Cryptosporidium parvum oocysts were exposed to ozone using two experimental systems. The first method involved producing residual concentrations of 1, 3 and 5 mg/L of ozone in 500 ml of water in a Drechsel gas bottle, which was then inoculated with oocysts. The second method involved inoculating 7 L of water with oocysts and then applying a constant dose of 1, 3 and 5 mg/L of ozone, circulating the water in a contactor system. Viability was assessed by the inclusion/exclusion of fluorogenic vital dyes. Comparison of these two methods showed that the second method was considerably more successful at reducing oocyst viability than the first method. Experiments performed at an increased temperature using method one indicated that temperature was an influencing factor on oocyst inactivation by ozone treatment.

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