Environmental Engineering Reference
In-Depth Information
for improvement. Genomics and a systems biology approach might bring contributions to these
developments.
A systemic approach seems to be one of the principal routes to be taken to understand functioning
of the sugarcane plants, their integration with the environment and also the production processes that
lead from the crop to ethanol. The bioenergy-producing system imposes an immense challenge that
includes not only the scientific approaches of agriculture, physics, chemistry, biology, and engineer-
ing but also humanities approaches related to economy, health, and sociology. Producing bioethanol
in the twenty first century is not an ordinary task as it has to be sustainable from all points of view.
For that to happen, top level research will have to be undertaken. This will certainly include the use
of synthetic biology strategies that will probably produce much better adapted plants with minimal
environmental and social impacts and the development of new methods for converting sugars to
biofuels and cellulose to sugars and then to biofuels. While the fermentation of sugar to ethanol is a
process that has been well known for centuries, the production of other biofuels remains a scientific
and technical challenge. A recent development has been that of engineering microbes to process sug-
ars and secrete certain fuels, including gasoline, diesel, jet fuel, and others. Lee et al. (2008) reviewed
several possibilities of metabolic engineering strategies for increasing yields of some biofuels. The
technology depends on R&D in metabolic engineering and synthetic biology that might create new
means for metabolic engineers to better understand how to adjust the cell pathways to create pheno-
types with sufficient efficiency for the production of economically viable biofuels.
Sustainability issues became more prominent as biofuels came to be recognized as serious
alternatives to oil, implying the possibility of large scale production. In this theme, land, water,
and fertilizer use are relevant topics, as is the precise determination of GHG emissions reduction.
In Land Use Change studies, a relevant challenge is to establish the behavior of soil organic car-
bon (SOC). This knowledge is essential for the correct determination of the GHG emissions bal-
ance for sugarcane ethanol. The behavior of SOC depends on the specifics of the land use change
action. Table 21.5 shows the expected changes in SOC content related to sugarcane in the Brazilian
Atlantic Region (Mello et al. 2006). Large gains in carbon sequestration seem to be obtainable
through management modifications and by adequate choice of land. Of course, the contrary is true:
for example, planting sugarcane in established forests will cause carbon emissions, as pointed out
by Searchinger et al. (2008). It should be mentioned that most of the sugarcane expansion verified
in Brazil has been over degraded pastures, and not over forest land (Goldemberg 2008). Much
more R&D is necessary, mostly because the behavior of SOC is strongly dependent on specific
characteristics of the crop, as shown by Anderson-Teixeira et al. (2009). Water usage is another
issue that relates to the sustainability theme. Gerbens-Leenes et al. (2009) reviewed the literature
and estimated the Water Footprint (WF) for several biofuels. They pointed out that the WF for
taBle 21.5
Potential for soc sequestration Because of land-use change in the
layer from 0 to 20 cm related to sugarcane estimated by several authors
total area
(mha)
Potential for soc
sequestration (tg/year)
land-use change from
land-use change to
Sugarcane, harvested with
burning
Machine harvesting
3.3
5.35
Degraded pasture
Sugarcane without burning
1.93
0.19-1.54
Sugarcane harvested with
burning
Reforestation
1.93
1.27
Source:
Modified from Mello, F.F.C., et al.
Carbon Sequestration in Soils of Latin America
. Haworth
Press, New York, pp 349-368, 2006.
