Electricity generation from swine wastewater using microbial fuel cells

Microbial fuel cells (MFCs) represent a new method for treating animal wastewaters and simultaneously producing electricity. Preliminary tests using a two-chambered MFC with an aqueous cathode indicated that electricity could be generated from swine wastewater containing 8320 +/- 190 mg/L of soluble chemical oxygen demand (SCOD) (maximum power density of 45 mW/m2). More extensive tests with a single-chambered air cathode MFC produced a maximum power density with the animal wastewater of 261 mW/m2 (200 omega resistor), which was 79% larger than that previously obtained with the same system using domestic wastewater (146 +/- 8 mW/m2) due to the higher concentration of organic matter in the swine wastewater. Power generation as a function of substrate concentration was modeled according to saturation kinetics, with a maximum power density of P(max) = 225 mW/m2 (fixed 1000 omega resistor) and half-saturation concentration of K(s) = 1512 mg/L (total COD). Ammonia was removed from 198 +/- 1 to 34 +/- 1 mg/L (83% removal). In order to try to increase power output and overall treatment efficiency, diluted (1:10) wastewater was sonicated and autoclaved. This pretreated wastewater generated 16% more power after treatment (110 +/- 4 mW/m2) than before treatment (96 +/- 4 mW/m2). SCOD removal was increased from 88% to 92% by stirring diluted wastewater, although power output slightly decreased. These results demonstrate that animal wastewaters such as this swine wastewater can be used for power generation in MFCs while at the same time achieving wastewater treatment.     

Hydrogen and electricity production from a food processing wastewater using fermentation and microbial fuel cell technologies

Hydrogen can be produced from fermentation of sugars in wastewaters, but much of the organic matter remains in solution. We demonstrate here that hydrogen production from a food processing wastewater high in sugar can be linked to electricity generation using a microbial fuel cell (MFC) to achieve more effective wastewater treatment. Grab samples were taken from: plant effluent at two different times during the day (Effluents 1 and 2; 735+/-15 and 3250+/-90 mg-COD/L), an equalization tank (Lagoon; 1670+/-50mg-COD/L), and waste stream containing a high concentration of organic matter (Cereal; 8920+/-150 mg-COD/L). Hydrogen production from the Lagoon and effluent samples was low, with 64+/-16 mL of hydrogen per liter of wastewater (mL/L) for Effluent 1, 21+/-18 mL/L for Effluent 2, and 16+/-2 mL/L for the Lagoon sample. There was substantially greater hydrogen production using the Cereal wastewater (210+/-56 mL/L). Assuming a theoretical maximum yield of 4 mol of hydrogen per mol of glucose, hydrogen yields were 0.61-0.79 mol/mol for the Cereal wastewater, and ranged from 1 to 2.52 mol/mol for the other samples. This suggests a strategy for hydrogen recovery from wastewater based on targeting high-COD and high-sugar wastewaters, recognizing that sugar content alone is an insufficient predictor of hydrogen yields. Preliminary tests with the Cereal wastewater (diluted to 595 mg-COD/L) in a two-chambered MFC demonstrated a maximum of 81+/-7 mW/m(2) (normalized to the anode surface area), or 25+/-2 mA per liter of wastewater, and a final COD of <30 mg/L (95% removal). Using a one-chambered MFC and pre-fermented wastewater, the maximum power density was 371+/-10 mW/m(2) (53.5+/-1.4 mA per liter of wastewater). These results suggest that it is feasible to link biological hydrogen production and electricity producing using MFCs in order to achieve both wastewater treatment and bioenergy production.     

