Kinetics of the formation and degradation of carbonaceous and nitrogenous disinfection by-products in Bangkok and Songkhla source waters

Abstract

© 2019 Elsevier B.V. The kinetics of the formation and degradation of disinfection by-products (DBPs) in the treated water from the Bangkhen and Hatyai water treatment plants in Thailand were investigated. The DBPs studied included trichloromethane (TCM), bromodichloromethane (BDCM), dibromochloromethane (DBCM), trichloroacetonitrile (TCAN), dichloroacetonitrile (DCAN), bromochloroacetonitrile (BCAN), and trichloronitromethane (TCNM). When the chlorination time was increased, the levels of TCM, BDCM, DBCM, and TCNM increased, while the levels of TCAN, DCAN, and BCAN decreased. The kinetic rates of DBPs’ formation were assessed based on the formation and degradation rates, which were best described by first-order kinetics. TCM had the highest formation rate with a range of rate constants from 5.5 × 10−3 to 7.3 × 10−3 h−1. TCAN had the lowest degradation rate with a range of rate constants from 0.6 × 10−3 to 2.9 × 10−3 h−1. Good correlations were observed between chlorination time and DBPs’ formation normalized by LC50, lowest cytotoxicity, and lowest genotoxicity. A high formation rate of TCM and a low degradation rate of TCAN normalized by their toxicity were observed. The optimal retention time providing low DBPs’ formation together with high DBPs’ degradation was determined. The retention time of three days decreased the sum of the DBPs/LC50, DBPs/lowest cytotoxicity, and DBPs/lowest genotoxicity from a retention time of one day by 40–60%, 45–65%, and 25–36%, respectively.