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| Fig. 1: A Corn Field - Representative of the Abundance of Available Biomass in the US. (Photo by Bob Nichols. Courtesy of the US Department of Agriculture.) |
The worldwide consumption of energy is expected to triple by 2025, and the supply of fossil fuel is being depleted at an increasing rate. [1] These facts and predictions lead R&D institutes to develop alternative energy technologies that are renewable and carbon-neutral. Biomass fuel is a good contender for an alternative energy considering its renewability and abundance, however biomass poses some challenges. Although biomass is easily combusted to generate electricity, the extraction of energy is inefficient and environmentally harmful. [1] Pollutants such as tar and volatile organic compounds (VOCs) are released during the biomass combustion process.
Of the biomass technologies, the production of ethanol is well-established, but limited by the inefficiency of the fermentation of starches and sugars to produce ethanol. [1] This dilemma has sparked researchers to investigate methods of increasing the amount of energy captured by plants and improve the efficiency of the fermentation process. [2]
Plant biomass is comprised of polysaccharides, Fig. 2, which can be utilized for energy production. Maximization of energy efficient biomass production depends on the minimization of nitrogen demand which is necessary for protein and lignin synthesis. [2] Since polysaccharides consist of biomass and do not contain nitrogen, it is desirable to maximized polysaccharide accumulation and minimize demand for nitrogen. [2] Some researchers at Stanford as well as other institutions are working toward genetically engineering plant DNA to develop plants that accumulate more fixed carbon per unit land area per unit time with no increased nutritional requirements. [2]
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| Fig. 2: Model of Polysaccharide. (Source: DOE Genome Programs. Courtesy of the U.S. Department of Energy) |
The development of a hybrid yeast strain capable of aggressively fermenting sugars into ethanol at elevated temperatures and ethanol concentrations from pretreated forests and agriculture residuals would greatly improve the efficiency of the biomass conversion process. Some researchers are trying to develop novel hybrid yeast strains that enhance the efficiency of industrial-scale biomass conversion. [3] Developing heat and ethanol tolerant yeast would allow a process which could convert xylose and glucose to ethanol which are cannot be fermented to ethanol with current processes. [3]
The Biomass Research and Development Technical Advisory Committee of the USDA and DOE set vision goals of 5% of energy, 20% of transportation fuel, and 25% of chemicals being derived from biomass by 2030. [4] Current practice of ethanol production is not enough to achieve these goals which are dependent on the net productivity of the plant used. [2] In order for these goals to be achieved research methods of increasing the amount of energy captured by plants and improving the efficiency of the fermentation process must be successful. Genetic modification for enhanced biomass production and the development of a hybrid yeast strain for the enhancement of fermentation are two methods in which researchers are trying to bridge the gap between vision goals to reality.
© Lauren Jaramillo. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] L. Yaris et al., Innovative Energy Solutions from the San Francisco Bay Area: Fueling a Clean Energy Future," Bay Area Science and Innovation Consortium (BASIC), June 2007.
[2] C. Somerville et al., "Toward a Systems Approach to Understanding Plant Cell Walls," Science 306 2206 (2004).
[3] K. Schwartz et al., "APJ1 and GRE3 Homologs Work in Concert to Allow Growth in Xylose in a Natural Saccharomyces sensu stricto Hybrid Yeast," Genetics 191, 621 (2012).
[4] "Vision for Bioenergy and Biobased Products in the United States," Biomass Research and Development Initiative, 2006.