In this study, the removal of carbon, nitrogen and phosphorus from a synthetic wastewater in an integrated rotating biological contactor (RBC) and activated sludge (AS) system was investigated. The experiments were conducted based on a central composite design (CCD) and analyzed using response surface methodology (RSM). In order to analyze the process, four significant independent variables viz. hydraulic retention time (HRT), chemical oxygen demand (COD) to nitrogen ratio (COD/N), internal recirculation from aerobic to anoxic zone (R) and disks rotating speed (r) and six dependent process and quality parameters as the process responses were studied. The region of the exploration for the process was taken as the area enclosed by hydraulic retention times (9.7, 18.7h), COD/N ratios (4,20), R (1, 4), and r (5, 15 rpm) boundaries. The most effective factors on the process performance were found to be HRT and R in terms of COD and TN removal. The optimal region was enclosed by the entire HRT (18, 18.7h) and r (5, 15 rpm) boundaries, at the medians of the COD:N:P (1000:83:30) and R (2.5). The present study provides valuable information about interrelations of quality and process parameters at different values of the studied variables. (C) 2011 Elsevier B.V. All rights reserved.