sugars including (D-glucose, D-galactose, D-xylose,
D-mannose, L-arabinose) and some organic acids. In hemicellulose, the arabinose to xylose ratio regulates the rate of
branching. An increased rate of polymerization and shorter
polymer chain is due to the low ratio and vice versa. Hydrogen
bonding is parent bonding in these polymers; however,
covalent bonding is also noted among hemicellulose and lignin structures that provide strength and stamina to these substances (Kumar 2019; Dhyani and Bhaskar 2018). Lignin is
considered to be the most complex, abundant aromatic, and
amorphous triple dimensional phenyl biopolymer. Lignin
biosynthesis forms from a combination of three different
monolignols: p-coumaryl, sinapyl, and coniferyl alcohol
responsible for solid structure formation. Different monolignols interact to form lignin namely guaiacyl (G), p-hydroxyphenyl (H), and syringyl (S) (Abu Yazid et al. 2017; Paul
and Dutta 2018; Bilal et al. 2017) acts as a cross-linking resin
that assists in the binding of fibrous cellulose and hemicellulose constituents. It is found on the exterior portion of
microfibrils and attached covalently with hemicellulose and
provides cell wall rigidity (Kumar 2019). The lignocellulosic
composition of different wastes is presented in Table 1.
Agro and agro-industrial waste contain complex substances such as bagasse, grass stems, cobs, fruit and husk
crabs, skin, bones, fat, or any portion of processed food
source (plant and animal) that can be used in the main
process (Abu Yazid et al. 2017; Obi et al. 2016). Now a
days, global trend shifts toward waste material utilization for
useful product production to boost the economic profit in
numerous industries. Lignocellulosic waste is used as a
substrate and is most vital feed as a renewable and natural
resource that is crucial for the operation of the modern
industrial sector (Mehmood et al. 2019; Nadeem 2019).
According to a study done domestically and internationally,
it has shown that all types of agricultural waste products,
especially poultry, animal feces, and agricultural grasses
have great potential for food and have the ability to expand
the soil for productive production capabilities. Therefore,
effective modification of the recycling of agricultural waste
and use has been crucial in controlling environmental pollution. Besides, dealing with a problem can also fix a major
energy problem (Maitan-Alfenas et al. 2015; Wang et al.
2016). In this era, it remains extremely important to turn
these wastes efficiently and economically into important
industrial and profitable products and decrease the harmful
effect of these pollutants on earth (Carota et al. 2018;
Murtaza et al. 2017; Naveed 2020).
1.1 Types of Lignocellulosic Biomass
The lignocellulosic biomass is categorized into three divisions: first (softwood), second (hardwood), and third
(grasses). Several differences are depending on the chemical
composition and composition that affect their ability to
rearrange or become disorganized (Zabed et al. 2016). The
hardwood is explained by the occurrence of large fluids that
drive vessels or pores that can remain separated through their
shape, size of plates formed, and structure of cell wall.
Generally, this second class of wood is identified in extensive leaves, parts of forests including moderate and tropical.
There is an important difference between hardwood and
softwood depending on the complexity and their biochemical confirmation. The hardwoods are commonly weightier
than softwoods and grow slowly in landscape. The maximum prominent geographies that distinguish hardwood from
softwood are the deficiency of pores. Northern hemisphere
region is a prominent source of this kind of wood. The
softwoods are well-packed with hemicellulose and lignin
that enable them to withstand the environment and need
strong durability conditions (Brandt et al. 2013).
Grasses are totally different from woods in terms of their
pores structure. Both perennial and annual grasses are
measured as widely used feed ingredients for biofuel production. Xylose is the main source of hemicellulose that
exists in the meadow and is easily breakable. Perennial
grasses have a high production rate but more environmentally friendly by comparison with annual grasses such as
corn stalks, rice, wheat straw, and sugarcane bagasse, e.g.,
the less content of lignin present in grasses makes good
desirable feedstock for biorefineries (Hassan et al. 2018).
Table 2 represents diverse types and sources of lignocellulosic material used for energy.
2 Biomass Conversion Methods
2.1 Pretreatment
The lignocellulosic biomass for trash often requires some
modification to its properties and structure before its usage in
some transformation process. Thus, biomass pretreatment is
a crucial parameter to break down multilayered molecular
structures into a simpler layer to obtain an effective result
that is followed by the conversion process. The main purpose of pretreatment is to improve the surface area, provide
easy access to enzymes, amend and solubilize the lignin in
the situation of biological methods and to reduce total
operating costs (Kan et al. 2016). Pretreatment methodology
requires lignocellulosic biomass to be categorized into different categories: Physical method of pretreatment requires
