Scientists turn seawater into fresh water without harmful brine
Scientists have developed a solar-powered desalination system that turns seawater into fresh water while removing nearly all of the leftover salt as a solid instead of producing harmful brine. The self-cleaning technology could also recover valuable minerals such as lithium, potentially turning desalination waste into a useful resource.
Billions of people worldwide lack access to safe drinking water, prompting regions like California and the Middle East to increasingly rely on desalination plants to convert seawater into fresh water. However, traditional desalination methods like reverse osmosis and thermal distillation consume significant amounts of energy, necessitate water treatment before and after the process, and generate highly concentrated salty waste known as brine.
When discharged back into the ocean, brine can raise local salinity and oxygen levels, creating harmful conditions for marine life.
Researchers at the University of Rochester have developed a solar-powered desalination system that could address these issues. Led by Chunlei Guo, a professor of optics and physics, the team created a system using black metal panels treated with femtosecond lasers. These lasers alter the metal's surface, making it highly effective at absorbing sunlight and exhibiting superwicking properties that allow water to spread rapidly across the surface.
The panels have an active region that draws a thin layer of seawater across its surface, absorbing nearly all incoming solar radiation and heating the water, causing it to evaporate. The salts and other dissolved minerals are directed toward untreated areas along the sides of the panel, known as the passive region. This movement prevents salt buildup, which is a major challenge in solar desalination systems.
To overcome the difficulty of desalinating real seawater, which contains hundreds of times more dissolved salts than ordinary tap water, the researchers designed microscopic grooves in the black metal. This design allows salts and minerals to be pushed away from the active region instead of forming a stubborn crust. The team also utilized the coffee ring effect, where suspended particles move toward the edge of a drying droplet, directing salts toward the passive region.
In tests using actual seawater collected from the Pacific, Atlantic, and Indian Oceans, the system effectively cleaned itself while producing fresh water, directing the remaining salts into the passive region for collection. Importantly, this process did not reduce the panel's desalination efficiency. Additionally, the system extracts nearly 100% of the dissolved salts in solid form, potentially turning the waste product into a resource.
Some of the salt could be used as table salt, while more valuable minerals like lithium could be recovered and used in batteries for electric vehicles and other electronic devices.
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