MIT Scientists Use Shockwaves to Remove Salt From Water

December 3, 2015 | Joanne Kennell

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Access to clean, drinkable water is becoming an urgent issue.

Clean water is becoming the new oil.  The planet’s 37 largest aquifers are being used at an unsustainable rate — they are being drained faster than natural processes can restore them.  The problem with overusing an aquifer is that, when the stress for replenishment becomes too much, the aquifer will collapse and no longer retain any inflow of water, causing a humanitarian disaster.

So, the news that an MIT team has invented a shockwave-based process for desalinization of water could not have come at a better time.  This process is not like traditional desalination systems — it does not separate ions and water molecules via membranes, nor does it involve boiling.  Instead, the process uses an electrically driven shockwave within a flow of water that pushes salty water to one side of the flow and fresh water to the other, allowing for easy separation.

The team, including a professor of chemical engineering and mathematics Martin Bazant, graduate student Sven Schlumpberger, undergraduate Nancy Lu, and former postdoc Matthew Suss, are the first to come up with this technique for desalinization.  This approach is “a fundamentally new and different separation system,” Bazant said.

SEE ALSO: “Drinkable Book” Filters Out Water Contaminants Through its Pages

The new process is called shock electrodialysis.  Water flows through a porous material of tiny glass particles, called frit, with membranes on each side.  When an electric current is applied through the system, the water divides into regions with enriched and depleted salt content.  Now, if the current is increased to a certain point, it generates a shockwave between these two regions, dividing the stream and allowing fresh and salty sections to be separated by a physical barrier at the center of the flow.  “It generates a very strong gradient,” Bazant said.

Although the system uses membranes similar to other desalination techniques as a barrier to contaminants, unlike other processes, water flows across these membranes instead of through them.  This means they are not as vulnerable to a buildup of impurities or degradation.   “This process looks similar, but it’s fundamentally different,”, said Brazant. “The salt doesn’t have to push through something.  The charged salt particles, or ions, just move to one side.”

Amazingly, this system can remove more than just salt from water; it can also be used to eliminate a variety of impurities and contaminants.  Additionally, because there is an electrical current passing through the water, it has the potential to sterilize the stream.  “The electric fields are pretty high, so we may be able to kill the bacteria,” Schlumpberger said.

The process could be used to clean large amounts of wastewater from fracking — the process of injecting liquid at high pressure into rocks to extract oil or natural gas — which tends to be salty and sometimes contains trace amounts of toxins.  

Since this process uses very inexpensive “frit” material, it should be relatively easy to upscale for large amounts of water desalination or purification.  Also, since this system does not require a large amount of infrastructure, it could be applied as a portable system for remote locations, or for emergency situations where there are disrupted water supplies.

This may be the start of a future with clean water available for everyone.

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