Electricity generation from cellulose by rumen microorganisms in microbial fuel cells

In microbial fuel cells (MFCs) bacteria generate electricity by mediating the oxidation of organic compounds and transferring the resulting electrons to an anode electrode. The objective of this study was to test the possibility of generating electricity with rumen microorganisms as biocatalysts and cellulose as the electron donor in two-compartment MFCs. The anode and cathode chambers were separated by a proton exchange membrane and graphite plates were used as electrodes. The medium in the anode chamber was inoculated with rumen microorganisms, and the catholyte in the cathode compartment was ferricyanide solution. Maximum power density reached 55 mW/m(2) (1.5 mA, 313 mV) with cellulose as the electron donor. Cellulose hydrolysis and electrode reduction were shown to support the production of current. The electrical current was sustained for over 2 months with periodic cellulose addition. Clarified rumen fluid and a soluble carbohydrate mixture, serving as the electron donors, could also sustain power output. Denaturing gradient gel electrophoresis (DGGE) of PCR amplified 16S rRNA genes revealed that the microbial communities differed when different substrates were used in the MFCs. The anode-attached and the suspended consortia were shown to be different within the same MFC. Cloning and sequencing analysis of 16S rRNA genes indicated that the most predominant bacteria in the anode-attached consortia were related to Clostridium spp., while Comamonas spp. abounded in the suspended consortia. The results demonstrated that electricity can be generated from cellulose by exploiting rumen microorganisms as biocatalysts, but both technical and biological optimization is needed to maximize power output.     

Power production in MFCs inoculated with Shewanella oneidensis MR‐1 or mixed cultures

Power densities and oxidation–reduction potentials (ORPs) of MFCs containing a pure culture of Shewanella oneidensis MR‐1 were compared to mixed cultures (wastewater inoculum) in cube shaped, 1‐, 2‐, and 3‐bottle batch‐fed MFC reactor configurations. The reactor architecture influenced the relative power produced by the different inocula, with the mixed culture generating 68–480% more power than MR‐1 in each MFC configuration. The mixed culture produced the maximum power density of 858 ± 9 mW m^?2 in the cubic MFC, while MR‐1 produced 148 ± 20 mW m^?2. The higher power by the mixed culture was primarily a result of lower internal resistances than those produced by the pure culture. Power was a direct function of ohmic resistance for the mixed culture, but not for strain MR‐1. ORP of the anode compartment varied with reactor configuration and inoculum, and it was always negative during maximum power production but it did not vary in proportion to power output. The ORP varied primarily at the end of the cycle when substrate was depleted, with a change from a reductive environment during maximum power production (approximately ?175 mV for mixed and approximately ?210 mV for MR‐1 in cubic MFCs), to an oxidative environment at the end of the batch cycle (～250 mV for mixed and ～300 mV for MR‐1). Mixed cultures produced more power than MR‐1 MFCs even though their redox potential was less negative. These results demonstrate that differences between power densities produced by pure and mixed cultures depend on the MFC architecture. Biotechnol. Bioeng. 2010; 105: 489–498. © 2009 Wiley Periodicals, Inc.     

Bioelectricity production from wastewater treatment in dual chambered microbial fuel cell (MFC) using selectively enriched mixed microflora: Effect of catholyte

The performance of aerated and ferricyanide catholytes on the bioelectricity production was evaluated in dual chambered microbial fuel cell (MFC) (mediatroless anode; graphite electrodes) employing selectively enriched H(2) producing mixed consortia as anodic inoculum. Two MFCs with aerated catholyte (MFC(AC)) and ferricyanide catholyte (MFC(FC)) were operated separately to elucidate the difference in power generation potential and carbon removal efficiency under similar operating conditions [ambient pressure; room temperature (28+/-2 degrees C); acidophilic microenvironment (pH 6)]. The experimental data demonstrated the feasibility of in situ bioelectricity generation along with wastewater treatment. Effective power generation and substrate removal efficiency was documented in the fuel cell operated with ferricyanide catholyte (586 mV; 2.37 mA; 0.559 kg COD/m(3) day) than aerated catholyte (572 mV; 1.68 mA; 0.464 kg COD/m(3) day). Maximum power yield (0.635 W/kg COD(R) and 0.440 W/kg COD(R)) and current density (222.59 mA/m(2) and 190.28 mA/m(2)) was observed at 100 Omega resistor with ferricyanide and aerated catholytes, respectively. The study documented both wastewater treatment and electricity production through direct conversion of H(2) in a single system.     

