AWWA WQTC64009

A multiphase computational fluid dynamics (CFD) model has been developed to address the major components of ozone disinfection processes: contactor hydraulics, ozone decay, and mass transfer. The model was applied to simulate ozone profiles and tracer residence time distributions of ozone contactors at the DesBaillets WTP in Montreal, Canada. The CFD model was applied to illustrate and improve ozone residual monitoring strategy. The modelling results show that ozone residuals at the cross section of the outlet of each chamber are very sensitive to monitoring point selection. Residuals at different locations can differ by an order of magnitude. The residual variation is affected by multiple factors, including water/gas flow rate, temperature, baffling conditions, etc. The potential optimum locations of ozone sensors can be predicted by CFD modelling. The CFD model was also used to study the factors affecting tracer residence time distribution (RTD). The results suggest that the method of tracer injection can slightly affect tracer RTD results while sampling location has a significant influence on tracer RTD prediction or measurement. The T₁₀ values calculated from the CFD predicted RTD curves at different outlet locations could have more than 10% variation. Therefore, multiple sampling points should be employed during tracer tests if possible. It is concluded that the CFD approach is an efficient tool for improving measurement or prediction of CT values, and it can be used in various ways for operating/designing full-scale ozone disinfection systems. Includes 33 references, figures.