Researchers from the Massachusetts Institute of Technology (MIT) have created a portable desalination unit that weighs less than 22 pounds, or 10 kilograms, that has the ability to remove particles and salts and make it into drinking water.
The device, which is said to be about the size of a suitcase, needs less power to operate that a cellphone charger. It can also be powered by a small, portable solar panel that costs just $50 when purchased online. The device can generate drinking water that exceeds World Health Organization (WHO) quality standards. This amazing new technology is also packaged into a very user-friendly device that can run with a single push of a button.
Unlike other portable desalination units that need the water to pass through filters, this new device uses electrical power to remove particles from drinking water. This removes the need for replacement filters, which also lessens the long-term maintenance requirements.
Because of this, it could make it easier to deploy the unit to remote and severely resource-limited areas, like communities that live on small islands or for those that live aboard seafaring cargo ships. The device could also be used to help refugees fleeing natural disasters or soldiers that are carrying out long-term military operations.
Senior author of the study and professor of electrical engineering and computer science, as well as biological engineering, Jongyoon Han, who is also a member of the Research Laboratory of Electronics (RLE), “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.”
Creating Filter-Free Technology
Yoon explains that usually commercially available portable desalination units normally need high-pressure pumps to push the water through filters. These are quite difficult to miniaturize without compromising the energy-efficiency of the device, says Yoon.
Rather, their unit depends on a technique that’s called ion concentration polarization (ICP) that was pioneered by Han’s group over 10 years ago. But rather than just filtering water, the ICP process uses an electrical field to membranes that are put above and below a channel of water. Then the membranes repel negatively or positively charged particles, such as salt molecules, viruses, and bacteria, as they flow past. Then the charged particles are funneled into a second stream of water that is eventually released.
During the process, both dissolved and suspended solids are removed, which allows clean water to pass through the channel. And since it requires such a low-pressure pump, the ICP uses less energy than any other technique.
However, the ICP doesn’t always remove all the salts that float in the middle of the channel. Because of this, the researchers incorporated a second process called electrodialysis in order to remove the remaining salt ions.
Researchers Yoon and Kang ‘use machine learning to find the ideal combination of ICP and electrodialysis modules.’ As a result, the optimal setup includes a two-stage ICP process that needs the water to flow through six modules in the first stage, then another three in the second stage, followed by one electrodialysis process. Yet this minimized energy usage ensures that the process remains self-cleaning.
Yoon shares, “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.”
After, they shrunk and stacked the ICP and electrodialysis modules in order to improve their energy efficiency while enabling them to fit inside a portable device. The researchers also designed the device to make it easy for nonexperts, which is why it just takes on button to launch the automatic desalination and purification process. Then the device notifies the user that the water is drinkable after the salinity level and the number of particles decrease to specific thresholds.
Then, the scientists also created a smartphone app that can control the unit wirelessly, alongside a report of real-time data on power consumption and water salinity.
Doing Beach Tests
After the team ran lab experiments using water with different salinity and turbidity (cloudiness) levels, they field-tested the device at Boston’s Carson Beach. They set the box near the shore of the beach, and placed the feed tube into the water. Then around half an hour later, the device managed to fill a plastic drinking glass with clear, drinkable water.
Han explained, “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.”
Moreover, the water even exceeded the WHO quality guidelines, and the unit managed to lessen the amount of suspended solids by at least a factor of 10. Their prototype makes drinking water at a rage of 0.3 liters per hour, while only needing 20 watts of power per liter.
Yoon shares, “Right now, we are pushing our research scale up that production rate.”
According to Han, one of the biggest challenges that came with designing this new portable system was engineering an intuitive device that could be used by anyone. The hope, according to Yoon, is to make the device more user-friendly, while improving its energy efficiency and production rate through a startup which he plans to launch in order to commercialize the technology.
In addition, Han wants to apply the lessons that he’s learned over the past decade in the lab to water-quality issues that go even beyond desalination, like being able to quickly detect contaminants in drinking water.
He adds, “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.”
You can see the research published in Environmental Science and Technology.
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