Use of acetate for enrichment of electrochemically active microorganisms and their 16S rDNA analyses

A fuel cell-type electrochemical device has been used to enrich microbes oxidizing acetate with concomitant electricity generation without using an electron mediator from activated sludge. The device generated a stable current of around 5 mA with complete oxidation of 5 mM acetate at the hydraulic retention time of 2.5 h after 4 weeks of enrichment. Over 70% of electrons available from acetate oxidation was recovered as current. Carbon monoxide or hydrogen did not influence acetate oxidation or current generation from the microbial fuel cell (MFC). Denaturing gradient gel electrophoresis showed that DNA extracted from the acetate-enriched MFC had different 16S rDNA patterns from those of sludge or glucose+glutamate-enriched MFCs. Nearly complete 16S rDNA sequence analyses showed that diverse bacteria were enriched in the MFC fed with acetate. Electron microscopic observations showed biofilm developed on the electrode, but not microbial clumps observed in MFCs fed with complex fuel such as glucose and wastewater from a corn-processing factory.     

Electricity generation from carbon monoxide and syngas in a microbial fuel cell

Electricity generation in microbial fuel cells (MFCs) has been a subject of significant research efforts. MFCs employ the ability of electricigenic bacteria to oxidize organic substrates using an electrode as an electron acceptor. While MFC application for electricity production from a variety of organic sources has been demonstrated, very little research on electricity production from carbon monoxide and synthesis gas (syngas) in an MFC has been reported. Although most of the syngas today is produced from non-renewable sources, syngas production from renewable biomass or poorly degradable organic matter makes energy generation from syngas a sustainable process, which combines energy production with the reprocessing of solid wastes. An MFC-based process of syngas conversion to electricity might offer a number of advantages such as high Coulombic efficiency and biocatalytic activity in the presence of carbon monoxide and sulfur components. This paper presents a discussion on microorganisms and reactor designs that can be used for operating an MFC on syngas.     

Enhancement of coulombic efficiency and salt tolerance in microbial fuel cells by graphite/alginate granules immobilization of Shewanella oneidensis MR-1

Coulombic efficiency and stability of electricity output are crucial for practical applications of microbial fuel cells (MFCs). In this study, a cell immobilization method for electrogenic microorganism in MFCs using graphite/alginate granules is developed. The MFC with immobilized cell granules delivered a much more stable electricity output than that with suspension cells, and resulted in a ～0.8 to 1.7 times improvement on coulombic efficiency compared to the suspension mode. Impressively, with the conductive graphite/alginate/cells granules, the internal resistance of the MFC decreased dramatically. Moreover, the cell immobilized MFC showed a much higher tolerance to the shock of high salt concentration than the MFC with suspension cells. The results substantiated that immobilization of electrogenic microorganism for MFCs could be achieved by the method developed here, and it is promising for practical application in energy harvesting from wastewater by MFCs.     

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.     

Thionine increases electricity generation from microbial fuel cell using Saccharomyces cerevisiae and exoelectrogenic mixed culture

Microbial fuel cells (MFCs) have been shown to be capable of clean energy production through the oxidation of biodegradable organic waste using various bacterial species as biocatalysts. In this study we found Saccharomyces cerevisiae, previously known electrochemcially inactive or less active species, can be acclimated with an electron mediator thionine for electrogenic biofilm formation in MFC, and electricity production is improved with facilitation of electron transfer. Power generation of MFC was also significantly increased by thionine with both aerated and non-aerated cathode. With electrochemically active biofilm enriched with swine wastewater, MFC power increased more significantly by addition of thionine. The optimum mediator concentration was 500 mM of thionine with S. cerevisae in MFC with the maximum voltage and current generation in the microbial fuel cell were 420 mV and 700 mA/m(2), respectively. Cyclic voltametry shows that thionine improves oxidizing and reducing capability in both pure culture and acclimated biofilm as compared to non-mediated cell. The results obtained indicated that thionine has great potential to enhance power generation from unmediated yeast or electrochemically active biofilm in MFC.     

