More than 70% of our planet is covered in water. Over 96% of that is from the oceans. Yet, around 1.1 billion people across the globe lack access to clean drinking water, and 2.7 billion must endure water scarcity. The cure is desalination of saltwater, but the process is cumbersome and pricey, and is largely limited to more affluent countries. Now, however, MIT has developed an easily portable briefcase-sized unit that can desalinate water at the push of a button.
The device, which weighs 22 pounds (10 kilograms), requires less power to operate than a cell phone charger and can be driven by a small, $50 portable solar panel. Their unit also generates drinking water that exceeds World Health Organization quality standards. While there are other portable desalination units out there, MIT’s device utilizes only electrical power to remove particles from drinking water. Others require water to pass through filters. Getting rid of these filters greatly reduces the long-term maintenance requirements.
“This is really the culmination of a 10-year journey that I and my group have been on. 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,” says senior author Jongyoon Han, a professor of electrical engineering and computer science and of biological engineering, and a member of the Research Laboratory of Electronics (RLE) at MIT.
The secret to MIT’s success is a technique called ion concentration polarization (ICP) which was pioneered more than a decade ago at the campus. Instead of using the filtering process, ICP applies an electrical field to membranes placed above and below a channel of water. The membranes repel positively or negatively charged particles — including salt molecules, bacteria, and viruses — as they flow past. The charged particles are funneled into a second stream of water that is eventually discharged. This removes both dissolved and suspended solids, allowing clean water to pass through the channel. Since it only requires a low-pressure pump, ICP doesn’t use as much energy as other existing techniques.
On top of that, the researchers used a second process known as electrodialysis, a process in which ions are transported through a semi-permeable membrane under the influence of an electric potential, as ICP doesn’t always completely remove the salts.
“While it is true that some charged particles could be captured on the ion exchange membrane, if they get trapped, we just reverse the polarity of the electric field and the charged particles can be easily removed,” said Junghyo Yoon, a research scientist in RLE who worked on the paper.
After completing lab experiments, the researchers took their new device to Boston’s Carson Beach where they set the box near the shore and tossed the feed tube into the water. In about half an hour, the device had filled a plastic drinking cup with clear, drinkable water.
“It was successful even in its first run, which was quite exciting and surprising. But I think the main reason we were successful is the accumulation of all these little advances that we made along the way,” said Han.
Yoon said that they are working to make the device more user-friendly and will try to improve its energy efficiency even further. After that, there are plans to commercialize the technology through a startup company.
Back in the lab, Han wants to employ the lessons he’s discovered over the past decade to water-quality issues that go beyond desalination, such as quickly finding contaminants in drinking water.
“This is definitely an exciting project, and I am proud of the progress we have made so far, but there is still a lot of work to do,” he says.
