Identification of the Electricity-Producing Bacteria in Wastewater for Microbial Fuel Cells （MFCs）

A microbial fuel cell （MFC） is a device that converts chemical energy to electrical energy during substrate oxidation by microorganisms. The characterization and identification of these microbial communities will allow better control of this electricity generation with simultaneous removal of carbon and nitrogen. This study aims to investigate the role of natural bacteria in electricity generation by studying three different sources of wastewater： the raw wastewater （RW）, wastewater from an aeration tank （AEW） and returned activated sludge （RAS） from an activated sludge treatment plant. The result showed that after the MFC treatment, the number of bacterial strains was reduced from twenty strains to eight strains. Microscopic observation further showed that fifteen isolate before the treatment were gram-positive, and five were gram-negative whereas all isolates after the treatment were gram-positive rods or cocci The four strains isolated from the RAS inoculums, β-Comamonas sp., γ-Enterobacter sp., Bacillus cereus sp. and Clostridium sp. produced the highest power density of 67.57 mW/m^2 which made them potential candidates for electrochemically active bacteria in MFCs. However, the level of chemical oxygen demand （COD） removal was 20% and the total kjeldahl nitrogen （TKN） removal was 66.7%. Key words：

A Comprehensive Review on Oxygen Reduction Reaction in Microbial Fuel Cells

The focus of microbial fuel cell research in recent years has been on the development of materials,microbes,and transfer of charges in the system,resulting in a substantial improvement in current density and improved power generation.The cathode is generally recognized as the limiting factor due to its high-distance proton transfer,slow oxygen reduction reaction(ORR),and expensive materials.The heterogeneous reaction determines power gen-eration in MFC.This comprehensive review describes-recent advancements in the development of cathode mate-rials and catalysts associated with ORR.The recent studies indicated the utilization of different metal oxides,the ferrite-based catalyst to overcome this bottleneck.These studies conclude that some cathode materials,in parti-cular,graphene-based conductive polymer composites with non-precious metal catalysts provide substantial ben-efits for sustainable development in the field of MFCs.Furthermore,it also highlights the potentiality to replace the conventional platinum air cathode for the large-scale production of the next generation of MFCs.It was evi-dent from the experiments that cathode catalyst needs to be blended with conductive carbon materials to make cathode conductive and efficient for ORR.This review discusses various antifouling strategies for cathode biofoul-ing and its effect on the MFC performance.Moreover,it also depicts cost estimations of various catalysts essential for further scale-up of MFC technology.

Utilization of Nanomaterials as Anode Modifiers for Improving Microbial Fuel Cells Performance

Microbial fuel cells(MFCs)are an attractive innovation at the nexus of energy and water security for the future.MFC utilizes electrochemically active microorganisms to oxidize biodegradable substrates and generate bioelectricity in a single step.The material of the anode plays a vital role in increasing the MFC’s power output.The anode in MFC can be upgraded using nanomaterials providing benefits of exceptional physicochemical properties.The nanomaterials in anode gives a high surface area,improved electron transfer promotes electroactive biofilm.Enhanced power output in terms of Direct current(DC)can be obtained as the consequence of improved microbe-electrode interaction.However,several limitations like complex synthesis and degeneration of property do exist in the development of nanomaterial-based anode.The present review discusses different renewable nanomaterial applied in the anode to recover bioelectricity in MFC.Carbon nanomaterials have emerged in the past decade as promising materials for anode construction.Composite materials have also demonstrated the capacity to become potential anode materials of choice.Application of a few transition metal oxides have been explored for efficient extracellular electron transport(EET)from microbes to the anode.

Progress in enhancing the remediation performance of microbial fuel cells for contaminated groundwater

Microbial fuel cells(MFCs)have become more prevalent in groundwater remediation due to their capacity for power generation,removal of pollution,ease of assembly,and low secondary contamination.It is currently being evaluated for practical application in an effort to eliminate groundwater pollution.However,a considerable majority of research was conducted in laboratories.But the operational circumstances including anaerobic characteristics,pH,and temperature vary at different sites.In addition,the complexity of contaminants and the positioning of MFCs significantly affect remediation performance.Taking the aforementioned factors into consideration,this reviewsummarizes a bibliography on the application of MFCs for the remediation of groundwater contamination during the last ten decades and assesses the impact of environmental conditions on the treatment performance.The design of the reactor,including configuration,dimensions,electrodes,membranes,separators,and target contaminants are discussed.This review aims to provide practical guidance for the future application of MFCs in groundwater remediation.

Microalgae Scenedesmus obliquus as renewable biomass feedstock for electricity generation in microbial fuel cells （MFCs）

Renewable algae biomass, Scenedesmus obliquus, was used as substrate for generating electricity in two chamber microbial fuel cells （MFCs）. From polarization test, maximum power density with pretreated algal biomass was 102mW·m^2 （951mW·m^3） at current generation of 276mA·m^-2. The individual electrode potential as a function of current generation suggested that anodic oxidation process of algae substrate had limitation for high current generation in MFC. Total chemical oxygen demand （TCOD） reduction of 74% was obtained when initial TCOD concentration was 534mg · L^-1 for 150 h of operation. The main organic compounds of algae oriented biomass were lactate and acetate, which were mainly used for electricity generation. Other byproducts such as propionate and butyrate were formed at a negligible amount. Electrochemical Impedance Spectroscopy （EIS） analysis pinpointed the charge transfer resistance （112Ω ） of anode electrode, and the exchange current density of anode electrode was 1214 nA·cm^-2.

