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Chlorine and Chloramine as Water Disinfection

Chlorine and Chloramine: Two Ways to Disinfect


Without the use of water disinfectants, most of the water that flows through our pipes would not be safe to drink. Our drinking water is sourced from rivers, streams, lakes—waterways which are all subject to waterborne pathogens. Both chlorine and chloramine are used as disinfectants to help protect us from illnesses that include vomiting, diarrhea, and more. [1]

But disinfecting with either chlorine or chloramine can result in a cocktail of byproducts in drinking water. We’ve covered disinfection byproducts and their risks in a previous article—but we’ve yet to take a more focused look at what separates chlorine and chloramine as disinfectants, and how the disinfection byproducts formed through the use of chloramine differ from chlorine. We’ll also learn about how water treatment plants approach effective chloramination.

Water Chlorination—A Short History

Throughout the mid to late 19th century, scientists gained a greater understanding of the sources and effects of drinking water contamination. Due to the rapid industrialization of the late 1800s, the uptick in densely populated urban zones brought concerns over water conditions to the fore. Initially, some city water systems began to implement rudimentary filtration systems to help remove contaminants that could cause typhoid, dysentery, and cholera.

It wasn’t until the 20th century that disinfectants (e.g. chlorine, chloramine, ozone) would make the largest impact on reducing the outbreaks of waterborne diseases in US cities. Chlorine was first added to water systems in the United States in 1908, in Jersey City, New Jersey. Federal regulation of water quality began in 1914 when the US Health Service set standards for bacterial content in water. Chloramine was introduced to water systems in the US in Cleveland, Ohio, Springfield, Illinois, and Lansing, Michigan in 1929.

While effective at removing harmful pathogens, scientists began to discover that chlorination could generate undesirable disinfection byproducts (DBPs) like trihalomethanes when natural organic matter and organism levels in the source water are high. A number of DBPs can cause negative long-term health effects, with some even known carcinogens. The EPA introduced regulations for DBPs in 1998 and further expanded them in 2006. 

Chlorine v. Chloramine

While technological developments have allowed for newer filtration techniques, chlorine is still the most common disinfectant used to treat American water.[2] Water chlorination is effective early in the distribution line, though chlorine levels can dissipate relatively quickly within the water distribution system. 

Chloramine is a compound that contains a combination of chlorine and ammonia. One in five Americans uses water treated with chloramines. The maximum concentration of chloramine allowed in drinking water is 4 PPM (mg/l). Chloramination is a weaker disinfectant (or only about one-quarter as effective as chlorine in upfront purification of organic contaminants), but water systems can maintain good residual levels of monochloramine for continued purification throughout the distribution system. [3] Formation of regulated DBPs like trihalomethanes is frequently less of a problem with chloramination compared with chlorination. However, DBPs like carcinogenic nitrosamines or iodinated disinfection byproducts can form with the use of chloramines.

Government bodies including the Center for Disease Control have deemed it a safer treatment alternative for water supplies compared with chlorine, but long term health risks are not entirely addressed.[2]

Two Approaches to Chloramination

Water treatment plants have to maintain a delicate balance of fluctuating source water contaminants, purification, DBPs, and residual levels of free chlorine. Water utilities achieve the appropriate residual level thanks to a series of measurements, decisions, and treatments. If any one point surveyed along the treatment system is above the regulatory limit of 0.08 mg/L for total trihalomethanes (TTHM) or 0.06 mg/L for haloacetic acids (HAA) (two of the leading disinfection byproducts), the utilities need to take action to reduce them.

Effective chloramination relies on having a good sense of water conditions throughout the treatment process. There are two general approaches to analysis and maintenance of proper levels: 

  • The amperometric method measures monochloramine and total ammonia. Then it subtracts the monochloramine value from the total ammonia to yield the free ammonia present. With this method, some free ammonia typically remains in the water distribution system. Treatment plant operators try to keep the free ammonia value as low as possible, because once it gets into the distribution system it can increase the risk of an unwanted phenomenon called nitrification (the oxidation of ammonium salts into nitrites and nitrates). 

  • The N,N Diethyl-p-phenylenediamine (DPD) colorimetric method provides an affordable alternative to generating a full spectrum of chlorine/chloramine measurements through a progression of samplings. First, free chlorine is measured from a water stream using only the addition of DPD and buffer. Next, the inclusion of buffer, DPD, and potassium iodide yields a measurement representing the sum of free chlorine and monochloramine. Simply by subtracting the free-chlorine value, monochloramine alone can be accurately calculated. With sample flow stopped, reagents can be added for a 2-minute period. This will allow the analyzer to provide a total value for all chlorine species.
  • The customizability of the colorimetric method allows water treatment plants to develop chloramination control strategies that meet their individual needs. 

    Chloramine and Disinfection Byproducts

    As we mentioned, DBPs are formed when chlorine or chloramine react with naturally occurring materials in water (e.g. organic matter or humic acids) or the surrounding pipe material. Disinfection byproducts can be harmful to human health. Regulation of DBPs inspired the use of chloramines as an alternative disinfectant because it forms less of the most common forms of DBPs. 

    Although the CDC and EPA both state that chloramine causes fewer disinfection byproducts, it isn’t all as simple as it seems.This is because when the CDC and EPA report on disinfection byproducts, they are speaking about regulated disinfection byproducts. Chloraminated water is going to contain different—not necessarily fewer—types of disinfection byproducts. Specifically, the EPA documents that water treated with chloramine does indeed contain fewer regulated disinfection byproducts linked to human health issues, and the ones present are often at lower concentrations than typically observed in chlorinated water. The EPA also notes that in contrast to chlorinated water, chloraminated water is more likely to contain both different and higher concentrations of unregulated disinfection byproducts.[4]

    The unregulated byproducts include iodo-trihalomethanes, iodo-acids, and nitrosodimethylamine (NDMA), the latter of which is particularly noted for its toxicity and carcinogenicity.[5] While present in lower concentrations, these DBPs may in fact be more toxic than regulated DBPs.

    Research Continues

    EPA scientists are currently evaluating chloramine-produced, unregulated disinfection byproducts, but their effects in humans as a result of ingesting contaminated drinking water isn’t entirely known.[4] We also aren’t sure at which concentrations they prove a legitimate human health risk. Of course, no level of exposure to a carcinogen is risk free.

    Further muddying the waters, so to speak, is the fact that when chloramine is used as a residual disinfectant, it can alter water’s chemical properties in a way that may lead to lead and copper leaching—the terrible results of which are well documented in Flint, Michigan and other American communities.

    So while chloramine is a longer lasting disinfectant that results in fewer of the better understood, regulated disinfection byproducts, it presents a greater risk when it comes to the disinfection byproducts we neither fully understand nor regulate, as well as increases the risk of lead and copper exposure in homes with older plumbing.

    In short, both chlorine and chloramine contain their own unique advantages and disadvantages. Regardless of which process is used to treat the water in your local system, disinfection byproducts remain a threat to keep in mind—and one that treatment plants work hard to combat.

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