Ultrasound Assisted Alkaline Pretreatment of Sugar Cane Bagasse for Bioethanol
production
Yalew W. Sitotaw1,2; Nigus Gabbiye1; Van Gerven T.2
1Bahir
Dar University, Bahir Dar Institute of Technology, Faculty Of Chemical And Food Engineering
2KULeuven, Department Of Chemical Engineering, ProcESS Division
Results
Introduction
 The objective of this work is to intensify the alkaline
pretreatment process of sugar cane bagasse by sonication.
Methods
Alkaline Pretreatment
 The effect of temperature, alkaline concentration and
ultrasonic power was studied in the pretreatment.
Parameters considered
Factors
Level 1
Temperature (oC)
30
Alkaline Concentration (%w/v)
0.5
Ultrasonic power (W)
50
Time (min)
30
0.2 – 0.5
Feed particle Size (mm)
1:40
Solid-Liquid Ratio (g/ml)
Duty Cycle (%)
100
24
Ultrasound Frequency (KHz)
50
Lignin Removal (%)
45
40
Level 3
80
4.5
200
 Sugar cane was purchased from the market and then
extracted, dried, milled and sieved in the laboratory.
30
20
10
Without Ultrasound
With Ultrasound
35
0
30
0
1
2
3
4
Alkali Concentration (%w/v)
25
5
Fig 8. Effect of alkali concentration on lignin removal
20
Without ultrasound
with ultrasound
15
20
30
40
50
60
Temperature (oC)
70
80
Reducing Sugars Conc. (g/L)
10
90
Fig 4. Effect of pretreatment temperature on lignin removal
 Increment in temperature favor delignification. Up to
39% increment in lignin removal can be achieved by
coupling alkali treatment with sonication. However,
higher temperature reduce cavitation effects, and bubble
implosion intensity becomes less.
50
40
30
20
10
Without Ultrasound
With Ultrasound
0
0
40
1
2
3
4
Alkali Concentration (%w/v)
5
Fig 9. Effect of alkali concentration on lignin removal
30
20
Effects of Sonication Power
Effect of US power On Lignin Removal
10
60
Without Ultrasound
With Ultrasound
0
0
1
2
3
Temperature (oC)
4
5
Fig 5. Effect of pretreatment temperature on reducing sugars concentration
Level 2
60
2.5
130
Lignin Removal (%)
Effects of Pretreatment Temperature
 The hydrolysis yield has found to have direct relation
with the extent of lignin removal. Increment in
temperature is not only facilitates the action of alkali in
lignin removal, but also increase the surface area
available for subsequent hydrolysis process.
SEM Micrographs
Smooth and Intact protective sheath
Fracturing and disruption of surfaces
Lignin Removal (%)
Objective
 Bagasse contain 44.7%cellulose, 21.0%hemicellulose,
22.4% lignin, 9.8% extractives and 2.1% Ash.
Reducing Sugars Conc. (g/L)
In conventional methods of treating lignocellulosic biomass,
alkaline pretreatment is relatively efficient in removal of lignin.
In addition, it causes less sugar decomposition and inhibitors
formation (Subhedar et al., 2014). However, requirement of
higher concentration of chemical and longer pretreatment
time are some of the associated drawbacks for the successful
implementation in large scale production (Subhedar et al.,
2018). In ultrasound assisted alkaline pretreatment, synergy
between ultrasound energy and alkali leads to intensification
of the process by decreasing the length of time and amounts of
chemicals required. Sonication leads to the formation and the
collapse of cavitation bubbles on the surface of the biomass
material which creates shear forces, higher temperature (up to
5000K) and pressure (1000bar) at the hotspot, and intense
micro-streaming (Santos et al., 2009). These all causes cell wall
disruption and mass transfer enhancement to increase the
lignin removal efficiency of alkaline pretreatment. Moreover,
the formation of free radicals from splitting of water molecules
catalyze the ether bond cleavage in lignin for its dissolution.
