Membrane filtration, widely used in chemical and biotechnology processes, is already established as a valuable means of filtering and cleaning wastewater and industrial process water. More recently, tubular and spiral membrane plants have begun to be used to filter impurities from drinking water in regions where conventional treatment proves to be uneconomical.
Although there are a number of different methods of filtration that incorporate membrane technology, the most mature is pressure driven membrane filtration. This relies on a liquid being forced through a filter membrane with a high surface area. There are four basic pressure driven membrane filtration processes for liquid separations. These are, in ascending order of size of particle that can be separated: reverse osmosis, nanofiltration, ultrafiltration and microfiltration.
The use of reverse osmosis is well-established for desalination of drinking water and the production of deionized water for process use. Ultrafiltration and microfiltration, which-unlike reverse osmosis and nanofiltration-utilize porous membranes, are now becoming increasingly common in water and wastewater treatments.