Efficient removal of halogenated phenols by vacuum-UV system through combined photolysis and OH oxidation: Efficiency, mechanism and economic analysis

In this study, efficient simultaneous degradation and dechlorination of the photo-recalcitrant emerging disinfection byproduct, 2-chlorophenol (2-CP), was achieved by vacuum-ultraviolet (VUV) system for the first time. Different from the conventional UV system, the combined action of direct photolysis and 'OH oxidation in VUV system led to a significantly higher removal efficiency for 2-CP. In UV system, 2-CP degradation rate constants was independent of the initial 2-CP concentration, and was increased with enhancing pH. To the contrary, in VUV system, higher initial concentration of 2-CP resulted in lower rate constant, and the degradation rates of 2CP under both acidic and alkaline conditions were higher than that at the neutral pH. Moreover, humic acid could inhibit 2-CP degradation more prominently in VUV system than in UV system, owing to the scavenging effect of 'OH by it. The degradation pathways of 2-CP were proposed based on the identified main degradation products by GC-MS/MS. Furthermore, degradation of the other seven typical halogenated phenols by VUV irradiation in tap water, ultrafiltrated water and Mill-Q water were investigated to verify the feasibility of the system. Based on the systematic economic analysis, VUV process is economically feasible for the advanced treatment of tap water to remove halogenated phenols.

Automated summary

Efficient simultaneous degradation and dechlorination of the photo-recalcitrant emerging disinfection byproduct 2-chlorophenol (2-CP) was achieved by vacuum-ultraviolet (VUV) system for the first time in this study. The combined action of direct photolysis and 'OH oxidation in VUV system led to a significantly higher removal efficiency for 2-CP. Moreover, the degradation rates of 2CP under both acidic and alkaline conditions were higher than that at the neutral pH in VUV system.