Effects of Water Quality on the Inactivation of Hepatitis A Virus and Enteroviruses by Free Chlorine

Free chlorine continues to be the most widely used as a disinfectant of large and small water and wastewater treatment systems. Although free chlorine has been previously studied for its ability to inactivate important waterborne viruses such as hepatitis A virus (HAV) and enteroviruses, the effects of water quality and virus physical state on virus inactivation have not been adequately characterized. Therefore, laboratory studies were done to determine the inactivation of purified, aggregated HAV, poliovirus type 1 and echovirus type 1 by 1 to 7 mg/l doses of free chlorine in both phosphate buffered, chlorine demand-free (clean) water and the same water containing 10 mg/l of a 1:1 mixture of humic and fulvic acids and 5 NTU of bentonite clay turbidity (worst case [WC] water). Virus inactivation studies in clean water were done at pH 4.5, 7.0 and 9.5 and at 5 and 25°C, and in WC water they were done at the same pH levels but at 5°C only. HAV was inactivated relatively rapidly by free chlorine under all conditions tested, with 99.99% or 4 log10 inactivation by 8 minutes or less. Free chlorine also rapidly inactivated 99.99% of polio 1 and echo 1 at pH 4.5 and 7. However, at pH 9.5 and 5°C, polio 1 and echo 1 were inactivated more slowly by a 1 mg/l dose of free chlorine, with 99.99% inactivation times of 57 minutes or more. Overall, HAV was generally more sensitive to free chlorine than were polio 1 or echo 1. However, a free chlorine dose of 5 mg/l inactivated 99.99% of HAV and the enteroviruses tested within 30 minutes at temperatures of 5 and 25°C in waters containing up to 5 NTU clay turbidity, up to 10 mg/l humic and fulvic acids and between pH 4.5 and 9.5. Virus inactivation by free chlorine was similar in worst case water and in buffered demand-free water at similar chlorine concentrations, indicating that humic and fulvic acids and clay turbidity do not appreciably reduce chlorination efficacy against enteric viruses. Therefore, as long as target free chlorine residuals are achieved, the presence of clay turbidity and humic organic matter do not appreciably interfere with virus inactivation.