Ultrafiltration, Nanofiltration and Reverse Osmosis

What Is Filtration?

Filtration is a process of removing particulate matter from water by forcing the water through a porous media. This porous media can be natural, as in the case of sand, gravel, and clay, or it can be a membrane wall made of various materials. Sometimes, large particles are settled before filtration; this is called sedimentation. For information on sedimentation and filtration in general, see the “Conventional Water Treatment: Coagulation and Filtration” fact sheet.

The size of materials that can be removed during filtration depends upon the size of the pores of the filter. The chart below summarizes the various separation processes relative to common materials that would be filtered out through each process. Particle filtration refers to conventional media filtration, while the other types are membrane filtrations.