By Rick Andrew
The US has a long history of using free chlorine residuals for drinking water disinfection, dating back to the 1800s. There has been great success in protecting the public against diseases that are caused by bacteria, viruses and microbiological cysts. Although chloramines, especially monochloramine, have also been used as a disinfectant in public water supplies for over 70 years, they have been gaining increasing popularity over the last decade. Chloramines are formed in drinking water by combining chlorine and ammonia. Although chlorine and chloramines can 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, making them weaker disinfectants, but they have greater stability, which 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. Additionally, this lower reactivity results in production of substantially lower concentrations of disinfection byproducts in the water distribution system. Some of these DBPs, such as trihalomethanes (THMs) and haloacetic acids (HAAs), have adverse health effects at high concentrations and are regulated by US 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. US EPA’s concern with respect to MRDLs is not toxicity of the disinfectants, but rather limitation of formation of DBPs.
Fountain beverage filtration systems
The presence of chloramines in drinking water can affect the taste of fountain soft drinks prepared by mixing concentrated syrup with water, which makes effective treatment of residual chloramines key for fountain beverage filtration systems. In fact, this need was the impetus for developing a claim for chloramine reduction under NSF/ANSI 42 Drinking water treatment units – Aesthetic effects. In order to meet this need, the Joint Committee on Drinking Water Treatment Units originally adopted these requirements in 1999.
Requirements for reduction claim
NSF/ANSI 42 requires reduction of a challenge of 3.0-mg/L monochloramine to less than 0.5 mg/L in the treated water. Samples are collected each 10 percent of manufacturer’s rated capacity through 100 percent of capacity as the end point of the test. 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. This type of breakthrough pattern is unusual. 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 effluent concentrations at subsequent sample points back down below 0.5 mg/L. This most commonly happens when samples are collected at the end of the 16-hour day of testing, and then additional samples are collected the following morning. The overnight rest period allows the test systems’ media to recover and perform adequately again the next morning. Additionally, systems making the claim of chloramine reduction must reduce monochloramine to 100 percent of their rated capacity as described in Table 1.
Chloramine is formed in public water supply treatment facilities by a reaction between chlorine and ammonia in water; i. t is not available for purchase as a chemical. In order to conduct chloramine reduction testing, NSF/ANSI 42 includes a method for formation of monochloramine. Additionally, the Standard allows for other methods of forming monochloramine, if those other methods can be demonstrated to result in challenge water that provides 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
Alternate methods of forming monochloramine are allowed, if the alternate methods can be demonstrated to result in 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 formation of monochloramine. Any such efforts must keep in mind safety considerations, 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.
Flowrates for reduction testing
Most contaminant reduction protocols under NSF/ANSI 42 and 53 require testing with a 60 psig dynamic influent pressure, which is not readjusted throughout the course of the test, even though flowrates 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 flowrate. If the flowrate cannot be maintained at 90 psig, the Standard requires that the test be terminated.
Chloramine reduction – a unique test
- Unusual breakthrough patterns
- In-place formation of monochloramine
- Test pressure increase to maintain initial flowrate, if necessary
All of these requirements are derived from 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 is the Operations Manager of the NSF Drinking Water Treatment Units Program for certification of POE and POU systems and components. Prior to joining NSF, 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 (800) NSF-MARK or email Andrew@nsf.org.