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/Cl₂ 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/Cl₂ 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/Cl₂. Also, the VUV/UV/Cl₂ 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 Cl₂•-. The findings of this research demonstrate the broader potential of the VUV/UV/Cl₂ AOP as a tailored, adaptable solution for optimizing micropollutant removal in potable reuse systems, based on contaminant type and water matrix.