Microfiltration

Microporous membrane filtration should be distinguished from conventional (depth) filtration and such membrane separation processes as ultrafiltration (UF) and reverse osmosis (RO).

The two basic types of microporous filtration are depth and screen.

Depth filters consist of matted fibers or materials compressed to form a matrix in which particles are retained by random adsorption or entrapment. Depth filters are usually used as pre-filters because they are an economical means of removing 98% or more of the suspended solids in order to protect elements downstream from fouling or clogging.

Screen filters, on the other hand, are inherently uniform structures that, like a window screen or a sieve, retain on their surface absolutely all particles larger than the precisely-controlled pore size. Microporous membrane (screen) filters are placed at the last-possible point in a system to remove the remaining traces of resin fragments, carbon fines, colloidal particles and microorganisms. For example, a 0.22-micron membrane filter will retain all bacteria. For this reason, they are used routinely for the sterilization of intravenous solutions, serums and antibiotics.