Continuous electricity generation from domestic wastewater and organic substrates in a flat plate microbial fuel cell

Scale-up single chamber of microbial fuel cell using agitator and sponge biocarriers

Despite the high efficiency of microbial fuel cells (MFCs), MFCs cannot be a suitable alternative for treatment plants because of insufficient power generation and tiny reactors. Additionally, the increased reactor size and MFC stack result in a reduction in production power and reverse voltage. In this study, a larger MFC with a volume of 1.5 L has been designed called LMFC. A conventional MFC, called SMFC, with a volume of 0.157 L, was constructed and compared with LMFC. Moreover, the designed LMFC can be integrated with other treatment systems and generate significant electricity. In order to evaluate MFC's ability to integrate with other treatment systems, the LMFC reactor was converted into MFC-MBBR by adding sponge biocarriers. A 9.5 percent increase in reactor volume resulted in a 60 percent increase in power density from 290 (SMFC) to 530 (LMFC). An agitator effect was also investigated for better mixing and circulating substrate, which positively affected the power density by about 18%. Compared with LMFCs, the reactor with biocarriers generated a 28% higher power density. The COD removal efficiency of SMFC, LMFC, and MFC-MBBR reactors after 24 h was 85, 66, and 83%, respectively. After 80 h of operation, the Coulombic efficiency of the SMFC, LMFC, and MFC-MBBR reactors was 20.9, 45.43, and 47.28%, respectively. The doubling of coulombic efficiency from SMFC to LMFC reactor shows the design's success. The reduction of COD removal efficiency in LMFC is the reason for integrating this reactor with other systems, which was compensated by adding biocarriers.

Influence of support materials on the electroactive behavior, structure and gene expression of wild type and GSU1771-deficient mutant of Geobacter sulfurreducens biofilms

Geobacter sulfurreducens DL1 is a metal-reducing dissimilatory bacterium frequently used to produce electricity in bioelectrochemical systems (BES). The biofilm formed on electrodes is one of the most important factors for efficient electron transfer; this is possible due to the production of type IV pili and c-type cytochromes that allow it to carry out extracellular electron transfer (EET) to final acceptors. In this study, we analyzed the biofilm formed on different support materials (glass, hematite (Fe2O3) on glass, fluorine-doped tin oxide (FTO) semiconductor glass, Fe2O3 on FTO, graphite, and stainless steel) by G. sulfurreducens DL1 (WT) and GSU1771-deficient strain mutant (Δgsu1771). GSU1771 is a transcriptional regulator that controls the expression of several genes involved in electron transfer. Different approaches and experimental tests were carried out with the biofilms grown on the different support materials including structure analysis by confocal laser scanning microscopy (CLSM), characterization of electrochemical activity, and quantification of relative gene expression by RT-qPCR. The gene expression of selected genes involved in EET was analyzed, observing an overexpression of pgcA, omcS, omcM, and omcF from Δgsu1771 biofilms compared to those from WT, also the overexpression of the epsH gene, which is involved in exopolysaccharide synthesis. Although we observed that for the Δgsu1771 mutant strain, the associated redox processes are similar to the WT strain, and more current is produced, we think that this could be associated with a higher relative expression of certain genes involved in EET and in the production of exopolysaccharides despite the chemical environment where the biofilm develops. This study supports that G. sulfurreducens is capable of adapting to the electrochemical environment where it grows.

Simultaneous naphthalene degradation and electricity production in a biowaste-powered microbial fuel cell

Naphthalene is a very common and hazardous environmental pollutant, and its biodegradation has received serious attention. As demonstrated in this study, naphthalene-contaminated wastewater can be biodegraded using a microbial fuel cell (MFC). Furthermore, the potential of MFC for electricity generation appears to be a promising technology to meet energy demands other than those produced from fossil fuels. Nowadays, efforts are being made to improve the overall performance of MFC by integrating biowaste materials for anode fabrication. In this study, palm kernel shell waste was used to produce palm kernel shell-derived graphene oxide (PKS-GO) and palm kernel shell-derived reduced graphene oxide (PKS-rGO), which were then fabricated into anode electrodes to improve the system's electron mobilization and transport. The MFC configuration with the PKS-rGO anode demonstrated greater energy production potential, with a maximum power density of 35.11 mW/m2 and a current density of 101.76 mA/m2, compared to the PKS-GO anode, which achieved a maximum power density of 17.85 mW/m2 and a current density of 72.56 mA/m2. Furthermore, there is simultaneous naphthalene biodegradation with energy production, where the biodegradation efficiency of naphthalene with PKS-rGO and PKS-GO is 85.5%, and 79.7%, respectively. In addition, the specific capacitance determined from the cyclic voltammetry curve revealed a value for PKS-rGO of 2.23 × 10-4 F/g, which is also higher than the value for PKS-GO (1.57 × 10-4 F/g) on the last day of operation. Anodic microbial analysis shows that electrogens thrive in the MFC process. Finally, a comparison with previous literature and the future prospects of the study are also presented.

Influence of carbon-based cathodes on biofilm composition and electrochemical performance in soil microbial fuel cells

Increasing energy demands and environmental pollution concerns press for sustainable and environmentally friendly technologies. Soil microbial fuel cell (SMFC) technology has great potential for carbon-neutral bioenergy generation and self-powered electrochemical bioremediation. In this study, an in-depth assessment on the effect of several carbon-based cathode materials on the electrochemical performance of SMFCs is provided for the first time. An innovative carbon nanofibers electrode doped with Fe (CNFFe) is used as cathode material in membrane-less SMFCs, and the performance of the resulting device is compared with SMFCs implementing either Pt-doped carbon cloth (PtC), carbon cloth, or graphite felt (GF) as the cathode. Electrochemical analyses are integrated with microbial analyses to assess the impact on both electrogenesis and microbial composition of the anodic and cathodic biofilm. The results show that CNFFe and PtC generate very stable performances, with a peak power density (with respect to the cathode geometric area) of 25.5 and 30.4 mW m^-2, respectively. The best electrochemical performance was obtained with GF, with a peak power density of 87.3 mW m^-2. Taxonomic profiling of the microbial communities revealed differences between anodic and cathodic communities. The anodes were predominantly enriched with Geobacter and Pseudomonas species, while cathodic communities were dominated by hydrogen-producing and hydrogenotrophic bacteria, indicating H₂ cycling as a possible electron transfer mechanism. The presence of nitrate-reducing bacteria, combined with the results of cyclic voltammograms, suggests microbial nitrate reduction occurred on GF cathodes. The results of this study can contribute to the development of effective SMFC design strategies for field implementation.

