Tuesday, June 20, 2017

Freshwater from salt water using only solar energy


The majority of the planet's surface may be water, but unfortunately a heaping pile of salt makes most of that undrinkable. Desalination makes saltwater more palatable and potable, but being a bit of an energy guzzler means it isn't the most practical solution in off-grid situations. A new system makes use of nanoparticles to harness the power of the sun and distill water more efficiently, without needing electricity.

Developed at Rice University's Center for Nanotechnology Enabled Water Treatment (NEWT), the new system is built around the membrane distillation method, where heated salty water runs across the top of a porous membrane. Water vapor is drawn through the membrane and collects underneath in the form of purified water, but plenty of energy is lost in the process.
To improve that efficiency, the researchers harnessed the power of the sun in a system they call "nanophotonics-enabled solar membrane distillation" (NESMD). Sunlight-absorbing carbon black nanoparticles are embedded into the membrane, which helps the material harvest up to 80 percent of the sunlight that hits it, evaporating the water faster and reducing the external power that the system needs.
The system was tested as a proof-of-concept study, using a chamber just a few millimeters thick and about the size of three postage stamps, with a half-millimeter thick layer of saltwater running over the membrane. Having also built a bigger version measuring 70 x 25 cm (27.6 x 9.8 in), the NEWT team says the system scales well, and concentrating the sunlight gives its output a healthy leg-up.
"The intensity got up 17.5 kilowatts per meter squared when a lens was used to concentrate sunlight by 25 times, and the water production increased to about six liters per meter squared per hour," says Qilin Li, corresponding author of the study. "Depending on the water production rate you need, you could calculate how much membrane area you would need. For example, if you need 20 liters per hour, and the panels produce six liters per hour per square meter, you would order a little over three square meters of panels."
Other solar-powered desalination plants are in the works from universities like MIT, companies like IBM and startups like Desolenator, but the NEWT team says its system is modular, relatively portable, and can be rolled out in areas with little or no electricity.
The research was published in the journal Proceedings of the National Academy of Sciences.
The team describes the NEWT project in the video below.
Source: Rice University

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