Algal growth in photosynthetic algal microbial fuel cell and its subsequent utilization for biofuels

<i>Harvesting Energy using Biocatalysts</i>

Promoting bioremediation of brewery wastewater, production of bioelectricity and microbial community shift by sludge microbial fuel cells using biochar as anode

5 - Removal of toxic pollutants using microbial fuel cells

Microbial fuel cell (MFC) is an emerging technology for sustainable energy generation and waste treatment. This paper reviews the potential of a gaseous substrate when it is combined with a mediator in an MFC to generate electricity and to treat toxic gaseous pollutants. Most MFCs for waste water treatment often cannot use mediator to enhance the electron transfer from the microbe to the anode because of the difficulty in recovering the expensive and potentially toxic compound. Combining gas feeds with mediators is possible since the soluble mediator would remain in the anode chamber as the gas passes through the reactor. In addition, this type of MFC is possible to be integrated into an anaerobic biofiltration system (BF-MFC), where the biofilter removes the gaseous contaminant and produces the reduced mediator and the MFC produces the electricity and recycles the reoxidised mediator. This paper also talks about the past research on gaseous feed MFCs, and reviews the mechanism and strategies of electron transfer in MFC using redox mediator. The advantages, process parameters and challenges of BF-MFC are discussed. This knowledge is very much required in the design and scale up of BF-MFC. This paper will be useful for those who work in the area of gaseous pollutant treatment and electricity generation.

Due to fossil fuel depletion and the rapid growth of industry, it is critical to develop environmentally friendly and long-term alternative energy technologies. Microbial fuel cells (MFCs) are a powerful platform for extracting energy from various sources and converting it to electricity. As no intermediate steps are required to harness the electricity from the organic substrate’s stored chemical energy, MFC technology offers a sustainable alternative source of energy production. The generation of electricity from the organic substances contained in waste using MFC technology could provide a cost-effective solution to the issue of environmental pollution and energy shortages in the near future. Thus, technical advancements in bioelectricity production from wastewater are becoming commercially viable. Due to practical limitations, and although promising prospects have been reported in recent investigations, MFCs are incapable of upscaling and of high-energy production. In this review paper, intensive research has been conducted on MFCs’ applications in the treatment of wastewater. Several types of waste have been extensively studied, including municipal or domestic waste, industrial waste, brewery wastewater, and urine waste. Furthermore, the applications of MFCs in the removal of nutrients (nitrogen and sulphates) and precious metals from wastewater were also intensively reviewed. As a result, the efficacy of various MFCs in achieving sustainable power generation from wastewater has been critically addressed in this study.

Agri‐food waste valorisation

Effects of salinity, growing media, and photoperiod on bioelectricity production in plant microbial fuel cells with weeping alkaligrass

Dissimilatory metal reducing bacteria can exchange electrons extracellularly and hold great promise for their use in simultaneous wastewater treatment and electricity production. This study investigated the role of riboflavin, an electron carrier, in the decolourisation of Congo red in microbial fuel cells (MFCs) using Shewanella oneidensis MR-1 as a model organism. The contribution of the membrane-bound protein MtrC to the decolourisation process was also investigated. Within the range of riboflavin concentrations tested, 20µM was found to be the best with >95% of the dye (initial concentration 200mg/L) decolourised in MFCs within 50h compared to 90% in the case where no riboflavin was added. The corresponding maximum power density was 45mW/m2. There was no significant difference in the overall decolourisation efficiencies of Shewanela oneidensis MR-1 ΔMtrC mutants compared to the wild type. However, in terms of power production the mutant produced more power (Pmax 76mW/m2) compared to the wild type (Pmax 46mW/m2) which was attributed to higher levels of riboflavin secreted in solution. Decolourisation efficiencies in non-MFC systems (anaerobic bottles) were similar to those under MFC systems indicating that electricity generation in MFCs does not impair dye decolourisation efficiencies. The results suggest that riboflavin enhances both decolourisation of dyes and simultaneous electricity production in MFCs.