Raoultella terrigena RtZG1 Electrical Performance Appraisal and System Optimization

The aims of this study are to provide a strain and its optimal application in electro-producting performance for revealing the electrical generating mechanism in the future.We constructed microbial fuel cells(MFCs)device that was a bipolar chamber MFC,using metal ion media(MIM)and water as anode and cathode reaction substation fluid,respectively.In this study,we identified an isolate as Raoultella terrigena,named RtZG1,which could produce electron.Also,we optimized the conditions of electrical energy generation.The continuous output current could reach about 200μA within 3 h when the ratio of electro-bacterial fluid to matrix fluid was 1∶4,the temperature was 37℃,the carbon-nitrogen ratio of the inorganic salt medium was 10∶1,as well as the concentration of MIM was 1.Based on the optimization,it is clear that the most suitable conditions of electricity production for this strain lay the foundation for the application of this strain.

Feasible design for electricity generation from Chlorella vulgaris using convenient photosynthetic conditions

Many recent studies are concerned with low cost,easy to handle and alternative renewable energy as a feasible solution for the upcoming crisis of energy shortage.Microalgae are unicellular entities the can only depend on CO_(2),water and solar power to cover their nutritional needs.The current study is concerned with using algal cells in a polymeric hydrogel,as a cheap source of energy for electricity generation.Chlorella vulgaris has been proved to be a promising algal species for electricity generation,as compared with Micractinium reisseri.PVA hydrogel has been used for the immobilization of both algal species in order to protect them from the adverse surrounding conditions in addition to its ability to slowly release the required water molecules according to needs.Under these conditions,C.vulgaris showed the ability to generate 60 mV compared with 15 mV generated by M.reisseri.Scanning electron micrographs showed nano-threads that bind the C.vulgaris cells to each other,indicating the ability of algae to create nanowires that facilitate the electron transfer among algal cells and from cells to the nearest electrode.However,we would expect an increase in the produced potential with simultaneous amendment of environmentally polluted water,such as sewage or waste water.Both of FTIR and raman spectroscopy proved the presence of the characteristic groups of PVA hydrogel and proved the proper integration of the algal cells inside the hydrogel cavities.

Electron transfer from sulfate-reducing bacteria biofilm promoted by reduced graphene sheets

Reduced graphene sheets (RGSs) mediate electron transfer between sulfate-reducing bacteria (SRB) and solid electrodes, and promote the development of microbial fuel cells (MFC). We have investigated RSG-promoted electron transfer between SRB and a glassy carbon (GC) electrode. The RGSs were produced at high yield by a chemical sequence involving graphite oxidation, ultrasonic exfoliation of nanosheets, and N2H4 reduction. Cyclic voltammetric testing showed that the characteristic anodic peaks (around 0.3 V) might arise from the combination of bacterial membrane surface cytochrome c3 and the metabolic products of SRB. After 6 d, another anodic wave gradually increased to a maximum current peak and a third anodic signal became visible at around 0 V. The enhancements of two characteristic anodic peaks suggest that RSGs mediate electron-transfer kinetics between bacteria and the solid electrode. Manipulation of these recently-discovered electron-transport mechanisms will lead to significant advances in MFC engineering.

Nitrogen recovery from wastewater using microbial fuel cells

Nitrogen is one of major contaminants in wastewater; however, nitrogen, as bio-elements for crop growth, is the indispensable fertilizer in agriculture. In this study, two-chamber microbial fuel cells （MFCs） were first operated with microorganisms in anode chamber and potassium ferricyanide as catholyte. After being success- fully startup, the two-chamber MFCs were re-constructed to three-chamber MFCs which were used to recover the NO-3 -N and NH＋4 -N of synthetic wastewater into value- added nitrogenous fertilizer from cathode chamber and anode chamber, respectively. Ferric nitrate was used as the sole electron acceptor in cathode, which also was used to evaluate the NO-3 -N recover efficiency in the case major anion of NO3 in cathode. The output voltage of these MFCs was about 600-700 mVat an external load of 500 Ω. About 47% NH＋4 -N in anode chamber and 83% NO-3 -N in cathode chamber could be recovered. Higher current density can selectively improve the recovery efficiency of both NH＋4-N and NO3 -N. The study demonstrated a nitrogen recovery process from synthetic wastewater using three-chamber MFCs.

