By Rick Andrew
NSF/ANSI 55 has historically covered only low-pressure mercury POU/POE UV systems. For years, this technology was the only one widely used for these systems, so this limitation of the scope was not really much of a limitation at all. In recent years, however, there have been significant technical advances in LED UV. These have stimulated interest in the technology, with an increasing focus on commercialization, especially in the POU market. Recognizing this trend, the NSF Joint Committee on Drinking Water Treatment Units, through their UV Task Group, initiated an effort in 2016 to expand the scope of NSF/ANSI 55 to include LED UV systems.
Technical challenges
This scope expansion is not simply an issue of revising the scope statement in the standard to state that it now also includes LED UVs. The reality is that the currently existing test method in NSF/ANSI 55 is valid only for UV technology with a single emission at 254 nm, which is basically low-pressure mercury lamps. The issue for LED UVs is that one of the technical advances in LED UVs has been the ability to tailor them to emit at other wavelengths, which could be beneficial from a germicidal point of view. Therefore, a large number of these LED UVs that are being introduced to the market emit radiation at wavelengths other than 254 nm. In order to cover the anticipated range of emission wavelengths LED UVs are expected to produce, the UV Task Group recommended to focus efforts on including UV systems that emit radiation in the range of 240 to 300 nm.
The biggest concern regarding emission wavelength and the current NSF/ANSI 55 test method is with the UV absorbing chemical. It is important to use a UV absorbing chemical to be able to test the UV system in conditions that are sub-optimal, such as when the water is turbid or other factors are confounding system performance. In the current test, parahydroxybenzoic acid (PHBA) is used. This chemical is very effective for evaluating low-pressure mercury lamps because it absorbs UV radiation very specifically at 254 nm. PHBA, however, does not absorb radiation at other wavelengths. In fact, it is visually clear. So testing UV systems that emit radiation at other wavelengths requires a different UV absorbing chemical.
Another concern is the test organism that is used. Under the current test, MS-2 coliphage American Type Culture Collection (ATCC)7 # 15597-BI is used for testing Class A systems and T1 coliphage ATCC # 11303 is used for testing Class B systems because these organisms have an appropriate response to the dosages for Class A and Class B when exposed to UV radiation at 254 nm. Other test organisms, however, might be better for evaluation of UV systems that emit at different wavelengths. With these technical issues squarely in front of them, the UV Task Group set about its work of addressing them to expand the scope of the standard.
Proposed approach
After considerable discussion, research and laboratory validation testing, the UV Task Group arrived at a proposed approach to adapt the test method in NSF/ANSI 55 to address these technical challenges. A significant portion of the effort centered around finding a better UV-absorbing chemical that would be commercially available, that would not be too damaging to laboratory equipment, that would not be too toxic to the test organisms and that would absorb relatively evenly over the range of germicidal wavelengths. After considerable research and multiple laboratory studies, the UV Task Group ultimately determined that the best absorbant would be comprised of vanillin (CAS# 121-33-5) and SuperHume®, which is available as Cropmaster®, SuperHume or AquaHume®. The vanillin and SuperHume are combined while maintaining a ratio of 1.0 mg vanillin to 0.02 mL of SuperHume. These compounds are diluted with deionized water as needed prior to addition to the test water to absorb UV radiation across the desired range.
The UV Task Group also determined, after considerable research, that the best test organism would be Qβ coliphage ATCC # 23631-B1. Qβ was confirmed by the task group to be a conservative surrogate for the UV inactivation of rotavirus, which has been the benchmark for UV inactivation of viruses as established in the Guide Standard and Protocol for Testing Microbiological Water Purifiers, Report of Task Force, US EPA, April 1987. Using the guide standard as their basis, the UV Task Group is recommending that a 4-log reduction of Qβ be required for Class A UV systems and a 2-log reduction of Qβ be required for Class B UV systems. The result of this extensive work is that use of Qβ and the formulation of a broadband UV absorbant allows an expansion of NSF/ANSI 55 to cover technologies, especially UV LED technologies, emitting radiation in the range to 240 to 300 nm wavelengths.
Next steps
The next step in the process is for the UV Task Group to present their proposed approach to the NSF Joint Committee on Drinking Water Treatment Units at their annual meeting at NSF headquarters on May 8. The goal of this presentation will be to obtain an approved motion from the joint committee to send the proposal to ballot. If that happens, the balloting process, if it goes smoothly, takes a few months. It is possible that NSF/ANSI 55 could be updated to expand the scope by late Q3 or Q4, 2019. It must be taken into consideration, however, that this timeline could be delayed by any technical concerns or issues identified by the joint committee, either at the meeting or during the balloting process.
Evolving to meet market needs
The water treatment industry, like many others, is constantly moving forward through technical innovations to provide more effective, safer and more accessible solutions. The NSF Joint Committee on Drinking Water Treatment Units plays an important role in supporting and vetting these technical innovations by working to adapt and evolve the standards to evaluate these new technologies in a scientifically based manner, with a focus on protection of public health. The expansion of the scope of NSF/ANSI 55 to include technologies beyond low-pressure mercury lamps, especially LED UV technologies, is only the most recent example of this process and committee at work.
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]