A renewed interest in bioenergy offers a solution to energy security.
The multi-lane, rush-hour collection of SUVs, sedans and trucks that choke the nation's highways, the incessant road construction projects that tease of faster routes to come, the suburban residential sprawl radiating from commercial urban centers, the acres of asphalt surrounding grocery stores and retail malls—all testify to the inextricable relationship between Americans and their automobiles.
Approximately 140 billion gallons of gasoline per year power this dependency, and the consequences of this addiction to America's economy and foreign policy are profound. While Americans consume 25 percent of the global oil supply, our nation claims just 3 percent of the world's known reserves. This simple fact reveals the uncomfortable truth that 60 percent of U.S. transportation fuel flows from foreign sources.
Buried deep inside the earth, the energy storehouses bequeathed by the living things of previous millennia threaten to become increasingly costly under modern society's ever more voracious appetite for fossil fuel. The debate over the exhaustibility of these reserves is no longer over "if" but "when," as burgeoning Asian economies demand an increasing share of the world's finite petroleum supply. The uncertainty of access to remaining fossil resources, divided unevenly among a handful of countries with varying levels of political stability, poses what many regard as the greatest threat to America's national security since World War II.
The threat of global climate change, influenced in part by emissions from U.S. cars and trucks, has intensified the need for fossil fuel alternatives. In 2004, American vehicles pumped 1.9 billion metric tons of carbon dioxide into the air, a number that is expected to grow to 2.7 billion tons by 2030. In China, emissions from factories and homes have produced the world's worst concentration of urban smog. Similar trends worldwide, coupled with historic increases in the price of petroleum, create what many researchers and policymakers believe is the critical impetus needed to at last develop energy sources capable of providing affordable and sustainable supplies of fuel to power the convertibles and minivans of generations to come.
The promise of providing Americans a practical source of affordable fuel at the corner quick-stop may not lie underground. According to a growing number of scientists and government policy makers, the solution grows above it. Already, ethanol distilleries have tapped the nation's largest crop, corn, to displace 3 percent of the current gasoline supply. But even as corn-based ethanol plants spring up across the country, experts recognize that corn, like petroleum, has limitations as a source of fuel.
The untapped potential of biofuels—that is, gas or liquid fuels derived from plant material—grows in cellulosic biomass, the fibrous, woody matter that gives a plant resilience and shape and is generally found distasteful to animals and people.
The possibilities contained in stalks, trunks and leaves of some plants—notably switchgrass and poplar trees, which offer the quickest path to market because much of their genetic make-up and production potential is already known—have caught the attention of government, scientists and industry at the highest levels. Governors and state legislatures in New York, Illinois, Indiana, Iowa, California and Tennessee (see "Tennessee Steps Up" article) have committed millions of dollars into biofuel initiatives. Established companies such as Archer Daniels Midland and start-ups such as Iogen of Canada are exploring new ways to generate cellulose-based ethanol and building pilot plants. Virgin Airlines' owner Sir Richard Branson is investing substantial sums dedicated to groundbreaking research in renewable fuels. The financial potential found in renewable fuels is evidenced by increasing interest from the oil industry itself. British Petroleum—which recently adopted the moniker "Beyond Petroleum"—is establishing research partnerships and making substantial investments in renewable energy alternatives.
Perhaps the most significant endorsement for bioenergy came when President George W. Bush in his 2006 and 2007 State of the Union address as mentioned wood chips, switch grass and the potential of biomass-based fuel sources. Spurred in part by a report known as the "Billion Ton" study and developed primarily by researchers at Oak Ridge National Laboratory and co-released by the U.S. departments of Energy and Agriculture (see sidebar), the Administration has promised new funding for biofuels research. The President has set a goal of displacing 30 percent of current U.S. liquid transportation fuel consumption with biofuels by 2030. Biofuels will include primarily ethanol from wood and switchgrass but also biodiesel made from soybeans and waste oils collected from the food service industry.
