With no twist, a portable desalination unit delivers drinking water from seawater

With no twist, a portable desalination unit delivers drinking water from seawater ...

MIT researchers have developed a portable desalination unit, which is capable of removal of particles and salts in order to produce drinking water.

A small, portable solar panel can be purchased online for $50 per suitcase. It automatically generates drinking water that meets World Health Organization standards. The technology is packaged into a user-friendly device that runs with the push of one button.

This device, which is able to travel through filters using electrical power to remove particles from drinking water. Long-term maintenance concerns are greatly reduced due to elimination of the need for replacement filters.

This may enable the unit to be deployed in remote and highly resource-limited areas, such as communities on small islands or aboard seafaring cargo ships. It may be also used to assist refugees in situations of natural disasters or by military deployments.

I and my group have had a 10-year journey on the back of individual desalination processes. Having all of these advancements into a box, building a system, and doing it in the ocean, was a fantastic and rewarding experience for me, according to senior author Jongyoon Han, who is a professor of electrical engineering and computer science and biology. RLE is a member of the Research Laboratory of Electronics (RLE).

Junghyo Yoon, a research scientist in RLE, Hyukjin J. Kwon, a former postdoc, Northeastern University, and Eric Brack of the United States Army Combat Capabilities Development Command (DEVCOM), among the authors.

Filter-free technology

Portable desalination units are usually pressed with high-pressure pumps to squeeze water through filters, which are often difficult to miniaturize, without compromising the energy-efficiency of the device.

The unit is based on an ICP concept, which was developed by the Hans group more than ten years ago. Rather than filtering water, the ICP process involves an electrical field to membranes placed above and below a channel of water. As they absorb positively or negatively charged particles, including salt molecules, bacteria, and viruses, and the charged particles are then flowed into a second stream of water.

The process removes both dissolved and suspended solids, thus allowing clean water to pass through the channel. Since it only requires a low-pressure pump, ICP uses less energy than other techniques.

However, ICP does not always remove all salts floating in the middle of the channel. So the researchers incorporated a second process, known as electrodialysis, to remove remaining salt ions.

Yoon and Kang used machine learning to select the best combination of ICP and electrodialysis modules. The ideal setup includes a two-stage ICP process, with water flowing through six modules in the first stage then through three in the second stage, followed by a single electrodialysis process. This reduced energy usage while ensuring the process remains self-clean.

While it is true that some charged particles might be captured on the ion exchange membrane, if they become trapped, we only reverse the polarity of the electric field and the charged particles can be easily removed, according to Yoon.

The researchers designed the device for nonexperts, with only one touch to initiate the automatic desalination and purification process. After the salinity level and the number of particles decrease to certain thresholds, the device notifys the user that the water is drinkable.

The researchers have also developed a smartphone app that can control the unit wirelessly and disclose real-time data on energy consumption and water salinity.

Beach tests

At Bostons Carson Beach, they performed lab experiments using water with different salinity and turbidity levels.

Yoon and Kwon 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 year, which was quite exciting and surprising. I believe that the main reason we were successful is the accumulation of all of these little advances that we made along the way.

The water that resulted in the transformation exceeded World Health Organization standards, and the unit reduced the amount of suspended solids by at least a factor of 10. Their prototype enables drinking water to be measured at a rate of 0.3 liters per hour, and requires only 20 watts of power per liter.

According to Yoon, we are accelerating our research to increase the production rate right now.

One of the biggest challenges of designing the portable system was developing an intuitive interface that could be used by anyone, according to Han.

Yoon hopes to make the device more user-friendly and reduce its energy efficiency and production rate through a startup that he intends to start to commercialize the technology.

Han hopes to apply the lessons he learned in the past decade to water-quality issues that go beyond desalination, such as rapidly detecting contaminants in drinking water.

It''s certainly a challenging task, and I am pleased of the progress we have made so far, but there''s still a lot of work to be done, according to the author.

While the development of portable electric devices using electro-membrane processes is an original and exciting strategy in off-grid, small-scale desalination, the impacts of fouling, particularly if the water has high turbidity, might significantly increase maintenance requirements and energy costs, according to Nidal Hilal, a professor of engineering and director of the New York University Water research center.

Another obstacle is the use of expensive materials, according to a professor. It might be interesting to see similar systems with low-cost materials in place.

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