By Sarah Thompson
By the middle of this century, the global population is estimated to reach 9 billion. There will not be just more mouths to feed: Demand will grow for animal feed, for land on which to grow feed and food, and for energy to produce it all. What if it was possible to spare cropland while simultaneously creating renewable sources of energy and feed, and improving human health? It’s the holy grail of sustainability, and researchers at CALS are part of the quest to develop a portfolio of systems—based on harvests from willow, grasses and algae—that work together to satisfy anticipated feed and energy demands, while using marginal lands, finding profitable uses for byproducts, and providing a buffer against the volatile fuel market.
Agricultural crops, aquatic plants, wood and animal wastes: All are biomass, the catch-all term for any renewable source of carbon-rich organic matter. The building block of life on Earth, carbon constantly cycles through the air, water, soil and all living things. The most basic way to release the stored energy in biomass is through burning it. As a renewable energy source, biomass combustion is very attractive: It can utilize a variety of waste streams, has lower emissions than coal, and is a proven, relatively inexpensive process. It’s a process that Larry Smart ’87, associate professor of horticulture in the School of Integrative Plant Science, is working to improve, and key players are starting to take notice.
“The industry is picking up steam. There’s a lot of interest right now in burning wood chips and pellets for heating, especially in small commercial and industrial settings. There’s been a lot of grassroots enthusiasm and government support in New York, Montana, Maine, Vermont and New Hampshire,” said Smart, who directs the New York shrub willow breeding program at Cornell’s New York State Agricultural Experiment Station in Geneva.
Smart’s group breeds shrub willow varieties for two main bioenergy applications: biomass combustion and transportation biofuel. Shrub willow is one of a group of perennial plants, including forage grasses like switchgrass and big bluestem, which researchers think can become important bioenergy crops. As a sustainable source for wood chips, shrub willow has several advantages over wood harvested from forests, according to Smart. It can be harvested every two to three years for at least 25 years without replanting, requires essentially no fertilizer or herbicide after initial establishment, and grows well on marginal soils that farmers aren’t using for other crops.
In partnership with the Northeast Woody/Warm-season Biomass Consortium (NEWBio) and the Northeast Sun Grant Initiative, Smart is breeding shrub willow to make it better adapted for bioenergy production. His newly patented ‘Preble’ variety is a prime example, bred to grow rapidly, produce nearly 30 percent more woody biomass on average than other current production cultivars, and to better resist rust disease and insect pests. ‘Preble’ also has been shown to have greater tolerance of salt-affected fields. And now that the U.S. Department of Energy and a group in China have sequenced the genomes of two shrub willow species, Smart said his work on genetic marker-assisted breeding will gain even more momentum.
“It’s all economics, but the main driver is yield, which is why breeding is so important,” Smart said.
In the Northeast, which uses the most fuel oil in the country for heating, Smart said shrub willow can provide communities the opportunity to grow and generate their own renewable energy to offset use of more expensive fossil fuels.
“There are still a large number of rural communities without access to cheap natural gas, so they heat with oil or propane. Willow can be less expensive, and folks can be proud that their energy is produced locally,” Smart said. “There is a strong push for local production of food these days; I would love to see us make the same push for local production of renewable energy.”
Bioenergy balancing act
Smart and colleagues are also assessing willow and switchgrass to reclaim mine sites and buffer sensitive waterways from farm field nutrient runoff. Multitasking is a common theme in bioenergy, because many biofuels can’t yet compete with petroleum-based fuels on cost alone. Corn ethanol and soy-based biodiesel production have become very established sectors—and produce large quantities of animal feed as a byproduct—but they rely on large amounts of prime land, water and fertilizers.
Cellulosic ethanol, made from the cellulose that stiffens plant cell walls, is viewed as more ecologically sound because it can be derived from the non-food parts of plants, such as wood and stems, rather than kernel and bean. However, breaking down wood or grass into sugars to ferment into bioethanol is complex because the carbon is locked in large molecules that bacteria can’t access without pretreatment with acids and enzymes. Lars Angenent, professor of biological and environmental engineering, is researching an ethanol production system that instead uses pyrolysis as a pretreatment.
The process begins with organic matter—crop residue left after harvest—which is converted into gases using the combination of high temperature and low pressure in the absence of oxygen, i.e., pyrolysis. According to Angenent, who works with biochar expert Johannes Lehmann, a professor of crop and soil science in the School of Integrative Plant Science, while 50 percent of the carbon can be returned to land as biochar, a fertility enhancing, carbon-sequestering soil amendment, most of the energy and 70 percent of the mass—as carbon monoxide and oil—is suitable for making biofuel, with a bit of help from microbes.
“All that the anaerobic fermentation requires, in addition to the carbon monoxide as a food source, are some trace elements needed by the bacteria,” Angenent said. “You bubble carbon monoxide gas in a system with no oxygen, and the bacteria produce ethanol that can be used for fuel.”
This system, which uses a strain of Clostridium bacteria, also produces some acetic acid—basically vinegar—and Angenent is working to determine which parameters, such as pH, maximize the production of ethanol relative to acetic acid. Other challenges are extracting the ethanol fuel from the rest of the bacterial broth and getting the carbon monoxide into the broth and accessible to bacteria. Even with these hurdles, it’s a versatile system that could be used as a platform for producing other materials as well, but that will require genetically modified bacteria.
“Carbon monoxide is actually very useful material that can be used to manufacture many different chemicals,” Angenent said. “Bioenergy is just one outcome. With changes in economics—when petroleum fuel is cheap—it could always be used to produce other chemicals with higher value. If you pair it with pyrolysis, you can produce both fuel for transportation or cooking and biochar, which is a very useful soil amendment in degraded and especially tropical areas.”
