Environmental Engineering Reference
In-Depth Information
500
450
400
350
300
Corn
Fuel alcohol
250
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100
50
0
2001
2002
2003
2004
2005
Ye ar
2006
2007
2008
2009
FIGure 12.1
Total U.S. production of corn and fuel ethanol between 2001 and 2009. (Adapted from USDA,
Feed grains database: Yearbook tables. U.S. Department of Agriculture, Economic Research Service, 2009.
Available at www.ers.usda.gov/Data/FeedGrains/FeedYearbook.aspx (accessed July 17, 2009)) feed grains
database—yearbook tables.
yield, as show in Figure 12.1. A study by the U.S. Department of Agriculture (USDA) concludes
that food prices have risen very modestly because of the growth of corn-based ethanol, and the price
rises have been largely in the beef sector (because most corn grown in the United States is used as
feed), not in corn-based products such as cereals. It was calculated that even if corn prices were
to increase 50%, overall food prices would raise less than 1% (Leibtag 2008). However, the debate
is far from over because a diversity of opinions remains on this subject (cf. Pimentel et al. 2009).
Ultimately, the constraining factor on increasing ethanol production will be the land available for
feedstock supply growth as the ethanol market expands.
Although almost all ethanol in the United States is currently made from corn, there is substantial
interest in producing cellulosic ethanol, i.e., ethanol that is produced from wood, farming, and for-
estry residues or grasses rather than the starch in grains. According to the optimistic 2005 “Billion
Ton Study,” cellulosic ethanol has the potential to offset at least 30% of the current petroleum con-
sumption in the United States (Perlack et al. 2005). Thus, the potential for cellulosic ethanol is much
higher than that of corn ethanol.
However, cellulosic ethanol is not yet market-efficient, and a widespread cellulosic ethanol mar-
ket has yet to be created. This could change in the near future; worldwide, approximately 15 or
so commercial cellulosic ethanol plants are expected to be commissioned in the next few years,
with capacities ranging from 3.8 × 10
6
to 3.8 × 10
8
L/year. Most of these plants will be located in
the United States. The cellulosic ethanol plants will use various feedstocks, including corn stover,
bagasse, wheat straw, wood waste and residues, wood chips, municipal solid wastes, and switch-
grass. About a dozen demonstration plants and 20 pilot plants have also been built (Solomon et al.
2009). The wood chips would probably be produced from fast-growing trees such as willow shrubs
or poplar (Volk et al. 2006).
Cellulosic ethanol is expensive to produce for three main reasons. First, achieving economies
of scale is difficult because processing plants must be located near ethanol feedstocks since trans-
portation of the feedstocks is expensive. Thus, processing plant necessarily have to be limited in
size because the maximum shipping range for the feedstock is approximately 120 km (Froese et
al. 2008). Interestingly, this could provide an opportunity for numerous small-scale markets to
be created, rather than one or several large markets, as is the case with grain. Second, the initial
capital costs for constructing processing plants are much larger than for grain ethanol plants. This
is because of the need for pretreatment of the biomass and the high cost of utilities. For example,
