Dynamic filtration with rotating disks, and rotating and vibrating membranes: an update

The advantages and drawbacks of dynamic filtration are discussed and currently available industrial filtration modules are presented. Since membrane shear rates are the key factor governing their performance, three equations are given to calculate the shear rates of various modules, with disks rotating near fixed membranes, rotating membranes on a single shaft and vibrating membranes such as in the VSEP. Recent applications taken from the literature confirm the large gains relatively to crossflow filtration in permeate flux and membrane selectivity, owing to large reductions in cake formation and concentration polarization. One of the advantages of this technology is that, with rotating membranes, it gives a choice between increasing the flux by factor of 3-5 as compared to crossflow filtration by using high rotation speeds or obtaining the same flux at low speed, but with a large energy saving. The power consumed by vibrations in large industrial VSEP units is small, owing to the use of resonance frequency.