Astronauts on a mission to Mars or beyond may be able to survive on plants watered with their own urine. Our liquid waste is 95 per cent water. The other five per cent is composed of nutrients, such as nitrogen, potassium, and phosphorous, which may pose harm to humans over the long term 鈥� but not to plants.
Using computer-generated test crops of dwarf wheat and soybeans, a team led by at the University of Sydney in Australia simulated how these plants take up nutrients from human urine. They simulated plants growing in natural soil 鈥� as opposed to artificial 鈥� in an isolated chamber with its own ventilation system.
This 鈥渃ropping unit鈥� would have both urine and water injection systems. The team analysed different injection modes 鈥� both periodic and continuous聽鈥� of untreated, unfiltered urine to determine how they would affect the plants鈥� growth.
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Over a simulated 20 years, urine 鈥渓argely met鈥� the plants鈥� nutritional demands without high levels of harmful byproducts or emissions, such as carbon dioxide or ammonia. It鈥檚 not just the urine that makes this system work 鈥� soil is key. Thanks to long-lived microbes, soil provides what Maggi calls 鈥渇orgiveness of neglect鈥�, which is an ability to adapt to a surrounding environment in a way that hydroponic and aeroponic systems may not be able to.
Faecal add-on
A twenty-year mission is longer than any human off-planet endeavor is likely to be in the near future, but no matter when a deep space mission happens, the crew will have to be somewhat self-sufficient. They鈥檒l have to use everything on board to get by 鈥� even their own urine.
鈥淚f you鈥檙e trying to operate independently and grow food, plants need fertiliser. And the only fertiliser that would be available would be [human] wastes,鈥� says at the Rich Earth Institute in Guilford, Vermont.
Because these elements aren鈥檛 destroyed between eating them and passing them, they could indeed be recycled indefinitely. However, Noe-Hays notes that urine may not provide enough nutrients because the bulk are expelled in faeces. While urine does have the necessary nutrients to support this kind of regenerative system, there simply wouldn鈥檛 be enough of them.
鈥淏ecause urine contains most, but not all, of the nutrients, you wouldn鈥檛 be able to maintain a plant agroecosystem indefinitely with only recycling the urine. You鈥檇 have to supplement that with nutrients to make up the difference,鈥� Noe-Hayes says. He concludes that astronauts would likely have to get comfortable with recycling their own faeces as well, which comes with bacteria risks that urine doesn鈥檛 have.
There are a few factors this study doesn鈥檛 take into account, namely the challenges of growing plants in microgravity. Soil consistency matters much more in microgravity, as astronauts have learned鈥� roots don鈥檛 grow downward and water and nutrients float. However, an experiment aboard the ISS has helped mitigate some of these problems with 鈥減lant pillows鈥� full of soil, nutrients, and water. Perhaps in the future, astronauts can try using urine to nourish these plants.
Life Science in Space Research
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