Multi-angle comparison of UV/chlorine, UV/monochloramine, and UV/chlorine dioxide processes for water treatment and reuse

Abstract

Advanced oxidation processes (AOPs) have been increasingly studied and practiced for micropollutant abatement in drinking water treatment and potable water reuse. This study conducted the multi-angle comparison of the UV/chlorine, UV/monochloramine (UV/NH₂Cl), and UV/chlorine dioxide (UV/ClO₂) AOPs with respect to reactive species generation, micropollutant degradation, byproduct formation, and toxicity change. The concentrations of radicals (HO^·, Cl^·, and ClO^·) generated in the three AOPs followed the order of UV/chlorine > UV/NH₂Cl > UV/ClO₂ at an oxidant dose of 70 μM, an irradiation wavelength of 254 nm, and a pH of 7.5. The concentration of ozone generated in the UV/ClO₂ AOP was higher than that in the UV/chlorine AOP, while ozone was not generated in the UV/NH₂Cl AOP. The effects of pH (pH 6.0, 7.5, and 9.0) and UV wavelength (254 nm, 285 nm, and 300 nm) on the three AOPs were evaluated and compared. Using the radical and ozone concentrations determined in this study, the pseudo-first-order degradation rate constants of 24 micropollutants by the three AOPs were predicted and compared. When the three AOPs were used to treat the water containing the same concentration of natural organic matter, the formation of total organic chlorine (TOCl) and the organic byproduct-associated toxicity followed the same order of UV/chlorine > UV/NH₂Cl > UV/ClO₂. On the contrary, the inorganic byproduct-associated toxicity followed the order of UV/ClO₂ > UV/chlorine > UV/NH₂Cl, due to the high concentrations of chlorite and chlorate formed in the UV/ClO₂ AOP. Findings in this study offer fundamental information useful for the selection and operation of AOPs for micropollutant abatement in drinking water treatment and potable water reuse.