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Gas From Woody Biomass Promising Way To Reduce Emissions
Two processes that turn woody biomass into transportation fuels have the potential to exceed current Environmental Protection Agency requirements for renewable fuels, according to research published in the Forest Products Journal and currently featured on its publications page. The Environmental Protection Agency’s standard for emissions from wood-based transportation fuels requires a 60 percent reduction in greenhouse gas emissions compared to using fossil fuels. The standards don’t just concern greenhouse gases generated when biofuel is burned to run vehicles or provide energy: What’s required is life-cycle analysis, a tally of emissions all along the growing, collecting, producing and shipping chain. The special Forest Products Journal issue does just that for energy produced in various ways from woody biomass. For instance, two processes for making ethanol reviewed in the issue – one a gasification process using trees thinned from forests and the other a fermentation process using plantation-grown willows – reduces greenhouse gas emissions by 70 percent or better compared with gasoline. In contrast, producing and using corn ethanol reduces greenhouse gas emissions 24 percent compared to gasoline, according Argonne National Laboratory research published in 2011. For the publication, researchers from the 17 research institutions that make up the Consortium for Research on Renewable Industrial Materials determined the life-cycle emissions of 15 processes where woody biomass was turned into liquid fuel, burned directly to create heat, steam or electricity, or processed into pellets for burning. The common advantage of these processes over fossil fuels is that trees growing in replanted forests reabsorb the carbon dioxide emitted when woody biomass burns as fuel in cars or other uses, said Elaine Oneil, a University of Washington research scientist in ecological and forest sciences and director of the consortium. While fossil fuels cause a one-way flow of carbon dioxide to the atmosphere when they burn, forests that are harvested for wood products or fuels and regrown represent a two-way flow, into and back out of the atmosphere. The processes reviewed have the added advantage of using woody debris not only as a component of fuels but to produce energy needed for manufacturing the biofuel. The fermentation process to produce ethanol, for example, ends up with leftover organic matter that can be burned to produce electricity. Only one-third of the electricity generated by the leftovers is needed to make the ethanol, so two-thirds can go to the power grid for other uses, offsetting the need to burn fossil fuels to produce electricity. This is among the reasons that ethanol from plantation-grown feedstock using the fermentation process approaches being carbon neutral, that is, during its life cycle as much carbon is removed as is added to the atmosphere, according to Rick Gustafson, UW professor of environmental and forest sciences and a co-author in the special issue. The researchers looking at the fermentation process also took into account such things as water consumption. They found that the process – which among other things needs water to support the enzymes – uses about 70 percent more water per unit of energy produced than gasoline. A biofuel industry using woody material will be a lot less water intense than today’s pulp and paper industry – still, water use should be taken into account when moving from pilot biofuel production to full-scale commercialization, Gustafson said. “The value of life-cycle analysis is that it gives you information such as the amount of energy you get in relation to how much you put in, how emissions are affected and the impacts to resources such as land and water,” Oneil said. In the U.S. last year, some 15 facilities produced about 20,000 gallons of fuels using cellulosic biomass such as wood waste and sugarcane bagasse, according to a U.S. Energy Information Administration website. The administration estimates this output could grow to more than 5 million gallons in 2013, as operations ramp up at several plants. In the special issue, the biofuels analyzed came only from forest residues, forest thinnings, wood bits left after manufacturing such things as hardwood flooring or fast-growing plantation trees like willow. That’s because, from a greenhouse emissions perspective, it makes no sense to produce biofuels using trees that can be made into long-lived building materials and furniture, said Bruce Lippke, UW professor emeritus of environmental and forest sciences, who oversaw the contents of the special issue. “Substituting wood for non-wood building materials such as steel and concrete, can displace far more carbon emissions than using such wood for biofuels,” Lippke said. “It’s another example of how life-cycle analysis helps us judge how to use resources wisely.” The modeling and simulations used for life-cycle analysis in the special Forest Products Journal issue can be used to evaluate other woody materials and biofuel processes in use now or in the future, with the models being refined as more data is collected. The data also will be submitted to the U.S. Life Cycle Inventory Database of the U.S. Department of Energy’s National Renewable Energy Laboratory, which has data available for everyone to use on hundreds of products. Read more at http://scienceblog.com/63592/gas-from-woody-biomass-promising-way-to-reduce-emissions/#RumeUVbtlPtxkUoF.99 Continue reading