This is not the first time bioenergy has been part of the national energy discussion. The energy crisis of the 1970s, with accompanying gasoline shortages and price spikes, motivated Washington to fund a number of alternative energy research programs in an attempt to harness the power of plant life. However, as gas prices retreated and availability was restored, attention and research funding switched to other priorities.
What may provide the current push for bioenergy with staying power to survive fluctuations in world oil prices, is that the more transient concerns of economics and the environment are no longer the dominant considerations of energy policy, says ORNL's Martin Keller. Keller recently left Diversa, a publicly traded enzyme development company, to become director of ORNL's Bioscience Division and help lead the Laboratory's accelerating bioenergy research initiatives.
"For the first time national security has emerged as a major driver toward bioenergy, Keller says. "Even climate change, as serious as it may be, is not a strong enough motivation to produce a fundamental change in the way Americans look at bioenergy. Much of our society views the future in terms of only one to two years. This mindset explains why many people do not put money into savings for retirement, which tells us that economics, at present, is also not a driver for bioenergy."
Keller believes that since Sept. 11, 2001, the nation's heightened awareness of national security threats has placed the bioenergy discussion in a new context and presents new opportunities for ORNL. Sixty-five years ago, similar threats to national security resulted in an extraordinary effort to develop an atomic weapon, made possible in large measure by scientific research in Oak Ridge. Today, the Laboratory, with a 25-year track record in biomass development and world-class capabilities in the biological, computational and materials sciences stands poised to address, in a different scientific arena, a major national security challenge.
"Addressing the energy issue is critical to sustaining our society and our freedom," Keller says. "We need to bring the energy deficit under control so our kids can enjoy the freedom we have now."
A molecular quest
The trees and grasses that hold great promise as future sources of fuel also present the greatest resistance. The lattice of cellulose, hemicellulose and lignin render plant cell walls resistant to breakage and the ravages of weather, insects and disease. They also serve as a barrier to transforming the plants into simpler sugars that can be processed into ethanol or other types of fuels and chemicals.
Methods exist to make ethanol from cellulose, says Jonathan Mielenz, who heads up ORNL's bioprocessing program. However, the process costs about $2.26 per gallon of ethanol—a price much higher than gasoline because ethanol typically is only 60 percent as efficient. A White House initiative calls for reduction of the cost of producing cellulosic ethanol to $1.07 per gallon by 2012.
"The technology for making cellulosic ethanol has been known for 30 years, but the challenge we have not yet solved is how to make the fuel economically competitive with gasoline," Mielenz says. "With fossil fuels, you just pump oil out of the ground, do some catalytic cracking and separations and get gasoline and petroleum chemicals. Even with transportation costs, it is still cheaper to import and refine oil into gasoline than to turn a coffee table into ethanol."
The steps of cellulosic bioprocessing include thermochemical pretreatment of plant matter to render cellulose and hemicellulose biopolymers more accessible to enzymatic breakdown into glucose and xylose sugars; application of enzymes called cellulases to break up the complex carbohydrates into simple sugars, and, finally, fermentation by microbes to transform the sugar into alcohol. The alcohol is purified through distillation to make ethanol for vehicular use. Byproducts of the process can be turned into valuable chemicals to replace petrochemicals as well as produce heat and electricity to bolster profitability of the plants. Biorefineries potentially could produce other forms of fuels for transportation and heating.
The secret to cracking the code of cheap cellulosic ethanol production, Mielenz and other scientists believe, will be found in probing the molecular mechanisms involved, identifying new and better bacteria and enzymes needed to improve the process and genetically manipulating them to do their jobs even more efficiently. Certain microbes, for example, show promise in replacing harsh and expensive chemicals and, perhaps, combining steps of the bioprocess. ORNL researchers are using microarray technology to determine particular genetic functions of Clostridium thermocellum, a microbe genetically engineered at Dartmouth College to take on the double duty of very rapidly hydrolyzing cellulose with its own cellulases and fermenting sugar to ethanol mixed with two acids.
Eventual success in large-scale ethanol production is linked to the creation of a new agricultural industry capable of growing approximately 1 billion tons of biomass needed to displace 30 percent of the nation's current consumption of liquid transportation fuels.