Current disinfection methods employed for treating wastewater are expensive and use chemicals harmful to the environment. Microbial fuel cells (MFCs) offer an excellent solution to tackle some of the major challenges currently faced by mankind: sustainable energy sources, waste management and water stress. Besides producing useful electricity from urine (1), MFCs can also generate catholyte in-situ, which can be used as disinfectant for practical applications (2). Anodic bio-electrochemical reactions oxidise the organic matter from the urine releasing electrons, which are captured by the anode and transferred to the cathode via the external circuit, resulting in the generation of electricity. The separation between anodic and cathodic chambers by ceramic clay offers a low cost alternative to the ionic exchange membrane. Cylindrical ceramic MFCs have been reported to produce useful catholyte in the cathode chamber, formed by a combination of factors, including the: i) ORR taking place in the cathode electrode, ii) electro-osmotic drag, iii) diffusion due to a concentration gradient on both sides of the ceramic membrane and iv) hydraulic pressure affected by porosity of the material and the MFC design. In order to obtain a useful catholyte, an optimization of the different parameters affecting its quality, include: i) ceramic thickness, ii) electricity production and iii) time during which the catholyte was accumulated in the cathode chamber. The first two parameters have been previously studied showing a correlation between the thickness of the ceramic membrane, the amount of catholyte collected and its properties. The current generated also showed a considerable effect as a consequence of the electro-osmotic drag, increasing the pH of the catholyte with the current generated. However, the accumulation time also needs optimisation, since a more concentrated product with a higher pH will be generated, increasing the possibility of generating a highly alkaline solution, which might act as a bacterial killing agent.Fine fire clay with three different thicknesses, 2.5, 5 and 10 mm, were tested under the optimum external load, 60 Ω, and under open circuit, and the catholyte generated was collected every 7 days. The daily production of catholyte was evaluated and the change in the catholyte properties was analysed including pH, conductivity, total solids, anion concentrations, COD reduction and cathode electrode redox potential. The effect of the catholyte properties on the MFC power was also monitored. Microbial analysis was also performed using plate count method and flow cytometry (FCM) for an accurate determination of live, dead, and total bacteria in the catholyte samples, and to determine whether the number of alive bacteria decreased with time as the solution becomes more concentrated and highly alkaline. The number of viable bacteria in the catholyte samples was also estimated.The results show a correlation between the catholyte properties and the thicknesses of the ceramic membrane, the electricity generated from the MFCs and the operation time. The MFCs generated a constant power throughout the duration of the experiment, producing an average of 1.1, 1.4 and 1.9 mW per MFC of 2.5, 5 and 10 mm thickness, respectively, showing also a correlation with the membrane thickness, as previously suggested. The catholyte pH showed a clear dependency on the thickness, starting from 9, 9.4 and 9.7, from the MFCs with ceramic thickness of 2.5, 5 and 10 mm, respectively after one day of operation. A pH increase with time was also observed, which was more pronounced as the ceramic thickness increased, reaching 9.2, 10.3 and 11.5, respectively after 42 days of operation under the optimum load. The catholyte generated revealed killing potential against bacterial cells, which was dependent on the membrane thickness, showing that the highest killing potential was observed from the catholyte generated in the thickest FFC MFCs (10 mm). The viable counting also showed a correlation between the time the catholyte was accumulated and the number of living bacteria in the catholyte. In this work a bio-electrochemical system, capable to decontaminate urine, generate electricity and produce catholyte with bacterial killing potential, is presented for the first time. The optimization of the FFC ceramic thickness and the catholyte accumulation time revealed that a 10 mm ceramic is required to produce good quality of catholyte after 42 days of operation, as well as generate useful constant power output. The possibility to electrochemically generate in-situ a bacterial killing agent from urine offers great opportunity for water reuse and resource recovery for practical implementations. Ieropoulos, I., Greenman, J. and Melhuish, C., 2012. PhysChem ChemPhys 14, 94-98. Gajda, I., Greenman, J., Melhuish, C., and Ieropoulos I., Sci Rep, Nature. In Press.

