A mathematical model was developed for a two-dimensional transient nitrate transport through an extractive membrane bioreactor (MBR) with a hollow-fiber membrane module which is used in the denitrifying system of drinking water. Denitrification takes place on the shell side of the membranes, creating a driving force for a mass transfer. The presented CFD model formulates and solves the couples of fundamental mass and momentum balance equations using numerical techniques. Simulation results showed that with an increase in feed flow rate. MBR efficiency decreases. Moreover, MBR efficiency increases as the feed concentration rises. In addition, when the effect of membrane structural parameters was investigated; it was shown that the restrictive factor. K-r, has a distinctive effect on MBR efficiency. Besides, using three correlations to estimate the tortuosity as a function of porosity, the effect of porosity was examined and it demonstrated that MBR efficiency was affected by a low value of 2.8% difference in the standard deviations of these three correlations. Finally, the simulation results demonstrate that the model is a good predictive one, especially from the hydrodynamics point of view. Comparing the simulation results with the experimental data a reasonable conformity with deviations of smaller than 8.00% was achieved. (C) 2012 Elsevier B.V. All rights reserved.