What can one possibly do with almost a half ton of rancid butter? Make biodiesel.

As one bioenergy specialist stresses, waste, in a manner of speaking, is being defined down. The growing interest in biofuels is forcing more Americans to reassign value to materials, particularly discarded fats, oils and grease, previously considered close to worthless.

That insight was driven home to organizers at the conclusion of the 2007 Pennsylvania Farm Show, held in Harrisonburg.

They needed to find some constructive way of getting rid of an 800-pound sculpture of Benjamin Franklin and the Liberty Bell made entirely from butter, which, at the conclusion of the event, had turned rancid.

That's when Michael Haas, a research biochemist at the United States Department of Agriculture, stepped forward with a suggestion: Turn it into biofuel.

As it turns out, Hass had previously collaborated with BlackGold Biofuels, a Philadelphia-based company, to convert a wide array of non-edible, low-value fats, oils and grease into biofuels.

And it makes perfect sense, experts say. Butter, after all, is a fat.

The 800-pounds of butter ultimately were converted into a 75-gallon mixture of biodiesel fuel and lower-grade bunker fuel, the New York Times reports.

Granted, Haas and other researchers are not advocating that the roughly billion pounds of butter produced in the United States should be converted into biodiesel.

Still, there is a lesson to be gained, says Mark Hall, an Alabama Cooperative Extension System bioenergy specialist who works with Alabama municipalities and other public and private entities to develop renewable energy projects.

Many of the products once discounted as utterly worthless could bring Americans considerably closer to energy self-sufficiency, he says, adding that this holds especially true for inedible oils, fats and grease.

In fact, Hall says the growing interest in renewable energy should challenge the way we define waste.

"We really do need to challenge people on this whole concept of waste," he says. "Is it waste or simply an unused resource?

In a disturbing number of instances, Hall says, what is being stuck in a landfill or emptied in a sewer could just as easily be converted into renewable energy.

Within the past few years, Hall, along with Auburn University's Center for Bioenergy and Bioproducts, has worked with roughly a dozen Alabama municipalities to explore ways that discarded cooking oil and similar cooking byproducts could be converted into biodiesel fuel to power city vehicles.

One of the state's most successful examples is in Gadsden. The practice not only provides a potential cost savings for cities but also relieves many small restaurants of the significant financial burden of disposing of these waste products on their own.

City infrastructures benefit too: With more cooking oil collected for city fleets, far less remains to clog sewer lines and or to place further strain on over-burdened landfills, Halls says.

Even so, Hall says the uses of oils and grease are only a few examples of how the growing interest in bioenergy is redefining our concept of waste.

Until a few years ago, the bulk of debris from commercial timber cutting was left to decay or was hauled off to landfills. Now much of is transported to biodiesel plants where its cellulose is converted into biofuel.

"More and more, the growing demand for bioenergy is forcing us to think out of the box and to ask ourselves the question: Is it really trash or could it be redeployed someplace else?" Hall says.

But the growing demand for biofuels may even force a redefining of some products already considered highly lucrative for other uses.

Hall cites hay, an excellent source of cellulose in addition to a highly efficient cattle feed, as a prime example.