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Bacterial Communities of Microbial Fuel Cells in Responses to the External Resistance
Mohammod MAHASIN ALI,Sokhee JUNG 한국생물공학회 2021 한국생물공학회 학술대회 Vol.2021 No.10
The external resistance (R ext) of microbial fuel cells (MFCs) regulates both the anode availability as an electron acceptor and the electron flux through the circuit. We evaluated the effects of R ext on MFCs using acetate or glucose. The average current densities (I) ranged from 40.5 ㎃/m2 (9,800 Ω) to 284.5 ㎃/m2 (150 Ω) for acetatefed MFCs (acetate-fed reactors [ARs]), with a corresponding anode potential (E an) range of -188 to -4 ㎷ (versus a standard hydrogen electrode [SHE]). For glucose-fed MFCs (glucose-fed reactors [GRs]), I ranged from 40.0 ㎃/m2 (9,800 Ω) to 273.0 ㎃/㎡ (150 Ω), with a corresponding E an range of -189 to -7 ㎷. ARs produced higher Coulombic efficiencies and energy efficiencies than GRs over all tested R ext levels because of electron and potential losses from glucose fermentation. Biogas production accounted for 14 to 18% of electron flux in GRs but only 0 to 6% of that in ARs. GRs produced similar levels of methane, regardless of the R ext. However, total methane production in ARs increased as R ext increased, suggesting that E an might influence the competition for substrates between exoelectrogens and methanogens in ARs. An increase of R ext to 9,800 Ω significantly changed the anode bacterial communities for both ARs and GRs, while operating at 970 Ω and 150 Ω had little effect. Deltaproteobacteria and Bacteroidetes were the major groups found in anode communities in ARs and GRs. Betaproteobacteria and Gammaproteobacteria were found only in ARs. Bacilli were abundant only in GRs. The anode-methanogenic communities were dominated by Methanosaetaceae, with significantly lower numbers of Methanomicrobiales. These results show that R ext affects not only the E an and current generation but also the anode biofilm community and methanogenesis.
Mohammod MAHASIN ALI,Sokhee JUNG 한국생물공학회 2021 한국생물공학회 학술대회 Vol.2021 No.10
Microbial fuel cells (MFCs) harness the electrochemical activity of certain microbes for the production of electricity from reduced compounds. Characterizations of MFC anode biofilms have collectively shown very diverse microbial communities, raising ecological questions about competition and community succession within these anode-reducing communities. Three sets of triplicate, two-chamber MFCs inoculated with anaerobic sludge and differing in energy sources (acetate, lactate, and glucose) were operated to explore these questions. Based on 16S rDNA-targeted denaturing gradient gel electrophoresis (DGGE), all anode communities contained sequences closely affiliated with Geobacter sulfurreducens (>99% similarity) and an uncultured bacterium clone in the Bacteroidetes class (99% similarity). Various other Geobacter-like sequences were also enriched in most of the anode biofilms. While the anode communities in replicate reactors for each substrate generally converged to a reproducible community, there were some variations in the relative distribution of these putative anode-reducing Geobacter-like strains. Firmicutes were found only in glucose-fed MFCs, presumably serving the roles of converting complex carbon into simple molecules and scavenging oxygen. The maximum current density in these systems was negatively correlated with internal resistance variations among replicate reactors and, likely, was only minimally affected by anode community differences in these two-chamber MFCs with high internal resistance.
Mahasin Ali MOHAMMOD,Sokhee JUNG 한국생물공학회 2021 한국생물공학회 학술대회 Vol.2021 No.4
Microbial fuel cells (MFCs) harness the electrochemical activity of certain microbes for the production of electricity from reduced compounds. Characterizations of MFC anode biofilms have collectively shown very diverse microbial communities, raising ecological questions about competition and community succession within these anode-reducing communities. Three sets of triplicate, two-chamber MFCs inoculated with anaerobic sludge and differing in energy sources (acetate, lactate, and glucose) were operated to explore these questions. Based on 16S rDNA-targeted denaturing gradient gel electrophoresis (DGGE), all anode communities contained sequences closely affiliated with Geobacter sulfurreducens (>99% similarity) and an uncultured bacterium clone in the Bacteroidetes class (99% similarity). Various other Geobacter-like sequences were also enriched in most of the anode biofilms. While the anode communities in replicate reactors for each substrate generally converged to a reproducible community, there were some variations in the relative distribution of these putative anode-reducing Geobacter-like strains. Firmicutes were found only in glucose-fed MFCs, presumably serving the roles of converting complex carbon into simple molecules and scavenging oxygen. The maximum current density in these systems was negatively correlated with internal resistance variations among replicate reactors and, likely, was only minimally affected by anode community differences in these two-chamber MFCs with high internal resistance.
Mahasin Ali MOHAMMOD,Sokhee JUNG 한국생물공학회 2021 한국생물공학회 학술대회 Vol.2021 No.4
pH oppositely influences anode and cathode performance in microbial fuel cells. The differential electrochemical effects at each electrode and the resultant full-cell performance were analyzed in medium pH from 6.0 to 8.0. Potentials changed -60 mV/pH for the anode and -68 mV/pH for the cathode, coincident with thermo-dynamic estimations. Open circuit voltage reached a maximum (741 mV) at pH 7, and maximum power density was highest (712 mW/m<sup>2</sup>) at pH 6.5 as the cathode performance improved at lower pH. Maximum current density increased and apparent half-saturation potential (EKA) decreased with increasing medium pH due to improved anode performance. An equivalent circuit model composed of two time constant processes accurately fit bioanode impedance data. One of these processes was consistently the rate-limiting step for acetate-oxidizing exoelectrogenesis, with its pH-varying charge transfer resistance R2 ranging from 2- to 321-fold higher than the pH-independent charge transfer resistance R1. The associated capacitance C2 was 2-3 orders of magnitude larger than C1. R2 was lowest near EKA and increased by several orders of magnitude at anode potentials above EKA, while R1 was nearly stable. However, fits deviated slightly at potentials above EKA due to emerging impedance possibly associated with diffusion and excessive potential.
Mohammod MAHASIN ALI,Sokhee JUNG 한국생물공학회 2021 한국생물공학회 학술대회 Vol.2021 No.10
pH oppositely influences anode and cathode performance in microbial fuel cells. The differential electrochemical effects at each electrode and the resultant full-cell performance were analyzed in medium pH from 6.0 to 8.0.Potentials changed -60 ㎷/pH for the anode and -68 mV/pH for the cathode, coincident with thermodynamic estimations. Open circuit voltage reached a maximum (741 ㎷) at pH 7, and maximum power density was highest(712 ㎷/m2) at pH 6.5 as the cathode performance improved at lower pH. Maximum current density increased and apparent half-saturation potential (EKA) decreased with increasing medium pH due to improved anode performance. An equivalent circuit model composed of two time constant processes accurately fit bioanode impedance data. One of these processes was consistently the rate-limiting step for acetate-oxidizing exoelectrogenesis, with its pH-varying charge transfer resistance R2 ranging from 2- to 321-fold higher than thepH-independent charge transfer resistance R1. The associated capacitance C2 was 2-3 orders of magnitude larger than C1. R2 was lowest near EKA and increased by several orders of magnitude at anode potentials above EKA,while R1 was nearly stable. However, fits deviated slightly at potentials above EKA due to emerging impedance possibly associated with diffusion and excessive potential.