Bioelectricity Production from Microbial Fuel Cell (MFC) Using Lysinibacillus xylanilyticus Strain nbpp1 as a Biocatalyst

Microbial fuel cells (MFCs) function by using microorganisms to decompose the substrate at the anode, producing electrons and protons. These charges are then transported to the cathode, where electricity is generated. Previous studies have shown their promising probabilities for practical applications. MFCs are praised for their ability to address energy shortages and environmental pollution simultaneously. They have the potential to generate electricity directly from organic substances, reducing energy losses that occur during intermediate conversion steps. The main challenge lies in transitioning these technologies from the laboratory setting to practical systems that can be implemented on a large scale for bioenergy production along with various engineering hurdles. This study focused on investigating the power production potential of a soil-isolated bacterial strain taxonomically classified as Lysinibacillus xylanilyticus nbpp1, which is a relatively new addition to the extensive range of biocatalysts known for their ability to generate electricity. The study analyzed the electrochemical performance of an H-type MFC setup. LB broth was used as the substrate, while aluminum and graphite served as electrode materials. Other parameters, such as Coulombic efficiency, internal resistance, and electrode corrosion rate, were also measured. The MFC produced a high open circuit voltage of 1127 mV and achieved a maximum power density of 6.71 mW/cm² at a current density of 11.14 mA/cm². The MFC setup successfully powered LED lamps when connected in a joint circuit, showcasing its potential for practical applications. These findings suggest the promising high electrochemical performance of the MFC system in terms of electricity generation using the specified conditions.

Industrial bioelectrochemistry for waste valorization: State of the art and challenges

Bioelectrochemistry has gained importance in recent years for some of its applications on waste valorization, such as wastewater treatment and carbon dioxide conversion, among others. The aim of this review is to provide an updated overview of the applications of bioelectrochemical systems (BESs) for waste valorization in the industry, identifying current limitations and future perspectives of this technology. BESs are classified according to biorefinery concepts into three different categories: (i) waste to power, (ii) waste to fuel and (iii) waste to chemicals. The main issues related to the scalability of bioelectrochemical systems are discussed, such as electrode construction, the addition of redox mediators and the design parameters of the cells. Among the existing BESs, microbial fuel cells (MFCs) and microbial electrolysis cells (MECs) stand out as the more advanced technologies in terms of implementation and R&D investment. However, there has been little transfer of such achievements to enzymatic electrochemical systems. It is necessary that enzymatic systems learn from the knowledge reached with MFC and MEC to accelerate their development to achieve competitiveness in the short term.

Assessment of Graphite, Graphene, and Hydrophilic-Treated Graphene Electrodes to Improve Power Generation and Wastewater Treatment in Microbial Fuel Cells

In this study, graphite, graphene, and hydrophilic-treated graphene electrodes were evaluated in a dual-chamber microbial fuel cell (DC-MFC). Free-oxygen conditions were promoted in anodic and cathodic chambers. Hydrochloric acid at 0.1 M and pH 1.1 was used as a catholyte, in addition to deionized water in the cathodic chamber. Domestic wastewater was used as a substrate, and a DuPontTM Nafion 117 membrane was used as a proton exchange membrane. The maximum power density of 32.07 mW·m-2 was obtained using hydrophilic-treated graphene electrodes and hydrochloric acid as catholyte. This power density was 1.4-fold and 32-fold greater than that of graphene (22.15 mW·m-2) and graphite (1.02 mW·m-2), respectively, under the same operational conditions. In addition, the maximum organic matter removal efficiencies of 69.8% and 75.5% were obtained using hydrophilic-treated graphene electrodes, for hydrochloric acid catholyte and deionized water, respectively. Therefore, the results suggest that the use of hydrophilic-treated graphene functioning as electrodes in DC-MFCs, and hydrochloric acid as a catholyte, favored power density when domestic wastewater is degraded. This opens up new possibilities for improving DC-MFC performance through the selection of suitable new electrode materials and catholytes.

Improving the performance of bioelectrochemical sulfate removal by applying flow mode

Treatment of wastewater contaminated with high sulfate concentrations is an environmental imperative lacking a sustainable and environmental friendly technological solution. Microbial electrochemical technology (MET) represents a promising approach for sulfate reduction. In MET, a cathode is introduced as inexhaustible electron source for promoting sulfate reduction via direct or mediated electron transfer. So far, this is mainly studied in batch mode representing straightforward and easy-to-use systems, but their practical implementation seems unlikely, as treatment capacities are limited. Here, we investigated bioelectrochemical sulfate reduction in flow mode and achieved removal efficiencies (E_sulfate , 89.2 ± 0.4%) being comparable to batch experiments, while sulfate removal rates (R_sulfate , 3.1 ± 0.2 mmol L^-1 ) and Coulombic efficiencies (CE, 85.2 ± 17.7%) were significantly increased. Different temperatures and hydraulic retention times (HRT) were applied and the best performance was achieved at HRT 3.5 days and 30°C. Microbial community analysis based on amplicon sequencing demonstrated that sulfate reduction was mainly performed by prokaryotes belonging to the genera Desulfomicrobium, Desulfovibrio, and Desulfococcus, indicating that hydrogenotrophic and heterotrophic sulfate reduction occurred by utilizing cathodically produced H₂ or acetate produced by homoacetogens (Acetobacterium). The advantage of flow operation for bioelectrochemical sulfate reduction is likely based on higher absolute biomass, stable pH, and selection of sulfate reducers with a higher sulfide tolerance, and improved ratio between sulfate-reducing prokaryotes and homoacetogens.

Binder-free NiO/MnO2 coated carbon based anodes for simultaneous norfloxacin removal, wastewater treatment and power generation in dual-chamber microbial fuel cell

Norfloxacin (NFX) is a commonly consumed synthetic antibiotic drug to cure many adverse infectious diseases of humans worldwide, but their presence in almost all aquatic environments has grown into severe global health concerns. In this study, the power performance of dual-chamber microbial fuel cells (MFCs) with two different types of base anodes (graphite felt and activated carbon cloth) were tested with a coating of NiO/MnO₂ for removal of NFX in wastewater. As transition metal oxides have excellent electrochemical stability and a higher specific capacitance, their application in MFC for antibiotic removal and wastewater treatment would be an interesting study. Four different NFX concentrations were studied in two different base material with a coating of NiO/MnO₂. Coating was done with 2 step hydro solvothermal method and modified anode surface was characterized by XRD and XPS analyses. Extracellular electron transfer between microorganisms and the modified anode improved significantly as a consequence of reduced internal resistance and a more biocompatible surface as measured by Electroscopy Impedance Spectroscopy (EIS) and polarization curves. NiO/MnO₂ coated graphite felt performed 1.2 fold better than the control plain graphite felt. Similar results were found for activated carbon cloth (ACC). Modified ACC performed 1.3 fold better than the control plain ACC.

