Water, water, everywhere, but unfortunately much of it is salty, brackish, or contaminated. At a time when delivering enough potable water to satisfy an increasingly thirsty world is becoming an urgent issue — some pundits even predict future “water wars” — finding the best way to make more water potable is a challenge technology must meet as soon as possible.
That’s why a team of MIT researchers is developing a new approach called shock electrodialysis that distinguishes itself from older technologies by avoiding both filtration, since filters easily become clogged, and boiling, which consumes great amounts of energy at great cost. Instead, the system uses an electrical shockwave to zap a stream of flowing water, pushing the salty water to one side of the flow and fresh water to the other.
According to MIT professor of chemical engineering and mathematics Martin Bazant, this “membraneless separation” of ions and particles is something entirely new. In traditional desalination systems, membranes are used to let H2O molecules through while blocking sodium and chlorine atoms.
In his process, water flows through a porous material made of tiny glass particles. When an electric current flows through the system, the salty water divides into regions where the salt concentration is either depleted or enriched. Increase the current enough, and it generates a shockwave between the two zones, dividing the streams and letting the fresh and salty regions be separated at the center of the flow. Because the water doesn’t flow through membranes, the system won’t clog or degrade over time, as often happens in membrane-based desalination. “The salt doesn’t have to push through something,” Bazant said in an MIT press release. The charged particles or ions “just move to one side.”
The design of the system should make it relatively easy to scale up for industrial-size desalination or water purification, and that could make it applicable not just for desalination but also in places like the fracking industry, which generates huge amounts of nasty wastewater. The electrical process not only catches a wide variety of contaminants but also has the ability to kill bacteria, essentially sterilizing the stream of water as it passes through.
Of course, over time the researchers will ultimately need to address the same two issues that always come up with water purification: just how much energy is needed to do it, and what happens to the brackish/contaminated leftovers? In the immediate future, however, practical applications may pop up via small-scale shock electrodialysis devices that could be set up in remote locations or disaster zones.