Every day, you flush a liter or two of urine down the toilet. But if humans are going to get to Mars, they won’t be able to afford throwing out this yellow water. Indeed, they are going to have to drink water from their own pee. Scientists have now built a recycling system that can turn astronauts’ urine into both clean drinking water and energy.
That two-step process could be important in making long-distance space travel possible, report chemist Eduardo Nicolau of the University of Puerto Rico, in San Juan, and his colleagues. They described their new pee-recycler in the April 7 issue of Sustainable Chemistry & Engineering.
The International Space Station would be a likely first place to try out such a system. It already recycles pee using a complex process to filter out the water and purify it. “It makes yesterday’s coffee into today’s coffee,” astronaut Don Pettit said when it was installed.
Before the space station, astronauts didn’t harvest pee. The Russian Mir craft had a recycling system that accepted urine. It was known for breaking down, however. In the end, it didn’t produce much drinkable water. NASA’s space shuttles jettisoned urine into space. This created lovely “shooting stars” of pee that were visible from Earth. (Fortunately, the shuttles brought home the solid wastes, which otherwise could have made for a really disgusting type of space junk).
Astronauts report that the water made from recycled urine on the space station tastes great. But the system, installed in 2008, keeps breaking down. It also takes a lot of power to run. What’s more, the system uses some filters and other materials that can’t be recycled. These will add to a spacecraft’s trash, notes Nicolau.
The system his team has come up with not only would remove water from pee, but also its urea. A nitrogen-rich chemical, urea is used as a fertilizer and as a raw ingredient in some fuel systems. Harvesting it from urine might reduce some of the weight and space that must be allotted for a spacecraft’s fuel, Nicolau says. Indeed, some chemicals recycled from pee can be used to generate electricity, according to his team (which includes NASA scientists).
The new recycling system relies on chemistry to pull pure water out of urine. Through a process called forward osmosis, it uses a concentrated salt or sugar solution. This draws the water from the urine and across a membrane barrier. A tank, called a bioreactor, uses enzymes to convert the leftover urea into ammonia. That ammonia is used to drive a fuel cell, which uses chemicals to produce electricity.
No shortage of raw materials
People urinate about 50 percent more each day than they drink, notes Sherwin Gormly. That’s crazy, you’re thinking: How could you pee out more than you take in? Well, for one thing, your body turns some of your food into water. (When you burn carbohydrates, your body makes energy with a side order of carbon dioxide and water.)
Gormly knows about such issues. As an engineer at NASA’s Ames Research Center in Mountain View, Calif., he helped design the system to recycle urine on the International Space Station. He now works for Desert Toad Water Technology Research in Carson City, Nev.
Managing water — including pee — ends up being one of the biggest obstacles to supporting people on a trip to Mars or any other distant space destination. Without urine recycling, water for a trip to Mars could take up 80 to 90 percent of the mass on a spaceship, Gormly says. Launching something into space can cost up to $10,000 per pound. So shooting mega-tons of water into space quickly becomes crazy expensive.
Any recycling system that people will rely on for months or years has to be extremely efficient. The space station’s system can reclaim 93 percent of the water on board. The new system that Nicolau’s team has developed still needs tweaking. But even in its early stages, it too recovers more than 90 percent of the water going into it.
It’s only generating a tiny trickle of electricity right now. In the lab, filtering one liter (or quart) of urine in eight hours produced about as much electricity as the static charge produced by rubbing a balloon on your hair. “Still,” says Nicolau, “our system is a proof of concept.” Now it’s up to engineers to make it work even better. Eventually, he says, it might produce enough power to run itself.
Another limitation: The system requires small amounts of oxygen to make that electricity. And oxygen, of course, is something else you’re going to need to travel in space. “We are using some breathable oxygen from the cabin,” Nicolau says. So the system would require another process to make up that lost oxygen. This might require breaking down water (via electrolysis) to recover some of its oxygen, or using other chemical processes.
