New method turns ocean water into drinking water, without wasteBig takeawaysA new desalination method produces drinking water from seawater with...

New method turns ocean water into drinking water, without waste
Big takeaways
A new desalination method produces drinking water from seawater without chemical additives.
The solar-powered system uses specially engineered black metal to absorb sunlight.
Its self-cleaning surface separates and collects salts, instead of dumping them as harmful brine waste.
From the salts, the system can extract lithium, a key material for rechargeable batteries.
The approach could help address global water shortages and growing mineral demand.
The United Nations estimates that 2.2 billion people lack safely managed drinking water, and communities from California to the Middle East rely on desalination plants to convert ocean water to fresh water. Common desalination techniques, such as reverse osmosis and thermal distillation, are energy-intensive, require pre- and post-water treatment, and leave behind a concentrated saltwater byproduct called brine. The brine byproduct wreaks havoc on sea life when it’s deposited back into the ocean by raising the salt level and lowering oxygen in the water.

But a novel approach developed at the University of Rochester offers a way to overcome these drawbacks. Researchers at URochester’s Institute of Optics developed a new solar-thermal desalination process to produce fresh water in an energy-efficient way that does not leave behind brine and requires no chemical additives to pre-treat the water. A team led by Chunlei Guo, a professor of optics and of physics and a senior scientist at URochester’s Laboratory for Laser Energetics, describes their method in a paper published in Light: Science & Applications.

A blue gloved hand holding two pieces of laser-etched superwicking black metal.
SUN-POWERED SOLUTION: Researchers developed a solar-powered desalination device featuring laser-etched superwicking black metal (right). Unlike existing solar desalination systems (left), Professor Chunlei Guo’s design prevents salt and mineral buildup from clogging the surface.

The technology uses solar panels made of black metal etched with femtosecond lasers to make the surface super light-absorbing and superwicking—or extremely attractive to water. The panels have a laser-treated active region that pulls a thin layer of water across the surface, absorbs nearly all solar radiation, distills the water, and deposits the leftover salts and minerals into the panel’s untreated sides or “passive” region so that the salt does not clog the active region and disrupt continuous desalination.

Leveraging the ‘coffee ring’ effect
Guo says other researchers have developed solar-thermal desalination techniques that work well in lab experiments using simulated seawater made of only water and sodium chloride. As the water evaporates, the sodium chloride crystallizes in a grainy and porous fashion allowing water to pass through to dissolve the salt. The solar panels, meanwhile, can be easily cleaned.

But real ocean has a much more complex composition, and these systems tend to encounter issues when tested in the field. Unlike sodium chloride, many other components in seawater, such as magnesium- and calcium-based materials, crystallize in a crusty and non-porous fashion on the solar panel’s surface, clogging it. Eventually, water can no longer seep through. This is the same phenomenon as your shower head clogging over time or your teapot lined with scales, except that seawater contains hundreds of times more salts than your tap water.

To keep their solar panel surface from gumming up similarly, Guo’s team precisely etched the black metal’s grooves so the various salts and minerals in ocean water would simply slough off. They also leveraged a physical phenomenon that has plagued clumsy javaphiles for centuries: the coffee ring effect.

“If you drop coffee on a surface, eventually the water evaporates, and there’s a ring left at the outer edge that is the concentrated coffee particles,” says Guo. “We use that same principle to advance the salts to the passive region.”

Testing their solar-thermal desalination technique using samples of water from the Pacific, Atlantic, and Indian Oceans, Guo and his team were able to make the surface self-cleaning. In other words, it extracted freshwater and directed the remaining salts to the passive region where they could be later collected without reducing the panel’s efficiency.