Chlorine has been safely used in the United States since the 1800s for drinking water disinfection, to protect the public against diseases which are caused by bacteria, viruses and microbiological cysts. Chloramines, monochloramine in particular, have also been used as a disinfectant in public water supplies for more than 70 years. Chloramines are produced by combining chlorine and ammonia. Although chlorine and chloramines cause health concerns at high concentrations, they are not a concern at the concentrations used for disinfection of public water supplies.
Chloramines are less reactive than chlorine. As a result, chloramines are weaker disinfectants, but they have greater stability. This allows them to provide better residual disinfection throughout a water utility’s distribution system. Chloramines are not used as the primary disinfectant for public water supplies.
The lower reactivity of chloramines results in production of substantially lower concentrations of disinfection byproducts in the distribution system. Some of these disinfection byproducts, such as the trihalomethanes (THMs) and haloacetic acids (HAAs), may have adverse health effects at high levels. Because of this potential, these disinfection byproducts are regulated by the U.S. Environmental Protection Agency (EPA). Total THMs have a maximum contaminant level (MCL) of 80 ug/L, while the MCL for total HAAs is set at 60 ug/L.
Chlorine and chloramines themselves each have a Maximum Residual Disinfectant Level (MRDL) of 4.0 mg/L. The EPA’s concern with respect to MRDLs is not toxicity of the disinfectants, but rather limitation of formation of the disinfection byproducts.
Establishing a claim for chloramine reduction
The requirements for manufacturers to make a claim that their system reduces chloramines are found in NSF/ANSI 42 Drinking water treatment units – Aesthetic effects. The Joint Committee on Drinking Water Treatment Units originally adopted these requirements in 1999. Systems making the claim of chloramine reduction must reduce monochloramine to 100 percent of their rated capacity as described in Table 1.
The Standard allows that prior to the 100 percent sample point, 90 percent of the product water sample concentrations must be less than 0.5 mg/L monochloramine measured as Cl2/L. Product water samples collected at the 100 percent sample point must be less than 0.5 mg/L monochloramine measured as Cl2/L. This method of determining conformance allows for an excursion of the product water sample monochloramine concentration above 0.5 mg/L, as long as subsequent samples are lower in concentration.
With a typical contaminant breakthrough curve, this type of effluent data would not occur. However, monochloramine reduction through the use of activated carbon is a catalytic process that is sensitive to many parameters. Because of these sensitivities, the NSF laboratory has seen effluent concentrations above 0.5 mg/L monochloramine followed by subsequent effluent concentrations back down below 0.5 mg/L. This most commonly happens when samples are collected at the end of the 16-hour testing day. The overnight rest period allows the test systems’ media to “recover” and perform adequately again the next morning.
Recognizing the sensitivity of chloramine reduction to rest periods, the Joint Committee allowed for a unique on/off test cycle of up to 5 percent on / 95 percent off to be used for testing chloramine reduction, at the manufacturer’s discretion. No other test methods in Standards 42 or 53 allow for a test cycle to exceed 10 percent on / 90 percent off.
Formation of monochloramine
As mentioned above, chloramine is formed by a reaction between chlorine and ammonia in water. It is not available for purchase as a chemical. Standard 42 contains a method for formation of chloramine. The Standards allows for other methods of forming monochloramine, if those other methods can be demonstrated to result in a challenge water that provide equivalent performance.
The challenge water chemistry is described in Table 2. The Standard recommends that all other water characteristics be adjusted before formation of monochloramine. Once those other characteristics have been adjusted, ammonium chloride (NH4Cl) is added to the challenge water to a concentration of 6 mg/L. Then, a solution of 12 percent w/w sodium hypochlorite, NaOCl (bleach) is added to achieve a concentration of 0.037 mL/L in the challenge water. The Standard recommends that the sodium hypochlorite solution be diluted at least 10:1 prior to the addition to the challenge water.
The chemical reaction that forms monochloramine can be a dangerous one. Under no circumstances should ammonium chloride and bleach be combined directly. (Hazardous reaction products can be formed if this kind of direct addition is performed.)
The amount of sodium hypochlorite that is added to the challenge tank is adjusted as needed to achieve the correct monochloramine concentration. In order to allow for the reaction to complete, the Standard recommends that the challenge water be prepared at least one hour before use.
Alternate formation of monochloramine
As mentioned above, alternate methods of forming monochloramine are allowed, if the alternate methods can be demonstrated to result in an equivalent challenge water. Because the method described in the Standard requires batch preparation and a one hour reaction time, this method is time consuming and labor intensive, resulting in significant cost considerations for running the test. This provides an incentive to develop alternate methods of monochloramine formation. Any such efforts must keep safety in mind as well as the requirement for equivalent performance. One consideration of equivalent performance is that a complete reaction to form monochloramine must occur. This equivalent performance could be demonstrated by achieving the same capacity rating for a given filtration system with an alternate method and the method described in the Standard.
Keeping the flow rate and analyzing monochloramine
Most contaminant reduction protocols under Standards 42 and 53 require testing with a 60 PSIG dynamic influent pressure, which is not readjusted throughout the course of the test, even though flow rates may vary. Chloramine reduction testing is an exception to this general rule. The test pressure may be increased from the initial 60 PSIG up to a maximum of 90 PSIG in order to maintain the specified flow rate. If the flow rate cannot be maintained at 90 PSIG, the Standard requires that the test be terminated.
Analysis of monochloramine can be tricky. Standard 42, Annex B, contains an analytical method for monochloramine analysis based on High Performance Liquid Chromatography (HPLC). This method must be used to validate laboratory results obtained on challenge water samples for more standard analytical methods before those methods can be used.
Unlike the simple procedures used testing for chlorine reduction, testing a filtration system for chloramine reduction is full of unique details and nuances that require a special section of Standard 42 to detail. These quirks include:
- Unusual breakthrough patterns
- The possibility of a 5 percent on / 95 percent off test cycle
- In-place formation of monochloramine
- Test pressure is increased to maintain the initial flow rate, if necessary
- Special validation of the monochloramine analytical method
All of these requirements exist out of necessity due to the unique aspects for conducting the test, which result from the technology and the contaminant. These requirements are a great example of the careful tailoring of the NSF/ANSI Drinking Water Treatment Unit (DWTU) Standards to the many different purposes they serve. As all good water treatment professionals know, there is not a “one size fits all” treatment system that will address all types of water. And because different types of water require different treatment, different contaminants require different contaminant reduction test protocols in the Standards.
About the author
Rick Andrew has been with NSF International for over six years, working with certification of residential drinking water products. He has been the Technical Manager of the Drinking Water Treatment Units Program for over three years. His previous experience was in the area of analytical and environmental chemistry consulting. Andrew has a bachelor’s degree in chemistry and an MBA from the University of Michigan. He can be reached at 1-800-NSF-MARK or email: [email protected].