In this study, the degradation kinetic model and pathways of a UV filter, 2-phenylbenzimidazole-5-sulfonic acid (PBSA) during UV/chlorination were investigated. PBSA hardly degraded under UV irradiation or chlorination alone, but its degradation in UV/chlorination was efficient and followed pseudo-first order kinetics at pH 7. Increasing the chlorine dosage from 12.5 to 200 μM can enhance PBSA degradation, while increasing pH from 5 to 9 caused opposite effect. The second-order rate constants between radicals (∙Cl, ∙ClO, and ∙OH) and PBSA and the contribution of ∙OH during UV/chlorination were determined. ∙Cl and ∙OH were confirmed to be the main contributors to PBSA degradation. The presence of background [Formula: see text] and humic acid can inhibit PBSA degradation, but the presence of Cl- showed negligible effect. Kinetic model was established, and the prediction correlated well to the experimental results. The mineralization rate in terms of total organic carbon increased with reaction time to 44.9% after 60 min UV/chlorination. The PBSA degradation intermediates in UV/chlorination were identified, and the transformation pathways were proposed accordingly. Furthermore, the formation of chlorinated disinfection by-products (Cl-DBPs) were evaluated in the sequential chlorination for comprehensively evaluation of the efficiency, mechanism, and safety of removing PBSA using UV/chlorination.
Keywords: Disinfection by-product (DBP); Kinetic model; Oxidation radicals; UV filter; UV/chlorination; Water treatment.
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