Microbial Fuel Cell For Generation Research Articles

Electricity generation from starch processing wastewater using microbial fuel cell technology

Microbial fuel cells (MFCs) represent a new method for simultaneous wastewater treatment and biological electricity generation. In this study, an air-cathode MFC with membrane electrode assembly was operated over four batch cycles (a total period of 140 d) and results indicated that starch processing wastewater containing 4852 mg/l of chemical oxygen demand could be used as substrate to produce electricity with this MFC. Maximum voltage output and power density of 490.8 mV and 239.4 mW/m 2 (a current density of 893.3 mA/m 2 ) were approached in the third cycle, which also had the minimum internal resistance of about 120 Ω and maximum coulombic efficiency of 8.0%. Removal efficiencies of chemical oxygen demand and ammonia-nitrogen increased as a function of time, and maximum amounted to 98.0% and 90.6%, respectively. Scanning electron microscope image revealed that short rod shaped bacillus were the dominant bacteria on the biofilm of the anode, whose electrochemical activity was proved by cyclic voltammetry. These results demonstrate that starch processing wastewater can be used for power generation in MFCs and also can be treated with high removal efficiencies of chemical oxygen demand and ammonia-nitrogen.

Electricity Generation in Microbial Fuel Cells Catalyzed by Mixed Culture and Pure Culture

Electricity Generation in Microbial Fuel Cells Catalyzed by Mixed Culture and Pure Culture

Enzymatic hydrolysis of cellulose coupled with electricity generation in a microbial fuel cell

Electricity can be directly generated by bacteria in microbial fuel cells (MFCs) from a variety of biodegradable substrates, including cellulose. Particulate materials have not been extensively examined for power generation in MFCs, but in general power densities are lower than those produced with soluble substrates under similar conditions likely as a result of slow hydrolysis rates of the particles. Cellulases are used to achieve rapid conversion of cellulose to sugar for ethanol production, but these enzymes have not been previously tested for their effectiveness in MFCs. It was not known if cellulases would remain active in an MFC in the presence of exoelectrogenic bacteria or if enzymes might hinder power production by adversely affecting the bacteria. Electricity generation from cellulose was therefore examined in two-chamber MFCs in the presence and absence of cellulases. The maximum power density with enzymes and cellulose was 100 +/- 7 mW/m(2) (0.6 +/- 0.04 W/m(3)), compared to only 12 +/- 0.6 mW/m(2) (0.06 +/- 0.003 W/m(3)) in the absence of the enzymes. This power density was comparable to that achieved in the same system using glucose (102 +/- 7 mW/m(2), 0.56 +/- 0.038 W/m(3)) suggesting that the enzyme successfully hydrolyzed cellulose and did not otherwise inhibit electricity production by the bacteria. The addition of the enzyme doubled the Coulombic efficiency (CE) to CE = 51% and increased COD removal to 73%, likely as a result of rapid hydrolysis of cellulose in the reactor and biodegradation of the enzyme. These results demonstrate that cellulases do not adversely affect exoelectrogenic bacteria that produce power in an MFC, and that the use of these enzymes can increase power densities and reactor performance.

Response to Comment on “Sustainable Power Generation in Microbial Fuel Cells Using Bicarbonate Buffer and Proton Transfer Mechanisms”

We appreciate that Ahn further emphasized the potential importance of the self-produced CO2 from the degradation of carbon sources in facilitating proton transfer (1). However, Ahn overestimated the possible CO2 (bicarbonate) concentration in our experiments. The claims “If the MFC had been operated under a continuous steady state condition, CO2 partial pressure in the headspace of MFC would be maintained at almost 1 atm.” and “if the MFC had well behaved under a steady state for a long-term period. The CO2 partial pressure of the MFC must be maintained to considerably high level, approximately 1 atm.” in the comment are not correct. Under steady state conditions, equilibrium is established between the dissolved CO2 in liquid phase and the CO2 gas in headspace. The concentrations of CO2 in the liquid and in the headspace remain constant since all the produced CO2 is carried away by the effluent. Based on the equation for calculating Columbic efficiency of MFCs under continuous flow mode (3), the maximum produced CO2 concentration (∆CCO2) can be calculated as: ∆CCO2 ) I FbqE c (1)

