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Utilities operating in cold regions face several challenges in the provision of microbiologically safe drinking water. In particular, these utilities must account for the low temperature of their source water in the design and operation of their water treatment processes. In some locations, source water temperature may approach 0 degrees C for extended periods during the year. Water at this temperature creates a dilemma for utilities that must meet reduction requirements for Giardia lamblia and Cryptosporidium parvum. At low temperatures, the cysts and oocysts of these parasites are extremely resistant to most conventional chemical treatments. In this paper, the design requirements for control of these parasites in low temperature waters by conventional chemical treatment methods, including chlorine, monochloramine and chlorine dioxide, will be reviewed. Ozone and ultraviolet (UV) light are two potential solutions to the problem of G. lamblia and C. parvum reduction for cold regions. The results of a recent laboratory study on the efficacy of ozone and ultraviolet light (UV) for inactivation of C. parvum at very low water temperature will be summarized. A kinetic model that predicts inactivation of C. parvum by ozone at various temperatures will be described. The model can be used by designers of water treatment facilities in cold regions to generate ozone design criteria for inactivation of C. parvum for water temperature as low as 1 degree C. In contrast to chemical treatments, temperature had little effect on inactivation of C. parvum oocysts by UV light at temperatures ranging from 0.5 to 22 degrees C. High levels of oocyst inactivation were measured in 0.5C water at UV doses as low 10 to 21 mJ/cm 2. Includes 17 references, figures.

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Edition: Vol. - No. Published: 06/01/2001 Number of Pages: 13File Size: 1 file , 360 KB