A four-air cathode single-chamber microbial fuel cell (4ACMFC) with MnO2 as cathode catalyst and a packed bed of graphite granules as anode was studied, aiming at continuous treatment of municipal wastewater in parallel to electric power production. When fed with synthetic wastewater, the system achieved a maximum power density of 13.6 W m(-3), a COD removal of 85 %, and a Coulombic efficiency (CE) of 21 %. When municipal wastewater was treated, the achieved COD removal was 45 %, and the CE 7.8 %. By increasing the municipal wastewater conductivity through salt addition, the CE increased to 22.3 %. During the long-term operation of the cell, non-exoelectrogenic bacteria and catalyst degradation were observed to be present. The 4ACMFC performance was assessed at different hydraulic retention times. The electrochemical impedance characterization of the 4ACMFC was also carried out.