Environmental Engineering Reference
In-Depth Information
2.2 Lignocellulosic Biomass
There are a large variety of lignocellulosic materials containing varying composi-
tions of lignin, cellulose and hemicellulose that are ideal feedstocks for a biorefin-
ery. These materials can also provide a complex mixture of phytochemicals which
may find use in high-value applications. In order to maximise the potential of such
feedstocks, a holistic approach with the use of innovative clean technologies
should be used to obtain the maximum value and number of products from these
renewable resources. Two agricultural residues which offer great potential as
feedstocks for biorefineries are sugarcane bagasse and wheat straw. Here we will
focus on how phytochemicals (waxes) from agricultural residues, such as sugar-
cane bagasse and wheat straw, can be utilised in higher-value applications.
Sugarcane (
Saccharumofficinarum
) is a tall, perennial, C
4
grass belonging to
the Poaceae family [3]. The plant originated from south and southeast Asia, but is
now widespread throughout various tropical and sub-tropical countries [3, 4]. It is
approximately 5 cm thick and generally grows to a height of 2-6 m. The crop is
cultivated in around 200 countries and a number of different horticultural varieties
exist, differing in length and stem colour [3]. According to the world crop sta-
tistics that have been gathered by the Food and Agriculture Organization (FAO),
the global harvest of sugarcane has drastically changed over the past six decades
from 260 million tonnes in 1950, to 770 million tonnes in 1980 to 1,525 million
tonnes in 2007. There has been nearly a six-fold increase in the global sugarcane
harvest from 1950 to 2007 [4]. The top three countries (Brazil, India and China)
contributed around 67% of the total sugarcane production in 2010; Brazil alone
contributed approximately 43%. The global sugarcane production and expansion
is therefore dominated by Brazil. From 2000 to 2007, 75% of sugarcane area
increases was solely attributed to Brazil [4].
The sugarcane is processed in conventional sugar mills, which involves crush-
ing the sugarcane to extract the juices followed by heating of the juices to form
syrup and crystallising out the sugar from the syrup [4]. A fibrous residue remains
after conventional milling, which is referred to as sugarcane bagasse [5]. This is a
lignocellulosic material which is collected in large amounts following sugarcane
processing. In a typical sugar mill, the processing of 1 metric tonne of sugarcane
yields around 270 kg of bagasse (with 50% moisture), which produces approxi-
mately 135 kg of dry matter [6, 7].
Sugar and ethanol plants normally use around 50% of this dry matter to gener-
ate heat and power. The rest is normally stockpiled by sugar mills, which poses an
environmental problem to both the sugar mills and surrounding districts since
stockpiling for long periods of time could increase the risk of spontaneous combus-
tion [8]. There have been various reports which highlight the use of this sugarcane
bagasse in a variety of applications ranging from animal feed to the production of
various industrial enzymes (cellulases, lipases, etc.), chemicals, pulp and paper
[8]. As such, sugarcane bagasse is an ideal feedstock for utilisation as part of an
