Single and multichamber laboratory scale fixed film anaerobic systems were studied using acidic petrochemical industrial wastewater. A single-phase system column reactor was used and for the biphasic system a special multichamber reactor was constructed. The effect of operational parameters such as hydraulic retention time (HRT), organic loading rate (OLR) and pH was investigated on single and multichamber systems. Using acidic wastewater the multichamber system had no advantage over the single-phase system but it was possible to have temporal separation of two phases efficiently up to a 4-day HRT, OLR of 20.4 kg COD per m(3) per day and pH of 2.5 using petrochemical wastewater. Significant degradation of aromatic compounds was observed in the acidogenic phase, the pH of which was maintained between 5 and 5.5. Maximum COD reduction of 95 +/-1.0% and methane yield of 0.37 m(3)/m(3) per day at an OLR of 20.4 kg COD per m(3) per day was obtained with the multichamber reactor by separating the two phases. In the single phase system 95 +/- 1.0% COD reduction with 0.45 m(3)/m(3) per day methane yield at feed pH of 2.5, OLR of 21.7 kg COD per m(3) per day and HRT of 2.5 days was obtained. (C) 2001 Elsevier Science Ltd. All rights reserved.