Wastewater treatment performance of a novel biofilm reactor named as rotating perforated tubes biofilm reactor (RPT) was investigated and compared with a rotating biodisc reactor (RBD) under the same conditions. The effects of major process variables such as feed wastewater flow rate, COD concentration and loading rate on COD removal performances of both reactors were evaluated. Rotating perforated tubes biofilm reactor was found to be more advantageous as compared to rotating biodisc system for COD removal efficiency. This difference becomes more significant at low A/Q ratios. Empirical design equations were developed for both systems to quantify the systems' performance as a function of major process variables. (C) 2002 Elsevier Science Ltd. All rights reserved.