Anodic concentration loss and impedance characteristics in rotating disk electrode microbial fuel cells

A rotating disk electrode (RDE) was used to investigate the concentration loss and impedance characteristics of anodic biofilms in microbial fuel cells (MFCs). Amperometric time–current analysis revealed that at the rotation rate of 480 rpm, a maximum current density of 168 µA cm^?2 can be achieved, which was 22.2 % higher than when there was no rotation. Linear sweep voltammetry and electrochemical impedance spectroscopy tests showed that when the anodic potential was set to ?300 mV vs. Ag/AgCl reference, the power densities could increase by 59.0  %, reaching 1385 mW m^?2, the anodic resistance could reduce by 19  %, and the anodic capacitance could increase by 36 %. These results concur with a more than 85 % decrease of the diffusion layer thickness. Data indicated that concentration loss, diffusion layer thickness, and the mixing velocity play important roles in anodic resistance reduction and power output of MFCs. These findings could be helpful to the design of future industrial-scale MFCs with mixed bacteria biofilms.     

Stable operation of microbial fuel cells at low temperatures (5–10 °C) with light exposure and its anodic microbial analysis

Performances of microbial fuel cells (MFCs) were studied at 5–10 and 25–30 °C. Results showed stable operation of the MFCs at low temperatures with only slight reductions of voltage and power generation (11 versus 14 % for double-chamber MFC, while 14 versus 21 % for single-chamber MFC, 1,000 Ω) compared to those at mesophilic temperatures. MFCs operated at low temperatures showed lower COD removal rates accompanied by higher coulombic efficiencies (CEs). PCR-DGGE analysis revealed that psychrotrophic microbes (mainly Arcobacter, Pseudomonas, and Geobacter) dominated on anodes of the MFCs at low temperatures. Interestingly, light-induced red substances appeared on anode of the MFCs operated at low temperature and were proven to be the main anodic microbes (Arcobacter and Pseudomonas). Co-existence of the aforementioned microbes could assist stable low-temperature operation of the MFCs. Cyclic voltammetry analysis supported the results of the CE and DGGE. Stable performance of MFCs at low temperatures might be achieved by the control of anodic bacteria.     

Differential biofilms characteristics of Shewanella decolorationis microbial fuel cells under open and closed circuit conditions

Biofilms formation capacities of Shewanella species in microbial fuel cells (MFCs) and their roles in current generation have been documented to be species-dependent. Understandings of the biofilms growth and metabolism are essential to optimize the current generation of MFCs. Shewanella decolorationis S12 was used in both closed-circuit and open-circuit MFCs in this study. The anodic S. decolorationis S12 biofilms could generate fivefold more current than the planktonic cells, playing a dominant role in current generation. Anodic biofilms viability was sustained at 98 ± 1.2% in closed-circuit while biofilms viability in open-circuit decreased to 72 ± 7% within 96 h. The unviable domain in open-circuit MFCs biofilms majorly located at the inner layer of biofilm. The decreased biofilms viability in open-circuit MFCs could be recovered by switching into closed-circuit, indicating that the current-generating anode in MFCs could serve as a favorable electron acceptor and provide sufficient energy to support cell growth and metabolism inside biofilms.     

Effect of different acclimation methods on the performance of microbial fuel cells using phenol as substrate

Single-chamber microbial fuel cells (MFCs) with air-cathode were constructed. MFCs were fed different feedstocks during their inoculation, their role on phenol degradation and MFC performance were investigated. The results showed that the MFC inoculated using glucose exhibited the highest power density (31.3 mW m^?2) when phenol was used as the sole substrate for MFC. The corresponding biodegradation kinetic constant was obtained at 0.035 h^?1, at an initial phenol concentration of 600 mg L^?1. Moreover, the phenol degradation rates in this MFC with closed circuit were 9.8–16.5 % higher than those in MFC with opened circuit. The cyclic voltammograms revealed a different electrochemical activity of the anode biofilms in the MFC, and this led to differences in performance of the MFCs with phenol as sole substrate. These results demonstrated that phenol degradation and power production are affected by current generation and type of acclimation.     

