Which of these fuels will play a major role in our future? The answer is not clear, as factors such as land availability, future technical innovation, environmental policy regulating greenhouse gas emissions, governmental subsidies for fossil fuel extraction/ processing, implementation of net metering, and public support for alternative fuels will all affect the outcome. A critical point is that as research and development continue to improve the efficiency of bio fuel production processes, economic feasibility will continue to improve.
Bio fuel production is best evaluated in the context of a bio refinery. In a bio refinery, agricultural feedstock and by-products are processed through a series of biological, chemical, and physical
processes to recover biofuels, biomaterials, nutraceuticals, polymers, and specialty chemical compounds.2,3 This concept can be compared to a petroleum refinery in which oil is processed to produce fuels, plastics, and petrochemicals. The recoverable products in a biorefinery range from basic food ingredients to complex pharmaceutical compounds and from simple building materials to complex industrial composites and polymers. Biofuels, such as ethanol, hydrogen, or biodiesel, and biochemicals, such as xylitol, glycerol, citric acid, lactic acid, isopropanol, or vitamins, can be produced for use in the energy, food, and nutraceutical/pharmaceutical industries. Fibers, adhesives, biodegradable plastics such as polylactic acid, degradable surfactants, detergents, and enzymes can be recovered for industrial use. Many biofuel compounds may only be economically feasible to produce when valuable coproducts are also recovered and when energyefficient processing is employed. One advantage of microbial conversion processes over chemical processes is that microbes are able to select their substrate among a complex mixture of compounds, minimizing the need for isolation and purification of substrate prior
to processing. This can translate to more complete use of substrate and lower chemical requirements for processing.
Early proponents of the biorefinery concept emphasized the zeroemissions goal inherent in the plan—waste streams, water, and heat from one process are utilized as feed streams or energy to another, to fully recover all possible products and reduce waste with maximized efficiency.2,3 Ethanol and biodiesel production can be linked effectively in this way. In ethanol fermentation, 0.96 kg of CO2 is produced per kilogram of ethanol formed. The CO2 can be fed to algal bioreactors to produce oils used for biodiesel production. Approximately 1.3 kg CO2 is consumed per kilogram of algae grown, or 0.5 kg algal oil produced by oleaginous strains. Another example is the potential application of microbial fuel cells to generate electricity by utilizing waste organic compounds in spent fermentation media from biofuel production processes.
Also encompassed in a sustainable biorefinery is the use of “green” processing technologies to replace traditional chemical processing. For example, supercritical CO2 can be used to extract oils and nutraceutical compounds from biomass instead of using toxic would allow for replacement of petroleum-derived products with sustainable, carbon-neutral, low-polluting alternatives. In addition to environmental benefits of biorefining, there are economic benefits as new industries grow in response to need.2,3 A thorough economic analysis, including ecosystem and environmental impact, harvest, transport, processing, and storage costs must be considered. The R&D Act of 2000 and the Energy Policy Act of 2005 recommend increasing biofuel production from 0.5 to 20 percent and biobased chemicals and materials from 5 to 25 percent,5 a goal that may best be reached through a biorefinery model. organic solvents such as hexane.4 Ethanol can be used in biodiesel production from biological oils in place of toxic petroleum-based methanol traditionally used.Widespread application of biorefineries