A group of scientists at Purdue University have created a portable refinery that efficiently converts food, paper and plastic trash into electricity. The machine, designed for the U.S. military, could have widespread civilian applications in the future.

"This is a very promising technology," said Michael Ladisch, the professor of agricultural and biological engineering at Purdue University who leads the project. "At any place with a fair amount of food and scrap waste the biorefinery could help reduce electricity costs, and you might even be able to produce some surplus energy to put back on the electrical grid."

The "tactical biorefinery" processes several kinds of waste at once, which it converts into fuel via two parallel processes. The system 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, a "green" fuel. Residual materials go to a gasifier where they are heated under low-oxygen conditions and eventually become low-grade propane gas and methane. The gas and ethanol are then combusted in a modified diesel engine that powers a generator to produce electricity. Ladisch said the machine's ability to burn multiple fuels at once, along with its mobility, make it unique.

Researchers tested the first tactical biorefinery prototype in November and found that it produced approximately 90 percent more energy than it consumed, said Jerry Warner, founder of Defense Life Sciences LLC, a private company working with Purdue researchers on the project.

The biorefinery generator initially runs on diesel oil for several hours until the gasifier and the bioreactor begin to produce fuel, Warner said. In the initial commissioning test, researchers measured the amount of diesel oil burned and electricity produced to calculate its efficiency.

The machine produces a very small amount of its own waste, Warner said, mostly in the form of ash that the Environmental Protection Agency has designated as "benign," or non-hazardous. Any leftover materials from the bioreactor are put into the gasifier, which has to be emptied every two to three days.

"It's about enough to fill a regular sized trash bag, and it represents about a 30-to-1 volume reduction," Warner said.

Source:
Purdue University News Release (http://news.uns.purdue.edu/x/2007a/070201LadischBio.html)