maize, wheat, etc. The major limitations of using feedstock are its cost, cost of
enzymes and cost of ethanol recovery which ultimately results in higher production
cost. So, attention is now given on the use of non-feedstock, agricultural wastes or
lignocellulosic feedstocks, like stalks, sawdust, wood and bagasse, which can be
used as a substrate for production of bioethanol by using advanced technology, in
order to produce the fuel with least carbon emission and to eliminate food security
issues (Ingale et al. 2014).
Lignocellulose is basically the part of the plant that remains undigested and it is a
mixture of lignin, hemicellulose and cellulose that can be hydrolysed into sugar and
fermented to ethanol directly. It contains hexose (glucose, galactose) and pentose
sugars (xylose, arabinose). Sugarcane bagasse (the pulpy fibrous residue which is
left after the sugarcane is crushed to extract the juice) is a by-product of sugar
industry which is available in an abundant amount and rich in cellulose that can be
hydrolysed for bioethanol production. Lignocellulose is the most abundant renewable resource and alternative for bioethanol production. As it covers the wastes that
can be collected from agriculture, forest and industries, the land use for bioethanol
production would be less. The use of lignocellulose has many advantages as it is less
expensive and can be produced with lower input of fertilizers, pesticides and energy.
On one hand, the production cost of bioethanol is affected by the purchase price of
feedstock with lignocellulose being less expensive as compared with prices of corn,
sugarcane, etc. On the other hand, the conversion cost of lignocellulosic biomass
using current technology is high which in turn can be overcome by incorporation of
improved and advanced technology (Jiang et al. 2017; Lamsal et al.
2015; Ramachandra and Hebbale 2020; Alfonsín et al. 2019).
2.5.2 Stages of Bioethanol Production
Production of bioethanol from lignocellulosic biomass is done in majorly three
important steps—the first step includes the pretreatment of substrates while the
next step is the saccharification process, i.e. converting polysaccharides present in
biomass into fermentable sugars. Fermentation is the final step wherein conversion
of released sugars into alcohol takes place by microorganisms in absence of oxygen.
The bioethanol produced can then be finally purified by distillation (Figs. 2.2 and
2.3).
Pretreatment is the primary and important step in bioethanol production from
lignocellulosic biomass. This process eases separation of complex carbohydrate
molecules like cellulose, hemicellulose and lignin into their constituent simple
sugars, thus, preparing the biomass for the hydrolysis. Therefore, pretreatment is
necessary to make them available easily to the enzymes required for saccharification.
The structure of cellulose (6-carbon sugar) and hemicellulose (5-carbon sugar) is
complex and after depolymerization, it requires efficient microorganisms for bioconversion of fermentable sugars into bioethanol.
2 Application of Microorganisms for Biofuel Production
45
enzymes and cost of ethanol recovery which ultimately results in higher production
cost. So, attention is now given on the use of non-feedstock, agricultural wastes or
lignocellulosic feedstocks, like stalks, sawdust, wood and bagasse, which can be
used as a substrate for production of bioethanol by using advanced technology, in
order to produce the fuel with least carbon emission and to eliminate food security
issues (Ingale et al. 2014).
Lignocellulose is basically the part of the plant that remains undigested and it is a
mixture of lignin, hemicellulose and cellulose that can be hydrolysed into sugar and
fermented to ethanol directly. It contains hexose (glucose, galactose) and pentose
sugars (xylose, arabinose). Sugarcane bagasse (the pulpy fibrous residue which is
left after the sugarcane is crushed to extract the juice) is a by-product of sugar
industry which is available in an abundant amount and rich in cellulose that can be
hydrolysed for bioethanol production. Lignocellulose is the most abundant renewable resource and alternative for bioethanol production. As it covers the wastes that
can be collected from agriculture, forest and industries, the land use for bioethanol
production would be less. The use of lignocellulose has many advantages as it is less
expensive and can be produced with lower input of fertilizers, pesticides and energy.
On one hand, the production cost of bioethanol is affected by the purchase price of
feedstock with lignocellulose being less expensive as compared with prices of corn,
sugarcane, etc. On the other hand, the conversion cost of lignocellulosic biomass
using current technology is high which in turn can be overcome by incorporation of
improved and advanced technology (Jiang et al. 2017; Lamsal et al.
2015; Ramachandra and Hebbale 2020; Alfonsín et al. 2019).
2.5.2 Stages of Bioethanol Production
Production of bioethanol from lignocellulosic biomass is done in majorly three
important steps—the first step includes the pretreatment of substrates while the
next step is the saccharification process, i.e. converting polysaccharides present in
biomass into fermentable sugars. Fermentation is the final step wherein conversion
of released sugars into alcohol takes place by microorganisms in absence of oxygen.
The bioethanol produced can then be finally purified by distillation (Figs. 2.2 and
2.3).
Pretreatment is the primary and important step in bioethanol production from
lignocellulosic biomass. This process eases separation of complex carbohydrate
molecules like cellulose, hemicellulose and lignin into their constituent simple
sugars, thus, preparing the biomass for the hydrolysis. Therefore, pretreatment is
necessary to make them available easily to the enzymes required for saccharification.
The structure of cellulose (6-carbon sugar) and hemicellulose (5-carbon sugar) is
complex and after depolymerization, it requires efficient microorganisms for bioconversion of fermentable sugars into bioethanol.
2 Application of Microorganisms for Biofuel Production
45