According to a new study, researchers team have shown that it is possible to rapidly break down solid and liquid waste to grow food with a series of microbial reactors, while simultaneously minimizing pathogen growth. Human waste may one day be a valuable resource for astronauts on deep-space missions. The study has published in Life Sciences in Space Research.

The researchers' study addresses multiple challenges facing deep-space missions to Mars or beyond, which would likely take months or years. Bringing enough food from Earth takes up volume and increases the mass and fuel cost of the spacecraft, while growing food in route using hydroponic or other methods would be an energy- and water-intensive process that takes up valuable room.

"Anaerobic digestion is something we use frequently on Earth for treating waste," said House. "It's an efficient way of getting mass treated and recycled. The team found that methane was readily produced during anaerobic digestion of human waste and could be used to grow a different microbe, Methylococcus capsulatus, which is used as animal feed today. The team concluded that such microbial growth could be used to produce a nutritious food for deep space flight.

Because pathogens are also a concern with growing microbes in an enclosed, humid space, the team studied ways to grow microbes in either an alkaline environment or a high-heat environment. The team found these bacteria to be 15% protein and 7% fats. At 158 degrees Fahrenheit, which kills most pathogens, they grew the edible Thermus aquaticus, which consisted of 61% protein and 16% fats.

The team's compact design drew inspiration from aquariums, which use a fixed-film filter to treat fish waste. These filters use a specially designed, bacteria-covered film material with high surface area. "We used materials from the commercial aquarium industry but adapted them for methane production," said House. "On the surface of the material are microbes that take solid waste from the stream and convert it to fatty acids, which are converted to methane gas by a different set of microbes on the same surface."

The team removed 49 to 59% of solids in 13 hours during their test. This is much faster than existing waste management treatment, which can take several days. Today, astronauts aboard the International Space Station recycle a portion of water from urine, but the process is energy intensive, said House. Solid waste management has been a bigger hurdle. This currently is ejected into the Earth's atmosphere where it burns up.

In further study, researchers get 85% of the carbon and nitrogen back from waste into protein without having to use hydroponics or artificial light. Author concludes that would be a fantastic development for deep-space travel.