Functional Nanomaterial-Modified Anodes in Microbial Fuel Cells: Advances and Perspectives

Microbial fuel cell (MFC) is a promising approach that could utilize microorganisms to oxidize biodegradable pollutants in wastewater and generate electrical power simultaneously. Introducing advanced anode nanomaterials is generally considered as an effective way to enhance MFC performance by increasing bacterial adhesion and facilitating extracellular electron transfer (EET). This review focuses on the key advances of recent anode modification materials, as well as the current understanding of the microbial EET process occurring at the bacteria-electrode interface. Based on the difference in combination mode of the exoelectrogens and nanomaterials, anode surface modification, hybrid biofilm construction and single-bacterial surface modification strategies are elucidated exhaustively. The inherent mechanisms may help to break through the performance output bottleneck of MFCs by rational design of EET-related nanomaterials, and lead to the widespread application of microbial electrochemical systems.

Microbial fuel cell: A green eco-friendly agent for tannery wastewater treatment and simultaneous bioelectricity/power generation

This review paper emphasised on the origin of hexavalent chromium toxicity in tannery wastewater and its remediation using novel Microbial Fuel Cell (MFC) technology, including electroactive bacteria, which are known as exoelectrogens, to simultaneously treat wastewater and its action in the production of bioenergy and the mechanism of Cr⁶⁺ reduction. Also, there are various parameters like electrode, pH, mode of operation, time of operation, and type of exchange membrane used for promising results shown in enhancing MFC production and remediation of Cr⁶⁺. Destructive anthropological activities, such as leather making and electroplating industries are key sources of hexavalent chromium contamination in aquatic repositories. When Cr⁶⁺ enters the food chain and enters the human body, it has the potential to cause cancer. MFC is a green innovation that generates energy economically through the reduction of toxic Cr⁶⁺ to less toxic Cr³⁺. The organic substrates utilized at the anode of MFC act as electrons (e^-) donors. This review also highlighted the utilization of cheap substrates to make MFCs more economically suitable and the energy production at minimum cost.

Organic Waste Substrates for Bioenergy Production via Microbial Fuel Cells: A Key Point Review

High-energy consumption globally has raised questions about the low environmentally friendly and high-cost processes used until now for energy production. Microbial fuel cells (MFCs) may support alternative more economically and environmentally favorable ways of bioenergy production based on their advantage of using waste. MFCs work as bio-electrochemical devices that consume organic substrates in order for the electrogenic bacteria and/or enzyme cultures to produce electricity and simultaneously lower the environmental hazardous value of waste such as COD. The utilization of organic waste as fuels in MFCs has opened a new research path for testing a variety of by-products from several industry sectors. This review presents several organic waste substrates that can be employed as fuels in MFCs for bioenergy generation and the effect of their usage on power density, COD (chemical oxygen demand) removal, and Coulombic efficiency enhancement. Moreover, a demonstration and comparison of the different types of mixed waste regarding their efficiency for energy generation via MFCs are presented. Future perspectives for manufacturing and cost analysis plans can support scale-up processes fulfilling waste-treatment efficiency and energy-output densities.

Contribution of configurations, electrode and membrane materials, electron transfer mechanisms, and cost of components on the current and future development of microbial fuel cells

Microbial fuel cells (MFCs) are a technology that can be applied to both the wastewater treatment and bioenergy generation. This work discusses the contribution of improvements regarding the configurations, electrode materials, membrane materials, electron transfer mechanisms, and materials cost on the current and future development of MFCs. Analysis of the most recent scientific publications on the field denotes that dual-chamber MFCs configuration offers the greatest potential due to the excellent ability to be adapted to different operating environments. Carbon-based materials show the best performance, biocompatibility of carbon-brush anode favors the formation of the biofilm in a mixed consortium and in wastewater as a substrate resembles the conditions of real scenarios. Carbon-cloth cathode modified with nanotechnology favors the conductive properties of the electrode. Ceramic clay membranes emerge as an interesting low-cost membrane with a proton conductivity of 0.0817 S cm^-1, close to that obtained with the Nafion membrane. The use of nanotechnology in the electrodes also enhances electron transfer in MFCs. It increases the active sites at the anode and improves the interface with microorganisms. At the cathode, it favors its catalytic properties and the oxygen reduction reaction. These features together favor MFCs performance through energy production and substrate degradation with values above 2.0 W m^-2 and 90% respectively. All the recent advances in MFCs are gradually contributing to enable technological alternatives that, in addition to wastewater treatment, generate energy in a sustainable manner. It is important to continue the research efforts worldwide to make MFCs an available and affordable technology for industry and society.

Scaled-up multi-anode shared cathode microbial fuel cell for simultaneous treatment of multiple real wastewaters and power generation

Microbial fuel cell (MFC) is lauded for its capacity to valorize organic substrates in wastes, providing a solution to environmental pollution and energy crisis. While different types of organic substrates affect removal efficiency and current output, most MFCs are designed to only be able to utilize one type of wastewater. However, many real wastewater treatment sites generate more than one type of wastewater which hinders the installation of most MFCs. This study aimed to investigate the performance of the novel-designed multi-anode shared cathode MFC (MASC-MFC) compared with a standard single anode/cathode MFC (SAC-MFC) and the simultaneous treatment of different types of real wastewaters (sewage, slaughterhouse, and hospital) in one MFC unit. The MASC-MFC (9025 mW/m² at 23.332 mA/m²) produced 1.7 times and 1.6 times higher in power density and current density and 2.2 times lower in internal resistance than the standard single anode/cathode MFC (SAC-MFC). A maximum COD removal efficiency of 62.7% was achieved with synthetic wastewater. Feeding the MASC-MFC with multiple real wastewaters decreased maximum power density 3.5 (2599 mW/m²) times and increased internal resistance 2.7 times. Stable current generation 1.575 mA was achieved over 300 h despite the different and complex wastewater physio-chemical compositions. The MASC-MFC achieved over 40% and approximately 30% coulombic efficiency independently in all the anode chambers irrespective of the type of real wastewater used, demonstrating the MASC-MFC's capacity to treat different real wastewaters with the added benefit of electricity production.