raising pressure and temperature causes modification in the
lignocellulosic structure that further causes a reduction in
biomass resistance. Chemical method of pretreatment uses
organic and inorganic substances, which causes interaction
between the intra- and inter-polymer bonding of cellulose,
350
T. Mehmood et al.
D-mannose, L-arabinose) and some organic acids. In hemicellulose, the arabinose to xylose ratio regulates the rate of
branching. An increased rate of polymerization and shorter
polymer chain is due to the low ratio and vice versa. Hydrogen
bonding is parent bonding in these polymers; however,
covalent bonding is also noted among hemicellulose and lignin structures that provide strength and stamina to these substances (Kumar 2019; Dhyani and Bhaskar 2018). Lignin is
considered to be the most complex, abundant aromatic, and
amorphous triple dimensional phenyl biopolymer. Lignin
biosynthesis forms from a combination of three different
monolignols: p-coumaryl, sinapyl, and coniferyl alcohol
responsible for solid structure formation. Different monolignols interact to form lignin namely guaiacyl (G), p-hydroxyphenyl (H), and syringyl (S) (Abu Yazid et al. 2017; Paul
and Dutta 2018; Bilal et al. 2017) acts as a cross-linking resin
that assists in the binding of fibrous cellulose and hemicellulose constituents. It is found on the exterior portion of
microfibrils and attached covalently with hemicellulose and
provides cell wall rigidity (Kumar 2019). The lignocellulosic
composition of different wastes is presented in Table 1.
Agro and agro-industrial waste contain complex substances such as bagasse, grass stems, cobs, fruit and husk
crabs, skin, bones, fat, or any portion of processed food
source (plant and animal) that can be used in the main
process (Abu Yazid et al. 2017; Obi et al. 2016). Now a
days, global trend shifts toward waste material utilization for
useful product production to boost the economic profit in
numerous industries. Lignocellulosic waste is used as a
substrate and is most vital feed as a renewable and natural
resource that is crucial for the operation of the modern
industrial sector (Mehmood et al. 2019; Nadeem 2019).
According to a study done domestically and internationally,
it has shown that all types of agricultural waste products,
especially poultry, animal feces, and agricultural grasses
have great potential for food and have the ability to expand
the soil for productive production capabilities. Therefore,
effective modification of the recycling of agricultural waste
and use has been crucial in controlling environmental pollution. Besides, dealing with a problem can also fix a major
energy problem (Maitan-Alfenas et al. 2015; Wang et al.
2016). In this era, it remains extremely important to turn
these wastes efficiently and economically into important
industrial and profitable products and decrease the harmful
effect of these pollutants on earth (Carota et al. 2018;
Murtaza et al. 2017; Naveed 2020).
1.1 Types of Lignocellulosic Biomass
The lignocellulosic biomass is categorized into three divisions: first (softwood), second (hardwood), and third
(grasses). Several differences are depending on the chemical
composition and composition that affect their ability to
rearrange or become disorganized (Zabed et al. 2016). The
hardwood is explained by the occurrence of large fluids that
drive vessels or pores that can remain separated through their
shape, size of plates formed, and structure of cell wall.
Generally, this second class of wood is identified in extensive leaves, parts of forests including moderate and tropical.
There is an important difference between hardwood and
softwood depending on the complexity and their biochemical confirmation. The hardwoods are commonly weightier
than softwoods and grow slowly in landscape. The maximum prominent geographies that distinguish hardwood from
softwood are the deficiency of pores. Northern hemisphere
region is a prominent source of this kind of wood. The
softwoods are well-packed with hemicellulose and lignin
that enable them to withstand the environment and need
strong durability conditions (Brandt et al. 2013).
Grasses are totally different from woods in terms of their
pores structure. Both perennial and annual grasses are
measured as widely used feed ingredients for biofuel production. Xylose is the main source of hemicellulose that
exists in the meadow and is easily breakable. Perennial
grasses have a high production rate but more environmentally friendly by comparison with annual grasses such as
corn stalks, rice, wheat straw, and sugarcane bagasse, e.g.,
the less content of lignin present in grasses makes good
desirable feedstock for biorefineries (Hassan et al. 2018).
Table 2 represents diverse types and sources of lignocellulosic material used for energy.
2 Biomass Conversion Methods
2.1 Pretreatment
The lignocellulosic biomass for trash often requires some
modification to its properties and structure before its usage in
some transformation process. Thus, biomass pretreatment is
a crucial parameter to break down multilayered molecular
structures into a simpler layer to obtain an effective result
that is followed by the conversion process. The main purpose of pretreatment is to improve the surface area, provide
easy access to enzymes, amend and solubilize the lignin in
the situation of biological methods and to reduce total
operating costs (Kan et al. 2016). Pretreatment methodology
requires lignocellulosic biomass to be categorized into different categories: Physical method of pretreatment requires
raising pressure and temperature causes modification in the
lignocellulosic structure that further causes a reduction in
biomass resistance. Chemical method of pretreatment uses
organic and inorganic substances, which causes interaction
between the intra- and inter-polymer bonding of cellulose,
350
T. Mehmood et al.