Disinfection By-Products in Drinking Water
DISINFECTION BY-PRODUCTS IN DRINKING WATER
Disinfection is the most important step in the water treatment process to destroy pathogenic bacteria and other harmful agents. Because chlorination is a very common and effective method for such disinfection, most drinking water is treated with chlorine. This has been the single most important process for assuring the bacteriological safety of potable water supplies. As a result of water treatment, waterborne epidemics have virtually disappeared in the industrialized world. When waterborne disease outbreaks have occurred, they have generally been traced back to a failure of the chlorination system. An important advantage in using chlorine is that a residual in the water continues to provide germ-killing potential as the water travels from the distribution point to end-users.
Trihalomethanes (THMs) are the major synthetic organic pollutants that are by-products of disinfection. THMs are formed at the water treatment plant when the chlorine is added to water that contains humic substances. Humic substances are naturally occurring leaves and other organic matter, and the dissolved compounds derived from organic matter, and they are found in all water. Among the THMs is chloroform, which is a carcinogen, along with other potential carcinogens. Chloroform has been detected in many water supplies, causing a number of individuals to call for the end of drinking water chlorination. The current consensus is that while there is a risk associated with chlorination, this risk is small compared to the risk of waterborne diseases in untreated water.
Some water suppliers have switched to alternatives to chlorination to eliminate the formation of THMs. Other methods for disinfection include ozone, bromine, iodine, or ultraviolet light. However, chlorine is a cost-effective disinfection process.
MARK G. ROBSON
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