August 25, 2004
Purdue agriculture, engineering create out-of-this-world recycling
WEST LAFAYETTE, Ind. - In possibly the ultimate in recycling, people who voyage to Mars may be able to quench their thirst with water recovered from waste.
Purdue University engineers and agronomists are testing plants to identify ones that can grow normally when fed sewage. The circle of life would be complete when drinkable water is reclaimed from the plants.
"One of the bigger challenges that will prevent human habitation on the moon or Mars is having a constant source of water," said Jeff Volenec, a crop physiologist in the Department of Agronomy. "For four to six astronauts to go to Mars, water is precious stuff."
He estimates that Mars travelers will be able to take only a little more than 1,000 gallons of water each due to space limitations, both on the vehicle and at a red planet settlement. The trip is expected to take about seven months each way, and the astronauts would remain on Mars for six to 18 months.
"When you think of the tens of thousands of gallons of water a family goes through in a month, 1,000 gallons isn't much," Volenec said.
The National Aeronautics and Space Administration funds the water salvage project as part of its Specialized Center of Research and Training (NSCORT) for Advanced Life Support. Purdue researchers lead the center under a $10 million, five-year grant to invent ways to make life on Mars possible.
Cary Mitchell, Purdue horticulture professor, is NSCORT/Advanced Life Support director. The center is a multidisciplinary effort that includes 24 researchers from Purdue, Howard University and Alabama A&M University.
"It will cost $140,000 per pound to launch anything from Earth to Mars," Mitchell said. "NASA wants to make sure that equipment and cargo needed for any system is minimized."
The water recycling project would transport seed or plant cuttings to grow the necessary vegetation on Mars and a special bioreactor to process waste. The astronauts also would need equipment to recover water from the greenery.
Volenec and his team are working with James Alleman, a Purdue civil engineering professor, to process solid waste in a special bioreactor and then reclaim the water through various plants grown in the liquid sewage. This project began about 16 months before President George W. Bush announced plans to send people back to the moon by 2015 and then on to Mars. Johnson Space Center in Houston is already the site of a village similar to those travelers from Earth would build on Mars. This village provides NSCORT researchers with a preview of the area potentially available on the red planet for growing crops for food and for recycling water.
As part of Purdue NSCORT projects, NASA gave Alleman and his group a $49,000 toilet with which to collect human waste. It's similar to an airline commode, which uses very little water.
The specialized toilet is located on the third floor of the Purdue civil engineering building. The waste flows through white PVC piping to a second-floor storage tank where researchers add food waste and plant waste in an effort to duplicate the type of material that would be processed on Mars. After that, the mixture is funneled into the bioreactor for processing to a useable consistency.
In order to live on Mars, astronauts will need innovative systems to reuse the waste products of daily life including human excrement, leftover food, and unusable and dead parts of plants. The water recovery project and others using the processed waste are part of the effort to meet that need.
"What we're doing is radically different than what is being done on the space station," Alleman said. "If you use a toilet there, you put a lid on top of the toilet, and then you open a valve to a port outside the spacecraft and sewage just evaporates. On the space shuttle, they've recently just been bagging the waste and bringing it back to Earth."
The bioreactor Alleman's team developed is like "nothing on Earth" or in space, he said. Called the "solids thermophilic aerobic reactor," or STAR, it originally was invented to treat hog manure by using bacteria, heat and circulated air to break down refuse.
The waste-eating bacteria used in the bioreactor are called thermophiles because they only survive at very hot temperatures. When STAR is processing waste, temperatures are more than 140 degrees Fahrenheit, Alleman said. Oxygen is pumped into the reactor, which, in combination with the high temperatures, keeps the bacteria alive. The microbes don't pose a health threat because they can't live in the same environment as people.
After STAR processes the waste for 10 days, Volenec and other researchers use some of the resulting material for their various NSCORT projects.
Volenec has been testing plants in different categories - grasses, legumes such as clover, and food crops. The goal is to find plants that grow well when fed the processed waste, which is about the consistency of diluted tomato soup and composed of approximately 97 percent water and 3 percent solids, Volenec said.
One of the first stumbling blocks in his waste-to-water project was to find something akin to Martian dirt. First, Volenec tried coarse river sand, because NASA couldn't give his team enough of the space agency's simulated soil. The dirt at the Martian village model in Houston is volcanic ash from Hawaii. Volenec's group now has switched to pea gravel that allows more oxygen to reach the plant roots.
So far food crops, such as tomatoes and peppers, wither in the processed waste. Even rice, which generally grows partially underwater, has not prospered under effluent ranging in depth from one-half inch to two inches. But Volenec is not concerned with producing food. Other NSCORT projects are focusing on that.
"We shovel the processed waste onto the plants, almost like a mini-marsh," he said. "Then we use the plants to filter water out. We'll recover the water in the atmosphere above the plant by running it through a 'cold finger,' much like pipes sweating in restrooms. Using something cold condenses the water so that it can be captured."
The plants that grow well in the sewage could serve as livestock or fish feed, or to cultivate mushrooms the astronauts may take along as protein sources, he said. The dead plants also could be fed into the bioreactor for decomposition by the microbes.
Among the plants that have grown well in the sewage mixture are tall fescue, reed canarygrass, switchgrass and some types of clovers. Like a lawn, these plants can be mowed or clipped, and the clippings can be further recycled.
Reed canarygrass previously has been shown to grow well in as much as one gallon per square foot of hog and bovine manure, Volenec said. However, further testing is necessary using the new waste mixture and different vegetation. The next candidate plants will be wetland varieties.
NSCORT director Mitchell said Volenec's project will provide data that NSCORT and NASA need to determine the combinations of technologies necessary to sustain life in various Mars and moon mission scenarios. One life-support system might be needed aboard the spacecraft as people travel to the moon and Mars. A different system, or combination of several systems, might be required at the destination.
Whether such things as water and energy sources are found on the moon or Mars also will impact which life-support systems are used, Mitchell said.
Allocation of space makes choice of plants for water recovery crucial, Volenec said. The optimum would be to use only 20-50 square feet in the Martian colony. This means the plants must be a manageable size, thrive in large amounts of effluent without dying, and be very efficient in their water and nutrient recovery.
"Failure is not an option; these plants can't die," Volenec said. "If they do die, the astronauts die."
Writer: Susan A. Steeves, (765) 496-7481, firstname.lastname@example.org
Sources: Jeffrey Volenec, (765) 494-8071, email@example.com
James Alleman, (765) 494-7705, firstname.lastname@example.org
Cary Mitchell, (765) 494-1347, email@example.com
Related Web site:
A publication-quality photograph is available at http://ftp.purdue.edu/pub/uns/+2004/volenec-mars.jpg
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