Experimental Study of Power Generation and COD Removal Efficiency by Air Cathode Microbial Fuel Cell Using Shewanella baltica 20

Microbial fuel cells (MFCs) are a kind of bioreactor for generating electricity, facilitated by exoelectrogens while treating wastewater. The present article focuses on the performance of an air cathode plexiglass MFC in terms of chemical oxygen demand (COD) removal efficiency and power output by performing two sets of experiments. The proton exchange membrane and electrode materials were Nafion 117 and carbon felts, whereas, for stable biofilm formation on the anode surface, a pure culture of Shewanella baltica 20 was used. Firstly, sterile Luria-Bertani (LB) media containing lactate, ranging from 20 to 100 mM, was continuously fed to an MFC, and a maximum power density of 55 mW/m2 was observed. Similarly, artificial wastewater with COD ranging from 3250 mg/L to 10,272 mg/L was supplied to the MFC in the second set of experiments. In this case, the maximum power density and COD removal efficiency were 12 mW/m2 and 57%, respectively. In both cases, the hydraulic retention time (HRT) was 1.5 h. It was found that electricity generation depends on the characteristics of the wastewater. These initial findings confirm that the design aspects of an MFC, i.e., surface area to volume ratio, and external resistance with respect to the quality of influent need to be optimised to improve the MFC’s performance.

Three-dimensional carbon nanofiber-based anode for high generated current and power from air-cathode micro-sized MFC

It is agreed that low mass transfer and poor reaction kinetics are the main reasons behind the low power density of microbial fuel cells (MFCs). Microscale MFCs can introduce a marvelous solution for the mass transfer dilemma. However, the volumetric power density and coulombic efficiency of present microscale MFCs are still limited due to the poor reaction kinetics. The size, shape, chemical properties and material of the electrodes are essential parameters controlling the reaction kinetics. In this study, a 3D carbon nanofiber disk is introduced as an effective anode for a single-chamber air-cathode micro-sized MFC as it improved the reaction kinetics. The proposed electrode was fabricated by a judicious combination of the electrospinning technique and thermal treatment. Owing to the intercalation of the microorganisms in the carbon nanofiber skeleton, compared to many previous reports, high power and current densities of 8.1 Wm^-2 and 44.9 Am^-2, respectively, were obtained from the 19.6 μL single-chamber air-cathode MFC. However, the thickness of the carbon nanofiber layer has to be optimized by adjusting the electrospinning time. The power density observed from a 10 min electrospinning time-based anode outperformed the 5- and 20 min ones by 1.5 and 2 times, respectively.

Bioelectricity generation from human urine and simultaneous nutrient recovery: Role of Microbial Fuel Cells

Urine is a 'valuable waste' that can be exploited to generate bioelectricity and recover key nutrients for producing NPK-rich biofertilizers. In recent times, improved and innovative waste management technologies have emerged to manage the rapidly increasing environmental pollution and to accomplish the goal of sustainable development. Microbial fuel cells (MFCs) have attracted the attention of environmentalists worldwide to treat human urine and produce power through bioelectrochemical reactions in presence of electroactive bacteria growing on the anode. The bacteria break down the complex organic matter present in urine into simpler compounds and release the electrons which flow through an external circuit generating current at the cathode. Many other useful products are harvested at the end of the process. So, in this review, an attempt has been made to synthesize the information on MFCs fuelled with urine to generate bioelectricity and recover value-added resources (nutrients), and their modifications to enhance productivity. Moreover, configuration and mode of system operation, and factors enhancing the performance of MFCs have been also presented.

Performance evaluation of microbial fuel cell using novel anode architecture and with low cost components

Microbial fuel cell (MFC) has proved to be an effective technology for treatment of wastewater with additional advantage of electricity generation. Though the power density obtained has increased many- folds over a last decade, the cost of treatment and cost of the electricity generation need to be brought down to make the process feasible. In the present research, an attempt has been made to use locally available, low cost and effective materials for the construction of the MFC using novel anode architecture. The MFC was made using multiple membranes in the single cell. The special design of anode proved to be very effective in getting higher power density. The volumetric power density of 2002 mW/m3 could be achieved without use of any chemical catholyte. The corresponding Coulombic efficiency obtained was 13.17%. When chemical catholyte was used, the power density increased to 5201 mW/m3, an increase by more than 2.5 times. The corresponding Coulombic efficiency of the MFC also increased to 29.16 %. Such novel anode architecture could take this technology step forward for practical implementation to harvest carbon neutral electricity from wastewater. The performance of MFC in the removal of COD from wastewater was found to be 93.9 to 97.75% which is highly satisfactory. The removal efficiency was found to be independent of the initial COD of the substrate.

Sustainable strategy on microbial fuel cell to treat the wastewater for the production of green energy

Microbial fuel cell (MFC) is one of the promising alternative energy systems where the catalytic conversion of chemical energy into electrical energy takes places with the help of microorganisms. The basic configuration of MFC consists of three major components such as electrodes (anode and cathode), catalyst (microorganism) and proton transport/exchange membrane (PEM). MFC classified into four types based on the substrate utilized for the catalytic energy conversion process such as Liquid-phase MFC, Solid-phase MFC, Plant-MFC and Algae-MFC. The core performance of MFC is organic substrate oxidation and electron transfer. Microorganisms and electrodes are the key factors that decide the efficiency of MFC system for electricity generation. Microorganism catalysis degradation of organic matters and assist the electron transfer to anode surface, the conductivity of anode material decides the rate of electron transport to cathode through external circuit where electrons are reduced with hydrogen and form water with oxygen. Not limited to electricity generation, MFC also has diverse applications in different sectors including wastewater treatment, biofuel (biohydrogen) production and used as biosensor for detection of biological oxygen demand (BOD) of wastewater and different contaminants concentration in water. This review explains different types of MFC systems and their core performance towards energy conversion and waste management. Also provides an insight on different factors that significantly affect the MFC performance and different aspects of application of MFC systems in various sectors. The challenges of MFC system design, operations and implementation in pilot scale level and the direction for future research are also described in the present review.

Bio-membrane integrated systems for nitrogen recovery from wastewater in circular bioeconomy

Wastewater contains a significant amount of recoverable nitrogen. Hence, the recovery of nitrogen from wastewater can provide an option for generating some revenue by applying the captured nitrogen to producing bio-products, in order to minimize dangerous or environmental pollution consequences. The circular bio-economy can achieve greater environmental and economic sustainability through game-changing technological developments that will improve municipal wastewater management, where simultaneous nitrogen and energy recovery are required. Over the last decade, substantial efforts were undertaken concerning the recovery of nitrogen from wastewater. For example, bio-membrane integrated system (BMIS) which integrates biological process and membrane technology, has attracted considerable attention for recovering nitrogen from wastewater. In this review, current research on nitrogen recovery using the BMIS are compiled whilst the technologies are compared regarding their energy requirement, efficiencies, advantages and disadvantages. Moreover, the bio-products achieved in the nitrogen recovery system processes are summarized in this paper, and the directions for future research are suggested. Future research should consider the quality of recovered nitrogenous products, long-term performance of BMIS and economic feasibility of large-scale reactors. Nitrogen recovery should be addressed under the framework of a circular bio-economy.

