The occurrence, formation and transformation of disinfection byproducts in the water distribution system: A review.

Disinfection is an effective process to inactivate pathogens in drinking water treatment. However, disinfection byproducts (DBPs) will inevitably form and may cause severe health concerns. Previous research has mainly focused on DBPs formation during the disinfection in water treatment plants. But few studies paid attention to the formation and transformation of DBPs in the water distribution system (WDS). The complex environment in WDS will affect the reaction between residual chlorine and organic matter to form new DBPs. This paper provides an overall review of DBPs formation and transformation in the WDS. Firstly, the occurrence of DBPs in the WDS around the world was cataloged. Secondly, the primary factors affecting the formation of DBPs in WDS have also been summarized, including secondary chlorination, pipe materials, biofilm, deposits and coexisting anions. Secondary chlorination and biofilm increased the concentration of regular DBPs (e.g., trihalomethanes (THMs) and haloacetic acids (HAAs)) in the WDS, while Br and I increased the formation of brominated DBPs (Br-DBPs) and iodinated DBPs (I-DBPs), respectively. The mechanism of DBPs formation and transformation in the WDS was systematically described. Aromatic DBPs could be directly or indirectly converted to aliphatic DBPs, including ring opening, side chain breaking, chlorination, etc. Finally, the toxicity of drinking water in the WDS caused by DBPs transformation was examined. This review is conducive to improving the knowledge gap about DBPs formation and transformation in WDS to better solve water supply security problems in the future.