Removal of odors from Swine wastewater by using microbial fuel cells

A single-chamber microbial fuel cell (MFC) was used to reduce 10 chemicals associated with odors by 99.76% (from 422 +/- 23 mug/ml) and three volatile organic acids (acetate, butyrate, and propionate) by >99%. The MFC produced a maximum of 228 mW/m(2) and removed 84% of the organic matter in 260 h. MFCs were therefore effective at both treatment and electricity generation.     

New exoelectrogen Citrobacter sp. SX-1 isolated from a microbial fuel cell

Aims: Isolation, identification and characterization of a new exoelectrogenic bacterium from a microbial fuel cell (MFC). Methods and Results: Exoelectrogenic bacterial strain SX‐1 was isolated from a mediator‐less MFC by conventional plating techniques with ferric citrate as electron acceptor under anaerobic condition. Phylogenetic analysis of the 16S rDNA sequence revealed that it was related to the members of Citrobacter genus with Citrobacter sp. sdy‐48 being the most closely related species. The bacterial strain SX‐1 produced electricity from citrate, acetate, glucose, sucrose, glycerol and lactose in MFCs with the highest current density of 205 mA m^?2 generated from citrate. Cyclic voltammetry analysis indicated that membrane‐associated proteins may play an important role in facilitating the electrons transferring from bacteria to electrode. Conclusions: This is the first study that demonstrates that Citrobacter species can transfer electrons to extracellular electron acceptors. Citrobacter strain SX‐1 is capable of generating electricity from a wide range of substrates in MFCs. Significance and Impact of the Study: This finding increases the known diversity of power generating exoelectrogens and provided a new strain to explore the mechanisms of extracellular electron transfer from bacteria to electrode. The wide range of substrate utilization by SX‐1 increases the application potential of MFCs in renewable energy generation and waste treatment.     

Enhanced Coulombic efficiency in glucose-fed microbial fuel cells by reducing metabolite electron losses using dual-anode electrodes

Glucose-fed microbial fuel cells (MFCs) have displayed low Coulombic efficiency (CE); one reason for a low CE is metabolite generation, causing significant electron loss within MFC systems. In the present study, notable electron loss (15.83%) is observed in glucose-fed MFCs due to residual propionate, a glucose metabolite. In order to enhance the low CE caused by metabolite generation, a dual-anode MFC (DAMFC) is constructed, which are separately enriched by dissimilar substrates (glucose and propionate, respectively) to effectively utilize both glucose and propionate in one-anode chamber. In the DAMFC, propionate ceases to exist as a source of electron loss, and thus the CE increased from 33 ± 6 to 59 ± 4%.     

A state of the art review on microbial fuel cells: A promising technology for wastewater treatment and bioenergy

A microbial fuel cell (MFC) is a bioreactor that converts chemical energy in the chemical bonds in organic compounds to electrical energy through catalytic reactions of microorganisms under anaerobic conditions. It has been known for many years that it is possible to generate electricity directly by using bacteria to break down organic substrates. The recent energy crisis has reinvigorated interests in MFCs among academic researchers as a way to generate electric power or hydrogen from biomass without a net carbon emission into the ecosystem. MFCs can also be used in wastewater treatment facilities to break down organic matters. They have also been studied for applications as biosensors such as sensors for biological oxygen demand monitoring. Power output and Coulombic efficiency are significantly affected by the types of microbe in the anodic chamber of an MFC, configuration of the MFC and operating conditions. Currently, real-world applications of MFCs are limited because of their low power density level of several thousand mW/m2. Efforts are being made to improve the performance and reduce the construction and operating costs of MFCs. This article presents a critical review on the recent advances in MFC research with emphases on MFC configurations and performances.     

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.     

