More bang for the biofuel buck

Microbes that ferment ethanol from glycerol, a by-product of biodiesel production, could add an economically valuable new ingredient to the biofuel industry, researchers report.

Industrial plants that make biodiesel by processing vegetable oils and animal fats churn out about 10 kilograms of glycerol for every 100 kg of fuel. Increasing biodiesel production has generated a glycerol glut, with much of this previously useful product now going to waste. Its market value has plummeted by 90 percent since 2004.

But certain microbes can anaerobically ferment glycerol into biofuels and other marketable chemicals, say Ramon Gonzalez and his colleagues at Rice University in Houston in the June Current Opinion in Biotechnology.

The researchers tweaked growth conditions for Escherichia coli so that the bacteria efficiently produced ethanol from glycerol in a benchtop fermenter. Although the process is currently about 40 percent slower than yeast fermentation of ethanol from corn, Gonzalez adds that genetic engineering of the bacteria could make fermentation faster. Other microbes can ferment glycerol to make useful industrial chemicals such as succinic acid and 1,3-propanediol, he says.

If the new process can be made to work on an industrial scale, it could enhance the economics of the biodiesel industry. “In one single plant they will get two biofuels—the biodiesel and the bioethanol,” Gonzalez says.

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