An assessment of depolarisation models of crossflow microfiltration by direct observation through the membrane

Direct observation through the membrane (DOTM) has been applied to monitor the deposition of supermicron particles (3-12 mu m) on microfiltration membranes and to identify the critical fluxes for cake formation as a function of crossflow. The observed critical fluxes are compared with predictions from various models. It is found that the shear-induced diffusivity model predicts acceptable critical flux for latex particles of 6.4 mu m and yeast (5 mu m). A modified shear-induced diffusivity model for dilute suspensions predicts closely for yeast and latex (6.4 and 11.9 mu m), with the exception of 3 mu m latex particles. The shear-induced hydrodynamic diffusivity model over-predicts the critical fluxes by a factor of about 2. The inertial lift model under-predicts the critical fluxes for the microfiltration of all the particles. This study also suggests that for smaller particles (3 mu m latex and 4 mu m algae), in addition to hydrodynamic effects, other factors such as surface charge may need to be considered for particle back-transport mechanisms. (C) 2000 Elsevier Science B.V. All rights reserved.