Electricity Generation by Rhodopseudomonas palustris DX-1

Bacteria able to generate electricity in microbial fuel cells (MFCs) are of great interest, but there are few strains capable of high power production in these systems. Here we report that the phototrophic purple nonsulfur bacterium Rhodopseudomonas palustris DX-1, isolated from an MFC, produced electricity at higher power densities (2720 +/- 60 mW/m2) than mixed cultures in the same device. While Rhodopseudomonas species are known for their ability to generate hydrogen, they have not previously been shown to generate power in an MFC, and current was generated without the need for light or hydrogen production. Strain DX-1 utilizes a wide variety of substrates (volatile acids, yeast extract, and thiosulfate) for power production in different metabolic modes, making it highly useful for studying power generation in MFCs and generating power from a range of simple and complex sources of organic matter. These results demonstrate that a phototrophic purple nonsulfur bacterium can efficiently generate electricity by direct electron transfer in MFCs, providing another model microorganism for MFC investigations.

The Effect of Bacterial Adhesion and Electrode Potentials on Electricity Generation of Microbial Fuel Cells (MFCs)

The Effect of Bacterial Adhesion and Electrode Potentials on Electricity Generation of Microbial Fuel Cells (MFCs)

Electricity generation using microbial fuel cells

Conversion of biomass into electricity is possible using microbial fuel cells (MFCs). The present paper deals with the studies of a two-chambered salt bridge MFC using Enterobacter cloacae IIT-BT 08 in MYG medium. The effect of different electron mediators, concentration of the mediator, ionic strength (salt concentration) of the medium and the surface area of the salt-bridge in contact with the anode and cathode chambers on the power generation in MFCs are reported. In the case of methyl viologen (MV) (0.1 mM) as the electron mediator, the voltage generation was 0.4 V but no current was detected. Different concentrations of methylene blue (MB) were also studied as the mediator. A maximum voltage of 0.37 V was seen at 0.05 mM MB, whereas a maximum current and power of 56.7 μ A and 19.2 μ W , respectively, were observed in the case of 0.03 mM MB with a voltage of 0.34 V. The corresponding power density and current density of 9.3 mW / m 2 and 27.6 mA / m 2 , respectively, were obtained. When the surface area of the salt bridge in contact with the anode and cathode chambers was increased, a proportionate improvement in the power output from 19.2 to 708 μ W was detected. The maximum power density and current density of 236 mW / m 2 and 666.7 mA / m 2 , respectively, which are found to be very promising for a salt bridge MFC were observed.

Tubular Membrane Cathodes for Scalable Power Generation in Microbial Fuel Cells

One of the greatest challenges for using microbial fuel cells (MFCs) for wastewater treatment is creating a scalable architecture that provides large surface areas for oxygen reduction at the cathode and bacteria growth on the anode. We demonstrate here a scalable cathode concept by showing that a tubular ultrafiltration membrane with a conductive graphite coating and a nonprecious metal catalyst (CoTMPP) can be used to produce power in an MFC. Using a carbon paper anode (surface area Aan = 7 cm2, surface area per reactor volume Aan,s = 25 m2/m3), an MFC with two 3-cm tube cathodes (Acat = 27 cm2, Acat,s = 84 m2/m3) generated up to 8.8 W/m3 (403 mW/m2) using glucose [0.8 g/L in a 50 mM phosphate buffer solution (PBS)], which was only slightly less than that produced using a carbon paper cathode with a Pt catalyst (9.9 W/m3, 394 mW/m2; Acat= 7 cm2, Acat,s= 25 m2/m3). Coulombic efficiencies (CEs) with carbon paper anodes were 25-40% with tube cathodes (CoTMPP), compared to 7-19% with a carbon paper cathode. When a high-surface-area graphite brush anode was used (Aan = 2235 cm2, Aan,s = 7700 m2/m3) with two tube cathodes placed inside the reactor (Acat = 27 cm2, Acas, = 93 m2/m3), the MFC produced 17.7 W/m3 with a CE = 70-74% (200 mM PBS). Further increases in the surface area of the tube cathodes to 54 cm2 (120 m2/m3) increased the total power output (from 0.51 to 0.83 mW), but the increase in volume resulted in a constant volumetric power density (approximately 18 W/m3). These results demonstrate that an MFC design using tubular cathodes coated with nonprecious metal catalysts, and brush anodes, is a promising architecture that is intrinsically scalable for creating larger systems. Further increases in power output will be possible through the development of cathodes with lower internal resistances.

