Study on the Inactivation of Cryptosporidium and Giardia by Chlorine Dioxide in Water

In order to study the effect of chlorine dioxide(ClO₂) inactivating Cryptosporidium and Giardia in water, different factors as ClO₂ concentration, contact time, pH, temperature, turbidity and organic content which might influence the inactivation were studied by using fluorescence staining method. With the Cryptosporidium and Giardia were 1×10⁶ cysts/ml, turbidity 1.0NTU, temperature 22¡æ, pH 7.5, under the condition that the ClO₂ concentrations was 2.0mg/L, the contact time arrive 240min, the inactivation ratio could be all more than 99%, and the effect of inactivation used by ClO₂ was Giardia stronger than Cryptosporidium. With increases in turbidity, the inactivating effect decreased. If the inactivating time achieved 240min, it could meet the presetting inactivation ratio with turbidity 0.1~10.0 NTU. The inactivating capability of ClO₂ was found to be stronger under acidic than that under alkalic conditions. Inactivation rate improves with a temperature increase from 5 to35°C. When the concentration of organic matter in the reaction system was increased, the competition between microorganism and organics with ClO₂ probably took place, thereby reducing the inactivation rate.