Ultrafiltration (UF) refers to a scale of separation between microfiltration and nanofiltration, used to purify, concentrate or fractionate macromolecules.
The region between MF and Ultrafiltration is a somewhat grey area; it is generally considered to be in the 0.01-micron (20,000 MWCO) range:
Ultrafiltration membranes reject or separate high molecular weight solutes as well as suspended solids, colloids, and macromolecules. They readily pass water and low MW dissolved solids such as salts and sugars.
Some Ultrafiltration membranes can reject particles having a molecular weight of about 1,000 MV, and a few manufacturers claim to make Ultrafiltration membranes which can reject a small percentage of low MW dissolved salts. However, most applications using Ultrafiltration membranes fall in the 10,000 to 100,000 MW ranges. Like MF membranes, the Ultrafiltration separation mechanism is commonly attributed to geometry, i.e. the opening or pore size of the membrane.
While some specialty dead end cartridges are used, primarily in the pharmaceutical industry, Ultrafiltration separations are principally done in cross flow mode. Systems operate at a relatively low transmembrane pressure, 0.7 to 10.3 bar (10 to 150 psig).
Generally, Ultrafiltration membranes require higher pressures than MF membranes because they are “tighter” and offer more resistance to liquid flow through the membrane.
Benefits of Ultrafiltration
Ultrafiltration membrane systems conserve energy with minimal operation and labour costs. The ability to retain high concentrates minimises disposal costs for a wide range of industries. In the bid to conserve water, using Ultrafiltration membrane systems to recycle water can yield zero discharge capabilities. Initial setup cost is low and minimal pretreatment chemicals are required compared to conventional systems.