From Waste to Watts: Updates on Key Applications of Microbial Fuel Cells in Wastewater Treatment and Energy Production

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.

Microbial fuel cells for bioelectricity production from waste as sustainable prospect of future energy sector

Microbial fuel cell (MFC) is lauded for its potentials to solve both energy crisis and environmental pollution. Technologically, it offers the capability to harness electricity from the chemical energy stored in the organic substrate with no intermediate steps, thereby minimizes the entropic loss due to the inter-conversion of energy. The sciences underneath such MFCs include the electron and proton generation from the metabolic decomposition of the substrate by microbes at the anode, followed by the shuttling of these charges to cathode for electricity generation. While its promising prospects were mutually evinced in the past investigations, the upscaling of MFC in sustaining global energy demands and waste treatments is yet to be put into practice. In this context, the current review summarizes the important knowledge and applications of MFCs, concurrently identifies the technological bottlenecks that restricted its vast implementation. In addition, economic analysis was also performed to provide multiangle perspectives to readers. Succinctly, MFCs are mainly hindered by the slow metabolic kinetics, sluggish transfer of charged particles, and low economic competitiveness when compared to conventional technologies. From these hindering factors, insightful strategies for improved practicality of MFCs were formulated, with potential future research direction being identified too. With proper planning, we are delighted to see the industrialization of MFCs in the near future, which would benefit the entire human race with cleaner energy and the environment.

Single-Chamber Microbial Fuel Cell with Multiple Plates of Bamboo Charcoal Anode: Performance Evaluation

In this study, three single-chamber microbial fuel cells (MFCs), each having Pt-coated carbon cloth as a cathode and four bamboo charcoal (BC) plates as an anode, were run in a fed-batch mode, individually and in series. Simulated potato-processing wastewater was used as a substrate for supporting the growth of a mixed bacterial culture. The maximum power output increased from 0.386 mW with one MFC to 1.047 mW with three MFCs connected in series. The maximum power density, however, decreased from 576 mW/m2 (normalized to the cathode area) with one MFC to 520 mW/m2 with three MFCs in series. The experimental results showed that power can be increased by connecting the MFCs in series; however, choosing low resistance BC is crucial for increasing power density.

Evaluation of electrical current production in microbial electrolysis cells fed with animal rendering wastewater

Anode-respiring bacteria (ARB) generate electrical current from the oxidation of short chain fatty acids (SCFA), primarily acetate, in microbial electrolysis cells (MECs). Animal rendering wastewater (RW) has high fat content, which under anaerobic conditions can yield acetate, making RW a potential feed for MECs. Yet, excess intermediate long chain fatty acids (LCFA) may limit conversion of LCFA and SCFA, and impact ARB activity. Here, we evaluated electrical current production in single-chamber MECs fed with RW. In RW-fed MECs, 34.26 ± 2.69% of the COD provided was converted to electrical current in an 80-day batch cycle. LCFA accumulated in RW-fed MECs, during which conversion of acetate to electrical current was limited. Diverse sulfate-reducing microorganisms were present in the anode biofilm in RW-fed MECs, whereas the genus Geobacter dominated in inoculum-only control MECs. Detection of H₂-utilizing homoacetogens suggested some internal cycling of H₂ produced at the cathode. Overall, this study shows that current production is possible from RW, but to be a viable process for RW treatment, further improvement in rates of COD conversion and current production is necessary along with identifying configurations and/or conditions in which the inhibitory effect of LCFA is reduced.

Rainwater-driven microbial fuel cells for power generation in remote areas

The possibility of using rainwater as a sustainable anolyte in an air-cathode microbial fuel cell (MFC) is investigated in this study. The results indicate that the proposed MFC can work within a wide temperature range (from 0 to 30°C) and under aerobic or anaerobic conditions. However, the rainwater season has a distinct impact. Under anaerobic conditions, the summer rainwater achieves a promised open circuit potential (OCP) of 553 ± 2 mV without addition of nutrients at the ambient temperature, while addition of nutrients leads to an increase in the cell voltage to 763 ± 3 and 588 ± 2 mV at 30°C and ambient temperature, respectively. The maximum OCP for the winter rainwater (492 ± 1.5 mV) is obtained when the reactor is exposed to the air (aerobic conditions) at ambient temperature. Furthermore, the winter rainwater MFC generates a maximum power output of 7 ± 0.1 mWm-2 at a corresponding current density value of 44 ± 0.7 mAm-2 at 30°C. While, at the ambient temperature, the maximum output power is obtained with the summer rainwater (7.2 ± 0.1 mWm-2 at 26 ± 0.5 mAm-2). Moreover, investigation of the bacterial diversity indicates that Lactobacillus spp. is the dominant electroactive genus in the summer rainwater, while in the winter rainwater, Staphylococcus spp. is the main electroactive bacteria. The cyclic voltammetry analysis confirms that the electrons are delivered directly from the bacterial biofilm to the anode surface and without mediators. Overall, this study opens a new avenue for using a novel sustainable type of MFC derived from rainwater.

Bio-electrochemically extracted nitrogen from residual resources for microbial protein production

Upcycling of nutrients from residual resources for producing microbial protein (MP) is an attractive method to valorize residues. In this study, we investigated bio-electrochemical methods to recover ammonia-N, for further production of MP. Reject water and digestate were used for ammonia-N recovery in microbial fuel cell (MFC) system. In one-stage process, ammonia-N recovery was 32 - 42% with 57 - 154 kJ/m³ waste stream of electricity generation. For further enhancing recovery efficiency, a two-stage process was developed, achieving efficiency of 53 - 61%. Subsequently, MP was grown with the extracted ammonia-N, and amino acid concentration was 421 and 272 mg/L under 25 °C and 35 °C, respectively. Similar essential amino acid content of MP (especially under 25 °C) with the one from fish demonstrated the attractiveness of upcycling residues to proteins. Based on simplified economic evaluation, the produced energy performed the potential to catch 1.63 - 6.54 €/m³ waste stream.

