Chloroacetonitriles (CANs) are highly toxic nitrogenous disinfection by-products (N-DBPs), which frequently appear in water supply systems and have attracted widespread attention. UV/persulfate (PS) is an effective method to degrade CANs. Bromide (Br-) is widespread in aquatic environments and reacts with oxidative radicals to produce secondary reactive bromine species (RBS), which affects the degradation of CANs by UV/PS. It was found that the degradation of CANs was highly inhibited by Br-. The apparent first-order reaction rate constants of monochloroacetonitrile (MCAN), dichloroacetonitrile (DCAN) and trichloroacetonitrile (TCAN) decreased from 2.63 × 10-3, 2.00 × 10-3 and 8.66 × 10-4 s-1 to 2.58 × 10-4, 1.61 × 10-4 and 1.59 × 10-4 s-1, respectively after adding 20 μM of Br-. HO• was the main radicals contributing to the degradation of CANs when the concentration of Br- was less than 10 μM, compared with SO4•- and direct photolysis. When the concentration of Br- was up to 20 μM, the contributions of RBS accounted for 85.7%, 90.7% and 89.9% of the apparent degradation rate constants of CANs, respectively. During the reaction, about 65% of nitrogen atoms were transformed into NO3- by the CC bond cleavage and oxidation. The yields of Cl- by dechlorination reaction accounted for 83.5%, 71.0% and 41.2% of the chlorine contents in MCAN, DCAN and TCAN, respectively. It was verified that CANs react with free bromine (HOBr) to produce bromochloroacetonitrile (BCAN). DCAN and TCAN are hydrolyzed to produce corresponding haloacetamides (HAMs), which are further reacted with HOBr to produce bromodichloroacetic acid (BDCAA). Furthermore, the generation of bromate was also worth noting via the oxidation of Br- in the UV/PS system.
Keywords: Bromide; Chloroacetonitriles; Kinetics; Persulfate; Radicals.
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