Behavior of non-regulated disinfection by-products in water following multiple chlorination points during treatment

In this study, the behavior of regulated (trihalomethanes-THMs, haloacetic acids-HAAs) and non-regulated (haloacetonitriles-HANs, haloketones-HKs, chloropicrin-CPK) disinfection by-products (DBPs) was investigated during treatment and distribution in a municipal drinking water system that adds chlorine at multiple points within the water treatment plant (WTP). Three to eight locations in the WTP and four locations in the distribution network were sampled weekly for DBP measurements during the warmest period of the year. The results show that most DBPs found in the study area are formed during treatment, not distribution. However, the DBP species studied behave differently during treatment and distribution. Moreover, the location where DBP concentration is the highest in the distribution network differs among species of the same family, especially HAAs and HKs, and between the sampling campaigns. As a result, the relevance of using the sum of the concentrations of the species of the same DBP family to select sampling sites for DBP monitoring is questionable. This study illustrates the difficulties that drinking water supply managers must face to control and monitor the presence of DBPs.