compared to that attained by using the rumen microbiome
alone. The MBM scheme with Trichoderma reesei biofilm
has resulted in 7.3 g/L SCFAs, which is 39% greater than
the simple rumen microbiome, utilizing 15 g/L of crystalline
cellulose as the substrate (Xiros et al. 2019). Oil palm empty
fruit bunch (EFB) is a rich source of polysaccharide and
potassium, but the conversion of the EFB lignocellulosic
biomass for biochemical and bioenergy is replete with
challenges due to its compact structure. The hydrothermal
(HT) pretreatment of the EFB in the presence or absence of a
sulfonated bentonite catalyst (HT cat ) has been reported, for
the evaluation of its impact on anaerobic digestion and
enzymatic hydrolysis. The catalyst and temperature in the
HT cat pretreatment have been shown to improve both the
production of biohydrogen and glucose up to 3.32–4.36 and
1.04–1.14-fold, respectively, as compared to the HT in the
absence of the catalyst. The catalyst present also improves
the lignin and hemicellulose removal from the EFB
(Charnnok et al. 2019).
Polyhydroxybutyrate (PHB), a polyhydroxyalkanoate
(PHA) polymers from polyester class, can be developed into
biodegradable plastics, to replace the fossil fuel-based
plastics. Different microorganisms have produced the
PHAs as intracellular (C) carbon and energy storage compounds, but the major challenge is for the production of
economically competitive PHAs. The use of inexpensive C
source for the microbial synthesis of PHAs could be an
effective strategy, such as the production of PHB by Ralstonia eutropha, utilizing an alkali-pretreated rice paddy
straw (Saratale and Oh 2015). The intracellular PHB accumulation of 75.5% within 48 h of fermentation has been
achieved, with the PHB yield of 11.4 g/L. Another important chemical, mainly synthesized using fossil resources, is
1,4-butanediol. It has a global production of around 2 million tons annually, for applications in plastics production and
other products. The commercial-scale microbial-based production of 1,4-butandiol from carbohydrates using Escherichia coli has been reported achieving relatively high yield
and efficiency (Burgard et al. 2016). A base-catalyzed pretreatment method with a naturally obtained Cupriavidus
strain has been developed with the potential to degrade
lignin and for PHAs biosynthesis. The use of Cupriavidus
basilensis B-8 enhances the rice straw digestibility for the
conversion of carbohydrate to achieve 984.2 mg/g of
reduced sugar, in combination with alkaline pretreatment. At
the same time, the PHA yield of 482.7 mg/L is attained via
the conversion of the detached lignin utilizing the ligninolytic bacteria (Si et al. 2018). One of the major challenge
for efficient biomass conversion is the presence of the inhibitor in the biomass hydrolysates that lowers the efficacy in
the bio-refinery setup involving the microbes as the biocatalyst. Acetic acid is the main inhibitor in the bioconversion
of xylose using S. cerevisiae strains, which limits the cell
growth, xylose consumption rate, and the product yield.
A new strain, XUSE, has been engineered for high tolerance
of acetic acid, during the bioconversion of xylose into
bioethanol. The developed XYSAE57 strain has efficiently
converted xylose to obtain the highest yield of 0.43–0.50 g
of ethanol/g of xylose, under the acetic acid stress of 2–
5 g/L. The XUSAE57 strain not only attains twofold
increase in ethanol production, but also enhances the xylose
consumption rate two-times greater than the XUSE at 4 g/L
acetic acid (Ko and Enkh-Amgalan 2020).
5.3 Biocomposites
The composite materials like fiber-board, plywood, particleboard, and oriented strand board, based on the use of
petroleum-derived adhesives, could result in hazardous
formaldehyde emission. A range of commercial oxidizing
enzymes (by oxidizing the phenolic compounds) and the
enzymatically pretreated lignin could be employed as
adhesives for lignocellulosic materials and also for boards
and laminates Enzymatic bonding techniques using peroxidase or laccase have been utilized in the lignocellulosicbased medium-density fiber-boards and particle-boards.
(Widsten and Kandelbauer 2008). The particle-board treated
with laccase has shown improved properties/stiffness. The
addition of enzyme mediators further elevates the enzymatic
oxidation of lignin (Batog et al. 2008). The adhesion property
of the fiber-boards from wheat straw is attributed to the
activation of fiber surface by oxidative pre-treatment during
defibration process (Halvarsson et al. 2009). The characteristics of dry-formed hardboard from soybean and wheat
straws biomass and from common soft wood fiber have been
evaluated, along with the adhesion characteristics of a
soybean-derived adhesive and the common ureaformaldehyde resin. The soybean and wheat straw exhibit
water resistance and mechanical properties suitable for the
manufacturing of hardboard, but with lesser water resistance
as compared to the hardboard from the wood fiber. The
soybean and wheat straw could be developed as co-fibers
without any treatment for both water resistance and
mechanical properties, comparable to the clean wood fiber
(Ye et al. 2005).
The biocomposites from wheat by-products, wheat straw
fibers and wheat gluten, have been fabricated utilizing the
thermomechanical method. The analyses of the mechanical
energy consumed during fabrication, contact angle dimensions, and the cryo-fractured surfaces prove that the adhesion at the wheat straw fiber/wheat gluten interface is
improved. This is due to the wheat straw fibers hydrophobicity as a result of consecutive grinding, and the large
surface area from the small fibers (Montaño-Leyva et al.
