hemicellulosic structure to be disrupted and solubilizing the lignin (Hendriks and
Zeeman 2009; Abdullah et al. 2020). Diluted and concentrated acids used in acidic
pretreatment are as follows: hydrochloric acid, sulfuric acid, acetic acid, formic acid,
phosphoric acid, nitric acid, oxalic acid, and maleic acid (Maurya et al. 2015; Bhatia
et al. 2017). However, as mentioned in a research conducted in 2010, concentrated
acids are less preferred in bioethanol production because they form inhibitory
compounds. The industrially preferred diluted acid method can be applied at both
high temperatures (180
C) in lesser time intervals and lower temperatures (120
C)
in a longer time scale (Alvira et al. 2010; Bhatia et al. 2017).
The alkali pretreatment method applied using various alkalis, such as NaOH,
KOH, Ca(OH) 2 , NH 4 OH, and Na 2 CO 3, is very effective in the solubility of lignin
compared to hemicellulose and cellulose (Singh and Satapathy 2018) because the
solubility of hemicellulose and cellulose is weaker in this technique compared to
other pretreatment methods (Carvalheiro et al. 2008). This method helps the access
of the enzyme to the material as it removes acetyl and uronic acid groups from the
structure of hemicellulose and cellulose (Mood et al. 2013).
Chemicals such as hydrogen peroxide (H 2 O 2 ) and ozone (O 3 ) are used in
pretreatment with oxidizing agents. Ozone gas is a strong water-soluble oxidant
and contributes to facilitating the use of cellulose by disrupting the structure of
hemicellulose and lignin (Balat 2011). Ozonolysis with ozone affects aromatic ring
structures (Maurya et al. 2015; Bhatia et al. 2017).
However, a deficiency of this method is that it is not suitable for all raw materials
containing lignocellulosic structure (Singh and Satapathy 2018). It has been used for
wastes from various agricultural products, such as wheat and rye straw, and has a
low yield (García-Cubero et al. 2009; Alvira et al. 2010).
9.2.3 Physiochemical Methods
Physiochemical pretreatment methods can be summarized as hot water, ammonia
fiber/freeze explosion (AFEX), steam explosion, and CO 2 explosion, respectively
(Bhatia et al. 2017). Biomass, which is subjected to other physical pretreatment
methods, is separated into its components by the steam-explosion method. In this
frequently used pretreatment method, the material is saturated using high pressure
(0.7–8.0 MPa) in the reactor, causing the temperature to increase by 160–260
C.
When the pressure suddenly decreases, the fiber structure of the biomass is destroyed
and the crystallinity of cellulose increases. Thus, hemicellulose and lignin are
dissolved, and the structure of cellulose becomes more accessible (Bhatia et al.
2017; Abdullah et al. 2020). This pretreatment method is generally preferred in
ethanol and biogas production (Singh and Satapathy 2018). Water is used in the
liquid hot water method in place of the steam, which is similar to the steam explosion
application and applied under pressure with high temperature (Mood et al. 2013).
According to the AFEX method, the hot liquid ammonia at 90–100
C for 30 min
and the high pressure are applied on the LCB, and its structure is disrupted.
9 Microbial and Bioinformatics Approach in Biofuel Production
263
Zeeman 2009; Abdullah et al. 2020). Diluted and concentrated acids used in acidic
pretreatment are as follows: hydrochloric acid, sulfuric acid, acetic acid, formic acid,
phosphoric acid, nitric acid, oxalic acid, and maleic acid (Maurya et al. 2015; Bhatia
et al. 2017). However, as mentioned in a research conducted in 2010, concentrated
acids are less preferred in bioethanol production because they form inhibitory
compounds. The industrially preferred diluted acid method can be applied at both
high temperatures (180
C) in lesser time intervals and lower temperatures (120
C)
in a longer time scale (Alvira et al. 2010; Bhatia et al. 2017).
The alkali pretreatment method applied using various alkalis, such as NaOH,
KOH, Ca(OH) 2 , NH 4 OH, and Na 2 CO 3, is very effective in the solubility of lignin
compared to hemicellulose and cellulose (Singh and Satapathy 2018) because the
solubility of hemicellulose and cellulose is weaker in this technique compared to
other pretreatment methods (Carvalheiro et al. 2008). This method helps the access
of the enzyme to the material as it removes acetyl and uronic acid groups from the
structure of hemicellulose and cellulose (Mood et al. 2013).
Chemicals such as hydrogen peroxide (H 2 O 2 ) and ozone (O 3 ) are used in
pretreatment with oxidizing agents. Ozone gas is a strong water-soluble oxidant
and contributes to facilitating the use of cellulose by disrupting the structure of
hemicellulose and lignin (Balat 2011). Ozonolysis with ozone affects aromatic ring
structures (Maurya et al. 2015; Bhatia et al. 2017).
However, a deficiency of this method is that it is not suitable for all raw materials
containing lignocellulosic structure (Singh and Satapathy 2018). It has been used for
wastes from various agricultural products, such as wheat and rye straw, and has a
low yield (García-Cubero et al. 2009; Alvira et al. 2010).
9.2.3 Physiochemical Methods
Physiochemical pretreatment methods can be summarized as hot water, ammonia
fiber/freeze explosion (AFEX), steam explosion, and CO 2 explosion, respectively
(Bhatia et al. 2017). Biomass, which is subjected to other physical pretreatment
methods, is separated into its components by the steam-explosion method. In this
frequently used pretreatment method, the material is saturated using high pressure
(0.7–8.0 MPa) in the reactor, causing the temperature to increase by 160–260
C.
When the pressure suddenly decreases, the fiber structure of the biomass is destroyed
and the crystallinity of cellulose increases. Thus, hemicellulose and lignin are
dissolved, and the structure of cellulose becomes more accessible (Bhatia et al.
2017; Abdullah et al. 2020). This pretreatment method is generally preferred in
ethanol and biogas production (Singh and Satapathy 2018). Water is used in the
liquid hot water method in place of the steam, which is similar to the steam explosion
application and applied under pressure with high temperature (Mood et al. 2013).
According to the AFEX method, the hot liquid ammonia at 90–100
C for 30 min
and the high pressure are applied on the LCB, and its structure is disrupted.
9 Microbial and Bioinformatics Approach in Biofuel Production
263