Air-cathodes in microbial fuel cells that can also filter wastewater provide the dual benefits of electricity production and reduction of the effluent chemical oxygen demand. Air-cathodes prepared using a novel activated carbon/graphene membrane (2, 5 or 10% graphene by weight) prepared by phase inversion have good conductivities (5.6 +/- 0.5 to 7.3 +/- 0.6 mS cm(-1)) compared to control (3.0 +/- 0.4 mS cm(-1), activated carbon, no graphene). The cathode with 5 wt% graphene produces the highest maximum power density of 1460 +/- 10 mW m(-2), which is 58% higher than that the control (928 +/- 8 mW m(-2)). The increased power is due to an 88% reduction in charge transfer resistance of 6.0 +/- 0.3 Omega (cathode with 5 wt% graphene) compared to the control. Following a cycle of treatment and current generation, 60 +/- 1% of the chemical oxygen demand is removed from the remaining chemical oxygen demand, producing an effluent chemical oxygen demand concentration of 20 +/- 1 mg L-1. Biomass (4.99 +/- 0.02 mg-protein cm(-2)) is decreased by 33% compared to the control. These results demonstrate that cathodes made with graphene can produce electricity and a high quality effluent with low cathode biofouling.