Biotic conversion of sulphate to sulphide and abiotic conversion of sulphide to sulphur in a microbial fuel cell using cobalt oxide octahedrons as cathode catalyst

Varying chemical oxygen demand (COD) and sulphate concentrations in substrate were used to determine reaction kinetics and mass balance of organic matter and sulphate transformation in a microbial fuel cell (MFC). MFC with anodic chamber volume of 1 L, fed with wastewater having COD of 500 mg/L and sulphate of 200 mg/L, could harvest power of 54.4 mW/m², at a Coulombic efficiency of 14%, with respective COD and sulphate removals of 90 and 95%. Sulphide concentration, even up to 1500 mg/L, did not inhibit anodic biochemical reactions, due to instantaneous abiotic oxidation to sulphur, at high inlet sulphate. Experiments on abiotic oxidation of sulphide to sulphur revealed maximum oxidation taking place at an anodic potential of −200 mV. More than 99% sulphate removal could be achieved in a MFC with inlet COD/sulphate of 0.75, giving around 1.33 kg/m³ day COD removal. Bioelectrochemical conversion of sulphate facilitating sulphur recovery in a MFC makes it an interesting pollution abatement technique.

     

Development of Enterobacter aerogenes fuel cells: From in situ biohydrogen oxidization to direct electroactive biofilm

This study described an Enterobacter aerogenes-catalyzed microbial fuel cell (MFC) with a carbon-based anode that exhibited a maximum power density of 2.51 W/m³ in the absence of artificial electron mediators. The MFC was started up rapidly, within hours, and the current generation in the early stage was demonstrated to result from in situ oxidation of biohydrogen produced by E. aerogenes during glucose fermentation. Over periodic replacement of substrate, both planktonic biomass in the culture liquid and hydrogen productivity decreased, while increased power density and coulombic efficiency and decreased internal resistance were unexpectedly observed. Using scanning electron microscopy and cyclic voltammetry, it was found that the enhanced MFC performance was associated with the development of electroactive biofilm on the anodic surface, proposed to involve an acclimation and selection process of E. aerogenes cells under electrochemical tension. The significant advantage of rapid start-up and the ability to develop an electroactive biofilm identifies E. aerogenes as a suitable biocatalyst for MFC applications.     

A microfluidic microbial fuel cell fabricated by soft lithography

Here we report a new microfluidic microbial fuel cell (MFC) platform built by soft-lithography techniques. The MFC design includes a unique sub-5 μL polydimethylsiloxane soft chamber featuring carbon cloth electrodes and microfluidic delivery of electrolytes. Bioelectricity was generated using Shewanella oneidensis MR-1 cultivated on either complex organic substrates or lactate-based minimal medium. These micro-MFCs exhibited fast start-ups, reproducible current generation, and enhanced power densities up to 62.5 W m⁻³ that represents the best result for sub-100 μL MFCs. Systematic comparisons of custom-made MFC reactors having different chamber sizes indicate volumetric power density is inversely correlated with chamber size in our systems: i.e., the smaller the chamber, the higher the power density is achieved.     

Simultaneous degradation of refractory contaminants in both the anode and cathode chambers of the microbial fuel cell

In this study, the microbial fuel cell (MFC) was combined with the Fenton-like technology to simultaneously generate electricity and degrade refractory contaminants in both anode and cathode chambers. The maximum power density achieved was 15.9 W/m³ at an initial pH of 3.0 in the MFC. In the anode chamber, approximately 100% of furfural and 96% COD were removed at the end of a cycle. In the cathode chamber, the Fenton-like reaction with FeVO₄ as a catalyst enhanced the removal of AO7 and COD. The removal rates of AO7 and COD reached 89% and 81%, respectively. The optimal pH value and FeVO₄ dosage toward degrading AO7 were about 3.0 and 0.8 g, respectively. Furthermore, a two-way catalyst mechanism of FeVO₄ and the contaminant degradation pathway in the MFC were explored.     