Electrocatalytic activity of anodic biofilm responses to pH changes in microbial fuel cells

This study investigates the effects of anodic pH on electricity generation in microbial fuel cells (MFCs) and the intrinsic reasons behind them. In a two-chamber MFC, the maximum power density is 1170 ± 58 mW m⁻² at pH 9.0, which is 29% and 89% higher than those working at pH 7.0 and 5.0, respectively. Electrochemical measurements reveal that pH affects the electron transfer kinetics of anodic biofilms. The apparent electron transfer rate constant (k_app) and exchange current density (i₀) are greater whereas the charge transfer resistance (R_ct) is smaller at pH 9.0 than at other conditions. Scanning electron microscopy verifies that alkaline conditions benefit biofilm formation in MFCs. These results demonstrate that electrochemical interactions between bacteria and electrodes in MFCs are greatly enhanced under alkaline conditions, which can be one of the important reasons for the improved MFC output.     

Alteration of bacterial communities and organic matter in microbial fuel cells (MFCs) supplied with soil and organic fertilizer

The alteration of the organic matter (OM) and the composition of bacterial community in microbial fuel cells (MFCs) supplied with soil (S) and a composted organic fertilizer (A) was examined at the beginning and at the end of 3 weeks of incubation under current-producing as well as no-current-producing conditions. Denaturing gradient gel electrophoresis revealed a significant alteration of the microbial community structure in MFCs generating electricity as compared with no-current-producing MFCs. The genetic diversity of cultivable bacterial communities was assessed by random amplified polymorphic DNA (RAPD) analysis of 106 bacterial isolates obtained by using both generic and elective media. Sequencing of the 16S rRNA genes of the more representative RAPD groups indicated that over 50.4% of the isolates from MFCs fed with S were Proteobacteria, 25.1% Firmicutes, and 24.5% Actinobacteria, whereas in MFCs supplied with A 100% of the dominant species belonged to γ-Proteobacteria. The chemical analysis performed by fractioning the OM and using thermal analysis showed that the amount of total organic carbon contained in the soluble phase of the electrochemically active chambers significantly decreased as compared to the no-current-producing systems, whereas the OM of the solid phase became more humified and aromatic along with electricity generation, suggesting a significant stimulation of a humification process of the OM. These findings demonstrated that electroactive bacteria are commonly present in aerobic organic substrates such as soil or a fertilizer and that MFCs could represent a powerful tool for exploring the mineralization and humification processes of the soil OM.     

Increased power generation from primary sludge in microbial fuel cells coupled with prefermentation

Raw primary sludge and the prefermentation liquor (PL) of primary sludge were used to generate electricity in single-chambered air-cathode microbial fuel cells (MFCs). The MFCs treating the primary sludge produced 0.53 V and 370 mW/m² for the maximum potential and power density, respectively. In the primary sludge-fed MFCs, only 5 % of the total energy production was produced from direct electricity generation, whereas 95 % of that resulted from the conversion of methane to electricity. MFCs treating the PL generated the maximum potential of 0.58 V and maximum power density of 885 mW/m², respectively. In the energy production analysis, direct electricity production (1,921 Wh/kg TCOD_rem) in the MFCs treating the PL was much higher than that of the primary sludge-fed MFC (138 Wh/kg TCOD_rem). Volatile suspended solids during 10 days were reduced to 18.3 and 38 % in the primary sludge-fed MFCs and prefermentation reactor, respectively. These findings suggest that a two-stage process including prefermentation and MFCs is of great benefit on sludge reduction and higher electricity generation from primary sludge.     

