186
7 Resource Utilization of Agricultural/Forestry Residues …
7.3.3 Extrusion
Extrusion is the most commonly used physical treatment method for lignocellulosic biomass for biogas and bioethanol production. In this method, the biomass
is subjected to heating, mixing and shredding by passing through screws that spin
into a tight barrel. The speed of the screws and the barrel temperature disrupt the
recalcitrant structure of biomass. Extrusion machines (or extruders) are available
in single screw and twin screw types. The design and configuration of the screws,
the screw speed and barrel temperature would affect the extrusion results [11, 18].
Extruders can be used combined with chemical solutions such as acids or alkali
during the process; however, this may lead to corrosion problems and require acidresistant material for the extruder screws and the barrel. The advantages of extrusion
pre-treatments are the low cost, no sugar degradation products, good adaptability to
different process modifications, continuous and high throughput, rapid heat transfer
and intensive mixing in a short residence time [22].
7.3.4 Ultrasonication
Ultrasonication is a new technique for pre-treatment of lignocellulosic biomass. It
involves the formation of small cavitation bubbles that generate shear forces and
disrupt the complex structure of lignocellulosic materials, leading to enhanced accessibility of cellulose and hemicellulose to enzymes and promoting the extraction of
desired compounds [18, 22]. The efficiency of the treatment process depends on a
number of factors, e.g., the ultrasound frequency, sonication time, power and temperature, reactor geometry and type, the type of solvent, biomass characteristics, reactor
kinetics, etc. [18, 22]. The advantages of ultrasound pre-treatment include the short
operating time, low temperature and lower amounts of chemicals used during further
valorization. This treatment can also be used in combination with other pre-treatment
methods [20]. Ultrasonication proved to be a viable pre-treatment method for lignocellulosic biomass due to its capability of disrupting various biomass structures;
however, the process requires high energy input and needs more research for applying
on a large scale [18].
7.4 Chemical Pre-treatment Methods
The conventional biomass refinery includes the production of bio-based products (mainly biofuels) using the whole biomass where saccharides from cellulose/hemicellulose are fermented into bio-ethanol, while the residues such as lignin
and the remaining cellulose and hemicelluloses are discarded or burned for power
generation [23]. Thus, only part of the feedstock is available for conversion. To
7 Resource Utilization of Agricultural/Forestry Residues …
7.3.3 Extrusion
Extrusion is the most commonly used physical treatment method for lignocellulosic biomass for biogas and bioethanol production. In this method, the biomass
is subjected to heating, mixing and shredding by passing through screws that spin
into a tight barrel. The speed of the screws and the barrel temperature disrupt the
recalcitrant structure of biomass. Extrusion machines (or extruders) are available
in single screw and twin screw types. The design and configuration of the screws,
the screw speed and barrel temperature would affect the extrusion results [11, 18].
Extruders can be used combined with chemical solutions such as acids or alkali
during the process; however, this may lead to corrosion problems and require acidresistant material for the extruder screws and the barrel. The advantages of extrusion
pre-treatments are the low cost, no sugar degradation products, good adaptability to
different process modifications, continuous and high throughput, rapid heat transfer
and intensive mixing in a short residence time [22].
7.3.4 Ultrasonication
Ultrasonication is a new technique for pre-treatment of lignocellulosic biomass. It
involves the formation of small cavitation bubbles that generate shear forces and
disrupt the complex structure of lignocellulosic materials, leading to enhanced accessibility of cellulose and hemicellulose to enzymes and promoting the extraction of
desired compounds [18, 22]. The efficiency of the treatment process depends on a
number of factors, e.g., the ultrasound frequency, sonication time, power and temperature, reactor geometry and type, the type of solvent, biomass characteristics, reactor
kinetics, etc. [18, 22]. The advantages of ultrasound pre-treatment include the short
operating time, low temperature and lower amounts of chemicals used during further
valorization. This treatment can also be used in combination with other pre-treatment
methods [20]. Ultrasonication proved to be a viable pre-treatment method for lignocellulosic biomass due to its capability of disrupting various biomass structures;
however, the process requires high energy input and needs more research for applying
on a large scale [18].
7.4 Chemical Pre-treatment Methods
The conventional biomass refinery includes the production of bio-based products (mainly biofuels) using the whole biomass where saccharides from cellulose/hemicellulose are fermented into bio-ethanol, while the residues such as lignin
and the remaining cellulose and hemicelluloses are discarded or burned for power
generation [23]. Thus, only part of the feedstock is available for conversion. To