Filtration essentially works in the same way as a sieve and provides a physical barrier based on pore size to the passage of particles in purified water systems. It uses membrane filters with pore size of typically 1 to 10 nm which can remove particles as small as protein macromolecules. Ultrafiltration is an excellent technology for ensuring consistent ultrapure water quality with respect to particles, bacteria and pyrogens.
Sub-micron filtration, including micro, ultra-micro and ultra filters (1-200 nm) are used as part of a 'polishing' loop, or at the point-of-use. Fine filtration is applied to remove bacteria (live or dead) and biologically active molecules. These absolute filters have pores smaller than their intended target and can retain the impurity while allowing water to pass through. Impurities that are removed by sub-micron filtration, include bacteria, colloids, enzymes, endotoxins and particulates.
How does it work?
The water flow is directed in one of two ways: either (1) directed straight through the membrane, or (2) in a “cross-flow” fashion where a portion of the input water flows across the membrane surface to reduce fouling by rinsing away contaminants.
Ultrafilters are usually installed near the outlet of a water purification system to reduce the concentration of microorganisms and large organic molecules. These filters need to be regularly maintained to ensure they remain effective.