New desalination process just needs a shockwave Monday, 16 November 2015

During recent droughts, a number of Australian states built desalination plants to shore up their water supplies. But away from drought conditions, these plants become expensive white elephants. Now a team from MIT in the US have developed a new desalination technology, which is much cheaper and doesn’t require as much energy to run.

The system doesn’t require filters instead using an electrically driven shockwave within a stream of flowing water, to push salty water to one side of the flow and fresh water to the other, allowing easy separation of the two streams.

Professor of Chemical Engineering Martin Bazant said membranes in traditional desalination systems, such as those that use reverse osmosis or electrodialysis, are “selective barriers”. That is, they allow molecules of water to pass through, but block the larger sodium and chlorine atoms of salt.

In his new process, the water flows through a porous material called a frit made of tiny glass particles, with membranes or electrodes sandwiching the porous material on each side. When an electric current flows through the system, the salty water divides into regions where the salt concentration is either depleted or enriched. If that current is increased to a certain point, it generates a shockwave between these two zones, sharply dividing the streams and allowing the fresh and salty regions to be separated by a simple physical barrier at the centre of the flow.

“It generates a very strong gradient,” Bazant said. “The salt doesn’t have to push through something. The charged salt particles, or ions, just move to one side.”

The work expands on an earlier discovery by Juan Santiago at Stanford University which didn’t involve flowing water or the removal of salt. Bazant says his breakthrough involves the engineering of a practical solution. It may also remove other contaminants in the water including toxic ions and possibly bacteria.

Because it requires little infrastructure, it might be useful for portable systems for use in remote locations, or for emergencies where water supplies are disrupted by storms or earthquakes.

There is, however, some work to be done to make sure that it can be scaled up from a single cell to a stack of thousands of cells successfully.

 

Image: MIT