In this study, a bio-electrochemical reactor comprising of anaerobic and aerobic chambers with filled granular activated carbon as biocarrier and third electrode was developed to investigate the effect of ammonium and COD concentrations on the power generation and COD removal. Two important operating parameters including initial COD concentrations (50-2000 mg/L) and initial ammonium concentrations (40-1000 mg/L) were optimized to attain the best response of electricity generation and COD removal using response surface methodology (RSM) through an experiments design software. A total of thirteen runs of experiments were employed for statistical analysis of data and developing empirical model, which has ability to predict optimum condition. Based on the results, the maximum COD removal efficiency was 96.8%, when the produced current at the maximum level was 1.149 mA. It was found that main variables as solely or combination effects significantly affect the efficiency of MFCs. (C) 2019 Published by Elsevier Ltd on behalf of Hydrogen Energy Publications LLC.