Comparative Study of Electrochemical Performance and Microbial Flora in Microbial Fuel Cells by Using Three Kinds of Substrates

This work aimed to investigate the distinct electrochemical performance and microbial flora of microbial fuel cells(MFCs)in relation to different single hazardous fed fuels.Three replicate MFCs were inoculated with the same microbial consortium from a coking wastewater treatment plants wherein ammonium chloride(ammoniiim chlo-ride-fed MFC,N-MFC),phenol(phenol-fed MFC,P-MFC)and potassium sulphide(potassium sulphide-fed MFC,S-MFC)were the sole substrates and main components of real coking wastewater.With initial concentrations of am-monium chloride,phenol and potassium sulphide of 0.75,0.60 and 0.55 g/L,the removal efficiencies reached 95.6%,90.6%and 99.9%,respectively,whereas the peak output power densities totalled 697,324 and 1215 mW/m^2.Micro-bial community analysis showed that the respective addition of substrate substantially altered the microbial community structure of anode biofllm,resulting in changes in relative abundance and emergence of new strains and further affecting the electrochemical properties of MFCs.The chemical oxygen demand(COD)removal efficiency of real coking wastewater,in which,the inoculum was the combined biomass from the three MFCs,reached 82.3%.

On the use of ferroelectric material LiNbO3 as novel photocatalyst in wastewater-fed microbial fuel cells

In this work, the use of lithium niobate （LiNbO3）, a ferroelectric and photocatalyst material, is investi- gated as a new type of cathode catalyst for wastewater-fed single-chamber microbial fuel cells （MFCs）. Carbon cloth electrodes coated with LiNbO3 were studied with and without UV-vis irradiation to assess its photocatalytic behavior in these devices. The synthesized phase of LiNbO3 was characterized by X- ray diffraction, differential scanning calorimetry, particle size distribution, and transmission electron microscopy analyses. The MFC containing a LiNbO3-based cathode exhibited a maximum open circuit potential and power output of 400 mV and 131 mW/m^3, respectively, under irradiation. This cathode configuration also achieved the maximum chemical oxygen demand removal of 84% after 120 h of MFC operation. These results show that ferroelectric materials such as LiNbO3 could be used as cathode cat- alysts in MFC devices. As a complementary analysis, the removal of the heavy metals detected in the wastewater was also monitored.

Sediment microbial fuel cell with floating biocathode for organic removal and energy recovery

A sediment microbial fuel cell （SMFC） with three dimensional floating biocathode （FBC） was developed for the electricity generation and biodegradation of sediment organic matter in order to avoid negative effect of dissolved oxygen （DO） depletion in aqueous environments on cathode performance and search cost-effective cathode materials. The biocathode was made from graphite granules with microbial attachment to replace platinum （Pt）-coated carbon paper cathode in a laboratory-scale SMFC （3 L in volume） filled with river sediment （organic content 49±4 g. kg^-1 dry weight）. After start-up of 10 days, the maximum power density of 1.00W.m^-3 （based on anode volume） was achieved. The biocathode was better than carbon paper cathode catalyzed by Pt. The attached biofilm on cathode enhanced power generation significantly. The FBC enhanced SMFC performance further in the presence aeration. The SMFC was continuously operated for an over 120-day period. Power generation peaked within 24 days, declined gradually and stabilized at a level of 1/6 peak power output. At the end, the sediment organic matter content near the anode was removed by 29% and the total electricity generated was equal to 0.251 g of chemical oxygen demand （COD） removed.

Electricity generation and brewery wastewater treatment from sequential anode-cathode microbial fuel cell

A sequential anode-cathode double-chamber microbial fuel cell （MFC）, in which the effluent of anode chamber was used as a continuous feed for an aerated cathode chamber, was constructed in this experiment to investigate the performance of brewery wastewater treatment in conjugation with electricity generation. Carbon fiber was used as anode and plain carbon felt with biofilm as cathode. When hydraulic retention time （HRT） was 14.7 h, a relatively high chemical oxygen demand （COD） removal efficiency of 91.7%-95.7% was achieved under long-term stable operation. The MFC displayed an open circuit voltage of 0.434 V and a maximum power density of 830 mW/m^3 at an external resistance of 300 0. To estimate the electrochemical performance of the MFC, electrochemical measurements were carried out and showed that polarization resistance of anode was the major limiting factor in the MFC. Since a high COD removal efficiency was achieved, we conclude that the sequential anode-cathode MFC constructed with bio-cathode in this experiment could provide a new approach for brewery wastewater treatment.

Scaling up a novel denitrifying microbial fuel cell with an oxic-anoxic two stage biocathode

A scaled up microbial fuel cell （MFC） of a 50 L volume was set up with an oxic-anoxic two-stage biocathode and activated semicoke packed electrodes to achieve simultaneous power generation and nitrogen and organic matter removals. An average maximum power density of 43.1 W·m^-3 was obtained in batch operating mode. By adjusting the two extemal resistances, the denitrification in the A-MFC and power production in the O-MFC could be enhanced. In continuous mode, when the hydraulic retention times were set at 6 h, 8 h and 12 h, the removal efficiencies of COD, NHf-N and total nitrogen （TN） were higher than 95%, 97%, and 84%, respectively. Meanwhile the removal loads for COD, NH4^＋-N and TN were10, 0.37 and 0.4 kg·（m^3·d）^-1, respectively.