Electron fluxes in a microbial fuel cell performing carbon and nitrogen removal

The electron recovery in microbial fuel cells (MFCs) is decreased by processes like methanogenesis, bacterial growth, and the accumulation of intermediates. Using a suite of analytical techniques, including electrochemical monitoring, chemical analysis, microsensor analysis, and Titration and Off-Gas Analysis (TOGA), this study aimed to (a) identify and quantify the electron losses occurring at the anode and the cathode of a MFC removing acetate and nitrate (NO₃^-), respectively, and (b) to investigate the impact of the operational characteristics of the cathode on the denitrification process. Our results show that methane (CH₄) production and estimated biomass formation at the anode and nitrous oxide (N₂O) accumulation at the cathode were responsible for the reduction of Coulombic efficiency (ε) during continuous feeding conditions. At the anode, up to 40.1% of the acetate consumed was released as methane at closed circuit. At the cathode, N₂O accumulation represented instead the main loss accounting for up to 10.0 ± 2.1% of the oxidation capacity of the electron acceptor provided as NO₃^-. Batch experiments at controlled potentials and currents revealed that for a given current the fraction of electron transferred and released as N₂O is significantly reduced by low cathodic potentials. © 2009 American Chemical Society.