A three-dimensional Eulerian-Eulerian two-phase approach has been used for the simulation of a cross-flow gas-liquid wastewater treatment reactor. Two different turbulence models have been tested: the k-epsilon and Reynolds Stress Model (RSM) models. Bubble induced turbulence source terms have been added to these models. Numerical results have been validated using Laser Doppler Velocimetry (LDV) measurements. Simulations with both turbulence models successfully predicted the hydrodynamics of the reactor. Then particle tracking with a stochastic approach has been used to calculate residence time distributions (RTD) with the flow previously simulated. It has been shown that dispersion in the reactor is primarily due to turbulence. Results have been compared with experimental RTD for various liquid and gas flowrates both on a bench scale and full scale plant. The RSM model accurately predicted the dispersion whereas the standard k-epsilon model slightly underestimated the dispersion. (c) 2008 Elsevier Ltd. All rights reserved.