The new recycling process does produce drinkable water. At least in theory it does. Nicolau admits that his team has not yet sampled any. The reason: It has not yet been tested for bacteria and other germs. He promises a photo, though, once he and his team are able to gather around the bioreactor and toast each other with glasses of a beverage made from recycled urine.
Closer to home
We could even get energy-producing urine recyclers here on Earth. “You could deploy this in developing countries where water is scarce,” Nicolau says. It also might appeal to military troops sent to remote desert sites.
If a future in which you drink water made from urine doesn’t sound attractive, think of it this way: Your drinking water already comes partly from the entire planet’s pee; it’s just been recycled a lot more slowly.
Yet one more use for urine at home and in space: growing food. Several years, ago, Finnish scientists reported fertilizing veggies with human pee. Their cabbages grew bigger — and had fewer germs — than those treated with regular fertilizer.
ammonia A colorless gas with a nasty smell. Ammonia is a compound made from the elements nitrogen and hydrogen. It is used to make food and applied to farm fields as a fertilizer. Secreted by the kidneys, ammonia gives urine its characteristic odor. The chemical also occurs in the atmosphere and throughout the universe.
astronaut People trained to travel into space for research and exploration.
carbohydrates Any of a large group of compounds occurring in foods and living tissues, including sugars, starch and cellulose. They contain hydrogen and oxygen in the same ratio as water (2:1) and typically can be broken down to release energy in the animal body.
carbon dioxide A gas produced by all animals when the oxygen they inhale reacts with the carbon-rich foods that they’ve eaten. This colorless, odorless gas also is released when organic matter (including fossil fuels like oil or gas) is burned. Carbon dioxide acts as a greenhouse gas, trapping heat in Earth’s atmosphere. Plants convert carbon dioxide into oxygen during photosynthesis, the process they use to make their own food.
chemistry The field of science that deals with the composition, structure and properties of substances and how they interact with one another. Chemists use this knowledge to study unfamiliar substances, to reproduce large quantities of useful substances or to design and create new and useful substances.
engineer A person who uses science to solve problems. As a verb, to engineer means to design a device, material or process that will solve some problem or unmet need.
fertilizer Nitrogen and other plant nutrients added to soil, water or foliage to boost crop growth or to replenish nutrients that removed earlier by plant roots or leaves.
fuel cell A device that converts chemical energy into electrical energy. The most common fuel is hydrogen, which emits only water vapor as a byproduct.
International Space Station An artificial satellite that orbits Earth. Run by the United States and Russia, this station provides a research laboratory from which scientists can conduct experiments in biology, physics and astronomy — and make observations of Earth.
mass A number that shows how much an object resists speeding up and slowing down — basically a measure of how much matter that object is made from.
National Aeronautics and Space Administration Created in 1958, this U.S. agency has become a leader in space research and in stimulating public interest in space exploration. It was through NASA that the United States sent people into orbit and ultimately to the moon. It has also sent research craft to study planets and other celestial objects in our solar system.
recycle To find new uses for something — or parts of something — that might otherwise by discarded, or treated as waste.
space shuttles The world’s first reusable vehicles, NASA’s five space shuttles (Columbia, Challenger, Discovery, Endeavor and Atlantic) ferried astronauts and cargo into orbit, including to service satellites (like the Hubble Space Telescope) and the International Space Station. The first shuttle launched on April 12, 1981. On July 21, 2011, a shuttle returned home for the last time. After that trip, the program was retired. In all NASA’s shuttles tackled 135 missions.
urea A nitrogen-rich chemical that the bodies of many animals produce after breaks down proteins, amino acids (the building blocks of proteins) or ammonia. People excrete excess nitrogen from the body — as urea — in urine. But many other mammals, amphibians and fish make urea as well. Synthetic urea is often a nitrogen source of plant fertilizers. In 1828, German chemist Friedrich Wöhler for the first time created urea in the laboratory. This discovery would lead to the widespread use of synthetic fertilizers in farming.
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