Sustainable Approach for Leachate Treatment: Electricity Generation in Microbial Fuel Cell

Electricity generation from landfill leachate was examined by using both a dual-chamber microbial fuel cell (MFC) and a single chamber MFC. Experimental results showed that the maximum power density of 2060.19 mW/m3 in the dual-chamber MFC and that of 6817.4 mW/m3 in the single chamber MFC were obtained. It was recognized that the difference in internal resistance for two MFC systems was the main reason for resulting in the difference of power generation. Power generation as function of chemical oxygen demand (COD) in single chamber MFC showed a Monod-type relationship with P max of 5920.96 mW/m3 and Ks of 251.39 mg/L at an external resistance of 500 Ω. Cyclic voltammetry showed that electrons were directly transferred onto the anode by bacteria in biofilms, rather than self-produced mediators of bacteria in the solutions. At low COD concentration, electricity generation was limited by the anode due to kinetic limitation; while at high COD concentration, the cathode was shown to have more significant effects on the electricity generation than the anode. COD in leachate could be removed when it increases, mainly because oxygen diffused from the cathode was substantially reduced by aerobic or anoxic bacteria in the anode chamber, leading to the substrate loss. Removal of ammonium-nitrogen was not observed in the single chamber MFC. This novel technology provides an economical route for electricity energy recovery in leachate treatment.

Procedure for Determining Maximum Sustainable Power Generated by Microbial Fuel Cells

Power generated by microbial fuel cells is computed as a product of current passing through an external resistor and voltage drop across this resistor. If the applied resistance is very low, then high instantaneous power generated by the cell is measured, which is not sustainable; the cell cannot deliver that much power for long periods of time. Since using small electrical resistors leads to erroneous assessment of the capabilities of microbial fuel cells, a question arises: what resistor should be used in such measurements? To address this question, we have defined the sustainable power as the steady state of power delivery by a microbial fuel cell under a given set of conditions and the maximum sustainable power as the highest sustainable power that a microbial fuel cell can deliver under a given set of conditions. Selecting the external resistance that is associated with the maximum sustainable power in a microbial fuel cell (MFC) is difficult because the operator has limited influence on the main factors that control power generation: the rate of charge transfer at the current-limiting electrode and the potential established across the fuel cell. The internal electrical resistance of microbial fuel cells varies, and it depends on the operational conditions of the fuel cell. We have designed an empirical procedure to predict the maximum sustainable power that can be generated by a microbial fuel cell operated under a given set of conditions. Following the procedure, we change the external resistors incrementally, in steps of 500 omega every 10, 60, or 180 s and measure the anode potential, the cathode potential, and the cell current. Power generated in the microbial fuel cell that we were using was limited by the anodic current. The anodic potential was used to determine the condition where the maximum sustainable power is obtained. The procedure is simple, microbial fuel cells can be characterized within an hour, and the results of the measurements can serve many purposes, such as: (1) estimating power generation in various MFCs, (2) comparing power generation in MFCs using different electroactive reactants, (3) quantifying the effects of the operational regime on the power generation in MFCs, and finally, (4) the purpose for which the procedure was designed, optimizing the performance of existing MFCs.

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/m 2). More extensive tests with a single-chambered air cathode MFC produced a maximum power density with the animal wastewater of 261 mW/m 2 (200 Ω resistor), which was 79% larger than that previously obtained with the same system using domestic wastewater (146±8 mW/m 2) 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 / m 2 (fixed 1000 Ω 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/m 2) than before treatment (96±4 mW/m 2). 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.

