A Novel UVA/ClO 2 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 (ClO 2 ) AOP based on the photolysis of ClO 2 using energy-efficient UV radiation sources in the UVA range (e.g., UVA-LEDs). At a ClO 2 dosage of 74 μM (5.0 mg L -1 as ClO 2 ) and a UV fluence at 47.5 mJ cm -2 , the UVA 365 /ClO 2 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 UVA 365 /ClO 2 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 UVA 365 /ClO 2 AOP. Compared to the well-documented UVC 254 /chlorine AOP, the UVA 365 /ClO 2 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.