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Solar power, wood and bacteria join forces to purify water for drinking

Solar power, wood and bacteria...
Researchers in China have developed a new type of solar-powered device that purifies water for drinking
Researchers in China have developed a new type of solar-powered device that purifies water for drinking
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Researchers in China have developed a new type of solar-powered device that purifies water for drinking
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Researchers in China have developed a new type of solar-powered device that purifies water for drinking
A diagram of the new solar water purifier. The top is a light-absorbing layer of carbon nanotubes, the middle is a heat-insulating layer of glass bubbles, and the bottom is wood
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A diagram of the new solar water purifier. The top is a light-absorbing layer of carbon nanotubes, the middle is a heat-insulating layer of glass bubbles, and the bottom is wood

Evaporation is one of the most enduring methods of purifying water to make it drinkable. Now researchers at the University of Science and Technology of China have developed a novel device made of wood that can do just that, by employing bacteria to help build key nanostructures.

The basic idea of an evaporative water purifier is something most of us would remember from science class at school. Concentrating sunshine onto the device, the water heats up and evaporates into steam, leaving behind any nasty contaminants. The steam can then be guided into a separate container where it re-condenses into clean, drinkable water.

We’ve seen this basic concept put to work many times in the past, using a variety of materials and configurations. That includes machines that float on the surface of a lake, absorbing water from below and cleaning it up, sponges encased in bubble wrap, foamy structures made of graphite flakes, solar stills made with carbon-dipped paper, and cellulose aerogels.

For this study, the new device is made up of several layers. The top is made of carbon nanotubes, which are efficient at absorbing heat from sunlight. In the middle sits a layer of tiny glass bubbles, forming a heat-insulating aerogel. Below that is a block of wood, with the water sitting underneath that.

A diagram of the new solar water purifier. The top is a light-absorbing layer of carbon nanotubes, the middle is a heat-insulating layer of glass bubbles, and the bottom is wood
A diagram of the new solar water purifier. The top is a light-absorbing layer of carbon nanotubes, the middle is a heat-insulating layer of glass bubbles, and the bottom is wood

But the key ingredient is bacteria. The team started by applying the bugs to the surface of the wood, leaving them to ferment. When the glass bubbles and carbon nanotube layers are added, the bacteria build cellulose nanofibers around them, which holds the whole thing together.

With this design, water is transported up through the wood, using the natural porous structure that helps trees stay hydrated. When it reaches the light-absorbing carbon nanotube layer on top, it heats up and evaporates. The glassy aerogel layer, meanwhile, acts as an insulator, keeping the heat from dissipating downwards.

The team says that this solar evaporator design is more effective than most. It boasts an evaporation rate of 2.9 kg m–2 h–1, and a solar-to-vapor efficiency of 80 percent. As an added bonus, wood and carbon nanotubes are relatively cheap and abundant materials.

The research was published in the journal Nano Letters.

Source: American Chemical Society

2 comments
Karmudjun
Well on paper this looks very good. But how abundant materials are, how easy the process is to scale, and how - or who - will fund or implement the process is the big question. It appears this will not be a backpacker's water filtration device anytime soon, even if the price is right. But the method is more efficient that past approaches, I hope it can be scaled up - it might reduce the need for desalination plants!
SiteGuy
Nice article. But the "2.9 kg m–2 h–1" evaporation rate quoted here seems like obfuscation for its own sake. The average reader will look at that and say "Wha?" Since one kilogram of water is one liter, why not just say "2.9 liters of water per square meter per hour"? Much easier to understand. And, for the record, that is indeed outstanding efficiency!