Production of Electricity from Acetate or Butyrate Using a Single-Chamber Microbial Fuel Cell

Hydrogen can be recovered by fermentation of organic material rich in carbohydrates, but much of the organic matter remains in the form of acetate and butyrate. An alternative to methane production from this organic matter is the direct generation of electricity in a microbial fuel cell (MFC). Electricity generation using a single-chambered MFC was examined using acetate or butyrate. Power generated with acetate (800 mg/L) (506 mW/m2 or 12.7 mW/ L) was up to 66% higher than that fed with butyrate (1000 mg/L) (305 mW/m2 or 7.6 mW/L), demonstrating that acetate is a preferred aqueous substrate for electricity generation in MFCs. Power output as a function of substrate concentration was well described by saturation kinetics, although maximum power densities varied with the circuit load. Maximum power densities and half-saturation constants were Pmax = 661 mW/m2 and Ks = 141 mg/L for acetate (218 ohms) and Pmax = 349 mW/m2 and Ks = 93 mg/L for butyrate (1000 ohms). Similar open circuit potentials were obtained in using acetate (798 mV) or butyrate (795 mV). Current densities measured for stable power outputwere higher for acetate (2.2 A/m2) than those measured in MFCs using butyrate (0.77 A/m2). Cyclic voltammograms suggested that the main mechanism of power production in these batch tests was by direct transfer of electrons to the electrode by bacteria growing on the electrode and not by bacteria-produced mediators. Coulombic efficiencies and overall energy recovery were 10-31 and 3-7% for acetate and 8-15 and 2-5% for butyrate, indicating substantial electron and energy losses to processes other than electricity generation. These results demonstrate that electricity generation is possible from soluble fermentation end products such as acetate and butyrate, but energy recoveries should be increased to improve the overall process performance.

Cathode performance as a factor in electricity generation in microbial fuel cells.

Although microbial fuel cells (MFCs) generate much lower power densities than hydrogen fuel cells, the characteristics of the cathode can also substantially affect electricity generation. Cathodes used for MFCs are often either Pt-coated carbon electrodes immersed in water that use dissolved oxygen as the electron acceptor or they are plain carbon electrodes in a ferricyanide solution. The characteristics and performance of these two cathodes were compared using a two-chambered MFC. Power generation using the Pt-carbon cathode and dissolved oxygen (saturated) reached a maximum of 0.097 mW within 120 h after inoculation (wastewater sludge and 20 mM acetate) when the cathode was equal size to the anode (2.5 x 4.5 cm). Once stable power was generated after replacing the MFC with fresh medium (no sludge), the Coulombic efficiency ranged from 63 to 78%. Power was proportional to the dissolved oxygen concentration in a manner consistent with Monod-type kinetics, with a half saturation constant of K(DO) = 1.74 mg of O2/L. Power increased by 24% when the cathode surface areas were increased from 22.5 to 67.5 cm2 and decreased by 56% when the cathode surface area was reduced to 5.8 cm2. Power was also substantially reduced (by 78% to 0.02 mW) if Pt was not used on the cathode. By using ferricyanide instead of dissolved oxygen, the maximum power increased by 50-80% versus that obtained with dissolved oxygen. This result was primarily due to increased mass transfer efficiencies and the larger cathode potential (332 mV) of ferricyanide than that obtained with dissolved oxygen (268 mV). A cathode potential of 804 mV (NHE basis) is theoretically possible using dissolved oxygen, indicating that further improvements in cathode performance with oxygen as the electron acceptor are possible that could lead to increased power densities in this type of MFC.

Production of electricity during wastewater treatment using a single chamber microbial fuel cell.

Microbial fuel cells (MFCs) have been used to produce electricity from different compounds, including acetate, lactate, and glucose. We demonstrate here that it is also possible to produce electricity in a MFC from domestic wastewater, while atthe same time accomplishing biological wastewater treatment (removal of chemical oxygen demand; COD). Tests were conducted using a single chamber microbial fuel cell (SCMFC) containing eight graphite electrodes (anodes) and a single air cathode. The system was operated under continuous flow conditions with primary clarifier effluent obtained from a local wastewater treatment plant. The prototype SCMFC reactor generated electrical power (maximum of 26 mW m(-2)) while removing up to 80% of the COD of the wastewater. Power output was proportional to the hydraulic retention time over a range of 3-33 h and to the influent wastewater strength over a range of 50-220 mg/L of COD. Current generation was controlled primarily by the efficiency of the cathode. Optimal cathode performance was obtained by allowing passive air flow rather than forced air flow (4.5-5.5 L/min). The Coulombic efficiency of the system, based on COD removal and current generation, was < 12% indicating a substantial fraction of the organic matter was lost without current generation. Bioreactors based on power generation in MFCs may represent a completely new approach to wastewater treatment. If power generation in these systems can be increased, MFC technology may provide a new method to offset wastewater treatment plant operating costs, making advanced wastewater treatment more affordable for both developing and industrialized nations.

