A recently developed rotating perforated tubes biofilm reactor (RTBR) was used for treatment of 2,4-dichlorophenol (DCP) containing synthetic wastewater. Effects of important operating variables such as A/Q ratio, feed wastewater DCP/COD ratio and DCP concentration on percent COD, DCP and toxicity removals were investigated. Percent COD, DCP and toxicity removals increased and effluent COD, DCP and toxicity levels decreased with increasing A/Q ratio because of larger biofilm surface area at high A/Q ratios. A/Q ratio above 130 m(2) dm(-3) resulted in more than 97% COD, DCP and toxicity removals when the feed COD and DCP contents were 5000 and 100mg l(-1), respectively. Increasing feed DCP concentrations did not affect percent DCP and toxicity removals considerably resulting in more than 97% removals for the feed DCP up to 393 mg l(-1). However, percent COD removal decreased with increasing feed DCP content probably because of natural selection of DCP degrading organisms and potential inhibitory effects of DCP degradation products on COD removing microorganisms. A kinetic model describing the COD removal rate was developed and the kinetic constants were determined by using the experimental data. Kinetic model estimations of the system performance were in good agreement with the experimental data. (c) 2006 Elsevier Inc. All rights reserved.