By Rick Andrew
Systems using ultraviolet (UV) technology based on a low pressure mercury source have been well established for use in POU and POE drinking water treatment. With sufficient UV radiation energy at the 254 nm wavelength, DNA in pathogenic microorganisms is destroyed so they cannot reproduce, which prevents them from causing disease in people drinking the water. In recent years, LED UV technology has been rapidly developing, with similar potential to destroy DNA in pathogenic microorganisms at wavelengths in the germicidal range.
As such, NSF/ANSI 55 for UV systems has become established for evaluating the safety, structural integrity, treatment performance, and user instructions for both low pressure mercury UV systems as well as LED UV systems. Each of the aspects of the product is important to assure high quality, safe, and effective usage in providing clean, safe drinking water for consumers. Addressing each of these aspects can improve and enhance the confidence of end users in products that conform to the standard. Let’s explore each of these aspects in a bit more detail.
Class A vs. Class B
NSF/ANSI 55 separates UV systems into two distinct classes. Class A devices are intended to inactivate and/or remove microorganisms, including bacteria, viruses, Cryptosporidium oocysts, and Giardia cysts, from water that may be contaminated. Class A UV systems are not intended for the treatment of water that has an obvious contamination or intentionally contaminated source, such as raw sewage, nor are they intended to convert wastewater to drinking water. They are intended to be installed on visually clear water (not colored, cloudy, or turbid).
Class B systems, on the other hand, are intended to be used for supplemental bactericidal treatment for the inactivation of microorganisms that may be present in drinking water (public or private) considered to be microbiologically safe and of known quality. Class B systems are intended to inactivate normally occurring nonpathogenic nuisance microorganisms only, and are not intended for the disinfection of microbiologically unsafe water. Individual or general cyst claims cannot be made on Class B systems. Microbiological health effects claims cannot be made on Class B systems. Class B systems are not intended to be used with water that is microbiologically unsafe or of unknown quality without adequate disinfection before or after the system.
Log Reduction Requirements
Qβ is a laboratory test organism that has characteristics that make it useful in testing the effectiveness of UV systems for drinking water treatment. It is a bacteriophage, meaning it is a virus that infects bacteria, but does not infect humans. It has been studied to see how effectively it is treated by UV compared to typical waterborne pathogens including bacteria, virus, and protozoan cyst. These studies have been used to establish reduction requirements for UV systems for Qβ that can provide assurance that sufficient reduction of waterborne pathogens will be achieved.
Accordingly, Class A systems are required to achieve 3.5 log reduction of Qβ when tested per the methodology in NSF/ANSI 55.
Class B systems are required to achieve 2.0 log reduction of Qβ when tested according to the methodology in NSF/ANSI 55.
Alarm or Fail-Safe
NSF/ANSI 55 requires that Class A systems have alarm and/or fail-safe design elements incorporated into them. Specifically, Class A systems must include a UV sensor. A sensor that detects radiation in the visible range is not sufficient to meet the Standard—it must be a UV sensor. The UV sensor must be connected to an alarm which provides a visual and/or audible indication that the system is not performing, and/or terminates the discharge of treated water. The Standard includes a test to ensure that the UV sensor and alarm perform properly in low dosage conditions.
Although Class B systems are not required to have a UV sensor, if they are so equipped, the sensor must meet the test requirements.
The effectiveness, and ultimately the log reduction of a UV treatment system, is inversely proportional to flow rate through the system. For this reason, NSF/ANSI 55 requires that UV systems include automatic fixed flow rate controls to prevent excessive flow over the manufacturer’s recommended operating pressure range. The Standard requires that the flow rate of the system be evaluated over the manufacturer’s operating pressure range and up to at least 100 psi (690 kPa), and that the bioassay testing for UV log reduction must be conducted at the highest flow rate achieved by the system.
Safety of Materials in Contact with Drinking Water
NSF/ANSI 55 requires that the system undergo extraction testing to ensure that no contaminants are leaching from drinking water contact materials at levels of toxicological concern. Prior to extraction testing, the materials in contact with drinking water must be reviewed to determine appropriate analytical test batteries of the extraction water such that any potential contaminants can be detected. Any contaminants that are detected must be assessed toxicologically to determine whether they are at a level of concern. Any UV systems that include pre- or post- filters that contain active media such as activated carbon must be assessed for extraction both with and without the active media.
POU and POE UV systems must be structurally sound so they can withstand the rigors of long-term use in residential plumbing systems without leaking. NSF/ANSI 55 requires that these systems be tested for structural integrity. Although specific test requirements vary by product configuration, most UV systems are required to withstand an elevated pressure of 240 psi (1654 kPa) for 15 minutes without leaking. Additionally, complete systems designed for open discharge are required to pass a cyclic pressure test. For more detailed information, please see Figure 1.
The user responsibility and operating requirements of POU and POE UV systems must be clearly communicated to consumers. NSF/ANSI 55 requires that specific information relevant to these considerations must be included in four basic pieces of product literature:
- Installation, operation, and maintenance instructions—a manual describing complete system requirements and features.
- Data plate—a permanent label on the system.
- Replacement element packaging—including information to help match replacement elements with associated treatment systems.
- Performance data sheet—a document summarizing performance of the system.
End users considering the purchase of a complex drinking water treatment system can have challenges assessing the quality of products. This confidence can span multiple dimensions of the product, including questions regarding whether the system performs as claimed by the manufacturer, whether the system is safe to use, whether the system will leak once installed, and what the user must do to install and use the product over its lifetime. NSF/ANSI 55 is structured to include requirements, many of them based on rigorous laboratory testing, to address each of these dimensions. The end result for products conforming to the standard is confidence by end users.
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]