Turning seawater into drinking water with less power than a cell phone charger
Our planet is absolutely swimming in water. More than 70% of Earth’s surface is covered in the stuff, making up a vast series of interconnected oceans. That water supports all of the life on Earth, but most of it isn’t drinkable. According to the United States Geological Survey, only 2.5% of the world’s water is freshwater, and much of it is locked up in glaciers, in the atmosphere, or so deep underground as to be out of reach. What remains is responsible for keeping global populations hydrated and alive.
In the 1995 film Waterworld, things get a whole lot worse when the ice caps melt. In the movie, melting ice covers the world in an unbroken sea, mixing up much of the previously available freshwater with seawater. Despite being surrounded by water, the Mariner — played by Kevin Costner — is reduced to filtering his own urine just to stay alive.
Things in the real world aren’t as bad as all that, but they aren’t as good as they could be. According to the World Health Organization, roughly one third of the global human population lacks reliable access to clean, safe drinking water.
Rounding up enough water for communities around the world involves building dams and reservoirs and pumping water across state or national boundaries. Factory-sized desalination plants have been built in coastal areas, pulling water from the oceans and removing the salt so that it can be safely consumed. Those systems, however, only serve communities with existing infrastructure, leaving developing communities out to dry.
Hoping to address this ongoing crisis, Junghyo Yoon, a scientist and engineer from the Department of Electrical Engineering and Computer Science at MIT, and colleagues, partnered with Eric Brack, a research chemist at the U.S. Army (DEVCOM) Soldier Center to develop a portable desalination device. Roughly the size of a suitcase, their device uses electricity to transform seawater or other non-potable water sources into fresh drinking water. The device was announced in a paper published in the journal Environmental Science and Technology.
“Our technology uses an electromembrane process called ion concentration polarization. When seawater travels through its water channels, it experiences an electric field which removes solids,” Yoon told SYFY WIRE.
Electromembrane processes aren’t new, but this new technology represents innovations making the whole process safer while also making it suitable for portable, individual use. Electrodialysis, another electromembrane process, uses alternative stacks of ionic and unionic change membranes to pull dissolved solids out of water. That successfully pulls salt out of water but doesn’t necessarily make it safe to drink. It could still contain pathogens or other contaminants which this new technology can address.
“What we’re really trying to do at DEVCOM soldier center is look at novel technologies to advance water purification. We need that for military use but it’s not just a military problem. Water security is huge, if we can create and foster future technologies to create better water security across the globe, that can help avoid wars over water,” Brack said.
Photo: Dr. Junghyo Yoon
This new device pushes water through water channels from left to right while an electric field is applied up and down. It successfully pulls out dissolved solids like salt, but also grabs hold of suspended solids like bacteria, viruses, and potentially heavy metals or chemical contaminants.
As water flows through the intake and moves through the electric field, it’s broken up into two separate streams. The first collects all of the solids and spits them back out into the ocean. The second collects purified drinking water. Given the amount of water in the oceans and the comparatively small amount of fresh drinking water being pulled out, there’s little risk of salinity or contaminants being significantly elevated. At present, the amount of fresh water being collected is relatively small, but scientists hope to improve the flow rate in the near future.
“In the lab, we achieved one liter per hour production rate. In field testing, we implemented a rate of 0.3 liters per hour. Roughly one can of drinking water every hour. Right now, we’re pushing to scale up to five liters per hour,” Yoon said.
Looking forward, the team is hoping their system could be improved even further, by at least an order of magnitude as compared to the current one liter per hour rate.
“Right now the goal is a liter an hour. We don’t have a lot of pre-filtration because we’re trying to optimize the technology itself, but with pre-filtration we could get that time down. I would like this to be able to support 10 to 12 people, so 10 liters per hour is what I’d like to get it to,” Brack said.
The full system uses roughly as much power as a cell phone charger, about 20 watts of power per hour, and can be powered by a 50-watt solar panel if access to electrical infrastructure isn’t available. According to Yoon, the team could have a finished prototype up and running over the next year or so. From there, their devices could be made commercially available or made available to communities in need through partnerships with global nonprofit organizations.
“Moving water around is a huge, costly, logistical burden. If we can create water at the source point, we can reduce the amount of bottled water we’re relying on,” Brack said.
Water security is a critical need, whether you’re living in the Waterworld or the real world, and technologies like these could make that a reality for billions of people who really need it.