Bacteria Convert Biodiesel Waste Into Valuable Chemicals

"Biodiesel producers used to sell their leftover glycerin, but the rapid increase in biodiesel production has left them paying to get rid of it," said lead researcher Ramon Gonzalez, an assistant professor in chemical and biomolecular engineering at Rice.

"The new metabolic pathways we have uncovered paved the way for the development of new technologies for converting this waste product into high-value chemicals," he said.

The latest research is published in the journal "Metabolic Engineering." The paper and others published earlier this year describe a new fermentation process that allows E. coli and other bacteria to convert glycerin - the major waste byproduct of biodiesel production - into formate, succinate and other useful organic acids.

One of the acids produced, succinate, is a chemical feedstock used to make everything from noncorrosive airport deicers and nontoxic solvents to plastics, drugs and food additives.

In nutraceutical form as a food additive and dietary supplement, it is approved by the U.S. Food and Drug Administration.

Most succinate used today is derived from nonrenewable fossil fuels.

The rapidly growing biodiesel industry is flooding U.S. and international markets with glycerol, also called glycerin, a by-product of biodiesel production. For this reason, Gonzalez says, research into the conversion of glycerin into other useful products "has the potential to revolutionize this industry and dramatically improve its economics."

About one pound glycerol is created for every 10 pounds of biodiesel produced.

According to the National Biodiesel Board, U.S. companies produced about 450 million gallons of biodiesel in 2007, and about 60 new plants with a production capacity of 1.2 billion gallons are scheduled to open by 2010.

Crude glycerin, a byproduct of biodiesel production, can vary in color, depending on the material it was derived from. (Photo by Brian Kerr courtesy USDA Agricultural Research Service)

If glycerol is refined to 99 percent purity, it can be used in pharmaceuticals, foods, drinks, animal feed, soap, cosmetics and toiletries. But supplies have been outstripping these uses, and some producers have been caught illegally dumping their waste glycerol.

Gonzalez's team last year announced a new method of glycerol fermentation that used E. coli to produce another biofuel - ethanol.

Even though the process was efficient, with operational costs estimated to be about 40 percent less that those of producing ethanol from corn, Gonzalez said new fermentation technologies that produce high-value chemicals like succinate and formate hold even more promise for biodiesel refiners because those chemicals are more profitable than ethanol.

"With fundamental research, we have identified the pathways and mechanisms that mediate glycerol fermentation in E. coli," Gonzalez said. "This knowledge base is enabling our efforts to develop new technologies for converting glycerol into high-value chemicals."

"The reason this probably hadn't been discovered before is that E. coli requires a particular set of fermentation conditions for this pathway to be activated," Gonzalez said. "It wasn't easy to zero in on these conditions, so it wasn't the sort of process that someone would stumble upon by accident."

Once the new metabolic pathways were identified, Gonzalez's team began using metabolic engineering to design new versions of E. coli that could produce a range of high-value products.

While ordinary E. coli ferments glycerol to produce a little succinate, Gonzalez's team has created a new version of the bacterium that produces up to 100 times more.

Gonzalez said he has had similar success with organisms designed to produce other high-value chemicals, including formate and lactate.

"Our goal goes beyond using this for a single process," he said. "We want to use the technology as a platform for the green production of a whole range of high-value products."

Technologies based on Gonzalez's work have been licensed to Glycos Biotechnologies Inc., a startup company based in Houston that plans to open its first demonstration facility within the next 12 months.

The research was supported by the U.S. Department of Agriculture, the National Science Foundation, Rice University and Glycos Biotechnologies Inc.

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