By Rick Andrew

In May, this column discussed the fact that historically, NSF/ANSI 55 was limited in scope to POU and POE UV systems using low-pressure mercury UV sources. It described progress regarding updating that standard to include requirements for UV systems with UV sources other than low-pressure mercury lamps, most notably LED UV systems. The column further discussed that next steps were 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 in Ann Arbor, MI on May 8. The goal of that presentation was to obtain an approved motion from the joint committee to send the proposal to ballot. That presentation occurred, which led to additional technical input from several LED UV manufacturers. This input resulted in valuable improvements in the testing approach included in the draft standard that was discussed in this column in May.

Additional input is a key aspect of the consensus process under which the NSF/ANSI standards are developed. It is important to consider input from experts in the specific technological area being addressed because these experts have insights and knowledge not necessarily available to others who have significant expertise in standards development and water treatment, but not in the details of a given technology. A summary of those improvements follows.

The original draft standard
The draft standard, as discussed previously, included three main updates to expand the scope to include non-low-pressure mercury lamp UV sources:

  • A change in the UV absorbing chemical used
    — Instead of PHBA, the proposal was to use a mixture of vanillin (CAS# 121-33-5) and SuperHume®, which is available from UAS of America as Cropmaster®, SuperHume or AquaHume®. The vanillin and SuperHume were proposed to be combined and used with a ratio of 1.0 mg vanillin to 0.02 mL SuperHume.
  • A change in the test organism used
    — Instead of MS-2, the proposal was to instead use Qβ coliphage ATCC # 23631-B1. Qβ was confirmed 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.
  • Moving from a dose-response curve and dosage-based criteria to a log- reduction criteria
    — The proposal was to require 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.

This basic framework of updates and adaptations was maintained in the final published version of the standard. There was some tweaking of the specifics related to evaluating UV systems without UV sensors, however, as well as the log reduction required for Class B UV systems.

Improvements based on stakeholder input
After the presentation to the joint committee in May and based on additional input, it was decided to change the approach so that systems without UV sensors would not have UV-absorbing chemical added to the challenge water during microbiological performance testing. So, under the now published standard, which is a change from what was proposed previously, systems without UV sensors are tested with essentially clear water (UV transmittance of 96 percent or higher).

Additionally, the log-reduction requirement for Class B systems was adjusted. Originally, a 2-log reduction of Qβ was to be required for Class B systems. This was adjusted to 1.5-log reduction for Class B systems that have a UV sensor and are evaluated at the alarm set-point or at 70-percent UV transmittance, whichever is lower. Class B systems that do not have a UV sensor and are tested without UV-absorbing chemical added are required to achieve 2.14-log reduction of Qβ. The rationale behind 2.14-log reduction is because it is equivalent to 1.5-log reduction at 70 percent UV transmittance. The log-reduction requirements of the published version of NSF/ANSI 55 are summarized in Figure 1.

The standard is published
With the improvements noted above, NSF/ANSI 55–2019 published on July 29, 2019 and is now available for conformity assessment, including third-party certification. It was very exciting to reach the goal of the UV Task Group working under NSF Joint Committee on Drinking Water Treatment Units, a goal originally established in 2016 to expand the scope of the standard to include UV sources other than low-pressure mercury and, most importantly of course, LED UVs. This group worked through a highly structured consensus process to obtain input from manufacturers, including LED UV manufacturers and other interested stakeholders, to develop the first standard for evaluation of the disinfection efficacy of these UV systems. This ability to benchmark the microbiological performance of LED UV systems is key to the advancement of the technology and the associated industry. Providing tools such as the updated NSF/ANSI 55–2019 is an important aspect of NSF’s mission to protect and improve human health, as well as supporting key stakeholders. Moving forward, third-party certifications to the standard will be valuable achievements for various manufacturers and will help to bolster the quality of products offered by the industry.

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:


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