Ozonation is often used for drinking water disinfection. Ozonation lower is usually used to dissolve the ozonated gas in water by mass transfer between the two phases. In particular, bubbly flow is chosen due to its high interfacial area. The main objective of the present paper is to upgrade industrial ozonation tower by using the computational fluid dynamics software ASTRID adapted to such flows. Hydrodynamics is simulated and numerical results are compared to global measurements of residence time distribution (RTD). Then ozone mass transfer is simulated and results are compared to local measurements of ozone concentration in water. A more complete validation of the methodology and the choice of closure relations has been done previously in an airlift reactor (Cockx, Chemical Engineering Science, 1997, 52(21/22) 3787-3793). Numerical results are in good agreement with experimental measurements. Accounting for the water quality and for the ozone consumption in the gas phase, it is possible to simulate in the two-phase flow reactor the zones with high ozone concentration and be able to predict the inactivation level for the micro-organisms. After validation, the same method is used to propose an upgraded tower allowing to double the efficiency of the disinfection process.