AWWA WQTC62377

Drinking water ozonation is continually facing new challenges because of more and more stringent regulations on disinfection and disinfection byproducts. The commonly used CT approach often underestimates disinfection efficiency, therefore it is not suitable to be used for optimization of system design and operation. In this study, a two phase CFD model has been developed to address all the major components of ozonation processes: contactor hydraulics, ozone mass transfer, ozone decay, microbial inactivation, and disinfection byproduct formation kinetics. The CFD model was applied to simulate ozone contactor performance at the Mannheim Water Treatment Plant in Ontario, Canada. The results show that the CFD method predicts significantly higher CT values than the traditional CT₁₀ method (up to 250%) using ozone residuals at 6 monitoring points within the contactor. The 13 year old Mannheim ozone system has recently been modified to include new liquid oxygen-fed ozone generators in order to enhance operational flexibility and remove some diffusers from the system. The modelling results suggest that these changes have led to an increase in effective residence time. The CFD model was also applied to optimize ozone contactor performance at the DesBaillets Water Treatment Plant in Montreal, Canada. Numerical results are in good agreement with full-scale tracer experimental data. The CFD predicted flow fields show that recirculation zones and short circuiting exist in the DesBaillets contactors. The current simulation results suggest that the installation of additional, appropriately located, baffles would increase the residence time and improve disinfection efficiency. It is anticipated that the work will demonstrate that the CFD approach is an efficient tool for improving the ozone disinfection performance of existing water treatment plants and designing new ozonation systems. Includes 15 references, figures.