Inactivation of Cryptosporidium and Giardia

Executive Summary:

• Cryptosporidium and Giardia are waterborne protozoan diseases that can cause diarrhea and threaten the lives of immunocompromised individuals.
• Chlorine disinfectant has limited effectiveness against Cryptosporidium and Giardia, making water transmission an ideal route for these diseases.
• Chlorine dioxide (ClO2) has been shown to be effective in treating wastewater and drinking water.
• This study investigated ClO2 inactivation of Cryptosporidium and Giardia in drinking water and how different factors, such as ClO2 concentration, contact time, pH, temperature, turbidity, and organic content, could affect the inactivation.
• The study used a fluorescence staining method to analyze the results.
• With Cryptosporidium and Giardia at 1×106 cysts/ml, turbidity at 1.0 NTU, temperature at 22°C, and pH at 7.5, a ClO2 concentration of 2.0 mg/L and a contact time of 240 min achieved an inactivation ratio of more than 99%.
• ClO2 was more effective against Giardia than Cryptosporidium.
• The inactivating effect decreased with an increase in turbidity, and the inactivation time needed to achieve the presetting ratio increased with increasing turbidity.
• The inactivating capability of ClO2 was stronger under acidic than alkaline conditions.
• Inactivation rate improved with an increase in temperature from 5 to 35°C.
• An increase in the concentration of organic matter in the reaction system reduced the inactivation rate, possibly due to competition between microorganisms and organics for ClO2.
• The study used purified Cryptosporidium cysts and Giardia cysts isolated from the feces of naturally infected canines.
• ClO2 was produced from a self-designed gas generator with a purity of above 99.5% and calibrated accurately before use.
• Estimated time to read: 5-7 minutes