogen production from different microalgae strains.
Table 14.4 Biogas production from different microalgae strains through anaer...
Chapter 15
Table 15.1 Orientation of database of accidents that took place.
List of Illustrations
Chapter 1
Figure 1.1 The basic mechanism of microbial fuel cells.
Figure 1.2 Basic components of microbial fuel cells.
Figure 1.3 Electron transfer mechanism from bacteria to the anode.
Figure 1.4 Lab-scale single-chamber MFC [18].
Figure 1.5 Tubular microbial fuel cell [113].
Figure 1.6 Dual-chamber H-shaped MFC.
Figure 1.7 U-tube MFC [116].
Figure 1.8 Up-flow MFC with cylindrical shape [117, 119].
Figure 1.9 Mini MFC.
Chapter 2
Figure 2.1 Volta’s cell. https://www.electrical4u.com/voltaic-cell/.
Figure 2.2 Daniell cell.
Figure 2.3 Leclanché cell. https://tel.archives-ouvertes.fr/tel-01159617.
Figure 2.4 Zinc–carbon cell. http://hyperphysics.phy-astr.gsu.edu/hbase/elec...
Figure 2.5 Lead–Acid battery [96].
Figure 2.6 Lithium-ion battery. https://www.felicitysolar.com.
Figure 2.7 Photovoltaic cell. https://circuitglobe.com/photovoltaic-or-solar...
Figure 2.8 Lead acid batteries design. https://www.pasin-accessorize.com. (C...
Figure 2.9 Sulfate distribution versus thickness of the negative plate. http...
Figure 2.10 The global lead-acid battery market. https://www.osnpower.com.
Figure 2.11 Schematic presentation of fabrication with Li-ion capacitors [97...
Figure 2.12 Schematic representation of hybrid capacitor with (a) two superc...
Figure 2.13 Pseudocapacitors [98].
Figure 2.14 Intercalation phenomena (the four primary phases of ion intercal...
Figure 2.15 Lithium-ion battery and silicon battery. Graphic/Interactive V. ...
Figure 2.16 Nanomaterials used in fuel cell.
Chapter 3
Figure 3.1 A schematic depiction developed conceptually of direct co-firing ...
Figure 3.2 A centralized biogas generating facility to power industrial area...
Chapter 4
Figure 4.1 Structure of monomer and polymer.
Figure 4.2 Plastic Europe market research group (PEMRG) report on plastic wa...
Figure 4.3 Global plastic production in 2019 [9].
Figure 4.4 Pyrolysis reactor at UPES.
Chapter 5
Figure 5.1 Consumption of energy [5].
Figure 5.2 Crude oil price [6].
Figure 5.3 Schematic layout of biodiesel reactor [16].
Figure 5.4 Transesterification process [17].
Figure 5.5 Brake specific fuel consumption with varying speed [36].
Figure 5.6 BTE of biodiesel blends with diesel [37].
Figure 5.7 NOx emission variation for the biodiesel blends with diesel [36]....
Figure 5.8 Hydrocarbon emission for the biodiesel blends with diesel [36].
Figure 5.9 CO for the biodiesel blends with diesel [36].
Figure 5.10 Smoke opacity of biodiesel blends with diesel [36].
Figure 5.11 Process flow diagram for Butanol production.
Figure 5.12 Current market share of n-butanol [59].
Figure 5.13 ABE fermentation metabolic pathway [65].
Figure 5.14 Thermophysical properties of isomers of butanol.
Figure 5.15 Methanol production flow chart
Chapter 6
Figure 6.1 Sector-wise CO
2
emission in India (2016) [32].
Figure 6.2 Rock sinks [34].
Figure 6.3 C sequestration in oceans [35].
Figure 6.4 Hellisheidi geothermal power in plant West Iceland [36].
Figure 6.5 Carbfix (eliminated CO
2
from steams enters (I) gas segregation unit...
Figure 6.6 Vehicles on Indian roads [37].
Figure 6.7 CO
2
emissions from varying fuel sources [22].
Figure 6.8 Aerodynamic lift and drag [38].
Figure 6.9 Effect of ground clearance and design in aerodynamic resistance [38...
Figure 6.10 Teardrop shaped Skoda 532 [40].
Figure 6.11 Cd reduction by rounded front edges [41].
Figure 6.12 Grille design of a passenger car [42].
Figure 6.13 Tractor-trailer turbulence.
Figure 6.14 Tractor-trailer turbulence.
Figure 6.15 Vehicle weight distribution [44].
Figure 6.16 Volkswagen reduced body weight material composition [44].
Figure 6.17 Quick plastic forming of Aluminium [45].
Chapter 7
Figure 7.1 Overall methanol production from the conventional process.
Figure 7.2 Pretreatment of biomass to utilization of biofuels.
Figure 7.3 MSW production and prediction till 2040 [34].
Figure 7.4 Schematic flowsheet of waste to biomethanol process.
Figure 7.5 Methanol production from waste biomass–distilled biogas is repres...
Chapter 8
Figure 8.1 The thermal decomposition of triglyceride.
Figure 8.2 The transesterification reaction mechanism.
Figure 8.3 Mechanism of base catalyzed transesterification.
Figure 8.4 Heterogeneous base catalyst transesterification mechanism with CaO ...
Figure 8.5 Transesterification process.
Figure 8.6 Schematic diagram of modified continuous microwave reactor [38]....
Figure 8.7 Schematic diagram of transesterification reaction via catalytically...
Chapter 9
Figure 9.1 Statistics of Indian bioenergy production in 2015 by state.
Figure 9.2 Types of biomass sources.
