From seawater to drinking water, with the push of a button
Massachusetts Institute of Technology
MIT researchers have developed a portable desalination unit, weighing less than 10 kilograms, that can remove particles and salts to generate drinking water.
The
suitcase-sized device, which requires less power to operate than a cell phone
charger, can also be driven by a small, portable solar panel, which can be
purchased online for around $50. It automatically generates drinking water that
exceeds World Health Organization quality standards. The technology is packaged
into a user-friendly device that runs with the push of one button.
Unlike
other portable desalination units that require water to pass through filters,
this device utilizes electrical power to remove particles from drinking water.
Eliminating the need for replacement filters greatly reduces the long-term
maintenance requirements.
This
could enable the unit 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 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. 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," says 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).
Joining
Han on the paper are 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 U.S. Army Combat Capabilities Development Command
(DEVCOM). The research has been published online in Environmental
Science and Technology.
Filter-free
technology
Commercially
available portable desalination units typically require high-pressure pumps to
push water through filters, which are very difficult to miniaturize without
compromising the energy-efficiency of the device, explains Yoon.
Instead,
their unit relies on a technique called ion concentration polarization (ICP),
which was pioneered by Han's group more than 10 years ago. Rather than
filtering water, 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 funneled into a second stream
of water that is eventually discharged.
The
process removes both dissolved and suspended solids, allowing clean water to
pass through the channel. Since it only requires a low-pressure pump, ICP uses
less energy than other techniques.
But
ICP does not always remove all the 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 find the ideal combination of ICP and
electrodialysis modules. The optimal 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 minimized
energy usage while ensuring the process remains 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.
They
shrunk and stacked the ICP and electrodialysis modules to improve their energy
efficiency and enable them to fit inside a portable device. The researchers
designed the device for nonexperts, with just one button to launch the
automatic desalination and purification process. Once the salinity level and
the number of particles decrease to specific thresholds, the device notifies
the user that the water is drinkable.
The
researchers also created a smartphone app that can control the unit wirelessly
and report real-time data on power consumption and water salinity.
Beach
tests
After
running lab experiments using water with different salinity and turbidity
(cloudiness) levels, they field-tested the device at Boston's Carson Beach.
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 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
resulting water exceeded World Health Organization quality guidelines, and the
unit reduced the amount of suspended solids by at least a factor of 10. Their
prototype generates drinking water at a rate of 0.3 liters per hour, and
requires only 20 watts of power per liter.
"Right
now, we are pushing our research to scale up that production rate," Yoon
says.
One
of the biggest challenges of designing the portable system was engineering an
intuitive device that could be used by anyone, Han says.
Yoon
hopes to make the device more user-friendly and improve its energy efficiency
and production rate through a startup he plans to launch to commercialize the
technology.
In
the lab, Han wants to apply the lessons he's learned 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.
The research was funded, in part, by the DEVCOM Soldier Center, the Abdul Latif Jameel Water and Food Systems Lab (J-WAFS), the Experimental AI Postdoc Fellowship Program of Northeastern University, and the Roux AI Institute.
