Comparison of static and dynamic disinfection models for bacteria and viruses in water of varying quality

Disinfection studies rarely use natural waters due to demands exerted on th e applied disinfectants and lack of consistent disinfectant residuals. This study compared the degree of disinfection achieved in natural waters betwe en conventional batch (static) models and a system of similar volume where disinfectant residuals were maintained at constant levels (dynamic). In the latter, disinfectant was delivered through a hollow fibre cartridge from a slipstream of a full-scale (chloramine) or pilot (chlorine) water treatmen t plant. The test organisms (hepatitis A virus, poliovirus, MS-2, Mycobacte rium terrae and Enterococcus durans) were selected with different resistanc e to the disinfectants. In general, for water of "good" quality, the differ ences between the two systems were often small or not apparent for monochlo ramine. However, for low chlorine residuals, or when additional demand was placed on the disinfectant, differences between the two systems became more apparent. Little difference was seen between disinfection of the test orga nisms singly or in mixtures, but injury of vegetative bacteria with monochl oramine was very apparent. This system could be useful for understanding th e fluctuations in disinfection efficacy that may occur in source water of v arying quality, or in distribution systems, as disinfectant residuals decli ne.