College of Engineering News • Iowa State University

Nature’s Way

Back in the bad old days of the 1970s oil embargoes, Iowa State food scientist Earl Hammond isolated an oil-producing yeast—Cryptococcus curvatus—from a floor drain in what was then called the Dairy Industries Building. Hammond tagged the specimen because he was looking for a yeast that could feed on sugars and convert them to oil—food-grade oil.

Despite long lines at service stations, cheap gas up to the ’70s embargoes made ethanol and other alternative fuels unattractive to the public. And without a robust biofuel industry competing for corn and soybeans, food oils weren’t expensive either. Hammond patented his discovery anyway, but for years it served only as a research tool, never achieving commercial viability.

A temporary retreat from $4 gasoline notwithstanding, those “bad old days” are back, this time in the form of climate change and a global economic crisis that could make consumers long for the 1970s. Fortunately, Hammond and his yeast are back too, along with a team of collaborators looking to exploit his original scheme to produce oil—only this time for fuel.

Led by Hammond’s protégé, microbiologist Sam Beattie, several collaborators from the Department of Food Science and Human Nutrition enlisted environmental and biological engineer Hans van Leeuwen and others from the College of Engineering. Their goal? To use existing techniques—and some novel twists—to produce industrial oil or biodiesel in a virtually closed carbon loop, combining economic viability with environmental sustainability.

A new use for old techniques

Beattie knew precisely what he needed in turning to van Leeuwen and his engineering colleagues. As a young researcher, van Leeuwen first used fungi to treat industrial wastewater, a practice he continued through faculty positions in South Africa, Australia, and, ultimately, at Iowa State, where in 2000 he joined the Department of Civil, Construction, and Environmental Engineering.

Once in Ames, van Leeuwen became intrigued with the possibility of bringing his expertise in industrial wastewater treatment to ethanol production, where he saw an opportunity to extract greater value from stillage, the wastewater that remains after distilling ethanol from the fermentation and removing distillers dry grains for use as animal feed. Convinced that certain organisms might thrive on the low-value waste stream, van Leeuwen returned to his fungus and made a surprising discovery.

“The fungi grow like mad in thin stillage,” he says. “They love it! But you end up with a lot of tiny organisms in water; it may not have as many dissolved substances, but you have all these suspended molds. And they’re not easy to remove.”

Undaunted, van Leeuwen introduced aeration techniques that cause the filamentous fungi to attach to each other and form small spheres about one-half inch in diameter that are easily screened from the stillage. “Those make a marvelous animal feed that contains certain proteins lacking in most vegetable diets,” he notes.

Through this innovation, van Leeuwen turned a money-losing waste stream into another potential value-added product for an ethanol industry that needs every advantage to compete in the alternative energy market. So when Beattie approached him, van Leeuwen was soon convinced of the potential in a similar process that might revive Hammond’s quest for a commercial application for his yeast.

“We envisioned a kind of two-stage process,” Beattie recalls. “We have the white-rot fungus producing sugars, and the yeast grow on that, producing yeast biomass—billions and billions of yeasts.”

However, Beattie adds, while sugars and nitrogen may reproduce yeast in great quantities, nitrogen inhibits yeast cells from gaining the mass they need to convert sugars into oil.

“What we have is lots of skinny yeasts,” Beattie continues. “So we’re going to turn those around, put them back into a sugar solution without the nitrogen, and let them go to town on that. And they’ll get fat.”

Innovation for a critical step

Yet rather than corn, Beattie and van Leeuwen decided they would use lignocellulosic feedstocks such as switchgrass and corn stover that require further processing—and further expense—toextract the sugars the yeast would then convert to valuable oils. That required additional expertise in the person of Tae Hyun Kim, a young chemical engineer on the agricultural and biosystems engineering (ABE) faculty.

In order to prepare a cellulosic feedstock for conversion into sugars, engineers must first remove the feedstock’s lignin, the organic biopolymer that is linked with cellulose and hemicellulose and gives it strength. By pretreating the feedstock with a 15% aqueous ammonia solution, Kim discovered, he could remove up to 70% of the lignin, sufficient for commercial enzymes to break down cellulose into the monomeric sugars on which the yeast could feed.

Ammonia pretreatment, Kim says, has significant advantages for stripping lignin from cellulose. Other alkaline treatments, for example, are highly effective at removing lignin, but the residual chemicals can damage the enzymes and yeast in the downstream processing. And, in addition to its toxicity, dilute acid pretreatment is non-volatile and therefore cannot be recovered and recycled, unlike aqueous ammonia. Finally, Kim’s signature innovation to ammonia pretreatment lies in a technique that allows him to process the biomass from 30 to 60 degrees Celsius—as low as room temperature—resulting in significant energy savings at the refinery.

“So after a lot of discussion among the group,” Kim says, “we concluded that an ammonia-based pretreatment was best for our process. It has a lot of desirable characteristics, and we can obtain a high purity of lignin.”

The process, Kim notes, is very simple with good economics: the ammonia is recovered and reused, and the lignin can be sold for binder, soil amendments, and road construction materials.

