Chapter Two - Dynamic Filtration with Rotating Disks, and Rotating or Vibrating Membranes

Abstract

This article describes various systems of dynamic filtration, also called shear-enhanced filtration, which consists in creating high shear rates at the membrane by a rotating disk, or by rotating or vibrating the membranes. This mode of operation permits to reach shear rates of the order of 1–3·105/s or almost one order of magnitude larger than in crossflow filtration and to increase both permeate flux and membrane selectivity. Its advantages and drawbacks relatively to crossflow modules are presented in the introduction. Then it describes existing industrial dynamic filtration modules: the VSEP vibrating system, multicompartments systems with metal disks or rotors rotating between fixed membranes and multishaft systems with overlapping rotating ceramic membranes. Equations permitting to calculate membrane shear rates in various modules, are presented, as they govern their performance. Recent applications published in the literature in microfiltration, ultrafiltration, nanofiltration, and reverse osmosis are presented with a comparison of permeate fluxes with crossflow filtration data when available. A comparison of performances between the vibrating VSEP and a rotating disk module in microfiltration of yeast suspensions and in reverse osmosis of model dairy effluent is also presented. The discussion is focused on energetic considerations and the complementarity between crossflow and dynamic filtration.