Kinetic removal of haloacetonitrile precursors by photo-based advanced oxidation processes (UV/HO, UV/O, and UV/HO/O).

The objective of the study is to evaluate the performance of conventional treatment process (i.e., coagulation, flocculation, sedimentation and sand filtration) on the removals of haloacetonitrile (HAN) precursors. In addition, the removals of HAN precursors by photo-based advanced oxidation processes (Photo-AOPs) (i.e., UV/HO, UV/O, and UV/HO/O) are investigated. The conventional treatment process was ineffective to remove HAN precursors. Among Photo-AOPs, the UV/HO/O was the most effective process for removing HAN precursors, followed by UV/HO, and UV/O, respectively. For 20min contact time, the UV/HO/O, UV/HO, and UV/O suppressed the HAN formations by 54, 42, and 27% reduction. Increasing ozone doses from 1 to 5 mgL in UV/O systems slightly improved the removals of HAN precursors. Changes in pH (6-8) were unaffected most of processes (i.e., UV, UV/HO, and UV/HO/O), except for the UV/O system that its efficiency was low in the weak acid condition. The pseudo first-order kinetic constant for removals of dichloroacetonitrile precursors (k') by the UV/HO/O, UV/HO and standalone UV systems were 1.4-2.8 orders magnitude higher than the UV/O process. The kinetic degradation of dissolved organic nitrogen (DON) tended to be higher than the k' value. This study firstly differentiates the kinetic degradation between DON and HAN precursors.