Development of innovative materials used in electrochemical devices for the renewable production of hydrogen and electricity

Biofuel cells generate electricity through biological processes. Conventional microbial fuel cells (MFCs) operate by converting organic substrates, such as glucose, acetate, starch, and lactate, to electrical bioenergy through microbial oxidation processes [1-3]. A typical MFC consists of an anodic and a cathodic chamber with electrodes partitioned by a proton exchange membrane (PEM) or a cation exchange membrane. This membrane functions as an insulator for maintaining the redox potential and only allows specific ion exchange [4]. While MFCs use suspension cultivation of microorganisms in the anodic chamber [5], some MFCs attach microorganisms to the electrodes to form a biofilm [6]. As microbial oxidation consumes the supplied substrates, the anode surface generates electrons and conducts them to the cathode through an external circuit. The resulting cations pass through the membrane to the cathode in the electrolyte. However, the following three factors limit MFC performance: (1) electron activation on the anode and cathode surfaces, (2) electron transfer from microbial cells to the anode, and (3) internal resistances of the circuit and anions passing through the membrane. Researchers have developed electrode modification, mediator addition, and membrane-free designs to address these issues and improve MFC performance [5]. Different electrode materials produce different activation polarization losses; for example, the noble metal platinum (Pt) offers superior catalytic activity. But, graphite, graphite felt, Pt-coated graphite, and other metal-coated materials are employed as cost-effective electrodes [5,7,8]. Since the cell surfaces of microorganisms are not electrically conductive, the electrons inside the cells cannot directly transfer to the surrounding electrolyte [9,10]. For this reason, previous designs adopt several kinds of toxic and unstable electro-chemicals as electrochemical mediators, or electron shuttles: neutral red (NR), methylene blue (MB), thionint, and phenolic compounds [4,10]. However, these active chemicals are expensive and toxic, rendering them unsuitable for long-term operation [4]. Exchange membranes are the most expensive components of typical MFC [10]. These membranes insulate and separate different kinds and/or concentrations of electrolytes into two chambers and restrict specific ion exchange. Once the permeability of the exchange membrane becomes poor, the resulting increase in ohmic resistance decreases MFC performance [11]. A membrane-free system may address these concerns. In a membrane-free system, the diffusion gradient of the dissolved reactants between the anode and cathode maintains the electrochemical

