Environmental Engineering Reference
In-Depth Information
TABLE 13.6 Comparison of gasoline and bioethanol on the basis of LCA
for driving 1 km
a
Gasoline
impact
Bioethanol
impact
Impact category
Unit
Global warming potential
0.25
0.05
kg CO
2
equivalent
10
-3
kg antimony equivalent
Abiotic depletion potential
1.7
0.3
10
-8
kg CFC-11 equivalent
Ozone layer depletion
potential
3.1
1.5
10
-4
kg ethylene equivalent
Photochemical oxidation
potential
1.6
1.5
Human and ecotoxicity
potential
0.017
0.078
kg 1,4-dichlorobenzene
equivalent
10
-4
kg SO
2
equivalent
Acidification potential
7.5
11
10
-4
kg PO
4
equivalent
Eutrophication potential
1.0
4.7
a
Based on values obtained from Luo et al. (2009).
problems caused by gasoline, which bioethanol might partly substitute, using life
cycle assessment (LCA). For comparison purposes, the functional unit used is the
amount of bioethanol or gasoline required for driving 1 km. The results of a
“
cradle
to grave
approach are shown in Table 13.6. Although bioethanol scores better on
CO
2
emission than gasoline does, because the sugarcane fixes CO
2
, there is still
net CO
2
emission. Regarding the other six used impact categories, bioethanol and gas-
oline each score best three times. It depends on the importance attributed to each
impact factor which fuel is to be preferred concerning LCA.
This LCA does not capture factors such as land use and competition between
agriculture for food and fuels. Cutting tropic rain forest for bioethanol production
is generally not accepted. However, much of the long-established agricultural area
in Brazil is used for extensive cattle breeding and would be suitable for sugarcane.
Also, the area used for soy far exceeds the sugarcane area. Thus, intensified sugarcane
growth leads indirectly and unintentionally to increased pressure on rain forests.
Besides economy and ecology, other factors play a role when choosing bioethanol
as fuel. It will lead to more jobs (in the agricultural sector) than gasoline does, and it
decreases dependency on oil-producing countries. This type of reasons has dominated
political discussions in the United States and led to subsidies for corn-based bioeth-
anol production, although in many studies corn-based bioethanol scores ecologically
lower than bioethanol based on sugarcane and even lower than gasoline.
”
13.3 SECOND-GENERATION BIOETHANOL PROCESSES
Alternative feedstocks that do not compete with food can be used for the production of
ethanol (and other fuels and chemicals) by fermentation. Alternative feedstocks can be
agricultural/forestry waste (often referred to as lignocellulosic or second-generation
feedstock), sludge from wastewater treatment plants, algae biomass, and so on. In this
section, we focus on lignocellulosic feedstocks.
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