Drinking Water Chlorination and Disinfection by-Products: Formation, History, and Regulations

Water is a vital element which supplies essential nutrients to the plants and animals on Earth and without water no life will exist on Earth. The raw water is conventionally treated by processes such as coagulation, flocculation, sedimentation, and filtration, followed by disinfection before supplying the treated water to the consumers. Disease-causing pathogens enter the water supply network through leakages thus contaminating water which may cause illness. During disinfection process disinfectants like chlorine and chloramine are used to kill the disease-causing microorganisms. When chlorine combines with the natural organic matter (NOM) in raw water, disinfection by-products (DBPs) are created. This led researchers to discover more DBPs formed in drinking water and to find their harmful health effects. According to a USEPA assessment, the four THMs are likely human carcinogens for chloroform, bromodichloromethane, bromoform, and dibromochloromethane, respectively. A few animals’ toxicity studies have reported a strong relationship between the DBPs and carcinogenic diseases. THMs were first regulated by the United States Environmental Protection Agency (USEPA) at 100 μg/L (ppb) in drinking water in 1979. In 1998, the Stage 1 Disinfection By-Products Rule limited THMs to 80 μg/L and for the first time regulated haloaceticacids (HAAs), chlorate, chlorite, and bromate. Since then, many countries have regulated the DBPs. There are several ways to manage DBP concentrations, including eliminating the precursor NOM before adding chlorine, removing DBPs once they have formed, or utilising other disinfectants.