Environmental Engineering Reference
In-Depth Information
In this example 75% of sugarcane bagasse produced in the mills is being used as raw material for
bioethanol production in the integrated process. The figure represents a feasible configuration in the
years to come, when sugarcane burning is abolished and sugarcane straw is efficiently recovered
from the field.
Although polysaccharides can be easily hydrolyzed with acids producing free sugars, when
this is done, part of the free monosaccharides produced will be destroyed by the acid and form
furfurals, which are toxic to yeast (Cortez et al. 2008). As a result, acid hydrolysis has never
become economically viable in industry. An alternative is the use of enzymes, which are much
more precise, to break the glycosidic linkages among monosaccharides. However, the prob-
lem in this case is to prompt enough water within the microfibrils so that hydrolysis can occur.
Hydrolases can be used directly on the fiber residue and a blind search may lead to good extracts
from microorganisms. However, if one understands what linkages have to be broken to loosen
the wall, much less energy can be used in the process, making it more efficient. The use of poly-
saccharide hydrolases obtained from microorganisms, insects and the plants themselves, is the
strategy that is now being developed in most initiatives to produce ethanol from biomass and sug-
arcane (Buckeridge et al. 2010). This is a very complex task and will probably be achieved by the
combination of the strategies of pretreatment of biomass using physical and chemical methods,
together with enzymatic hydrolysis.
21.11 Future ProsPects: research and develoPment
For ProductIvIty and sustaInaBIlIty
Since 1975 R&D has improved the productivity of ethanol from sugarcane more than 80% (from
4200 to 7650 L/ha). The main contributions to these productivity gains came from the develop-
ment of new varieties through classical breeding, improvements in the fermentation processes and
improvements in the agricultural processes. R&D has also been instrumental in obtaining more
efficient use of energy in ethanol mills, reducing GHG emissions from the agricultural processes
and reducing water, negative environmental impacts and defensive use.
In almost all studies of sugarcane physiology and biochemistry, the ability of the plant to pro-
duce sucrose has been the main target of research. This is plausible as this plant is so important to
sugar and ethanol world production. As a consequence, several authors have focused their lines of
research in sugar biochemistry and source-sink relationships. Moore (2005) has reviewed sugarcane
physiology from the viewpoint of systems biology. He proposes that any scientific approach should
target the interactions among the several network connections that lead to higher sugar accumula-
tion. These networks include the layers of gene transcription, which leads to protein production
and interactions and subsequently leads to metabolic changes in plant tissues. A few relevant ques-
tions can be asked such as (1) How is photosynthesis connected to sucrose biosynthesis? (2) How
is carbon partitioned between nonstructural and structural carbohydrates? (3) How are the carbon
pathways connected with nitrogen metabolism? (4) How is all this integrated or how do hormones
perform the cross talk so that communication among biochemical, physiological and ecophysi-
ological stimuli is controlled? and finally (5) Can we alter physiology and metabolism regulation
to achieve the attributes of an Energy-Cane? Tools are needed if we want to improve sugarcane
either through marker-assisted breeding or transgenic approaches and the sequencing of the sugar-
cane genome will be an important step toward the development of the biotechnology for this crop.
Furthermore, these questions are very complex but interdisciplinary work and integrated databases
may solve some of these problems. This is so also because the morphology and physiological per-
formance of the plant is an emergent property of the integration of all of these factors. On the other
hand, such an approach can be considerably simplified by using modularity (Wagner et al. 2007).
Understanding how plants use the same module in different parts of its body will probably be key
not only to understanding how these modules connect, but also to applying what is learnt from how
different modules work, by using synthetic biology.
