Nanofiltration

Nanofiltration

Nanofiltration is a relatively recent membrane filtration process used most often with low total dissolved solids water such as surface water and fresh groundwater, with the purpose of softening (polyvalent cation removal) and removal of disinfection by-product precursors such as natural organic matter and synthetic organic matter. [1] [2]

Nanofiltration is also becoming more widely used in food processing applications such as dairy, for simultaneous concentration and partial (monovalent ion) demineralisation.

Contents

Principle

Nanofiltration (NF) is a cross-flow filtration technology which ranges somewhere between ultrafiltration (UF) and reverse osmosis (RO). The nominal pore size of the membrane is typically about 1 nanometre. Nanofilter membranes are typically rated by molecular weight cut-off (MWCO) rather than nominal pore size. The MWCO is typically less than 1000 atomic mass units (daltons). The transmembrane pressure (pressure drop across the membrane) required is lower (up to 3 MPa) than the one used for RO, reducing the operating cost significantly. However, NF membranes are still subject to scaling and fouling and often modifiers such as anti-scalants are required for use.

Water purification applications

In much of the developing world, clean drinking water is hard to come by, and nanotechnology provides one solution. While nanofiltration is used for the removal of contaminants from a water source, it is also commonly used for desalination. In a study in South Africa, tests were run using polymeric nanofiltration in conjunction with a reverse osmosis process to treat brackish groundwater. These tests produced potable water, but as the researchers expected, the reverse osmosis removed a large majority of solutes. This left the water void of any essential nutrients (calcium, magnesium ions, etc.), placing the nutrient levels below that of the required World Health Organization standards. This process was probably a little too much for the production of potable water, as researchers had to go back and add nutrients to bring solute levels to the standard levels for drinking water consumption.[3]

Providing nanofiltration methods to developing countries, to increase their supply of clean water, is a very inexpensive method compared to conventional treatment systems. However, there remain issues as to how these developing countries will be able to incorporate this new technology into their economy without creating a dependency on foreign assistance.[4]

See also: Water purification

See also

References

  1. ^ Raymond D. Letterman (ed.)(1999). "Water Quality and Treatment." 5th Ed. (New York: American Water Works Association and McGraw-Hill.) ISBN 0070016593.
  2. ^ Dow Chemical Co. Nanofiltration Membranes and Applications
  3. ^ Hillie, Thembela; Hlophe, Mbhuti (2007). "Nanotechnology and the challenge of clean water". Nature Nanotechnology 2 (11): 663–664. doi:10.1038/nnano.2007.350. PMID 18654395. 
  4. ^ Prüss-Üstün, Annette; Bos, Robert; Gore, Fiona; Bartram, Jamie. Safer water, better health. WHO, 2008

External links

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