Degradability of selected azo dye metabolites in activated sludge systems

The stability of eight environmentally relevant azo dye metabolites [o-amin otoluene (2), 4,4 ' -thiodianiline (4), 4,4 '- diaminodiphenylmethane (6), p-chloroaniline (7), 2,4-toluylenediamine (9), p-kresidine (14), 2,4-diamin oanisole (15), and 2-naphthylamine (18)] was investigated in activated slud ge systems and compared to their hydrolysis stability. For both studies, te st systems of the EC and EPA were used. The results show that degradation u nder aerobic conditions proceeds via oxidation of the substituents located on the aromatic ring or on the side chain. Under anaerobic conditions, the azo bond is reductively cleaved, which leads to the substituted amines. The se are toxic and potentially hazardous to the environment. (C) 2001 Elsevie r Science Ltd. All rights reserved.