Nanofiltration

Nanofiltration is a membrane filtration process using membranes with pores on the order of one to ten nanometers, placing it between ultrafiltration and reverse osmosis in the range of particle sizes it can separate. Originally developed to soften water by removing scale-forming ions, nanofiltration membranes are also used to disinfect water supplies and to purify pharmaceuticals and food products such as milk and juice; the membranes are typically thin polymer films, sometimes track-etched by bombarding a polymer sheet with high-energy particles and then chemically developing the resulting tracks into pores. Newer applications include petroleum refining, natural-product extraction, and medical uses such as extracting amino acids from biological material. The cost and maintenance of the membranes themselves remain the technology's principal drawback, and no single clean origin date or inventor is established in the source consulted.