Reduction of azo dyes by desulfovibrio desulfuricans

Azo dyes are widely used in textile finishing, and have become of concern i n wastewater treatment because of their color, bio-recalcitrance, and poten tial toxicity to animals and humans. Thus, wastewater with aro dyes must be decolorized and furthermore mineralized in appropriate systems combining b iological and chemical processes. In this study, the potential for sulfate reducing bacteria (SRB) to decolorize azo dyes was studied, employing the p ure culture of Desulfovibrio desulfuricans (D. desulfuricans) with varying sulfate levels. Under sulfate-rich conditions, the sulfide produced from su lfate respiration with pyruvate (electron donor) by D. desulfuricans chemic ally decolorized the azo dyes C. I. Reactive Orange 96 (RO 96) and C. I. Re active Red 120 (RR 120). Under sulfate-depleted conditions (less than or eq ual to 0.1 mmol/L), the decolorization of RO 96 and RR 120 occurred in corr elation with the fermentation of pyruvate by D. desulfuricans. It is sugges ted that the electrons liberated from the pyruvate oxidation were transferr ed via enzymes and/or coenzymes (electron carriers) to the dyes as alternat ive terminal electron accepters, giving rise to decolorization, instead of to the protons (H+), resulting in the production of H-2. Both decolorizatio n pathways were compared in light of bioenergetics and engineering aspects.