A single-chamber microbial fuel cell as a biosensor for wastewaters

The traditional 5-day test of the biochemical oxygen demand (BOD₅ test) has many disadvantages, and principally it is unsuitable for process control and real-time monitoring. As an alternative, a single-chamber microbial fuel cell (SCMFC) with an air cathode was tested as a biosensor and the performance analysed in terms of its measurement range, its response time, its reproducibility and its operational stability. When artificial wastewater was used as fuel, the biosensor output had a linear relationship with the BOD concentration up to 350 mg BOD cm⁻³; very high reproducibility; and stability over 7 months of operation.The system was further improved by reducing by 75% the total anolyte volume. In this way a response time close to the hydraulic retention time (HRT) of the biosensor (i.e. 40 min) was reached. When the small volume SCMFC biosensor was fed with real wastewater a good correlation between COD concentration and current output was obtained, demonstrating the applicability of this system to real effluents. The measurements obtained with the biosensor were also in accordance with values obtained with standard measurement methods.     

Electricity generation using membrane and salt bridge microbial fuel cells

Microbial fuel cells (MFCs) can be used to directly generate electricity from the oxidation of dissolved organic matter, but optimization of MFCs will require that we know more about the factors that can increase power output such as the type of proton exchange system which can affect the system internal resistance. Power output in a MFC containing a proton exchange membrane was compared using a pure culture (Geobacter metallireducens) or a mixed culture (wastewater inoculum). Power output with either inoculum was essentially the same, with 40+/-1mW/m2 for G. metallireducens and 38+/-1mW/m2 for the wastewater inoculum. We also examined power output in a MFC with a salt bridge instead of a membrane system. Power output by the salt bridge MFC (inoculated with G. metallireducens) was 2.2mW/m2. The low power output was directly attributed to the higher internal resistance of the salt bridge system (19920+/-50 Ohms) compared to that of the membrane system (1286+/-1Ohms) based on measurements using impedance spectroscopy. In both systems, it was observed that oxygen diffusion from the cathode chamber into the anode chamber was a factor in power generation. Nitrogen gas sparging, L-cysteine (a chemical oxygen scavenger), or suspended cells (biological oxygen scavenger) were used to limit the effects of gas diffusion into the anode chamber. Nitrogen gas sparging, for example, increased overall Coulombic efficiency (47% or 55%) compared to that obtained without gas sparging (19%). These results show that increasing power densities in MFCs will require reducing the internal resistance of the system, and that methods are needed to control the dissolved oxygen flux into the anode chamber in order to increase overall Coulombic efficiency.     

Identifying the microbial communities and operational conditions for optimized wastewater treatment in microbial fuel cells

Microbial fuel cells (MFCs) are devices that exploit microorganisms as “biocatalysts” to recover energy from organic matter in the form of electricity. MFCs have been explored as possible energy neutral wastewater treatment systems; however, fundamental knowledge is still required about how MFC-associated microbial communities are affected by different operational conditions and can be optimized for accelerated wastewater treatment rates. In this study, we explored how electricity-generating microbial biofilms were established at MFC anodes and responded to three different operational conditions during wastewater treatment: 1) MFC operation using a 750 Ω external resistor (0.3 mA current production); 2) set-potential (SP) operation with the anode electrode potentiostatically controlled to +100 mV vs SHE (4.0 mA current production); and 3) open circuit (OC) operation (zero current generation). For all reactors, primary clarifier effluent collected from a municipal wastewater plant was used as the sole carbon and microbial source. Batch operation demonstrated nearly complete organic matter consumption after a residence time of 8–12 days for the MFC condition, 4–6 days for the SP condition, and 15–20 days for the OC condition. These results indicate that higher current generation accelerates organic matter degradation during MFC wastewater treatment. The microbial community analysis was conducted for the three reactors using 16S rRNA gene sequencing. Although the inoculated wastewater was dominated by members of Epsilonproteobacteria, Gammaproteobacteria, and Bacteroidetes species, the electricity-generating biofilms in MFC and SP reactors were dominated by Deltaproteobacteria and Bacteroidetes. Within Deltaproteobacteria, phylotypes classified to family Desulfobulbaceae and Geobacteraceae increased significantly under the SP condition with higher current generation; however those phylotypes were not found in the OC reactor. These analyses suggest that species related to family Desulfobulbaceae and Geobacteraceae are correlated with the electricity generation in the biofilm and may be key players for optimizing wastewater treatment rates and energy recovery in applied MFC systems.     

