Azo-dye degradation in an anaerobic-aerobic treatment system operating on simulated textile effluent

Decolorisation of azo dyes during biological effluent treatment can involve both adsorption to cell biomass and degradation by azo-bond reduction duri ng anaerobic digestion. Degradation is expected to form aromatic amines, wh ich may be toxic and recalcitrant to anaerobic treatment but degradable aer obically. Methods for the quantitative detection of substituted aromatic am ines arising from azo-dye cleavage are complex. A simple qualitative method is suggested as a way in which to investigate whether decolorisation is ac tually due to degradation, and whether the amines generated are successfull y removed by aerobic treatment. Samples from a combined anaerobic-aerobic s ystem used for treating a simulated textile wastewater containing the react ive azo dye Procion Red H-E7B were analysed by high-performance liquid chro matoraphy/ultraviolet (HPLC-UV) methods. Anaerobic treatment gave significa nt decolorisation, and respiration-inhibition tests showed that the anaerob ic effluent had an increased toxicity, suggesting azo-dye degradation. The HPLC method showed that more polar, UV-absorbing compounds had been generat ed. Aerobically, these compounds were removed or converted to highly polar compounds, as shown by HPLC analysis. Since the total organic nitrogen (TON ) decreased aerobically as organic N-containing compounds were mineralised, aromatic amine degradation is suggested. Although only a simple qualitativ e HPLC method was used, colour removal, toxicity and TON removal all suppor t its usefulness in analysing biotreatment of azo dyes.