Science

Astronaut pee to be bottled for water in space

by William Atkins

Friday, 23 March 2007

Millions are spent to transport water to crew members at the International Space Station (ISS). NASA has a better idea: Recycle urine from humans and lab animals and water used for washing and other necessities to make water better than from any city tap.

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Would it make you squeamish to drink recycled rat pee? It shouldn’t because NASA's high-tech water recovery system (WRS) will recycle this waste water—everything from humidity taken through respiration, perspiration, and microwave use to used water of hand washing, showering, toothbrushing, and even urine—to make drinkable water.

Plus, it will save NASA millions of dollars each year. NASA scientists estimate that the recycled water is thousands of times better than the water taken from water treatment plants on the Earth.

Currently, each ISS crew member uses about 4.4 liters (1.2 gallon) each day for various needs. Even with a limited Russian water processor now in use, it still costs about $24 million to transport water up to the ISS each year. NASA estimates that one liter of water costs about $11,000.

Hoping to transport the WRS machine to the ISS via Shuttle Discovery in October 2008, the machine will recycle about 93% of all water used on the station. About 85% of expelled urine will be reused.

The process entails using a chemical dispenser to add sulfuric acid and chromium trioxide to the waste water. The mixture is then spun with a distillation cylinder to separate the urine from the water. It is then heated so the water evaporates, leaving the urine behind in a urine tank. A compressor pressurizes the water vapor so it condenses onto the outer surface of the cylinder, called a brine tank. The brine water is re-circulated through the distiller (distillation cylinder) until almost all of the water is recovered.

The brine is then combined with other waste water (like from brushing teeth and shaving) where it is scrubbed in a water processor assembly. A particle filter traps larger impurities while multiple filtration beds remove dissolved contaminants. Activated carbon takes out organic compounds and an ion-exchange resin removes inorganic compounds. The remaining water then flows into a catalytic reactor that heats the water to around 130 degrees Celsius (265 degrees Fahrenheit) (to remove bacteria) and injects oxygen gas (to oxidize alcohol and ethanol into carbon dioxide). The carbon dioxide and other impurities are removed by ion-exchange beds. The water is monitored so that only the water that is ready to drink is stored in a clean water tank.

So next time you go to a convenience store for bottled water, would you dare ask for that purified NASA rat pee water?

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