Environmental Protection

Keerthi Venkataramanan

Bacteria Eats Glycerol and Makes New Products

A University of Alabama graduate student is using Clostidium pasteurianum bacteria to break down a biodiesel waste product and find uses for its byproducts: butanol, propanediol, and ethanol.

A strain of bacteria found in soil is being studied for its ability to convert waste from an alternative fuel into other useful materials, including another alternative 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 doctoral 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 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 United States 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.

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

The bacteria use 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.

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.

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