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Scientists Turn Salt Water Into Drinking Water By Shocking The Salt Out With Electricity

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Scientists at MIT say they've turned to electricity and shockwaves to desalinate water, knocking the salt right out of it as it flows to deliver safe, drinkable water.

The process doesn't require filters, which eventually clog up and become inefficient, or boiling the water, which requires unsustainable amounts of energy, they say.

In a process the MIT team calls "shock electrodialysis," an electrically-generated shockwave applied to a stream of flowing water separates the salts out of the water, according to the team's study appearing in the journal Environmental Science and Technology Letters.

The result is a "membraneless separation" of the salt ions and water molecules, the researchers say.

"[It is] a fundamentally new and different separation system," says team leader Martin Bazant, an MIT math and chemical engineering professor.

In their desalination process, salt water is pumped through a porous material of tiny glass particles with electrodes on either side.

When electricity is applied to the system, the salt water separates into regions of either enriched or depleted salt concentrations.

"It generates a very strong gradient," Bazant says.

When the electricity is increased to a certain level, a shockwave is created between the two regions. The shockwave separates the flowing water into two streams so the fresh and salty regions can be diverted to either side of a physical barrier in the center of the flowing water.

The researchers explain that, even though the system has membranes that carry the electrodes, they refer to the process as "membraneless" because the water flows across rather than through the membranes, as it would in a conventional filter system.

"The salt doesn't have to push through something," Bazant explains, noting that the charged salt particles, or ions, "just move to one side."

While the principle behind the MIT system isn't new, the application they've created from it is, the researchers say.

"The breakthrough here is the engineering," says Bazant.

Previous research had applied the principle to non-flowing water, but Bazant says he realized it could be applied to flowing water to create an inexpensive, easy-to-create desalination system.

Simple and portable, the system would be ideal for emergency use in disaster zones to quickly clean up contaminated water or desalinate seawater to provide temporary supplies of fresh drinking water, he says.

In addition to removing the salt, the system could also deal with unwanted bacteria in the source water, the researchers say.

"The electric fields are pretty high, so we may be able to kill the bacteria," says research team member and graduate student Sven Schlumpberger.

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