Large quantity of bio-wastes is produced from different
sources including forestry, agriculture, industries, and
household solid waste in the world. These biomasses are
considered as waste materials particularly in the developing
countries and creating several environmental issues (Chen
et al. 2017; Worden et al. 2017). However, recent researches
have indicated that they can be used as the energy sources to
contribute in the global energy production such as bioethanol, biohydrogen, methane, and other value-added products
(Limayem and Ricke 2012; Xu et al. 2019; Keskin et al.
2019). Therefore, this review provides recent progress and
findings on biohydrogen production from lignocellulosic
biomass with a special focus on hemicellulose and discusses
the techno-economic bottleneck involved in hydrogen production from plant biomass.
1.1 Classification of Energy Sources
1.1.1 Biomass and Biofuels
Biomass originates from biological materials (plants or
animals) that can be used in energy production. Lignocellulosic biomass is a reliable source of energy since the early
age of human civilization. Fire is the major energy source
from biomass and provides thermal energy to keep warm
and be used for cooking food. There are several ways to
produce energy from biomass, for example, burning biomass
to produce heat in thermal plants (to run the steam engine
and generate electricity), and turning feedstocks into liquid
biofuels (ethanol) or biogas (hydrogen, oxygen, or methane)
(Giampietro et al. 1997). Biofuels are fuel(s) either solid,
liquid, or gaseous produced directly or indirectly from biomass (FAO 2004; Lee and Lavoie 2013). Biofuels are
grouped as first, second, and third-generation biofuels based
on the feedstock used and their technological innovation
(Lee and Lavoie 2013).
1.1.2 First-Generation Biofuels
First-generation biofuels are derived from edible food like
corn, sugar, and vegetable oil (Aro 2016). Bioethanol is a
major by-product produced from the fermentation of edible
crops like corn and sugars. Other feedstocks are widely used
to produce first-generation bioethanol including barley,
potato, sugar-beets, and sugarcane. The first-generation
biofuels can blend with petroleum-based fuels and potential improvement on exhaust emissions (Mancaruso et al.
2011). Though the first-generation biofuels have significant
positive impacts on environmental pollution and carbon
emission, it is not a sustainable energy production because
food security versus fuels is its major challenge. Still, it is
claimed that biodiesel is not a cost-efficient emission
reduction technology. Therefore, more cost-efficient alternative technologies are recommended.
1.1.3 Second-Generation Biofuels
Second-generation biofuels are derived from lignocellulosic
biomass such as crop and forest residues, and municipal
solid wastes (Begum and Dahman 2015). These biofuels are
more sustainable because they are cheap and produced from
abundant non-food plant materials. However, their production methods are still quite expensive and have several
technical barriers during the bioconversion processes
(Mancaruso et al. 2011).
1.1.4 Third-Generation Biofuels
Third-generation biofuels are produced by using algal biomass to manufacture diesel and gasoline (Neto et al. 2019).
The microalgae (examples: Nannochloropsis granulate,
Spirulina maxima) can provide different types of renewable
biofuel like methane, biodiesel, gasoline, biohydrogen,
and jet fuel. Thus, algae can provide a promising source
of future fuel and other valuable products (Chowdhury et al.
2019).
2 Lignocellulosic Biomass
Lignocellulosic biomass is the most abundant plant material
and is inexpensive, eco-friendly, and abundant renewable
resource. It can be used in biofuels, chemicals, and polymer
production (Li et al. 2007). There are three major components of lignocellulosic biomass: cellulose (40–60%),
hemicellulose (20–40%), and lignin (10–24%) (Sharma et al.
2019). However, the composition of these three primary
components varies based on plant type, age, cultivation, and
climate conditions.
2.1 Cellulose
Cellulose is the most abundant and major structural component of the plant cell wall (Fig. 1). It is an organized
fibrous structure consisting of D-glucose subunits connected
by b-1,4 glycosidic bonds (Fengel and Wegener 1989; Pérez
et al. 2002). This linkage in carbohydrate or polysaccharide
makes cellulose as a straight chain polymer (also called as
cellulose microfibrils) (Pérez et al. 2002). The microfibril
structure of cellulose is composed of alternating crystalline
and amorphous regions (Fengel and Wegener 1989; Nanda
et al. 2014). The amorphous form of cellulose is susceptible
to enzymatic decomposition (Kumar et al. 2009).
