Degradation of roxarsone in UV-based advanced oxidation processes: A comparative study

Highlights: • The degradation of ROX follows the order of UV/H₂O₂ > UV/PDS > UV/PMS. • The second-order rate constant of ROX with SO₄^{• −} is (7.68 ± 0.37) × 10⁸ M⁻¹ s⁻¹. • The pH (5.0–9.0) exhibits negligible effect on ROX removal. • ROX is mainly converted to As(V) in the three UV-based AOPs. Organoarsenicals such as roxarsone (ROX) pose a great threat to the eco-environment and human health. Herein, the degradation of ROX via UV-based advanced oxidation processes (AOPs) including UV/hydrogen peroxide (UV/H₂O₂), UV/peroxydisulfate (UV/PDS), and UV/peroxymonosulfate (PMS) processes are comparatively investigated. The removal efficiency of ROX in the UV-based AOPs follows the order of UV/H₂O₂ > UV/PDS > UV/PMS at pH 7.0, while UV/PDS is the most effective process in reducing the total organic carbon (TOC). The second-order rate constants of ROX with hydroxyl radicals (^• OH) and sulfate radicals (SO₄^{• −}) are determined to be (2.71 ± 0.27) × 10⁹ and (7.68 ± 0.37) × 10⁸ M⁻¹ s⁻¹, respectively. The degradation of ROX obeys the pseudo-first-order kinetics model, and the apparent rate constants (k) linearly increase with increasing the oxidants dosage from 0.10 to 1.0 mM. The solution pH (5.0–11.0) exhibits a limited effect on the oxidation of ROX in UV/H₂O₂ and UV/PDS processes, but a great enhancement is observed at pH 11.0 in UV/PMS process. Humic acid and bicarbonate obviously suppress the photodegradation of ROX. In addition, arsenic in ROX is mainly converted to As(V) in the three UV-based AOPs. Overall, this study provides essential information for the degradation of ROX via the traditional UV-based AOPs.