Power Production by Sediment-Hosted Microbial Fuel Cells: The Influence of Substrate Availability and Microbial Ecology

In recent years, microbial fuel cells (or MFCs) have been deployed in a variety of natural environments, and shown to produce electrical energy from the biocatalytic oxidation of sedimentary organic matter. However, the relationships between organic carbon decomposition, microbial diversity and density, and power production remain largely unknown. In particular, our understanding of which metabolic processes are active within the anode-hosted community—and thereby most directly contributing to MFC power production—is limited. To examine the influence of the particular reductants on the anode-hosted microbial community and net power production, we conducted a time-series experiment in which MFC anodes were incubated in columns of coastal marine sedimenets for up to four months. Individual columns were irrigated with methane, sulfide, or acetate at seepage rates and concentrations comprable to those in situ. Our data demonstrate that all three reductants stimulated power production, though stoichiometrically acetate produced the most power per mole, followed by methane and sulfide, respectively. Our quantitative molecular analyses further implicate sulfate- and iron-reducing bacteria, anaerobic methanotrophs, and sulfur disproportionators in power production. These may be a mechanism that contributes to power production. We posit that power production results from the catabolism of a variety of reductants by the anode-hosted community, including methane, and subsequent shuttling of electrons to the anode likely occurs via both direct electron transfer and chemical mediators such as sulfide.