A new concept for the combination of membrane bioreactors and microbial fuel cells is introduced, that aims at the production of electricity for reducing the overall energy consumption of wastewater treatment. In contrast to previous approaches, the anode is integrated as microfiltration membrane in sidestream crossflow configuration. Using a stainless steel filtration membrane with G. sulfurreducens and an acetate-based synthetic medium, up to 4-fold higher current densities are achieved. In a standard setup without filtration, a membrane of filter grade 1 mu m shows current densities of 5.8 Am-2 +/- 0.5 Am-2 compared to > 11 Am-2 when it is used simultaneously as membrane filter. With smaller pore sizes of filter grade 0.5 mu m, 4.4 Am-2 +/- 0.5 Am-2 in a standard setup and > 15 Am-2 in a filtration setup are achieved. The permeate flow was identified as the main parameter leading to increased current densities.