(ORDO NEWS) — MIT researchers have developed a portable desalination device weighing less than 10 kilograms that can remove particles and salts to produce drinking water.
The suitcase-sized device, which uses less power than a cell phone charger, can be powered by a small portable solar panel that can be purchased online for about $50.
It automatically generates drinking water, the quality of which exceeds the standards of the World Health Organization. The technology is packaged in a user-friendly device that is launched with the push of a button.
Unlike other portable water makers that require passing water through filters, this device uses electrical energy to remove particles from drinking water. Eliminating the need for replacement filters greatly reduces long-term maintenance requirements.
This may allow the device to be used in remote areas with limited resources, such as communities on small islands or aboard marine cargo ships. It can also be used to assist refugees fleeing natural disasters or soldiers conducting long-term military operations.
“This is really the culmination of a 10-year journey that my team and I have taken. We have been working on the physics of individual desalination processes for years, but putting all these achievements into a single whole, building a system and demonstrating it in the ocean was a really meaningful and rewarding experience for me,” says senior author Jongyun Khan, a professor of electrical and computer science, biological engineering, and a member of the Electronics Research Laboratory (RLE).
Along with Han, first author Junghyo Yoon, researcher at RLE; Hyukjin J. Kwon, former postdoc; Sung-Ku Kang, postdoc at Northeastern University; and Eric Brack of the U.S. Army Combat Capabilities Development Command (DEVCOM). The results of the study were published online in the journal Environmental Science and Technology.
Commercially available portable water makers typically require high-pressure pumps to push water through filters, which are very difficult to miniaturize without compromising the device’s energy efficiency, Yoon explains.
Instead, their device uses a technique called “ion concentration polarization” (ICP), which was pioneered by Khan’s group over 10 years ago. Instead of filtering the water, the ICP process applies an electric field to the membranes above and below the water channel.
The membranes repel positively or negatively charged particles, including salt molecules, bacteria and viruses, as they pass by. The charged particles enter the second stream of water, which is eventually discharged to the outside.
This process removes both dissolved and suspended solids, allowing clean water to pass through the channel. Because it only requires a low pressure pump, ICP uses less energy than other methods.
But ICP does not always remove all the salts floating in the middle of the channel. So the researchers turned on a second process, known as electrodialysis, to remove the remaining salt ions.
Yun and Kang used machine learning to find the perfect combination of ICP and electrodialysis modules. The optimal setup includes a two-stage ICP process where water passes through six modules in the first stage, then through three in the second stage, followed by one electrodialysis process. This made it possible to minimize energy consumption and ensure a self-cleaning process.
“While it is true that some charged particles can be trapped on the ion exchange membrane if they get trapped, we just reverse the polarity of the electric field and the charged particles are easily removed,” Yoon explains.
They shrunk and folded the ICP and electrodialysis modules to improve their energy efficiency and allow them to fit in a portable device.
Researchers have developed a device for non-specialists: just one button starts an automatic process of desalination and purification. As soon as the salinity and particle count fall below certain thresholds, the device notifies the user that the water is safe to drink.
The researchers also created a smartphone app that can wirelessly control the device and report real-time power consumption and water salinity data.
After conducting laboratory experiments using water with different levels of salinity and turbidity (turbidity), they tested the device in the field on Boston’s Carson Beach.
Yoon and Kwon set up the box near the shore and dropped the feeding tube into the water. After about half an hour, the device filled a plastic cup with clean, drinkable water.
“It turned out to be successful even at the first launch, which was quite interesting and amazing. But I think the main reason for our success is the accumulation of all these small achievements that we made along the way,” Khan says.
The resulting water exceeded World Health Organization quality standards, and the amount of suspended particles in it was reduced by at least 10 times. “Their prototype generates drinking water at a rate of 0.3 liters per hour and requires only 20 watts of energy per liter.
“Now we are doing research to increase the speed of production,” says Yun.
According to Khan, one of the biggest challenges in developing a portable system was to create an intuitive device that anyone could use.
Yoon hopes to make the device more user-friendly and improve its energy efficiency and production speed through a startup he plans to launch to commercialize the technology.
In the lab, Khan wants to apply lessons learned over the past decade to address water quality issues that go beyond desalination, such as the rapid detection of contaminants in drinking water.
“It’s definitely an interesting project and I’m proud of the progress we’ve made to date, but there’s still a lot of work ahead,” he says.
For example, while “the development of portable systems using electromembrane processes is an original and exciting development in off-grid, small-scale desalination,” the effects of pollution, especially if the water is highly turbid, can greatly increase maintenance requirements and energy costs, notes Nidal Hilal, Professor engineering and director of the New York University Abu Dhabi Water Research Center, who was not involved in this study.
“Another limitation is the use of expensive materials,” he adds. “It would be interesting to see similar systems using inexpensive materials.”
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