AWWA PATH56561

AWWA PATH56561 Application of Surrogate Microorganisms for UV Reactor Validation
Conference Proceeding by American Water Works Association, 09/22/2002

Battigelli, David A.; Hargy, Tom M.; Marshall, Marilyn M.; Nicholson, Wayne L.; Clancy, Jennifer L.

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The limited effectiveness of chemical disinfection methods for control of Cryptosporidium has spurred research to validate alternative treatment processes for the production of high quality drinking water. Perhaps the most promising disinfection process currently being implemented for the inactivation of Cryptosporidium is ultraviolet (UV) disinfection. However, effective implementation of UV requires adequate characterization of reactor hydraulics and careful measurements of the UV dose received by pathogenic microorganisms in the water stream. A number of physical and chemical approaches exist for measuring the intensity and distribution of UV wavelengths for a specific water condition, but measurement may be complicated by many factors including sensor design and long term reliability. Moreover, microorganisms passing through a reactor will generally experience a range of doses due to variations in the distance from the lamp array, short circuiting within the reactor, water quality conditions and other factors. Hence, the industry has adopted biodosimetric procedures to validate reactors in the bench-scale, pilot-scale and full-scale stages of operation. Biodosimetry relies upon the application of test microorganisms with well characterized UV dose-response profiles in order to produce standard curves of UV dose. Although a number of microorganisms have been used for reactor validation studies, the two most common include UV resistant organisms such as coliphage MS-2 and the spores of Bacillus subtilis. However, to be certain there are no reactor characteristics which would limit the log inactivation of more UV-sensitive organisms such as Cryptosporidium, surrogates with UV disinfection kinetics similar to that of Cryptosporidium are desirable. This report describes efforts to characterize the dose responses of candidate microorganisms for potential application in reactor validation studies. Includes 8 references.