You are here:
Evaluation of an Innovative Approach to Validation of Ultraviolet (UV) Reactors for Disinfection in Drinking Water Systems
Citation:
Adams, Jeff. Evaluation of an Innovative Approach to Validation of Ultraviolet (UV) Reactors for Disinfection in Drinking Water Systems. Presented at CECAR7, Civil Engineering Conference in Asia Region, ASCE, Oahu, HI, August 30 - September 02, 2016.
Impact/Purpose:
Abstract submission to CECAR7, Civil Engineering Conference in Asia Region, ASCE, August 30-September 2, 2016; Oahu, Hawaii. presentation on USEPA UV Demo effort and anticipated outcomes from a UV testing and analysis Recommendations Document for future UV testing?
Description:
UV disinfection is an effective process for inactivating many microbial pathogens found in source waters with the potential as stand-alone treatment or in combination with other disinfectants. For surface and groundwater sourced drinking water applications, the U.S. Environmental Protection Agency (USEPA) provided guidance on the validation of UV reactors nearly a decade ago. The focus of the guidance was primarily for inactivation of Cryptosporidium and Giardia. Over the last ten years many lessons have been learned, validation practices have been modified, new science issues discovered, and changes in operation & monitoring of UV systems need to be addressed. Also, there remains 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 & Industry collaborators, are evaluating new approaches for validating UV reactors to meet groundwater & surface water pathogen inactivation including viruses for low-pressure and medium-pressure UV systems. A particular challenge for medium-pressure UV is the monitoring of low-wavelength germicidal contributions for appropriate crediting of disinfection under varying reactor conditions of quartz sleeve fouling, lamp aging, and changes in UV absorbance of the water over time. In the current effort, bench and full-scale studies are being conducted on a low pressure (LP) UV reactor and a medium pressure (MP) UV reactor, each challenged with adenovirus (AD2), MS2 bacteriophage, and B. pumilus test microbes. One objective is to evaluate surrogate test organisms for predicting virus inactivation. Validation tests involve operating a UV reactor at different flows, UV-transmittance (UVT), and lamp power settings. Over 60 test conditions conducted with the LP system, and more than 120 conditions for the MP system. At each test condition, the log inactivation of the challenge test microbes are measured, and correlated to a UV reduction equivalent dose (RED) using bench-derived UV dose-response curves. Results from numerous test conditions are analyzed to define the UV dose monitoring & control algorithm for operating the UV reactor at a water utility.This emerging analysis approach allows normalizing challenge data from multiple test microbes with varying UV sensitivities, and may be useful for predicting inactivation of a target organism, i.e., AD2. 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, and action spectra correction factors (ASCFs). Results to-date appear favorable for predicting UV inactivation of adenovirus with surrogate test microbes by accounting for the differences in organism sensitivity to UV & its action spectra, and UV reactor conditions of UV intensity sensor readings, UVT, and flowrate. Preliminary results shows that MS2 data alone or MS2 combined with B. pumilus may predict UV inactivation of Adenovirus. Validated range of UV system operation may also be defined based on surrogate microbe prediction analysis.