微生物燃料电池中脱色希瓦氏菌S12的产电特性研究

为了确定脱色希瓦氏菌S12的电化学活性,采用循环伏安法(cyclic voltammograms, CV)对厌氧培养的菌株S12进行曲线扫描,所得曲线表明S12具有一定的电化学活性,可以用来进行产电实验.研究了不同电子供体和供体浓度对菌株S12产电的影响,结果表明,以浓度为10mmol/L的不同有机酸(甲酸钠、乳酸钠和丙酮酸钠)分别作为电子供体时,乳酸钠产电量最大,其最大功率密度Pmax为21.93mW/m2增加乳酸钠的浓度,菌株S12的产电量也相应增加,当乳酸钠的浓度为20mmol/L时,所产生的最大功率密度达55.72 mW/m2.     

微生物燃料电池中脱色希瓦氏菌S12的产电特性研究

为了确定脱色希瓦氏菌S12的电化学活性, 采用循环伏安法(cyclic voltammograms, CV)对厌氧培养的菌株S12进行曲线扫描, 所得曲线表明S12具有一定的电化学活性, 可以用来进行产电实验。研究了不同电子供体和供体浓度对菌株S12产电的影响, 结果表明, 以浓度为10 mmol/L 的不同有机酸(甲酸钠、乳酸钠和丙酮酸钠)分别作为电子供体时, 乳酸钠产电量最大, 其最大功率密度Pmax为21.93 mW/m2, 增加乳酸钠的浓度, 菌株S12的产电量也相应增加, 当乳酸钠的浓度为20 mmol/L时, 所产生的最大功率密度达55.72 mW/m2。     

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.     

Electricity generation using a baffled microbial fuel cell convenient for stacking

To make sure that microbial fuel cells (MFCs) are more convenient to stack, a baffled single-chambered MFC with two groups of electrodes sharing only one anode chamber was designed and the performance was examined. The experiments showed that the prototype MFC generated electrical power (maximum of 133 mW/m(2)) while removing up to 88% of chemical oxygen demand (COD) in 91 h. Volumetric power increased as electrode area per anode compartment volume increased, indicating that the MFC with two groups of electrodes was better than that with one group. Power density as a function of wastewater concentration was modeled according to saturation kinetics, with a maximum power density of P(max)=164 mW/m(2) (fixed 100 Omega resistor) and half-saturation concentration of K(s)=259 mg/l. The hydraulic retention time (HRT) was examined as a factor influencing the power generation. When it was 15.5h, the voltage and the power density reached the maximum 0.413 V and 108 mW/m(2).     

Electricity generation from glucose by a Klebsiella sp. in microbial fuel cells

As electrochemically active bacteria play an important role in microbial fuel cells (MFCs), it is necessary to get a comprehensive understanding of their electrogenesis mechanisms. In this study, a new electrochemically active bacterium, Klebsiella sp. ME17, was employed into an “H” typed MFC for electrogenesis, with glucose as the electron donor. The maximum power density was 1,209 mW/m² at a resistance of 340 Ω and the maximum current was 1.47 mA. Given the original anode medium, fresh medium, and the supernatant of the anode medium in the same MFC, respectively, the polarization curves illustrated that the strain produced mediators to promote extracellular electron transfer. The anode medium supernatant was electrochemically active, based on cyclic voltammogram, and the supernatant was very likely to contain quinone-like substances, as indicated by spectrophotometric and excitation–emission matrix fluorescence spectroscopy analysis. Further investigation on the color and ultraviolet absorbance at 254 nm of the filtered anode medium showed that the redox states of mediators strongly associated with the electricity generation states in MFCs.     

Continuous electricity production from artificial wastewater using a mediator-less microbial fuel cell

A microbial fuel cell (MFC) was optimized in terms of MFC design factors and operational parameters for continuous electricity production using artificial wastewater (AW). The performance of MFC was analyzed through the polarization curve method under different conditions using a mediator-less MFC. The highest power density of 0.56 W/m2 was achieved with AW of 300 mg/l fed at the rate of 0.53 ml/min at 35 degrees C. The power per unit cell working volume was 102 mW/l, which was over 60 times higher than those reported in the previous mediator-less MFCs which did not use a cathode or an anode mediator. The power could be stably generated over 2 years.     

