The anode of a two-chamber methane-producing microbial electrolysis cell (MEC) was poised at +0.200 V vs. the standard hydrogen electrode (SHE) and continuously fed (1.08 gCOD/L d) with acetate in anaerobic mineral medium. A gas mixture (carbon dioxide 30 vol.% in N-2) was continuously added to the cathode for both pH control and carbonate supply. At the anode, 94% of the influent acetate was removed, mostly through anaerobic oxidation (91% coulombic efficiency); the resulting electric current was mainly recovered as methane (79% cathode capture efficiency). Low biomass growth was observed at the anode and ammonium was transferred through the cationic membrane and concentrated at the cathode. These findings suggest that the MEC can be used for the treatment of low-strength wastewater, with good energy efficiency and low sludge production. (C) 2012 Elsevier Ltd. All rights reserved.