A Novel UVA/ClO₂ Advanced Oxidation Process for the Degradation of Micropollutants in Water

Ultraviolet (UV)-based advanced oxidation processes (AOPs) are increasingly used for the degradation of micropollutants in water and wastewater. This study reports a novel UVA/chlorine dioxide (ClO₂) AOP based on the photolysis of ClO₂ using energy-efficient UV radiation sources in the UVA range (e.g., UVA-LEDs). At a ClO₂ dosage of 74 μM (5.0 mg L^-1 as ClO₂) and a UV fluence at 47.5 mJ cm^-2, the UVA₃₆₅/ClO₂ AOP generated a spectrum of reactive species, including chlorine oxide radicals (ClO^•), chlorine atoms (Cl^•), hydroxyl radicals (HO^•), and ozone at a concentration of ∼10^-13, ∼10^-15, ∼10^-14, and ∼10^-7 M, respectively. A kinetic model to simulate the reactive species generation in the UVA₃₆₅/ClO₂ AOP was established, validated against the experimental results, and used to predict the pseudo-first-order rate constants and relative contributions of different reactive species to the degradation of 19 micropollutants in the UVA₃₆₅/ClO₂ AOP. Compared to the well-documented UVC₂₅₄/chlorine AOP, the UVA₃₆₅/ClO₂ AOP produced similar levels of reactive species at similar oxidant dosages but was much less pH-dependent and required much lower energy input, with much lower formation of chloro-organic byproducts and marginal formation of chlorite and chlorate.