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You can remove suspended solids larger than to 0.1 - 1.0 m. It is particularly effective at removing large pathogens such as Giardia or Cryptosporidium. Ultrafiltration is common to use in cases where the concentration of STD is not a problem. This is because the membrane pores are too large to filter out particles as small. Generally used as a pretreatment for systems using much more sensitive membranes, such as reverse osmosis or nanofiltration.

Ultrafiltration It basically used to remove most of the colloidal particles and some major pollutants dissolved (0.01  m). It is useful when you must eliminate most of the colloidal particles (also including pathogens). This system, like microfiltration, has the ability to kill bacteria and viruses and is often used as a pretreatment for other systems. Because colloids are removed, the water, once treated has a negligible turbidity.

Nanofiltration You can remove those contaminants that are larger than the nanometer (0.001  m). NF membranes are widely used in water treatment, as needed to virtually eliminate most of the dissolved solids. This technology is called membrane softening, because water is removed from those characteristic of the hardness ions (calcium and magnesium).

Reverse Osmosis In this membrane technology, the solvent (water) is transported through a dense membrane specifically designed to retain salts and solutes which have a low molecular weight. Reverse osmosis can remove almost all the salts and low molecular weight solutes. Therefore, reverse osmosis membranes are the best choice when you need to get very pure water or water to drink.

Electrodialysis reversible The EDR is the ability to separate molecules or ions in an electric field. This is due to a marked difference in charge and transport speed by the membrane. In an electrodialysis cell, there are a number of membrane devoted to the exchange of ions between an anode and cathode.

Thus, when electrical current is generated, positively charged ions move through the cation exchange membrane and negatively charged ions do it for the anion exchange membrane.