Glycerol-fed microbial fuel cell with a co-culture of <Emphasis Type="Italic">Shewanella oneidensis</Emphasis> MR-1 and <Emphasis Type="Italic">Klebsiella pneumonae</Emphasis> J2B

Glycerol is an attractive feedstock for bioenergy and bioconversion processes but its use in microbial fuel cells (MFCs) for electrical energy recovery has not been investigated extensively. This study compared the glycerol uptake and electricity generation of a co-culture of Shewanella oneidensis MR-1 and Klebsiella pneumonia J2B in a MFC with that of a single species inoculated counterpart. Glycerol was metabolized successfully in the co-culture MFC (MFC-J&M) with simultaneous electricity production but it was not utilized in the MR-1 only MFC (MFC-M). A current density of 10 mA/m² was obtained while acidic byproducts (lactate and acetate) were consumed in the co-culture MFC, whereas they are accumulated in the J2B-only MFC (MFC-J). MR-1 was distributed mainly on the electrode in MFC-J&M, whereas most of the J2B was observed in the suspension in the MFC-J reactor, indicating that the co-culture of both strains provides an ecological driving force for glycerol utilization using the electrode as an electron acceptor. This suggests that a co-culture MFC can be applied to electrical energy recovery from glycerol, which was previously known as a refractory substrate in a bioelectrochemical system.     

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.     

Performance and microbial diversity of palm oil mill effluent microbial fuel cell

Aim: To evaluate the bioenergy generation and the microbial community structure from palm oil mill effluent using microbial fuel cell. Methods and Results: Microbial fuel cells enriched with palm oil mill effluent (POME) were employed to harvest bioenergy from both artificial wastewater containing acetate and complex POME. The microbial fuel cell (MFC) showed maximum power density of 3004 mW m^?2 after continuous feeding with artificial wastewater containing acetate substrate. Subsequent replacement of the acetate substrate with complex substrate of POME recorded maximum power density of 622 mW m^?2. Based on 16S rDNA analyses, relatively higher abundance of Deltaproteobacteria (88·5%) was detected in the MFCs fed with acetate artificial wastewater as compared to POME. Meanwhile, members of Gammaproteobacteria, Epsilonproteobacteria and Betaproteobacteria codominated the microbial consortium of the MFC fed with POME with 21, 20 and 18·5% abundances, respectively. Conclusions: Enriched electrochemically active bacteria originated from POME demonstrated potential to generate bioenergy from both acetate and complex POME substrates. Further improvements including the development of MFC systems that are able to utilize both fermentative and nonfermentative substrates in POME are needed to maximize the bioenergy generation. Significance and Impact of the Study: A better understanding of microbial structure is critical for bioenergy generation from POME using MFC. Data obtained in this study improve our understanding of microbial community structure in conversion of POME to electricity.     

Power generation from cellulose using mixed and pure cultures of cellulose-degrading bacteria in a microbial fuel cell

Microbial fuel cells (MFCs) have been used to generate electricity from various organic compounds such as acetate, glucose, and lactate. We demonstrate here that electricity can be produced in an MFC using cellulose as the electron donor source. Tests were conducted using two-chambered MFCs, the anode medium was inoculated with mixed or pure culture of cellulose-degrading bacteria Nocardiopsis sp. KNU (S strain) or Streptomyces enissocaesilis KNU (K strain), and the catholyte in the cathode compartment was 50mM ferricyanide as catholyte. The power density for the mixed culture was 0.188mW (188mW/m(2)) at a current of 0.5mA when 1g/L cellulose was used. However, the power density decreased as the cellulose concentration in the anode compartment decreased. The columbic efficiencies (CEs) ranged from 41.5 to 33.4%, corresponding to an initial cellulose concentration of 0.1-1.0g/L. For the pure culture, cellobioase enzyme was added to increase the conversion of cellulose to simple sugars, since electricity production is very low. The power densities for S and K strain pure cultures with cellobioase were 162mW/m(2) and 145mW/m(2), respectively. Cyclic voltammetry (CV) experiments showed the presence of peaks at 380, 500, and 720mV vs. Ag/AgCl for the mixed bacterial culture, indicating its electrochemical activity without an external mediator. Furthermore, this MFC system employs a unique microbial ecology in which both the electron donor (cellulose) and the electron acceptor (carbon paper) are insoluble.     

