CLEMSON — Astronauts on deep-space missions won’t be able to run to the store for disinfectant wipes, but they may have another way of cleaning surfaces inside their spaceship, and it could involve human waste.
Sudeep Popat of Clemson University is developing a way of making hydrogen peroxide for use on long-term space missions. He proposes to do it by feeding human waste to microbial fuel cells that produce hydrogen peroxide.
Popat, an assistant professor of environmental engineering and earth sciences, said the hydrogen peroxide could be used to clean potentially infectious biofilms from surfaces inside spacecraft. Or it may be possible to use the hydrogen peroxide to disinfect wastewater for reuse, he said.
Even better, the electrochemical reactions inside microbial fuel cells produce a tiny amount of voltage as bacteria break down organic substances, Popat said. That means making hydrogen peroxide could also produce a small amount of excess energy for other uses, he said.
Several questions need to be answered before the technology is ready for liftoff, and Popat and his team are now working to advance the technology with a new research project that is backed by $750,000 from NASA.
It is among the latest projects nationwide aimed at helping astronauts use every last resource when they venture into the depths of space for months or even years.
Other projects at Clemson have focused on deep-space hydroponic farming and converting waste molecules into products astronauts need, such as polyesters and nutrients.
The idea for Popat’s project goes back to when he first learned about microbial fuel cells while he was a Ph.D. student at the University of California, Riverside. He continued the work as a postdoctoral researcher at Arizona State University.
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Microbial fuel cells were originally designed to produce electrical power from the chemical energy in wastewater, he said.
“I got to work with a couple of leading scientists who work in this area while doing my postdoc at Arizona State University,” Popat said. “From then on, I learned a lot about the technology and started looking at ways in which it could be tweaked to produce chemicals of interest rather than electrical power.”
Earthlings are generally accustomed to flushing their waste, but reusing it for hydrogen peroxide production isn’t as gross as it might sound.
The microbial fuel cells that Popat is developing have two chambers separated by a membrane. Wastewater is fed into an anode chamber, and a cathode chamber is filled with a dilute saltwater solution.
“The contents of the anode chamber do not mix with the contents of the cathode chamber,” Popat said.
Bacteria in the anode chamber break down organic matter, releasing electrons. The electrons pass through an external circuit to the cathode, resulting in production of electrical current.
When microbial fuel cells are used primarily to generate electricity, oxygen is electrochemically reduced to water in the cathode chamber. But in the system that Popat is creating, the cathode reaction is modified so that it produces hydrogen peroxide instead.
Researchers have shown that they can produce solutions that are 1-2% hydrogen peroxide, Popat said. That’s lower than what you buy in the drugstore but could be high enough to clean surfaces and treat wastewater in space, he said.
The research aligns with two of NASA’s goals, Popat said. NASA would like to increase the amount of wastewater recovered on the International Space Station from 74% to 98%, he said. And the agency wants to ensure surfaces inside space vehicles are clean and especially devoid of biofilms, Popat said.
Co-investigators on the grant include Ezra Cates, Tanju Karanfil and Michael Carbajales-Dale, all of Clemson, and R. Sean Norman from the University of South Carolina and Benedict College’s Jessica Furrer. Michael Flynn and John Hogan at the NASA Ames Research Center will serve as the primary NASA collaborators.
Also partnering on the grant are Savannah River National Laboratory, the Naval Research Laboratory and the companies Synbiohm, Greenway Energy, Aquacycl, AquiSense Technologies and WK Dickson.
The funding comes through NASA’s Established Program to Stimulate Competitive Research.
David Freedman, chair of the Department of Environmental Engineering and Earth Sciences at Clemson, congratulated Popat and his team on the grant.
“Dr. Popat and his team are well positioned to strengthen research in an area of strategic importance to NASA, while providing students with valuable, hands-on lab experience,” Freedman said. “The grant is well deserved.”
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