Enhanced Cathodic Oxygen Reduction and Power Production of Microbial Fuel Cell Based on Noble‐Metal‐Free Electrocatalyst Derived from Metal‐Organic Frameworks

Microbial fuel cell (MFC) can generate electricity from organic substances based on anodic electrochemically active microorganisms and cathodic oxygen reduction reaction (ORR), thus exhibiting promising potential for harvesting electric energy from organic wastewater. The ORR performance is crucial to both power production efficiency and overall cost of MFC. A new type of metal‐organic‐framework‐derived electrocatalysts containing cobalt and nitrogen‐doped carbon (CoNC) is developed, which is effective to enhance activity, selectivity, and stability toward four‐electron ORR in pH‐neutral electrolyte. When glucose is used as the substrate, the maximum power density of 1665 mW m^?2 is achieved for the optimized CoNC pyrolyzed at 900 °C, which is 39.8% higher than that of 1191 mW m^?2 for commercial Pt/C catalyst in the single‐chamber MFC. The improved performance of CoNC catalyst can be attributed to large surface area, microporous nature, and the involvement of nitrogen‐coordinated cobalt species. These properties enable the efficient ORR by increasing the active sites and enhancing mass transfer of oxygen and protons at “water‐flooding” three‐phase boundary where ORR occurs. This work provides a proof‐of‐concept demonstration of a noble‐metal‐free high‐efficiency and cost‐effective ORR electrocatalyst for effective recovery of electricity from biomass materials and organic wastewater in MFC.     

Acetate oxidation by syntrophic association between Geobacter sulfurreducens and a hydrogen-utilizing exoelectrogen

Anodic microbial communities in acetate-fed microbial fuel cells (MFCs) were analyzed using stable-isotope probing of 16S rRNA genes followed by denaturing gradient gel electrophoresis. The results revealed that Geobacter sulfurreducens and Hydrogenophaga sp. predominated in the anodic biofilm. Although the predominance of Geobacter sp. as acetoclastic exoelectrogens in acetate-fed MFC systems has been often reported, the ecophysiological role of Hydrogenophaga sp. is unknown. Therefore, we isolated and characterized a bacterium closely related to Hydrogenophaga sp. (designated strain AR20). The newly isolated strain AR20 could use molecular hydrogen (H₂), but not acetate, with carbon electrode as the electron acceptor, indicating that the strain AR20 was a hydrogenotrophic exoelectrogen. This evidence raises a hypothesis that acetate was oxidized by G. sulfurreducens in syntrophic cooperation with the strain AR20 as a hydrogen-consuming partner in the acetate-fed MFC. To prove this hypothesis, G. sulfurreducens strain PCA was cocultivated with the strain AR20 in the acetate-fed MFC without any dissolved electron acceptors. In the coculture MFC of G. sulfurreducens and strain AR20, current generation and acetate degradation were the highest, and the growth of strain AR20 was observed. No current generation, acetate degradation and cell growth occurred in the strain AR20 pure culture MFC. These results show for the first time that G. sulfurreducens can oxidize acetate in syntrophic cooperation with the isolated Hydrogenophaga sp. strain AR20, with electrode as the electron acceptor.     

Factors affecting current production in microbial fuel cells using different industrial wastewaters

This study evaluated how different types of industrial wastewaters (bakery, brewery, paper and dairy) affect the performance of identical microbial fuel cells (MFCs); and the microbial composition and electrochemistry of MFC anodes. MFCs fed with paper wastewater produced the highest current density (125 ± 2 mA/m²) at least five times higher than dairy (25 ± 1 mA/m²), brewery and bakery wastewaters (10 ± 1 mA/m²). Such high current production was independent of substrate degradability. A comprehensive study was conducted to determine the factor driving current production when using the paper effluent. The microbial composition of anodic biofilms differed according to the type of wastewater used, and only MFC anodes fed with paper wastewater showed redox activity at −134 ± 5 mV vs NHE. Electrochemical analysis of this redox activity indicated that anodic bacteria produced a putative electron shuttling compound that increased the electron transfer rate through diffusion, and as a result the overall MFC performance.     

Enhancement of electricity production in a mediatorless air–cathode microbial fuel cell using <Emphasis Type="Italic">Klebsiella</Emphasis> sp. IR21

A novel dissimilatory iron-reducing bacteria, Klebsiella sp. IR21, was isolated from the anode biofilm of an MFC reactor. Klebsiella sp. IR21 reduced 27.8 % of ferric iron to ferrous iron demonstrating that Klebsiella sp. IR21 has electron transfer ability. Additionally, Klebsiella sp. IR21 generated electricity forming a biofilm on the anode surface. When a pure culture of Klebsiella sp. IR21 was supplied into a single chamber, air–cathode MFC fed with a mixture of glucose and acetate (500 mg L^?1 COD), 40–60 mV of voltage (17–26 mA m^?2 of current density) was produced. Klebsiella sp. IR21 was also utilized as a biocatalyst to improve the electrical performance of a conventional MFC reactor. A single chamber, air–cathode MFC was fed with reject wastewater (10,000 mg L^?1 COD) from a H₂ fermentation reactor. The average voltage, current density, and power density were 142.9 ± 25.74 mV, 60.5 ± 11.61 mA m^?2, and 8.9 ± 3.65 mW m^?2, respectively, in the MFC without inoculation of Klebsiella sp. IR21. However, these electrical performances of the MFC were significantly increased to 204.7 ± 40.24 mV, 87.5 ± 17.20 mA m^?2, and 18.6 ± 7.23 mW m^?2, respectively, with inoculation of Klebsiella sp. IR21. The results indicate that Klebsiella sp. IR21 can be utilized as a biocatalyst for enhancement of electrical performance in MFC systems.     