Figure 9.3 Methods of biomass pretreatment.
Figure 9.4 Biomass to biofuel conversion methods.
Figure 9.5 Various types of biofuels with examples.
Chapter 10
Figure 10.1 Solar Thermal technologies are available for processing biomass ...
Figure 10.2 Effect of solar pyrolysis; (a) woody biomass, (b) coconut shell,...
Figure 10.3 Pyrolysis products yield with respect to heating rate; (a) beech...
Figure 10.4 Pyrolysis products yield with respect to particles size: (a) Kad...
Chapter 11
Figure 11.1 Biofuel classification.
Chapter 12
Figure 12.1 Transesterification reaction.
Chapter 13
Figure 13.1 Year-wise CO
2
emission trend in India in the last decade [7].
Figure 13.2 The hydrogen channel [20–24, 28, 29].
Figure 13.3 The basic operation of PEMFC [35].
Figure 13.4 The schematic of PEMFC stack deployment and power generation [35]....
Figure 13.5 Challenges of PEM fuel cell [35].
Figure 13.6 The performance of typical PEM fuel cell [35].
Chapter 14
Figure 14.1 Microalgal cells as source of bioenergy.
Figure 14.2 Different processes for biohydrogen production from microalgae....
Figure 14.3 Process of biogas production from microalgae.
Chapter 15
Figure 15.1 A biodiesel plant. Location - United States (thermochemical).
Figure 15.2 Jatropha seeds used to make biodiesel.
Figure 15.3 Algal ponds for biodiesel processing & production (biochemical)....
Figure 15.4 Process flowchart of algae-based biorefinery system [11].
Figure 15.5 Fire breakout & explosion in a biodiesel plant.
Figure 15.6 Frequency of accidents in biodiesel plants from 2003-2013 [12].
Figure 15.7 Count of accidents in a few of the countries shown from 2003-13 [1...
Figure 15.8 Consequences of the accidents as per database [12].
Figure 15.9 Mode of operation during the accident [12].
Figure 15.10 Life cycle analysis (LCA) of biodiesel.
Figure 15.11 Cause-effect fishbone diagram for hazards occurred in biodiesel p...
Figure 15.12 Causes of biodiesel plant hazard [12].
Figure 15.13 A palm oil cultivation was burnt in Africa due to forest fires....
Figure 15.14 Wooden logs used as biomass production for small-scale utilities....
Figure 15.15 An example of HIRA matrix for preventive maintenance feature [16]...
Guide
Cover Page
Series Page
Title Page
Copyright Page
Table of Contents
Begin Reading
Index
Also of Interest
WILEY END USER LICENSE AGREEMENT
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Renewable Energy Innovations
Biofuels, Solar, and Other Technologies
Edited by
Alok Patel
and
Amit Kumar Sharma
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1Microbial Fuel Cells – A Sustainable Approach to Utilize Industrial Effluents for Electricity Generation
Manisha Verma and Vishal Mishra*
School of Biochemical Engineering, IIT (BHU), Varanasi, India
Abstract
Microbial fuel cell (MFC) makes an appearance as a fascinating technology for green electricity, and more importantly, it is suitable for simultaneously assisting power generation with wastewater treatment. Recently, major trends follow a technology that fulfills energy demands with minimum waste generation. MFC is a technology which proposed to capitalize on waste as a substrate (industrial effluents, sludge, urea, agricultural waste, etc.) and generate electrical energy. Work done in the area of fuel cells has many configurations and variations based on types of substrate utilized, microorganism associated with electrodes, mediators requirement, and architecture of microbial fuel cell. The most common microbial fuel cells are: two compartments or H-shaped MFC, Single compartment or cube-shaped MFC, Up-flow MFC, Stacked MFC, Sediment MFC in wetlands and their variations. However, as compared to conventional power generation methods, power densities are significantly less in MFC. Therefore, the challenge is to improve MFC efficiency and to reduce the cost of this technology. At the current stage, it is difficult to use them in real-world applications. Efforts are being made to develop a commercial prototype in the coming years.
Keywords: Microbial fuel cells, microorganisms, wastewater, power generation, sustainable energy
Abbreviation
MFC
Microbial fuel cells
BOD
Biological oxygen demand
COD
Chemical oxygen demand
CE
Coulombic efficiency
H
+
Proton
e
-
electron
PEM
Proton exchange membrane
LED
Light emitting diode
1.1 Introduction
Microbial fuel cells (MFCs) is a technology which utilizes microorganism as the biocatalysts for the oxidation of inorganic/organic matter and produces current. Bacteria produce electrons inside a cell passed to the anode and traveled towards the cathode [1]. Another modification of the system is the application of enzymes instead of in situ growth of the microorganism, so this is considered as enzymatic biofuel cells [2]. It is found in studies that MFCs that utilize mixed cultures achieve more increment in power densities than pure cultures [3, 4]. Multiple varieties of materials have been used in the construction of MFC, and hence increasing diversity in the MFCs configurations working under various parameters like at different temperatures, pH, electron surface areas, electron acceptor, duration of operation, and reactor size [1]. MFC is an ideal method for generating renewable electricity from biomass. This biomass can utilize bio-wastes (containing protein, carbohydrate, etc.) obtained from the complex organic source of human/animal waste and food processing wastewaters [5–7]. In some early studies, the addition of mediators/electron shuttles (for carrying electrons from cells to the electrode) was proven for noteworthy increment in power densities [8, 9]. Only certain bacterial species can a dissimilatory iron reduction if exogenous mediators are not present there [10, 11], so power production without chemical mediators is a rare trait. Bacteria that can transfer extracellular electron without mediators are known as Exoelectrogen [12]. Some classes of Proteobacteria, Acidobacteria, and Firmicutes have been found active in electrical current generation [12]. Pichia anomala (a yeast) contains redox enzyme in the outer membrane of the cell [13], and a cyanobacteria Synechocystis sp. has conductive appendages known as nanowires [14]. These nanowires help to build mediator-less MFCs, which are considered to be more useful as compared to mediators containing fuel cells [15, 16]. Synthetic mediators used in MFCs are toxic as well as expensive. MFCs includes mainly two electrodes: [a] Anode (negative terminal), and [b] Cathode (positive terminal) [17]. Electrodes are placed within one- or two-chambered MFC, primarily separated by a proton exchange membrane [17]. Two-chamber MFC needs additional expense in terms of aeration for providing oxygen at the cathode. Power output is affected by cathode efficiency by using mediators like ferricyanide [17, 18]. Graphite electrodes in their solid form are relatively more expensive than graphite felt and carbon cloth; also, the utilization of air-driven cathodes minimizes the requirement of energy for air sparging in water [19]. The power density of MFCs is much less as compared to other fuel cells. If we want to consider it as a commercial and economical way of power production, then it is needed to reduce the cost of the construction and operation of MFCs. Utilizing wastewater for making this technique commercial, sustainable, and economical is a further area of research in wastewater treatment [20, 21]. Hydrogen production and photosynthetic algae fuel cells utilizing wastewater for biological fermentation and algae production, respectively, caught much attention as a technique for producing some products like hydrogen, algae for biodiesel production simultaneously with wastewater treatment [22, 23].
