that 2% (w/v) NaOH followed by 2% (w/v) sulfuric acid with autoclaving at 121
C
for 15 min produced maximum ethanol of 48.17 g/L [1].
The combination of microwave with alkaline pretreatment studies was also an
efficient hybrid method in producing reducing sugars. Pretreatment of SCT using
this method was able to remove 67% of the lignin from the biomass and hence
increases the cellulose and hemicellulose content making it more accessible for the
enzymes for the saccharification process. Furthermore, optimization of hydrolysis
process parameters using Box-Behnken design resulted in higher sugar yield of
0.376 g/g which represented 90.24% of the theoretical maximum based on the
contents of cellulose and hemicellulose present in the pretreated biomass [15].
6 Ultrasound Pretreatment
Ultrasound pretreatments are considered to be efficient technique due to the fractionation of the lignocelluloses present in the biomass into bioethanol. Most of the
other pretreatments including acid, alkali, ionic liquids, and steam are said to form
unwanted by-products which then result in the loss of carbohydrates. However
ultrasonic irradiation helps in the intensification of various pretreatment methods
employed in biomass, the principle behind the ultrasonication is the cavitation,
which involves the spontaneous growth and collapse of microsize cavities caused
due to the propagation of ultrasonic waves, further causing high temperatures and
pressure gradients. This results in the enhanced surface areas and leads to higher
transfer rate. It helps to accomplish the necessities for bioethanol production by the
formation of reactive cellulose fraction for reducing sugar formation along with
reduction in power requirements as well as permitting the usage of sources which are
inexpensive. The degree of fractionation can be increased by the combination of
ultrasound with conventional pretreatment techniques. The ultrasound when applied
to the biomass helps in disrupting the structure of the cell wall, increases the specific
surface area, and therefore decreases the degree of polymerization to higher extent
thereby enhancing the utilization of lignocellulosic biomass [21].
Yuan et al. [22] showed that the extent of delignification brought about by the
ultrasound pre-treatment is 96% as well as 75% removal of the hemicellulose present
by the ultrasound-assisted organosolv pretreatment [22].
Studies were also done on SCT based on surfactant-assisted ultrasound
pretreatment. Tween-40 being the surfactant produced reducing sugar of 0.661 g/g
after enzyme saccharification with process conditions as 3% (w/w) Tween-40 for
60 min, followed by sonication for 1 min and biomass loading at 20% w/w. SEM
results showed distorted structure of the pretreated sample since it helps in the
removal of some of the fibers present externally which appears to be in the form
of a complex [14].
96
S. Niju and M. Swathika
C
for 15 min produced maximum ethanol of 48.17 g/L [1].
The combination of microwave with alkaline pretreatment studies was also an
efficient hybrid method in producing reducing sugars. Pretreatment of SCT using
this method was able to remove 67% of the lignin from the biomass and hence
increases the cellulose and hemicellulose content making it more accessible for the
enzymes for the saccharification process. Furthermore, optimization of hydrolysis
process parameters using Box-Behnken design resulted in higher sugar yield of
0.376 g/g which represented 90.24% of the theoretical maximum based on the
contents of cellulose and hemicellulose present in the pretreated biomass [15].
6 Ultrasound Pretreatment
Ultrasound pretreatments are considered to be efficient technique due to the fractionation of the lignocelluloses present in the biomass into bioethanol. Most of the
other pretreatments including acid, alkali, ionic liquids, and steam are said to form
unwanted by-products which then result in the loss of carbohydrates. However
ultrasonic irradiation helps in the intensification of various pretreatment methods
employed in biomass, the principle behind the ultrasonication is the cavitation,
which involves the spontaneous growth and collapse of microsize cavities caused
due to the propagation of ultrasonic waves, further causing high temperatures and
pressure gradients. This results in the enhanced surface areas and leads to higher
transfer rate. It helps to accomplish the necessities for bioethanol production by the
formation of reactive cellulose fraction for reducing sugar formation along with
reduction in power requirements as well as permitting the usage of sources which are
inexpensive. The degree of fractionation can be increased by the combination of
ultrasound with conventional pretreatment techniques. The ultrasound when applied
to the biomass helps in disrupting the structure of the cell wall, increases the specific
surface area, and therefore decreases the degree of polymerization to higher extent
thereby enhancing the utilization of lignocellulosic biomass [21].
Yuan et al. [22] showed that the extent of delignification brought about by the
ultrasound pre-treatment is 96% as well as 75% removal of the hemicellulose present
by the ultrasound-assisted organosolv pretreatment [22].
Studies were also done on SCT based on surfactant-assisted ultrasound
pretreatment. Tween-40 being the surfactant produced reducing sugar of 0.661 g/g
after enzyme saccharification with process conditions as 3% (w/w) Tween-40 for
60 min, followed by sonication for 1 min and biomass loading at 20% w/w. SEM
results showed distorted structure of the pretreated sample since it helps in the
removal of some of the fibers present externally which appears to be in the form
of a complex [14].
96
S. Niju and M. Swathika