Astronaut Urine May Help Power Future Spacecrafts, Experts

Urine is typically considered something to get rid of. But urine is largely water, and that’s a valuable resource in space. If a new process can be successfully scaled up from recent lab tests, future space travelers could more efficiently recycle their own urine to reclaim its water and make a little electrical power to boot.
Getting water and other supplies to the International Space Station (ISS) is expensive. It costs about $33,000 per kilogram to launch materials into low-Earth orbit, says Eduardo Nicolau, an analytical chemist at the University of Puerto Rico, Rio Piedras. Launching them higher is even more costly. Resupplying spaceships carrying people far outside Earth’s orbit—to Mars, say—probably would be prohibitively expensive even if possible.

Thus, Nicolau says, crews of long-term space missions will have to recycle their water. And the biggest source of that water is their own urine. Each astronaut on such a mission will likely produce more than 1.5 liters each day, accounting for more than 81% of the spacecraft’s wastewater, Nicolau estimates.
Right now, astronauts on board the ISS filter wastewater and then distill it to recover pure water, says Layne Carter, a systems engineer at NASA’s Marshall Space Flight Center in Huntsville, Alabama, who is in charge of the space station’s water systems (and who is not involved in the new study). Current processes, he notes, recover only 75% of the water from urine. But with efforts now under way, NASA engineers hope to increase that percentage to 85% next year and then to nearly 100%.

The space station’s current recycling process disposes of urea, the main nitrogen-rich compound in urine, Nicolau says. But urea can be used to make power, and now Nicolau and colleagues have developed a technique that may simultaneously use urea to improve the efficiency of recycling a spacecraft’s wastewater.
In the first step, the researchers used osmosis—a process in which some substances pass through a membrane—to separate large organic molecules from the water, urea, and other small dissolved molecules or atoms, which pass through the membrane into a salty solution.
Then the researchers forced the urea-laden solution through a device they call a bioreactor, which is packed with activated charcoal that’s been soaked with urease, the enzyme that breaks down urea. In that step of the lab tests, about 86% of the urea is converted into ammonia, the researchers report in the 7 April issue of ACS Sustainable Chemistry & Engineering.

Finally, the ammonia is collected and fed into a batterylike fuel cell, which converts the ammonia into nitrogen and water, emitting power. In the tests, the amount of electrical power generated is small: Voltages are about 0.2 volts, and currents about 2 milliamps, Nicolau says. But the team hopes to improve the power output in its next version of the system, he says.
“This sounds like a clever process, but I’m skeptical about whether it will work at a larger scale or in the uncontrolled environment of space,” says Carter, who has worked on wastewater systems at NASA for 25 years. He also notes that urea is a relatively small component of urine, so the limited amount of power that might be harvested from the team’s new process might not recoup the effort or expense.