Among 170 strains of acetogenic bacteria, a strain No.BP103 showed the highest decolorization yield (76.4 +/- 3.2%) when cultivated at 30degreesC for 5 days in molasses pigments medium containing glucose 3.0%, yeast extract 0.5%, KH2PO4 0.1% and MgSO4 (.) 7H(2)O 0.05% and the pH adjusted to 6.0. In addition this strain could decolorize 32.3 +/- 3.2% and 73.5 +/- 3.5% of molasses pigments in stillage and anaerobically treated molasses wastewater, both supplementing glucose 3.0%, yeast extract 0.5%, KH2PO4 0.1% and MgSO4 (.) 7H(2)O 0.05%. However without nutrients supplement, the decolorization yields were 9.75 +/- 3.0% and 44.36 +/- 3.4%. respectively. In a replacement culture system involving six times replacement (30 days), the strain No.BP103 showed a constant decolorization yield of 72.0 +/- 3.2-84.0 +/- 3.2% and caused decreases of biological oxygen demand and chemical oxygen demand values of approximately 58.5 +/- 6.4-82.2 +/- 7.1% and 35.5 +/- 0.42-71.20.58%, respectively. Under a periodical feeding system, the decolorization yield was 30.0 +/- 2.1-45.0 +/- 3.5%. (C) 2003 Elsevier Ltd. All rights reserved.