Microbial fuel cells: novel biotechnology for energy generation

Microbial fuel cells (MFCs) provide new opportunities for the sustainable production of energy from biodegradable, reduced compounds. MFCs function on different carbohydrates but also on complex substrates present in wastewaters. As yet there is limited information available about the energy metabolism and nature of the bacteria using the anode as electron acceptor; few electron transfer mechanisms have been established unequivocally. To optimize and develop energy production by MFCs fully this knowledge is essential. Depending on the operational parameters of the MFC, different metabolic pathways are used by the bacteria. This determines the selection and performance of specific organisms. Here we discuss how bacteria use an anode as an electron acceptor and to what extent they generate electrical output. The MFC technology is evaluated relative to current alternatives for energy generation.     

Metabolites produced by <Emphasis Type="Italic">Pseudomonas</Emphasis> sp. enable a Gram-positive bacterium to achieve extracellular electron transfer

Previous studies revealed the abundance of Pseudomonas sp. in the microbial community of a microbial fuel cell (MFC). These bacteria can transfer electrons to the electrode via self-produced phenazine-based mediators. A MFC fed with acetate where several Pseudomonas sp. were present was found to be rich in a Gram-positive bacterium, identified as Brevibacillus sp. PTH1. Remarkably, MFCs operated with only the Brevibacillus strain in their anodes had poor electricity generation. Upon replacement of the anodic aqueous part of Brevibacillus containing MFCs with the cell-free anodic supernatants of MFCs operated with Pseudomonas sp. CMR12a, a strain producing considerable amounts of phenazine-1-carboxamide (PCN) and biosurfactants, the electricity generation was improved significantly. Supernatants of Pseudomonas sp. CMR12a_Reg, a regulatory mutant lacking the ability to produce PCN, had no similar improvement effect. Purified PCN, together with rhamnolipids as biosurfactants (1 mg L⁻¹), could clearly improve electricity generation by Brevibacillus sp. PTH1, as well as enable this bacterium to oxidize acetate with concomitant reduction of ferric iron, supplied as goethite (FeOOH). When added alone, PCN had no observable effects on Brevibacillus’ electron transfer. This work demonstrates that metabolites produced by Pseudomonas sp. enable Gram-positive bacteria to achieve extracellular electron transfer. Possibly, this bacterial interaction is a key process in the anodic electron transfer of a MFC, enabling Brevibacillus sp. PTH1 to achieve its dominance. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Isolation of the exoelectrogenic bacterium Ochrobactrum anthropi YZ-1 by using a U-tube microbial fuel cell

Exoelectrogenic bacteria have potential for many different biotechnology applications due to their ability to transfer electrons outside the cell to insoluble electron acceptors, such as metal oxides or the anodes of microbial fuel cells (MFCs). Very few exoelectrogens have been directly isolated from MFCs, and all of these organisms have been obtained by techniques that potentially restrict the diversity of exoelectrogenic bacteria. A special U-tube-shaped MFC was therefore developed to enrich exoelectrogenic bacteria with isolation based on dilution-to-extinction methods. Using this device, we obtained a pure culture identified as Ochrobactrum anthropi YZ-1 based on 16S rRNA gene sequencing and physiological and biochemical characterization. Strain YZ-1 was unable to respire using hydrous Fe(III) oxide but produced 89 mW/m(2) using acetate as the electron donor in the U-tube MFC. Strain YZ-1 produced current using a wide range of substrates, including acetate, lactate, propionate, butyrate, glucose, sucrose, cellobiose, glycerol, and ethanol. Like another exoelectrogenic bacterium (Pseudomonas aeruginosa), O. anthropi is an opportunistic pathogen, suggesting that electrogenesis should be explored as a characteristic that confers advantages to these types of pathogenic bacteria. Further applications of this new U-tube MFC system should provide a method for obtaining additional exoelectrogenic microorganisms that do not necessarily require metal oxides for cell respiration.     

