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.
The research has been published online in Environmental Science and 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.
Instead, their unit relies on a technique called ion concentration polarization
(ICP), which was pioneered by the research 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.
The researchers 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.
The researcher says that while it is true that some charged particles could be
captured on the ion exchange membrane, if they get trapped, the researchers just
reverse the polarity of the electric field and the charged particles can be easily removed.
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.
After running lab experiments using water with different salinity and
turbidity (cloudiness) levels, they field-tested the device at Boston’s Carson Beach.
The team 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.
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.
One of the biggest challenges of designing the portable system was
engineering an intuitive device that could be used by anyone.
The researcher 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.