Effect of enrichment procedures on performance and microbial diversity of microbial fuel cell for Congo red decolorization and electricity generation

The purpose of this study was to determine the effect of enrichment procedure on the performance and microbial diversity of an air-cathode microbial fuel cell (MFC) which was explored for simultaneous azo dye decolorization and electricity generation. Two different enrichment procedures in which glucose and Congo red were added into the MFCs sequentially (EP1) or simultaneously (EP2) were tested by operating parallel MFCs independently for more than 6 months. The power density, electrode potential, Congo red decolorization, biofilm morphology, and bacterial diversity of the MFCs under the two enrichment procedures were compared and investigated. The results showed that the enrichment procedures have a negligible effect on the dye decolorization, but significantly affected the electricity generation. More than 90% decolorization at dye concentration of 300 mg/L was achieved within 170 h for the two tested enrichment procedures. However, the MFC with EP2 achieved a maximum power density of 192 mW/m², which was 75% higher than that of the MFC with EP1 (110 mW/m²). The depressed surfaces of the bacteria in the MFC with EP1 indicated the allergic response caused by the subsequent addition of Congo red. 16S rRNA sequencing analysis demonstrated a phylogenetic diversity in the communities of the anode biofilm and showed clear differences between the anode-attached populations in the MFCs with a different enrichment procedure. This study suggests that the enrichment procedure is important for the MFC explored for simultaneous dye decolorization and electricity generation.     

A comparison of air and hydrogen peroxide oxygenated microbial fuel cell reactors

In this study, a two-compartment continuous flow microbial fuel cell (MFC) reactor was used to compare the efficiencies of cathode oxygenation by air and by hydrogen peroxide. The MFC reactor had neither a proton-selective membrane nor an electron transfer mediator. At startup, the cathodic compartment was continuously aerated and the anodic compartment was fed with a glucose solution. An increase of electrical power generation from 0.008 to 7.2 mW m(-2) of anode surface with a steady-state potential of 215-225 mV was observed within a period of 12 days. The performance of the air-oxygenated MFC reactor progressively declined over time because of biofilm proliferation in the cathodic compartment. Oxygenation of the cathodic compartment using 300 mL d(-1) of 0.3% hydrogen peroxide solution resulted in a power density of up to 22 mW m(-2) (68.2 mA m(-2)) of anode surface at a potential of 340-350 mV. The use of H2O2 for oxygenation was found to improve the long-term stability of the MFC reactor.     

Electrochemical analysis of Clostridium propionicum and its acrylic acid production in microbial fuel cells

Currently, acrylic acid is produced at a low yield by the resting cells of Clostridium propionicum with the supplement of extra electron acceptors. As an alternative way, acrylic acid production coupled with electricity generation was achieved by C. propionicum‐based microbial fuel cells (MFCs). Electricity was generated in the salt‐bridge MFCs with cysteine and resazurin in the anode chamber as mediators, and K₃Fe(CN)₆ as the cathode electron acceptor. Power generation was 21.78 mW/m² with an internal resistance of 9809 Ω. Cyclic voltammograms indicated the main mechanism of power production was the electron transfer facilitated by mediators in the system. In the salt‐bridge MFC system, 0.694 mM acrylic acid was produced together with electricity generation.     

Layer-by-layer construction of graphene-based microbial fuel cell for improved power generation and methyl orange removal

Development of highly efficient anode is critical for enhancing the power output of microbial fuel cells (MFCs). The aim of this work is to investigate whether modification of carbon paper (CP) anode with graphene (GR) via layer-by-layer assembly technique is an effective approach to promote the electricity generation and methyl orange removal in MFCs. Using cyclic voltammetry and electrochemical impedance spectroscopy, the GR/CP electrode exhibited better electrochemical behavior. Scanning electron microscopy results revealed that the surface roughness of GR/CP increased, which was favorable for more bacteria to attach to the anode surface. The MFCs equipped with GR/CP anode achieved a stable maximum power density of 368 mW m^?2 under 1,000 Ω external resistance and a start time for the initial maximum voltage of 180 h, which were, respectively, 51 % higher and 31 % shorter than the corresponding values of the MFCs with blank anode. The anode and cathode polarization curves revealed negligible difference in cathode potentials but obviously difference in anode potentials, indicating that the GR-modified anode other than the cathode was responsible for the performance improvement of MFC. Meanwhile, compared with MFCs with blank anode, 11 % higher decolorization efficiency and 16 % higher the chemical oxygen demand removal rate were achieved in MFC with GR-modified anode during electricity generation. This study might provide an effective way to modify the anode for enhanced electricity generation and efficient removal of azo dye in MFCs.     

