NSF/ANSI 55 for UV Systems Including LED UVC
By Rick Andrew
NSF/ANSI 55 Ultraviolet Microbiological Water Treatment Systems was first adopted as an American National Standard almost 20 years ago in May, 1991. At that time (and for years afterward), the dominant technology for POU and POE UV systems was low-pressure, mercury lamp systems. So not surprisingly, NSF/ANSI 55 was written specifically to address effective and rigorous evaluation of low-pressure, mercury lamp systems. Over the last five years or so, rapid advances have occurred in LED UVC technology. As these advances have continued, the NSF Drinking Water Treatment Units Task Group on UV has worked to develop an appropriate evaluation protocol for evaluating the efficacy of POU and POE LED UVC systems.
The end result of these efforts is the publication of NSF/ANSI 55–2019 (on July 29, 2019). This new version of NSF/ANSI 55 includes an expanded scope that covers not only low-pressure, mercury UV POU/POE systems, but now also LED UVC POU/POE systems.
Evaluation of POU/POE LED UVC systems
There are several key elements to the method used to evaluate these systems, including the following:
Classes of treatment
As with traditional low-pressure, mercury UV systems, there are two classes of systems established for POU/POE LED UVC systems: Class A and Class B. Class A systems are considered to be water purification devices and Class B systems are considered to be devices for supplemental treatment of potable water.
Criteria based on log reduction
Instead of using a dose-response curve and criteria based on calculated dose, the new standard evaluates pass/fail based on log reduction. Class A systems require a 4-log reduction, whereas Class B systems require 1.5-log reduction for those systems that have a UV sensor, or 2.14-log reduction for those systems that do not have a UV sensor. The rationale behind 2.14-log reduction is that it is equivalent to 1.5-log reduction at 70-percent UV transmittance.
Reduction of UV transmissivity (UVT) using a UV absorbing chemical for systems with a UV sensor
A mixture of vanillin (CAS# 121-33-5) and SuperHume®, which is available from UAS of America as Cropmaster®, SuperHume or AquaHume®, is used to reduce the UVT of the test water to the alarm set-point or to 70-percent UVT, whichever is lower, for those systems that have a UV sensor and alarm. The vanillin and SuperHume are combined in a ratio of 1.0-mg vanillin to 0.02-mL SuperHume. Systems without a UV sensor are restricted to being Class B only and are tested without addition of UV-absorbing chemicals to the test water.
A test organism
Qβ coliphage ATCC # 23631-B1 has been 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. By establishing effective inactivation of Qβ, the overall microbiological treatment efficacy of a POE or POE LED UVC system can be established.
A test protocol
NSF/ANSI 55 establishes the protocol used to introduce the test water with the Qβ to test units. In this protocol, two test systems are operated over a seven-day period with sampling of untreated (influent) and treated (effluent) water according to Figure 1. For systems connected to the water supply, the flowrate for testing is the highest achievable flowrate over the range of 15 psig to the system’s maximum operating pressure.
Beyond evaluating the effectiveness of POU and POE LED UVC systems, NSF/ANSI 55 requires that they be manufactured with materials that won’t contaminate the drinking water. This is accomplished through extraction testing, in which test units are exposed to water that has specific characteristics under controlled conditions and then that water is analyzed for potential contaminants that may have leached from the materials of the test units into the water. The concentration of any contaminants detected is evaluated to determine if it is posing risks to human health.
Systems that are connected to a pressurized water supply are also evaluated for structural integrity through a hydrostatic pressure test, which is a 15-minute test at an elevated pressure that is based on the type of system being evaluated and its maximum pressure rating. Additionally, open-discharge POU systems are subjected to a cyclic test of 10,000 cycles from zero to 50 psi. NSF/ANSI 55 also spells out information requirements that must be included in the product’s installation and operation instructions, on the system’s data plate, on the packaging of system replacement elements and in the system’s performance data sheet.
A thorough and appropriate evaluation
Building on requirements established for low-pressure, mercury POU/POE UV systems, while making selected scientifically based adjustments for the evaluation of the LED UVC systems, NSF/ANSI 55–2019 provides a comprehensive evaluation framework for both low-pressure mercury and LED UVC technologies. Detailed protocols and requirements exist for establishing Class A or Class B UV performance for these systems. The new protocol for LED UVC systems was developed to be a rigorous test of this technology, which can emit radiation at different wavelengths throughout the UVC range, depending on the design and manufacturing of the specific LED being evaluated. Additionally, like all of the NSF/ANSI DWTU Standards, NSF/ANSI 55–2019 includes additional relevant criteria for a complete system evaluation, including material safety, structural integrity and product literature.
Ultimately, NSF/ANSI 55 has been and will continue to be a valuable tool to help manufacturers, end users and regulators establish fitness for the purpose for POU/POE UV systems. The milestone accomplishment of NSF/ANSI 55–2019 is that the scope is expanded beyond low-pressure mercury technology to now also include LED UVC technology, as well.
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