Small-scale Desalination

These units could deliver enough fresh water to supply the needs of a family or small village.
14/04/2010 Ámbito: Asia (Noticia leida 785 veces)

EWP- A new approach to desalination being developed by researchers at MIT and in Korea could lead to small, portable desalination units that could be powered by solar cells or batteries.

As well as removing many contaminants, these units could deliver enough fresh water to supply the needs of a family or small village.
The new approach, called ion concentration polarisation, is described in a paper by Postdoctoral Associate Sung Jae Kim and Associate Professor Jongyoon Han, both in MIT's Department of Electrical Engineering and Computer Science, and colleagues in Korea.

The system works at a microscopic scale, using fabrication methods developed for microfluidics devices. This is similar to the manufacture of microchips, but uses materials such as silicone (synthetic rubber).

Each individual device only processes a minute amount of water, but a large number of them (the researchers envision an array with 1,600 units fabricated on an 8-inch-diameter wafer) could produce about 15 litres of water per hour, enough to provide drinking water for several people.

The whole unit could be self-contained and driven by gravity. Salt water is poured in at the top, and fresh water and concentrated brine are collected from two outlets at the bottom.


The small size of the unit has an important advantage for some applications, Kim explains.

For example, in an emergency situation such as the aftermath of Haiti's earthquake, there was no delivery infrastructure to get fresh water to the people who needed it.

Small portable units which individuals could carry would have been especially useful.

So far, the researchers have successfully tested a single unit using seawater they collected from a Massachusetts beach.

The water was then deliberately contaminated with small plastic particles, protein and human blood. The unit removed more than 99% of the salt and other contaminants. "We clearly demonstrated that we can do it at the unit chip level", says Kim.

While the amount of electricity required by this method is actually slightly more than for present large-scale methods such as reverse osmosis, there is no other method that can produce small-scale desalination with anywhere near this level of efficiency, the researchers say.


If properly engineered, the proposed system would only use as much power as a conventional light bulb.

The basic principle that makes the system possible, called ion concentration polarisation, is a ubiquitous phenomenon that occurs near ion-selective materials (such as Nafion, often used in fuel cells) or electrodes.

Researchers have been applying the phenomenon to other applications such as biomolecule preconcentration. This application to water purification has not been attempted before, however.