Disinfection By-product - Chlorination Disinfection Byproducts (DBPs)

Chlorination Disinfection Byproducts (DBPs)

Chlorinated disinfection agents such as chlorine, chlorine dioxide, and chloramine are strong oxidising agents introduced into water in order to destroy pathogenic microbes, to oxidise taste/odour-forming compounds, and to form a disinfectant residual so water can reach the consumer tap safe from microbial contamination. These disinfectants may react with naturally present fulvic and humic acids, amino acids, and other natural organic matter, as well as iodide and bromide ions, to produce a range of DBPs such as the trihalomethanes (THMs), haloacetic acids (HAAs), and chlorite (which are regulated in the US), and so-called "emerging" DBPs such as halonitromethanes, haloacetonitriles, haloamides, halofuranones, iodo-acids, iodo-THMs, nitrosamines, and others.

Chloramine has become a popular disinfectant in the US, and it has been found to produce N-nitrosodimethylamine (NDMA), which is a possible human carcinogen, as well as highly genotoxic iodinated DBPs, such as iodoacetic acid, when iodide is present in source waters.

Residual chlorine (and other disinfectants) may also react further within the distribution network—both by further reactions with dissolved natural organic matter and with biofilms present in the pipes. In addition to being highly influenced by the types of organic and inorganic matter in the source water, the different species and concentrations of DBPs vary according to the type of disinfectant used, the dose of disinfectant, the concentration of natural organic matter and bromide/iodide, the time since dosing, temperature, and pH of the water.

Swimming pools using chlorine have been found to contain trihalomethanes, although generally they are below current EU standard for drinking water (100 micrograms per litre). Concentrations of trihalomethanes (mainly chloroform) of up to 0.43 ppm have been measured. In addition, trichloramine has been detected in the air above swimming pools, and it is suspected in the increased asthma observed in elite swimmers. Trichloramine is formed by the reaction of urea (from urine and sweat) with chlorine and gives the indoor swimming pool its distinctive odor. Salt-water pools generate higher levels of trihalomethanes (mainly bromoform) than freshwater chlorine pools with levels measured of close to 1.3 ppm.

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