Decolorization of an azo dye by unacclimated activated sludge under anaerobic conditions

Studies on the reductive decolorization of a complex azo dye, Reactive Red 3.1, were made as part of the development of a practical approach to better exploit the metabolic potential of biomass in wastewater treatment. Decolorization was achieved at low and variable rates by mixed microbial cultures under various environmental conditions, including low pH and high salt concentration. It was caused by reductive cleavage of the azo bond to yield two aromatic amines. More reliable and effective decolorization rates, of up to 20–30 mg l−1 h−1, were given by unadapted activated sludge, (6 g l−1) incubated with 400 mg l−1 of Reactive Red 3.1 under anaerobic conditions. Decolorization also occurred best in static conditions.