Clean drinking water for underdeveloped areas with the push of a button

Researchers at the Massachusetts Institute of Technology (MIT) have developed a portable desalination unit weighing less than 10 kilograms that removes particles and salts to produce drinking water.

More than 785 million people globally do not have access to basic water services and more than 884 million people do not have safe water to drink, according to the latest information on access to clean water published in 2019 by WHO and UNICEF.

The portable desalination unit, the size of a suitcase, operates on less power than a cell phone charger. It can also be powered by a small, portable solar panel that costs about $50 online. 

It’s straightforward to use—with the push of a button, the desalination process begins, producing drinking water that exceeds World Health Organization quality standards.

What’s unique about this device is that it does not require filters but uses electrical power to remove particles from drinking water. 

Without replacement filters, the portable desalination unit hardly requires any long-term maintenance.

With these qualities, the device can be put to use in remote and under-resourced areas; for example, the news release lists people in communities on small islands, sailors on seafaring cargo ships, refugees fleeing natural disasters, or soldiers carrying out long-term military operations.

“This is really the culmination of a 10-year journey that I and my group have been on,” Jongyoon Han, a senior author and a professor of electrical engineering and computer science and of biological engineering, says. 

“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.”

The paper was published online in Environmental Science and Technology. In addition to Han, contributors include first author Junghyo Yoon, a research scientist in RLE; Hyukjin J. Kwon, a former postdoc; SungKu Kang, a postdoc at Northeastern University; and Eric Brack of the US Army Combat Capabilities Development Command (DEVCOM).

How they did it

Previous versions of portable desalination units are available in markets. But the problem with those is they typically require high-pressure pumps to push water through filters, which are very difficult to miniaturise without compromising the energy-efficiency of the device, Yoon explains.

The new device, however, utilises ion concentration polarisation (ICP), which was first developed by Han’s group more than 10 years ago.

Instead of filtering water, the ICP process applies an electrical field to membranes placed above and below a channel of water, the news release explains. 

The membranes repel positively- or negatively-charged particles – including salt molecules, bacteria, and viruses – as they flow past. 

The charged particles are moved into a second stream of water that gets discharged.

This way, both dissolved and suspended solids are removed, allowing the water to emerge clean from the channel. And because of the low-pressure pump, ICP consumes less energy than previous models.

The researchers have also built a second process called electrodialysis to ensure all the salt ions are removed, as ICP alone may sometimes fail to remove the salts floating in the middle of the channel.

They used machine learning to find the ideal combination of ICP and electrodialysis modules, the news release notes. 

The optimal set-up has a two-stage ICP process, with water flowing through six modules in the first stage and three in the second stage, which is then followed by a single electrodialysis process. 

That way, the energy usage is minimised while the process stays self-cleaning. 

“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,” Yoon explains.

The researchers shrunk and stacked the ICP and electrodialysis modules to boost their energy efficiency so they would fit into a small portable device. 

The device was carefully designed to be user-friendly and has only one button that needs to be pushed to start the automatic desalination and purification process.

Once the salinity level and the number of particles decrease to thresholds low enough for drinkable water, the device notifies the user that the potable water is ready.

The device also comes with a smartphone app that can wirelessly control the unit and report real-time data on power usage and water salinity.

Testing the device

The researchers took the unit out to sea after tests in a lab environment with various water samples, different salinity and turbidity (cloudiness) levels. Boston’s Carson Beach was their destination.

Yoon and Kwon set the box near the ocean and threw the feed tube into the water. It took the unit about half an hour to process the ocean water into a plastic drinking cup of 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,” Han says. 

The water from the shore passed with flying colours, exceeding WHO guidelines on drinking water, and the unit apparently reduced the amount of suspended solids by at least a factor of 10.

The prototype generates drinking water at a rate of 0.3 litres (300 millilitres) per hour, and requires only 20 watts of electricity per litre.

“Right now, we are pushing our research to scale up that production rate,” Yoon says.

Challenges on the way

One of the biggest challenges of designing the portable system was engineering an intuitive device that anyone could use, Han says.

Yoon is looking for a way to make the device even easier to use and improve its energy efficiency and production rate through a startup where he also plans to commercialise the technology.

In the lab, Han, on the other hand, wants to apply the information he gathered over the past decade to water-quality issues that go beyond desalination – such as rapidly detecting 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.