Ultra- and nanofiltration can be defined as pressuredriven
membrane processes for the separation and concentration
of substances having a molecular weight
between 103 and 106 Da for ultrafiltration and between
100 and 500 Da for nanofiltration. In both processes a
solution flows under pressure along the surface of a suitably
supported membrane (cross-flow filtration). The
solvent and certain dissolved components pass through
the membrane and are collected as permeate. Depending
on the characteristics of the applied membrane some
other components from the solution are retained by
the membrane and concentrated, as the retentate fraction
(Fonyo & Fabry, 1998; Porter, 1990).