Microbial Fuel Cell (MFC) technology has been heralded as a tool for energy conservation, resource recovery and valuable compound synthesis, amongst others. The MFC concept is possible due to the ability of electrochemically active bacteria (EcAB) to transfer the electrons produced from substrate degradation, out of the bacterial cell and onto the electrode surface via different mechanisms; a process called exocellular electron transfer (EET). However, despite advances and extensive studies on EET mechanisms and EcAB, like the Fe(III)-reducing Geobacter sulfurreducens PCA, the technology has not reached yet the stage of broad applicability. This thesis investigates characteristics and performance of EcAB in the anodic compartment of pure- and mixed-culture MFCs in an effort to shed light to processes important to MFC performance and efficiency. In order to reliably study EcAB in a microbial fuel cell environment, a gas-tight, sterile MFC setup was developed and optimized for electrochemical and microbiological studies of the anodic bacteria and consequently the electrochemically active biofilm/bioanode. In addition, a method for Geobacter species quantification with quantitative PCR (qPCR) was developed. Furthermore, a multiple-unit MFC setup was designed for convenient and simultaneous operation of identical MFCs ‘in-parallel’. A design for a new compact, multi-array MFC to be used as a small-scale culturing platform of EcAB based solely on their electrochemical properties is also introduced. Our research with different titanium (Ti) electrodes in the same MFC setup, suggests that the MFC electrode surface is critical as it determines attachment of EcAB and bioanode formation that leads ultimately to efficient electrochemical activity. Pt- and Ta- coated Ti electrodes performed the best while uncoated Ti with either smooth or rough surfaces performed the worst. Future MFC research could benefit greatly from enhancing the electrode interface for optimum bioanode formation and electron transfer. Our studies with flat-plate, graphite-electrode, mixed-culture microbial fuel cells (Pmax ≈ 1 W/m2) operated for several months with external load (Rext), indicated stable and reproducible characteristics including Coulombic efficiencies, average values of cell voltage, anode potentials, and current densities as well as main microbial populations of both the anolyte and the bioanode. However, transient testing of power maxima values (Pmax) that required lower Rext, or applied potential showed result variability, that might be linked to differences in electrochemical impedance factors, redox-active centers and electron-producing states of the bioanodes. Differences in the quantities of the bioanode microbial species did not seem to correlate with this variability. Since energy-conserving applications like waste-water treatment MFCs would ideally be operated with an Rext rather than applied voltage, addressing interface impedance factors, such as charge transfer resistance and electrical double layer capacitance, is important especially when MFCs are operated at lower Rext. Furthermore, mixed-culture MFCs were shown to be selective for certain bacterial consortia, including Geobacter- and Pseudomonas- related species. Geobacter-related species were dominant on the surface of different electrodes suggesting a pivotal role of the species in electrochemical activity and EET. This was not surprising as the original mixed-culture inoculum - used for starting up several bioelectrochemical systems at our research facilities - was amended with pure cultures of G. sulfurreducens PCA. However, the strain specifically selected for and present in most bioanodes was a novel Geobacter, strain T33 that was phylogenetically closely related (99% by 16S rRNA sequence similarity) to several strains detected in a variety of MFCs operated by other research groups under various conditions and anodic substrates. These strains formed a new phylogenetic Geobacter cluster, distinct from G. sulfurreducens. This observation suggested that strain T33 might have an ecological advantage in MFCs over G. sulfurreducens PCA. In-depth characterization of strain T33 in pure-culture experiments showed that strain T33 forms efficient bioanodes with high Pmax similar to strain PCA, but exhibits different redox-centers than strain T33. Furthermore, strain T33 has a more limited electron acceptor range, but a wider electron donor range than strain PCA, including glucose and succinate. Phylogenetic analysis indicated that strain T33 and recently described electrochemically active strains G. soli GSS01 and G. anodireducens SD-1 are closely related (99% by 16S rRNA) and form a new phylogenetic cluster within the Geobacters, 98% by 16S rRNA similar to G. sulfurreducens strains PCA and KN400. Genome-based analyses indicates that even though the two clusters share common metabolic properties, some differences exist with respect to electron donor utilization, attachment and conductive cell surface components (e-pili) production and genome rearrangement and gene acquisition. It is not sufficiently clear how the differences in the genome of strain T33 are relevant to persistence of the strain in MFCs, biofilm formation and EET, our studies overall suggest that strain T33 even though producing similar power densities as G. sulfurreducens PCA, might be more stable and versatile in MFCs, and therefore a better candidate for waste-water treatment if it can couple the oxidation of several organic substrates, as observed with Fe(III)-respiration, also to electrode-respiration.