Promising Technique Improves Production of Biofuels from Lignocellulosic Biomass
Published on May 16, 2013 at 5:01 AM The production of biofuels from lignocellulosic biomass would benefit on several levels if carried out at temperatures between 65 and 70 degrees Celsius. Researchers with the Energy Biosciences Institute (EBI) have employed a promising technique for improving the ability of enzymes that break cellulose down into fermentable sugars to operate in this temperature range. Energy Biosciences Institute researchers substantially improved the thermal stability of Trichoderma reesei EGI, an enzyme that catalyzes the hydrolysis of cellulose, through a technique called “B-factor guided mutagenesis.” Using this technique, they successfully engineered a high-temperature enzyme variant with greater activity and stability over the desired temperature range, and have shown that not all microbes are alike when it comes to making enzymes with improved properties. The EBI research team, which includes Douglas Clark and Harvey Blanch, who hold joint appointments with Berkeley Lab’s Physical Biosciences Division and UC Berkeley’s Chemical and Biomolecular Engineering Department, and postdoctoral researcher Harshal Chokhawala, used a strategy they call “B-factor guided mutagenesis.” They used it to enhance the thermal stability of TrEGI, an endoglucanase enzyme produced by Trichoderma reesei, a fungus considered to be the gold standard for secreting cellulase enzymes. “Lignocellulose hydrolysis using cellulases at high temperatures offers several potential advantages, including higher solid loadings due to reduced viscosity, lower risk of microbial contamination, greater compatibility with high temperature pretreatments, enhanced mass transfer and faster rates of hydrolysis,” Clark says. “However, T.reesei cellulases are not very stable at temperatures above 50 degrees Celsius. We’ve shown that we can improve the thermal stability of T.reesei cellulases with the B-factor approach.” Like all proteins, cellulase enzymes are comprised of chains of individual amino acids that are linked together into uniquely shaped structures. Every amino acid in a given enzyme has a “B-factor” value that corresponds to the flexibility of that amino acid. The higher the B-factor value, the greater the amino acid’s flexibility. “Just like the loosest knots in a rope will unravel first, the most flexible amino acids in an enzyme are the most likely to fall out of place when the protein is thermally stressed,” Clark says. “Tightening up these portions of the enzyme by mutating the amino acids and decreasing their B factor values represents one way to shore up the structure and increase the thermal stability of the protein.” In a presentation at the recent American Chemical Society national meeting in New Orleans, Clark described how he and his colleagues screened some 11,000 mutant versions of TrEGI then used a heat treatment at 50 degrees Celsius to identify some 500 variant candidates. Applying the B-factor guided mutagenesis, they engineered a TrEGI that was up to twice as active on insoluble lignocellulosic substrates as the native enzyme at temperatures ranging from 50-65 degrees Celsius. Engineered TrEGI expressed in the model fungus Neurospora crassa was able to hydrolyze lignocellulosic biomass at 60 degrees Celsius as efficiently as the native TrEGI at 50 degrees Celsius. By comparison, TrEGI mutants expressed in extracts of Escherichia coli or in the model yeast Saccharomyces cerevisiae had much lower activity at the higher temperatures. “Our results demonstrate that the host used for recombinant cellulase production can have a profound impact on the activity and stability of the expressed enzyme, which means favorable mutagenesis results observed for one host may not carry over to another,” Clark says. “So far the mutants we’ve produced in N. crassa exhibit very favorable properties and the results we’re getting will help guide further efforts in engineering optimal enzyme performance for biofuels applications.” The EBI, which provided the funding for this research, is a collaborative partnership between BP, the funding agency, UC Berkeley, Berkeley Lab and the University of Illinois at Urbana-Champaign. Source: http://www.lbl.gov/ Continue reading
