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Clean Power "Researchers show two ways that solar steam can be used for sterilization — one setup to clean medical instruments and another to sanitize human waste."
Image Credit: Rice University

Published on July 24th, 2013 | by James Ayre

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Solar Steam — Off-Grid Solar-Powered Sterilization System Created



An impressive new solar-powered sterilization system — capable of converting as much as 80% of the energy found in sunlight into sterilization heat — was recently created by nanotechnology researchers at Rice University. The researchers think that the new “solar steam” sterilization system could be of great utility to those in many of the poorer regions of the world — providing a cheap means of sterilization to those living in such circumstances, and helping to improve sanitation.

"Researchers show two ways that solar steam can be used for sterilization — one setup to clean medical instruments and another to sanitize human waste." Image Credit: Rice University

“Researchers show two ways that solar steam can be used for sterilization — one setup to clean medical instruments and another to sanitize human waste.”
Image Credit: Rice University

The researchers — from Rice University’s Laboratory for Nanophotonics (LANP) — already have two particular uses in mind for the new system — cleaning medical instruments and sanitizing human wastes.

“Sanitation and sterilization are enormous obstacles without reliable electricity,” stated Rice photonics pioneer Naomi Halas, the director of LANP and lead researcher on the project, with senior co-author and Rice professor Peter Nordlander. “Solar steam’s efficiency at converting sunlight directly into steam opens up new possibilities for off-grid sterilization that simply aren’t available today.”

During previous work done by the researchers, it was even found that solar steam worked so well at converting solar energy directly into heat that it could create steam directly from ice water.

“It makes steam directly from sunlight,” Halas continued. “That means the steam forms immediately, even before the water boils.”



The great efficiency is the result of light-harvesting nanoparticles created by Rice graduate student Oara Neumann — the lead author on the new study.

The press release from Rice University continues:

Neumann created a version of nanoshells that converts a broad spectrum of sunlight — including both visible and invisible bandwidths — directly into heat. When submerged in water and exposed to sunlight, the particles heat up so quickly they instantly vaporize water and create steam. The technology has an overall energy efficiency of 24%. Photovoltaic solar panels, by comparison, typically have an overall energy efficiency of around 15%.

When used in the autoclaves in the tests, the heat and pressure created by the steam were sufficient to kill not just living microbes but also spores and viruses. The solar steam autoclave was designed by Rice undergraduates at Rice’s Oshman Engineering Design Kitchen and refined by Neumann and colleagues at LANP. In the PNAS study, standard tests for sterilization showed the solar steam autoclave could kill even the most heat-resistant microbes.

Sounds like a very promising system! So long as costs can be kept relatively low, the system will no doubt prove very useful. :)

“The process is very efficient,” Neumann stated. “For the Bill & Melinda Gates Foundation program that is sponsoring us, we needed to create a system that could handle the waste of a family of four with just two treatments per week, and the autoclave setup we reported in this paper can do that.”

The researchers are currently planning to work with waste-treatment pioneer Sanivation to conduct field tests of the solar steam waste sterilizer at three locations within Kenya.

“Sanitation technology isn’t glamorous, but it’s a matter of life and death for 2.5 billion people,” Halas stated. “For this to really work, you need a technology that can be completely off-grid, that’s not that large, that functions relatively quickly, is easy to handle and doesn’t have dangerous components. Our Solar Steam system has all of that, and it’s the only technology we’ve seen that can completely sterilize waste. I can’t wait to see how it performs in the field.”

The new research was just published on July 8th in the Proceedings of the National Academy of Sciences Early Edition.

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About the Author

James Ayre's background is predominantly in geopolitics and history, but he has an obsessive interest in pretty much everything. After an early life spent in the Imperial Free City of Dortmund, James followed the river Ruhr to Cofbuokheim, where he attended the University of Astnide. And where he also briefly considered entering the coal mining business. He currently writes for a living, on a broad variety of subjects, ranging from science, to politics, to military history, to renewable energy. You can follow his work on Google+.



  • JamesWimberley

    This is a great solution – small-scale direct solar steam generation – looking desperately for a problem. There just aren’t many small industrial processes using steam any more. Add a turbine, and you have a solar generator more expensive than PV. Sterilizing medical instruments is a tiny niche, more cheaply filled with PV and batteries, and sterilizing sewage is overkill. I hope they find a use for their great idea.

  • Marion Meads

    the ubiquitous PET water bottles are now very effective for water sterilization just using plain old sunlight. practically free.
    http://www.wikihow.com/Sterilize-Water-With-Sunlight

    And if you have cloudy, murky water, the seeds of Moringa oleifera, which is abundant in many third world countries, especially the tropics, are excellent for clarifying the water, removing impurities and toxic metals. After the clarifying the water, you can use the sunlight treatment using clear plastic bottles made of PET. this is practical, free, and wonderful reuse of what would have been plastic bottle garbage.
    http://phys.org/news/2012-01-miracle-tree-substance-inexpensively-sustainably.html

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