Characterization of the rumen microbiome of Indian Kankrej cattle (Bos indicus) adapted to different forage diet

Present study described rumen microbiome of Indian cattle (Kankrej breed) to better understand the microbial diversity and largely unknown functional capacity of the rumen microbiome under different dietary treatments. Kankrej cattle were gradually adapted to a high-forage diet (four animals with dry forage and four with green forage) containing 50 % (K1), 75 % (K2) to 100 % (K3) forage, and remaining concentrate diet, each for 6 weeks followed by analysis of rumen fiber adherent and fiber-free metagenomic community by shotgun sequencing using ion torrent PGM platform and EBI-metagenomics annotation pipeline. Taxonomic analysis indicated that rumen microbiome was dominated by Bacteroidetes followed by Firmicutes, Fibrobacter, Proteobacteria, and Tenericutes. Functional analysis based on gene ontology classified all reads in total 157 categories based on their functional role in biological, molecular, and cellular component with abundance of genes associated with hydrolase activity, membrane, transport, transferase, and different metabolism (such as carbohydrate and protein). Statistical analysis using STAMP revealed significant differences (P?相似文献   

Electricity from microorganisms

Over the last ten years, the recently discovered process of direct electron transfer from anaerobically grown microorganisms to an electrode of a fuel cell has been the object of intense study. The microorganisms responsible for such electron transport were termed electrogenic; the devices using them to generate electric current, microbial fuel cells (MFCs). The review discussed the molecular mechanisms of electron transfer to the environment in the case of the two best studied microorganisms, Shewanella oneidensis and Geobacter sulfurreducens. The discovery of bacterial conducting pili (nanowires) used for electron transfer to the electrode and between bacterial cells was sensational. In the real MFCs, which use complex substrates (industrial liquid waste), microbial associations are active, often as biofilms. The progress in MFCs design and the prospects of their practical application are considered.     

Exploring characteristics of bioelectricity generation and dye decolorization of mixed and pure bacterial cultures from wine-bearing wastewater treatment

This study uncovered microbial characteristics of bioelectricity generation and dye decolorization in single-chamber microbial fuel cells (MFCs) using activated sludge for wine-containing wastewater treatment. Phylogenetic tree analysis on 16S rRNA gene fragments indicated that the predominant strains on anodic biofilm in acclimatized MFCs were Gamma-Proteobacteria Aeromonas punctata NIU-P9, Pseudomonas plecoglossicida NIU-Y3, Pseudomonas koreensis NIU-X8, Acinetobacter junii NIU-Y8, Stenotrophomonas maltophila NIU-X2. Our findings showed that the current production capabilities of these pure strains were only ca. 10% of those of their mother activated sludge, indicating that synergistic interactions among microbes might be the most influential factor to maximize power generation in MFCs. Plus, these electrochemically active strains also performed reductive decolorization of C.I. reactive blue 160, suggesting that bioelectricity generation might be directly associated to azo dye decolorization to deal with electron transfer on anodic biofilm in MFCs.     

Production of Electricity and Butanol from Microalgal Biomass in Microbial Fuel Cells

Chlorella vulgaris (a freshwater microalga) and Dunaliella tertiolecta (a marine microalga) were grown for bulk harvest, and their biomass was tested as feedstock for electricity production in cubic two-chamber microbial fuel cells (MFCs) at 37°C. The anode inoculum was anaerobic consortium from a municipal sewage sludge digester, enriched separately for the two microalgal biomass feedstocks. After repeated subculturing of the two anaerobic enrichments, the maximum power density obtained in MFCs was higher from C. vulgaris (15.0 vs. 5.3 mW m^?2) while power generation was more sustained from D. tertiolecta (13 vs. 9.8 J g^-1 volatile solids). Anolytes of algal biomass-fed MFCs also contained substantial levels of butanol (8.7–16 mM with C. vulgaris and 2.5–7.0 mM with D. tertiolecta), which represents an additional form of utilizable energy. Carryover of salts from the marine D. tertiolecta biomass slurry resulted in gradual precipitation of Ca and Mg phosphates on the cathode side of the MFC. Polymerase chain reaction-denaturing gradient gel electrophoresis profiling and sequencing of bacterial communities demonstrated the presence of Wolinella succinogenes and Bacteroides and Synergistes spp. as well as numerous unknown bacteria in both enrichments. The D. tertiolecta enriched consortium contained also Geovibrio thiophilus and Desulfovibrio spp. Thus, the results indicate potential for combining fermentation and anaerobic respiration for bioenergy production from photosynthetic biomass.     

