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FUELS FROM BIOMASS 259

sugars present in the cellulose and hemicellulose fractions of the lignocellulosic feedstock.
Although engineering technology exists to effectively separate the sugar containing frac-
tions from the lignocellulose, the enzyme technology to economically convert the five-ring
sugars to useful products requires further development.
The construction of both large biofuel and renewable chemical production facilities
coupled with the pace at which bioscience is being both developed and applied demon-
strates that the utilization of nonfood crops will become more significant in the near term
(Bourne, 2007). The biorefinery concept provides a means to significantly reduce produc-
tion costs such that a substantial substitution of petrochemicals by renewable chemicals
becomes possible. However, significant technical challenges remain before the biorefinery
concept can be realized.

8.7 THE FUTURE

To secure a quality life for current and future generations, sufficient land, water, and energy
must be available (Pimentel and Pimentel, 2006). By 2030, the world is projected to con-
sume two-thirds more energy than today, with developing countries replacing the indus-
trialized world as the largest group of energy consumers (Dorian et al., 2006). Energy
consumption clearly is an important factor in future energy planning. In this century, green
energy consumption may become an important parameter for indicating social, industrial,
economical, and technological development (Ermis et al., 2007).
Therefore, the issue is not whether renewable biofuels will play a role in providing
energy for transportation but to what extent and the implications of their use for the econ-
omy, for the environment, and for global security.
The rapidly growing interest in biofuels is being fueled by the realization that biofuels
represent the only large near-term substitute for the petroleum-based fuels. As a result,
biofuels are poised to be the potential solution to some very pertinent issues, such as rising
oil prices, increasing national and global insecurity, climate instability, and local as well as
global pollution levels.
The method chosen for biofuel production will be determined in part by the characteris-
tics of the biomass available for processing. The majority of terrestrial biomass available is
typically derived from agricultural plants and from wood grown in forests, as well as from
waste residues generated in the processing or use of these resources. The primary barrier to
utilizing this biomass is generally recognized to be the lack of low-cost processing options
capable of converting these polymers into recoverable base chemical components (Lynd
et al., 1999).
Currently, in the United States, much of the biomass being used for biofuel production
includes agricultural crops that are rich in sugars and starch. Because of the prevalence of
these feedstocks, the majority of U.S. activity toward developing new products has focused
on bioconversion (BRDTAC, 2002). Bioconversion isolates sugars from biomass, which
can then be processed into value-added products. Native sugars found in sugarcane and
sugar beet can be easily derived from these plants, and refined in facilities that require the
lowest level of capital input. Starch, a storage molecule which is a dominant component
of cereal crops such as corn and wheat, is comprised wholly of glucose. Starch may be
subjected to an additional processing in the form of an acid- or enzyme-catalyzed hydro-
lysis step to liberate glucose using a single family of enzymes, the amylases, which makes
bioconversion relatively simple. Downstream processing of sugars includes traditional fer-
mentation, which uses yeast to produce ethanol; other types of fermentation, including
bacterial fermentation under aerobic and anaerobic conditions, can produce a variety of
other products from the sugar stream.