1.2 History of Microbial Fuel Cell
M.C. Potter (1911), a botany professor at the University of Durham, while working on microbial degradation of organic compounds, found that electric energy also generates during the degradation of compounds [24]. Later, this concept was applied to harvest the new source of power by the construction of a primitive MFC in 1931 using E. coli. half cells and arranging these half cells into series, which generate potential up to 35 volts while the current generated by the system is only 2 mA [25]. For hydrogen production, Clostridium butyricum is used at the anode (glucose fermentation) [26]. After some time, synthetic mediators were used to enhance electron transfer towards the electrode from the bacterial cell. In the early 1980s, M. J. Allen and H. Peter Bennetto, two researchers in King’s College London, studied fuel cells and explained microbial fuel cell mechanism [27]. In 1990, Habermann and Pommer constructed the first MFC wastewater treatment system, with a mixed culture of bacteria in activated sludge; they reported that electrogenic bacteria produce natural mediators for electron transfer [28]. Electron conduction property of some soil bacteria/Geobacter species was found in 1994 [29] while in 2003 anodophillic property of Geobacter was found [30]. Direct electron transport in some bacteria occurs naturally via pili like nanowires [12]. In association with Fosters Brewing Company, the University of Queensland (Australia), in May 2007, designed an MFC (10 liters) to convert brewery wastewater into electricity and clean water [31]. It was a successful operation, and after that, the University of Queensland planned to develop a 600 gallon of the same MFC design for the brewery, and the estimated power production from the unit is 2 kilowatts [31]. MFCs are currently the most needful area in research for bringing out its true potential for power production by optimizing electrodes, microorganisms, mediators, and proton exchange membrane [1, 20, 21].
1.3 Principle of Microbial Fuel Cell
A general MFC has a single chamber or double chamber compartments containing a cathode and an anode as shown in Figure 1.1. At the anodic compartment, microbe utilizes chemical energy obtained from organic substrates via their cellular respiration pathways and transfer this energy into the form of electrical power. In the anaerobic environment inside the anode chamber, carbohydrates convert into protons, electrons, and carbon dioxide [32, 33]. Hence electrons are generated at the anode and move towards the cathode via an external load. At the cathode, oxygen is reduced in contact with electron and proton, so a charge difference is created between the two electrodes and generates a little current, and the reactions occurring at the electrodes are the following [34]:
Figure 1.1 The basic mechanism of microbial fuel cells.
The reaction at the anode:
Reaction at cathode:
1.4 Material Used in MFC System
There are various factors such as electron transfer mechanism within the MFC chamber, Substrate, pH, Various MFC configuration, electrode material, and type of membrane used that influence MFCs performance. Figure 1.2 illustrates a general view of various essential components of microbial fuel cells.
Table 1.1 illustrates several components like bacteria, industrial effluents, electrode material, and substrates used in various microbial fuel cell studies [17, 35–47]. Studies show up to 98% COD removal efficiency by using starch processing effluent for bioremediation inside the microbial fuel cell.
Figure 1.2 Basic components of microbial fuel cells.
Table 1.1 Power density obtained from various material used in diff erent studies.