Microbial Fuel Cells and Microbial Ecology: Applications in Ruminant Health and Production Research

Microbial fuel cell (MFC) systems employ the catalytic activity of microbes to produce electricity from the oxidation of organic, and in some cases inorganic, substrates. MFC systems have been primarily explored for their use in bioremediation and bioenergy applications; however, these systems also offer a unique strategy for the cultivation of synergistic microbial communities. It has been hypothesized that the mechanism(s) of microbial electron transfer that enable electricity production in MFCs may be a cooperative strategy within mixed microbial consortia that is associated with, or is an alternative to, interspecies hydrogen (H₂) transfer. Microbial fermentation processes and methanogenesis in ruminant animals are highly dependent on the consumption and production of H₂in the rumen. Given the crucial role that H₂ plays in ruminant digestion, it is desirable to understand the microbial relationships that control H₂ partial pressures within the rumen; MFCs may serve as unique tools for studying this complex ecological system. Further, MFC systems offer a novel approach to studying biofilms that form under different redox conditions and may be applied to achieve a greater understanding of how microbial biofilms impact animal health. Here, we present a brief summary of the efforts made towards understanding rumen microbial ecology, microbial biofilms related to animal health, and how MFCs may be further applied in ruminant research.     

Use of Pyrosequencing to Characterize the Microbiota in the Ileum of Goats Fed with Increasing Proportion of Dietary Grain

This study evaluated the effects of an increasing proportion of dietary grain on changes in bacterial populations in the goat ileum. Nine ruminally fistulated, castrated male goats were assigned to three diets in a completely randomized design. Goats were fed three different dietary treatments containing different proportions of corn grain (0, 25, and 50 %). The pH of the ileal contents and rumen fluid (P = 0.015) linearly decreased (P < 0.001), and the acetate, propionate, butyrate, and total volatile fatty acid in ileal contents increased (P < 0.05) with increases in dietary corn, and similar results were also observed in rumen fluid. The barcoded DNA pyrosequencing method was used to reveal 8 phyla, 70 genera, and 1,693 16S operational taxonomic units (OTUs). At the genus level, the proportions of Acetitomaculum, Enterococcus, Atopobium, unclassified Coriobacteriaceae, and unclassified Planctomycetaceae were linearly decreased (P < 0.05) with increases in corn grain. At the species level, high grain feeding linearly decreased the percentage of OTU8686 (unclassified Bacteria) (P = 0.004). To the best of our knowledge, this is the first study using barcoded DNA pyrosequencing method to survey the ileal microbiome of goats and the results suggest that increasing levels of dietary corn change the composition of the ileal bacterial community. These findings provide previously unknown information about the ileal microbiota of goats and a new understanding of the ileal microbial ecology, which may be useful in modulating the gut microbiome.     

Effect of different substrates on the performance,bacterial diversity,and bacterial viability in microbial fuel cells

Four microbial fuel cells (MFCs) were inoculated with anaerobic sludge and fed four different substrates for over one year. The Coulombic efficiency (CE) and power output varied with different substrates, while the bacterial viability was similar. Acetate fed-MFC showed the highest CE (72.3%), followed by butyrate (43.0%), propionate (36.0%) and glucose (15.0%). Glucose resulted in the lowest CE because of its fermentable nature implying its consumption by diverse non-electricity-generating bacteria. 16S rDNA sequencing results indicated phylogenetic diversity in the communities of all anode biofilms, and there was no single dominant bacterial species. A relative abundance of β-Proteobacteria but an absence of γ-Proteobacteria was observed in all MFCs except for propionate-fed system in which Firmicutes dominating. The glucose-fed-MFC showed the widest community diversity, resulting in the rapid generation of current without lag time when different substrates were suddenly fed. Geobacter-like species with the most representative Geobactersulfurreducens PCA^T were integral members of the bacterial community in all MFCs except for the propionate-fed system.     

