Ethanol from waste

The first license for a strain of yeast developed at Purdue University that makes ethanol from agricultural residues more effectively has been issued to biotechnology company Iogen.

The first license for a strain of yeast developed at Purdue University that makes ethanol from agricultural residues more effectively has been issued to biotechnology company Iogen.

Purdue’s genetically altered yeast allows about 40% more ethanol to be made from sugars derived from agricultural residues, such as corn stalks and wheat straw, compared with “wild-type” yeasts that occur in nature.

Agricultural residues are primarily made up of cellulose and hemicellulose, which are known as cellulosic materials. Unlike traditional ethanol feedstocks, such as corn kernels, the cellulosic materials contain two major sugars, glucose and xylose, which cannot both be fermented into ethanol by natural Saccharomyces yeast, the microorganism used by industry to produce ethanol.

Unfortunately, Xylose makes up about 30% of the sugar from agricultural residues. So the Purdue researchers altered the genetic structure of the natural yeast so that it contains three additional genes that make it possible to simultaneously convert glucose and xylose to ethanol. The ability to ferment xylose increases the yield of ethanol from straw by about 40%.

“It would cost too much money to separate the two sugars before proceeding with fermentation to ethanol, so being able to ferment both sugars together to ethanol is critical,” she said. “To be more cost competitive with gasoline, the two sugars have to be converted together to ethanol,” said Nancy Ho, a senior research scientist and leader of the molecular genetics group in Purdue’s Laboratory of Renewable Resources Engineering, or LORRE.

“Until we developed our yeast, no suitable microorganism could convert these two sugars together,” she added.

Iogen has obtained a non-exclusive license from the Purdue Research Foundation for the yeast and related patents. Its Ottawa, Canada, demonstration facility is the first plant in the world to produce ethanol from cellulosic materials. Iogen is using the Purdue yeast to produce ethanol from the sugars the company derives from wheat straw.

“We have confirmed that Purdue’s recombinant glucose- and xylose-fermenting yeast is the most effective microorganism available for the production of ethanol from cellulosic materials,” said Jeffrey S. Tolan, senior research scientist for Iogen. “The ethanol yield and productivity from the Purdue yeast in our plant matches that obtained by Dr. Ho’s group in the lab at Purdue.”

The ethanol made in Iogen’s plant is blended into gasoline at the Petro-Canada refinery in Montreal. Cars use the ethanol-gasoline blend without any modifications; typically, drivers are not even aware of the presence of the ethanol, except for the label on the petrol pump. The Ottawa plant represents the latest step toward Iogen’s goal of making ethanol from cellulosic materials widely available as a fuel, Tolan said.

In Iogen’s process, about two-thirds of the straw is converted to ethanol, with a yield of about 75 gallons of ethanol per ton of straw. Most of the remaining one-third of the agricultural residue, which cannot be fermented, is burned to generate power to run the plant, and there is little waste or use of fossil fuels, he said.