Electricity generation from cysteine in a microbial fuel cell

In a microbial fuel cell (MFC), power can be generated from the oxidation of organic matter by bacteria at the anode, with reduction of oxygen at the cathode. Proton exchange membranes used in MFCs are permeable to oxygen, resulting in the diffusion of oxygen into the anode chamber. This could either lower power generation by obligate anaerobes or result in the loss in electron donor from aerobic respiration by facultative or other aerobic bacteria. In order to maintain anaerobic conditions in conventional anaerobic laboratory cultures, chemical oxygen scavengers such as cysteine are commonly used. It is shown here that cysteine can serve as a substrate for electricity generation by bacteria in a MFC. A two-chamber MFC containing a proton exchange membrane was inoculated with an anaerobic marine sediment. Over a period of a few weeks, electricity generation gradually increased to a maximum power density of 19 mW/m(2) (700 or 1000 Omega resistor; 385 mg/L of cysteine). Power output increased to 39 mW/m(2) when cysteine concentrations were increased up to 770 mg/L (493 Omega resistor). The use of a more active cathode with Pt- or Pt-Ru, increased the maximum power from 19 to 33 mW/m(2) demonstrating that cathode efficiency limited power generation. Power was always immediately generated upon addition of fresh medium, but initial power levels consistently increased by ca. 30% during the first 24 h. Electron recovery as electricity was 14% based on complete cysteine oxidation, with an additional 14% (28% total) potentially lost to oxygen diffusion through the proton exchange membrane. 16S rRNA-based analysis of the biofilm on the anode of the MFC indicated that the predominant organisms were Shewanella spp. closely related to Shewanella affinis (37% of 16S rRNA gene sequences recovered in clone libraries).     

Efficient electricity generation from sewage sludge using biocathode microbial fuel cell

Microbial fuel cells (MFCs) with abiotic cathodes require expensive catalyst (such as Pt) or catholyte (such as hexacynoferrate) to facilitate oxidation reactions. This study incorporated biocathodes into a three-chamber MFC to yield electricity from sewage sludge at maximum power output of 13.2 ± 1.7 W/m³ during polarization, much higher than those previously reported. After 15 d operation, the total chemical oxygen demand (TCOD) removal and coulombic efficiency (CE) of cell reached 40.8 ± 9.0% and 19.4 ± 4.3%, respectively. The anolyte comprised principally acetate and propionate (minor) as metabolites. The use of biocathodes produced an internal resistance of 36-46 Ω, lower than those reported in literature works, hence yielding higher maximum power density from MFC. The massively parallel sequencing technology, 454 pyrosequencing technique, was adopted to probe microbial community on anode biofilm, with dominant phyla belonging to Proteobacteria (45% of total bacteria), Bacteroidetes (19%), Uncultured bacteria (9%), Actinobacteria (7%), Firmicutes (7%), Chloroflex (7%). At genera level, Rhodoferax, Ferruginibacter, Propionibacterium, Rhodopseudomonas, Ferribacterium, Clostridium, Chlorobaculum, Rhodobacter, Bradyrhizobium were the abundant taxa (relative abundances > 2.0%).     

The effect of real-time external resistance optimization on microbial fuel cell performance

This work evaluates the impact of the external resistance (electrical load) on the long-term performance of a microbial fuel cell (MFC) and demonstrates the real-time optimization of the external resistance. For this purpose, acetate-fed MFCs were operated at external resistances, which were above, below, or equal to the internal resistance of a corresponding MFC. A perturbation/observation algorithm was used for the real-time optimal selection of the external resistance. MFC operation at the optimal external resistance resulted in increased power output, improved Coulombic efficiency, and low methane production. Furthermore, the efficiency of the perturbation/observation algorithm for maximizing long-term MFC performance was confirmed by operating an MFC fed with synthetic wastewater for over 40 days. In this test an average Coulombic efficiency of 29% was achieved.     

