What is membrane?
A membrane is a selective barrier; it allows some things to pass through but stops others.
Such things may be molecules, ions, or other small particles.
The influent of an artificial membrane is known as the feed-stream, the liquid that passes through the membrane
is known as the permeate, and the liquid containing the retained constituents is the retentate or concentrate.
The first use of membranes on a large scale was with micro-filtration and ultra-filtration technologies. Since the 1980s, these separation processes,
along with electro-dialysis, are employed in large plants and, today, a number of experienced companies serve the market.
The degree of selectivity of a membrane depends on the membrane pore size. Depending on the pore size,
they can be classified as micro-filtration (MF), ultra-filtration (UF), nano-filtration (NF) and reverse osmosis (RO) membranes.
