BACKGROUNDHigh cost and ohmic loss are two issues that microbial fuel cells (MFC) face before becoming economically viable. To address the high cost and ohmic loss issues, a flat-plate MFC (FPMFC) configuration applying a passive air-breathing cathode and a three-dimensional anode was introduced. Electricity generation was examined in the FPMFC through operation in the presence and absence of a proton exchange membrane (PEM), and in batch and continuous modes. RESULTSContinuous operation of the FPMFC in the presence of a PEM favored power generation, mainly due to elimination of oxygen and biomass in the anode. Peak power density of 18 Wm(-3) was produced in the presence of a PEM (ohmic resistance 40 cm(2)), which was more than 5-fold higher than that with J-cloth. During batch operation, the power density increased and reached maximum in the third batch (18 W m(-3) at 60 A m(-3)). Greater stability was observed during continuous operation resulting in a 2.5-fold increase in peak power density (44 W m(-3) at 146 A m(-3)). CONCLUSIONThe passive air-breathing FPMFC showed promising performance, offering a more economically viable configuration than the conventional FPMFCs using active (air, ferricyanide, and ferric iron) cathodes. (c) 2014 Crown copyright. Journal of Chemical Technology & Biotechnology (c) 2014 Society of Chemical Industry