New Desalination Method may be just what is Needed on Mars
Wouldn't you know it ...
Recently, we published an article on the methods and means of making clean, potable water for a large settlements on Mars.
And then this happens.
A team at MIT has come up with an innovative approach for desalinating water that is cheaper, faster, and produces more clean water than anything seen before.
Unlike most traditional desalination systems, this new desalination method does not separate ions or water molecules with filters, which can become clogged, or boiling, which consumes great amounts of energy.
Instead, the system uses an electrically driven shockwave within a stream of flowing water, which pushes salty water to one side of the flow and fresh water to the other.
This allows easy separation of the two streams.
The new approach is described in the journal Environmental Science and Technology Letters, in a paper by professor of chemical engineering and mathematics Martin Bazant, graduate student Sven Schlumpberger, undergraduate Nancy Lu, and former postdoc Matthew Suss.
...fundamentally new and different...
This approach is "a fundamentally new and different separation system," Bazant says. And unlike most other approaches to desalination or water purification, he adds, this one performs a "membraneless separation" of ions and particles.
Membranes in traditional desalination systems, such as those that use reverse osmosis, are "selective barriers," Bazant explains: They allow molecules of water to pass through, but block the larger sodium and chlorine atoms of salt. "This process looks similar, but it's fundamentally different," he says.
In the new process, called shock electrodialysis, water flows through a porous material --in this case, made of tiny glass particles, called a frit - 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.
When 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 center of the flow.
As Bazant says:
It generates a very strong gradient.
Even though the system can use membranes on each side of the porous material, Bazant explains, the water flows across those membranes, not through them. That means they are not as vulnerable to fouling - a buildup of filtered material - or to degradation due to water pressure, as happens with conventional membrane-based desalination, including conventional electrodialysis.
In other words, the salt doesn't have to push through anything that might break or clog.
As Bazant says. The charged salt particles, or ions, "just move to one side" .
The underlying phenomenon of generating a shockwave of salt concentration was discovered a few years ago by the group of Juan Santiago at Stanford University. The initial experiments used a tiny microfluidic device and no flowing water and was not used to remove salt from the water.
The new system, by contrast, is a continuous process that could be easily scaled up for desalination or water purification. Bazant addded:
The breakthrough here is the engineering.
One possible application here on Earth would be in cleaning the vast amounts of wastewater generated by hydraulic fracturing, or fracking. This contaminated water tends to be salty, sometimes with trace amounts of toxic ions, so finding a practical and inexpensive way of cleaning it is highly desirable.
This new desalination method not only removes salt, but it also removes a wide variety of other contaminants.
And because of the electrical current passing through, it may also sterilize the stream.
As Schlumpberger says:
The electric fields are pretty high, so we may be able to kill the bacteria.
The research at MIT produced both a laboratory demonstration of the process as well as a theoretical analysis that explains why the process works. The next step is to design a scaled-up system that could go through practical testing.
Initially, this process would not be competitive with current desalination or water purification methods such as reverse osmosis for large-scale seawater desalination. According to Schlumpberger, however, it could find other uses in the cleanup of contaminated water -- like in areas hit by massive storms or earthquakes.
Since this process requires very little infrastructure or power, portable systems could easily be developed and deployed in those emergency situations where the delivery of clean drinking water has been disrupted.
And that easy, cheap deployment is exactly why this new desalination method may be such a good way of making clean water on Mars.
What do you think? Share your thoughts in the comments section below.