Bacteria
Anode material
Cathode material
Membrane
Substrate/wastewater source
COD removal efficiency
Power density
Reference
Activated Sludge
Woven graphite felt
Woven graphite felt
_
Wastewater from a starch processing plant
98%
8 mW/m
2
[35]
Activated sludge (at the anode)
Chlorella vulgaris
(at the cathode)
Toray carbon cloth with 10% Teflon
Toray carbon cloth with 10% Teflon
Fruit processing industry effluent
60-80%
14.40 mW/m
2
[36]
Mixed culture/ Bacteria present in wastewater
Toray carbon paper
Carbon cloth
Polymeric protonexchangemembrane (PEM)
Glucose and wastewater
_
146 mW/m
2
[37]
Mixed culture/bacteria present in wastewater
Toray carbon paper
Carbon cloth
No membrane
Glucose and wastewater
_
494 mW/m
2
[37]
Mixed bacteria culture
Plain graphite rod
Plain graphite rod
Ultrex
Glucose
85%
2200 mW/m
2
[38]
Rhodoferax ferrireducens
Plain graphite
Plain graphite
_
Glucose
_
8 mW/m
2
[39]
Rhodoferax ferrireducens
Woven graphite
Woven graphite
_
Glucose
_
17 mW/m
2
[39]
Rhodoferax ferrireducens
Graphite foam
Graphite foam
_
Glucose
_
33 mW/m
2
[39]
Proteus vulgaris
Glassy Carbon
Ferricyanide platinum
_
Glucose
_
4.5 mW/m
2
[40]
Proteus vulgaris & Escherichia coli
Reticulated vitreous carbon plate
Platinum plate
Nafion
Glucose
_
85 mW/m
2
[41]
Pseudomonas aeruginosa
Plain graphite rod
Plain graphite rod
Ultrex membrane
Glucose
_
88 mW/m
2
[42]
Escherichia coli
Woven graphite
Woven graphite
_
Lactate
_
1.20 mW/m
2
[17]
Escherichia coli
Plain graphite
Plain graphite
_
Lactate
_
91 mW/m
2
[17]
Activated sludge
Woven graphite
Woven graphite
_
Lactate
_
5.3 mW/m
2
[17]
Activated sludge
Plain graphite
Plain graphite
_
Lactate
_
788 mW/m
2
[17]
Mixed consortium
Granular graphite
Granular graphite
_
Sucrose
50%
23 mW/m
2
[43]
Mixed consortium
Granular graphite
Granular graphite
_
Glucose
50%
18mW/m
2
[43]
Mixed consortium
Carbon paper
Carbon paper
Proton exchange membrane
Acetate + domestic wastewater
_
506mW/m
2
[44]
Mixed consortia
Carbon paper
Carbon paper
Proton exchange membrane
Butyrate+ domestic wastewater
_
306mW/m
2
[44]
Shewanellaoneidensis MR-1
3DGraphene-Nickel Foam
Carbon cloth substrates
Cation exchange membrane
Trypticase soy broth
_
661 W/m
3
[45]
Swine wastewater
Carbon paper
carbon paper
Nafion
Swine wastewater
_
261 mW/m
2
[46]
Geobacter sulfurreducens
Plain graphite
Plain graphite
Nafion
Acetate
_
13mW/m
2
[47]
1.4.1 Anode
The selection of requisite anode material for the efficient execution of MFC is a very critical step that includes the parameters for electrode selection such as electron transport from microbial cells to the terminal electron acceptor, adhesion of microbes to the surface of anode material, and their efficiency in terms of electrochemistry [48]. A considerable range of anode materials, including metal-based and carbon-based, have been evolved to improve the performance of MFC [49]. An anode material should be highly conductive, chemically stable, and have a large surface area with proper microbe adhesion properties. The widely used anode material is carbon-based materials, among them, graphite variants (plates, rods, felt) and carbon variants (brush, cloth, mesh, viel, felt, paper, etc.), which are are readily available and verified anode materials for MFCs [50]. Metallic anode materials have an antimicrobial activity that makes bacterial growth impossible on the anode surface. However, a recent study demonstrates that electrogens could form colonies on the metal surface and form a highly efficient electrochemically active biofilm on the metallic anode [51]. Metallic anodes are highly conductive, such as copper, gold, nickel, titanium, and silver [52].
1.4.2 Cathode
1.4.2.1 Carbon Fiber Fabrics and Papers
Carbon fiber fabrics and carbon papers are stiff and brittle in texture and available as wet proof and plain versions; they can connect easily with the wire. Carbon cloth is more flexible and porous as compared to carbon paper. The outer exposed surface of electrodes should be covered by using epoxy. Copper wire is commonly used to attach with a cathode; however, it could release copper ions into the electrolytic solution. As copper has antimicrobial activity, it could be toxic to the microorganism and also have corrosion problems after prolonged operational activity, so as much as possible, either titanium wires or stainless steel wires are used to attach with electrode [53].
1.4.2.2 Carbon Foam
As compared to carbon cloths, carbon foam are a little thicker and have more space for the growth of microorganism but have been less reported in MFC researches [54].
1.4.2.3 Graphite Rods
The most widely used form of graphite electrodes for MFC electrochemical researches is graphite rods, as it has defined surface area, low porosity, defined composition, high conductivity [55].
1.4.2.4 Graphite Sheets
Graphite sheets are available in various forms and different thicknesses, such as soft pencil rods. Graphite sheets also have a much defined flat surface suitable for biofilm formation. However, nonporous hence less effective for power generation. A comparative study found that porosity can be introduced in graphite sheets by pouring them into the saline solution and making holes throughout the sheets for increasing the surface area so that a thick biofilm can form over it and assist more power generation [56].
1.4.2.5 Graphite Granules
Like a pencil tip, graphite granules are chunks of graphite as an electrode. It is useful for both as a cathode and the anode in packed bed reactors [57].
1.4.2.6 Graphite Fiber Brushes
Graphite fiber electrodes are used at the anodes as it has porosity, large surface area. Industrial brush machines manufacture graphite fiber brushes, and the core of the fibers made up of non-corrosive metal [58].
