Ultrafiltration membranes will typically filter particulate sizes greater than 0.01 to 0.1 microns. The materials used to manufacture ultrafiltration membranes are polymers that are naturally hydrophobic. Common materials include polyethersulfone (PES), polysulfone (PS), polypropylene (PP), or polyvinylidene flouride (PVDF). These materials can also be mixed to form a hybrid material that may produce superior characteristics for a given situation.
Membrane modules must be cleaned periodically, depending on the quality of water being cleaned.
The process of microfiltration is very similar to that of ultrafiltration. The key difference is the pore size for filtration, which is of the larger scale of 0.1 to 10 microns. The other difference is that while microfiltration can use a pressurised system, it can also function in an unpressurised system. Microfiltration is used to filter particles, sediment, algae and large bacteria, however finer filtration is required in order to remove smaller particulates such as dissolved organic matter, colloids, viruses and metallic ions.
Carbon filters filter a larger scale again, with pore sizes of 0.5 to 50 micron. These filters are effective at removing chlorine, sediment and volatile organic compounds from the influent water. They are commonly used in water treatment as pre-filtration devices for reverse osmosis systems.