No, it’s not a mirage! This device harvests water from desert air
23 March 2018
MIT’s new system, now field-tested on a rooftop in the dry air of Arizona, could provide drinking water in extremely arid locations such as a desert.
The device is based on the concept proposed last year in a paper in Science. Evelyn Wang, the Gail E. Kendall Professor in the Department of Mechanical Engineering, was the senior author of both papers. MIT postdoc Sameer Rao and former graduate student Hyunho Kim SM ’14, PhD ’18 were the lead authors of the latest paper, along with four others at MIT and the University of California at Berkeley.
The system, based on relatively new high-surface-area materials called metal-organic frameworks (MOFs), can extract potable water from even the driest of desert air, the researchers say, with relative humidities as low as 10 percent. Current methods for extracting water from air require much higher levels – 100 percent humidity for fog-harvesting methods, and above 50 percent for dew-harvesting refrigeration-based systems, which also require large amounts of energy for cooling. So the new system could potentially fill an unmet need for water even in the world’s driest regions.
Researchers tested the device on a rooftop at Arizona State University in Tempe. The test device was powered solely by sunlight, and although it was a small proof-of-concept device, if scaled up its output would be equivalent to more than a quarter-litre of water per day per kilogram of MOF, the researchers say. With an optimal material choice, output can be as high as three times that of the current version, says Kim. Unlike any of the existing methods for extracting water from air at very low humidities, “with this approach, you actually can do it, even under these extreme conditions,” Wang says.
Not only does this system work at lower humidities than dew harvesting does, says Rao, but those systems require pumps and compressors that can wear out, whereas “this has no moving parts. It can be operated in a completely passive manner, in places with low humidity but large amounts of sunlight.”
Whereas the team had previously described the possibility of running the system passively, Rao says, “now we have demonstrated that this is indeed possible.” The current version can only operate over a single night-and-day cycle with sunlight, Kim says, but “continuous operation is also possible by utilising abundant low-grade heat sources such as biomass and waste heat.”
The next step, Wang says, is to work on scaling up the system and boosting its efficiency.