Critical effect of hydrogen peroxide in photochemical oxidative decolorization of dyes: Acid Orange 8, Acid Blue 74 and Methyl Orange

Advanced oxidation processes (AOPs) have proved. very effective in treatment of the various hazardous organic pollutants in water. The photochemical decolorization of three dyes, namely Acid Orange 8 (AO8), Acid Blue 74 (AB74) and Methyl Orange (MO) was studied in the UV/hydrogen peroxide process by using a continuous photochemical reactor with a 15 W low pressure mercury lamp. Decolorization was complete in relatively short time and follows apparent first order kinetics with respect of dye concentration. The, rate of disappearance of a given dye was monitored spectrophotometrically at the visible maximum absorption wavelength. It was found that the rate of decolorization rises by increasing the initial dosage of H2O2 up to a "critical" value at which it is maximum and beyond which it is inhibited. A simple reactions pathway, describing adequately the process, has been studied. Based on this reaction schema, we have established a-mathematical relation between the apparent rate constant of the dye removal and applied H2O2 dosage presented by the ratio of its initial mass concentration to that of the dye. The rate constant values obtained by model for the three dye solutions are in good agreement with the experimental data. The model parameters have been determined. (C) 2003 Elsevier Science Ltd. All rights reserved.