Electricity generation using chocolate industry wastewater and its treatment in activated sludge based microbial fuel cell and analysis of developed microbial community in the anode chamber

Feasibility of using chocolate industry wastewater as a substrate for electricity generation using activated sludge as a source of microorganisms was investigated in two-chambered microbial fuel cell. The maximum current generated with membrane and salt bridge MFCs was 3.02 and 2.3 A/m², respectively, at 100 Ω external resistance, whereas the maximum current generated in glucose powered MFC was 3.1 A/m². The use of chocolate industry wastewater in cathode chamber was promising with 4.1 mA current output. Significant reduction in COD, BOD, total solids and total dissolved solids of wastewater by 75%, 65%, 68%, 50%, respectively, indicated effective wastewater treatment in batch experiments. The 16S rDNA analysis of anode biofilm and suspended cells revealed predominance of β-Proteobacteria clones with 50.6% followed by unclassified bacteria (9.9%), α-Proteobacteria (9.1%), other Proteobacteria (9%), Planctomycetes (5.8%), Firmicutes (4.9%), Nitrospora (3.3%), Spirochaetes (3.3%), Bacteroides (2.4%) and γ-Proteobacteria (0.8%). Diverse bacterial groups represented as members of the anode chamber community.     

Characterization of bacterial communities in anode microbial fuel cells fed with glucose,propyl alcohol and methanol

Bacterial communities in anode microbial fuel cells (MFC) obtained from anaerobic digester sludge in a municipal wastewater treatment plant (Nanjing, China) were investigated. Glucose, propyl alcohol and methanol were used as sole carbon source in two-chamber MFC. The results showed that a reproducible cycle of power production can be formed in MFC fed with 3 substrates and glucose-fed MFC had the highest peak power density of 1499 ± 33 mW/m³, followed by methanol- (1264 ± 47 mW/m³) and propyl alcohol-fed MFC (1192 ± 36 mW/m³). Firmicutes, Bacteroidetes, Verrucomicrobia, Proteobacteria, Synergistetes and Armatimonadetes were dominant phyla in 3 MFC. Firmicutes was the most dominant phylum in glucose-fed MFC samples and Bacteroidetes prevailed in methanol- and propyl alcohol-fed MFC. These data indicate that propyl alcohol and methanol along with glucose can be used as substrates of MFC.     

Convergent development of anodic bacterial communities in microbial fuel cells

Microbial fuel cells (MFCs) are often inoculated from a single wastewater source. The extent that the inoculum affects community development or power production is unknown. The stable anodic microbial communities in MFCs were examined using three inocula: a wastewater treatment plant sample known to produce consistent power densities, a second wastewater treatment plant sample, and an anaerobic bog sediment. The bog-inoculated MFCs initially produced higher power densities than the wastewater-inoculated MFCs, but after 20 cycles all MFCs on average converged to similar voltages (470±20 mV) and maximum power densities (590±170 mW m⁻²). The power output from replicate bog-inoculated MFCs was not significantly different, but one wastewater-inoculated MFC (UAJA3 (UAJA, University Area Joint Authority Wastewater Treatment Plant)) produced substantially less power. Denaturing gradient gel electrophoresis profiling showed a stable exoelectrogenic biofilm community in all samples after 11 cycles. After 16 cycles the predominance of Geobacter spp. in anode communities was identified using 16S rRNA gene clone libraries (58±10%), fluorescent in-situ hybridization (FISH) (63±6%) and pyrosequencing (81±4%). While the clone library analysis for the underperforming UAJA3 had a significantly lower percentage of Geobacter spp. sequences (36%), suggesting that a predominance of this microbe was needed for convergent power densities, the lower percentage of this species was not verified by FISH or pyrosequencing analyses. These results show that the predominance of Geobacter spp. in acetate-fed systems was consistent with good MFC performance and independent of the inoculum source.     

