Influence of External Resistance on Electrogenesis, Methanogenesis, and Anode Prokaryotic Communities in Microbial Fuel Cells

Abstract

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 mA/m 2 (9,800 ⍀) to 284.5 mA/m 2 (150 ⍀) for acetate-fed MFCs (acetate-fed reactors [ARs]), with a corresponding anode potential (E an ) range of ؊188 to ؊4 mV (versus a standard hydrogen electrode [SHE]). For glucose-fed MFCs (glucose-fed reactors [GRs]), I ranged from 40.0 mA/m 2 (9,800 ⍀) to 273.0 mA/m 2 (150 ⍀), with a corresponding E an range of ؊189 to ؊7 mV. 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 ⍀ significantly changed the anode bacterial communities for both ARs and GRs, while operating at 970 ⍀ and 150 ⍀ 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.The bioanode, a crucial component in bioelectrochemical systems (BESs), is composed of an anode biofilm and a conductive electrode. The main catalytic components of interest in anode biofilms are exoelectrogens, microorganisms that are capable of exocellular electron transfer (31). In mixed-culture systems, exoelectrogens compete for electron donors with other functional groups such as fermenters, acetogens, and methanogens. The complexity of anode biofilms makes it hard to elucidate electrochemical mechanisms at the bioanode, but a precise understanding of exoelectrogenesis and competition in anode biofilms will aid in improving the performance of BESs. Several reviews provide insightful summaries and perspectives regarding bioanodes (31,34,40,43,51).The anode potential (E an ) is defined as the potential difference between the anode and the surrounding electrolyte (14). E an also refers to the electromotive force that drives electrons to flow into an anode, and it is regarded as a measure of electron affinity (14). E an is affected by intrinsic factors such as electrode material, electrolyte composition, electrochemical reactions, and catalysts (anode biofilm in BESs) (14). E an also can be controlled extrinsically using a potentiostat ...

Microbial Fuel Cells: Influence of External Resistors on Power, Current and Power Density

“…Many research have be carried out to investigate the applicability of maximum power transfer theorem [26][27][28][29][30][31][32]. Figure 4 shows the power density and the current density obtained in this work.…”

Biocathodic Methanogenic Community in an Integrated Anaerobic Digestion and Microbial Electrolysis System for Enhancement of Methane Production from Waste Sludge

“…With respect to previous studies on the competition between Geobacter and Methanosaeta for the same substrate, acetate would be the most primarily oxidized into electrons and protons by exoelectrogenic bacteria rather than methanogens. 45,46 Recent finding of direct interspecies electron transfer (DIET) for methane production implied that Methanosaeta were more likely to accept electrons from Geobacter rather than surviving through acetate metabolism. 38,47 However, methane production from interspecies electron transport did not result in obvious change in methane production rate because of the slow grow rate of Methanosaeta.…”

Microbial population and functional dynamics associated with surface potential and carbon metabolism

“…The medium replacement process removed suspended microbes and reduced the contribution of any redox-active soluble electron shuttles that may have been produced by the bacteria. To establish electrogenic communities, the external resistor was decreased stepwise from 510 O to 22 O (Figure 1), which has been successfully demonstrated to improve MFC electron recovery (Fan et al, 2008;Shimoyama et al, 2008;Hong et al, 2011;Jung and Regan, 2011 (Figure 2). The SP-L-b reactor started generating current more slowly than the SP-L-a reactor, indicating that an anode potential of À 200 mV vs SHE may not have been a favorable selective pressure to reproducibly select for similar microbial EET activities.…”