Decolorization of the azo dye Reactive Black 5 by Fenton and photo-Fenton oxidation

The oxidative decolorization of Reactive Black 5 (RB5) in aqueous solution has been studied using Fenton (H2O2/Fe2+) and photo-Fenton (H2O2/Fe2+/UV) processes. This investigation reveals that both methods can remove the color of RB5. Batch experiments were carried out to investigate the process's optimal operational conditions: pH, H2O2 dosage, Fe2+ dosage, RB5 concentration and optimal [Fe2+]0/[H2O2]0/[RB5]0 ratio, to obtain the bests results at low cost, render AOP competitive with other processes. The optimal conditions found were a ratio [H2O2]0/[RB5]0 of 4.9:1, a ratio [H2O2]0/[Fe2+]0 of 9.6:1 and pH = 3.0. The decolorization experiments indicate that RB5 can be effectively decolorized using Fenton and photo-Fenton processes with a little difference between the two processes, 97.5% and 98.1%, respectively, for optimal conditions. This small difference in dye decolorization is not similar to TOC removal: with photo-Fenton process there is a significant increment (46.4% TOC removal) relatively to Fenton process (only 21.6% TOC removal). This fact indicates that although UV low-pressure mercury lamp has little effect on dye decolorization it is particularly important in dye mineralization.