Even when humans travel beyond the Earth and venture to Mars and beyond, the inconvenient realities of human biology will come along with us. Future pioneers will still be piloting the same squishy, imperfect vessel that humans have piloted for thousands of years: the human body. And unless we figure out a way to run our brains and hearts with batteries, humans will always have to eat and drink and poop and pee.

Fortunately, researchers have been hard at work trying to figure out how to accommodate humans’ pesky biological requirements while keeping space flight as efficient as possible. To this end, astrobiologists at Penn State University have developed a method to treat human waste with bacteria to produce an edible product.

“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’,” said Christopher House, Ph.D., professor of geosciences and co-author on the article, in a statement. He and his co-authors published their findings in the November 2017 issue of the journal Life Sciences in Space Research.

Astrobiologists are working to find a better way for astronauts to poop and eat in space.
Astrobiologists are working to find a better way for astronauts to poop and eat in space.

One of the major challenges during space missions, especially longer voyages to Mars and beyond, will be keeping astronauts supplied with sufficient nourishment without cramming the whole vessel with boxes of food and jugs of water. Even systems to grow vegetables will take up lots of space, energy, and water. And once the astronauts eaten and drunk their supplies, they’ll need to store their waste.

This is why House, together with Lisa Steinberg, Ph.D., and Rachel Kronyak at the Penn State Astrobiology Research Center, came up with a system that solves both of these issues at once by using two stages of bacterial waste treatment to produce a nutrient goo that’s high in protein and fat. The researchers say that this substance could either be eaten directly by astronauts or fed to another organism, such as fish, which they would then eat.

“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 House.

To obtain this microbial goo, the researchers first ran an artificial wastewater mixture that’s commonly used in water treatment experiments through an anaerobic digestion device. This piece of equipment contains bacteria that break down the waste without oxygen present, much like a human digests food.

Perfect Vegemite Toast
In this reporter's opinion, bacteria-digested poop and pee is a huge improvement over Vegemite.

“Anaerobic digestion is something we use frequently on Earth for treating waste,” explained 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.”

The researchers found that the methane produced during anaerobic digestion could be used to grow Methylococcus capsulatus, a bacterium that feeds on methane and has desirable concentrations of fat and protein, 36 percent and 52 percent, respectively. By keeping the pH of the mixture very high, they say that pathogenic bacteria, like E. coli, wouldn’t be able to survive.

While the researchers haven’t actually put human poop and pee into the device to produce the nutrient goo, they say this experiment proves their concept. Plus, all the pieces are commercially available already.

“Each component is quite robust and fast and breaks down waste quickly,” said House in the statement. “That’s why this might have potential for future space flight. It’s faster than growing tomatoes or potatoes.”

Abstract: Future long-term manned space missions will require effective recycling of water and nutrients as part of a life support system. Biological waste treatment is less energy intensive than physicochemical treatment methods, yet anaerobic methanogenic waste treatment has been largely avoided due to slow treatment rates and safety issues concerning methane production. However, methane is generated during atmosphere regeneration on the ISS. Here we propose waste treatment via anaerobic digestion followed by methanotrophic growth of Methylococcus capsulatus to produce a protein- and lipid-rich biomass that can be directly consumed, or used to produce other high-protein food sources such as fish. To achieve more rapid methanogenic waste treatment, we built and tested a fixed-film, flow-through, anaerobic reactor to treat an ersatz wastewater. During steady-state operation, the reactor achieved a 97% chemical oxygen demand (COD) removal rate with an organic loading rate of 1740 g d^−1 m^−3 and a hydraulic retention time of 12.25 d. The reactor was also tested on three occasions by feeding ca. 500 g COD in less than 12 h, representing 50x the daily feeding rate, with COD removal rates ranging from 56–70%, demonstrating the ability of the reactor to respond to overfeeding events. While investigating the storage of treated reactor effluent at a pH of 12, we isolated a strain of Halomonas desiderata capable of acetate degradation under high pH conditions. We then tested the nutritional content of the alkaliphilic Halomonas desiderata strain, as well as the thermophile Thermus aquaticus, as supplemental protein and lipid sources that grow in conditions that should preclude pathogens. The M. capsulatus biomass consisted of 52% protein and 36% lipids, the H. desiderata biomass consisted of 15% protein and 7% lipids, and the *Thermus aquaticus biomass consisted of 61% protein and 16% lipids. This work demonstrates the feasibility of rapid waste treatment in a compact reactor design, and proposes recycling of nutrients back into foodstuffs via heterotrophic (including methanotrophic, acetotrophic, and thermophilic) microbial growth.