Isolation,selection, and biological characterization research of highly effective electricigens from MFCs for phenol degradation

The microbial fuel cells (MFCs) are recognized to be highly effective for the biodegradation of phenol. For isolating the phenol-degrading bacteria, the sample containing 500 mg/L phenol was collected from the MFCs. The strain (WL027) was identified basing on the 16S rRNA gene analysis and phylogenetic analysis as Bacillus cereus. The effects of pH, temperature, concentrations of phenol, heavy metal ions, and salt on the growth of strain as well as the degradation of phenol have been carefully studied. The WL027-strain exhibited favorable tolerance for the metal cations including Cr²⁺, Co²⁺, Pb²⁺, and Cu²⁺ with the concentration of 0.2 mg/L and NaCl solution with a high concentration of 30 g/L. In 41 h, 86.44% of 500 mg/L phenol has been degraded at the initial pH at 6 and the temperature of 30 °C. The strain was highly active electrogenesis bacteria and the coulombic efficiency reached 64.25%, which showed significant advantage on the efficient energy conversion. Therefore, due to the highly efficient degradation of phenol, WL027-strain could be used in the treatment of phenol-containing wastewater.     

Enhancing electrical outputs of the fuel cells with Geobacter sulferreducens by overexpressing nanowire proteins

Protein nanowires are critical electroactive components for electron transfer of Geobacter sulfurreducens biofilm. To determine the applicability of the nanowire proteins in improving bioelectricity production, their genes including pilA, omcZ, omcS and omcT were overexpressed in G. sulfurreducens. The voltage outputs of the constructed strains were higher than that of the control strain with the empty vector (0.470–0.578 vs. 0.355 V) in microbial fuel cells (MFCs). As a result, the power density of the constructed strains (i.e. 1.39–1.58 W m⁻²) also increased by 2.62- to 2.97-fold as compared to that of the control strain. Overexpression of nanowire proteins also improved biofilm formation on electrodes with increased protein amount and thickness of biofilms. The normalized power outputs of the constructed strains were 0.18–0.20 W g⁻¹ that increased by 74% to 93% from that of the control strain. Bioelectrochemical analyses further revealed that the biofilms and MFCs with the constructed strains had stronger electroactivity and smaller internal resistance, respectively. Collectively, these results demonstrate for the first time that overexpression of nanowire proteins increases the biomass and electroactivity of anode-attached microbial biofilms. Moreover, this study provides a new way for enhancing the electrical outputs of MFCs.     

Electricity generation and microbial community changes in microbial fuel cells packed with different anodic materials

Four materials, carbon felt cube (CFC), granular graphite (GG), granular activated carbon (GAC) and granular semicoke (GS) were tested as packed anodic materials to seek a potentially practical material for microbial fuel cells (MFCs). The microbial community and its correlation with the electricity generation performance of MFCs were explored. The maximum power density was found in GAC, followed by CFC, GG and GS. In GAC and CFC packed MFCs, Geobacter was the dominating genus, while Azospira was the most populous group in GG. Results further indicated that GAC was the most favorable for Geobacter adherence and growth, and the maximum power densities had positive correlation with the total biomass and the relative abundance of Geobacter, but without apparent correlation with the microbial diversity. Due to the low content of Geobacter in GS, power generated in this system may be attributed to other microorganisms such as Synergistes, Bacteroidetes and Castellaniella.     

