Although microbial fuel cells are potential candidates for electricity generation with concomitant treatment of wastewater, operational and technological improvements are still required to make them a cost effective process. In this paper, a full factorial design in combination with a central composite design were employed to probe the effects of pH and buffer concentration of catholyte on the performance of a two chamber microbial fuel cell. It was observed that at high level of buffer concentration (150 mM) varying the pH between 5.8 and 7.4 did not markedly influence the maximum power density and columbic efficiency. However, at a low level of buffer concentration (25 mM) reducing the pH led to higher power density. Furthermore, it was observed that higher concentrations of buffer were beneficial to power generation when pH was at its high level, but negatively impacted the cell performance at low pH levels. The highest maximum power was predicted to be 461 mWm(-2) (at a pH of 6.3 and a buffer concentration of 82 mM) and this was confirmed by experimental results. The findings of this paper highlight the importance of the joint effect of pH and buffer concentration, which is even more influential than their main individual effects. (C) 2015 Elsevier Ltd. All rights reserved.