Simultaneous nitrification, denitrification and carbon removal in microbial fuel cells

Microbial fuel cells (MFCs) can use nitrate as a cathodic electron acceptor, allowing for simultaneous removal of carbon (at the anode) and nitrogen (at the cathode). In this study, we supplemented the cathodic process with in situ nitrification through specific aeration, and thus obtained simultaneous nitrification and denitrification (SND) in the one half-cell. Synthetic wastewater containing acetate and ammonium was supplied to the anode; the effluent was subsequently directed to the cathode. The influence of oxygen levels and carbon/nitrogen concentrations and ratios on the system performances was investigated. Denitrification occurred simultaneously with nitrification at the cathode, producing an effluent with levels of nitrate and ammonium as low as 1.0 ± 0.5 mg N L⁻¹ and 2.13 ± 0.05 mg N L⁻¹, respectively, resulting in a nitrogen removal efficiency of 94.1 ± 0.9%. The integration of the nitrification process into the cathode solves the drawback of ammonium losses due to diffusion between compartments in the MFC, as previously reported in a system operating with external nitrification stage. This work represents the first successful attempt to combine SND and organics oxidation while producing electricity in an MFC.     

Effect of nitrate on the performance of single chamber air cathode microbial fuel cells

The effect of nitrate on the performance of a single chamber air cathode MFC system and the denitrification activity in the system were investigated. The maximum voltage output was not affected by 8.0mM nitrate in the medium solution at higher external resistance (270-1000Omega), but affected at lower resistance (150Omega) possibly due to the low organic carbon availability. The Coulombic efficiency was greatly affected by the nitrate concentration possibly due to the competition between the electricity generation and denitrification processes. Over 84-90% of nitrate (0.8-8.0mM) was removed from the single chamber MFCs in less than 8h in the first batch. After 4-month operation, over 85% of nitrate (8.0mM) was removed in 1h after the MFC was continuously fed with a medium solution containing nitrate. Only a small amount of nitrite (<0.01mM) was detected during the denitrification process. The similar denitrification activity observed at different external resistances (1000 and 270Omega) and open circuit mode indicates that the denitrification was not significantly affected by the electricity generation process. No electricity was generated when the MFC fed with 8.0mM nitrate was moved to a glove box (no oxygen), indicating that the bacteria on the cathode did not involve in accepting electrons from the circuit to reduce the nitrate. Denaturing Gradient Gel Electrophoresis (DGGE) profiles demonstrate a similar bacterial community composition on the electrodes and in the solution but with different dominant species.     

Ammonium recovery and energy production from urine by a microbial fuel cell

Nitrogen recovery through NH₃ stripping is energy intensive and requires large amounts of chemicals. Therefore, a microbial fuel cell was developed to simultaneously produce energy and recover ammonium. The applied microbial fuel cell used a gas diffusion cathode. The ammonium transport to the cathode occurred due to migration of ammonium and diffusion of ammonia. In the cathode chamber ionic ammonium was converted to volatile ammonia due to the high pH. Ammonia was recovered from the liquid-gas boundary via volatilization and subsequent absorption into an acid solution. An ammonium recovery rate of 3.29 g_N d⁻¹ m⁻² (vs. membrane surface area) was achieved at a current density of 0.50 A m⁻² (vs. membrane surface area). The energy balance showed a surplus of energy 3.46 kJ g_N⁻¹, which means more energy was produced than needed for the ammonium recovery. Hence, ammonium recovery and simultaneous energy production from urine was proven possible by this novel approach.     

