Assessment of degradation of eight commercial reactive azo dyes individually and in mixture in aqueous solution by ozonation

Degradation of eight commercial reactive azo dyes with different structures containing different substituted groups has been investigated in a semi-batch reactor by ozonation individually and in mixture. The results showed that pH 10 was effective for color and COD removal of these dyes. Different dyes needed different time of ozonation for decolorization. Dyes even if decolorized to 95–99%, COD removal was different for different dyes indicating that the complexicity of structures play a major role. Oxidation and cleavage of substituent groups were evidenced by the release of chloride, nitrate and sulfate during ozonation. Increase in biodegradability was observed after ozonation, as measured by the BOD5/COD ratio. The ozonation reaction followed a pseudo first order kinetics. The study revealed that ozonation of reactive dye is a viable technique for dye containing wastewater treatment.