Bugs Might Convert Biodiesel Waste Into New Fuel

A graduate student at The University of Alabama in Huntsville is developing biological tools to make products from crude glycerol — a waste material from the production of biodiesel. The research is being funded by the National Science Foundation.

Disposing of glycerol has been a problem for the biodiesel industry, according to Keerthi Venkataramanan, a student in UAHuntsville's biotechnology Ph.D. program. “Many companies have had problems disposing of it. The glycerol you get as a byproduct isn't pure, so it can't be used in cosmetics or animal feeds. And purifying it costs three times as much as the glycerol is worth.”

The volume of glycerol produced is also daunting: About 100,000 gallons of glycerol is produced with every million gallons of biodiesel manufactured from animal fats or vegetable oils. (In 2009 more than 500 million gallons of biodiesel were produced in the U.S. while more than 2.75 billion gallons were produced in Europe.)

Two major American companies “were made to close biodiesel plants in Europe because they couldn't dispose of their crude glycerol,” Venkataramanan said.

He is working with the Clostidium pasteurianum bacteria, which “eats” glycerol and produces several potentially useful byproducts.

“This strain is found deep in the soil,” he said. “It was originally studied for its ability to 'fix' nitrogen from the air.”

The bacteria uses glycerol as a carbohydrate source. From that they produce three alcohol byproducts — butanol, propanediol and ethanol — plus acetic acid and butyric acid. Butanol is a particularly interesting byproduct.

“Butanol is a big alcohol molecule, twice as big as ethanol,” Venkataramanan said. “You can use it as an industrial solvent and it can be used in cars, replacing gasoline with no modifications. It doesn't have some of the problems you have with ethanol, such as rapid evaporation. And ethanol is a two-carbon molecule, but butanol is a four-carbon molecule so its energy value is much higher. In fact, there are plans to use it for jet fuel.

“You can also get butanol from crude oil, but this biological process is less polluting.”

In their present form, the bacteria convert about 30 to 35 percent of their gylcerol meals into butanol and another 25 to 30 percent into a chemical used to make plastics.

Venkataramanan is looking at different strategies to improve that yield. He is also studying the bacteria's genes to see if a more productive strain can be bioengineered.

Other groups in the U.S. and abroad are studying a variety of fungi, bacteria and algae for glycerol conversion, but Venkataramanan says his strain has several advantages. Some of the bacteria being studied are dangerous pathogens, while Clostidium pasteurianum “is a completely non-pathogenic strain,” he said. “An accidental release is not a big deal. You get it from the soil, so if you spill any you're putting it back in the soil.”