By Rick Andrew
UV systems are successfully employed across a range of water treatment applications, from pools and spas, to municipal water treatment, to POU and POE. In each case, the purpose of the UV system is to disinfect the water. Each of these end uses, however, brings with it nuances in terms of specific system characteristics to be considered and addressed. Given this broad range of end uses and the specific concerns associated with the use of UV in them, there are multiple NSF/ANSI standards that address UV systems with various requirements.
Different standards for various end uses
Following is an overview of each of the NSF/ANSI standards that address UV systems and some of the scope and main focus addressed by each of them with respect to UV systems. See Figure 1 for a brief summary.
NSF/ANSI 50. This standard covers materials, components, products, equipment and systems related to public and residential recreational water-facility operation. It includes a broad range of requirements for UV systems used as supplemental treatment for recreational water with primary disinfection. This range includes requirements for safety of materials, cleanability, design pressure, flow control, performance indication, user instructions, operational protection, life testing, hydrostatic pressure resistance and supplemental disinfection performance.
There are requirements for systems with claims of Cryptosporidium inactivation applicable only to those systems with such claims. These systems must demonstrate supplemental disinfection performance through 3-log reduction of bacteria when tested according to the method specified by the standard. E. faecium and P. aeruginosa are used for this testing. The systems are installed on a test apparatus containing a volume of water such that a minimum of five turnovers of water through the UV system in 30 minutes is achieved when operating. The UV system and test apparatus are operated and samples are collected after each system turnover until the required turnovers have been completed. After each, a minimum of 3-log reduction must be achieved as demonstrated by analysis of the collected samples.
Additionally, NSF/ANSI 50 includes requirements for those UV systems that are intended to inactivate Cryptosporidium in a recreational water application. These systems must achieve 3-log reduction in a single pass of treatment.
NSF/ANSI 55. This standard covers UV water treatment systems and components for POU and POE applications. It addresses the safety of materials in contact with drinking water through extraction testing and toxicological assessment of extraction testing results. The standard includes requirements for structural integrity of UV systems to assure that they will not leak when installed in plumbing systems. Clear user instructions conveying installation and operation requirements and user responsibility are required.
It also includes requirements for UV disinfection claims for two different classes: A and B. Class A systems are intended for disinfection purposes to inactivate pathogens. A UV dosage of 40 mJ/cm2 is required, along with a flow restrictor to prevent excess flowrates and a UV sensor and alarm. The UV dosage is determined at the highest achievable flowrate with UV-absorbing material (parahydroxybenzoic acid, PHBA) added until the alarm is activated or until UV transmissivity is reduced to 70 percent, whichever has lower UV transmissivity.
Class B systems are designed for supplemental bactericidal treatment of disinfected public drinking water or other drinking water that has been tested and deemed acceptable for human consumption by the state or local health agency having jurisdiction. A UV dosage of 16 mJ/cm2 is required, along with a flow restrictor to prevent excess flowrates. The UV dosage is determined at the highest achievable flowrate with PHBA added until the UV transmissivity is reduced to 70 percent.
NSF/ANSI 61. This standard is intended to cover specific materials or products that come into contact with drinking water. The standard focuses on safety of materials in contact with drinking water through extraction testing and toxicological evaluation of the extraction testing results. NSF/ANSI 61 does not address structural integrity, disinfection efficacy or any other product performance-related attributes. In addition to the extraction testing and toxicological assessment, NSF/ANSI 61 requires conformance of the product to NSF/ANSI 372, which is described below.
NSF/ANSI 372. This standard applies to any drinking water system component that conveys or dispenses water for human consumption through drinking or cooking. It addresses lead content requirements consistent with US federal and state regulations. The standard requires that products intended for contact with water for human consumption must be designed and constructed such that the weighted average lead content in the materials and components in contact with water is 0.25 percent or less. As such, it includes methods for measuring and calculating the weighted average lead content.
Similarities and differences
One common theme throughout these standards, regardless of end use, is the requirement for material safety. For drinking water applications, safety of materials is of paramount importance. This is reflected especially in NSF/ANSI 372 and NSF/ANSI 61, which are solely focused on attributes of material safety in terms of contaminant leaching and lead content, respectively. NSF/ANSI 55 also has a primary focus on material safety, even though it is not focused on drinking water but rather water used for swimming and recreation. It includes detailed requirements regarding safety of materials in contact with water.
Disinfection efficacy is a major focus of both NSF/ANSI 50 and NSF/ANSI 55. These end uses in recreational water and POU/POE water treatment involve UV systems amenable to disinfection efficacy testing in a laboratory. These end uses also involve installations in situations where there is less monitoring of system performance by users with less formal training and understanding than for applications such as treatment of public water supplies. So, it is both more reasonably achievable and also more important to include disinfection efficacy requirements in NSF/ANSI 50 and NSF/ANSI 55 for recreational and POU/POE UV systems as opposed to NSF/ANSI 61 for UV systems used in public water supplies.
That said, there are certainly federal regulations related to use of UV systems for treatment of surface water and groundwater under the influence of surface water that could be incorporated into product standards. Specifically, the Long Term 2 Enhanced Surface Water Treatment Rule (LT2)—supported by the Ultraviolet Disinfection Guidance Manual (UVDGM) as a guide for utilities, UV equipment manufacturers and engineering consultants in the application of the LT2 rules—could be used to determine standard requirements for UV systems used for treatment of public water supplies. There is currently an early stage effort underway at NSF to do just this and create NSF/ANSI 420 Public Drinking Water Equipment Performance–Ultraviolet at some point in the future.
One technology—multiple standards
A challenge faced by manufacturers, users, code officials, inspectors and certification bodies is to understand the vast landscape of product standards. Here we see how one technology, used for the same broad application of water treatment, but slightly different end uses (such as recreational versus POU/POE versus public water supply) has four standards to be considered for potential applicability, with another one in the works. One can imagine how this landscape becomes even more difficult to navigate when considering international implications and requirements. There are certainly valid reasons underlying the existence and value of these multiple standards, so it is not likely that this landscape will become rationalized with fewer standards over time. Rather we must continue to educate and be educated so we can understand the landscape and successfully find our pathways through it.
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]