2.2 Hemicellulose
It is the second most abundant polysaccharide found in plant
biomass (Fig. 1). Hemicellulose is composed of short lateral
268
J. R. Khatiwada et al.
sources including forestry, agriculture, industries, and
household solid waste in the world. These biomasses are
considered as waste materials particularly in the developing
countries and creating several environmental issues (Chen
et al. 2017; Worden et al. 2017). However, recent researches
have indicated that they can be used as the energy sources to
contribute in the global energy production such as bioethanol, biohydrogen, methane, and other value-added products
(Limayem and Ricke 2012; Xu et al. 2019; Keskin et al.
2019). Therefore, this review provides recent progress and
findings on biohydrogen production from lignocellulosic
biomass with a special focus on hemicellulose and discusses
the techno-economic bottleneck involved in hydrogen production from plant biomass.
1.1 Classification of Energy Sources
1.1.1 Biomass and Biofuels
Biomass originates from biological materials (plants or
animals) that can be used in energy production. Lignocellulosic biomass is a reliable source of energy since the early
age of human civilization. Fire is the major energy source
from biomass and provides thermal energy to keep warm
and be used for cooking food. There are several ways to
produce energy from biomass, for example, burning biomass
to produce heat in thermal plants (to run the steam engine
and generate electricity), and turning feedstocks into liquid
biofuels (ethanol) or biogas (hydrogen, oxygen, or methane)
(Giampietro et al. 1997). Biofuels are fuel(s) either solid,
liquid, or gaseous produced directly or indirectly from biomass (FAO 2004; Lee and Lavoie 2013). Biofuels are
grouped as first, second, and third-generation biofuels based
on the feedstock used and their technological innovation
(Lee and Lavoie 2013).
1.1.2 First-Generation Biofuels
First-generation biofuels are derived from edible food like
corn, sugar, and vegetable oil (Aro 2016). Bioethanol is a
major by-product produced from the fermentation of edible
crops like corn and sugars. Other feedstocks are widely used
to produce first-generation bioethanol including barley,
potato, sugar-beets, and sugarcane. The first-generation
biofuels can blend with petroleum-based fuels and potential improvement on exhaust emissions (Mancaruso et al.
2011). Though the first-generation biofuels have significant
positive impacts on environmental pollution and carbon
emission, it is not a sustainable energy production because
food security versus fuels is its major challenge. Still, it is
claimed that biodiesel is not a cost-efficient emission
reduction technology. Therefore, more cost-efficient alternative technologies are recommended.
1.1.3 Second-Generation Biofuels
Second-generation biofuels are derived from lignocellulosic
biomass such as crop and forest residues, and municipal
solid wastes (Begum and Dahman 2015). These biofuels are
more sustainable because they are cheap and produced from
abundant non-food plant materials. However, their production methods are still quite expensive and have several
technical barriers during the bioconversion processes
(Mancaruso et al. 2011).
1.1.4 Third-Generation Biofuels
Third-generation biofuels are produced by using algal biomass to manufacture diesel and gasoline (Neto et al. 2019).
The microalgae (examples: Nannochloropsis granulate,
Spirulina maxima) can provide different types of renewable
biofuel like methane, biodiesel, gasoline, biohydrogen,
and jet fuel. Thus, algae can provide a promising source
of future fuel and other valuable products (Chowdhury et al.
2019).
2 Lignocellulosic Biomass
Lignocellulosic biomass is the most abundant plant material
and is inexpensive, eco-friendly, and abundant renewable
resource. It can be used in biofuels, chemicals, and polymer
production (Li et al. 2007). There are three major components of lignocellulosic biomass: cellulose (40–60%),
hemicellulose (20–40%), and lignin (10–24%) (Sharma et al.
2019). However, the composition of these three primary
components varies based on plant type, age, cultivation, and
climate conditions.
2.1 Cellulose
Cellulose is the most abundant and major structural component of the plant cell wall (Fig. 1). It is an organized
fibrous structure consisting of D-glucose subunits connected
by b-1,4 glycosidic bonds (Fengel and Wegener 1989; Pérez
et al. 2002). This linkage in carbohydrate or polysaccharide
makes cellulose as a straight chain polymer (also called as
cellulose microfibrils) (Pérez et al. 2002). The microfibril
structure of cellulose is composed of alternating crystalline
and amorphous regions (Fengel and Wegener 1989; Nanda
et al. 2014). The amorphous form of cellulose is susceptible
to enzymatic decomposition (Kumar et al. 2009).
2.2 Hemicellulose
It is the second most abundant polysaccharide found in plant
biomass (Fig. 1). Hemicellulose is composed of short lateral
268
J. R. Khatiwada et al.