Chemical pre-treatment of textile dye carriers with ozone: Effects on acute toxicity and activated sludge inhibition

In the present study partial oxidation, detoxification and biodegradability improvement of two extremely recalcitrant dye carriers, namely Carrier I Carrier II, subjected to ozonation (1200 mg/L) at their natural acidic pH (≈ 3.0-3.2) were investigated. The relative inhibition of the heterotrophic activity was assessed for raw carrier samples running OUR (oxygen uptake rate) measurements. The effectiveness of the combined oxidation systems was tested by monitoring ozone absorption rates, COD removal efficiencies, acute toxicity, biological inhibition rates as well as the BOD₅/COD ratios of raw and ozonated (2.5 g/L) aqueous dye carrier solutions. It could be established that ozonation resulted in poor COD abatement rates for both dye carriers, due to the fact that both chemical agents were not completely soluble in aqueous medium. However, due to its high volatility, Carrier I removal reached values as high as 91 % as a consequence of simultaneous air stripping. However, Carrier II appeared to be more toxic after ozonation indicating the formation of toxic intermediates. This observation was also reflected in the BOD₅ data.