Water treatment such as desalination and wastewater reuse could become much cheaper for developing countries, thanks to a purification membrane developed using nanotechnology. Researchers at the US-based University of California in Los Angeles have designed nanoparticles to create a membrane that does not clog easily, allowing the water to be pumped through using less energy.

Population growth and freshwater pollution have put pressure on water supplies in developing countries, making desalination and wastewater reuse attractive alternatives. The membrane is designed for use in reverse osmosis (RO) desalination, in which salty or polluted water is pumped at extremely high pressure through the membrane's pores, letting the water pass through but blocking the transit of salt ions and other impurities.

Traditional RO membranes tend to get dirty as bacteria and other particles build up on the surface. As a result more energy is needed to pump the water, and they eventually require costly cleaning and replacement. In the new membrane, the nanoparticles are designed to attract water, soaking it up like a sponge, while repelling nearly all contaminants that might ordinarily stick to the surface, says Eric Hoek, civil and environmental engineering assistant professor at the University of California in Los Angeles, who led the research.

This creates a water purification process that is as effective as current methods but may use half the energy, reducing the total cost of water desalination by 25 per cent. Hoek told SciDev.Net that although RO membranes, first designed in the 1960s, are already made on a nanoscale, this is probably the first time that a material made of nanoparticles has been created specifically for RO. After a long period of neglect, the past decade has seen an upsurge in research into water treatment, with new techniques being developed that produce better results, are less costly and have greater potential for water reuse.

David Johnstone, a consultant in water and wastewater says that the cheap, low-energy methods that nanotechnologies offer could make water treatment more widely available to developing countries, where they could be used to treat contaminated water at the local level. "At present most of the world's sewage is untreated and discarded. However, sewage is usually more than 99.5 per cent water. [It] is a natural water resource that is generally not exploited," he told SciDev.Net. "If simple nanotech membrane systems could be developed to remove bacteria and viruses at little cost, the benefits [to developing countries] would be enormous." Hoek and colleagues hope that their membrane will be commercially available within one or two years.
By Eva Tallaksen
(SciDev.Net, 14/11/2006)
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