2013). The wheat straw-based biocomposites with high
378
B. A. Palvasha et al.
alone. The MBM scheme with Trichoderma reesei biofilm
has resulted in 7.3 g/L SCFAs, which is 39% greater than
the simple rumen microbiome, utilizing 15 g/L of crystalline
cellulose as the substrate (Xiros et al. 2019). Oil palm empty
fruit bunch (EFB) is a rich source of polysaccharide and
potassium, but the conversion of the EFB lignocellulosic
biomass for biochemical and bioenergy is replete with
challenges due to its compact structure. The hydrothermal
(HT) pretreatment of the EFB in the presence or absence of a
sulfonated bentonite catalyst (HT cat ) has been reported, for
the evaluation of its impact on anaerobic digestion and
enzymatic hydrolysis. The catalyst and temperature in the
HT cat pretreatment have been shown to improve both the
production of biohydrogen and glucose up to 3.32–4.36 and
1.04–1.14-fold, respectively, as compared to the HT in the
absence of the catalyst. The catalyst present also improves
the lignin and hemicellulose removal from the EFB
(Charnnok et al. 2019).
Polyhydroxybutyrate (PHB), a polyhydroxyalkanoate
(PHA) polymers from polyester class, can be developed into
biodegradable plastics, to replace the fossil fuel-based
plastics. Different microorganisms have produced the
PHAs as intracellular (C) carbon and energy storage compounds, but the major challenge is for the production of
economically competitive PHAs. The use of inexpensive C
source for the microbial synthesis of PHAs could be an
effective strategy, such as the production of PHB by Ralstonia eutropha, utilizing an alkali-pretreated rice paddy
straw (Saratale and Oh 2015). The intracellular PHB accumulation of 75.5% within 48 h of fermentation has been
achieved, with the PHB yield of 11.4 g/L. Another important chemical, mainly synthesized using fossil resources, is
1,4-butanediol. It has a global production of around 2 million tons annually, for applications in plastics production and
other products. The commercial-scale microbial-based production of 1,4-butandiol from carbohydrates using Escherichia coli has been reported achieving relatively high yield
and efficiency (Burgard et al. 2016). A base-catalyzed pretreatment method with a naturally obtained Cupriavidus
strain has been developed with the potential to degrade
lignin and for PHAs biosynthesis. The use of Cupriavidus
basilensis B-8 enhances the rice straw digestibility for the
conversion of carbohydrate to achieve 984.2 mg/g of
reduced sugar, in combination with alkaline pretreatment. At
the same time, the PHA yield of 482.7 mg/L is attained via
the conversion of the detached lignin utilizing the ligninolytic bacteria (Si et al. 2018). One of the major challenge
for efficient biomass conversion is the presence of the inhibitor in the biomass hydrolysates that lowers the efficacy in
the bio-refinery setup involving the microbes as the biocatalyst. Acetic acid is the main inhibitor in the bioconversion
of xylose using S. cerevisiae strains, which limits the cell
growth, xylose consumption rate, and the product yield.
A new strain, XUSE, has been engineered for high tolerance
of acetic acid, during the bioconversion of xylose into
bioethanol. The developed XYSAE57 strain has efficiently
converted xylose to obtain the highest yield of 0.43–0.50 g
of ethanol/g of xylose, under the acetic acid stress of 2–
5 g/L. The XUSAE57 strain not only attains twofold
increase in ethanol production, but also enhances the xylose
consumption rate two-times greater than the XUSE at 4 g/L
acetic acid (Ko and Enkh-Amgalan 2020).
5.3 Biocomposites
The composite materials like fiber-board, plywood, particleboard, and oriented strand board, based on the use of
petroleum-derived adhesives, could result in hazardous
formaldehyde emission. A range of commercial oxidizing
enzymes (by oxidizing the phenolic compounds) and the
enzymatically pretreated lignin could be employed as
adhesives for lignocellulosic materials and also for boards
and laminates Enzymatic bonding techniques using peroxidase or laccase have been utilized in the lignocellulosicbased medium-density fiber-boards and particle-boards.
(Widsten and Kandelbauer 2008). The particle-board treated
with laccase has shown improved properties/stiffness. The
addition of enzyme mediators further elevates the enzymatic
oxidation of lignin (Batog et al. 2008). The adhesion property
of the fiber-boards from wheat straw is attributed to the
activation of fiber surface by oxidative pre-treatment during
defibration process (Halvarsson et al. 2009). The characteristics of dry-formed hardboard from soybean and wheat
straws biomass and from common soft wood fiber have been
evaluated, along with the adhesion characteristics of a
soybean-derived adhesive and the common ureaformaldehyde resin. The soybean and wheat straw exhibit
water resistance and mechanical properties suitable for the
manufacturing of hardboard, but with lesser water resistance
as compared to the hardboard from the wood fiber. The
soybean and wheat straw could be developed as co-fibers
without any treatment for both water resistance and
mechanical properties, comparable to the clean wood fiber
(Ye et al. 2005).
The biocomposites from wheat by-products, wheat straw
fibers and wheat gluten, have been fabricated utilizing the
thermomechanical method. The analyses of the mechanical
energy consumed during fabrication, contact angle dimensions, and the cryo-fractured surfaces prove that the adhesion at the wheat straw fiber/wheat gluten interface is
improved. This is due to the wheat straw fibers hydrophobicity as a result of consecutive grinding, and the large
surface area from the small fibers (Montaño-Leyva et al.
2013). The wheat straw-based biocomposites with high
378
B. A. Palvasha et al.