Photodegradation of micropollutants by vacuum-UV (VUV) radiation in potable reuse waters: Promotive and inhibitory effects of free chlorine oxidant

The occurrence of a variety of harmful micropollutants in potable reuse trains has been a matter of concern. In this study, the performance of the vacuum-ultraviolet / ultraviolet advanced oxidation process (VUV/UV AOP) without and with free chlorine (VUV/UV/Cl 2 AOP) for elimination of carbamazepine (CBZ) and 1,4-dioxane (1,4-D) from potable reuse systems was evaluated. The addition of free chlorine improved CBZ degradation by ∼12 % while reducing the rate of 1,4-D removal by ∼50 %, highlighting the selective effectiveness of the VUV/UV/Cl 2 AOP based on micropollutant type. The effects of operational conditions, including free chlorine dosage, solution pH and contributions of different radical species, were also determined. Both high chlorine concentrations as well as alkaline pH were shown to slow down the removal of both contaminants in the VUV/UV/Cl 2 . Also, the VUV/UV/Cl 2 AOP was considered to be promising for treatment of 1,4-D in reverse osmosis (RO) permeate due to photochemical chain reactions between the added chlorine and water constituents which lead to effective formation of Cl 2 •- . The findings of this research demonstrate the broader potential of the VUV/UV/Cl 2 AOP as a tailored, adaptable solution for optimizing micropollutant removal in potable reuse systems, based on contaminant type and water matrix. • 97 % removal of 1,4-D was achieved by VUV/UV and VUV/UV/Cl 2 AOPs. • Increased chlorine doses reduced the rate of micropollutants removal in VUV/UV/Cl 2 . • • OH are the primary driver of 1,4-D and CBZ degradation in the VUV/UV/Cl 2 AOP. • In the VUV/UV/Cl 2 AOP, Cl 2 •- is the major RCS contributing to 1,4-D degradation. • VUV/UV/Cl 2 AOP is highly efficient in RO permeate compared to O 3 /BAC effluent.