Microaerophilic-aerobic sequential batch reactor for treatment of azo dyes containing simulated wastewater

Azo dyes are considered to be resistant to attack by aerobic microorganisms and not amenable to aerobic effluent treatment process. Azo dyes are decolorized under anaerobic or microaerophilic condition by the enzyme azoreductase secreted by microorganisms. The present study is a new approach to decolorization and biodegradation of azo dyes from simulated wastewater in an aerobic sequencing batch reactor. Facultative microorganisms under microaerophilic conditions decolorize azo dyes and total biodegradation occurs under aerated conditions. Laboratory flask experiments with various combination modes of aeration and static have shown 92.84% initial COD reduction along with 99.0% decolorization. Accordingly, an investigation was made on a laboratory scale to assess the feasibility of microaerophilic fixed film bed reactor system to decolorize simulated textile wastewater including the influence of operating conditions. Work was carried out with a laboratory scale down flow reactor, equipped with beads used in insulation as support. A continuous reactor for decolorization/biodegradation of azo dyes in aerobic sequencing reactor needs an understanding of a sequence. The first reactor was always operated under microaerophilic down flow fixed film fixed bed conditions, where the azo dyes from simulated wastewater were decolorized at 7.72 h hydraulic retention time with 2.2392 kg/m(3) per day loading rate. COD reduction of 74.67% was achieved. The second reactor operated in a down flow fixed bed, and shows a significant decrease in COD along with ammonia, nitrite and nitrate. (C) 2004 Elsevier Ltd. All rights reserved.