Validating UV Systems
Communities, towns and cities are quickly learning what residential, commercial and industrial water professionals have known for years—that ultraviolet (UV) disinfection is effective at inactivating waterborne microorganisms. While UV has become a standard product for many residential and commercial well water applications, recent acceptance by the U.S. Environmental Protection Agency (EPA) will make it a standard product for many community-based drinking water plants.
So why the change? The EPA’s Long Term 2 Enhanced Surface Water Rule (LT2ESWTR) allows communities to receive inactivation credit for Cryptosporidium parvum and Giardia lamblia by using UV disinfection. This rule is specifically for surface water or groundwater under the influence of surface water. The main reasons for this newfound acceptance are that UV inactivates many microorganisms that are becoming chlorine resistant and reduces harmful byproducts associated with the chlorination process.
The key to regulatory acceptance is that the UV disinfection system must be properly validated by a recognized testing organization or procedure.
Understanding and selecting a validation process has proved to be a confusing endeavor for both engineers and their clients.
Most water professionals are familiar with the NSF Mark, which has become a standard in water product certification. In the UV world, NSF/ANSI Standard 55 is recognized for point-of-entry systems that generally treat flows under 50 gal per minute (gpm). For the larger community/ municipal applications, the validation process involves a variety of options.
At its most basic level, a validation involves introducing a test microorganism into a UV reactor and taking sample counts before and after the UV. The test, which is referred to as a bioassay and is administered by an independent and recognized third party, indicates the applied dosage and is an indication of whether the UV system will be accepted for a certain set of operating parameters. The target dosage is 40 mJ/cm2 (40,000 uWs/cm2). Currently, these tests are being conducted at onsite locations at test centers in Johnstown, N.Y., Portland Ore., the ONORM facility in Austria, and at the DVGW facility in Germany.
While the U.S. UV drinking water market is in its infancy, UV has been an accepted disinfection practice in Europe for years. As a result, the European community has well-established testing organizations and guidelines.
One of the most recognized, stringent and established testing certification organizations for UV validation is the DVGW, which is the German Technical and Scientific Association for Gas and Water. The DVGW standard is often cited in UV disinfection technical specifications, but because it is not a U.S.-based organization, not much is known about their rigorous protocols.
DVGW, which is similar to testing agencies like Underwriters Laboratories, is one of the world’s most recognized standards organizations. A UV system that has been tested to the DVGW W294 Protocol will meet U.S. drinking water requirements.
DVGW W294 Testing Overview
The DVGW facility is capable of treating up to 20 million gal per day (mgd) and is located in Germany (the Johnstown, N.Y., centers can test in excess of 40 mgd). The main goal of its UV validation program is to certify the performance of reactors and the subsequent monitoring of the system. Validation under DVGW ensures that the unit has been certified to deliver a Reduction Equivalent Dose of 40 mJ/cm2 at all times and under all conditions.
Performance testing. The actual test units are piped into the test facility using the worst-case hydraulic scenario, which is represented by placing elbows before and after the UV unit. Once in place, the unit is subjected to various flow rates and different water quality conditions. During the testing, the transmittance of the water (the energy absorbing material in the water) is adjusted to simulate different and worst-case operating scenarios. A non-pathogenic (disease-causing) microorganism (B. subtilis for DVGW and ONORM, MS-2 for other centers) is injected into the flow and multiple samples are taken pre- and post-UV unit. Once in the lab, the applied UV dosage is calculated and a result is furnished.
Monitoring. The protocol requires a minimum number of monitoring ports containing UV irradiance sensors. The quantity is based on the number and power of the UV lamps. The individual sensors, the windows and the reference sensors (radiometers) also have to be standardized to the W294 protocol.
Throughout the life of the validated UV reactor, each sensor will need to be checked to ensure proper operation. This is accomplished by using a reference sensor. By testing the various UV sensors, the regulators can ensure that the system is operating properly.
The release of the EPA’s long awaited rule has put a spotlight on the UV disinfection and filtration markets. In order for UV disinfection to get a foothold in the community drinking water market, regulators, engineers and owners will need to understand more about UV and its validation protocols.
The good news is that the validation centers have been preparing themselves for this rule, and they are ready to validate.