Single chamber mediatorless microbial fuel cell (MFC; non-catalyzed graphite electrodes; open air cathode) behaviour was evaluated under different pH microenvironments [acidophilic (pH 6), neutral (pH 7) and alkaline (pH 8)] during chemical wastewater treatment employing anaerobic mixed consortia as anodic biocatalyst at room temperature (29 ± 2 °C). The performance was found to depend on the feed pH used. Higher current density was observed at acidophilic conditions [pH 6; 186.34 mA/m2; 100 Ω] compared to neutral [pH 7; 146.00 mA/m2; 100 Ω] and alkaline [pH 8; 135.23 mA/m2; 100 Ω]. On the contrary, substrate degradation was found to be effective at neutral pH conditions (ξCOD – 58.98%; SDR – 0.67 kg COD/m3-day) followed by alkaline (ξCOD – 55.76%; SDR – 0.62 kg COD/m3-day) and acidophilic (ξCOD of 47.80%; SDR 0.58 kg COD/m3-day) conditions studied. However, relatively higher specific power yield was observed at acidophilic microenvironment (46 mW/kg CODR) compared to neutral (35 mW/kg CODR) and alkaline (34 mW/kg CODR) conditions. The behaviour of the MFC was also evaluated employing electron discharge, cyclic voltammetry, cell potentials, Coulombic efficiency and sustainable power analysis. Acidophilic operation showed higher Coulombic efficiency and effective electron discharge at relatively higher resistance compared to neutral and alkaline conditions studied. © 2009 International Association for Hydrogen Energy.