Microbial fuel cells for simultaneous carbon and nitrogen removal

The recent demonstration of cathodic nitrate reduction in a microbial fuel cell (MFC) creates opportunities for a new technology for nitrogen removal from wastewater. A novel process configuration that achieves both carbon and nitrogen removal using MFC is designed and demonstrated. The process involves feeding the ammonium-containing effluent from the carbon-utilising anode to an external biofilm-based aerobic reactor for nitrification, and then feeding the nitrified liquor to the MFC cathode for nitrate reduction. Removal rates up to 2 kg COD m(-3)NCC d(-1) (chemical oxygen demand: COD, net cathodic compartment: NCC) and 0.41 kg NO(3)(-)-Nm(-3)NCC d(-1) were continuously achieved in the anodic and cathodic compartment, respectively, while the MFC was producing a maximum power output of 34.6+/-1.1 Wm(-3)NCC and a maximum current of 133.3+/-1.0 Am(-3)NCC. In comparison to conventional activated sludge systems, this MFC-based process achieves nitrogen removal with a decreased carbon requirement. A COD/N ratio of approximately 4.5 g COD g(-1) N was achieved, compared to the conventionally required ratio of above 7. We have demonstrated that also nitrite can be used as cathodic electron acceptor. Hence, upon creating a loop concept based on nitrite, a further reduction of the COD/N ratio would be possible. The process is also more energy effective not only due to the energy production coupled with denitrification, but also because of the reduced aeration costs due to minimised aerobic consumption of organic carbon.     

Nitrogen removal from wastewater using membrane aerated microbial fuel cell techniques

Nitrogen removal mainly relies on sequential nitrification and denitrification in wastewater treatment. Microbial fuel cells (MFCs) are innovative wastewater treatment techniques for pollution control and energy generation. In this study, bench-scale wastewater treatment systems using membrane-aerated MFC (MAMFC) and diffuser-aerated MFC (DAMFC) techniques were constructed for simultaneous removal of carbonaceous and nitrogenous pollutants and electricity production from wastewater. During 210 days of continuous flow operation, when the dissolved oxygen (DO) in the cathodic compartment was kept at 2 mg/L, both reactors demonstrated high COD removal (>99%) and high ammonia removal (>99%) but low nitrogen removal (<20%). When a lower DO (0.5 mg/L) was maintained after day 121, both the MFC-based reactors still had excellent COD removal (>97%). However, the nitrogen removal of MAMFC (52%) was 2-fold higher than that of DAMFC (24%), indicating an enhanced performance of denitrification after DO reduction in the cathodic compartment of the MAMFC. Meanwhile, terminal restriction fragment length polymorphism (T-RFLP) analysis of ammonia-oxidizing bacteria (AOB) population in the MAMFC indicated the diversity of AOB with equally important Nitrosospira and Nitrosomonas species present in the cathodic biofilm after DO reduction. The average voltage output in the MAMFC was significantly higher than that in DAMFC under both DO conditions. The results suggest that MAMFC systems have the potential for wastewater treatment with improved nitrogen removal and electricity production.     

Redistribution of wastewater alkalinity with a microbial fuel cell to support nitrification of reject water

In wastewater treatment plants, the reject water from the sludge treatment processes typically contains high ammonium concentrations, which constitute a significant internal nitrogen load in the plant. Often, a separate nitrification reactor is used to treat the reject water before it is fed back into the plant. The nitrification reaction consumes alkalinity, which has to be replenished by dosing e.g. NaOH or Ca(OH)₂. In this study, we investigated the use of a two-compartment microbial fuel cell (MFC) to redistribute alkalinity from influent wastewater to support nitrification of reject water. In an MFC, alkalinity is consumed in the anode compartment and produced in the cathode compartment. We use this phenomenon and the fact that the influent wastewater flow is many times larger than the reject water flow to transfer alkalinity from the influent wastewater to the reject water. In a laboratory-scale system, ammonium oxidation of synthetic reject water passed through the cathode chamber of an MFC, increased from 73.8 ± 8.9 mgN/L under open-circuit conditions to 160.1 ± 4.8 mgN/L when a current of 1.96 ± 0.37 mA (15.1 mA/L total MFC liquid volume) was flowing through the MFC. These results demonstrated the positive effect of an MFC on ammonium oxidation of alkalinity-limited reject water.     

