August 13, 2008

Nanofilter Cleans Water in Disaster Zones

By Luntz, Stephen

A nanomaterial coating on silica particles could offer the solution to one of the world's oldest and most destructive health challenges: how to remove bacteria and other pollutants from drinking water. In disasters like the Burmese cyclone, many of the deaths come from the destruction of water supplies. Flying in a few tonnes of food may keep thousands alive temporarily, but many times as much clean water is still usually inadequate.

However, Prof Peter Majewski of the University of South Australia's School of Advanced Manufacturing and Mechanical Engineering foresees a day when aid agencies could bring in coated sand and pour even the most polluted water through the equivalent of a coffee filter to obtain clean water. The nanomaterial on the surface of the silica would trap the cholera bacteria or Cryptosporidium parasites so reliably that the water could be drunk in safety.

Furthermore, Majewski believes that these nanofilters should be possible to produce at an affordable price. "We're using water, which is still not expensive, silica and a surfactant," he says. Majewski and his PhD students have experimented with quartz sand, priced at around $20 per tonne, for their silica and are also testing more upgraded silica from chemical industries.

Even the surfactant is not so expensive for use in the developing world, where 6000 people die each day due to a lack of clean drinking water. Furthermore, Majewski says it may be possible to reuse the filters after washing them in a slight acid. Alternatively, the pollutants and nanomaterials could be burnt off and the silica reused.

Majewski says it is not yet clear if the process is suitable for the vast purification plants of the developed world, but there are many other markets that may have potential. For example, the filtration system could prove suitable for removing bacteria from home swimming pools or to treat the waste from industrial plants such as pulp mills.

It even offers a way of desalinating seawater without electricity, although Majewski does not think this will be commercially viable on a large scale.

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