Photo by Tom Campbell

Professor Nathan Mosier fine-tunes the tactical biorefinery that Purdue scientists helped develop for the U.S. Army to turn waste into electricity

The problem with garbage is just that — it is waste, and it uselessly takes up space. But what if you could turn garbage into something useful?

Scientists at Purdue are turning this science-fiction hypothetical into reality: They have created a portable refinery that efficiently converts food, paper and plastic rubbish into electricity.

The machine, designed for the military, would allow soldiers to convert field waste into power at remote locations anywhere in the world, and could have widespread civilian applications in the future.

"This is a very promising technology," says Michael Ladisch, a professor of agricultural and biological engineering who leads the project. "In a very short time, it would be ready for use in the military, and I think it could be used outside the military shortly thereafter."

The "tactical biorefinery" processes several kinds of garbage at once and converts it into fuel via two parallel processes — and then burns the different fuels in the same diesel engine, which powers a generator and which initially powered the conversion of some of the materials into fuel.

Roughly the size of a U-Haul trailer, the biorefinery could provide soldiers with electricity in remote locations while simultaneously disposing of waste. This would alleviate the expense and potential danger associated with transporting waste and fuel. And, by eliminating trash, it could also protect a military unit's security, since garbage may reveal valuable information about a unit's location, movement and activities.

"We've designed a device that converts military field waste into electrical energy, and we've shown that it works very well," says Jerry Warner, founder of Defense Life Sciences LLC, a collaborating company based in McLean, Va. "I believe the biorefinery could be of immediate use to our military personnel after we complete the fine-tuning process."

Ladisch and Warner say they could see the biorefinery used in a disaster situation such as Hurricane Katrina or any crisis in which people are stranded in areas without power. The machine could turn debris such as wood chips, organic material and assorted garbage into electricity.

The biorefinery first separates organic food material from residual trash, such as paper, plastic, Styrofoam and cardboard. The food waste goes to a bioreactor, where industrial yeast ferments it into ethanol. Residual materials go to a gasifier, where they are heated under low-oxygen conditions and eventually become producer gas, or low-grade propane and methane. The gas and the ethanol then become the fuel for a modified diesel engine that powers a generator. The only residue from the two processes is a small amount of ash that must be removed from the biorefinery every two or three days.

In November, the researchers fired up the machine and demonstrated that it produced 90 percent more energy than it consumed, Warner said. The U.S. Army subsequently commissioned the tactical biorefinery, signifying that the team had successfully completed a functional prototype. In December, Army officials presented Army Certificates of Appreciation to the researchers, including Ladisch and Nathan Mosier, a professor of agricultural and biological engineering.

The next steps are to improve the existing prototype and build a second, after which the devices will be tested on-site at an overseas location.

Ladisch foresees a time when the biorefinery could be used at a variety of factories, restaurants or stores.

"The biorefinery could probably be used to generate a little extra electricity at any place that generates a fair amount of food and scrap waste," he says. "This could help reduce electricity costs, and you might even be able to produce some surplus energy to put back onto the electrical grid."

The biorefinery is also earth-friendly, Mosier says, because much of the fuel it combusts is carbon-neutral. Carbon-neutral fuels — such as ethanol — do not cause a net increase in atmospheric carbon dioxide because they release carbon that already was in the atmosphere until it recently was taken up by a plant during photosynthesis. The same is not true for petroleum, because its carbon contents were removed from the atmosphere millions of years ago.

Contact Ladisch at ladisch@purdue.edu