The degradation, kinetics and biotransformation of Direct Red 80 and chemical oxygen demand (COD) were examined under a sulfate reducing environment. Complete color and sulfate removal with more than 87% COD removal were obtained in the batch experiments at different dye (50-800 mg/l) and sulfate (100-5000 mg/l) concentrations. Dye degradation, COD and sulfate removal followed first order kinetics. An increase in dye concentration from 0 to 800 mg L-1 decreased the rate constant (k(1)) for dye, COD and sulfate removal from 0.0843 to 0.035 h(-1), 0.019 to 0.009 h(-1) and 0.108 to 0.075 h(-1), respectively. In particular, the sulfate concentration had no significant effect on dye degradation. Unlike other anaerobic cultures, the sulfate-reducing bacteria culture showed excellent dye mineralization and desulfonation ability. Fourier transform infrared spectroscopy and gas chromatography-mass spectrometry revealed aniline and 1,4-diamino benzene to be the resulting metabolites after the decolorization of Direct Red 80. (C) 2013 Elsevier B.V. All rights reserved.