The "Billion Ton" study estimated that about 50 million acres could be employed in production of biomass products such as switch grass and poplar trees. These are two of the most likely candidates for early production of biofuel because of their broad adaptability, the ability to modify easily existing agriculture methods to produce them and their current readiness for production, enabled by a 25-year DOE biomass program managed at ORNL.
In addition to looking at the economic and societal implications of creating such a large agri-industry from scratch, Laboratory researchers also are working to develop plants most ideal for growing and harvesting as bioenergy crops. ORNL plant geneticist Gerald Tuskan recently led a two-year effort to sequence the genome of black cottonwood, or Populus trichocarpa, a hybrid poplar that scientists are seeking to develop into a tree uniquely suited to the needs of the bioenergy business. With the complete genome sequence in hand, Tuskan and his colleagues hope to find and identify genes responsible for promoting fast growth, increased biomass production and other characteristics such as drought tolerance and resistance to disease. Potentially, genetics could also be used to create a tree with cellulose and hemicellulose that are less resistant to breakdown, reducing cost at the bioprocessing plant. Such genetic tools allow scientists to accelerate the kinds of selective breeding that typically takes place over centuries.
"Farmers have spent thousands and thousands of years domesticating traditional agriculture crops in an almost serendipitous way," Tuskan says. "We hope to use genomics and modern genetics to shorten that domestication period to just a few decades."
The big picture
The multidisciplinary systems strategy required to meet bioenergy's scientific challenges makes ORNL uniquely qualified to carry out such a project.
"The reason I came to Oak Ridge is because I saw that national labs can provide an environment that enables research across lots of disciplines," Keller says. "I feel strongly that the future of science needs interaction of disciplines to work on bigger problems. With bioenergy, our challenge is to find a creative way to understand data and develop models to understand how cells really work."
Such collaborative investigation involves not only biologists, ecologists and geneticists, but also researchers in the fields of computational simulation, materials, nanotechnology, engineering and physics. At ORNL, researchers utilize one of the world's most powerful supercomputers to model mechanisms by which bacterial and fungal cellulases break down and chemically process cellulose. At the Laboratory's newly opened Nanoscience Center, researchers Tim McKnight and Udaya Kalluri will use DNA-coated carbon nano-fibers to test whether a suspect cellulose-synthesizing gene introduced into a single naked poplar cell builds a cell wall. Potential also exists to examine the properties of biological materials at the Laboratory's Spallation Neutron Source, a $1.4 billion new instrument that will reach full beam power in the next couple of years. At the University of Tennessee — one of ORNL's managing partners — microbiologists are working with electrical and chemical engineers to apply engineering principles to questions of how cells are regulated, evolve and can be manipulated.
"Potentially, one could envision integrating cells directly onto some type of nanostructure or material to carry out a bioprocess," says Gary Sayler, head of the Joint Institute of Biological Sciences, a partnership between ORNL and UT.
A more holistic approach to biology promises to bear fruit in the quest for new energy sources as well, says Brian Davison, chief scientist for systems biology and biotechnology at ORNL. "We are in the middle of the second wave of the biotechnology revolution. The first wave of the biological revolution was the ability to amplify and manipulate a gene," he says. "The second wave seeks to analyze and understand biological systems. The essence of systems biology is the intent to approach the whole organism or pathway or community as a system rather than a reductionist single gene or single enzyme or ‘black box' organism."
ORNL's historic expertise is now bolstered by a strategy to employ rapid improvements in instrumentation and simulation needed to explore and process that information. "First, we intend to attack this problem aggressively," Davison says. "Second, we have strong capabilities in bioinformatics and computation. Third, we have historical strengths in biology, environment, plants and microbes and knowledge about their relevance to bioenergy."
Mark Downing, an ORNL agricultural economist, casts a likely historic effort in these terms: "Bioenergy is not the science, it is the result of doing good science. You get good science from superior work of a dozen different researchers, and that is what ORNL does best."—Larisa Brass
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