Comparative OH radical oxidation using UV-Cl2 and UV-H2O2 processes

Hydroxyl radicals (•OH) are a direct photolysis product of both aqueous free chlorine and hydrogen peroxide under UV irradiation. The photooxidation rates of an OH-radical probe compound, nitrobenzene, were compared in aqueous solutions of free chlorine, and H 2 O 2 , exposed to monochromatic UV irradiation (254 nm). Acidic ( 2 (pH 7) 2 O 2 2 (pH 6) 2 (pH 5). However, water quality had a significant impact; background photon and radical scavengers led to reduced rates of nitrobenzene decay in natural waters. Analysis of the necessary energy input required to achieve 90% nitrobenzene degradation showed UV-Cl 2 at pH 5 to be the most efficient oxidation process whereas at neutral pH, process efficiency was a function of the initial concentration of the oxidant; at 0.05 or 0.06 mM initial oxidant, UV-Cl 2 was the most efficient oxidation process, while at >0.15 mM initial oxidant, UV-H 2 O 2 was most efficient.