Microbial fuel cells (MFC) haves drawn much attention as a potential approach for sludge treatment and renewable energy production. In this study, a single chamber air‐cathode in a membrane‐less MFC (ML‐MFC) was operated in batch mode with dewatered sludge from a municipal wastewater treatment plant as the substrate. Electrogenic bacterial species in the sludge acted as a catalyst for the generation of electricity. The performance of the ML‐MFC was evaluated using one‐factor‐at‐a‐time (OFAT) method followed by response surface methodology (RSM) via Central Composite Design using a quadratic model. In the preliminary OFAT study, the highest voltage generation (852.7 mV) and COD removal (149.2 mg/L) were obtained when the pH, electrode distance, moisture content, and temperature were at 6.0, 3 cm, 30% (vol/wt), and 35°C, respectively. After incubation of the ML‐MFC using optimum conditions suggested by the RSM, the voltage was successfully increased to 927.7 mV (improved 9%), while COD removal increased to 170.8 mg/L (improved 15%). This showed that optimization using RSM gave better results than the OFAT method. The maximum power density recorded from the optimum conditions was 41.3 mW/m². © 2018 American Institute of Chemical Engineers Environ Prog, 38: 208–219, 2019