Desalination
Membranes
Americas
Tuesday, 10 May 2022

Desalination on the go: MIT reveals filterless, pumpless

Researchers at the Massachusetts Institute of Technology have built a portable destination that does not require any filters or pumps. Aquatech Online looks at how it works and potential applications.

A 10-year desalination journey

Researchers at the Massachusetts Institute of Technology (MIT) have built a portable destination that does not require any filters or pumps.

Weighing less than 10kg and the potential to fit inside a suitcase, the unit can remove particles and salts to generate drinking water that can be powered by a phone charger.

“This is really the culmination of a 10-year journey that I and my group have been on," said 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).

"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."

In comparison to similar portable desalination devices that require water to pass through filters, this unit uses electrical power to remove particles from drinking water.

“This is really the culmination of a 10-year journey that I and my group have been on."

This completely removes the need for replacement filters and requires less maintenance.

The development follows the announcement by MIT of Bloom Alert winning the University's Water Innovation Prize for its analytics platform for coastal desalination.

No filter? No pump?

The unit does not require a filter or a pump and instead makes use of ion concentration polarization (ICP).

The ICP process 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 funnelled into the second stream of water that is eventually discharged. Removing both dissolved and suspended solids, the process allows for clean water to pass via the channel.

However, the research team did encounter a challenge when they found the ICP did not always remove all the salts floating in the middle of the channel.

The researchers looked to solve this by incorporating a second process, electrodialysis, to remove the remaining salt ions.

Machine learning was used to find the optimal combination of ICP and electrodialysis. The result? A two-stage ICP process, with water flowing through six modules in the first stage and then through three in the second stage, followed by a single electrodialysis process.

Not only did this minimise energy usage, but it also ensured the process remained 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,” said Junghyo Yoon, first author and research scientist in RLE.

The unit reduced the number of suspended solids by at least a factor of 10. The prototype generates drinking water at a rate of 0.3 litres per hour and requires only 20 watts of power per litre.

Once this process was designed, the team shrunk and stacked the ICP and electrodialysis modules to improve their energy efficiency and enable them to fit inside a portable device.

A complete game-changer

Designed with non-experts in mind, the unit features a single button to launch the automatic desalination and purification process.

The team also developed a smartphone app that can control the unit wirelessly and report real-time data on power consumption and water salinity.

The suitcase-sized device automatically generates drinking water that exceeds World Health Organization quality standards, MIT said. Furthermore, the unit can be powered via a $50 solar panel that can be bought online.

“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.”

The device has the capacity to be deployed in remote and severely resource-limited areas, such as communities on small islands or aboard seafaring cargo ships.

It could also be used to aid refugees fleeing natural disasters or by the military carrying out long-term operations.

This device is still a work in progress with the research team looking further develop the technology to make it more energy-efficient and even easier to use.

“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,” said Han.

 


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