Effect of vitamins and cell constructions on the activity of microbial fuel cell battery

Construction of efficient performance of microbial fuel cells (MFCs) requires certain practical considerations. In the single chamber microbial fuel cell, there is no border between the anode and the cathode, thus the diffusion of the dissolved oxygen has a contrary effect on the anodic respiration and this leads to the inhibition of the direct electron transfer from the biofilm to the anodic surface. Here, a fed-batch single chambered microbial fuel cells are constructed with different distances 3 and 6?cm (anode- cathode spacing), while keeping the working volume is constant. The performance of each MFC is individually evaluated under the effects of vitamins & minerals with acetate as a fed load. The maximum open circuit potential during testing the 3 and 6?cm microbial fuel cells is about 946 and 791?mV respectively. By decreasing the distance between the anode and the cathode from 6 to 3?cm, the power density is decreased from 108.3?mW?m^?2 to 24.5?mW?m^?2. Thus, the short distance in membrane-less MFC weakened the cathode and inhibited the anodic respiration which affects the overall performance of the MFC efficiency. The system is displayed a maximum potential of 564 and 791?mV in absence & presence of vitamins respectively. Eventually, the overall functions of the acetate single chamber microbial fuel cell can be improved by the addition of vitamins & minerals and increasing the distance between the cathode and the anode.     

Fate of three bioluminescent pathogenic bacteria fed through a cascade of urine microbial fuel cells

Microbial fuel cell (MFC) technology is currently gaining recognition as one of the most promising bioenergy technologies of the future. One aspect of this technology that has received little attention is the disinfection of effluents and the fate of pathogenic organisms that find their way into the waste stream. In this study, three independent trials were carried out to evaluate the fate of three bioluminescent pathogenic bacteria (Salmonella enterica serovar Typhimurium, Pseudomonas aeruginosa and Staphylococcus aureus) introduced into the anodic chamber of a urine-fed cascade of 9 MFCs with matured, electroactive biofilms. These are common examples of enteric human pathogens, which could contaminate urine or waste streams. The results showed that the average power generation in the closed circuit cascade reached 754 ± 16 µW, with an average pathogen log-fold reduction of 6.24 ± 0.63 compared to 2.01 ± 0.26 for the open circuit cascade for all three pathogens. The results suggest that the bio-electrochemical reactions associated with electricity generation were the primary driving force for the inactivation of the introduced pathogens. These findings show that pathogenic organisms introduced into waste streams could be inactivated by the power-generating process within the MFC cascade system, thereby preventing propagation and thus rendering the effluent safer for possible reuse.

     

Identification of (S)-11-cycloheptyl-4-methylundecanoic acid in acylphosphatidylglycerol from Alicyclobacillus acidoterrestris

A method is described for the identification of molecular species of acylphosphatidylglycerols containing a branched cyclo fatty acid ((S)-11-cycloheptyl-4-methylundecanoic acid; brc19:0) from Alicyclobacillus acidoterrestris and its identification as picolinyl ester by means of GC-MS. The combination of TLC, negative RP-HPLC-ESI-MS/MS, enzymatic hydrolysis, and GC-MS was used to identify unusual molecular species of acylphosphatidylglycerols with cyclic and branched FA. The acid, brc19:0, was also synthesized to unambiguously confirm its structure. According to feeding experiments with ¹³C-labeled propionate, the C₃ internal unit (branched methyl) of brc19:0 is assembled from propionate and not from methionine.     

Effects of inoculation strategy and cultivation approach on the performance of microbial fuel cell using marine sediment as bio-matrix

Aims: To investigate the effects of inoculation strategy and cultivation approach on the performance of microbial fuel cell (MFC). Methods and Results: A dual‐chamber sediment fuel cell was set up fed with glucose under batch condition. At day 30, the supernatant consortium was partly transferred and used as inoculum for the evaluation of cultivation approach. Power output gradually increased to 9·9 mW m^?2 over 180 days, corresponding to coulombic efficiency (CE) of 29·6%. Separated biofilms attached anode enabled power output and CE dramatically up to 100·9 mW m^?2 and over 50%, respectively, whereas the residual sediment catalysed MFC gave a poor performance. MFC catalysed by in situ supernatant consortium demonstrated more than twice higher power than MFC catalysed by the supernatant consortium after Fe(OH)₃ cultivation. However, the re‐generation of biofilms from the latter largely enhanced the cell performance. Conclusions: MFC exhibited a more efficient inducement of electroactive consortium than Fe(OH)₃ cultivation. MFC performance varied depending on different inoculation strategies. Significance and Impact of the Study: This is the first time to study cultivation approach affecting electricity generation. In addition, anodic limitations of mass and electron transfer were discussed through MFC catalysed by sediment‐based bio‐matrix.     

