“Critical” effect of hydrogen peroxide in photochemical dye degradation

Tertiary or pretreatment of dyeing effluents by advanced oxidation processes (AOP) catalyzed by a source of UV light and a powerful oxidant is a promising alternative for the effective removal of color and refractory organics from the effluent. A crucial feature in designing such systems is the optimization of operating conditions (such as UV and oxidant dosages), which yield maximum removal at acceptable costs. The present study describes a modeling approach to keep the oxidant dosage at the most “effective” level to sustain maximum rate of dye removal at the selected experimental conditions. The method of study involved monitoring the rate of dye degradation in a synthetic azo dye solution of nearly constant concentration during irradiation by a medium pressure light source and varying H2O2 dosages, followed by predicting a mathematical relation between the pseudo-first order rate constant and the “effective H2O2 level” in the photoreactor. It was found that this “effective level” can be set by controlling the initial mass ratio of H2O2 to dye, or the light fraction absorbed by hydrogen peroxide within the UV emission spectra of the light source.