Renewable and clean forms of energy are one of the major needs at present. Microbial Fuel Cells (MFC’s) offers unambiguous advantages over other renewable energy conversion methods. Production of energy resources while minimizing waste is one of the best ways for sustainable energy resource management practices. The application of Microbial Fuel Cells (MFCs) may represent a completely new approach to wastewater treatment with the production of sustainable clean energy. The increase in energy demand can be fulfilled by Microbial Fuel Cell (MFC) in the future. In recent years, researchers have shown that MFCs can be used to produce electricity from water containing glucose, acetate, or lactate. Studies on electricity generation using organic matter from wastewater as substrate are in progress. Waste biomass is a cheap and relatively abundant source of electrons for microbes capable of producing electrical current outside the cell. Rapidly developing microbial electrochemical technologies, such as microbial fuel cells, are part of a diverse platform of future sustainable energy and chemical production technologies. In the present investigation to study the two wastewater samples, municipal wastewater from nearby areas of Guntur (A.P.) and Dairy waste from Guntur (A.P.) were used as substrates in Microbial Fuel Cells (MFCs) to generate electricity. Along with electricity generation, the MFCs can successfully help in treating the same sewage samples. The parameters like pH, TS, TSS, TDS, BOD, and COD were analyzed for all two samples. The COD removal efficiency of the MFCs was analyzed using the standard reflux method. All the MFCs were efficient in COD removal. 50%, 75%, and 85% COD removal was observed after 10, 15, and 30 days respectively of operation of MFCs with municipal waste as substrate.

Lignocellulosic biomass plays a pivotal role in sustainable energy production, with a focus on indirect biomass fuel cells (IDBFC) and direct biomass fuel cells (DBFC). IDBFCs require the initial conversion of biomass into simpler forms like sugars, biogas, syngas, or biocharfor subsequent electricity generation. In contrast, DBFCs offer a more direct approach, generating electricity from biomass without intermediate steps. Lignocellulosic biomass, composed of cellulose, lignin, and hemicellulose, has diverse applications, from bioethanolto direct electricity generation. However, the complex composition of lignocellulosic compounds, including carbon, hydrogen, oxygen, phosphorus, nitrogen, and sulfur, poses challenges for efficient enzymatic hydrolysis, a crucial factor in achieving high power density inMicrobial Fuel Cells (MFCs). MFCs use microorganisms to convert substrates into electricity, influenced by factors like substrate degradation rate, circuit resistance, electron transfer rates, proton mass transfer, electrode materials, and operational conditions. The selection of proper electrode materials is vital for optimising MFC performance. At the heart of MFC performance are electricigens, microorganisms facilitating electron transfer from biomass to the anode through direct or indirect mechanisms. Direct electron transfer (DET), relying on physical contact between microorganism membranes and the anode, is preferred for its efficiency and eco-friendliness. The paper also explores the importance of nutrient supplements (macro and micro) in enhancing bio-methane production and process stability in agro-industrial biogas mono-digestion plants. Nutrient balance significantly affects microbial generation time, degradation rates, and gas production in anaerobic digestion processes. In conclusion, understanding the intricate interplay between lignocellulosic biomass energy fuel cells, electricigens, and their performance factors is crucial for advancing sustainable energy production. MFCs show promise in utilising sludge and various waste biomasses, positioning them as practical, reliable, and versatile power sources in the evolving landscape of renewable energy technologies.&#x0D; Keywords: Lignocellulosic waste, bioenergy, microbial fuel cells (MFCs), electricigens

Global warming and the accumulation of organic waste constitute a serious environmental problem. Therefore, microbial fuel cells (MFC) are an eco-friendly device that have significant capability for the production of electricity using biodegradable waste as fuel. Microorganisms used as catalysts in the anode compartment, execute a principal function in operating MFCs. The present study was conducted to isolate and to screen potential bioelectricity generating microorganisms from dumpsite soil samples and also to construct a domestic dual-chambered microbial fuel cell (MFC). Streptomyces fimicarius was found to be the best isolate for the degradation of cellulose and the production of bioelectricity. The bacterial isolate was identified based on morphological characteristics, biochemical characteristics and molecular identification using 16S rRNA. Double-chambered MFC was constructed by using two polypropylene plastic containers of 1.4 L volume each. The two chambers were joined by using an agar salt bridge and carbon rods were utilized as electrodes. The generation of electricity by the isolate was compared using glucose and cellulose as sole carbon source in a minimal medium. The maximum voltage was found to be 322 mV in the presence of cellulose used as substrate after 5 days of incubation at room temperature and last for 10 days.