[Distribution Characteristics of Disinfection By-Products and the Effects of Booster Chlorination in Long-Distance Water Supply Systems].

It is difficult for waterworks that add chlorine into finished water once to maintain sufficient residual chlorine at unfavorable points of the pipe network that supply water for large areas of coverage. Therefore, booster chlorination was employed for a long-distance water distribution system. The study was performed in H City with a water supply system serving about 400 km of downtown and rural areas. The purpose of this work is to obtain the distribution characteristics of disinfection by-products (DBPs) in the booster chlorination disinfection pipe network through uniformly distributed sampling analysis. The results showed that detected DBPs include trichloromethane (TCM), bromodichloromethane (BDCM), dibromochloromethane (DBCM) and tribromomethane (TBM), dichloroacetic acid (DCAA), trichloroacetic acid (TCAA), dichloroacetonitrile (DCAN), bromochloroacetonitrile (BCAN), and trichloronitromethane (TCNM). The concentrations of the regulated DBPs were found to be lower than the standard limits specified in the Sanitary Standard for Drinking Water (GB5749-2006). Before booster chlorination, the average concentrations of the DBPs mentioned (expressed as mean±deviation) were (8.08±3.34), (9.77±2.91), (7.38±4.82), (2.65±2.02), (2.95±3.26), (6.02±6.06), (3.13±2.48), (1.61±2.05), and (0.15±0.10) μg·L, while afterwards, they were increased to (10.30±4.55), (11.73±3.60), (8.23±5.22), (2.95±2.45), (3.29±3.60), (8.15±7.58), (3.31±2.61), (1.33±2.04), and (0.12±0.06) μg·L, respectively. Trihalomethanes (THMs) and haloacetic acids (HAAs) increased by 6.32%-26.60% and 5.32%-42.71%, respectively, after booster chlorination. In addition, raw water quality and seasonal changes had a certain impact on the occurrence of DBPs. The levels of DBPs in summer were generally higher than those in spring or autumn. According to the analysis of DBP formation potential of source water, finished water, and tap water, it was found that the risk of DBPs exceeding the standard limit may exist in the water supply system of H City; therefore, further optimization of the treatment process should be considered to ensure water quality.