Partial oxidation of hydrolysed and unhydrolysed textile azo dyes by ozone and the effect on biodegradability

This work involved a series of batch tests where Acid Yellow 17, and unhydrolysed and hydrolysed Reactive Black 5 textile dyes were ozonated to assess the efficacy of partial oxidation and associated decolourization, and parent compound degradation. Absorbance readings and a decrease in the chemical oxygen demand/total organic carbon (COD/TOC) confirmed that partial oxidation was the predominant degradation mechanism. An applied dose of 0.6 g1(-1) caused 100% colour removal through dye chromophore cleavage whilst higher doses resulted in fur ther degradation. Biodegradability improvement in ozonated hydrolysed Reactive Black 5 was tracked through biological oxygen demand (BOD5) increase and BOD/COD and BOD/TOC ratios. Partial oxidation improved the biodegradability of hydrolysed Reactive Black 5 and the optimal applied dose requirement for maximum biodegradability improvement was 1.8 g1(-1) which increased the BOD/TOC and BOD/COD ratios from 0 to 0.58 and 0.27, respectively. This suggested that fur maximum biodegradability improvement, partial oxidation must proceed beyond decolourization.