Effect of conductive polymers coated anode on the performance of microbial fuel cells (MFCs) and its biodiversity analysis

Conductive polymer, one of the most attractive electrode materials, has been applied to coat anode of MFC to improve its performance recently. In this paper, two conductive polymer materials, polyaniline (PANI) and poly(aniline-co-o-aminophenol) (PAOA) were used to modify carbon felt anode and physical and chemical properties of the modified anodes were studied. The power output and biodiversity of modified anodes, along with unmodified carbon anode were compared in two-chamber MFCs. Results showed that the maximum power density of PANI and PAOA MFC could reach 27.4 mW/m(2) and 23.8 mW/m(2), comparing with unmodified MFC, increased by 35% and 18% separately. Low temperature caused greatly decrease of the maximum voltage by 70% and reduced the sorts of bacteria on anodes in the three MFCs. Anode biofilm analysis showed different bacteria enrichment: a larger mount of bacteria and higher biodiversity were found on the two modified anodes than on the unmodified one. For PANI anode, the two predominant bacteria were phylogenetically closely related to Hippea maritima and an uncultured clone MEC_Bicarb_Ac-008; for PAOA, Clostridiales showed more enrichment. Compare PAOA with PANI, the former introduced phenolic hydroxyl group by copolymerization o-aminophenol with aniline, which led to a different microbial community and the mechanism of group effect was proposed.     

An electricity-generating prosthecate bacterium strain Mfc52 isolated from a microbial fuel cell

Rod-shaped Alphaproteobacteria possessing long prosthecae-like appendages have been detected abundantly in biofilms attaching onto anode graphite of cellulose-fed microbial fuel cells (MFCs). To identify their ecological roles, the present study isolated a corresponding bacterium (strain Mfc52) by direct plating of a biofilm suspension onto a solid medium containing glucose and ferric ion. Phylogenetic analysis revealed that this strain is deeply branched in the class Alphaproteobacteria and may represent a novel order. Strain Mfc52 fermented sugars and produced lactate, acetate, and fumarate, whereas ferric ion stimulated the growth on glucose. When an MFC was inoculated with this strain and supplemented with glucose, it fermented glucose and generated electricity by oxidizing organic acids produced from glucose. Electron micrographs showed that a fraction of cells in a liquid culture had prosthecae-like appendages that were abundantly observed in anode biofilm. These observations suggest that the bacterial population represented by strain Mfc52 shared an important niche in the cellulose-fed MFC, where it generated electricity by oxidizing intermediate metabolites from cellulose degradation.     

Isolation of the exoelectrogenic denitrifying bacterium Comamonas denitrificans based on dilution to extinction

The anode biofilm in a microbial fuel cell (MFC) is composed of diverse populations of bacteria, many of whose capacities for electricity generation are unknown. To identify functional populations in these exoelectrogenic communities, a culture-dependent approach based on dilution to extinction was combined with culture-independent community analysis. We analyzed the diversity and dynamics of microbial communities in single-chamber air-cathode MFCs with different anode surfaces using denaturing gradient gel electrophoresis based on the 16S rRNA gene. Phylogenetic analyses showed that the bacteria enriched in all reactors belonged primarily to five phylogenetic groups: Firmicutes, Actinobacteria, α-Proteobacteria, β-Proteobacteria, and γ-Proteobacteria. Dilution-to-extinction experiments further demonstrated that Comamonas denitrificans and Clostridium aminobutyricum were dominant members of the community. A pure culture isolated from an anode biofilm after dilution to extinction was identified as C. denitrificans DX-4 based on 16S rRNA sequence and physiological and biochemical characterizations. Strain DX-4 was unable to respire using hydrous Fe(III) oxide but produced 35 mW/m² using acetate as the electron donor in an MFC. Power generation by the facultative C. denitrificans depends on oxygen and MFC configuration, suggesting that a switch of metabolic pathway occurs for extracellular electron transfer by this denitrifying bacterium.     

Sustained generation of electricity by the spore-forming,Gram-positive, <Emphasis Type="Italic">Desulfitobacterium hafniense</Emphasis> strain DCB2

Desulfitobacterium hafniense strain DCB2 generates electricity in microbial fuel cells (MFCs) when humic acids or the humate analog anthraquinone-2,6-disulfonate (AQDS) is added as an electron-carrying mediator. When utilizing formate as fuel, the Gram-positive, spore-forming bacterium generated up to 400 mW/m² of cathode surface area in a single-chamber MFC with a platinum-containing air-fed cathode. Hydrogen, lactate, pyruvate, and ethanol supported electricity generation, but acetate, propionate, and butyrate did not. Scanning electron microscopy indicated that strain DCB2 colonized the surface of a current-generating anode but not of an unconnected electrode. The electricity was recovered fully within minutes after the exchange of the medium in the anode chamber and within a week after an exposure of a colonized anode to 90°C for 20 min. Of the six strains of Desulfitobacteria tested, all of which would reduce AQDS, only D. hafniense strain DCB2 continued to reduce AQDS and generate electricity for more than 24 h, indicating that reduction of the humate analog alone is insufficient to sustain electrode reduction.     

