Solar steam sterilization system

Rice University graduate student Oara Neumann, left, and scientist Naomi Halas with their solar steam-powered autoclave

Rice University nanotechnology researchers have unveiled a solar-powered sterilization system that could be a boon for more than 2.5 billion people who lack adequate sanitation. The "solar steam" sterilization system uses nanomaterials to convert as much as 80 percent of the energy in sunlight into germ-killing heat.

Researchers from Rice's Laboratory for Nanophotonics (LANP) show two ways that solar steam can be used for sterilization -- one setup to clean medical instruments and another to sanitize human waste.

Researchers show two ways that solar steam can be used for sterilization — one setup to clean medical instruments and another to sanitize human waste

Nanoparticles heat up so quickl that when submerged in water and exposed to sunlight that the surrounding water instantly vaporizes to form steam. As an example of its effectiveness, the system even works with icy-cold water and boasts an overall energy efficiency of 24 percent. This is superior even to commercial photovoltaic solar panels that typically have an overall energy efficiency of around 15 percent. Despite the electricity-generation potential of the system, the researchers chose to first focus on sterilization applications for the developing world.

A highly efficient method of turning sunlight into heat is expected to have an initial impact as an ultra-small-scale system to treat human waste in developing nations without sewer systems or electricity

“Sanitation technology isn’t glamorous, but it’s a matter of life and death for 2.5 billion people,” says Naomi Halas, the director of Rice’s Laboratory for Nanophotonics (LANP) and lead researcher on the project. “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.”

"Sanitation and sterilization are enormous obstacles without reliable electricity," said 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."

The researchers tested the solar-steam autoclaves in two set ups – one for sterilizing medical and dental equipment and another for sanitizing human waste. They found the heat and pressure generated by the steam was not only sufficient to kill even the most heat-resistant living microbes, but also spores and viruses.

"The process is very efficient," Neumann said. "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."

Halas said her team hopes to work with waste-treatment pioneer Sanivation to conduct the first field tests of the solar steam waste sterilizer at three sites in Kenya.

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Write by: RC - Tuesday, July 23, 2013