Aquatic Alchemy

Article excerpt

The average Earthbound American, estimates the U.S. Environmental Protection Agency (EPA), uses nearly 24 gallons of water daily for personal uses such as drinking, toilet flushing, hygiene, and cleaning. International Space Station (ISS) crew members, on the other hand, are limited to little more than half a gallon per day. Yet, with that little bit of water weighing about 5 pounds and the cost of lifting something into low Earth orbit reaching as high as $10,000 per pound, it would make far better economic sense to provide astronauts with water on-site.

Aerospace engineers are busy working on a modern-day form of alchemy, finding new ways to find water in space without having to lug it along from Earth. And while many of the technologies are being developed with an cyc toward the stars, certain aspects may be suitable for use here at home on planet Earth.

Pulling Water from the Air

Every time an astronaut exhales, washes up, or urinates, water is involved. In an effort to minimize the amount of fluid lifted into orbit, the National Aeronautics and Space Administration (NASA) is seeking ways to recapture that water, clean it, and store it for reuse.

The ISS currently provides clean water through the use of a water recovery system that reclaims wastewater such as used oral hygiene water, urine, and cabin humidity condensate. But the space environment offers unique challenges to the provision of water. For example, water must contain no dissolved gases, as gas doesn't separate well at zero gravity, either in tanks or in the body. Therefore, the water must be purified to a level exceeding EPA standards for Earth drinking water. The water recovery system consists of a urine processor assembly (essentially a still that boils off water, leaving a thick waste layer behind) and a water processor assembly developed by researchers at NASA's Marshall Space Flight Center and Hamilton Sundstrand Space Systems International.

According to Dave Parker, program manager for Hamilton Sundstrand's water processor program, the water processor assembly is a multistage system that uses filters to remove particulate matter and salts. The water is then run through a catalytic oxidizer to remove low-molecular-weight organic molecules such as alcohols. This part of the process takes place at a temperature of 275[degrees]F and under pressure so it doesn't flash to steam, Parker explains. The system then removes any by-products and remaining dissolved gasses. Finally, the fluid goes through an ion exchange process to remove the oxidation products.

This process, according to Parker, can produce about 1.5 gallons of treated water per hour, and uses approximately 700 watts of power. To reduce maintenance times and the volume of" consumables that must be delivered from Earth, the system has been designed with an 80- to 90-day change-out schedule for particulate filters, and a 60- to 70-day schedule for chemical filters, with no more than 12 hours of maintenance time required per year.

The water processor assembly is designed to provide limited amounts of highly purified water with minimal energy consumption and maintenance, but Parker believes the system could be scaled up for Earth usage. "We're producing as nearly pure potable water as you're likely to find anywhere," he says. "The question you'd have to answer on Earth is whether you need water of that purity."

Parker suggests the system could perhaps be used in military applications, to protect crews against chemical or biological attack, or aboard naval vessels. Another potential use is in hospitals, where high-quality water is important. "We're also working with the Army to design a system to create potable water from diesel exhaust," he says.

There are also substances often encountered in terrestrial water that you'll never find aboard the space station, such as arsenic, mercury, and heavy metals, but Parker says the water processor assembly could be adjusted to deal with these substances in a limited-application water stream. …