Degradation of reactive azo dyes by UV/H2O2: impact of radical scavengers.

Hydroxyl radical (*OH) scavenging effects of carbonate (CO3(2-)), bicarbonate (HCO3-) and chloride (Cl-) ions on the performance of an ultraviolet light-hydrogen peroxide (UV/H2O2) advanced oxidation process were investigated using a reactive azo dye, C.I. Reactive Red 141 as the model compound. It was found that in the absence of scavengers, complete color removal was possible in 15 min under the experimental conditions employed. The rate of color decay was inhibited remarkably with increasing concentrations of bicarbonate and carbonate species, especially when the distribution of alkalinity favored the dominance of carbonate ions. It was further observed that chloride inhibited the rate only when it was between 100-1250 mM as Cl, and was ineffective at higher concentrations.