This paper presents a practical design of a new ozone contactor (the deep U tube). It is a based on the modeling of upward and downward bubbly flow of air and water, derived from a balanced equation of continuity and momentum. Two hydrodynamic parameters are estimated: the void fraction and the frictional pressure drop. Experimental data carried out on full-scale plant and pilot plant are compared to theoretical results predicted by the model. Flow of the liquid phase is performed from tracer tests in order to determine the detention time which is introduced into the CT concept for disinfection. The influence of flow model shows that a plug flow reactor is more efficient than a CSTR; the DUT is close to plug flow.