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 μm) 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 μm and yeast (5 μm). A modified shear-induced diffusivity model for dilute suspensions predicts closely for yeast and latex (6.4 and 11.9 μm), with the exception of 3 μm 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 μm latex and 4 μm algae), in addition to hydrodynamic effects, other factors such as surface charge may need to be considered for particle back-transport mechanisms.