Anodic Fenton process assisted by a microbial fuel cell for enhanced degradation of organic pollutants

The electro-Fenton process is efficient for degradation of organic pollutants, but it suffers from the high operating costs due to the need of power investment. Here, a new anodic Fenton system is developed for energy-saving and efficient treatment of organic pollutants by incorporating microbial fuel cell (MFC) into an anodic Fenton process. This system is composed of an anodic Fenton reactor and a two-chamber air-cathode MFC. The power generated from a two-chamber MFC is used to drive the anodic Fenton process for Acid Orange 7 (AO7) degradation through accelerating in situ generation of Fe²⁺ from sacrificial iron. The kinetic results show that the MFC-assisted anodic Fenton process system had a significantly higher pseudo-first-order rate constant than those for the chemical Fenton methods. The electrochemical analysis reveals that AO7 did not hinder the corrosion of iron. The anodic Fenton process was influenced by the MFC performance. It was also found that increasing dissolved oxygen in the cathode improved the MFC power density, which in turn enhanced the AO7 degradation rate. These clearly demonstrate that the anodic Fenton process could be integrated with MFC to develop a self-sustained system for cost-effective and energy-saving electrochemical wastewater treatment.     

Extracellular biological organic matters in microbial fuel cell using sewage sludge as fuel

The microbial fuel cell (MFC) was applied to produce electricity using sewage sludge as a fuel. The extracellular biological organic matter (EBOM) of sludge, before and after MFC operation, was extracted using ammonium hydroxide whose hydrophobicity was characterized with XAD resin fractionation technique. Following MFC operation, the hydrophilic fraction (HPI) of EBOM was enriched (48.0%-64.5%), the hydrophobic acid (HPO-A) fraction was reduced (32.0%-14.5%), and the dissolved organic carbon (DOC) was removed by 36.8% and the sludge aromaticity decreased by 65.7%. The fluorescence tests indicated that the MFC removed the aromatic proteins-like and soluble microbial byproduct-like materials in sludge. Fourier-transform infrared (FT-IR) results showed that the aliphatic (C-H related) components, hydrocarbon and carbohydrate were easily hydrolyzed and biodegraded in the studied MFC.     

Enhanced removal of 1,2-dichloroethane by anodophilic microbial consortia

1,2-Dichloroethane (1,2-DCA) is a well-known recalcitrant groundwater contaminant. New environment-friendly approaches for the removal of 1,2-DCA that does not bring about volatilization of the compound are required. In this study, different anodophilic consortia enriched in microbial fuel cells (MFCs) operated under airtight conditions were shown to effectively degrade 1,2-DCA (up to 102 mg per liter reactor volume per day), while concomitantly generating a current. An anodophilic consortium previously enriched with acetate as the electron donor changed its composition at the rate of 48% per week and increased its richness (Rr) 3-fold, upon adapting to 1,2-DCA as the new electron donor. After being stable, during 1 month of operation, it removed up to 95% of the 1,2-DCA amount in the medium in the first 2 weeks, while converting 43 ± 4% of electrons available from the removal to electricity. A natural consortium from a 1,2-DCA contaminated site changed its composition at the rate of 9% per week and increased its Rr 2-fold, upon adapting to the MFC anode conditions with 1,2-DCA as the electron donor. After being stable, during 1 month of operation, it removed up to 85% of the 1,2-DCA amount in the medium in the first 2 weeks and the coulombic efficiency was 25 ± 4%. The operation of the MFCs under closed circuit conditions resulted in higher 1,2-DCA removal rates than the operation under open circuit conditions, indicating that bioelectrochemical activities enhanced the removal of 1,2-DCA in the MFC anode. The production of ethylene glycol, acetate and carbon dioxide indicated that the anodophilic bacteria oxidatively metabolized 1,2-DCA, probably by means of a hydrolysis-based pathway. The results show that MFCs can be potentially used as a practically convenient technology for the biological removal of 1,2-DCA.     

