Formation of Iodinated Trihalomethane Disinfection By-products by Co-oxidation of Natural Organic Matter with Sodium Hypochlorite and Lead Dioxide

Iodinated trihalomethanes(I-THMs) in drinking water pipelines have attracted wide attention due to their high toxicity. The coexistence of widely present lead dioxide(PbO 2 ) with commonly used disinfectant sodium hypochlorite(NaClO) in drinking water might change the formation characteristics of I-THMs due to the strongly oxidizing properties of PbO 2 . This study investigated the formation of I-THMs during the co-oxidation of natural organic matter including humic acid(HA), extracellular organic matter(EOM), and intracellular organic matter(IOM) of algogenic organic matter by PbO 2 and NaClO. Triiodomethane(CHI 3 ) is the dominant product in the single oxidation system of PbO 2 , whereas trichloromethane (CHCl 3 ), chlorodiiodomethane(CHClI 2 ), and dichloroiodomethane (CHCl 2 I) are the major products in the single NaClO system. In the co-oxidation system, the dominant I-THMs are similar to those in the single NaClO system. However, the CHCl 3 content decreased to 56.4% whereas I-THMs concentrations remained unchanged with the increase of PbO 2 concentration. The main reason is attributed to the reduced residual chlorine content due to the reaction of PbO 2 with NaClO. IOM is more prone to forming I-THMs than HA and EOM due to the specified structures. This study suggested that PbO 2 in the drinking water supply pipelines might change the risk of THMs.