Squeezing Fresh Water from Waste Brine
Marie Donlon | May 31, 2017
A team of Engineers from the University of California, Riverside, has developed a technique for recovering 100 percent of the water from highly concentrated salt solutions reducing water shortages in arid regions and reducing concerns about the disposal of high salinity brine.
Published in the journal Nature Nanotechnology, the research details the development of a carbon nanotube-based heating element designed to improve the recovery of fresh water during membrane distillation processes.
Current methods—namely, reverse osmosis—are unable to treat highly concentrated salt solutions (or brines). The solutions are produced in vast amounts during reverse osmosis (as waste products) and hydraulic fracking (as produced water) and require proper disposal to prevent damage to the environment.
A common method to treat brine—membrane distillation—is a thermal desalination technology where heat forces water vapor across a membrane, allowing additional water recovery with salt staying behind. Because hot brines are highly corrosive, it makes the heat exchangers expensive in traditional membrane distillation systems.
Additionally, because the process is reliant on the heat capacity of water, single pass recoveries are low (under 10 percent), resulting in complex heat management requirements.
“In an ideal scenario, thermal desalination would allow the recovery of all the water from brine, leaving behind a tiny amount of a solid, crystalline salt that could be used or disposed of,” David Jassby, an assistant professor of chemical and environmental engineering in UCR’s Bourns College of Engineering, said. “Unfortunately, current membrane distillation processes rely on a constant feed of hot brine over the membrane, which limits water recovery across the membrane to about six percent.”
In an attempt to improve the process, researchers developed a self-heating carbon nanotube-based membrane that only heats the brine at the membrane surface. The system reduces the heat needed in the process and increases the yield of recovered water to almost 100 percent.
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