Enhanced bioelectricity output of microbial fuel cells via electrospinning zeolitic imidazolate framework-67/polyacrylonitrile carbon nanofiber cathode

In this study, the zeolitic imidazolate framework-67 (ZIF-67) and electrospinning polyacrylonitrile membrane were combined to prepare electrospinning carbon nanofibers composite cathode (ZIF-67/CNFs) which could enhance the oxygen reduction reaction (ORR) performance of microbial fuel cells (MFCs) cathode. The optimum electrode 3 wt% ZIF-67/CNFs revealed the excellent ORR performance with a half-wave potential of -0.03 V vs. Ag/AgCl, which was more positive than Pt/C-CC (-0.09 V vs. Ag/AgCl). The highest output voltage (607±9 mV) and maximum power density (1.191±0.017 W m^-2) were obtained when the prepared ZIF-67/CNFs electrode was applied to the cathode of MFC (ZIF-67/CNFs-MFC). In addition, ZIF-67/CNFs-MFC showed the best pollutant removal effect. Geobacter was the highest proportion of microbial in ZIF-67/CNFs-MFC. The results have shown that the application of ZIF-67/CNFs electrode to MFC cathode is promising.

Progress in microbial fuel cell technology for wastewater treatment and energy harvesting

The global energy crisis has stimulated the development of various forms of green energy technology such as microbial fuel cells (MFCs) that can be applied synergistically and simultaneously toward wastewater treatment and bioenergy generation. This is because electricigens in wastewater can act as catalysts for destroying organic pollutants to produce bioelectricity through bacterial metabolism. In this review, the factors affecting energy production are discussed to help optimize MFC processes with respect to design (e.g., single, double, stacked, up-flow, sediment, photosynthetic, and microbial electrolysis cells) and operational conditions/parameters (e.g., cell potential, microorganisms, substrate (in wastewater), pH, temperature, salinity, external resistance, and shear stress). The significance of electron transfer mechanisms and microbial metabolism is also described to pursue the maximum generation of power by MFCs. Technically, the generation of power by MFCs is still a significant challenge for real-world applications due to the difficulties in balancing between harvesting efficiency and upscaling of the system. This review summarizes various techniques used for MFC-based energy harvesting systems. This study aims to help narrow such gaps in their practical applications. Further, it is also expected to give insights into the upscaling of MFC technology while assisting environmental scientists to gain a better understanding on this energy harvesting approach.

An Old Technique with A Promising Future: Recent Advances in the Use of Electrodeposition for Metal Recovery

Although the first published works on electrodeposition dates from more than one century ago (1905), the uses of this technique in the recovery of metals are attracting an increasing interest from the scientific community in the recent years. Moreover, the intense use of metals in electronics and the necessity to assure a second life of these devices in a context of circular economy, have increased the interest of the scientific community on electrodeposition, with almost 3000 works published per year nowadays. In this review, we aim to revise the most relevant and recent publications in the application of electrodeposition for metal recovery. These contributions have been classified into four main groups of approaches: (1) treatment and reuse of wastewater; (2) use of ionic liquids; (3) use of bio-electrochemical processes (microbial fuel cells and microbial electrolysis cells) and (4) integration of electrodeposition with other processes (bioleaching, adsorption, membrane processes, etc.). This would increase the awareness about the importance of the technology and would serve as a starting point for anyone that aims to start working in the field.

Microbial fuel cells for remediation of environmental pollutants and value addition: Special focus on coupling diatom microbial fuel cells with photocatalytic and photoelectric fuel cells

With the advent of global industrialisation and adaptation of smart life there is rise in anthropogenic pollution especially in water. Remediation of the pollutants (such as metals, and dyes) present in industrial effluents is possible via microbes and algae present in the environment. Microbes are used in a microbial fuel cell (MFC) for remediation of various organic and inorganic pollutants. However, for industrial scale application coupling the MFCs with photocatalytic and photoelectric fuel cell has a potential in improving the output of power. It can also be used for remediation of pollutants more expeditiously, conserving fossil fuels, cleaning environment, hence making the coupled hybrid fuel cell to run economically. Furthermore, such MFC inbuilt with algae in living or powder form give additional value addition products like biofuel, polysaccharides, biopolymers, and polyhydroxy alkanoates etc. This review provides bird's eye view on the removal of environmental pollutants by different biological sources like bacteria and algae. The article is focussed on diatoms as potential algae since they are rich source of crude oil and high value added products in a hybrid photocatalytic MFC. It also covers bottle necks, challenges and future in this field of research.

α-FeOOH nanowires loaded on carbon paper anodes improve the performance of microbial fuel cells

Nanowires synthesized from metal oxides exhibit better conductivity than nanoparticles due to their greater aspect ratio which means that they can transmit electrons over longer distances; in addition, they are also more widely available than pili because their synthesis is not affected by the bacteria themselves. However, there is still little research on the application of metal oxides nanowires to enhance power generation of microbial fuel cells (MFC). In this study, a simple hydrothermal synthesis method was adopted to synthesize α-FeOOH nanowires on carbon paper (α-FeOOH-NWs), which serve as an anode to explore the mechanism of power generation enhancement of MFC. Characterization results reveal α-FeOOH-NWs on carbon paper are approximately 30-50 nm in diameter, with goethite structure. Electrochemical test results indicate that α-FeOOH nanowires could enhance the electrochemical activity of carbon paper and reduce the electron transfer resistance (R_ct). Furthermore, α-FeOOH-NWs made the power density of MFC 3.2 times of the control device. SEM result demonstrates that nanowires are beneficial to the formation of biofilms and increase biomass on the electrode surface. Our results demonstrate that nanowires not only improve the electrochemical activity and conductivity of carbon paper but also facilitate the formation of biofilms and increase the biomass of the anode surface. These two mechanisms work together to boost extracellular electron transfer and power generation efficiency of MFC with α-FeOOH-NWs. Our study provides further evidence for the electrical conductivity of metal nanowires, promoting their potential applications in electricity generation such as MFC or other energy development fields.

Microbial fuel cells: a comprehensive review for beginners

Microbial fuel cells (MFCs) have shown immense potential as a one-stop solution for three major sustainability issues confronting the world today-energy security, global warming and wastewater management. MFCs represent a cross-disciplinary platform for research at the confluence of the natural and engineering sciences. The diversity of variables influencing performance of MFCs has garnered research interest across varied scientific disciplines since the beginning of this century. The increasing number of research publications has made it necessary to keep track of work being carried out by research groups across the globe and consolidate significant findings on a regular basis. Review articles are often the nodal points for beginners who are required to undertake an exploratory survey of literature to identify a suitable research problem. This 'review of reviews' is a ready-reckoner that directs readers to relevant reviews and research articles reporting significant developments in MFC research in the last two decades. The article also highlights the areas needing research attention which when addressed could take this technology a few more steps closer to practical implementation.

