The UV/Cl₂ process was investigated for its efficiency to destruct DEET at various conditions. The formation of total organic halogens (TOX) and genotoxicity from natural organic matter (NOM) during the UV/Cl₂ process and the following post-chlorination was assessed and compared with that of the UV/H₂O₂ process at similar radical exposure. Effect of ammonia on kinetics of nitrobenzene (NB) and benzoic acid (BA) degradation and formation of disinfection byproducts (DBPs) from NOM during the UV/Cl₂ process was investigated. The correlations between NOM change and formation of DBPs during the UV/Cl₂ process at various conditions were investigated.

The reactive chlorine species (RCS) were found to react with DEET at a rate constant similar to that of HO•. The pseudo first-order rate of D...[ Read more ]

The UV/Cl₂ process was investigated for its efficiency to destruct DEET at various conditions. The formation of total organic halogens (TOX) and genotoxicity from natural organic matter (NOM) during the UV/Cl₂ process and the following post-chlorination was assessed and compared with that of the UV/H₂O₂ process at similar radical exposure. Effect of ammonia on kinetics of nitrobenzene (NB) and benzoic acid (BA) degradation and formation of disinfection byproducts (DBPs) from NOM during the UV/Cl₂ process was investigated. The correlations between NOM change and formation of DBPs during the UV/Cl₂ process at various conditions were investigated.

The reactive chlorine species (RCS) were found to react with DEET at a rate constant similar to that of HO•. The pseudo first-order rate of DEET degradation by the UV/Cl₂ process was kinetic model based on the steady-state concentration of radicals. During degradation of DEET by the UV/Cl₂ process, six known DBPs, trichloromethane (TCM), chloral hydrate (CH), 1,1-dichloro-2-propanone (DCP), 1,1,1-trichloro-2-propanone (TCP), dichloroacetic acid (DCAA) and trichloroacetic acid (TCAA) were detected which comprised 13.5% of total organic chlorine (TOCl). The UV/Cl₂ process enhanced the yields of known DBPs and TOCl from DEET during the post-chlorination compared to the UV/H₂O₂ process.

The TOCl formation from NOM after 1 day of post-chlorination following the UV/Cl₂ process was similar to that following the UV/H₂O₂ process with similar radical exposure. Higher radical exposure led to the formation of higher amounts of DBP precursors in both the UV/Cl₂ and UV/H₂O₂ processes. Strong linear correlation was observed between the concentrations of TOCl and genotoxicity in the samples treated by chlorination, UV/Cl₂, UV/Cl₂ followed by post-chlorination, and UV/H₂O₂ followed by post-chlorination.

The presence of ammonia significantly affected the degradation of NB and BA and formation of DBPs from NOM by the UV/Cl₂ process. Breakpoint chlorination reactions generated reactive species (R_brk) which contributed more to the degradation of BA and NB than did the radicals formed from photolysis of chlor(am)ine species (R_ph). Higher initial ammonia and chlorine concentrations, which led to the same residual chlorine after the breakpoint chlorination reactions, generated more R_brk. However, increasing initial chlorine concentrations in the presence of certain amount of ammonia decreased the contribution of R_brk to the degradation of NB and BA and increased that of R_ph.

UV irradiation during the breakpoint chlorination (the UV/breakpoint chlorination) increased the DBP formation compared to the breakpoint chlorination in the dark at different initial ammonia and chlorine concentrations and different pHs. R_brk was found to significantly contribute to the formation of dichloroacetonitrile (DCAN). Increasing pHs increased the formation of DBPs during both the UV/breakpoint chlorination and breakpoint chlorination in the dark. The cumulative normalized excitation-emission matrix (EEM) areas at specific regions obtained from fluorescence spectroscopy correlated linearly with yields of DCAN and TCP.