Therefore, with the crystallization of cellulose, the surface area where enzymes can
act on biomass is expanded (Bhatia et al. 2017; Singh and Satapathy 2018). Another
method, carbon dioxide (CO 2 ) explosion application, is based on the use of high
pressure (1000–4000 psi) supercritical CO 2 . CO 2 used in this method, which is
similar to AFEX and steam explosion methods, hydrolyzes cellulose, hemicellulose
structure with high pressure and provides the delignification by entering very small
pores of lignocellulosic structure. Hence, the surface area of the substrate for
enzymatic processes is increased (Alvira et al. 2010; Agbor et al. 2011).
9.2.4 Biological Methods
Biofuels obtained as a result of the biological transformation of lignocellulosic
biomass with biological pretreatment have been highly demanded as a promising
alternative to fossil fuels in recent years (Saha et al. 2016; da Silva and Ferraz 2017).
Biological pretreatment is an environmentally friendly, a reliable, an inexpensive,
and a green method used in the conversion of lignocellulosic raw material to biofuel
since it does not require chemical treatment compared to other pretreatment methods
(Singh et al. 2008a; Mood et al. 2013) and is carried out by means of microorganisms
and enzyme systems. Therefore, biological pretreatment methods can be divided into
two main groups as microbial pretreatment and enzymatic pretreatment. In addition,
the preprocessing time depends on the structure and composition of the biomass used
and the type of microorganism preferred. For example, the lignin removal of the
lignocellulosic material takes a long time. Pretreatment methods using fungal organisms take longer than bacterial or enzymatic pretreatments (Zabed et al. 2019).
According to some researches, white-rot fungi (Ceriporia lacerate, Cyathus
stercoreus, and Pycnoporus cinnarbarinus (Kumar et al. 2009), Ceriporiopsis
subvermispora, Phanerochaete chrysosporium, and Pleurotus ostreatus (Shi et al.
2008)), brown rot fungi (Coniophora puteana (Zabed et al. 2019), Serpula
lacrymans (Sánchez 2009), and Gleophyllum trabeum (Bhatia et al. 2017), and
soft-rot fungi (Paecilomyces sp., Daldinia concentrica, and Cadophora spp.)
(Bhatia et al. 2017) can easily break down lignin and hemicellulose structures by
its high delignification performance (Sánchez 2009).
A number of researchers have stated that the use of white-rot fungi is more
efficient in the biological pretreatment of lignocellulosic material than other processes (Balat 2011). White-rot fungi, involved in lignin degradation, synthesize
lignin-degrading enzymes such as peroxidase and laccase in the biological
pretreatment of lignocellulosic material (Kumar et al. 2009).
However, in delignification, fungi that are capable of degrading lignin are more
preferred rather than bacteria (Rashid et al. 2017). Furthermore as reported in a
research, some bacterial strains, such as Bacillus sp. AS3, Bacillus circulans,
Sphingomonas paucimobilis, Cellulomonas, and Zymomonas sp., produce less
ligninolytic enzymes than fungi (Bhatia et al. 2017). According to a study, among
some aerobic bacteria that can degrade lignin are actinomycetes, γ-proteobacteria,
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act on biomass is expanded (Bhatia et al. 2017; Singh and Satapathy 2018). Another
method, carbon dioxide (CO 2 ) explosion application, is based on the use of high
pressure (1000–4000 psi) supercritical CO 2 . CO 2 used in this method, which is
similar to AFEX and steam explosion methods, hydrolyzes cellulose, hemicellulose
structure with high pressure and provides the delignification by entering very small
pores of lignocellulosic structure. Hence, the surface area of the substrate for
enzymatic processes is increased (Alvira et al. 2010; Agbor et al. 2011).
9.2.4 Biological Methods
Biofuels obtained as a result of the biological transformation of lignocellulosic
biomass with biological pretreatment have been highly demanded as a promising
alternative to fossil fuels in recent years (Saha et al. 2016; da Silva and Ferraz 2017).
Biological pretreatment is an environmentally friendly, a reliable, an inexpensive,
and a green method used in the conversion of lignocellulosic raw material to biofuel
since it does not require chemical treatment compared to other pretreatment methods
(Singh et al. 2008a; Mood et al. 2013) and is carried out by means of microorganisms
and enzyme systems. Therefore, biological pretreatment methods can be divided into
two main groups as microbial pretreatment and enzymatic pretreatment. In addition,
the preprocessing time depends on the structure and composition of the biomass used
and the type of microorganism preferred. For example, the lignin removal of the
lignocellulosic material takes a long time. Pretreatment methods using fungal organisms take longer than bacterial or enzymatic pretreatments (Zabed et al. 2019).
According to some researches, white-rot fungi (Ceriporia lacerate, Cyathus
stercoreus, and Pycnoporus cinnarbarinus (Kumar et al. 2009), Ceriporiopsis
subvermispora, Phanerochaete chrysosporium, and Pleurotus ostreatus (Shi et al.
2008)), brown rot fungi (Coniophora puteana (Zabed et al. 2019), Serpula
lacrymans (Sánchez 2009), and Gleophyllum trabeum (Bhatia et al. 2017), and
soft-rot fungi (Paecilomyces sp., Daldinia concentrica, and Cadophora spp.)
(Bhatia et al. 2017) can easily break down lignin and hemicellulose structures by
its high delignification performance (Sánchez 2009).
A number of researchers have stated that the use of white-rot fungi is more
efficient in the biological pretreatment of lignocellulosic material than other processes (Balat 2011). White-rot fungi, involved in lignin degradation, synthesize
lignin-degrading enzymes such as peroxidase and laccase in the biological
pretreatment of lignocellulosic material (Kumar et al. 2009).
However, in delignification, fungi that are capable of degrading lignin are more
preferred rather than bacteria (Rashid et al. 2017). Furthermore as reported in a
research, some bacterial strains, such as Bacillus sp. AS3, Bacillus circulans,
Sphingomonas paucimobilis, Cellulomonas, and Zymomonas sp., produce less
ligninolytic enzymes than fungi (Bhatia et al. 2017). According to a study, among
some aerobic bacteria that can degrade lignin are actinomycetes, γ-proteobacteria,
264
T. Karaytuğ et al.