Seen as an Attractive Option for Meeting Disinfection Byproduct Requirements
In recent years, cities such as Maui and Santa Barbara have started using chloramines as a component of their drinking water disinfection process. Last November, Washington, DC and Arlington, Virginia also made the switch, citing improvements to taste and a desire to decrease disinfection byproduct levels. The completed Stage 1 and pending Stage 2 Disinfectants and Disinfection Byproducts Rules (DBPR) issued by the Environmental Protection Agency (EPA) are likely to spark an increase in the number of communities utilizing chloramines.
The Stage 1 rule is currently being implemented; the Stage 2 rule was issued in December 2000 as an agreement in principle. They seek to improve microbial protection while enacting more stringent rules reducing the level of allowed disinfection byproducts (DBPs).
Stage 2 Microbial/Disinfection Byproducts Rule
The agreement calls for a two-phase approach to control disinfection byproduct peaks in distribution systems. During phase one, the maximum contaminant levels (the maximum permissible level of a contaminant in water which is delivered to any user of a public water system) for total trihalomethanes and five haloacetic acids will be 0.080 and 0.060 mg/L respectively (based on individual utilities system-wide running annual averages). Additionally, standards for locational running annual averages (annual averages at each sampling site) of 0.120 and 0.100 mg/L will be introduced.
During phase 2, the maximum levels for the more stringent locational running annual averages will be reduced to 0.080 mg/L for trihalomethanes and 0.060 mg/L for the five haloacetic acids and the compliance locations will be changed to those identified under an intensive DBP monitoring and characterization program.
Benefits of chloramines
Chloramines are an attractive disinfectant choice in this new regulatory environment because they stop the formation of trihalomethanes that occurs if free chlorine remains in the distribution system. According to the US Environmental Protection Agency (EPA), utilities using chloramines can minimize DBP levels by maintaining an optimal three to five ratio of chlorine to ammonia in the water.
Chloramines have additional benefits that have been known for more than 80 years. Recognizing that chloramines are less likely to react with organic compounds in water distribution systems and therefore produce water with improved taste and odor, the City of Denver began using chloramines in 1917. Because it was inexpensive and easy to make, chloramination was used regularly during the 1930s and 1940s until a shortage of ammonia during World War II decreased its use.
According to the American Water Works Association, chloramines are the second most popular water disinfectant with nearly 30 percent of large- and medium-sized water agencies in the US using them in 1998. In addition to reduced DBP levels and taste and odor benefits, chloramines also provide strong protection against bacterial regrowth because it offers a stable and long-lasting residual. Chloramine residual is very effective at penetrating and controlling biofilms, thereby reducing coliform concentrations and biofilm-induced corrosion.
Even with these benefits, chloramines are rarely used as a primary disinfectant because they are relatively ineffective at inactivating certain viruses. Instead, they are often employed as a secondary disinfectant in combination with a primary chlorine treatment.
This combination is effective because chlorine disinfection occurs in two distinct phases. During the initial phase in the treatment plant, organic compounds cause the rapid disappearance of free available chlorine; however, when ammonia is present (in the form of chloramines), the water is still actively disinfected even though the amount of free chlorine in the water has been reduced. During the second phase, inorganic chloramines provide additional disinfection for added protection in the distribution system.
Impacts on dialysis patients and pet fish
Utilities considering a change to chloramines should be prepared to address the important effects of such a transition. Chloramines are toxic to pet fish, reptiles and amphibians, and must therefore be removed from water these pets inhabit. Chloramines do not dissipate rapidly in water and must be removed by biological filters, natural zeolites and pH control methods to reduce the toxic effects of ammonia to these animals.
Water treated with chloramines must be specially filtered for use in kidney dialysis machines because it comes in contact with a patients blood across a permeable membrane as part of the dialysis process. In such cases, chloramines can be removed by adding ascorbic acid or using granular activated carbon treatment. Hospitals are well-prepared to implement such simple precautions when properly notified of future changes.
Utilities should also be prepared to monitor and control nitrate levels in water associated with chloramine imbalances. According to the EPA, if ammonia is in excess of the required chlorine, it can promote the growth of bacteria, which in turn converts excess ammonia to nitrates. If this persists, the total chlorine residual will be reduced to very low or zero levels, leading to potential increases in HPC bacteria and coliforms. Excessive levels of nitrate in drinking water can cause serious illness.
Nitrification can be controlled by monitoring strategic locations throughout the distribution system for monochloramine residuals. The problem can then be neutralized by decreasing the detention time, temperature, or excess ammonia concentration; or by increasing the pH or the chlorine-to-ammonia ratio.
Implementing the changeover
With many utilities considering a changeover to chloramines, Janice M. Skadsen of the American Water Works Association and the Ann Arbor Water Utilities Department reminds agencies that project planning and preparation are essential to ensuring an efficient changeover, maintaining a dependable and safe system and preserving public confidence in the water purveyor.
The EPA recommends that the following areas should be considered in preparation for a changeover: raw water composition and suitability to chloramination, a comprehensive monitoring program, employee training, potential environmental impacts and public notification and education. Providing local residents, businesses and health care providers with comprehensive information about changeover impacts is extremely important, particularly for those with special concerns such as fish owners and kidney dialysis patients.
Gerald F. Connell has been involved in the study and application of drinking water and wastewater treatment technologies for more than 30 years. He is the author of "The Chlorination/Chloramination Handbook," published by the American Water Works Association in 1996.
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