Principle of membrane filtration
Membrane filtration is based on the use of a physical interface (barrier) called a membrane. Its porosity, which is very precisely calibrated, provides selective permeability for certain solutes below a given size. If a pressure differential is applied, the solvent passes through the membrane, whose pore size means that specific solutes are retained. By maintaining circulation parallel to the filtration surface, it is possible to control material build-up, limit membrane fouling, and optimize flow rate.
Two output flows are produced: a concentrated fraction (the retentate), enriched by the elements retained by the membrane; and a more diluted fraction (the permeate), which contains only the substances able to pass through the membrane. The filtration flow rate results from the balance between the transmembrane pressure and the tangential velocity.