‘We’re imitating nature’

Once separated from the lignin, van Leeuwen introduces into the biomass a white-rot fungus of the genus Phanerochaete that can break down the polymer chains of the cellulose into a variety of monomeric sugars, which are then fed to the oil-producing yeast.

“In a way, what we’re doing is biomimicry,” van Leeuwen notes. “We’re imitating nature.”

Depending upon the variety, the yeast will either ferment the sugars into ethanol or, as with Hammond and Beattie’s specimen, gorge on the sugars and convert them into oil. Along with any remaining residues, the fungus, van Leeuwen observes, can be used as animal feed or a soil amendment.

Yet the challenge of this method lies not so much in getting yeast to fatten on the sugars—removal of nitrogen from the biomass does that—but instead in harvesting oil from the yeast. So Kim’s ABE colleague David Grewell brings to the project a unique set of skills and knowledge in ultrasonics that, like van Leeuwen’s work with fungi, was developed in order to treat municipal and industrial wastewater.

“This technology is directly applicable,” Grewell observes. “We can take equipment used in municipal wastewater treatment residues and drop it right into biofuels production, whether turning corn into ethanol or switchgrass into some type of fundamental chemical building blocks or biodiesel.”

Tuned precisely, the ultrasound not only ruptures yeast cells to release their oil, but also can significantly increase esterification rates when used in conjunction with specific heterogeneous catalysts, such as those developed by Professor John Verkade of Iowa State’s Department of Chemistry. This, Grewell says, has the added benefit of eliminating another step in the production chain of the biofuel.

“We hit the yeast with the ultrasonics,” he notes, “and at the same time that oil comes out, it’s pretty much instantaneously and directly turned into biodiesel.”

Grewell is quick to note that the application of ultrasonics to increase biofuels production isn’t new, and that researchers have been publishing papers on the technique since the 1970s. Besides the comparatively low demand for biofuels even in the face of OPEC embargoes, however, early efforts were limited by their inability to scale up equipment and techniques to production levels.

Not today: over the past 10 years, Grewell says, power supply technology and the design of transducers capable of turning electricity into the mechanical energy needed for large-scale ultrasonics have combined with greater knowledge of the mediums to which the technology is applied to allow research to go beyond bench-scale applications.

Getting the economics right

The greatest challenge facing them, team members agree, is the economics of “green” energy in the face of continuing volatility in traditional energy markets, particularly oil. Recently, that volatility has thrown much of the biofuels industry—particularly ethanol—back on its heels, as gasoline and diesel shot to more than $4 a gallon in 2008 only to tumble back to earth this year.

As a result, refineries that would benefit most from processes the team is developing have retrenched their R&D and are reluctant to venture into new areas as they struggle to remain viable. One Iowa producer, van Leeuwen notes, expressed interest in his fungal treatment of ethanol stillage to recycle the effluent back into production but hesitated on concerns that ramping up the unproven methods might hamper an operation already strained economically.

“This is critical,” van Leeuwen says. “They want to do this, but at the same time they don’t want to do this experimentally.”

In order to combine these various components that have succeeded separately in bench-scale tests, van Leeuwen is constructing a pilot refinery at the Biomass Energy Conversion Center, a facility of the Iowa Energy Center administered by Iowa State that serves as a bridge between lab experiments and real-world applications. There, he will demonstrate his proof-of-concept for recycling water in a closed-loop ethanol production process while simultaneously producing high-grade animal feed from the fungus used to purify that water. If successful, not only would producers save up to one-third of energy costs over the ethanol production process, they would also have a valuable byproduct that could benefit Iowa’s livestock industry.

A similar proof-of-concept will be needed to make oil from lignocellulosic feedstocks. Led by Beattie, the team is seeking funding for that effort, but the project must compete with many others pursuing a limited pool of funds. The researchers know this so are especially quick to tout the ecological advantages of the process.

“We can capture every aspect of the cellulosic material,” Beattie emphasizes. “We harvest the lignin if it’s available, we sell the lignin if there’s a market for it; otherwise, we burn that material for energy. The glycerol left over from the biodiesel can be fed back to the yeast as an energy source. So everything gets recycled. Even the water gets recycled.”

Making the ‘sell’

Those cost savings and value-added byproducts must be there. Global warming or any other form of environmental degradation notwithstanding, van Leeuwen insists, no producer is going to place the welfare of the planet over profits.

“That’s not something that’s going to happen with private enterprise,” he says. “No one is going to sacrifice their share of all this money to make their own small contribution to rising ocean levels, right? That’s a very, very hard sell.”

Still, if the response of the research community is any indication, that “sell” is looking better with each passing year: van Leeuwen’s ethanol and biofuels research projects—including those discussed here—have won the Grand Prize for University Research Award from the American Academy of Environmental Engineers in each of the past three years, and last year his efforts to grow microscopic fungus in ethanol stillage resulted in the prestigious R&D 100 Award.

Of course, accolades from the research community are no guarantee of success in an unforgiving commercial marketplace. But if Sam Beattie’s confidence in the project is any indication, you shouldn’t bet against that lignocellulosic biodiesel refinery one day rising above the Iowa prairie.

“If someone were to give me $30 million tomorrow, I’d build it,” Beattie says.