Scientists can use the sun to make seawater safe to drink

While access to clean drinking water remains an issue in many parts of the world, there’s no shortage of water on the planet: 97% of Earth's water can be found in our oceans. Turning the ocean’s saltwater into freshwater is generally an elaborate process that requires a lot of energy, but a team of scientists at Rice University's Center for Nanotechnology Enabled Water Treatment (NEWT) have created a new method using nothing but sunlight.

The traditional way to get potable water from saltwater is a process called distillation: saltwater is boiled and the steam produced is captured and processed through a condensing coil. This method is inefficient in terms of energy, as it takes a tremendous amount of heat to boil the water alone.

And then there’s membrane distillation — a technique where hot and cold saltwater flow through a porous membrane and the vapor is captured. While this is more energy efficient than distillation, it still requires a significant amount.

Now, thanks to researchers at Rice University, an off-grid desalination technology is available requiring only solar energy. The federally funded study, published in the journal Proceedings of the National Academy of Sciences, developed the "nanophotonics-enabled solar membrane distillation" technology, or NESMD.

This technique combines the membrane-distillation water treatment method with nanotechnology that turns sunlight into heat. Specifically, by embedding sunlight-absorbing carbon black nanoparticles into the membrane, the researchers are able to harvest 80% of sunlight that comes in contact with the membrane. This results in faster water evaporation and a decrease in the amount of power the entire process needs.

"Unlike traditional membrane distillation, NESMD benefits from increasing efficiency with scale," Naomi Halas, a corresponding author on the paper, said in a statement. "It requires minimal pumping energy for optimal distillate conversion, and there are a number of ways we can further optimize the technology to make it more productive and efficient."

The most significant application for this technology is providing clean drinking water to those without access to it. And since the system is modular and relatively portable, it can be taken to remote regions with little to no access to electricity.

“Direct solar desalination could be a game changer for some of the estimated 1 billion people who lack access to clean drinking water,” Qilin Li, a Rice scientist and water treatment expert and a corresponding author on the study, said in a statement. "This off-grid technology is capable of providing sufficient clean water for family use in a compact footprint, and it can be scaled up to provide water for larger communities."