Kinetics of decolorization and mineralization of the azo dye Reactive Black 5 by hydrogen peroxide and UV light

C.I. Reactive Black 5 is one of the most used reactive dyes for textile finishing. It is a diazo dye, which can be decolorized by facultative anaerobic bacteria, sulfate reducing bacteria and aerobic white rot fungi. Mineralization by microorganisms has proven difficult. Advanced oxidation processes are promising alternatives for the decolorization and mineralization of Reactive Black 5, alone and in combination with aerobic biodegradation. The kinetics of the decolorization of Reactive Black 5 using a combination of hydrogen peroxide and UV radiation have been investigated. The rate of decolorization is first order with respect to dye concentration. It is enhanced with increasing hydrogen peroxide concentrations up to an optimum value. In our model we have correlated an empirical reaction rate expression which considers the contribution of both hydrogen peroxide and UV flux radiation based on the reaction kinetics. This empirical correlation agrees well with the experimental data for these conditions. Complete decolorization corresponded with 40-50% mineralization of the dye. Further mineralization can be achieved with extended radiation time.