Biodiesel production from traditional oil-rich crops is limited by land availability, climate, and environmental and social issues regarding the use of feed and food crops for fuel. But there's another way to produce biodiesel that is green and sustainable and doesn't compete with food crops. All it takes is some yeast - and research from Iowa State University.

Well, it's not quite that simple, said Sam Beattie, an ISU Extension food safety specialist and the yeast expert on the ISU research team. And in a complicated research paper J. (Hans) van Leeuwen, a professor in the Department of Civil, Construction and Environmental Engineering, Beattie and other ISU researchers explain how they took lignocellulosic biomass - corn stover - treated it with ammonia and various wood rot fungi, then mixed it with yeast. The end results include yeast oil (which may be made into biodiesel), protein-rich animal feed and several usable co-products including lignin and gum.

The research won van Leeuwen, Beattie and their team the Grand Prize for University Research from the American Academy of Environmental Engineers. They received the award in Washington, D.C., earlier this month.

But to take this research from the laboratory to large-scale production requires an integrated bio-oil refinery, van Leeuwen said. What otherwise would be waste, in an integrated refinery can be recycled and converted into additional products.

"Our approach is to break down lignocellulosic materials to sugars using ammonia pretreatment and in-situ produced fungal enzymes, and convert these to oil using oleaginous yeasts," Beattie said.

"An integrated refinery will use virtually every part of the cellulosic biomass feedstock, resulting in a primary product of biodiesel, plus animal feed and co-products," van Leeuwen said.

The ISU researchers ran a cost analysis assuming the use of 1,000 tons per day of corn stover or switchgrass to produce 35,000 tons of yeast oil per year.

"The conversion of lignocellulosic material to lipids and yeast biomass is highly economical with a payback period of 2.5 years," van Leeuwen said. "The facility in this cost analysis could produce 70 million pounds of oil annually, equivalent to the oil extracted from more than 7 million bushels of soybeans (9.8 pounds of oil per bushel), which is equivalent to 143,000 acres or 223 square miles of soybean crop (at 50 bushels per acre)."

van Leeuwen added, "The concept is therefore very green and sustainable and not competitive with food crops. The process itself is non-polluting and carbon negative when allowing for the carbon dioxide recycled into new crops."

Source: Iowa State University Extension