Evaluation of ozone disinfection systems: Characteristic concentration C

The U.S. Environmental Protection Agency (EPA) has recently promulgated drinking water regulations known as the surface water treatment rule (SWTR) to control viruses, Giardia lamblia, Legionella, and heterotrophic bacteria. The SWTR specifies overall minimum removal and inactivation efficiencies by filtration and disinfection for Giardia lamblia and viruses. The CT concept is used to predict inactivation efficiencies. CT stands for the product of characteristic exposure time (T) and the characteristic concentration (C) of the disinfectant in the disinfection chamber. This paper presents an analysis of ways to characterize ozone concentration in water disinfection systems for the purpose of calculating ozone inactivation efficiencies. Guidelines to predict the characteristic (or average) ozone concentration are developed for four types of ozone reactors, including rigorously mixed systems, cocurrent and countercurrent contactors, and flow segments (i.e., where no ozone gas is introduced but where residuals in a water phase remain).