Rice University researchers (from left) Naomi Halas, Qilin Li, Peter Nordlander, Seth Pederson, Alessandro Alabastri and Pratiksha Dongare with a scaled up test bed of the NEWT Center’s direct solar desalination system. (Photo by Jeff Fitlow/Rice University)
Up until now, turning salt water into fresh water hasn’t been the easiest thing on earth. New solar technology, however, might’ve just changed all that.
When I was a kid in first grade, Mrs. Roberts showed us an experiment. We all walked down to the beach (the good ol’ days, right?) collected a cup of water from the ocean, then poured the salt water into a bowl. We covered those bowls with Saran Wrap, poked a hole in the middle, put a pebble on top, then put our cup right in the middle of the bowl with salt water surrounding it. After a few days in the sun, if I remember correctly, there was a film of salt in the bowl and the cup was nearly full of fresh water. Simple enough, right? Well, on a large scale, not really. Not at all.
The energy requirements for most forms of desalinization are prohibitively high. There are somewhere around 20,000 plants in various countries all over the world, but essentially boiling billions of gallons of water and collecting the condensation takes a lot of heat, which takes a lot of energy. Sure, there’s more to it than that, but that’s the Cliffs Notes.
A paper recently published in the Proceedings of the National Academy of Sciences shows research that could very possibly have an enormous global impact. The research, conducted at Rice University’s Center for Nanotechnology Enabled Water Treatment (NEWT), uses something called “light-harvesting nanophotonics” and membrane distillation.
“Direct solar desalination could be a game changer for some of the estimated 1 billion people who lack access to clean drinking water,” said Qilin Li, a water treatment expert and one of the authors of the study. “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.”
Like most great inventions, though, it’s not entirely new–instead, it improves on the technology already in use. With membrane distillation, heated salt water and cold fresh water flow on opposite sides of a membrane. Since cold saps heat, the water vapor is sucked from one side to the other, leaving the salt in the membrane. But like I said before, boiling millions of gallons of water ain’t cheap. That’s where those light-harvesting nanophotonics come into play.
Here comes the sun, doot n doodooo.
“NEWT’s new technology builds upon research…to create engineered nanoparticles that harvest as much as 80 percent of sunlight to generate steam,” reads Rice University’s press release. “By adding low-cost, commercially available nanoparticles to a porous membrane, NEWT has essentially turned the membrane itself into a one-sided heating element that alone heats the water to drive membrane distillation.”
Right now, it’s not much good. The studies were merely a proof-of-concept, but they proved the concept. The chamber they used was tiny–about the size of three postage stamps and just a few millimeters thick–but the distillation membrane was covered with a layer of black nanoparticles that heat the membrane with solar energy. The amount of heat, of course, will only increase as the membrane gets bigger. “Unlike traditional membrane distillation,” said Rice’s Naomi Halas, who also wrote the paper, “NESMD benefits from increasing efficiency with scale.”
The team’s ultimate goal is to get their technology into the hands of people who need it. “You could assemble these together, just as you would the panels in a solar farm,” said Li. “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 6 liters per hour per square meter, you would order a little over 3 square meters of panels.”