Making the Switch
has the potential to become a feasible source of cellulosic ethanol, and New York has the right climate to grow biomass grasses in three seasons.
“Before the interest in biofuels, there were some switchgrass breeders in the Midwest, but they bred more for quality to feed beef cows. Our goals are much different. We’re growing a crop of stems,” said Donald Viands, professor of plant breeding and genetics and leader of the Cornell Forage Breeding Project, an ongoing perennial forage improvement program with a strong track record with alfalfa.
Viands and Gary Bergstrom, professor of plant pathology, are assessing switchgrass yields, quality and disease management to improve it as a feedstock for biomass energy. Before their efforts, Bergstrom said there were reports of more than 40 diseases on switchgrass in natural settings, but no one knew what might happen in commercial plantings.
“In New York state we identified several switchgrass diseases, but the problems weren’t all that severe at first. One lesson was that as fields of the grass become older and more numerous in the region, minor problems become more intense,” Bergstrom said.
Bergstrom has identified certain diseases of switchgrass that could reduce its profitability as a biofuel crop. In particular, he’s focused on a fungal disease recently identified in New York called smut (Tilletia maclaganii). A systemic smut infection can cause up to a 50-percent reduction in grass biomass, which Bergstrom said “might be a deal breaker” for the cellulosic ethanol industry and other bio-based industries, such as industrial absorbents used by the oil and gas industries, animal bedding, and bio-based plastics. Research associates in the Bergstrom lab are studying the biology of the smut infection process to develop insights that might be exploited for new disease management methods.
According to Bergstrom, diversity may be key to control, whether that diversity comes from mixed cropping of different native grasses—including Indiangrass, big bluestem, and coastal panicgrass—or breeding new varieties of switchgrass with disease resistance. To that end, Viands and senior research associate Julie Hansen are helping identify diverse grass populations with disease resistance or tolerance. They are using them for selective breeding, while Bergstrom works with breeders across the United States to diagnose localized switchgrass diseases, to anticipate and assess future disease threats.
“Switchgrass remains productive in the field for 10 to 20 years, but we need to have pest and disease resistance, and the yields, to make it worthwhile,” Viands said.
Next generation and net-positive
Even though the promise of cellulosic biofuel is great, Bergstrom said that low fuel prices are pushing researchers and biomass producers to find additional applications and markets for switchgrass, such as animal feed, industrial absorbents and plastics. It’s a challenge facing every bioenergy solution.
“Biofuels are [currently] not cost competitive with cheap oil,” said Beth Ahner, CALS senior associate dean and professor of biological and environmental engineering.
This is why the algal biofuel industry continues to move in “fits and starts,” Ahner said, even though single-celled marine algae have many advantages over land plants used for biomass. They can be grown rapidly in reactors or ponds placed on poor soils; use less water than some agricultural crops; can thrive in salty water; and selected species can produce more than three-quarters of their weight as fuel’s raw materials—oils and sugars—under optimal conditions. And, aside from dealing with its high water content, turning algae into biodiesel, diesel or aviation fuel is fairly straightforward.
Ahner is working to make algal biofuel production more efficient and, therefore, more cost competitive and attractive to potential investors. In one project, she and Ruth Richardson, associate professor of civil and environmental engineering, are working to identify biomarkers of stress in commercial algae pools, which have lower growth rates than lab populations. After reaching a certain density in these pools, algae are “starved” of nutrients to promote natural accumulation of oils. By measuring the level of gene expression in these algae under varying stressors, Ahner and Richardson hope to find five to six biomarkers that producers can use to tweak and optimize the process.
“This work will allow us to understand the stresses going on inside these commercial systems, which are ‘black boxes’ right now,” Ahner said.
At the other end of the algal biofuel process, Xingen Lei, professor of animal science, is turning an algal biofuel byproduct into profits by testing defatted algae remaining after biofuel production as a high-nutrient, healthier and more sustainable ingredient in animal feed and potentially human diets.
“Our purpose was to see if this defatted algae is better for animal feed, if it has more protein and less fat, and how much we can use to replace the soy protein in animal feed and spare it for human use,” Lei said.
Lei’s lab has conducted 20 experiments with algae-based feed for pigs, broiler chickens, laying hens and mice, finding that defatted algal feed (DFA) has excellent nutritional quality and high protein, and can safely replace five to 20 percent of the corn and soy protein in animals’ diets. Lei’s team estimated that, based on these replacement rates, DFA could save up to 23 million tons of corn and soy for human consumption annually—and spare a land area the size of the state of Tennessee for other uses.
Lei also found that the meat and eggs of chickens fed DFA accumulated high levels of omega-3 fatty acids, a family of essential polyunsaturated fats our bodies acquire from diet alone. Lei said research continues to point to a key role for omega-3s in healthy aging and managing heart disease. In addition, Lei found that the form of iron in algae is absorbed by animals more rapidly than iron from other sources, alleviating anemia in mice and pigs at very low doses. Soon, eggs enriched with omega-3s from algae and algal iron supplements may become key tools for improving global health and nutrition.
This idea and others being investigated by CALS scientists are new twists on Earth’s constant cycling of carbon. Their goal is to hit the sustainable sweet spot: a planet fueled by complementary systems that don’t just create as much energy as they consume but have a net-positive effect on our economies, environment and health.
“That’s the beauty of science,” Lei said. “We can make all the components work together, not against each other.”