Bench-scale Cryptosporidium inactivation, pilot-scale disinfection by-product (DBP) formation and bench-scale inorganic DBP control experiments were conducted to evaluate the effectiveness of chlorine dioxide in meeting the current and future enhanced surface water treatment and disinfectant/disinfection by-product rules. A new chlorine dioxide generation process in which dilute, humidified chlorine gas is in contact with solid sodium chlorite was employed for this study. Chlorine dioxide was found to be effective in achieving CT values (pH=8 and temperature=20°C) of approximately 50 and 100 mg · min/l for 1-log and 2-log Cryptosporidium inactivation, respectively. Chlorine dioxide did not form significant amounts of trihalomethanes or haloacetic acids. Water spiked with high bromide concentrations resulted in insignificant amounts of organic DBPs after reaction with chlorine dioxide. Reaction of chlorine dioxide with water constituents resulted in the formation of chlorite and chlorate ions. Addition of ferrous ion is an effective treatment strategy for chlorite ion control.

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