Ozonation of high strength segregated effluents from a woollen textile dyeing and finishing plant

Effluents from dyeing processes of woollen textile finishing industries are highly polluted with recalcitrant compounds compared to effluents from rinsing and finishing processes. Oxidation of woollen textile dyeing effluent consisting of wastewater generated from spent dye baths and first and second rinses (remaining composite wastewater) were investigated. Ozone oxidation (C-O3 = 18.5 mg/l; input rate) was applied on remaining composite wastewater, before and after the biological treatment, for various time intervals. Treatment efficiency was monitored by decolorization and by COD removal rates. Additionally, toxicity tests (bioluminescence test) were carried out to determine the effect of oxidation process. The results indicated that 40 min ozonation of biologically treated wastewater yielded almost colorless effluent with a decolorization efficiency of around 98-99% and with a corresponding ozone absorption rate of 58.0 mg/l. Biological treatment followed by 10 min ozone oxidation reduced the overall toxicity significantly (92%). However, ozonation was found to have only slight effect on COD removal. (C) 2003 Elsevier Science Ltd. All rights reserved.