Degradation of 2-phenylbenzimidazole 5-sulfonic acid by UV/chlorine advanced oxidation technology: Kinetic model, degradation byproducts and reaction pathways

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 mu M can enhance PBSA degradation, while increasing pH from 5 to 9 caused opposite effect. The second-order rate constants between radicals (center dot Cl, center dot ClO, and center dot OH) and PBSA and the contribution of center dot OH during UV/chlorination were determined. center dot Cl and center dot OH were confirmed to be the main contributors to PBSA degradation. The presence of background HCO3- 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.

Automated summary

The degradation kinetic model and pathways of a UV filter, PBSA, during UV/chlorination were investigated. The efficient degradation of PBSA was observed under UV/chlorination conditions and followed pseudo-first order kinetics. The contribution of radicals and the effect of different factors on PBSA degradation were determined. The study also proposed transformation pathways and evaluated the formation of chlorinated disinfection by-products. Overall, the study provides insights into the efficiency, mechanism, and safety of removing PBSA using UV/chlorination.