Study on the Inactivation of Giardia by Chlorine in Water

In order to study the effect of chlorine (Cl₂) inactivating Giardia in water, different factors as Cl₂ concentration, contact time, pH, temperature, turbidity and organic content which might influence the inactivation were studied by using fluorescence staining method. With the Giardia was 1×10⁶ cysts/mL, turbidity 1.0NTU, temperature 22°C, pH 7.0, and after 240 min reaction, under the condition that the Cl₂ concentrations was 6.0mg/L, the inactivation ratio could be more than 99%. With increases in turbidity, the inactivating effect decreased. If the inactivating time achieved 360min, it could meet the presetting inactivation ratio with turbidity 0.1~10.0 NTU. The inactivating capability of Cl₂ was found to be stronger under acidic than that under alkalic conditions. Inactivation rate improves with a temperature increase from 5 to 25°C, but decreases beyond this. When the concentration of organic matter in the reaction system was increased, the competition between Giardia and organics with Cl₂ probably took place, thereby reducing the inactivation rate.