Dynamic shear-enhanced membrane filtration: A review of rotating disks, rotating membranes and vibrating systems

This paper reviews various systems of dynamic filtration, also called shear-enhanced filtration, which consists in creating the membrane shear rate necessary to maintain the filtration by a rotating disk, or by rotating or vibrating the membranes. This mode of operation permits to reach very high shear rates, of the order of (1-3) x 10(5) s(-1) and to increase both permeate flux and membrane selectivity. Several types of industrial dynamic filtration systems are available, but their share of the market is still small. This paper reviews the operating principles and fluid dynamics basics of various types, cylindrical rotating membranes, disks or blades rotating near a fixed membrane, rotating flat circular membranes, multi-shaft systems with overlapping rotating ceramic membranes and vibrating systems with toroidal membrane oscillations around an axis, or vibrating hollow fibers cartridges. It also reviews their main applications published in the literature in microfiltration, ultrafiltration, nanofiltration and reverse osmosis with a comparison of permeate fluxes with cross-flow filtration data when available. A comparison of performances between the vibrating VSEP system and a rotating disk module in MF of yeast suspensions and in UF of skim milk is also presented. The discussion is focused on a comparison of merits of various designs in the light of fluid mechanics and energetic considerations. (C) 2008 Elsevier B.V. All rights reserved.