UV/Sodium percarbonate for bisphenol A treatment in water: Impact of water quality parameters on the formation of reactive radicals

Abstract

Reported herein is an investigation of the impact of water quality parameters on the formation of carbonate radical anion (${\text{CO}}_3^{•-}$) and hydroxyl radical ($H{O}^{•}$) in UV/sodium percarbonate (UV/SPC) system versus in UV/hydrogen peroxide (UV/H₂O₂) system for bisphenol A (BPA) degradation in water. Pathways of ${\text{CO}}_3^{•-}$ oxidation of BPA were proposed in this study based on the evolution of direct transformation products of BPA. Observed in this study, the degradation of BPA in the UV/SPC system was slower than that in the UV/H₂O₂ system in the secondary effluents collected from a local wastewater treatment plant due to the significant impact of coexisting constituents in the matrices on the former system. Single water quality parameter (e.g., solution pH, common anion, or natural organic matter) affected radical formations and BPA degradation in the UV/SPC system in a way similar to that in the UV/H₂O₂ system. Namely, the rise of solution pH decreased the steady state concentration of $H{O}^{•}$ resulting in a decrease in the observed pseudo first-order rate constant of BPA ($k_{obs}$). Chloride anion and sulfate anion played a negligible role over the examined concentrations; nitrate anion slightly suppressed the reaction at the concentration of 20 mM; bicarbonate anion decreased the steady state concentrations of both ${\text{CO}}_3^{•-}$ and $H{O}^{•}$ exerting significant inhibition on BPA degradation. Different extents of $H{O}^{•}$ scavenging were observed for different types of natural organic matter in the order of fulvic acid > mixed NOM > humic acid. However, the impact was generally less pronounced on BPA degradation in the UV/SPC system than that in the UV/H₂O₂ system due to the existence of ${\text{CO}}_3^{•-}$. The results of this study provide new insights into the mechanism of ${\text{CO}}_3^{•-}$ based oxidation and new scientific information regarding the impact of water quality parameters on BPA degradation in the sytems of UV/SPC and UV/H₂O₂ from the aspect of reactive radical formation, which have reference value for UV/SPC application in wastewater treatment.