1.4.3 Membranes
1.4.3.1 Cation Exchange Membrane
In double-chamber MFC configurations, an ion-selective membrane is used to separate anode and cathode into two different compartments and also permit protons to transfer towards the cathode from the anode and also maintain the anaerobic environment of the anodic compartment by preventing oxygen diffusion as well as prevent anode electrolyte migration towards the cathode. A membrane should have a good ability for proton exchange [59]. PEM is also known as the cation exchange membrane when it allows other cations such as Na+, K+, NH4+, Ca++, Mg++, along with hydrogen ions/protons transport [59]. The three major issues that affect the performance of the membrane in a fuel cell are oxygen permeability, conductivity, and stability of membrane [59]. PEM is further categorized as a nonporous exchange membrane (dense) and porous exchange membranes [60]. Nafion, Ultrex, Zirfons, Hyflons are widely used cation exchange membranes, while Nafion has high proton conductivity as Nafion has a negative sulfonate group (hydrophilic) associated with fluorocarbon chain (hydrophobic), which allows proton transport from membrane pores [60–63].
1.4.3.2 Anion Exchange Membranes
In a study, it was found that when an anion exchange membrane is used in MFC, higher power density is obtained in comparison to the cation exchange membrane (CMI-7000 and Nafion), protons are carried by phosphate buffer in the form of phosphate ions to maintain pH in the anode chamber [64].
1.4.3.3 Bipolar Membrane
A cation and anion membrane attached in a series called a bipolar membrane. To balance charge, protons pass through the membrane, and hence energy required for water to split is less, as it already breaks down into OH-and H+. Transport of H+ towards the cathode and OH- towards the anode. In a study, the bipolar membrane is used with ferric ion (catholyte) and reported it could maintain a balance neutral pH at the anode and maintain a lower pH into the cathode chamber [65].
1.4.4 Substrates
In a Microbial fuel cell, various range of substrates have been used, and all of them give different results in terms of power density or other parameters of power generation, ranging from complex organic mixtures of compounds and pure substrate to wastewater from various sources. Here are some of the commonly used substrates.
1.4.4.1 Glucose
A study demonstrates MFC performance based on P. vulgaris growth, which further concludes its dependency on initial carbon compounds (Glucose, Galactose, Maltose, Sucrose, Trehalose) used as a substrate. Studies demonstrate the possibility of increased MFC performance by changing the primary carbon source used for the growth of microorganisms [66]. Electricity generation in a membrane-less baffle chamber MFC with anaerobic sludge and glucose obtains a power density of 0.3 mW/m2 and 161 mW/m2, respectively [67].
1.4.4.2 Acetate and Butyrate
Acetate is an extensively used substrate and is found as a carbon source of choice for power generation as at room temperature; it is inert to the fermentation, methanogenesis, and other microbial conversions. Acetate is also a product of some metabolic reactions [68]. Power density of 506 mW/m2 generated using acetate (800 mg/L) in single-chambered MFC which is up to 66% more as power density generated 305 mW/m2 by using butyrate (1000 mg/L) [68]. A study compares the coulombic efficiency of MFC utilizing four substrate Acetate, Butyrate, Glucose, Propionate, where acetate produces coulombic efficiency of 72.3% while butyrate, glucose, and propionate produce coulombic efficiency (CE) of 43.0%, 15.0%, and 36.0%, respectively [69].
1.4.4.3 Lignocellulose
As lignocellulosic biomass is widely available in agricultural waste to be used as a substrate for cost-effective power generation, the only problem is that lignocellulosic biomass could not be metabolized directly by microbes. Proper utilization of lignocellulosic material requires hydrolysis of biomass and then conversion of cellulose into simple carbohydrates. Another alternative to this pretreatment is utilizing such a microbe with cellulolytic activity and electrogens simultaneously [70]. Pentoses like xylose are one of the components obtained from hydrolysis of lignocellulosic biomass, and no efficient microbial species are available for pentose conversion for bioethanol bioproduction. In research, a power density of 69 mW/m2 was obtained by lignocellulosic degradation in MFC [71].
1.4.4.4 Cellulose
Cellulose is the primary form of carbohydrate available as organic matter in agricultural, municipal, and industrial wastewater; it is widely available and cheap. Electrogenic microorganisms, which can perform anaerobic hydrolytic conversion of cellulose, are used for direct utilization of cellulose as a substrate in MFCs. An experiment obtains power density up to 0.055 W/m2 by utilizing microorganisms present in the rumen of cattle and using cellulose as a substrate [72]. Power density up to 0.153 W/m2 obtained by feeding carboxymethyl cellulose for microbes as a substrate in MFC [73].
1.4.4.5 Wastewater
The main aim of wastewater treatment processes is to remove or minimizing the organic component load from water resources by oxidizing organic materials. Wastewater from agricultural and industrial effluent contains high organic matter rich in energy value [74]. Microbial systems present at anodes can obtain electrical energy from converting complex organic compounds present in wastewater by utilizing them into their metabolic pathways [75]. Table 1.2 summarizes the role of waste biomass/wastewater as a substrate in MFC.
1.5 Electrogenic Microorganisms
Three types of microorganism are found that can operate MFCs by three different mechanisms [84–86]: i) Microorganisms that are capable of transferring electrons direct to the electrode surface (via outer membrane proteins) [87, 88]; ii) Microorganisms which need redox mediator for passing electrons across the cell membrane to the anode surface [89]; iii) Microbes that can transfer electrons to the anode via nanowire/pili [88]. Table 1.3 lists some electrogenic microorganisms.
A microbial film formed over the anode (anodophillic microorganisms) generally contains electrogenic bacteria like Shewanella and Geobacter during MFC operation with wastewater or any other substrate [96–98]. A diverse range of microbial diversity, including families such as Alteromonadaceae, Clostridiaceae, Geobacteraceae, etc., has been used in MFCs [99]. A minimal number of various research about the performance of gram-positive bacteria in MFCs are available that include Bacillus subtilis, Bacillus cereus, Clostridium beijerinckii, Corynebacterium species, etc. [100, 101]. A big range of gram-negative bacteria is found to be active for power generation while assisting them in MFC with anode such as Bacillus violaceous, Desulfomonas acetoxidans, Escherichia coli, Enterobacter species, Gluconobacter oxydans, Geobacter sulfurreducens, Rhodoferax ferrireducens, Shewanella species, etc. [10, 39, 47, 89, 94, 102–104].