Microfabricated Microbial Fuel Cell Arrays Reveal Electrochemically Active Microbes

Microbial fuel cells (MFCs) are remarkable “green energy” devices that exploit microbes to generate electricity from organic compounds. MFC devices currently being used and studied do not generate sufficient power to support widespread and cost-effective applications. Hence, research has focused on strategies to enhance the power output of the MFC devices, including exploring more electrochemically active microbes to expand the few already known electricigen families. However, most of the MFC devices are not compatible with high throughput screening for finding microbes with higher electricity generation capabilities. Here, we describe the development of a microfabricated MFC array, a compact and user-friendly platform for the identification and characterization of electrochemically active microbes. The MFC array consists of 24 integrated anode and cathode chambers, which function as 24 independent miniature MFCs and support direct and parallel comparisons of microbial electrochemical activities. The electricity generation profiles of spatially distinct MFC chambers on the array loaded with Shewanella oneidensis MR-1 differed by less than 8%. A screen of environmental microbes using the array identified an isolate that was related to Shewanella putrefaciens IR-1 and Shewanella sp. MR-7, and displayed 2.3-fold higher power output than the S. oneidensis MR-1 reference strain. Therefore, the utility of the MFC array was demonstrated.     

Enhancement of extracellular electron transfer and bioelectricity output by synthetic porin

The microbial fuel cell (MFC), is a promising environmental biotechnology for harvesting electricity energy from organic wastes. However, low bacterial membrane permeability of electron shuttles is a limiting factor that restricts the electron shuttle‐mediated extracellular electron transfer (EET) from bacteria to electrodes, thus the electricity power output of MFCs. To this end, we heterologously expressed a porin protein OprF from Pseudomonas aeruginosa PAO1 into Escherichia coli, which dramatically increased its membrane permeability, delivering a much higher current output in MFCs than its parental strain (BL21). We found that the oprF‐expression strain showed more efficient EET than its parental strain. More strikingly, the enhanced membrane permeability also rendered the oprF‐expression strain an efficient usage of riboflavin as the electron shuttle, whereas its parental strain was incapable of. Our results substantiated that membrane permeability is crucial for the efficient EET, and indicated that the expression of synthetic porins could be an efficient strategy to enhance bioelectricity generation by microorganisms (including electrogenic bacteria) in MFCs. Biotechnol. Bioeng. 2013; 110: 408–416. © 2012 Wiley Periodicals, Inc.     

Effect of static magnetic field on electricity production and wastewater treatment in microbial fuel cells

The effect of a magnetic field (MF) on electricity production and wastewater treatment in two-chamber microbial fuel cells (MFCs) has been investigated. Electricity production capacity could be improved by the application of a low-intensity static MF. When a MF of 50 mT was applied to MFCs, the maximum voltage, total phosphorus (TP) removal efficiency, and chemical oxygen demand (COD) removal efficiency increased from 523?±?2 to 553?±?2 mV, ～93 to ～96 %, and ～80 to >90 %, respectively, while the start-up time and coulombic efficiency decreased from 16 to 10 days and ～50 to ～43 %, respectively. The MF effects were immediate, reversible, and not long lasting, and negative effects on electricity generation and COD removal seemed to occur after the MF was removed. The start-up and voltage output were less affected by the MF direction. Nitrogen compounds in magnetic MFCs were nitrified more thoroughly; furthermore, a higher proportion of electrochemically inactive microorganisms were found in magnetic systems. TP was effectively removed by the co-effects of microbe absorption and chemical precipitation. Chemical precipitates were analyzed by a scanning electron microscope capable of energy-dispersive spectroscopy (SEM-EDS) to be a mixture of phosphate, carbonate, and hydroxyl compounds.