NEW UV TECHNOLOGY FOR DRINKING WATER

This article originally appeared in the November 2019 issue of Water Quality Products magazine as "Years in the Making."

Low-pressure mercury bulbs have long been used as an ultraviolet (UV) method to reduce microbes in residential drinking water, but the inherent toxicity of mercury poses handling and transportation risks. A major revision to a nearly three-decades-old drinking water treatment standard incorporates new UV technology for microbial reduction, paving the way to eliminate the need for potential hazards from mercury bulbs. The update to NSF/ANSI Standard 55: Ultraviolet Microbiological Water Treatment Systems allows for the introduction of LED technology (light-emitting diodes), for microbial reduction in drinking water and provides a new test method to certify claims. 

Changing Times

NSF/ANSI Standard 55 was developed in 1991 to establish minimum requirements for the reduction of microorganisms using UV radiation. Treatment systems covered by the standard use UV light to inactivate or kill bacteria, viruses and cysts in microbiologically unsafe water (Class A systems) or to reduce the amount of non-disease-causing bacteria in disinfected drinking water (Class B systems). The standard’s original scope was limited to low-pressure systems available in the marketplace at the time, namely low-pressure mercury lamps. In recent years, however, the Drinking Water Treatment Units Joint Committee has recognized that there are newer technologies using polychromatic light, such as LEDs, or something other than a UV wavelength of 254 nanometers.

The water industry has been eagerly anticipating incorporation of this new UV technology within the standard, as well as the ability to certify manufacturer’s claims. Other examples of LEDs to eliminate microorganisms are in hospital settings, as well as inside refrigerators and even in kitchen cabinet task lighting. With an increase in the use of LEDs in various industries, the joint committee developed a task group to determine an appropriate test method to incorporate LED bulbs into NSF/ANSI Standard 55 for microbial disinfection of drinking water.

A Group Effort

In 2014, the UV task group was given the charge to develop a protocol to address these alternate technologies for UV drinking water treatment systems that operate across a broader range of wavelengths. After considering several options, the task group recommended the approach of running a direct log-reduction test with an organism that would represent an entire class of organisms. This approach also would reduce the cost of having to do the collimated beam test.

Several rounds of validation testing were completed by NSF on systems with UV wavelength ranges from 254 nanometers to 285 nanometers. From these studies the task group concluded that Q-beta is an acceptable surrogate to rotavirus and performs in a slightly more conservative way. This holds true at both ends of the UV range being examined (254 nanometers to 285 nanometers). It also was determined that the most stable absorber across the proposed UVT range is a superhume-vanillian mix. 

For devices with wavelengths other than 254 nanometers, the new method using Q-beta would be required and would have the following criteria: 

• 4-log reduction of Q-beta at the alarm set point for Class A devices; and

• 1.5-log reduction of Q-beta for Class B with UV source irradiance at 70% normal output or 2.14-log reduction with UV source irradiance at 100% normal output.

NSF/ANSI Standard 55 was developed following the American National Standards Institute (ANSI) process designed to ensure openness, balance, consensus and due process for all stakeholders. The Drinking Water Treatment Units Joint Committee is comprised of stakeholders representing consumers, the water industry and state and federal health and environmental agencies in the U.S. and Canada. The joint committee includes 28 voting members and 108 people altogether, including observers who offer input and expertise during the standard development process and is facilitated by NSF Intl.’s standards development group.

SOURCE TO COMPLETE ARTCLE BY BY STEFAN BUCK

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• UV Disinfection