Table 1.2 List of various industrial or domestic effl uent used as substrates in MFCs.
Industrial effluent used as a substrate
Cathode
Anode
Power density
Current density
COD removal efficiency
Reference
Starch processing Unit
Air cathode
Carbon paper
239.4 mW/m
2
893.3 mA/m
2
98%
[76]
Beer brewery industry
Air cathode
Carbon fiber
830 mW/m
3
-
91.7%-95.7%
[77]
Food processing industry
Carbon paper
Carbon paper
371±10 mW/m
2
-
95%
[78]
Meat processing unit
Toray Carbon paper
Toray Carbon paper
354±10 mW/m
2
0.11 mA/cm
2
87%
[79]
Urban wastewater
Graphite cylinder
Graphite cylinder
25 mW/m
2
-
-
[80]
Chocolate industry
Graphite rod
Graphite rod
-
3.02 A/m
2
75%
[81]
Paper recycling Unit
Graphite fiber brush
Graphite fiber
501±20 mW/m
2
-
-
[82]
Animal waste
Graphite Rod
Graphite Rod
31.92±4 mW/m
2
190±9 mA/m
2
-
[83]
Table 1.3 List of microorganisms used in MFC.
Microorganisms
Mediator
Substrate
Reference
Geobacter metallireducens
Mediator-less MFC
Acetate
[90]
Geobacter sulfurreducens
Mediator-less MFC
Acetate
[47]
Shewanella putrefaciens
Mediator-less MFC
Lactate, Pyruvate
[10]
Shewanella oneidensis
Anthraquinone-2,6 disulfonate
Lactate
[91]
Escherichia coli
Methylene blue
Glucose, Sucrose
[92]
Enterobacter cloacae
Mediator less MFC
Acetate, sucrose
[93]
Actinobacillus succinogens
Neutral red or thionine
Glucose
[94]
Desulfovibrio desulfuricans
Sulfate/sulfides mediator
Sucrose
[95]
1.6 Electron Transport Mechanism in MFCs
1.6.1 Direct Electron Transfer
Most metal-reducing bacteria can transport their electrons from cells to the anode surface such as Rhodoferax ferrireducens, Geobacter sulfurre-ducens, and Shewanella putrefaciens; these are electrogenic as they have special cytochromes and charge conducting cellular nanowires (pili) on the cell surface [105]. Figure 1.3 shows direct and indirect electron transfer mechanism in electrogenic bacteria. Shewanella and Geobacter species act as metal-reducing bacteria and generally utilize manganese oxide (IV) and Iron oxide (III) [87, 88, 105].
Figure 1.3 Electron transfer mechanism from bacteria to the anode.
1.6.2 Indirect Electron Transfer
Most microorganisms are unable to perform direct electron transfer to the anode. Such microbes need a substrate to mediate electron transfer and are known as electron shuttles or mediators [89, 106]. Mediators are secreted naturally by microbial activity such as flavins and quinones, or some synthetic mediators added externally such as neutral red, potassium ferricyanide, anthraquinone-2, 6-disulfonate, and artificially synthesized phospholipid polymers [106–108]. Mediators have redox activity for electron transport from the cell membrane to the surface of the anode. For efficient electron transfer, mediators must have some characteristics such as the redox potential of a mediator should be near to the potential of biocatalyst, must be stable that support readily transfers of electrons in both forward (towards anode) and reversible (towards microbial cell) way [109].
1.7 Configuration of MFC
For a realistic approach to MFC in day-to-day life, it is necessary to develop such an MFC configuration that is cost-effective in the manufacturing process, affordable, easy to scale up, produce high coulombic efficiencies and power density. Generally, the following MFC configurations are applicable in recent researches nowadays.
1.7.1 Single-Chamber Microbial Fuel Cell
Single-chamber MFCs are very simple in construction and easy to scale up compared to double-chamber MFCs; it is unnecessary to install a proton exchange membrane but it could be used wherever needed [110, 111]. The cathode should be either with PEM placed at one side of the chamber to allow protons to diffuse via the porous cathode surface and utilize atmospheric oxygen [18, 111]. Anodes could be either regular carbon/ graphite or metal electrodes, etc. In a study, single-chambered MFC with an air cathode (porous) obtained lower coulombic efficiency compared to MFC with proton exchange membrane as oxygen diffuses towards the anode [17]. In anaerobic conditions, higher concentration of hydrogen gas at anode promotes the growth of methanogens, which cause lower recoveries of bio-hydrogen and contaminate the chamber with methane gas [112]. Figure 1.4 demonstrates a single-chamber MFC that includes a graphite anode and an air cathode, used for wastewater treatment using domestic effluents as substrate [18]. In Figure 1.5, a tubular microbial fuel (continuous mode) design is constructed using a single chamber with graphite granules at the anode, and the cathode chamber is filled with ferricyanide; it has generated the maximum power density of 90 W m-3 for acetate feed streams [113]. Elimination of the proton exchange membrane also cut the expenditure on fouling of the membrane and construction of MFCs while oxygen diffusion takes place towards anode cause lowering the number of electrons available to recover as current [90].
Figure 1.4 Lab-scale single-chamber MFC [18].
Figure 1.5 Tubular microbial fuel cell [113].
