Graphite fiber brush electrodes provide high surface areas for exoelectrogenic bacteria in microbial fuel cells (MFCs), but the cylindrical brush format limits more compact reactor designs. To enable MFC designs with closer electrode spacing, brush anodes were pressed up against a separator (placed between the electrodes) to reduce the volume occupied by the brush. Higher maximum voltages were produced using domestic wastewater (COD = 390+/-89 mg L(-1)) with brush anodes (360+/-63 mV, 1000 Omega) than woven carbon mesh anodes (200+/-81 mV) with one or two separators. Maximum power densities were similar for brush anode reactors with one or two separators after 30 days (220 +/- 1.2 and 240 +/- 22 mW m(-2)), but with one separator the brush anode MFC power decreased to 130 55 mW m(-2) after 114 days. Power densities in MFCs with mesh anodes were very low (<45 mW m(-2)). Brush anodes MFCs had higher COD removals (80+/-3%) than carbon mesh MFCs (58+/-7%), but similar Coulombic efficiencies (8.6+/-2.9%brush; 7.8+/-7.1% mesh). These results show that compact (hemispherical) brush anodes can produce higher power and more effective domestic wastewater treatment than flat mesh anodes in MFCs. (C) 2011 Elsevier B.V. All rights reserved.