The performance of an over 10 times larger microbial fuel cell (MFC) with double cloth electrode assemblies (CEAs) during 63 days of continuous operation demonstrates that the excellent performance of CEA-MFCs can be further improved during scale-up. With a new separator material and U-shaped current collectors, the larger MFC produced a maximum power density of 4.30 W m⁻² at a current density of 16.4 A m⁻², corresponding to a volumetric power density of 2.87 kW m⁻³ at 10.9 kA m⁻³ for a double CEA-MFC. The high current density led to a high average coulombic efficiency (CE) of 83.5% as well as a high potential COD removal rate of 93.5 kg m⁻³ d⁻¹. Energy efficiency is estimated in the range of 21–35%, depending on the operating voltage. The low-cost non-woven cloth separator further reduced the anode–cathode spacing and internal resistance, greatly enhancing the power generation. The enhanced self-production of bicarbonate buffer, which can be manipulated by adjusting hydraulic retention time and substrate concentration, also contributed to the improved performance. The results demonstrate the great potential of MFC technology in competing with methanogenic anaerobic digestion for waste-to-electricity and wastewater treatment.