Pretreatment of plant biomass can be achieved through various methods such as
physical or physical-chemical method like steam explosion, ammonia fibre explosion, CO 2 explosion; chemical method, like ozonolysis, acid hydrolysis, alkali
hydrolysis, organo-solvent; and biological method, like biomass treatment by fungus. Pretreatment process leads to reduction of crystallinity in cellulose, breakup of
lignin, removal of hemicellulose, etc. depending on the pretreatment method used.
The most frequent method used is steam explosion as inclusion of sulphuric acid,
sulphur dioxide or carbon dioxide in steam explosion can result in hemicellulose
elimination completely and effectiveness of enzymatic hydrolysis can also be
improved by preventing the production of inhibitory compounds. Hydrolysis rate
can be increased by CO 2 explosion because of carbonic acid formation and degradation of lignin and hemicellulose can be achieved through ozonolysis. The acid
hydrolysis is first diluted and then can be used for pretreatment process as concentrated acid is corrosive and damaging in nature and requires special reactors which
are resistant to corrosion. Alkaline hydrolysis is also one of the methods which
results in saponification of intermolecular ester bonds cross-linked and increase in
the porosity of lignocellulosic biomass. Biological pretreatment processes carried
out by various microorganisms such as fungi have many advantages as they require
less energy, mild environmental conditions and produce various enzymes which
attack cellulose, hemicellulose and lignin for their degradation; however, the hydrolysis rate is very low (Sun and Cheng 2002; Luque et al. 2016; Luque and Clark
2010; Rastogi and Shrivastava 2018; Lin and Tanaka 2006; Devarapalli and Atiyeh
2015; Peralta-Yahya and Keasling 2010; Balan 2014).
Fig. 2.2 Ethanol fermentation (Adapted from Open source)
46
N. Jaiswal et al.
physical or physical-chemical method like steam explosion, ammonia fibre explosion, CO 2 explosion; chemical method, like ozonolysis, acid hydrolysis, alkali
hydrolysis, organo-solvent; and biological method, like biomass treatment by fungus. Pretreatment process leads to reduction of crystallinity in cellulose, breakup of
lignin, removal of hemicellulose, etc. depending on the pretreatment method used.
The most frequent method used is steam explosion as inclusion of sulphuric acid,
sulphur dioxide or carbon dioxide in steam explosion can result in hemicellulose
elimination completely and effectiveness of enzymatic hydrolysis can also be
improved by preventing the production of inhibitory compounds. Hydrolysis rate
can be increased by CO 2 explosion because of carbonic acid formation and degradation of lignin and hemicellulose can be achieved through ozonolysis. The acid
hydrolysis is first diluted and then can be used for pretreatment process as concentrated acid is corrosive and damaging in nature and requires special reactors which
are resistant to corrosion. Alkaline hydrolysis is also one of the methods which
results in saponification of intermolecular ester bonds cross-linked and increase in
the porosity of lignocellulosic biomass. Biological pretreatment processes carried
out by various microorganisms such as fungi have many advantages as they require
less energy, mild environmental conditions and produce various enzymes which
attack cellulose, hemicellulose and lignin for their degradation; however, the hydrolysis rate is very low (Sun and Cheng 2002; Luque et al. 2016; Luque and Clark
2010; Rastogi and Shrivastava 2018; Lin and Tanaka 2006; Devarapalli and Atiyeh
2015; Peralta-Yahya and Keasling 2010; Balan 2014).
Fig. 2.2 Ethanol fermentation (Adapted from Open source)
46
N. Jaiswal et al.