Research projects and innovation devoted to finding new and effective ways to provide clean, potable water sources typically focus on treating salty, brackish or contaminated water in order to make it safe to drink.
An unusual new approach to desalination uses an electrically-driven shockwave within a stream of flowing water to separate salts out of the water in a “membraneless separation” of the salt ions and water molecules.
Called “shockwave electrodialysis,” the process was developed by a team of chemical engineers at MIT.
The system works by having water flow through a porous material, in this case tiny glass particles called a frit. Membranes or electrodes sandwich the porous material on either 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 the current is increased to a certain level, it generates a shockwave between these two zones.
The shockwave divides the streams, allowing the fresh and salty regions to be separated by a physical barrier at the center of the flow.
Though the team describes the process as “membraneless,” there are still membrane components involved. The difference with this process is that the water flows across these membranes, not through them.
This means that they are less vulnerable to fouling from filtered material. They are also resistant to degradation due to water pressure, a common issue with conventional membrane-based reverse osmosis desalination processes.
As the shockwave is applied to a running stream of water it is a continuous process and the porous medium used is fairly inexpensive. These factors mean that the system should be relatively easy to scale up for high-volume desalination and purification applications.
The current research produced a laboratory demonstration of the process and a theoretical analysis exploring how the process works. The next step will be to design a scaled-up system to use for practical testing.
This process will not be competitive with large-scale reverse osmosis seawater desalination at first, but there is the potential for future commercial-scale versions of the system.
Researchers say the new desalination method could be useful for cleaning the contaminated water generated by hydraulic fracturing, or fracking. Shown here is a holding pit for fracking water. (Image courtesy of MIT/Sven Schlumpberger.)
The team sees more likely applications for cleanup of contaminated water, such as the vast amounts of wastewater generated by hydraulic fracturing or fracking.
This wastewater tends to be salty and often contains trace amounts of toxic ions. An affordable, practical method of dealing with this water is highly desirable.
Another consideration is that this system can also potentially remove a wide variety of other contaminants. For example, the high electric current passing through the water stream may also be able to sterilize it by killing bacteria.
Because this approach to desalination requires little infrastructure, it could be applied to developing the technology into portable systems that can be deployed in remote locations. It could also be used in emergency situations where water supplies are disrupted by storms, floods and earthquakes.
This type of system would offer an advantage over conventional filter membrane systems and those that rely on energy-intensive boiling processes.
If successful at a commercial scale, desalination technology like this could bring huge changes to those parts of the world currently struggling to supply safe, clean water to people in areas lacking sophisticated infrastructure.
The full paper describing the shockwave electrodialysis process is published in the journal Environmental Science and Technology Letters and is available to read here.