Coagulation of colloids retained by porous wall

The structure of a colloidal deposit retained by a porous wall is described accounting for surface interactions and hydrodynamic forces. The balance of forces acting over spherical, charged particles allows the calculation of the interparticular distances inside the cake according to the physicochemical conditions (ionic strength, particle potential, pH, particle size) and to the experimental parameters (flux). The model predicts that beyond a critical mass deposited on the porous wall, the structure of the layers near the membrane changes where the particles are in close contact with each other. Experimental data obtained with latex monodisperse particles filtered over various types of ultrafiltration membranes for various physicochemical and flux conditions are compared to the model predictions. These results explain the existence of irreversible colloidal deposits in filtration and suggest strategies to optimize backflush or pulsed pressure procedures often used to improve the efficiency of ultrafiltration or microfiltration.