REALITY: A new generation of cellulosic ethanol
One of the most contentious policy arguments in the energy debate is captured by a 2008 cover story in Time magazine that asks rhetorically whether ethanol is a "clean energy scam" that forces a Catch-22 choice between growing crops for food or for liquid fuel as an alternative to imported oil. The article's indictment of biofuels included, in addition to world food shortages and higher food prices, an equally alarming contribution to environmental degradation.
The story produced a passionate rebuttal from many researchers who insist that little real competition exists between food and energy crops and that, in fact, a new generation of biofuels actually has the potential to lower food prices, minimize water pollution, and prevent deforestation. Lost at times in the high-volume debate is the ability to distinguish between valid concerns and alarmist criticisms that see in biofuels a simple explanation for complex problems. The reality, according to Oak Ridge National Laboratory analysts, is that biofuels are potentially one answer to the energy challenge if they can be developed economically and sustainably.
"Plant-based biofuels can help combat global warming without damaging our environment if we make the right choices," says Reinhold Mann, ORNL's associate laboratory director for biological and environmental sciences.
First-generation ethanol, the kind often blamed for food shortages, is produced from starchy grains, such as corn, in the United States and Europe and from sugarcane in Brazil. Mann says the next generation of ethanol is likely to be developed from a variety of nonfood crops rich in cellulose, the complex carbohydrates made of sugar units that form cell walls in stalks, trunks, stems and leaves of most plants.
Cellulosic ethanol has the potential for dramatically changing the biofuels debate. Because much of the feedstock for cellulosic ethanol can be grown on marginal land, expanded use of biofuels would not require choosing between growing food or fuel crops on fertile land. And because several cellulosic sources are perennial crops that demand little water and no fertilizer, their environmental impact is far less than that of annual crops like corn. Researchers with the Department of Energy's new Bioenergy Science Center at ORNL are confident that cellulosic ethanol ultimately can provide more energy than corn ethanol or gasoline. In approximately five years, commercially viable technology may be able to unlock sugars economically from cellulose and ferment them to produce a new generation of ethanol that will not require a choice between food and fuel.
The International Energy Agency predicts that global demand for energy will grow by more than 50% by 2030. The financial and environmental costs of foreign oil and rising greenhouse-gas levels motivated Congress to enact the Energy Independence and Security Act of 2007, which established a renewable fuels standard that starts with domestic production of 9 billion gallons per year in 2008 and increases to 36 billion gallons per year by 2022. Any hope of reaching these ambitious goals will require cellulose-busting technologies that take advantage of America's 1.3 billion tons of biomass (see "Myth: America Does Not Have Enough Biomass").
Food, carbon and deforestation
The myths surrounding biofuels are many, including the notion that the growth of biofuel crops in America sets in motion a process that leads to deforestation in the Amazon. The logic asserts that when Kansas farmers use existing cropland for fuel feedstock instead of food, the resulting increase in world food prices encourages Brazilian farmers to expand food production by clear-cutting the jungle and burning native vegetation, with a commensurate increase in carbon emissions.
Keith Kline, a project manager at ORNL working on social and environmental challenges in developing nations, says, "Several recent studies document the large environmental impacts of forest clearing. If biofuel plantations were responsible for this indirect land use change, then biofuels would appear to cause more greenhouse gas emissions than the oil they displace. The argument—'An acre removed from food production in America is offset by a new acre cleared in Brazil'—is persuasive because of its simplicity and apparent common sense. In reality, the processes driving deforestation are much more complex."
Kline points to an analysis released in 2001 of the findings of 152 case studies that explored the factors that resulted in tropical deforestation. "The major finding was that there was no single cause," Kline says. Rather, interactions among cultural, technological, biophysical, political, economic and demographic forces drive the process.
In another study, the U.S. Department of Agriculture (USDA) calculated that global food prices rose 43% between April 2007 and April 2008. ORNL landscape ecologist Virginia Dale, a corporate fellow who studies causes and effects of land-use changes, points out that according to a USDA calculation, biofuels accounted for only 3% to 4% of the cost increase. Far more responsible for rising food prices was the cost of energy associated with fertilizing, harvesting and transporting crops. Other factors included poor harvests caused by heavy rains and drought, export restrictions and, perhaps most significantly, increased demands for food in developing nations as populations grow and standards of living rise.
Dale and Kline work with ORNL colleagues Russell Lee, a geographer who analyzes environmental and energy plans, and Paul Leiby, an economist who evaluates the effects of public policies on alternative fuels and energy security. The group makes a variety of data available to policymakers.
Other pioneering work at ORNL in the area of biofuels is being conducted by Corporate Fellow David Greene, who analyzes the economics of renewable transportation fuels, and by climate researcher John Drake, who uses one of the world's most powerful supercomputers to simulate the impact of biofuel crops on climate change.
Research at ORNL suggests the argument that a biofuel boom will require the cultivation of forested land and grassland rests on the inaccurate assumption that additional land is unavailable for food production. Dale contends the amount of land needed to raise crops for biofuels is on the order of 20 million hectares worldwide, a relatively small portion compared with the 6 billion hectares of non-forested land recently identified by the United Nations Food and Agriculture Organization as suited for rainfed agriculture. In Tennessee, for example, at least 400,000 hectares of marginal land are available for biofeed-stock such as switchgrass.
"The amount of existing cleared and underutilized land is far greater than what is needed to produce food crops and biofuels," Kline says. "Increasing production does not necessarily require more land. U.S. agricultural output has grown consistently using less and less land. Meanwhile tropical agricultural frontiers lack incentives for proper soil management, and extensive areas are allowed to burn repeatedly."
