Influence of the UV/chlorine process in the formation of disinfection byproducts and toxicity from natural organic matter

Abstract

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.

Date of Award	2018
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology