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United States Department of Agriculture

Agricultural Research Service

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Trap Grease!

Have you ever watched a hamburger or a piece of bacon frying in a pan? If you have, you know that the pan quickly fills with grease.

If you're only making one hamburger, that's not a lot of grease. But what if you make 200 hamburgers? For restaurants, grease can be a big problem. Foods like hamburgers and French fries create a lot of grease, and restaurant owners need to get rid of it when they finish cooking.

So where does it go? Sometimes it gets washed down the drain. If you go to a pizza parlor, the restaurant will clean your dishes after you eat, and any grease left on them will be washed off. Restaurants and food companies trap that grease in their drains and collect it before it can clog up the sewers. They call it "trap grease."

U.S. restaurants collect millions and millions of gallons of trap grease every month! It looks gross, it smells gross, and it's totally useless. Or is it?

Mike Haas, an ARS biochemist in Wyndmoor, Pa., is working with a company called "Philadelphia Fry-o-Diesel" (PFOD). They want to demonstrate that trap grease can be converted into biodiesel, a clean-burning, renewable fuel for diesel engines.

Clean-burning means it won't make a lot of pollution. And renewable means that it's easy to get more of it. Biodiesel is made using things that grow on our farms.

Every year, farmers raise crops and animals that produce more fats and oils that can be used to make fuel.

Using this technology, Americans could someday use biodiesel made from restaurant grease to run their buses, trucks and cars! Biodiesel is fuel made from natural, biological ingredients. It's renewable (unlike fossil fuels, which take millions of years to form) and it's environmentally friendly.

Right now, trap grease is unmarketable, which means that nobody wants it, and restaurants have to pay people to get rid of it. This can be expensive. And sometimes the grease doesn't go into the trap. If the collectors are sloppy, or if restaurant owners don't maintain their grease traps, the grease can spill—clogging sewers and polluting water.

PFOD and Haas are researching whether trap grease can be used to make biodiesel. Haas and ARS biologist Karen Scott looked at trap grease samples, helped design a trial operation, and analyzed the trial results.

So far, they've created the chemical compounds that make up biodiesel (called "fatty acid methyl esters") from trap grease. There's some neat science behind this, but basically it means taking fatty acids from the restaurant grease and combining them with methanol, a kind of alcohol, to make a liquid that burns like diesel fuel in an engine.

This is the first step towards making biodiesel from trap grease. Now the researchers have to develop ways to make the biodiesel in large batches, not just small amounts in their laboratory.

If successful, this research could solve many problems someday. Giving trap grease a new purpose would reduce waste and create a valuable new market for it. Water quality would improve. Cleaner-burning diesel fuels would improve air quality. And we would be making fuel with products grown on American farms.

—By Laura McGinnis, formerly, Agricultural Research Service, Information Staff


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Last Modified: 8/12/2016
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