Ultrafiltration is a membrane-filtration technology — the membrane can be used to remove small colloids and large molecules from water and other liquids. The ultrafiltration process falls between reverse osmosis and microfiltration, with ultrafiltration removing particles in the 0.002-to-0.1-micron range and typically removing organics of over 1,000 molecular weight while passing ions and smaller organics.
The process works by forcing untreated water against a semipermeable membrane. The membrane allows the water molecules to pass through and screens out the colloids, much like a sieve. Excess water is used to wash the colloids off the surface and to a drain. Unlike most filtration, the sieve does not fill up with trapped material because the colloids are too large to fit into the sieve opening.
Ultrafiltration systems are commonly used by Trucent to remove contamination from washer baths and for various waste-treatment applications.