CONDUCTING UV EQUIPMENT DOSE VERIFICATIONS - LESSONS LEARNED FROM REAL WORLD EXPERIENCES

Protocols for the verification of a commercial system's ability to deliver targeted UV doses have been promulgated by various private and public entities in recent years, and have at times led to conflicting requirements for meeting the same goals. These place the UV equipment manufacturers in a difficult and potentially costly position and raise concerns about the uniformity of information being generated within the industry. This paper addresses and compares the protocols that are prevalent in the industry with respect to their objectives, approach and specific testing requirements. These include protocols under the EPA Environmental Technology Verification (ETV) Program (Wet Weather, Source Water and Drinking Water Pilots), the German Drinking Water Verification Protocol, and the National Water Research Institute's new guidance for reuse and drinking water UV disinfection.Currently, two UV equipment verifications are being carried out on commercial systems under the EPA's Environmental Technology Verification (ETV) Wet-Weather Pilot. Additionally, standard UV dose assays have been conducted with an MS2 phage for a number of manufacturers, and investigations have been performed in anticipation of the National Water Research Institute's new guidance for UV applications to reuse and drinking water disinfection. HydroQual, in cooperation with NSF International and the USEPA is drafting a generic test protocol to conduct verifications for secondary effluent and reuse applications as part of the ETV program.Specific topics addressed which are a part of these testing programs, include the growth, storage and enumeration of MS2 phage, sampling procedures, hydraulic measurements, and methods to establish prescribed operating conditions related to transmittance, lamp output and quartz surface fouling. Validation of dose-response collimator equipment and procedures including the effect of mixing, sample depth, collimator length, radiation uniformity, and transmittance have been investigated, and selected results are presented herein.Further discussion is provided that explores the basic commonality among the maj or protocols, as well as some important differences. It is hoped that these specific insights and experiences will be helpful in the design and conduct of UV equipment verifications, and provide a basis of support for the establishment a single uniform protocol in the future.