UV REACTOR VALIDATION: MATCHING THE MICROBE WITH THE TARGET DOSE

The application of UV radiation to the disinfection of treated wastewaters and drinking water is rapidly advancing, and with this, the need for effective validation of the dose-delivery performance of commercial reactors. Advances in modeling the dose-distribution within a reactor, coupled with the observed inactivation kinetics of targeted microbes, demonstrates that selection of the challenge microbe used for dose-delivery validation plays a critical role in the validation process. The dose-distribution theory explained in this paper shows that direct validation testing must be performed with organisms that reflect the same dose sensitivity as the targeted microbes. Use of the MS2 coliphage, widely practiced for validation of reuse and drinking water reactors at dose levels greater than 30 mJ/cm2, may not identify a poorlyperforming reactor at lower dose levels, such as those prescribed for coliform or E. coli inactivation in treated wastewaters. The theory of this dose-distribution effect is discussed and examples are presented for hypothetical poorly- and well-performing reactors. The paper advances the recommendation that indigenous organisms, or surrogates of similar UV sensitivity, should be used when validating, and subsequently sizing, reactors at lower dose levels.