1.7.2 Dual-Chamber Microbial Fuel Cells
There are a variety of configurations available in dual-chamber MFCs such as H-shape (Figure 1.6), U-shape (Figure 1.7), Up-flow tubular MFCs (Figure 1.8), having cathode in one chamber, and anode in another chamber, and an ion-selective membrane/Salt bridge used for separation of these two chambers [1, 114–117]. The ion-selective membrane is used to avoid oxygen diffusion toward cathodes and allow passes of protons through it. The dual-chamber microbial fuel cell is the most utilized configuration for checking the electrogenic activity of microbes and for the optimization of materials because of its inexpensive design; however, such MFCs have been found difficult for scale-up [1]. In H type and U type microbial fuel cell (Figure 1.6 and Figure 1.7), membrane or Salt Bridge is placed in the tube connecting both the chambers [116]. As it is elementary and cost-effective to construct H type MFCs, it is widely used to check basic parameters in MFC research. It is very less efficient in terms of power density because of electrode high internal resistance [1, 116]. In Figure 1.9, a different kind of dual-chamber MFC configuration is a mini construction called Mini-MFC, which has 1.2 cm3 total volume, using graphite felt electrodes. Mini-MFC has a large surface area to volume ratio, which allows gaining high power output [118]. Another design in dual-chamber MFCs is the Up-flow microbial fuel cell (Figure 1.8), which operates in continuous flow mode, assisting with the Up-flow anaerobic sludge blanket system that can achieve a maximum power density 29.2 W/m3. Comparatively, it is easy to scale up for practical applications [117, 119].
Figure 1.6 Dual-chamber H-shaped MFC.
Figure 1.7 U-tube MFC [116].
Figure 1.8 Up-flow MFC with cylindrical shape [117, 119].
Figure 1.9 Mini MFC.
1.8 Applications of Microbial Fuel Cell
Because of the unique design and useful advances of the microbial fuel cells, researchers and engineers of various fields such as chemical engineering, mechanical engineering, microbiologists, biotechnology, electrical engineering, and environmental engineering are paying huge attention to them. So nowadays, MFC technology is progressed as a well-developing area. By the continuous efforts of researchers, MFC has been proved as a device not only for electricity generation but also for other useful aspects like wastewater treatment. This section describes an update for this emerging technology utility.
1.8.1 Electricity Generation
The main aim of the microbial fuel cell is to utilize microbes for electricity generation via the conversion of the biochemical energy of microorganisms into electrical energy. Any organic substrate or wastewater has been utilized by the metabolic pathway to produce electrons at the anode. Production of bioelectricity was discovered more than a century ago [15] by using any organic or inorganic compound as a substrate that can metabolize by the bacterial system [120]. Microbial fuel cells offer many advantages over other fuel cells, as it is safe to operate and a sustainable source of energy. Table 1.4 represents some studies on varieties of MFCs to obtain electricity.
A single LED light requires approximately 1.7 V constant voltage supply; one single MFC could not be so efficient and so there is a need to connect a minimum three or more than three MFCs in a series connection. In an experiment, three MFCs are put together in a series connection, and it is successful in operating a red LED [129]. It is also found that urine could be an excellent feedstock for the anode chamber to produce electricity. Urine is highly conductive, rich in nutrients, cheap, and widely available to serve as a substrate for microorganisms [130]. A range of waste materials are used to construct stack (40 MFCs) of biodegradable MFC; these stacks are arranged into parallel/Series configuration and fed with urine for 3 days [131]. In a study of two lab-scale, MFC connected in series can energize a digital wristwatch by an energy harvesting module [132]. With urine as substrate, 24 stacks of MFC configured as 12-in-series/2-in-parallel, were able to charge a lithium-ion battery (1000mA/h, 3.7 V) of a mobile phone for 24 hours [133].
Table 1.4 Application of MFC in electricity generation.
Type of MFC
Anode
Cathode
Power density
Specificity
Reference
Single-chamber MFC
Graphite fiber brush
Fe-N-C/AC Cathodes
2400 mW m
-2
Low-cost Fe-N-C Catalyst on activated carbon used as the cathode
[121]
H-shaped dual-chamber MFC
3D Cu
2
O Nanowire array
Cu
2
O@Au Nanowire array
2315.7 mW m
-2
Visible light assisted MFC
[122]
Cube-shaped single-chamber MFC
Graphite fiber brush
Activated carbon with 60% Polytetrafluro ethylene
426.00 mWm
-2
Using methane as a substrate
[123]
Membrane free air cathode
Porous carbon cloth
Air cathode consist Polytetrafluorethylene
30.51 mW m
-2
Uses natural bioresources ex-green tea extract
[124]
Dual-chamber MFC
Stainless steel as fiber felt
Graphene like MoS
2
Nano-flower
713.6 mW m
-2
Anode modification using MoS
2
Nano-flowers
[125]
Photosynthetic MFC
Plain graphite plate
Plain graphite plate
41.5±1.2 mWm
-2
MFC performance was investigated using kitchen wastewater as a substrate
[126]
Sediment microbial fuel cell (mSMFC)
Carbon fiber brushes
Macrophyte biocathode
80.22 mW m
-3
mSMFC with floating Macrophyte as biocathode
[127]
Constructed wetland MFC
Graphite rod along with graphite gravel
Graphite rod along with graphite gravel
11.67 mW/m
3
Integration of an MFC into a horizontal subsurface constructed wetland
[128]
1.8.2 Wastewater Treatment
Wastewater has a rich content of inorganic and organic compounds that are worthless for industries or any other human activity as they have several serious issues with the health of organisms and cause ecological imbalance. Some microbial flora can survive in an extreme condition of these effluents; they metabolize these complex chemical substances and convert them into electrical energy with simultaneous reduction of COD or heavy metals content, which drives interest to develop many modern microbial cells [134]. The advantage of using microbial fuel cells for wastewater treatment along with electricity generation is itself a big deal. Table 1.5 represents a simplified view on COD removal efficiencies of MFC with different industrial effluents used as substrate.
