Biodegradation of Azo Dyes in Anaerobic–Aerobic Sequencing Batch Reactors

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Abstract

Effluent discharge from textile and dyestuff industries to neighboring water bodies is currently causing significant health concerns to environmental regulatory agencies due to the toxicity, mutagenicity, and carcinogenicity of the dyes and their breakdown products. Therefore, considerable attention has been given to evaluate the removal of dyes during wastewater treatment and in the natural environment. The most widely used dyes in industries are azo dyes, which require an anaerobic and aerobic phases for their complete biodegradation. Anaerobic stage is the first step of the treatment process in which azo dyes are reduced, resulting in toxic and colorless aromatic amines. Since breakdown products of azo dyes, which are formed when the azo bond is cleaved and color is removed, are resistant to anaerobic biodegradation, aerobic phase is therefore essential for complete biodegradation of colored effluents. Biological treatment has long been known, and the use of sequencing batch reactors (SBRs) for treating textile wastewater has attracted interest. The cyclic operations of SBR provide both color removal in anaerobic stage and aromatic amine removal in aerobic stage.