Five minutes behind a school bus and you know pretty much what you need to know about diesel fuel. It’s dirty, it smells bad, and it’s right up there with coal-powered power plants in contributions to global pollution. All of which may be beginning to change, in fits and starts, thanks to the increasing popularity of biodiesel fuel.

Biodiesel is diesel fuel made from vegetable or animal fats. The common “feedstocks” are soybean oil, canola oil, animal fat and restaurant waste oil, also called “yellow grease.” The current industry standard–the biodiesel most frequently in use today–is a blend of 20 percent pure biodiesel and 80 percent petroleum diesel. That blend, known as B20, is already in relatively wide use, and not just by the local organic farmer. Several local municipalities, including the cities of Durham, Raleigh, Chapel Hill, Cary and Garner all use biodiesel fuel in a least a portion of their fleets. Across the country, government and private business used 20 million gallons of biodiesel in 2003, a figure the U.S. Dept. of Energy expects to double with each year.

This is the science of biodiesel, in a soybean shell: Like petroleum diesel, biodiesel works in compression-ignition engines. The fats and oils used in biodiesel are filtered and processed to remove contaminants; these oils and fats are then mixed with an alcohol, like methanol, and a catalyst such as sodium or potassium hydroxide. The triglycerides, or oil molecules, reconstitute into esters, a fuel, and glycerol, a by-product often used in drugs and cosmetics. Biodiesel blends can be used in any diesel engine; pure biodiesel (B100) can be used in engines built since 1994. (Buy yours at the Durham Exxon at the corner of Roxboro Road and N. Duke Street!)

Because biodiesel fuel is made with new or used vegetable oils, which are non-toxic, biodegradable and renewable and home-grown, the environmental benefits are enormous. Use of biodiesel, even blended with petroleum diesel, reduces emissions of carbon monoxide, particulate matter, toxic contaminants, sulfur dioxide and hydrocarbons. And vehicles running on pure biodiesel don’t smell bad or smoke the way conventional diesel cars and trucks do.

The cost of biodiesel varies with the feedstock. It takes about seven pounds of soybean oil to produce a gallon of biodiesel. At 20 cents a pound, that’s about $1.50 per gallon of soy biodiesel. Used restaurant oil, which is less expensive while producing the same quality fuel, lowers the cost to about $1.00. Overall, with production and transportation costs, biodiesel is more expensive to produce than petroleum diesel, but government subsidies have kept prices for the alternative fuel competitive. (Biodiesel is used in many federal, state and local public utility fleets to help meet requirements for using alternative fuels.)

Most newer diesel engines can run without problems on pure biodiesel, rather than the B20 blend currently popular in the market. The trick, of course, for environmentalists pushing biofuels is to get the current oil-friendly administration to accept a true substitute for petroleum. The cynical view, of course, is that incentives for biodiesel will last only so long as the fuel doesn’t threaten the oil industry. Until then, B20 is about as good as it gets.