By Rick Andrew
An important consideration when testing a water treatment system for effectiveness in reducing contaminants is the end point of the test. Consider a test that covers only initial system performance. There is certainly some value associated with installing the treatment system and flushing and conditioning in accordance with the manufacturer’s instructions and then testing with just a small volume of challenge water that contains the contaminant, with analysis of the challenge water and the treated water to assess effectiveness. This is especially true if the treatment system is found to be not effective based on this sampling – the treatment system can be ruled out based on failure during an initial contaminant reduction performance test.
If, however, the treatment system is found to be effective based on treating a small volume of water, the question inevitably comes up as to how long that system will remain effective and what type of continued testing would be appropriate to establish that the system will be effective over an extended period of time. The NSF Joint Committee on Drinking Water Treatment Units has considered this question as the standards for drinking water treatment units (DWTU) have been developed and they have found that the answer to this question varies depending on the technology being evaluated, as well as the type of contaminants being reduced. In some cases, the answer also depends on an a understanding of how the user will be alerted to replace any treatment media or components.
Various test end points for various technologies and contaminants
Replaceable active media filters and aesthetic chemical contaminants. POU and POE active media treatment systems using replaceable media being evaluated for aesthetic chemical contaminants are tested and sampled periodically until the manufacturer’s rated treatment capacity has been reached, thus assuring effective treatment through the life of the filter. Once the manufacturer’s rated capacity has been surpassed and end user starts noticing the appearance of the aesthetic contaminants in the drinking water due to exhaustion of the media, the end user is thereby alerted to replace the treatment media.
Replaceable active media filters and health chemical contaminants. POU and POE active media treatment systems using replaceable media being evaluated for health-related chemical contaminants are tested and sampled periodically beyond the manufacturer’s rated treatment capacity. The end point is 200 percent of the rated capacity, providing an ample safety margin for the user to recognize that the capacity has been exhausted and replace the media. If the system includes a performance indication device that alerts the user to replace the media, then the end point of the test is 120 percent of the rated capacity. This also provides an ample safety margin after the user has been alerted to replace the media.
Replaceable mechanical filters. POU and POE systems with replaceable mechanical filters being evaluated for reduction of mechanical contaminants filtered by size exclusion (particulate, asbestos, cyst, turbidity) are evaluated over the course of their life, with end of life being defined as the flowrate being reduced significantly enough that the user will notice the filter is plugged and replace it. This flow reduction is defined as 50 percent for particulate reduction, which is an aesthetic contaminant, and then 75 percent to provide even more assurance that the system will perform until the user recognizes a drop in flow rate and replaces the filter for the health effects claims (asbestos, cyst and turbidity).
Reverse osmosis. POU reverse osmosis systems are evaluated under a seven-day test protocol with multiple sampling points for challenge water and treated water to assure that the system will perform effectively under various operating conditions. Reverse osmosis elements, however, can last for a year or longer, so the test definitely does not cover the entire useful life of the RO membrane. Therefore, manufacturers of POU RO systems with health claims must provide a sampling service, either directly or through an authorized dealer, at least once every six months; or provide a sampling kit for analysis of TDS or other appropriate contaminants; or provide a TDS monitor to measure the product water quality. In this way, ongoing effectiveness of the system is assured. Additionally, manufacturers of systems with nitrate-nitrite reduction claims must provide a sampling and analysis kit for nitrate/nitrite with explicit instructions of recommended frequency of analysis to assure ongoing effectiveness.
Regenerating and backwashing systems for aesthetic contaminants. POU and POE systems that use regeneration as part of the operating cycle are required to meet the applicable requirements after the completion of a minimum of three operating/regeneration cycles with regeneration occurring between cycles. Non-regenerating systems that recommend backwashing over the life of the system are backwashed at the manufacturer’s recommended interval, with a minimum of one backwash at the midpoint of the test, as they are evaluated for reduction of aesthetic contaminants.
Ultraviolet systems. Ultraviolet systems evaluated for health effects must have a UV sensor and alarm to warn the user when the UV intensity is too low to provide effective treatment. So UV systems are evaluated at the alarm set point to assure that they deliver effective treatment even at the point where intensity is reduced enough to trigger the alarm. This is another case in which the seven-day test does not cover the life of the UV source, but the standard includes a mechanism to alert the user when any type of maintenance, including UV source replacement, is required for systems with health claims.
Various test end points to provide consistent assurance of performance
A consideration of the specific combination of treatment technology and nature of the contaminant being evaluated is vital to establishing appropriate and protective end points for contaminant reduction testing. The NSF Joint Committee on Drinking Water Treatment Units has done just that in their approach to the NSF DWTU Standards. Reduction of contaminants that are treated through mechanical means has one logical approach to setting test end points, whereas chemical contaminants treated by active media have different factors to help create the test protocol and end point to the test.
Reverse osmosis, with the potential long life of the RO membrane, has a different approach to test protocol that doesn’t attempt to address testing over the life of the membrane. The same is true of UV systems. Rather, for these technologies, the treatment effectiveness of the technology is evaluated in the test, but then the end of life is addressed through other means incorporated into the applicable standard.
And regenerating and backwashing systems are evaluated with a test method that includes the regeneration or backwash function to make sure the treatment remains effective afterwards. These protocols and how they vary accordingly are yet another example of the scientific and rigorous nature of the standards and understanding the logic behind them helps manufacturers, regulators and product end users be confident in products that conform to them.
About the author
Rick Andrew is NSF’s Director of Global Business Development–Water Systems. Previously, he served as General Manager of NSF’s Drinking Water Treatment Units (POU/POE), ERS (Protocols) and Biosafety Cabinetry Programs. 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: [email protected]