Enhanced methane production in an up-flow microbial electrolysis assisted reactors: Hydrodynamics characteristics and electron balance under different spatial distributions of bioelectrodes

Compared with common anaerobic digestion, microbial electrolysis has been proven feasibly to accelerate biodegradation and methanogenesis with the advantages of effective electron flow regulation. However, its actual application and scale-up required a full understanding and further investigation on electrode size and distribution. For making full use of the space of the integrated reactor and improve methane recovery, an effective interior configuration was significant. In this work, three types of reactors with different cathode spatial distributions, that is, different cathode space ratios (ratio of cathode surface area to reaction region volume), were studied to form a good flow pattern for obtaining high methane production. Tracer experiments and numerical simulation were employed simultaneously for understanding the hydrodynamics characters of the interior flow field. The results showed that by increasing the cathode space ratio to 1.33 cm²/cm³ and 2 cm²/cm³, respectively, better flow patterns with the residence time of 1.336 times and 1.363 times of theoretical hydraulic retention time could be obtained. The stacked structure of nickel meshes was beneficial to prolong the contact time of contaminant and improve the mass transfer. Increasing the cathode space ratio could also enhance the electrochemical performance. Considering the organic removal, methane recovery, electrons generation, and material consumption, the recommended cathode space ratio was 1.33 cm²/cm³. With this structure, COD removal efficiency reached 93.2 ± 1.9% and 94.1 ± 1.5%, methane production rate reached 332.0 and 334.8 mL CH₄/L reactor/day, and methane yield was 171.3 and 246.4 mL CH₄/g COD under the HRT of 24 h and 36 h, respectively.

Advanced microbial fuel cell for waste water treatment-a review

Petroleum, coal, and natural gas reservoir were depleting continuously due to an increase in industrialization, which enforced study to identify alternative sources. The next option is the renewable resources which are most important for energy purpose coupled with environmental problem reduction. Microbial fuel cells (MFCs) have become a promising approach to generate cleaner and more sustainable electrical energy. The involvement of various disciplines had been contributing to enhancing the performance of the MFCs. This review covers the performance of MFC along with different wastewater as a substrate in terms of treatment efficiencies as well as for energy generation. Apart from this, effect of various parameters and use of different nanomaterials for performance of MFC were also studied. From the current study, it proves that the use of microbial fuel cell along with the use of nanomaterials could be the waste and energy-related problem-solving approach. MFC could be better in performances based on optimized process parameters for handling any wastewater from industrial process.

An overview of microbial fuel cell usage in wastewater treatment, resource recovery and energy production

Wastewater treatment is a high-cost and energy-intensive process not only due to large amounts of pollutants but also for the large volumes of water to be treated, which are mainly generated by human activities and different industries. In this regard, biological wastewater treatments have become substitutes to the current technologies, owing to the improved treatment efficiency and added value. Microbial fuel cells (MFCs) as one of the promising biological treatments have arisen as a viable solution for chemical oxygen demand (COD) removal and electricity generation simultaneously. Therefore, in this article, the effects of various operating conditions on the COD removal and power production from MFCs are thoroughly discussed. In addition, the advantages and weaknesses of current MFCs technologies used for different types of wastewater are summarized. Finally, the technical barriers facing by MFCs operation and the economic feasibility of using MFCs for wastewater treatment are provided.

Dye reduction-based electron-transfer activity monitoring assay for assessing microbial electron transfer activity of microbial fuel cell inocula

Microbial fuel cells (MFC) utilize microbes as catalysts to convert chemical energy to electricity. Inocula used for MFC operation must therefore contain active microbial population. The dye reduction-based electron-transfer activity monitoring (DREAM) assay was employed to evaluate different inocula used in MFCs for their microbial bioelectrical activity. The assay utilizes the redox property of Methylene Blue to undergo color change from blue to colorless state upon microbial reduction. The extent of Methylene Blue reduction was denoted as the DREAM assay coefficient. DREAM assay was initially performed on a microbial culture along with the growth curve and estimation of colony forming units (CFUs). DREAM coefficient correlated to the CFU/mL obtained over time as growth progressed. The assay was then extended to water samples (domestic sewage, lake and a man-made pond) serving as inocula in MFCs. Domestic wastewater gave the highest DREAM coefficient (0.300 ± 0.05), followed by pond (0.224 ± 0.07) and lake (0.157 ± 0.04) water samples. Power density obtained conformed to the DREAM coefficient values, with the three samples generating power densities of 46.45 ± 5.1, 36.12 ± 3.2 and 25.08 ± 4.3 mW/m² respectively. We have also studied the role of addition of various carbon sources and their concentrations towards improving the sensitivity of the assay. The DREAM assay is a rapid, easy-to-perform and cost-effective method to assess inocula for their suitability as anolytes in terms of electron transfer potential in MFCs.

The Membrane-Less Microbial Fuel Cell (ML-MFC) with Ni-Co and Cu-B Cathode Powered by the Process Wastewater from Yeast Production

Research related to measurements of electricity production was combined with parallel wastewater parameter reduction in a membrane-less microbial fuel cell (ML-MFC) fed with industry process wastewater (from a yeast factory). Electrodes with Ni–Co and Cu–B catalysts were used as cathodes. A carbon electrode (carbon cloth) was used as a reference due to its widespread use. It was demonstrated that all analyzed electrodes could be employed as cathodes in ML-MFC fed with process wastewater from yeast production. Electricity measurements during ML-MFC operations indicated that power (6.19 mW) and current density (0.38 mA·cm−2) were the highest for Ni–Co electrodes. In addition, during the exploitation of ML-MFC, it was recorded that the chemical oxygen demand (COD) removal per time for all types of electrodes was similar to the duration of COD decrease in the conditions for wastewater aeration. However, the COD reduction curve for aeration took the most favorable course. The concentration of NH4+ in ML-MFC remained virtually constant throughout the measurement period, whereas NO3− levels indicated almost complete removal (with a minimum increase in the last days of cell exploitation).

