Environmental Engineering Reference
In-Depth Information
Breeding for Improvement
of Biofuel Crops
Past, Present, and Future
Anjanabha Bhattacharya
University of Georgia
Joseph E. Knoll
U.S. Department of Agriculture
contents
1.1 Introduction .............................................................................................................................. 3
1.2 The Past and Present—Ethanol and Biodiesel: The First-Generation Biofuels ....................... 4
1.2.1 Ethanol from Sugarcane ............................................................................................... 4
1.2.2 Ethanol from Grain ....................................................................................................... 6
1.2.2.1 Sweet Sorghum .............................................................................................. 6
1.2.3 Biodiesel from Conventional Oilseed Crops ................................................................ 7
1.2.4 Jatropha—A Possible Dedicated Source of Biodiesel .................................................. 7
1.3 The Present and Near Future—Cellulosic Ethanol from Crop Residues and Second-
Generation Biofuel Crops ......................................................................................................... 8
1.3.1 Crop Residues as a Source of Biofuels ......................................................................... 9
1.3.2 Perennial Grasses as Dedicated Biofuel Crops .......................................................... 10
1.3.3 Trees as a Biofuel Source ........................................................................................... 14
1.4 Conclusions and Future Prospects for Biofuel Crops ............................................................. 14
Disclaimer ........................................................................................................................................ 16
References ........................................................................................................................................ 16
1.1 IntroductIon
Initially when the potential of plants to produce liquid fuels was realized, the immediate focus was
to use food and feed crops such as sugarcane (sugar), maize (starch), or soybean (oil) for biofuel
production. Sugar can be directly fermented by yeast to produce ethanol, and starch can be easily
converted into fermentable sugars. Many types of fats and oils can be chemically converted into
biodiesel. Collectively, these fuels are known as first-generation biofuels. However, it was soon
realized that these crops alone cannot meet the current demand for fuel because converting these
crops into fuels is relatively inefficient with respect to the ratio energy output to input, mostly
because only a fraction of the plant is utilized. Also, increased production of crops for fuel use
has raised concerns about the environmental impacts of intensive agriculture and changing land
usage. In addition, with the rapidly growing human population and increasing demand for animal
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