The performance of granular activated carbon (GAC)-biofilm configured sequencing batch reactor (SBGR) in aerobic environment was investigated for the treatment of composite chemical wastewater Pow BOD/COD ratio (similar to 0.3), high sulfate content (1.75 g/l) and high TDS concentration (11 g/l)]. Composite wastewater was a combined mixture of effluents from about 100 chemical based industries. Reactor was operated under anoxic-aerobic-anoxic microenvironment conditions with a total cycle period of 24 h (fill: 15 min; reaction (aeration with recirculation): 23 h; settle: 30 min; decant: 15 min) and the performance of the system was studied at organic loading rates (OLR) of 1.7 kg COD/cum-day, 3.5 kg COD/cum-day and 5.5 kg COD/cum-day. The reactor showed efficient performance with respect to substrate degradation rate and sustained its performance at higher operating OLR (5.5 kg COD/cum-day) and at low BOD/COD ratio. Substrate utilization was found to increase with increase in the operating OLR. Maximum non-cumulative substrate utilization of 1.837 kg COD/cum-h, 2.99 kg COD/cum-h and 3.821 kg COD/cum-h was observed after 15 h of the cycle operation for operating OLRs of 1.7 kg COD/cum-day, 3.5 kg COD/cum-day and 5.5 kg COD/cum-day, respectively. Sulfate removal efficiency of 11 +/- 2% was recorded in the SBGR due to the induced anoxic conditions prevailing during the sequence phase operation of the reactor and the existing internal anoxic zones in the biofilm. Effective performance of the reactor may be attributed to sorption capacity of GAC as carrier material facilitating low toxicant concentration in the mixed liquor. The existing high flow rates around the GAC particle results in good mass transfer of the substrate from the bulk liquid. The long retention of biofilm on GAC increases the potential for the treatment of recalcitrant industrial wastewater. GAC configured biofilm configuration coupled with sequencing batch mode operation appears to be promising for the effective treatment of complex industrial wastewater containing poorly degradable compounds. (c) 2005 Elsevier B.V. All rights reserved.