Biodegradation of azo dye C.I. Acid Red 88 by an anoxic–aerobic sequential bioreactor

The potential of a sequential anoxic–aerobic bioreactor to decolorize and degrade azo dye C.I. Acid Red 88 (AR-88) was evaluated. An up flow fixed-film column reactor (UFCR) having polyurethane foam (PUF) as immobilization support was built using a consortium based on four acclimatized bacterial strains belonging to Stenotrophomonas sp., Pseudomonas sp. and Bacillus sp., isolated from waste disposal sites of textile processing industries (TPI) as inoculum. The UFCR was operated at flow rate of 7 mL h−1 with hydraulic retention time (HRT) of 12 h. The effluent of anoxic UFCR was fed to continuously stirred aerobic reactor (CSAR). The sequential anoxic–aerobic treatment of synthetic dye wastewater (SDW) feed having 100 mg L−1 of AR-88 dye resulted in the 98% color and 95% COD removal. The aromatic metabolic intermediates produced under anoxic conditions were transformed to non-aromatic metabolites during aerobic treatment. The UV–visible spectrophotometry, TLC and NMR analyses confirmed the biotransformation of parent dye into unrelated non-aromatic compounds. The azo dye AR-88 was transformed to non-aromatic metabolic intermediates after treatment in sequential anoxic–aerobic bioreactor.