Impact of Chloride Ions on UV/H₂O₂ and UV/Persulfate Advanced Oxidation Processes

Chloride ion (Cl^-) is one of the most common anions in the aqueous environment. A mathematical model was developed to determine and quantify the impact of Cl^- on the oxidization rate of organic compounds at the beginning stage of the UV/persulfate (PS) and UV/H₂O₂ processes. We examined two cases for the UV/PS process: (1) when the target organic compounds react only with sulfate radicals, the ratio of the destruction rate of the target organic compound when Cl^- is present to the rate when Cl^- is not present (designated as r_R^Cl/ r_R) is no larger than 1.942%; and (2) when the target organic compounds can react with sulfate radicals, hydroxyl radicals and chlorine radicals, r_R^Cl/ r_R, can be no larger than 60%. Hence, Cl^- significantly reduces the organic destruction rate in the UV/PS process. In the UV/H₂O₂ process, we found that Cl^- has a negligible effect on the organic-contaminant oxidation rate. Our simulation results agree with the experimental results very well. Accordingly, our mathematical model is a reliable method for determining whether Cl^- will adversely impact organic compounds destruction by the UV/PS and UV/H₂O₂ processes.