Inactivation of Adenovirus Types 2, 5, and 41 in Drinking Water by UV Light, Free Chlorine, and Monochloramine

Abstract

A bench-scale study was conducted to determine the inactivation of adenovirus (Ad) types 2, 5, and 41 by ultraviolet (UV) light, chlorine, and monochloramine. The motivation for this study was to determine whether UV disinfection followed by chlorine or monochloramine for a very short contact time (e.g., a minute) could satisfy regulatory requirements for four-log virus inactivation. In order to overcome the difficulty Ad 41 presents for enumeration of the virus in cell culture, a technique was used that combined immunofluorescent staining of viral antigen with traditional scoring of cytopathic effect. A UV dose of $40\mathrm{mJ}∕{\mathrm{cm}}^2$ (millijoules per square centimeter) (applied using a collimated beam apparatus) achieved approximately one-log inactivation of adenovirus types 2, 5 and 41, confirming previous research. Ad 41 was found to be more UV resistant to UV light than Ad 2 or Ad 5 at UV doses $>70\mathrm{mJ}∕{\mathrm{cm}}^2$ to a statistically significant degree (95% confidence); however, at lower UV doses there were no statistically significant differences. Experiments with Ad 5 and Ad 41 at $5°\mathrm{C}$ and pH 8.5 showed that chlorine was very effective against Ad 5 and Ad 41, with a product of disinfectant concentration and contact time (CT) of $0.22\mathrm{mg\; min}∕\mathrm{L}$ providing four-log inactivation. Monochloramine was less effective against these adenoviruses, with a CT of $350\mathrm{mg\; min}∕\mathrm{L}$ required to achieve 2.5-log inactivation of Ad 5 and 41 at $5°\mathrm{C}$ and pH 8.5.