Human waste might be a lot more valuable to getting people to Mars than originally believed. A team of researchers from Penn State University developed special microbe reactors to break down solid and liquid waste. This waste could then be recycled and used for food.
"We envisioned and tested the concept of simultaneously treating astronauts' waste with microbes while producing a biomass that is edible either directly or indirectly depending on safety concerns," said Christopher House, professor of geosciences, Penn State. "It's a little strange, but the concept would be a little bit like Marmite or Vegemite where you're eating a smear of 'microbial goo.'"
While one might immediately opt for the Vegemite spread before human waste on toast, the researchers quickly explained why their solution could actually save resources for the ISS and other space teams. Food adds mass to a space craft, and having a lot of food for long distance space travel would add significantly to the weight of the craft and thus the fuel needed to carry the weight.
The team also said that while methods like hydroponic growing could be feasible in space, they drain energy and other resources such as water.
Thus, the researchers wanted to use a relatively common practice that works well on Earth that could easily transfer to space. They used an artificial solid and liquid waste frequently used in waste management tests. They then made a cyllindrical system that's about four feet long by four inches in diameter. They then exposed the artificial waste to various microbes. Those microbes used anaerobic digestion -- breaking down biodegradable materials without oxygen -- to break down the waste.
"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. What was novel about our work was taking the nutrients out of that stream and intentionally putting them into a microbial reactor to grow food."
One of the biggest results of the anaerobic digestion was actually methane. Rather than look to get rid of the gas, the researchers figured out they could recycle the methane and grow yet another functional type of microbe. And that microbe, Methylococcus capsulatus, is currently used in animal feed and could thus be used to produce food during flight.
The team actually drew inspiration from aquariums and how they filtered and treated out fish waste.
"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."
House and his team determined that the microbes they grew for consumption contained 52 percent protein and 36 percent fat, giving future astronauts a solid source of nutrition.
"Each component is quite robust and fast and breaks down waste quickly," said House. "That's why this might have potential for future space flight. It's faster than growing tomatoes or potatoes."
NASA and ISS astronauts have been looking for more ideas into how to remove or recycle space waste. In 2016, NASA even developed the Space Poop Challenge to figure out how to best remove human waste from astronauts' suits during long duration tasks like space walks. Currently, part of the waste management solution for the ISS is ejecting it into Earth's atmosphere where it burns up. House said the Penn State team's research could provide a much more useful solution.
"Imagine if someone were to fine-tune our system so that you could get 85 percent of the carbon and nitrogen back from waste into protein without having to use hydroponics or artificial light," said House. "That would be a fantastic development for deep-space travel."