Future Tense

Scientists Use “Solar Steam” to Sterilize Medical Equipment, Human Waste

Rice University graduate student Oara Neumann, left, and scientist Naomi Halas are co-authors of a new study about a highly efficient method of turning sunlight into heat

Photo by Jeff Fitlow/Rice University

Earlier this year, I wrote about a contest to build a better toilet for the developing world. (Also, Matt Damon.) Now, researchers have developed a sanitation device that uses an old technology in a revolutionary new way—they call it solar steam.

According to Rice University, more than 2.5 billion people lack proper sanitation in this world. We tend to think of sanitation in terms of clean food, washing your hands after using the bathroom or, you know, having a bathroom, but the problem also extends to sterile medical and dental equipment. One-quarter of the Earth’s population still lacks the electricity to run expensive sterilization technology, like an autoclave, even if they could get their hands on one. That’s why researchers at Rice University have been experimenting with a sanitation device that focuses the sun’s rays, a la Indiana Jones and the Staff of Ra, to create a chamber of pathogen-obliterating steam.

The device uses gold nanomaterials created by research scientist Oara Neumann, lead author of the paper. These nanoparticles are capable of absorbing most of the spectrum of wavelengths in sunlight, both visible and invisible, and channeling that energy into extreme heat. Now, you’re probably picturing someone holding a fancy magnifying glass over a pot of boiling water, but the light-absorbing particles are so good at what they do and the reaction is so localized, the researchers are able to draw steam off a glass of ice water. The solar steam is then trapped into an autoclave that can maintain temperature of 284 degrees Fahrenheit, well over the heat required to fry bacteria, viruses, and spores on medical or dental equipment.

Perhaps even more interesting, another version of the project can completely sterilize human or animal waste. Using funds from the Bill & Melinda Gates Foundation, Neumann and her team have been able to build a standalone, closed-loop geometry (picture a small satellite dish) that’s capable of using just a small battery and the sun to process enough solid and liquid waste to service four adults. After sterilization, the waste might even be repurposed as fertilizer or building materials. (What, didn’t know you know you could make bricks out of human feces?)

Right now, Neumann declined to hazard a guess at how much one of these things might actually cost. However, she said the main component, the nanoparticles, are actually pretty cheap. “We wanted to prove the concept. Optimizing it is another story,” she told me. “But we’re going to do it.” She also said that generating electricity from the steam may be yet another use for the nanoparticles, but right now the energy efficiencies don’t quite work out.

Certainly, it’s an intriguing technology that stands to benefit a whole heckuva lot of people. It also makes the other solar-ish plan getting headlines this week seem a little frivolous—but I guess if you lived somewhere with five months of darkness, you’d want to attach enormous sun-catching mirrors to the mountaintops, too. Even if it’s just to light up an ice skating rink.