Treatment of colored textile wastewater in SBR with emphasis on the biodegradation of sulfonated aromatic amines

Azo dyes represent a problematic contaminant class in textile effluents because they are normally resistant to aerobic biodegradation and are consequently difficult to eliminate by conventional wastewater treatment systems. Since the mineralization of azo dyes is not likely to occur under the anaerobic conditions generally required for their reductive decolorization, anaerobic/aerobic SBR are promising systems for the decolorization of textile effluents containing azo dyes integrated with the mineralization of the resulting aromatic amines. In the present study, high decolorization yields (up to 90% with an initial dye concentration of 100 mg l^-1) of a monoazo dye were achieved in the anaerobic phase of an anaerobic/aerobic SBR. However, the aromatic amines formed were not mineralized in the subsequent aerated phase. The development a bacterial community able to mineralize specific sulfonated aromatic amines was attempted in an aerobic SBR, operated downstream of the anaerobic/aerobic SBR. This attempt was not successful, since the microbial population was able to convert the primary aromatic amines, though not to full mineralization, but resulted in the identification of different chromatographic patterns arising from the bioconversion of azo dye metabolites in different oxygen-availability conditions. Oxygen-sensitivity of the involved intermediates is, however, an interfering factor possibly impairing biodegradation