Year after year around the world, Kline says, hundreds of millions of hectares of forests burn. "The growing demand for biofuels, with incentives for sustainable production, could create opportunities to recuperate degraded land, improve rural welfare and reduce annual emissions rather than cause more deforestation. Providing tenure and incentives for stable production reduces pressure to clear more forests."
Kline notes that Brazil plans to document the sustainability of sugarcane for biofuels, aiming to improve productivity while minimizing downstream environmental impacts. The Swedish firm SEKAB recently signed a contract with the Brazilian government to produce ethanol through an environmentally sustainable process. The criteria prohibit forest clearing and call for a reduction in carbon dioxide emissions by at least 85% of those from fossil fuel combustion.
The technological challenge
All of these arguments in support of cellulosic biofuel are predicated on the basic question: "Will it work?" Developing consolidated bioprocessing technologies that produce ethanol by using microbial enzymes to free and ferment sugars from cellulose is one of the grand scientific challenges of the 21st century. Some liken the task to turning your coffee table into a liquid you can pour into your gas tank.
The current state of the technology shows that certain enzymes can digest cellulose, but at present are too expensive and inefficient for commercial production of cellulosic ethanol, says microbiologist Martin Keller, director of ORNL's Biosciences Division.
To make transformational breakthroughs that will enable commercially viable biofuel production on a national scale with minimal environmental impact, the Department of Energy has established three multi-disciplinary, multi-institutional bioenergy research centers—led by ORNL, by the University of Wisconsin-Madison in partnership with Michigan State University and by DOE's Lawrence Berkeley National Laboratory. Between 2007 and 2012, each center will receive $135 million to improve understanding of systems biology and transmit solutions to industry.
The Oak Ridge-led team is focusing on tackling the fundamental problem of biomass recalcitrance, or the resistance of cell walls to deconstruction. Mann says the center's strength is the breadth of the research team assembled, which includes, in addition to ORNL experts, leaders in plant science from the University of Georgia, the Noble Foundation in Oklahoma, and the University of Tennessee.
Given that ethanol is an emerging industrial sector with both established and start-up companies, the ORNL team addresses questions that their industrial partners, which include Verenium, Mascoma and Arborgen, are unlikely to explore: What does the biosynthesis of cell walls look like and what factors influence it? Why are some plants more easily degradable than others? Which enzyme is most effective at breaking down sugars in each cell wall so they can be fermented into alcohols? How can natural systems, such as microbial communities, most efficiently accomplish cellulose degradation? Can a single enzyme be designed to degrade cellulose and ferment sugars in one step? Answering each question represents a fundamental step toward making biofuels economically and environmentally viable.
"These questions represent a big lever that we're working on," Mann says. "If we can move that lever, we will have tremendous impact on the ability to get the sugars out of the biomass for fermentation into ethanol and other products. Because petroleum is a feedstock for many products, the ORNL-led team has a large opportunity if we get the biomass production right in a sustainable way to go beyond just transportation fuels and use biomass as a feedstock for other value-added chemicals, such as possibly plastics, solvents, lubricants, adhesives, pharmaceuticals, cosmetics and building materials." Mann cites the 2007 opening by DuPont and corn refiner Tate & Lyle of a nearby facility in Loudon, Tennessee, that manufactures the biomaterial 1,3 propanediol (PDO™), which uses corn instead of petroleum as the raw material. Bio-PDO™ is now available for carpeting, textiles and de-icing fluids.
At ORNL, the primary feedstock candidates for cellulosic ethanol are switchgrass, a drought-resistant native grass that takes about three years to establish and that can be harvested annually for a decade before reseeding, and poplar trees, a short-rotation woody crop that can mature to harvest in seven to ten years.
"We are focusing on switchgrass and poplar trees because they are two genuine bioenergy crops, not just model systems," Mann says. "We use them as paradigm crops. The knowledge derived from those two crops would be applicable to other cellulosic feedstock."
Keller, director of the Oak Ridge- led Bioenergy Science Center, says breakthroughs in automation have emerged less than a year after the center opened. "These advances would not have happened without the collaboration of experts from different disciplines," he adds. "For the first time in the history of biofuels research, the new centers founded by DOE have provided the opportunity to integrate research across many different disciplines—microbiology, plant biology, supercomputing, mass spectrometry, chemistry—and work together on this common goal. The multidisciplinary approach of our partners will enable the breakthroughs we need in this field."
Keller's colleagues are attacking the recalcitrance problem from two perspectives. While some researchers investigate new microorganisms and enzymes, others seek to engineer the cell walls of plants to make them easier to digest.
One project explores extremophiles, microorganisms that thrive in environments that would kill most life forms. The researchers went to Yellowstone National Park to collect microorganisms that live in hot springs and digest cellulose from trees that fall into the scalding water. The scientists now have about 40 cultures growing at ORNL that subsist only on switchgrass and poplar trees. Another novel technology under investigation is gasification of cellulose to produce "syngas," a mixture of hydrogen and carbon monoxide that can be chemically catalyzed to make biofuel, Keller says.
If scientists find microorganisms that can convert biomass to ethanol efficiently, Keller believes industrial implementation of solutions will quickly follow. On the other hand, if solutions entail reengineering some green plants, the process may take a decade as researchers try to identify or modify a gene that can overcome recalcitrance, engineer the gene to express itself in plants, obtain enough seed to scale up ethanol production, conduct field trials and get approval from the Environmental Protection Agency. "Humankind took 100 years to get into the problem we are facing now with oil," Keller says. "Finding the solution will not happen overnight."
Keller's guarded optimism in some respects reflects the current thinking about the future and potential of biofuels. A new generation of biofuels based on inedible green plants could be a sustainable and affordable alternative to imported oil that does not require a moral choice between food and fuel. Nevertheless, supplying humankind with sufficient food and energy remains one of the critical challenges of the 21st century. —Dawn Levy
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