FACTORS INFLUENCING THE INFECTIVITY OF GIARDIA-MURIS CYSTS FOLLOWING OZONE INACTIVATION IN LABORATORY AND NATURAL-WATERS

Factors affecting the inactivation of Giardia muris cysts using ozone were examined using 48 independent, experimentally designed trials in a bench-scale, batch reactor. Cohorts of 5 male, inbred C3H/HeN mice were used to establish the significance of temperature, turbidity, pH, ozone dose and contact time on G. muris cyst infectivity. Temperature, pH, applied ozone dose and the ozone dose x pH and temperature x pH interactions were found to be statistically significant (P less-than-or-equal-to 0.05) in ozone demand-free 0.05 M phosphate buffer. Contact time in demand-free buffer was significant up to 2 min (P less-than-or-equal-to 0.05), but not beyond. When experiments were done using natural surface waters, contact times up to 5 min were required for inactivation, indicating that caution must be used in the application of laboratory water results to real waters. It was found that residual and utilized ozone both had important influences in G. muris cyst inactivation. It was more difficult to achieve 2 or 3 log inactivation of G. muris cysts in the natural waters at 22-degrees-C than at 5-degrees-C.