Testing POU RO Systems for Uranium Reduction
By Rick Andrew
Uranium is a naturally occurring element, 51st among all of the earth’s elements in terms of abundance. Its average concentration in the earth’s crust is estimated to be two to four ppm, which makes it about 40 times as abundant as silver.1 Given this natural occurrence, uranium can become a contaminant in groundwater, which can be a source for drinking water. Consumption of uranium can have impacts on human health, including kidney damage. It is actually the heavy-metal properties of uranium as opposed to the radioactivity that cause health concerns. As such, US EPA regulates uranium in drinking water with an established maximum contaminant level (MCL) of 30 µg/L.2 Health Canada also regulates uranium in drinking water, establishing a maximum acceptable concentration (MAC) of 20 µg/L.3
Treatment techniques for uranium in drinking water
Uranium in drinking water can be treated by several techniques, with RO and strong-base anion exchange resins being two of the more prevalent. The fact that there is already an American National Standard for POU RO, NSF/ANSI 58, led to consideration of development of a test method to prove the effectiveness of POU RO for reduction of uranium.
Test method development
The NSF Joint Committee on Drinking Water Treatment Units charged a task group with developing criteria and a test method for establishing uranium reduction by POU RO in 2016. This task group conducted a series of conference calls in which they discussed testing approaches, occurrence of uranium in groundwater, technological capabilities, laboratory safety concerns and other topics relevant to their charge. When they reached the stage of having developed proposed requirements, the group presented their findings and recommendations to the joint committee at the 2017 annual meeting. At this meeting, the joint committee approved the work the group had done and recommended proceeding with validation testing of the proposed test method.
Typically, multiple laboratories participate in validation testing of proposed new test methods to help assure that the results are reproducible. In the case of uranium, however, many laboratories were hesitant or not approved to work with it because of its radioactive properties. Although the NSF laboratory was prepared to participate, no other laboratories could be identified. The group ultimately decided that, because of the peer-reviewed literature that already existed supporting the use of RO as an effective treatment technology, in this case they would move forward with only the NSF laboratory participating in validation testing of the proposed new method. Validation testing was successfully completed in 2018, allowing the group to report back to the joint committee at the 2018 annual meeting. The joint committee at this time advised the group to summarize their work, prepare proposed language for the addition of the requirements to NSF/ANSI 58 and submit a ballot to the Joint committee to make their proposal.
The group has now finished that effort and the ballot is out to the joint committee as this column is being written. Once balloting is completed, any negative ballots will need to be adjudicated, which could require modifications to the proposal. The timing of updating NSF/ANSI 58 to include the uranium reduction requirements cannot be determined at least until after the balloting is complete and, even then, it could still be uncertain if modifications to the proposal are made. If all goes well, we can hope to see these requirements added to NSF/ANSI 58 yet in 2019.
The task group has proposed to use the seven-day contaminant reduction test protocol currently existing in NSF/ANSI 58 for uranium reduction testing. This protocol involves operating the RO system and conducting sampling under multiple-use scenarios over the course of the seven days, including a 54-hour stagnation period. The test water proposed for testing uranium reduction is the TDS reduction test water as currently specified in NSF/ANSI 58, with the inclusion of 50 mg/L sodium bicarbonate (NaHCO3) as part of the 750 mg/L TDS that is added to chlorine-free deionized water, with sodium chloride making up the rest of the TDS. Uranyl nitrate is added to the challenge water, either at a concentration of 100 µg/L or 400 µg/L of uranium. This choice in challenge level of either 100 µg/L or 400 µg/L of uranium is at the discretion of the manufacturer, based on the capabilities of their system and the claim they would like to make. The maximum allowable product water concentration is 20 µg/L, based on the Health Canada MAC, which is lower than the 30 µg/L MCL used by US EPA. In order to pass the test, all samples of product water from both test units must have analyzed concentrations of uranium ≤ 20 µg/L throughout the course of the seven-day test period.
Consensus process at work
The NSF Joint Committee operates under a highly formalized consensus process. In part, this process is specified and overseen by ANSI, although NSF goes above and beyond the ANSI requirements by including oversight of all standards development activities by the NSF Council of Public Health Consultants. This consensus process allows continual development and refinement of the standards to serve more needs over time, as well as to keep up to date with the latest scientific, public health and technological developments. In the case of uranium reduction, the joint committee has worked via their membership, as well as operating through a focused task group, to expand the scope of NSF/ANSI 58 in a highly scientific and vetted manner to better serve the needs of manufacturers, public health officials and of course, end users who have specific water treatment needs.
(1) “Uranium.” Wikipedia. https://en.wikipedia.org/wiki/Uranium.
(2) “Drinking Water Requirements for States and Public Water Systems: Radionuclides Rule.” US EPA. https://www.epa.gov/dwreginfo/radionuclides-rule.
(3) “Water Talk–Uranium in Drinking Water.” Government of Canada. https://www.canada.ca/en/health-canada/services/environmental-workplace-health/reports-publications/water-quality/water-talk-uranium-drinking-water-2010-health-canada-brochure.html.
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: Andrew@nsf.org