Mechanistic investigation of decolorization and degradation of Reactive Red 120 by Bacillus lentus BI377

Bacillus lentus BI377, isolated from textile effluent-contaminated soil, was able to degrade 97% and 92% of Reactive Red 120 dye when 1200 and 1500 mg/l, respectively, of dye was added to nutrient broth (NB) at 35 °C within 12 h. UV-vis spectroscopy, GC-MS, FTIR and ¹H NMR revealed the formation of catechol which may be further utilized by the bacterium via the TCA cycle, leading to complete mineralization. Structural analysis of metabolites in conjunction with enzyme activity studies confirmed the involvement of azoreductase, cytochrome P450 monooxygenase and other antioxidant enzymes. Decreases in total organic carbon and in biological and chemical oxygen demand suggest formation of low molecular weight metabolites that could be completely mineralized. These results suggest the potential use of B. lentus BI377 towards online treatment of textile dye effluents by using an appropriate bioreactor over a wide range of pH. This study opens-up a dependable and proficient way to use industrially viable non-pathogenic strains for biotransformation of carcinogenic dyes to ecofriendly compounds.     

Composite vegetable waste as renewable resource for bioelectricity generation through non-catalyzed open-air cathode microbial fuel cell

Single chambered mediatorless microbial fuel cell (MFC; non-catalyzed electrodes) was operated to evaluate the potential of bioelectricity generation from the treatment of composite waste vegetables (EWV) extract under anaerobic microenvironment using mixed consortia as anodic biocatalyst. The system was operated with designed synthetic wastewater (DSW; 0.98 kg COD/m³-day) during adaptation phase and later shifted to EWV and operated at three substrate load conditions (2.08, 1.39 and 0.70 kg COD/m³-day). Experimental data illustrated the feasibility of bioelectricity generation through the utilization of EWV as substrate in MFC. Higher power output (57.38 mW/m²) was observed especially at lower substrate load. The performance of MFC was characterized based on the polarization behavior, cell potentials, cyclic voltammetric analysis and sustainable resistance. MFC operation also documented to stabilize the waste by effective removal of COD (62.86%), carbohydrates (79.84%) and turbidity (55.12%).     

Direct Biotransformation of Dioscin into Diosgenin in Rhizome of Dioscorea zingiberensis by Penicillium dioscin

Diosgenin is an important precursor for synthesis of more than 200 steroidal hormone medicines. Rhizome of Dioscorea zingiberensis C. H. Wright (RDZ) contained the highest content of diosgenin in Dioscorea plant species. Diosgenin is traditionally extracted by acid hydrolysis from RDZ. However, the acid hydrolysis process produces massive wastewater which caused serious environment pollution. In this study, diosgenin extraction by direct biotransformation with Penicillium dioscin was investigated. The spawn cultivation conditions were optimized as: Czapeks liquid culture medium without sugar and agar (1,000 ml) + 6.0 g dioscin/6.0 g DL, 30 °C, 36 h; solid fermentation of RDZ: mycelia/RDZ of 0.05 g/kg, 30 °C, 50 h; the yield of diosgenin was over 90 %. Spawn cultivation was crucial for the direct biotransformation. In the spawn cultivation, amount and ratio of dioscin/DL were the key factors to promote biotransformation activity of P. dioscin. This biotransformation method was environment-friendly, simple and energy saving, and might be a potential substitute for acid hydrolysis in diosgenin extraction industry.     

A rapid fingerprinting approach to distinguish between closely related strains of Shewanella

One of the big operational problems facing laboratories today is the ability to rapidly distinguish between strains of bacteria that, while physiologically distinct, are nearly impossible to separate based on 16S rRNA gene sequence differences. Here we demonstrate that ITS-DGGE provides a convenient approach to distinguishing between closely related strains of Shewanella, some of which were impossible to separate and identify by 16 rRNA gene sequence alone. Examined Shewanella genomes contain 8-11 copies of rrn (ribosomal RNA gene) operons, and variable size and sequence of 16S-23S ITS (intergenic transcribed spacer) regions which result in distinct ITS-DGGE profiles. Phylogenetic constructions based on ITS are congruent with the genomic trees generated from concatenated core genes as well as with those based on conserved indels, suggesting that ITS patterns appear to be linked with evolutionary lineages and physiology. In addition, three new Shewanella strains (MFC 2, MFC 6, and MFC 14) were isolated from microbial fuel cells enriched from wastewater sludge and identified by ITS-DGGE. Subsequent physiological and electrochemical studies of the three isolates confirmed that each strain is phenotypically/genotypically distinct. Thus, this study validates ITS-DGGE as a quick fingerprint approach to identifying and distinguishing between closely related but novel Shewanella ecotypes.