Decomposition in vacuum ultraviolet-based advanced oxidation/reduction processes and its relationship to...

Vacuum ultraviolet (VUV)-based treatment for water supplies can potentially be applied to a wide range of compounds because they enable enhancement of either oxidative or reductive decomposition through the addition of ozone (O₃) or the reduction of dissolved oxygen (DO), respectively. In the present study, we applied three VUV-based treatments (VUV alone, VUV/O₃, and VUV/low-DO) to five ozone-resistant compounds (1,4-dioxane, epichlorohydrin, acephate, N-nitrosodimethylamine [NDMA], and dichloroacetonitrile [DCAN]), and evaluated the extent of oxidative and reductive enhancements for each contaminant. Simple correlation analysis revealed that oxidative and reductive enhancements were more effective for compounds with a high highest occupied molecular orbital (HOMO) energy level and low lowest unoccupied molecular orbital (LUMO) energy level, respectively. These findings suggested that the effective VUV-based treatment for a contaminant might be identified by simply calculating its HOMO and LUMO energy levels. Further optimizations of O₃ and DO concentrations reduced the electric energy per order values for epichlorohydrin and DCAN to approximately 4/5 and 1/3, respectively, of their values for VUV alone.