Understanding the threats associated with disinfection byproducts
Chlorine has been used to treat drinking water in the U.S. since 1908 and often is cited as one of the most important advances in human health in the 20th century. Its use has included disinfection, taste and odor (T&O) control, iron and manganese oxidation, and removal of some organic chemicals. Chlorine also has been used to control microbiological growth in water distribution systems. Utilities often use alternatives to chlorine, such as ozone and chlorine dioxide for primary disinfection, depending on their source water analysis, and chlorine or chloramines for secondary disinfection in the distribution system. Public utilities have used chloramines since the 1930s and an estimated one in five people in the U.S. uses water treated with chloramines.
Meet the Chloramine Family
The U.S. Environmental Protection Agency (EPA) regulations give two choices for disinfectant residual: chlorine or chloramine. Many major water agencies are changing to chloramine to meet current and anticipated federal drinking water regulations. Since the Safe Drinking Water Act of 1974 and its amendments, utilities around the country have made changes to their disinfection strategies to meet more stringent regulations for either microbial contaminants or disinfection byproducts (DBPs). Both chlorine and chloramine react with other compounds in the water to form DBPs.
Chlorine forms many byproducts, including trihalomethanes (THMs) and haloacetic acids (HAAs), whereas chloramine forms a significantly lower amount of THMs and HAAs but also forms N-nitrosodimethylamine (NDMA), which is unregulated but suspected of being carcinogenic and EPA is studying it. NDMA is formed when chloramine decays in the water and releases ammonia through a process called nitrification, which converts to nitrosamines from ammonia-oxidizing bacteria.
Regardless of the disinfectant used, the types and concentrations of DBPs typically vary from each utility depending on source water, the level of organic matter, temperature, amount of disinfectant used and other factors. Chloramine will last longer in the distribution system than chlorine before dissipating. Less chlorine is required for the residual to reach the last house and can eliminate the problem of high dosage requirements affecting the homes at the front of the distribution system with an objectionable end product.
While the term “chloramine” is commonly used, the actual compound used is monochloramine. Monochloramine is a different chemical from dichloramine and trichloramine, which are chloramines formed by other complex chemical reactions. Dichloramine and trichloramine are sometimes found in and around indoor swimming pools and can cause skin, eye and respiratory problems. It often is formed when chlorine in the pool reacts with ammonia released from human bodies’ perspiration and other organic matter.
The three forms of chloramine are chemically related and, depending on water conditions, can be converted into each other. The species that predominates is dependent on pH, temperature, turbulence and the chlorine-to-ammonia ratio. Even time plays a factor. After a day or so with no changes in conditions, monochloramine in a water system slowly degrades to form dichloramine and some trichloramine. Chloramines can be respiratory irritants, with trichloramine being the most toxic. In contrast to what some water utilities claim, it is impossible to have only monochloramine, and it is not unusual in water systems for di- and trichloramines to occur.
Overall, a utility should experience fewer T&O complaints with the switch from a free chlorine residual to a monochloramine residual. There should be a reduction in T&O complaints, particularly chlorine odors. More consistent residuals should result in more consistent T&Os in the water. However, chloramines cannot oxidize algal or microbial odors and may create T&Os from dichloramine and trichloramine formation. T&Os can be generated from anaerobic conditions associated with nitrification.
In an EPA study of 11 water utilities around the U.S., the utilities reported reductions in the number of T&O complaints after the switch to chloramines. Several of the participating utilities documented not only the number of complaints, but also the type of complaint. The general description of T&O complaints changed from chlorinous to musty, earthy or metallic. It is possible that these T&Os were present when using chlorine but were masked by the chlorine’s T&O. With the elimination of the chlorine’s T&O, customers detected the other descriptions.
Chlorine is a strong oxidizer and can form stable, passivating oxide scales that limit the release of metals into drinking water. Chlorine-induced scale consists of iron oxide in iron pipe, lead oxide in lead pipe, and copper oxide in copper pipe. The corresponding scales that have been observed with chloramine, a weaker oxidizer, are composed of less stable compounds, including iron oxide and hydroxide and carbonates in iron pipe, lead carbonate in lead pipe, and copper oxide in copper pipe. Chloramines react with certain types of rubber hoses and gaskets, such as those on washing machines and hot water heaters. Black or greasy particles may appear as these materials degrade. Additionally, chloramination, if not properly optimized, can result in nitrification in the presence of bacteria. Nitrification can lower the pH of the water, which can increase corrosion of lead and copper.
H2O Care Inc. installed many reverse osmosis (RO) water cooler filtration systems in Boston. In the early 2000s, the Massachusetts Water Resources Authority changed secondary disinfection to chloramine from chlorine without much fanfare, therefore, the company was not aware of the switch. Soon after, it received calls of T&O issues from customers. Thinking there were bacterial issues, it dispatched service staff to fully sanitize independent distribution lines with chlorine, let them sit overnight, and returned the next day to flush out the systems. It had not solved the problem. Upon speaking with city officials and determining the problem was probably the chloramine releasing the T&O, H2O Care replaced the activated carbon component of the RO system to catalytic carbon, which fixed the problem. The activated carbon had been stripping the ammonia from the chlorine and was the cause of the bad T&Os.
Drinking water research indicates that certain DBPs have the potential to be harmful. Some research indicates that certain byproducts are linked to increases in cancer incidence, including bladder cancer. Some research indicates that certain DBPs can be linked to liver, kidney, central nervous system problems and reproductive effects. Other research indicates that certain DBPs can be linked to anemia.
Scientists from many organizations have conducted research on the effects of DBPs. In some cases, research results are contradictory; some studies show links to adverse health effects and others do not. Regulatory documents describe the uncertainties in DBP risk assessments.
It is the job of regulators to weigh the public health benefits of disinfection against the risks of the potentially harmful DBPs. EPA sets limits for certain DBPs that are linked to the health effects previously described.
Because the chloramine conversion reaction is catalytic in nature, activated carbons that exhibit enhanced catalytic activity are more efficient. In theory, monochloramine removal is a two-step reaction. It is theorized that chloramine removal is enhanced with catalytic activated carbons because of their high number of catalyst sites compared to conventional carbons. The chloramine removal efficiencies of catalytic carbons cut required contact time, extend bed life and enable the use of smaller equipment. These advantages translate into cost savings for the end user without the sacrifice of the carbon’s capabilities. NDMA has been shown to degrade relatively quickly when exposed to ultraviolet light.
It is essential to keep up with EPA changes in water quality demands and seek out technologies to meet customer needs. Additionally, continually testing and applying new technologies where beneficial will help water treatment providers become better service providers.