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Basic principle of membrane filtration

Filtration is convective discriminating mass transport of liquid mixtures or gaseous dispersions (aerosols) through porous barriers, mass transport ideally being confined to the void space of the barriers. Membrane filtration, accordingly, is pressure driven barrier separation of aqueous solutions, loosely grouped into a number of process variants with reference to the size brackets of the solutes handled:  nanofiltration (NF) 0.01−0.001 μm (<10nm), ultrafiltration (UF) 0.2−0.005 μm (5−200nm) and microfiltration (MF) 10−0.1 μm (>100nm) [1]. The artificial membrane as a barrier differs to a wide variety, like polymer, ceramic, metal and liquid based materials, microporous and dense membrane based structure characteristics, or symmetric and anisotropic refers to the distribution of the pores. Membrane filtration is the surface or screening removal that differs from depth filtration [2]. Filtration operations are performed in one of two modes: tangential flow filtration (TFF) or normal flow filtration (NFF), with the latter commonly called cross-flow filtration and dead-end filtration. Viscous feed suspensions or ones that have high particulate concentrations are typically processed by cross-flow filtration to reduce the accumulation of retained material at the membrane surface, while dead-end filtration tends to be used for more dilute suspensions or smaller batch sizes [3].


  1. K. W. Böddeker, Liquid separations with membranes, an introduction to barrier interference. Spriger-Verlag Berlin Heidelberg, 2008, 146 pp.
  2. M. Cheryan, Ultrafiltration Handbook, Technomic Publishing Company, Inc., Pennsylvania, 1986.
  3. M. A. Chandler, Fouling mechanisms during depth and membrane filtration of yeast cell suspensions, PhD Thesis, The Pennsylvania State University, 2006.
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