The present study takes an interest in the description of the fouling mechanisms by a numerical approach at the microscopic scale. At first, an X-ray tomography has enabled the modelling of the membrane structure for the numerical simulations. Next, for different particle size, a same volume of particles has been sent in the modelled membrane and the final permeability has been computed. Thus, the influence of the particle size on the fouling has been seen. An observation of the particles penetration in the membrane has been realised to detail this influence. The Hermia relations were used in order to determinate the predominant fouling mechanism or the succession of predominant fouling mechanisms. But, without an accurate calculation of the first derivative, it is not possible to define cleanly the predominant fouling mechanism for a low filtered volume. Nevertheless, the perspectives of the local approach with the numerical simulation seem interesting.