Influence of substrate on electron transfer mechanisms in chambered benthic microbial fuel cells.

This research investigated whether the addition of an exogenous electron donor would affect power production in laboratory-scale benthic microbial fuel cells (BMFC) by differentially influencing microbially mediated electron transfer processes. Six BMFCs were operated for over one year in a temperature-controlled laboratory. Three BMFCs relied on endogenous electron donors, and three were supplemented with lactate. The supplemented BMFCs generated more cumulative charge, but did not generate higher average current between periods of lactate enrichment. Coulombic efficiencies during the lactate treatments ranged from 25 to 65% suggesting that lactate utilization was variably coupled to power production. Cumulative electron flux resulting from lactate additions and chemical changes within the anode chamber, as well as a difference in the anode-hosted microbial communities indicated that lactate supplementation promoted sulfate reduction. After the addition of molybdate to suppress sulfate reduction and sulfur disproportionation, all BMFCs continued to produce current, but no longer responded to lactate additions. Chemical data support a two-step cycle in which endogenous organic carbon and/or supplemented lactate fuel sulfate reduction resulting in sulfide and simple organic molecules (such as acetate) that can act as the electron donors for the BMFC.