New micro- and macro- perspective on the removal process of 1H-benzotriazole by UV/PDS: Degradation mechanism, kinetics and multi-factor impact on removal efficiency.

Abstract

1H-benzotriazole (BTH), a high-volume industrial chemical, poses serious environmental concerns due to its toxicity and resistance to biodegradation, underscoring the urgent need for effective wastewater treatment solutions. This work evaluated the BTH removal efficiency under different conditions, including initial concentrations of Cl^-, Br^-, and HCO₃^- (i.e., [Cl^-]₀, [Br^-]₀, and [HCO₃^-]₀), pH levels, and coexisting ions. A multi-physics approach was employed, integrating reaction kinetics, computational fluid dynamics, and UV radiation models. Numerical results indicate that low [Cl^-]₀ promotes the oxidative degradation of BTH, whereas high [Cl^-]₀ inhibit this process by reducing the concentration of active radicals (HO•, Cl•, and SO₄^•-). Conversely, high [Br^-]₀ facilitates BTH removal due to the participation of Br• and BrO•. The existence of HCO₃^- introduces an obvious hysteresis effect in BTH removal, which intensifies with increasing [HCO₃^-]₀, attributed to the decreased concentrations of HO• and SO₄^•- and the low reactivity of CO₃^•-. Additionally, an increase in pH levels further accelerates BTH removal. When Cl^-, Br^-, and HCO₃^- coexist, the generated active bromine and chlorine species significantly enhance BTH degradation. This work provides a combined micro- and macro-level perspective on the efficient removal of organic contaminants by advanced oxidation techniques, intrinsically clarifying the complicated influences of multiple factors in practical sewage treatment scenarios.