Residence time distribution (RTD) experiments are carried out in a pilot plant (QL = 1 m3.h−1). The RTD curves are analyzed by the completely mixed reactors in series model or by the axial dispersion model. Measurements are performed either on the overall bubble column or on four equal parts of the reactor. The bottom part (gas introduction) is completely mixed. The top part (water introduction) is a mixed reactor in which the middle parts are plug flow reactors with a weak axial dispersion coefficient. Dissolved ozone measurements along the column are in agreement with that model which allows a reactor modelization to compute the dissolved ozone profiles.