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New Desalination Method Shocks The Salts Out Of Water

Environment: Prototype device uses electrodialysis to produce freshwater

by Elizabeth K. Wilson
November 23, 2015 | A version of this story appeared in Volume 93, Issue 47

Credit: Martin Bazant
Electric current running through this device generates a shockwave that separates salty and fresh water.
A prototype device with input for salty water, which flows through porous glass beads sandwiched between two electrodes.
Credit: Martin Bazant
Electric current running through this device generates a shockwave that separates salty and fresh water.

A novel method for water desalination separates salt water into briny and fresh streams with the help of an electric shock wave (Env. Sci. & Tech. Lett. 2015, DOI: 10.1021/acs.estlett.5b00303)

As more and more people live in areas affected by drought or contaminated water, desalination is becoming an important way to meet global drinking water needs. So scientists continue to develop ever simpler and less expensive desalination methods.

Current technologies, for example, frequently rely on membranes to filter out ions. These membranes eventually get clogged and must be replaced, increasing costs.

In recent years, scientists have been exploring electrochemical methods of removing salts from water. For example, one group has designed a method where pairs of capacitive electrodes are first dipped in salt water to absorb salt, and then in a brine chamber, where they discharge the salt.

Now, a team led by Martin Z. Bazant at Massachusetts Institute of Technology has demonstrated another method with a prototype device composed of porous glass beads, known as a frit, sandwiched between two electrodes. They applied a current across the electrodes as salt water flowed through the frit, causing some areas of the stream to collect more ions while others became ion depleted.

When the electrical current became strong enough, it induced a shockwave that separated these regions into two streams—one briny, one fresh—a phenomenon known as shock electrodialysis.

The device continuously removed up to 99.99% of salts, including sodium, chloride and other ions, from a saltwater stream.

“This new system seems very promising indeed,” says P. Maarten Biesheuvel, a principal scientist at Wetsus, European Centre of Excellence for Sustainable Water Technology, who helped develop the capacitive electrode desalination technology.

Biesheuvel says that compared with his method, the electroshock method “has the major advantage that we don’t need any moving parts,” he says.

The method may have other advantages, says the new study’s coauthor Sven Schlumpberger. For example, the electoral current might kill pathogenic bacteria.

The MIT team says the next step will be to design scaled-up versions of their prototype to test the method’s industrial feasibility.



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