This Portable, Solar-Powered Device Purifies Seawater on Demand

Imagine having the ability to purify water anywhere, any time, with one solar-powered device. While that may not be of key importance to many in wealthy nations, it is for the 785 million people around the world who, as of 2017, lacked access to clean drinking water.

A group of researchers at the Massachusetts Institute of Technology have created a filter-less portable desalination device that uses an electrical field generated by solar energy to repel charged particles like salt, bacteria, and viruses. 

“All indicators tell us that water scarcity is a growing problem for everyone due to rising sea levels,” Junghyo Yoon, first author on the study, told Motherboard in an email. “We don’t hope for a grim future, but we want to help people be prepared for it.” 

The device is the result of 10 years of work, per a press release published by MIT. Dr. Jongyoon Han, senior author on the paper and professor of Electrical and Biological Engineering at MIT, first came up with Ion Concentration Polarization (ICP), the purification technique that the device relies on in 2012, and has since developed it for use for salty brines from fracking waste and for liquids that contain non-salt contaminants and heavy metals

“Our process does not push water through a membrane,” Bruce Crawford, graduate student at the MIT Sloan School of Management who did not co-author the study but who is a commercialization partner to the study’s first author Junghyo Yoon, said in an email to Motherboard. “Without pushing water through a membrane, we eliminate the possibility for membrane clogging and fouling, and we can operate with super low power draw, which means our devices can be way smaller than incumbent devices and use way less electricity.”

Han and his teams’ most recent finding, published last week in the journal Environmental Science and Technology, takes this process and applies it to a portable device around the size of a carry-on suitcase. Unlike other industrial desalination processes, like reverse osmosis—a centuries-old technology in which pressure is used to push water through a semipermeable membrane, like a filter or net that removes contaminants—ICP can be used at a small scale in remote settings and does not require the use of replacement filters.  

“We worked for years on the physics behind individual desalination processes, but pushing all those advances into a box, building a system, and demonstrating it in the ocean, that was a really meaningful and rewarding experience for me,” Han said in a release. 

Han and his team foresee the device being ideal for deployment in communities on small islands or aboard seafaring ships, to assist refugees and soldiers carrying out military operations, the press release notes.

The way the box works is this: Water flows into a channel in the box, in which an electrical field is applied to membranes that repel positively and negatively charged particles (including various impurities) into one stream while pushing water into another that is eventually discharged. Any extra salt ions floating in the middle of the channel are caught by a process known as electrodialysis. Because the system uses a low-pressure pump, it uses less energy than other approaches.  

The team tested the device both in the lab and on the beach, at which point they set the box along the shoreline of Carson Beach in Boston, and threw the feeding tube into the water. 30 minutes later, they had a full cup of drinkable water. A video released by MIT shows Junghyo Yoon, the study’s first author, taking a drink of water purified by the device at the beach. 

“It was successful even in its first run,” Han said in the release. “But I think the main reason we were successful is the accumulation of all these little advances that we made along the way.”

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