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Ultraviolet (UV) Disinfection for Drinking Water Systems
Adams, Jeff. Ultraviolet (UV) Disinfection for Drinking Water Systems. Presented at 2015 USEPA Drinking Water Workshop, Cincinnati, OH, August 25 - 27, 2015.
Poster for 2015 USEPA Drinking Water Workshop, August 25-27 Cincinnati, Ohio. Workshop focuses on issues of concern for State Regulatory Offices, Water utilities, and drinking water industry community.
UV disinfection is an effective process for inactivating many microbial pathogens in water with potential to serve as stand-alone treatment or in combination with other disinfectants. USEPA provided guidance on the validation of UV reactors nearly a decade ago. Since then, lessons have been learned, validation practices have been modified, and changes in operation and monitoring of UV systems have been considered. Also, there continues to be no standard approach for validating UV reactors to meet a 4-log (99.99%) inactivation of viruses.USEPA in partnership with the Cadmus Group, Carollo Engineers, and other State and Industry collaborators, is evaluating new approaches for validating low pressure (LP) and medium pressure (MP) UV systems with a focus on inactivating viruses in groundwater and surface water applications. A particular challenge for MP UV is the monitoring of low wavelength germicidal contributions for appropriate crediting of disinfection under varying reactor conditions such as quartz sleeve fouling, lamp aging, and changes in UV absorbance of the water over time.Bench and full-scale studies were conducted on a LP UV reactor, and testing is ongoing with a MP UV reactor. Test microbes included adenovirus (AD2), MS2 bacteriophage, and B. pumilus. Testing involved operating a UV reactor at varying flows, UVT, and lamp power. Over 60 operating conditions were conducted with the LP system, and 120 anticipated for the MP system. The inactivation of the test microbes were measured, and correlated to a UV reduction equivalent dose (RED) using bench-derived dose-response curves. Results were analyzed to define a UV dose monitoring algorithm. Typically, an algorithm is programmed into the PLC instrumentation of the UV system for operation at a water utility.The analysis approach allows normalization of inactivation results from multiple test microbes with varying UV sensitivities over the germicidal range, and may be useful for predicting inactivation of a target organism, i.e., AD2 with surrogates. For the MP UV reactor, the UV dose-monitoring algorithm accounts for both contributions of low-and high-wavelength UV light, using a newly developed duty sensor technology.