Development of an improved reactor configuration of anaerobic filter was carried out for the elimination of clogging of filter media. The experiments over different hydraulic retention times (HRTs) indicated that the HRT of 12 h was the most appropriate one for the system studied while treating the municipal wastewater, which resulted 90% and 95% BOD and COD reduction, respectively. Reduction up to 95% in suspended solids concentration could be achieved without any pretreatment. The specific biogas yield obtained was 0.35 in 3 CH4/kgCODr with 70% of CH4 content in the biogas generated from the system at the HRT of 12 h. Operational problems such as clogging of filter media were not observed throughout the period of study over 600 d. (c) 2006 Elsevier Ltd. All rights reserved.