A Generation of Microbial Fuel Cells with Current Outputs Boosted by More Than One Order of Magnitude

Ever-ready microbes: A microbial fuel cell (depicted) that continuously generates a current output more than one order of magnitude greater than known microbial fuel cells (up to 1.5 mA cm−2) is reported. The novel fuel cell concept uses polymer-modified catalytically active anodes that shuttle electrons from the bacterial suspension to the anode.

A Generation of Microbial Fuel Cells with Current Outputs Boosted by More Than One Order of Magnitude

A Generation of Microbial Fuel Cells with Current Outputs Boosted by More Than One Order of Magnitude

Electricity generation in microbial fuel cells using neutral red as an electronophore.

Neutral red (NR) was utilized as an electron mediator in microbial fuel cells consuming glucose to study both its efficiency during electricity generation and its role in altering anaerobic growth and metabolism of Escherichia coli and Actinobacillus succinogenes. A study of chemical fuel cells in which NADH, NR, and ferricyanide were the electron donor, the electronophore, and the electron acceptor, respectively, showed that electrical current produced from NADH was proportional to the concentration of NADH. Fourfold more current was produced from NADH in chemical fuel cells when NR was the electron mediator than when thionin was the electron mediator. In microbial fuel cells in which E. coli resting cells were used the amount of current produced from glucose when NR was the electron mediator (3.5 mA) was 10-fold more than the amount produced when thionin was the electron mediator (0.4 mA). The amount of electrical energy generated (expressed in joules per mole of substrate) and the amount of current produced from glucose (expressed in milliamperes) in NR-mediated microbial fuel cells containing either E. coli or A. succinogenes were about 10- and 2-fold greater, respectively, when resting cells were used than when growing cells were used. Cell growth was inhibited substantially when these microbial fuel cells were making current, and more oxidized end products were formed under these conditions. When sewage sludge (i.e., a mixed culture of anaerobic bacteria) was used in the fuel cell, stable (for 120 h) and equivalent levels of current were obtained with glucose, as observed in the pure-culture experiments. These results suggest that NR is better than other electron mediators used in microbial fuel cells and that sludge production can be decreased while electricity is produced in fuel cells. Our results are discussed in relation to factors that may improve the relatively low electrical efficiencies (1.2 kJ/mol) obtained with microbial fuel cells.

Multipartitioning of power system state estimation networks using simulated annealing

Microbial fuel cells (MFCs) present a novel method for simultaneous bioelectricity generation and wastewater treatment. In this study, an air–cathode MFC with membrane-electrode assembly was operated over three batch cycles (total of 160 days) and results indicated that molasses mixed sewage wastewater (high strength wastewater) containing 9978 mg/L of chemical oxygen demand (COD) could be used as substrate to produce bioelectricity with this system. Three different compositions of wastewater were used as substrate. The original wastewater, half-diluted wastewater and centrifuged wastewater were used as substrate in MFCs. Maximum voltage output of 762 mV and maximal power density of 382.5 mW/m2 (5.06 W/m3) were obtained with the original wastewater by the 14th day of operation. During this time the system evolved to 0.93 Ω cm−2 internal resistance and 59% removal of the total COD were achieved. Centrifuged wastewater showed poor performance in terms of power production (0.12 mW/m2 or 4.2 mW/m3), presumably due to organic substrate limitations. The MFC running on diluted wastewater showed a power density of 56.17 mW/m2 (2.25 mW/m3), with 70% COD removal. Energy-Dispersive X-ray spectroscopy (EDX) analysis, together with other characterization methods, confirmed the breakdown of organic compounds in the wastewater, EDX and Scanning Electron Microscopy (SEM) revealed the surface morphology of the materials utilized and showed the evolution in electrode and membrane composition after the long term MFC processes. Denaturing Gradient Gel Electrophoresis (DGGE) profiles showed the presence of mixed populations enclosing the electrochemically-active bacteria that established a biofilm on the anode surface and as such differed from the suspended bacterial community in the anode medium. These results demonstrate that complex wastewater can be used as a substrate for power generation in MFCs and also can be treated with high COD removal efficiencies.