The U.S. Environmental Protection Agency’s (EPA) Water Infrastructure Resiliency and Finance Center, in collaboration with the...
The process of choosing a UV system is becoming much more selective, as an increasing number of drinking water facilities are using UV as a primary disinfectant. According to Canadian and U.S. drinking water guidelines, UV is accepted as an alternative disinfectant; however, this acceptance comes with limitations. Each UV system must have a third-party validation of the dose it delivers. Based on theoretical calculations, UV manufacturers can tell what a system should deliver; nonetheless, if a water supply is regulated, the UV system in question must provide proof of performance.
The Canadian view on drinking water treatment is changing. Stringent water chemistry requirements, continuous turbidity readings, strict chlorine residuals and alternate means of disinfection are but a few of the changes that have come into play. Certain Canadian provinces have chosen to draft their own drinking water regulations, while others are following existing requirements to ensure the safety of public drinking water.
The two main Canadian provinces that have rewritten their regulations to include requirements for UV disinfection are Ontario and Alberta. Both provinces provide a section in their regulations titled Alternative Disinfectants that lists UV technology. In order to install a UV system on a regulated drinking water supply in either of these provinces, the system must have a third-party validation, regardless of its size.
The U.S. EPA UV Disinfection Guidance Manual has defined third-party validation as “the process by which a UV reactor’s disinfection performance is determined relative to operating parameters that can be monitored. The reactors are validated to indicate that they achieve a certain delivered UV dose for a range of flow, UV intensity and water quality conditions.”
There are many different ways to obtain a third-party validation for a UV system.
For residential (point-of-entry) applications (under 30 gpm), there is the NSF 55 validation, which only tests for one specific UV dose level. NSF defines a point-of-entry system as “a system used to treat all or part of the water for the facility at the point where the drinking water comes into the facility. For Class A systems, a single-family dwelling shall be considered a facility.” The only condition that the NSF 55 protocol tests for is the delivered dose of the system when it is in alarm, not over a range of water quality levels or conditions. A UV system can be in alarm for various reasons such as low UV intensity (which can be due to low water quality or stained quartz) or a lamp failure.
For private seasonal applications (from 60 to 100 gpm) and large municipal applications (>100 gpm), UV systems can be validated under several different validation protocols. Some of these include the U.S. EPA UVDGM draft, the DVGW W294 German standard, the ONORM 5873-1 Austrian standard and the NWRI/AWWARF guidelines for UV validation.
Third-party validation can be conducted at the intended installation site (onsite validation), at a facility designed specifically for UV validation or at an alternative site where a witness is present.
Regardless of the protocol you follow, the main focus of a UV validation is the biodosimetry/bioassay analysis. Biodosimetry can be defined as the procedure used to determine the performance or dose delivery of a UV system. Through a measurement of the inactivation of a challenge microorganism (MS-2 bacteriophage) following UV exposure, the reduction equivalent dose of a UV reactor can be determined following a dose-response curve comparison. A dose-response curve is generated through a controlled laboratory test, called a collimated beam, which measures both the exposure time and UV intensity at which the MS-2 is exposed and inactivated.
MS-2 is typically used as a challenge microorganism due to its high resistance to UV, the ease to culture and its highly reproducible inactivation results. MS-2 is also a non-pathogenic microorganism; therefore, there is no concern of possible infection when working with MS-2.
The dose-response curve is a base line standard of the experiment. The creation of the MS-2 dose-response curve is the first step of biodosimetry. The next step is introducing MS-2 to the UV equipment in question. This is done by dosing the feedwater with a known concentration of MS-2; running the contaminated water into the UV; and finally collecting both influent and effluent samples. The concentration of MS-2 in the influent and effluent is determined through the plating of the collected samples. The log inactivation of MS-2 is calculated through the comparison of influent and effluent results. This log inactivation is compared to the dose-response curve.
For example, if a log inactivation of 2.2 was found during the validation, a comparison to a dose-response curve would give a UV dose of approximately 40 to 42 mJ/cm2.
It is important to collect multiple samples at each condition in order to show that results fall under an acceptable confidence interval. The U.S. EPA UVDGM states: “Tier 1 criteria for the challenge microorganism measurements are as follows: Five influent and five effluent samples should be collected per test condition evaluated as per section C.4.9.5 ... The standard deviation of the challenge microorganism concentration measured with the influent and the effluent samples should be less than or equal to 0.20 log.”
It is important to test UV reactors at various conditions in order to generate a type of operational curve that can be used across a wide range of drinking water applications.
The biodosimetry aspect of the third-party validation is important; however, careful consideration must be taken with regard to the validation protocol, third-party expert (witness) and creditability of the microbiological laboratory that is culturing the MS-2 and running the samples.
The protocol is important, as specific drinking water regulations require UV systems to be validated under specific protocols. The Alberta government has recently released a draft of their new drinking water regulations, which states that UV systems shall be designed to follow standards set out in “(i) the U.S. EPA UVDGM (UV Disinfection Guidance Manual) draft (ii) DVGW (German UV validation protocol) (iii) NWRI/AWWARF.” Regardless of the protocol followed, UV systems must demonstrate a sufficient dose in order to inactivate both Giardia and Cryptosporidium.
It is very important for UV manufacturers to choose an appropriate UV expert to witness the validation. Two large UV validation facilities in the U.S. are HydroQual, Inc.’s facility in New York state and Carollo Engineering’s Portland, Ore., facility. These organizations take the role of UV validation expert, recognized microbiological laboratory as well as the authority on equipment certification under specific UV validation protocols. A UV manufacturer can also choose a different validation location, as long as the location has a sufficient water supply. The manufacturer must provide a UV expert to witness the testing.
The U.S. EPA UVDGM defines a third-party expert as “a registered professional engineer with knowledge and experience in testing and evaluating UV reactors.” This individual holds the responsibility to “... witness the validation testing to verify that the documented validation protocol was followed and the reported data and results are accurate.” Not only will the UV manufacturer have to find a third-party validation expert, but they will also need to find a creditable micro-biological laboratory.
When looking for a microbiological laboratory, it is important to consider the lab’s experience and background with regard to the selected challenge microorganism. For example, the GAP EnviroMicrobial, London, Ontario, lab has an extensive background with MS-2 and has provided this challenge microorganism for UV validation projects all over the world. GAP is a member of the Canadian Association for Environmental Analytical Laboratories with accreditation by the Standards Council of Canada.
The demand for UV equipment will continue to grow amongst various drinking water applications. In order for a UV system to be deemed acceptable by regulators, it must come equipped with proof of performance. As a result, third-party validation has ultimately become the UV seal of approval.