Tangential flow filtration (TFF) or Cross-flow filtration is a membrane-based process that relies on microporous membranes, generally with a pore size of between 0.1 and 10µ. Depending on the application, different membranes may be used:

• Ceramic,
• Organic polymer,
• Stainless steel with a titanium dioxide coating.

The treated solution flows in parallel to the surface of the membrane and a transmembrane pressure of a few bars is applied.

Ultrafiltration (UF) is a membrane-based process for the extraction of a solvent (generally water), ions, or molecular solutes from a solution containing macrosolutes. The membrane pore size is generally between 1 to 100 nm. The solution to be treated flows in parallel to the surface of the membrane and a transmembrane pressure of a few bars is applied. The membranes retain any molecules with a molecular weight of over 5,000-10,000 Da.

Nanofiltration (NF) is a pressure-driven membrane separation technique that falls between ultrafiltration (UF) and reverse osmosis (RO), using membranes with a pore diameter of around 1 nm. The technique is used to extract water at the same time as monovalent ions and substances with a molecular weight not exceeding approx. 200 Da. The applied transmembrane pressure is of the order of 10 to 25 bars. In the agro-food industry, nanofiltration is used to concentrate and partially demineralize solutions.

Reverse osmosis (RO) is a separation technique that uses dense, semi-permeable membranes to extract pure water from solutions containing salts (or other substances in solution). The applied pressure must be sufficient to reverse the normal osmotic flow (several dozen bars).