Assessing the Chemical-Free Oxidation of Trace Organic Chemicals by VUV/UV as an Alternative to Conventional UV/HO.

Low-pressure mercury lamps with high-purity quartz can emit both vacuum-UV (VUV, 185 nm) and UV (254 nm) and are commercially available and promising for eliminating recalcitrant organic pollutants. The feasibility of VUV/UV as a chemical-free oxidation process was verified and quantitatively assessed by the concept of HO equivalence (EQ), at which UV/HO showed the same performance as VUV/UV for the degradation of trace organic contaminants (TOrCs). Although VUV showed superior HO activation and oxidation performance, its performance highly varied as a function of light path length () in water, while that of UV/HO proportionally decreased with decreasing HO dose regardless of . On increasing from 1.0 to 3.0 cm, the EQ of VUV/UV decreased from 0.81 to 0.22 mM HO. Chloride and nitrate hardly influenced UV/HO, but they dramatically inhibited VUV/UV. The competitive absorbance of VUV by chloride and nitrate was verified as the main reason. The inhibitory effect was partially compensated by OH formation from the propagation reactions of chloride or nitrate VUV photolysis, which was verified by kinetic modeling in Kintecus. In water with an of 2.0 cm, the EQ of VUV/UV decreased from 0.43 to 0.17 mM (60.8% decrease) on increasing the chloride concentration from 0 to 15 mM and to 0.20 mM (53.5% decrease) at 4 mM nitrate. The results of this study provide a comprehensive understanding of VUV/UV oxidation in comparison to UV/HO, which underscores the suitability and efficiency of chemical-free oxidation with VUV/UV.