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CRYPTOSPORIDIUM LOG-INACTIVATION WITH OZONE USING EFFLUENT CT 10, GEOMETRIC MEAN CT 10 EXTENDED INTEGRATED CT 10 AND EXTENDED-CSTR CALCULATIONS
Citation:
RAKNESS, K. L., I. NAJM, M. ELOVITZ, D. REXING, AND S. VIA. CRYPTOSPORIDIUM LOG-INACTIVATION WITH OZONE USING EFFLUENT CT 10, GEOMETRIC MEAN CT 10 EXTENDED INTEGRATED CT 10 AND EXTENDED-CSTR CALCULATIONS. B.L. Loeb (ed.), OZONE, SCIENCE & ENGINEERING. CRC Press - Taylor & Francis Group, LLC, Boca Raton, FL, 27(5):335-350, (2005).
Description:
The draft Long Term 2 Enhanced Surface Water Treatment Rule ("LT2ESWTR") contains Cryptosporidium log-inactivation CT tables. Depending on the water temperature, the Cryptosporidium CT values that are listed are 15 to 25 times greater than CT values for equivalent Giardia log-inactivation credit. The elevated operating dose required for Cryptosporidium log-inactivation credit has the potential to increase bromate formation in addition to other disinfection by-products. Calculating CT value accurately will minimize ozone dose and disinfection by-product formation, and at the same time maintain disinfection protection through implementation of scientifically based safety factors.
Various methods are available for calculating CT value. The method chosen depends largely on the available information concerning ozone residual characteristics and hydrodynamic features of the ozone contactor. Appendix O of the Surface Water Treatment Rule Guidance Manual introduces CT10 for calculating ozone CT value for Giardia and virus log-inactivation. The "LT2ESWTR" Pre-proposal Draft Regulatory Language for Stakeholder Review mentions Geometric Mean methodology for calculating CT value for Cryptosporidium log-inactivation. Chapter 11 and Appendix B of the draft "LT2ESWTR" Toolbox Guidance Manual describes the Extended-CSTR (continuous-flow stirred tank reactor) method for calculating Cryptosporidium log-inactivation, which is applicable for compartmentalized ozone contactors such as over-under or serpentine baffled basins. The Extended Integrated CT10 method outlined in this paper is a variation of Extended-CSTR and T10 methodologies, and may be suitable for non-compartmentalized ozone contactors such as pipelines or long-channels.