Chlorination of bensulfuron-methyl: Kinetics, reaction factors and disinfection by-product formation

The kinetics of bensulfuron-methyl chlorination were studied at pH 4-9 at room temperature (25 +/- 1 degrees C), which can be described well by a second-order kinetic model, first-order in chlorine and first-order in bensulfuron-methyl concentrations. Bensulfuron-methyl reacted very rapidly with aqueous chlorine with the maximum reaction rate constant at pH 6 and minimum at pH 9. The superior reactions were the reactions between HOC and ionized/nonionized bensulfuron-methyl. The reaction factors including bromide and ammonium concentrations as well as temperature were also evaluated. It was found that bromide accelerated the chlorination of bensulfuron-methyl and the reaction rate increased linearly with the increase of bromide concentration. In contrast, the presence of ammonium inhibited the degradation of bensulfuron-methyl due to its quick conversion of chlorine to chloramines. Bensulfuron-methyl chlorination is an endothermic reaction with the activation energy being estimated as 13.74 kJ/mol using the Arrhenius equation. Four volatile disinfection by-products (DBPs) were identified after bensulfuron-methyl chlorination, including chloroform, dichloroacetonitrile, 1,1,1-trichloroacetone and nitrotrichloromethane. Trihalomethanes were the dominant species with a maximum reached at pH 8, which could cause potential risks to public health during bensulfuron-methyl chlorination, especially with the presence of bromide because the concentration and species of brominated DBPs increased with increasing bromide concentration. (C) 2015 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.