Mixed cultures of sulfate reducing bacteria (SRB) were isolated from anaerobic cultures and enriched with SRB media. Studies on batch and continuous reactors for the removal Of SO2 with bulk drug industry wastewater as an organic source using isolated mixed cultures of SRB revealed that isolation and enrichment methodology adopted in the present study were apt to suppress the undesirable growth of anaerobic bacteria other than SRB. Studies on anaerobic reactors showed that process was sustainable at COD/S ratio of 2.2 and above with optimum sulfur loading rate (SLR) of 5.46 kg S/(m(3) day), organic loading rate (OLR) of 12.63 kg COD/(m(3) day) and at hydraulic residence time (HRT) of 8 h. Free sulfide (FS) concentration in the range of 300-390 mg FS/1 was found to be. inhibitory to mixed cultures of SRB used in the present studies. (c) 2007 Elsevier B.V. All fights reserved.