Consequently, efficient removal of lignin by pretreatment
provides pretreated material which can be easily hydrolyzed
by enzymes to yield fermentable sugars.
40
50
40
30
20
10
0
0
50
100
150
200
250
US Power (W)
Fig 10. Effect of ultrasound power on lignin removal
 Ultrasonication provided better delignification even at lower
power (50W). High power leads to bubble formation near tip
of the probe and hindered the transfer of energy to the liquid
medium
Temperature
probe
Ultrasonic processor
a
Conclusions
c
b
Figure 6. SEM micrographs,1000X: (a)Untreated bagasse, (b) Alkaline treated
@ 60oC, (c) Sono-assisted alkaline treated @ 60oC.
Parafilm cover
Smooth and Intact protective
sheath
Jacketed glass
reactor
Fracturing and disruption of surfaces
Magnetic
stirrer
Inlet and
outlets of
heating/cooling
water
Fig 1. formation and the collapse of
cavitation bubbles
Fig 2. Ultrasound assisted
alkaline pretreatment setup
Enzymatic Hydrolysis
5ml sodium acetate buffer (pH=4.9)
25µl β-glucasidase
25µl Endoglucanase
a
b
c
Figure 7. SEM micrographs,5000X: (a)Untreated bagasse, (b) Alkaline treated
@ 80oC, (c) Sono-assisted alkaline treated @ 80oC,
 As indicated on the SEM micrographs, sonication has
provided disrupted surfaces which weakened the cell
wall and aided the lignin dissolution in alkali solution.
Moreover, the new surfaces crated have improved
hydrolysis.
Effects of Alkali Concentration
Pretreated SCB
(0.250gm)
Hydrolysate to
reducing sugars
analysis
Fig 3. Enzymatic hydrolysis set up
 Increment in alkali concentration favor delignification
up to 2.5%w/v NaOH concentration and further
increment provided no additional benefit with in the
parameters considered (Fig. 8). In addition, synergetic
effect between sonication and alkali treatment facilitates
lignin removal.
 In general, Ultrasound energy has proven to increase
delignification of sugar cane bagasse. Up to 39.2%
delignification increment has been achieved compared
to conventional alkali pre-treatment. More over,
sonication with lower power, has the potential to provide
synergetic effect in enhancing the removal of lignin and
change surface morphology of the bagasse. Eventually,
these improved the hydrolysis yield.
Reference
A. Sluiter, B. Hames, R. Ruiz, C. Scarlata, J. Sluiter, D. Templeton, D. Crockr (2008),
Determination of structural carbohydrates and lignin in biomass Laboratory
Analytical Procedure, NREL/TP-510-42618.
Miller, G.L. (1959) Use of dinitrosalicylic acid reagent for determination of
reducing sugar. Analytical Chemistry. 31, 426-428.
P.B. Subhedar, Pearl Ray, Parag R. Gogate, (2018), Intensification Of
Delignification And Subsequent Hydrolysis For The Fermentable Sugar
Production From Lignocellulosic Biomass Using Ultrasonic Irradiation.
Ultrasonics Sonochemistry 40:140–150.
P.B. Subhedar, P.R. Gogate (2014), Alkaline and ultrasound assisted alkaline
pretreatment for intensification of delignification process from sustainable rawmaterial, Ultrason. Sonochem., 21, pp. 216-225.
Santos, Hugo Miguel, Carlos Lodeiro and José‐Luis Capelo‐Martínez. “The Power
of Ultrasound.” (2009).
Acknowledgment
A special gratitude is forwarded to Prof. Tom Van Gerven and staffs of ProcESS division in chemical engineering department of KULeuven for material and
academic supports. Appreciaciation is also forwarded to, Dr. Nigus Gabbiye in BiT, Prof. Ivo Vankelecom and Dr. Abaynesh Yihdego in KULeuven.