When pressure-driven flow through a membrane or other filter medium is used to separate micron-sized particles from fluids, the process is called microfiltration. Although the exact size range is a matter of debate, microfiltration is generally defined to be the filtering of a suspension containing colloidal or fine particles with linear dimensions in the approximate range of 0.02 to 10 µm. This size range encompasses a wide variety of natural and industrial particles, as shown in Figure 31-1. These particles are generally larger than the solutes that are separated by reverse osmosis and ultrafiltration. Consequently, the osmotic pressure for micro-filtration is negligible, and the transmembrane pressure drop, which drives the microfiltration process, is relatively small (1 to 50 psi, typically). Also, the membrane pore size and permeate flux are typically larger for microfiltration than for ultrafiltration and reverse osmosis.
KeywordsReverse Osmosis Filter Medium Membrane Fouling Cake Layer Surface Filtration
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