Hydrogen production profiles using furans in microbial electrolysis cells

Microbial electrochemical cells including microbial fuel cells (MFCs) and microbial electrolysis cells (MECs) are novel biotechnological tools that can convert organic substances in wastewater or biomass into electricity or hydrogen. Electroactive microbial biofilms used in this technology have ability to transfer electrons from organic compounds to anodes. Evaluation of biofilm formation on anode is crucial for enhancing our understanding of hydrogen generation in terms of substrate utilization by microorganisms. In this study, furfural and hydroxymethylfurfural (HMF) were analyzed for hydrogen generation using single chamber membrane-free MECs (17 mL), and anode biofilms were also examined. MECs were inoculated with mixed bacterial culture enriched using chloroethane sulphonate. Hydrogen was succesfully produced in the presence of HMF, but not furfural. MECs generated similar current densities (5.9 and 6 mA/cm² furfural and HMF, respectively). Biofilm samples obtained on the 24th and 40th day of cultivation using aromatic compounds were evaluated by using epi-fluorescent microscope. Our results show a correlation between biofilm density and hydrogen generation in single chamber MECs.     

The role of riboflavin in decolourisation of Congo red and bioelectricity production using <Emphasis Type="Italic">Shewanella oneidensis</Emphasis>-MR1 under MFC and non-MFC conditions

Dissimilatory metal reducing bacteria can exchange electrons extracellularly and hold great promise for their use in simultaneous wastewater treatment and electricity production. This study investigated the role of riboflavin, an electron carrier, in the decolourisation of Congo red in microbial fuel cells (MFCs) using Shewanella oneidensis MR-1 as a model organism. The contribution of the membrane-bound protein MtrC to the decolourisation process was also investigated. Within the range of riboflavin concentrations tested, 20 µM was found to be the best with >95% of the dye (initial concentration 200 mg/L) decolourised in MFCs within 50 h compared to 90% in the case where no riboflavin was added. The corresponding maximum power density was 45 mW/m². There was no significant difference in the overall decolourisation efficiencies of Shewanela oneidensis MR-1 ΔMtrC mutants compared to the wild type. However, in terms of power production the mutant produced more power (P_max 76 mW/m²) compared to the wild type (P_max 46 mW/m²) which was attributed to higher levels of riboflavin secreted in solution. Decolourisation efficiencies in non-MFC systems (anaerobic bottles) were similar to those under MFC systems indicating that electricity generation in MFCs does not impair dye decolourisation efficiencies. The results suggest that riboflavin enhances both decolourisation of dyes and simultaneous electricity production in MFCs.     

A first insight into the intestinal microbiota of snow trout (<Emphasis Type="Italic">Schizothorax zarudnyi</Emphasis>)

This study addresses the biodiversity profile of bacterial community in the intestinal lumen and mucosa of snow trout fish by applying 16S rRNA gene 454-pyrosequencing. A total of 209,106 sequences with average length 689 (±53) were filtered, denoised, trimmed, and then sorted into OTUs based on 97 % sequence similarity using the USEARCH software pipeline. Bacteria representing 10 phyla were found in the samples investigated. Fimicutes ribotypes were present in intestinal-mucosa and lumen in all fish and often dominated the libraries (average 43 and 38 %, respectively). Proteobacteria were also prevalent, but at a lower relative abundance, at 22 and 29 % in mucosa and lumen, respectively. The autochthonous microbiota was dominated by sequences belonging to the Bacilli (mean sequence abundance 24 %), in particular the Lactobacillaceae, with Lactobacillus and Pediococcous being the most abundant genera. Fewer Bacilli (mean sequence abundance 22 %) and Actinobacteria (2 %) were present in the lumen, and allochthonous communities consisted of a more even split among the bacterial classes, with increases in sequences assigned to members of the γ-Proteobacteria (16 %) and Fusobacteriia (8 %). The principal bacterial genera recorded in the lumen belonged to the lactic acid bacteria group, Cetobacterium, Clostridium and Synechococcus. Results obtained suggest that the lumen and mucosal layer of the snow trout intestine may host different microbial communities. Moreover, both regions harbour a diverse microbiome with a greater microbial diversity in the intestinal mucus compared with the luminal communities of the fish. Many of these microbes might be of high physiological relevance for the fish and may play key roles in the functioning of its gut.