Treatment of dyehouse liquors in a biological sequencing batch reactor with recursive chemical oxidation

A new developed sequencing batch process for the purification of residual w ater containing concentrated azo dye was investigated. Within a treatment c ycle the biological anoxic decolorization, followed by an aerobic mineraliz ation of organic metabolites in combination with the biodegradability-achie ving partial oxidation with ozone are carried out sequentially. The split f low can be destructively purified to 90% with respect to the parameter DOC. It was decolorized to an extent of 98% and the toxicity measured by the bi oluminescence test decreased up to 99%. With an unspecific facultative anae robic bacterial mixed culture anoxic decolorization of the residual liquor (20 g(dye)/L) without addition of an external auxiliary substrate was obser ved. In the first phase of the treatment cycle, the azo dye-molecules are c left at the azo bond by biochemical reduction which leads to the correspond ing sulfonated aromatic amines. In the following aerobic phase the cleft pr oducts were mineralized by the same microorganisms in the same reactor. Bec ause of the recalcitrant and respectively toxic character of a part of the remaining metabolites, further aerobic mineralization was initialized by pa rtial oxidation with ozone. The recursive ozonization in a recircled stream with biological post-treatment of the transformed substances led to an inc reased reaction selectivity and lower consumption of ozone. The results hav e shown that the chosen sequencing batch reactor with the ozonization bypas s is suitable for an effective treatment of high concentrated dyehouse liqu ors.