In this study, a combined anaerobic-aerobic treatment process based on mixed culture of bacteria was used to degrade azo dyes (AY-36). The experiment was integrated by exposing anaerobic granular sludge and aerobic aromatic amine degrading bacterial enrichment cultures. Under anaerobic conditions UASFB bioreactor using sodium acetate as a co-substrate, the AY-36 was reduced and resulting in a temporary accumulation of aromatic amines by the bacterial biomass. Hydraulic residence time (HRT) was fixed (24 h) through out the experiment. The two aromatic amine p-amino diphenylamine (p-ADPA) and 4-aminobenzenesulfonic acid (4-ABS) were detected from the reduction of AY-36. Subsequently, 4-ABS was degraded in the aerobic reactor which was earlier accumulated for 30 days. But p-ADPA was not degraded in aerobic condition, The combined anaerobic-aerobic bioreactor was able to completely remove the AY-36 at a maximum loading rate of 100 mg AY-36 L(-1) d(-1). (C) 2009 Elsevier Ltd. All rights reserved.