A microporous membrane filter removes particles according to pore size. By contrast, an ultrafiltration (UF) membrane functions as a molecular sieve. It separates dissolved molecules on the basis of size by passing a solution through an infinitesimally fine filter.
The ultrafilter is a tough, thin, selectively permeable membrane that retains most macromolecules above a certain size including colloids, microorganisms and pyrogens. Smaller molecules, such as solvents and ionized contaminants, are allowed to pass into the filtrate. Thus, UF provides a retained fraction (retentate) that is rich in large molecules and a filtrate that contains few, if any, of these molecules.
Ultrafilters are available in several selective ranges. In all cases, the membranes will retain most, but not necessarily all, molecules above their rated size.
| Table 5. Ultrafiltration |
| Advantages |
Disadvantages |
- Effectively removes most particles, pyrogens, microorganisms, and colloids above their rated size.
- Produces highest quality water for least amount of energy.
- Regenerable.
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- Will not remove dissolved inorganics.
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