Three-dimensional electrodes enhance electricity generation and nitrogen removal of microbial fuel cells

One of the critical problems for practical application of microbial fuel cells (MFCs) is the poor electron transfer between microbial cells and anode. Hence, good biocompatibility and high specific surface area of electrodes are indispensable for MFC scale-up. In this study, three-dimensional electrode MFC (3DEMFC) was developed by filling biochar between anode and cathode. Three types of biochar electrodes (biochar, biochar and zeolite mixture, and MgO-modified biochar) were employed, and the performance of 3DEMFCs treating nitrogen in wastewater was investigated. The results showed that the highest power density of MFCs was 4.45 ± 0.21 W m^-3 achieved by 3DEMFC filled with MgO-modified biochar, and the overall power generation of 3DEMFCs (2.40 ± 0.28 ~ 4.45 ± 0.21 W m^-3) was higher than that of MFC without biochar (1.31 ± 0.24 W m^-3). The linear sweep voltammetry (LSV) results also demonstrated biochar addition to MFC was conducive to electron transfer between microbes and anode and MgO-modified biochar presented the highest coulombs transfer ability. Moreover, the highest removal efficiencies of ammonium, total nitrogen, and COD (93.6 ± 3.2%, 84.8 ± 2%, and 91.6 ± 1.3%, respectively) were achieved by 3DEMFC containing MgO-modified biochar, and simultaneous short-cut nitrification and denitrification were observed in MFCs. Furthermore, the SEM images displayed the bacteria adhesion on biochar and the biofilm dry weights of MgO-modified biochar after experiment was the highest of 103 ± 4 mg g^-1 among three kinds of biochar electrodes. Therefore, the power generation and nitrogen removal conspicuously enhanced in 3DEMFCs and biochar exhibited excellent biocompatibility and distinct electrochemical performance for MFC practical applications in wastewater treatment.

Effective Treatment of Acid Mine Drainage with Microbial Fuel Cells: An Emphasis on Typical Energy Substrates

Acid mine drainage (AMD), characterized by a high concentration of heavy metals, poses a threat to the ecosystem and human health. Bioelectrochemical system (BES) is a promising technology for the simultaneous treatment of organic wastewater and recovery of metal ions from AMD. Different kinds of organic wastewater usually contain different predominant organic chemicals. However, the effect of different energy substrates on AMD treatment and microbial communities of BES remains largely unknown. Here, results showed that different energy substrates (such as glucose, acetate, ethanol, or lactate) affected the startup, maximum voltage output, power density, coulombic efficiency, and microbial communities of the microbial fuel cell (MFC). Compared with the maximum voltage output (55 mV) obtained by glucose-fed-MFC, much higher maximum voltage output (187 to 212 mV) was achieved by MFCs fed individually with other energy substrates. Acetate-fed-MFC showed the highest power density (195.07 mW/m2), followed by lactate (98.63 mW/m2), ethanol (52.02 mW/m2), and glucose (3.23 mW/m2). Microbial community analysis indicated that the microbial communities of anodic electroactive biofilms changed with different energy substrates. The unclassified_f_Enterobacteriaceae (87.48%) was predominant in glucose-fed-MFC, while Geobacter species only accounted for 0.63%. The genera of Methanobrevibacter (23.70%), Burkholderia-Paraburkholderia (23.47%), and Geobacter (11.90%) were the major genera enriched in the ethanol-fed-MFC. Geobacter was most predominant in MFC enriched by lactate (45.28%) or acetate (49.72%). Results showed that the abundance of exoelectrogens Geobacter species correlated to electricity-generation capacities of electroactive biofilms. Electroactive biofilms enriched with acetate, lactate, or ethanol effectively recovered all Cu2+ ion (349 mg/L) of simulated AMD in a cathodic chamber within 53 h by reduction as Cu0 on the cathode. However, only 34.65% of the total Cu2+ ion was removed in glucose-fed-MFC by precipitation with anions and cations rather than Cu0 on the cathode.

Effect of substrate type and concentration on the performance of a double chamber microbial fuel cell

The microbial fuel cell (MFC) provides new opportunities for energy generation and wastewater treatment through conversion of organic matter into electricity by electrogenic bacteria. This study investigates the effect of different types and concentrations of substrates on the performance of a double chamber microbial fuel cell (DCMFC). Three mediator-less laboratory-scale DCMFCs were used in this study, which were equipped with graphite electrode and cation exchange membrane. The MFCs were fed with three different types of substrates (glucose, acetate and sucrose) at a chemical oxygen demand (COD) concentration of 1,000 mg/L. The selected substrate (acetate) was studied for three different concentrations of 500, 2,000 and 3,000 mg/L of COD. Results demonstrated that acetate was the best substrate among the three different substrates with maximum power density and COD removal of 91 mW/m² and 77%, respectively. Concentration of 2,000 mg/L was the best concentration in terms of performance with maximum power density and COD removal of 114 mW/m² and 79%, respectively. The polarization curve shows that ohmic losses were dominant in DCMFCs established for all three substrates and concentrations.

Energy capture from thermolytic solutions and simulated sunlight coupled with hydrogen peroxide production and wastewater remediation

A novel solar salinity energy nexus was developed by combining a photocatalytic fuel cell (PFC) and a reverse electrodialysis (RED). The hybrid cell (called a PRC) can effectively transfer the solar energy and salinity gradient energy (which is regenerated by low grade industrial waste heat) to electrical energy coupled with enhanced pollutant (Rhodamine B, RhB) degradation and H₂O₂ production. Energy-Environment win-win will be realized. The open circuit voltage of the PRC was the sum of those of the PFC and the RED, and the RED stack made the larger contribution to the electricity production of PRC. The bias voltage generated from the RED stack accelerated the separation of photo-induced holes and electrons on the three-dimensional TiO₂ array photoanode, which enhanced RhB degradation and H₂O₂ production. The flow rate and concentration of the working fluids (ammonium bicarbonate) and the reaction conditions in the electrode chambers had substantial effects on the PRC performance. Under the optimal condition, the peak power density and energy efficiency of PRC reached 1500 mW m^-2 and 4.21% respectively. The performance of PRC on electricity production is better than photocatalytic electrolytic cell driven by desalination(PFCD), but not good as microbial reverse electrodialysis electrolysis cell (MREC).

Toward Optimization of Wood Industry Wastewater Treatment in Microbial Fuel Cells—Mixed Wastewaters Approach

Microbial fuel cell (MFC) has the potential to become a promising sustainable technology of wastewater treatment. Usually, the investigations on MFCs are aimed at maximized power production in the system. In this article, we focused on the optimization of wood industry wastewater treatment in MFC, in combination with municipal wastewater as a source of microorganisms. We investigated the influence of different external resistance (2000 Ω, 1000 Ω, 500 Ω, and 100 Ω) on power density and wastewater treatment efficiency (chemical oxygen demand (COD) removal) in 1-month MFC operation time. We found that the highest COD removal was for MFCs under R = 1000 Ω after 22 days of MFC operation, while the highest current density was obtained for the lowest applied resistance. The results imply that wastewater treatment parameters such as resistance and time of MFC operation should be a subject of optimization for each specific type of wastewater used, in order to maximize either wastewater treatment efficiency or power production in MFC. Thus, optimization of power production and COD removal efficiency in MFCs need to be run separately as different resistances are required for maximizing these two parameters. When COD removal efficiency is a subject of optimization, there is no universal value of external resistance, but it should be set to the specific wastewater characteristics.