Food processing effluents are rich in biodegradable organic acids and sugar. MFCs are able to generate electricity as a product by utilizing food processing waste and effluents. Up to 46MW of power could be generated by utilizing low BOD wastewater like milk dairy farms, while the maximum power of 1960 MW could be obtained from high BOD dairy effluents [140]. Animal wastewater is high in organic content (approximately 105 mg/L COD) and proteins (nitrogen-containing) [141]. Brewery wastewater has 10 times more concentrated than domestic discharge. The approximate range of COD found in brewery effluents is 3000-5000 mg/L [142]. Wastewater generated from human feces is also examined as a substrate in MFCs the removal efficiencies for NH4, soluble COD, and Total COD are found up to 44%, 88%, and 71%, respectively, while a maximum power density of 70.8 mW/m2 was obtained [143].
1.8.3 Bio-Hydrogen Generation
Bio-Hydrogen production from microbial activities in a Microbial fuel cell is a thermodynamically unfavorable reaction. Microbial fuel cells that operate under normal conditions produce protons from the anode and travels toward the cathode, where oxygen is the ultimate electron acceptor and combine with protons to produce water at the cathode [144]. In 2005, it was found that the supply of additional current to the MFC could be helpful to generate hydrogen [144, 145]. A complete biological microbial electrolysis cell with bio electrodes used in batch mode found a high hydrogen recovery of 65% and 0.45 m3 H2/(m3·d) at cathode [146].
Table 1.5 Application of MFC in wastewater treatment.
Type of MFC
Wastewater
Anode
Cathode
COD/metal reduction rate %
Reference
Dual-chamber MFC
Lake water+ molasses wastewater
Carbon cloth
Carbon cloth
25.24 %
[135]
Dual-chamber MFC
Dairy wastewater
Cu doped iron oxide nanoparticle decorated Toray carbon paper
Cu doped iron oxide nanoparticle decorated Toray carbon paper
75%
[136]
Two-chamber MFC
Fermentation wastewater
Nickle coated sponge
Carbon paper
75.59%
[137]
Plant-Sediment Microbial Fuel Cells
Chromium containing wastewater
Graphite felts
3-D Co
3
O
4
nanowires on Graphite felt
99.76% chromium removal
[138]
Modularized MFC system
Municipal wastewater
Coal granular activated carbon
Coal granular activated carbon
66 ± 4%
[139]
Single-chambered MFC
Starch processing wastewater
Carbon paper
Air cathode
98%
[76]
Double-chamber MFC
Beer brewery wastewater
Carbon fiber
Air cathode
91.7%-95.7%
[77]
Two-chambered MFC
Food processing industry
Carbon paper
Carbon paper
95%
[78]
Single- chamber MFC
Meat processing unit
Toray Carbon paper
Toray Carbon paper
87%
[79]
Two-chambered MFCs
Chocolate industry
Graphite rod
Graphite rod
75%
[81]
1.8.4 Biosensor
Microbial fuel cell technology could be used for in situ observation, control, and monitoring for pollutant sensing [147]. For a quick BOD analysis, MFC has been involved with a microbial sensing unit combined with a transducer. Employing MFC over other sensors could be advantageous because of its stability over the long run and simultaneous real-time monitoring of pollutants [148]. Shewanella putrefaciens is used to develop a biosensor for lactate detection, as utilizing lactate these bacteria can produce current in the absence of any redox mediator where the current generation ultimately depends on the concentration of lactate [149]. A successful trial is observed on volatile fatty acids for sensing them in situ inside a microbial electrochemical biosensor as they have ordinary reactor design and smooth operation. MFC has driven as a promising volatile fatty acids sensor due to effective reactor design and suitable operating conditions among microbial electrochemical biosensors [150].
1.9 Future Perspectives
Microbial fuel cells find a new way in the recovery of heavy metals and COD reduction from wastewater effluent of domestic and industrial effluent. Hence, it is necessary to work on the various parameters that signify the importance of MFC in terms of power generation and wastewater treatment. Some parameters like (i) the mechanism of extracellular electron transfer that will contribute to selecting a highly efficient electrogens, and (ii) design a cost-effective scale-up configuration of MFC, are highly recommended to improve MFCs efficiency in terms of wastewater remediation. As electricity generation is the main feature of MFCs, it is needful to investigate the capabilities of MFC with all possible parameters that could be producing power efficiently at a low cost. As a combined technique for bioelectricity generation and wastewater remediation, MFCs emerged as an effective solution for sustainable energy.
1.10 Conclusion
MFC technology contains the multidisciplinary confluence of biotechnology, microbiology, chemical, and physical sciences applied in research to obtain the potential application of MFC systems. In recent years, it has been widely studied for its effectiveness in wastewater remediation along with the simultaneous generation of electricity. However, its practical or industrial implementation needs more efforts in scale-up and optimization of this technology for reducing potential losses. For the broad-scale approach of MFC for wastewater remediation, the target should be treating various effluents ranging from heavy metals to domestic wastewater and reducing capital cost. More scale-up strategies need to be a target on MFC to degrade the complex heavy metal at a low cost. In upcoming years, MFC technologies will prove to be helpful for engineers who want to focus on waste and energy management.
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