Nano-structured manganese oxide as a cathodic catalyst for enhanced oxygen reduction in a microbial fuel cell fed with a synthetic wastewater

Microbial fuel cells (MFCs) provide new opportunities for the simultaneous wastewater treatment and electricity generation. Enhanced oxygen reduction capacity of cost-effective metal-based catalysts in an air cathode is essential for the scale-up and commercialization of MFCs in the field of wastewater treatment. We demonstrated that a nano-structured MnO_x material, prepared by an electrochemically deposition method, could be an effective catalyst for oxygen reduction in an MFC to generate electricity with the maximum power density of 772.8 mW/m³ and remove organics when the MFC was fed with an acetate-laden synthetic wastewater. The nano-structured MnO_x with the controllable size and morphology could be readily obtained with the electrochemical deposition method. Both morphology and manganese oxidation state of the nano-scale catalyst were largely dependent on the electrochemical preparation process, and they governed its catalytic activity and the cathodic oxygen reduction performance of the MFC accordingly. Furthermore, cyclic voltammetry (CV) performed on each nano-structured material suggests that the MnO_x nanorods had an electrochemical activity towards oxygen reduction reaction via a four-electron pathway in a neutral pH solution. This work provides useful information on the facile preparation of cost-effective cathodic catalysts in a controllable way for the single-chamber air-cathode MFC for wastewater treatment.     

Innovative self-powered submersible microbial electrolysis cell (SMEC) for biohydrogen production from anaerobic reactors

A self-powered submersible microbial electrolysis cell (SMEC), in which a specially designed anode chamber and external electricity supply were not needed, was developed for in situ biohydrogen production from anaerobic reactors. In batch experiments, the hydrogen production rate reached 17.8 mL/L/d at the initial acetate concentration of 410 mg/L (5 mM), while the cathodic hydrogen recovery (RH₂) and overall systemic coulombic efficiency (CE_os) were 93% and 28%, respectively, and the systemic hydrogen yield (YH₂) peaked at 1.27 mol-H₂/mol-acetate. The hydrogen production increased along with acetate and buffer concentration. The highest hydrogen production rate of 32.2 mL/L/d and YH₂ of 1.43 mol-H₂/mol-acetate were achieved at 1640 mg/L (20 mM) acetate and 100 mM phosphate buffer. Further evaluation of the reactor under single electricity-generating or hydrogen-producing mode indicated that further improvement of voltage output and reduction of electron losses were essential for efficient hydrogen generation. In addition, alternate exchanging the electricity-assisting and hydrogen-producing function between the two cell units of the SMEC was found to be an effective approach to inhibit methanogens. Furthermore, 16S rRNA genes analysis showed that this special operation strategy resulted same microbial community structures in the anodic biofilms of the two cell units. The simple, compact and in situ applicable SMEC offers new opportunities for reactor design for a microbial electricity-assisted biohydrogen production system.     

Modelling study of an upflow microbial fuel cell catalysed with anaerobic aged sludge

An electrochemical model for an upflow dual-chambered microbial fuel cell (MFC) process is proposed in this study. The model was set up on the basis of the experimental results and the analysis of biochemical and electrochemical processes in the MFC biocatalysed with anaerobic aged sludge and alternatively fuelled with a synthetic acetate-based and actual domestic wastewaters. Simulation of the process shows that the model describes the process reasonably well with correlation coefficients higher than 0.97. The analysis of model simulation illustrates how the current output depends mainly on the substrate concentration as well as other main variables. The relationship between the current output and over-voltage is revealed by the modelling study. For acetate-based wastewaters with initial chemical oxygen demand (COD) concentrations of 350, 700, 1050, and 1400 mg/L, maximum observed power densities were 290, 405, 448, and 525 mW/m² associated with maximum COD removals of 84%, 88%, 83%, and 82%, respectively.