Use of Pseudomonas species producing phenazine-based metabolites in the anodes of microbial fuel cells to improve electricity generation

The rate of anodic electron transfer is one of the factors limiting the performance of microbial fuel cells (MFCs). It is known that phenazine-based metabolites produced by Pseudomonas species can function as electron shuttles for Pseudomonas themselves and also, in a syntrophic association, for Gram-positive bacteria. In this study, we have investigated whether phenazine-based metabolites and their producers could be used to improve the electricity generation of a MFC operated with a mixed culture. Both anodic supernatants obtained from MFCs operated with a Pseudomonas strain (P-PCA) producing phenazine-1-carboxylic acid (PCA) and those from MFCs operated with a strain (P-PCN) producing phenazine-1-carboxamide (PCN) exerted similarly positive effects on the electricity generation of a mixed culture. Replacing supernatants of MFCs operated with a mixed culture with supernatants of MFCs operated with P-PCN could double the currents generated. Purified PCA and purified PCN had similar effects. If the supernatant of an engineered strain overproducing PCN was used, the effect could be maintained over longer time courses, resulting in a 1.5-fold increase in the production of charge. Bioaugmentation of the mixed culture MFCs using slow release tubes containing P-PCN not only doubled the currents but also maintained the effect over longer periods. The results demonstrated the electron-shuttling effect of phenazine-based compounds produced by Pseudomonas species and their capacity to improve the performance of MFCs operated with mixed cultures. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

The effect of flavin electron shuttles in microbial fuel cells current production

The effect of electron shuttles on electron transfer to microbial fuel cell (MFC) anodes was studied in systems where direct contact with the anode was precluded. MFCs were inoculated with Shewanella cells, and flavins used as the electron shuttling compound. In MFCs with no added electron shuttles, flavin concentrations monitored in the MFCs' bulk liquid increased continuously with FMN as the predominant flavin. The maximum concentrations were 0.6 μM for flavin mononucleotide and 0.2 μM for riboflavin. In MFCs with added flavins, micro-molar concentrations were shown to increase current and power output. The peak current was at least four times higher in MFCs with high concentrations of flavins (4.5–5.5 μM) than in MFCs with low concentrations (0.2–0.6 μM). Although high power outputs (around 150 mW/m²) were achieved in MFCs with high concentrations of flavins, a Clostridium-like bacterium along with other reactor limitations affected overall coulombic efficiencies (CE) obtained, achieving a maximum CE of 13%. Electron shuttle compounds (flavins) permitted bacteria to utilise a remote electron acceptor (anode) that was not accessible to the cells allowing current production until the electron donor (lactate) was consumed.     

Electricity generation and microbial community analysis of alcohol powered microbial fuel cells

Two different microbial fuel cell (MFC) configurations were investigated for electricity production from ethanol and methanol: a two-chambered, aqueous-cathode MFC; and a single-chamber direct-air cathode MFC. Electricity was generated in the two-chamber system at a maximum power density typical of this system (40+/-2 mW/m2) and a Coulombic efficiency (CE) ranging from 42% to 61% using ethanol. When bacteria were transferred into a single-chamber MFC known to produce higher power densities with different substrates, the maximum power density increased to 488+/-12 mW/m2 (CE = 10%) with ethanol. The voltage generated exhibited saturation kinetics as a function of ethanol concentration in the two-chambered MFC, with a half-saturation constant (Ks) of 4.86 mM. Methanol was also examined as a possible substrate, but it did not result in appreciable electricity generation. Analysis of the anode biofilm and suspension from a two-chamber MFC with ethanol using 16S rDNA-based techniques indicated that bacteria with sequences similar to Proteobacterium Core-1 (33.3% of clone library sequences), Azoarcus sp. (17.4%), and Desulfuromonas sp. M76 (15.9%) were significant members of the anode chamber community. These results indicate that ethanol can be used for sustained electricity generation at room temperature using bacteria on the anode in a MFC.