It has been more than 100 years since chlorination disinfection was first used as a disinfection method for drinking water in 1902. For more than a century, chlorination disinfection has effectively controlled water-borne infectious diseases caused by pathogenic microorganisms in water. Therefore, As an important means to ensure the biological safety of drinking water, chlorination has been used until now. Chlorination disinfection has become a widely used drinking water disinfection method all over the world due to its high efficiency, economy, and mature water treatment process. About 94.5% of water plants in the United States use chlorine for disinfection, and it is estimated that more than 99.5% of water plants in China use chlorine for disinfection.
While disinfecting drinking water, it also brings chemical pollution. Chlorine reacts with natural organic matter (NOM) and some specific pollutants in water, then generate disinfection by-products (DBPs) which are potentially harmful to human health. At present, more than 700 types of DBPs have been discovered, mainly including THMs, HAAs, HANs, nitrosamines, HNMs, halogenated aldehydes, halogenated ketones, halogenated furanones (represented by 3-chloro-4-dichloromethyl-5-hydroxy-2(5-hydro)-furanone, abbreviated as MX), etc. THMs and HAAs are the two most common types of chlorinated disinfection by-products. These two kinds of disinfection by-products have been shown to have carcinogenic, teratogenic, and mutagenic effects.
People concerned about the potential health hazards since the discovery of chlorinated disinfection by-products (DBPs) in drinking water in 1974. A large number of domestic and foreign studies have shown that drinking water with chlorination disinfection results in mutagenicity significantly enhanced. Short-term biological tests, animal carcinogenicity tests, and epidemiological surveys all support the conclusion that DBPs are harmful to human health.
Epidemiological findings suggest that DBPs are closely associated with bladder, colon, rectal, pancreatic, breast, brain, and lung cancers. The results of the study suggest that the concentration of THMs in drinking water is related to bladder cancer, colon cancer, rectal cancer, and breast cancer, and it was found that chlorination of the earth's surface water can significantly increase the risk of colon cancer and brain cancer. Epidemiological surveys show that long-term drinking of chlorinated water may lead to an increase in the incidence of bladder cancer. And the latest research points out that exposure to chlorinated water through bathing, swimming, etc. is more likely to develop bladder cancer than chlorinated drinking water.
While animal carcinogenicity tests show chlorine by-products are related to reproductive barriers. Some chlorinated disinfection by-products in drinking water can lead to premature birth, low birth weight, and congenital defects in newborns, resulting in spontaneous maternal abortion. Another study suggests that when rats were exposed to BDCM at a dose of 50 mg/kg, it could cause an increase in fetal absorption,a decrease in sperm motility, and sperm deformity in male rats. The study also found that a variety of HAAs and their salts have reproductive toxicity, which can cause testicular damage in male rats, hinder sperm formation, reduce sperm motility, and also affect the male rat's gonad development and reduce testicular and epididymal weights.
In order to ensure healthy drinking water for human beings, we should take strong measures to control the generation of DBPs when eliminating drinking water-borne diseases.
1) Before adding chlorine-containing disinfectant, remove NOM in water through strengthening coagulation, oxidation, adsorption, etc.;
2) Improve the disinfection process or use other chlorine-free disinfectants, such as Potassium Monopersulfate.
3) Before using the water with chlorine disinfection we should adopt aeration, adsorption, membrane separation, and other processes to remove chlorine by-products.