Researchers Find Fuel in Odd Places

While much of the national attention on biofuels has been directed at corn-based ethanol, NC State researchers are looking at creating fuel from everything from animal fat to pond scum. Even microbes that eat carbon dioxide while producing ethanol are being investigated as a possible future source of fuel.

The focus on corn for fuel production has shifted thousands of acres from agricultural production into the ethanol pipeline, raising food prices in the process as U.S. demand for corn-based ethanol begins to outstrip the amount of available crop. Producing enough ethanol to replace gasoline in the U.S. for a single day would require more than 100 million acres of corn—more than farmers nationwide have planted this year. “You plant corn and get one crop a year,” says Dr. Jay Cheng, an associate professor in the Department of Biological and Agricultural Engineering (BAE). “We need to develop sources for fuel that
are more renewable and won’t divert our nation’s
food resources.”

Cheng and Dr. Anne-Marie Stomp, an associate professor of forestry, believe duckweed fits the bill on both counts. The tiny aquatic plant, which creates a scum on the surface of ponds, doubles its mass every few days and can be manipulated as it grows so that up to three-quarters of that mass is starchy content that can be broken down and fermented into ethanol. Because the duckweed can be harvested almost daily, it can produce four times the amount of ethanol per acre as corn, says Stomp, who previously modified the plant to produce proteins for pharmaceuticals.

The two NC State professors recently won a grant from the North Carolina Biofuels Center to grow duckweed on hog-waste lagoons in eastern North Carolina for ethanol production. The plant consumes the excess nutrients from waste lagoons, cleaning the water as it grows. Farmers would need to be trained to grow and harvest duckweed, Stomp says, but the crop could produce jobs in rural North Carolina—as well as fuel and cleaner water. “George Washington Carver made the peanut into a multiple-use crop,” she says, “NC State will do it with duckweed.”

NC State researchers are looking at creating fuel from everything from animal fat to microbes to pond scum.

The University also could do it with microbes known as clostridia and methanogens, which Drs. Amy Grunden and Mari Chinn are using as a tag team to convert carbon dioxide and carbon monoxide into ethanol and methane. Clostridium ljungdahlii, for example, lives in the soil and naturally consumes carbon dioxide and carbon monoxide for energy, producing acetate and a small amount of ethanol in the process. Grunden, an associate professor of microbiology, says fooling the organism is the trick to transforming it into an effective fuel-producer. Treating the cells with chemicals like hydrogen peroxide, oxygen and hydrogen convinces them to alter their metabolism, she says, so they give off more ethanol and less acetate. Methanosarcina barkeri, an organism more known for making swamp gas, can then be used to consume the acetate and create methane.

Chinn, a BAE assistant professor, is trying to improve the efficiency of the fermentation processes in which the two microbes become a cellular-level refinery. With the help of Dr. Michael Flickinger, a professor in the Department of Chemical and Biomolecular Engineering and the Department of Microbiology, she and Grunden are embedding the organisms in a latex film to protect them from noxious compounds in the gas stream that can inhibit the ethanol production—or even kill the organisms. Chinn and Grunden recently won a grant from the North Carolina Biotechnology Center to test their process. “We’ve shown that different parts of this process work,” Grunden says. “Now, we have to put it together and prove it can be an efficient production model.”

“George Washington Carver made the peanut into a multiple-use crop.
NC State will do it with duckweed.”

Chemical and biomolecular engineering professor Henry Lamb, mechanical and aerospace engineering professor William Roberts, and BAE professor Larry Stikeleather are using the proven model of an oil refinery to convert animal fat and vegetable oils into gasoline, jet fuel, and diesel. Their three-step process, dubbed Centia for “green power” in Latin, uses high-temperature hydrolysis to break triglycerides in the fats and oils into free fatty acids. Proprietary catalysts are then introduced to produce hydrocarbons and refine them into the desired fuel type. “We knew there was chemistry out there to get us started,” Lamb says, noting that mechanical and aerospace engineering graduate student Tim Turner found published research in which scientists were able to remove CO2 from fatty acids to make hydrocarbons. “The hydrolysis step allows us to start with any type of fat,” he says, “and we’ve synthesized the process from there.”

“We need to develop sources for fuel that are more renewable and won’t divert our nation’s food resources.”

The team recently won a North Carolina Biofuels Center grant to demonstrate that the process can produce different fuels and to test the fuels in standard engines. Lamb is convinced Centia fuels, like the duckweed research, could be a boon to North Carolina’s agricultural economy. He grew up on a hog farm in southeastern North Carolina and says farmers have expressed interest in making fuel from hog rendering—as close to making a silk purse from a sow’s ear as you can get. “Ethanol has limitations,” he says. The fuel delivers less energy per gallon than gasoline and is difficult to transport because it absorbs moisture from the atmosphere. “Instead, we’re trying to develop conventional transportation fuels from non-petroleum sources.”


Drs. Anne-Marie Stomp and Jay Cheng say duckweed, a rapidly growing aquatic plant, can be engineered to produce starches that can be used to make ethanol. Duckweed (below) can also filter excessive nutrients out of hog-waste lagoons as it grows.

By using a bit of trickery, Drs. Mari Chinn (left, at right) and Amy Grunden can get two types of microbes, clostridia (right) and methanogens (below far right) to consume carbon dioxide and acetate, respectively, and produce ethanol and methane.

Drs. Henry Lamb (left) and Bill Roberts are part of an NC State team to develop a three-step process to convert animal fat and vegetable oils into fuel.