A comparative study of UV/H₂O₂ and UV/PDS for the degradation of micro-pollutants: kinetics and effect of water matrix

Organic micro-pollutants such as pesticides and endocrine disruptors cause serious harm to human health and aquatic ecosystem. In this study, the potential degradation of atrazine (ATZ), triclosan (TCS), and 2,4,6-trichloroanisole (TCA) by UV-activated peroxydisulfate (UV/PDS) and UV-activated H₂O₂ (UV/H₂O₂) processes were evaluated under different conditions. Results showed that UV/PDS process was more effective than UV/H₂O₂ under the same conditions. Increasing oxidant dosage or decreasing the initial ATZ, TCS, and TCA concentrations promoted the degradation rates of these three compounds. The presence of natural organic matter (NOM) could effectively scavenge sulfate radical (SO₄•⁻) and hydroxyl radical (HO•) and reduced the removal rates of target compounds. Degradation rates of ATZ and TCA decreased with pH increasing from 5.0 to 9.0 in UV/PDS process, while in UV/H₂O₂ process, the increase of solution pH had little effect on ATZ and TCA degradation. In the UV/PDS and UV/H₂O₂ oxidation process, when the solution pH increased from 5 to 8, the removal rates of TCS decreased by 19% and 1%, while when the solution pH increased to 9, the degradation rates of TCS increased by 23% and 17%. CO₃²⁻/HCO₃⁻ had a small inhibitory effect on ATZ and TCA degradation by UV/H₂O₂ and UV/PDS processes but promoted the degradation of TCS significantly (> 2 mM). Cl⁻ had little effect on the degradation of ATZ, TCA, and TCS in UV/H₂O₂ process. Cl⁻ significant inhibited on the degradation of ATZ and TCS, but the influence of Cl⁻ on the degradation of TCA was weak in UV/PDS process. Based on these experimental results, the various contributions of those secondary radicals (i.e., carbonate radical, chlorine radical) were discussed. This study can contribute to better understand the reactivities when UV/PDS and UV/H₂O₂ are applied for the treatment of micro-pollutant-containing waters.