Microwave assisted pretreatment and enzymatic hydrolysis for sugar production from Sago palm bark
Sago palm bark (SPB) is lignocellulosic biomass feedstock and a by-product of starch industry in Malaysia. The complex structure of lignocellulosic materials makes it resistant to enzymatic hydrolysis. Current technologies including physical and chemical pretreatment methods result in relatively...
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| Format: | Thesis |
| Language: | English |
| Published: |
2017
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| Subjects: | |
| Online Access: | http://psasir.upm.edu.my/id/eprint/70987/1/FK%202017%2011%20-%20IR.pdf |
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| Summary: | Sago palm bark (SPB) is lignocellulosic biomass feedstock and a by-product of starch
industry in Malaysia. The complex structure of lignocellulosic materials makes it
resistant to enzymatic hydrolysis. Current technologies including physical and
chemical pretreatment methods result in relatively low sugar yields, severe reaction
conditions and high processing costs. A green and low energy pretreatment process is
proposed using microwave irradiation. SPB was subjected to microwave-assisted
pretreatment to assess the effects of pretreatment using diluted acid and alkaline
solvents on sago palm bark characteristics and inhibitor formation. The effects of
microwave-assisted pretreatment parameters (operating conditions) was also
evaluated on glucose and xylose yield via enzymatic hydrolysis. Additionally, an
estimation model for glucose and xylose yield from the enzymatic hydrolysis of SPB
based on microwave-assisted pretreatment conditions was developed.
The microwave-assisted pretreatments utilized three solvents which are 0.1 N H2SO4
(MSA), 0.1 N NaOH (MSH), and 0.01 N NaHCO3 (MSB). The microwave-assisted
methods were compared to conventional heating pretreatment. The experimental
design was done using a response surface methodology (RSM) and Box Bekhen
Design (BBD) was used to evaluate the main and interaction effects of the
pretreatment parameters on glucose and xylose yield obtained after the enzymatic
hydrolysis step. The pretreatment parameters ranged from 5-15% solid loading (SL),
5-15 minutes of exposure time (ET) and 80-800 W of microwave power (MP). The
enzymatic hydrolysis was carried out using 24 FPU/g of cellulase, 2 UN/g of xylanase
and 50 U/g of β-glucosidase. An estimation model for glucose and xylose yield from
the enzymatic hydrolysis of SPB was developed by using artificial neural network
(ANN) and particle swarm optimization (PSO). The above-mentioned artificial
intelligent systems were combined to form a hybrid PSO–ANN model.
The MSA pretreatment resulted in higher lignin and hemicellulose degradation giving
more porous structure of SPB compared to microwave-assisted alkaline and
conventional pretreatments. No degradation products such as furfural, acetic acid and HMF were found in MSA pretreatment liquor. Conversely, conventional pretreatment
using 0.1 N H2SO4 produced 0.47 mg/ml of acetic acid. After the enzymatic hydrolysis
steps, it is revealed that the microwave-assisted pretreatment methods resulted in a
higher sugar yield than conventional pretreatment methods. The results also show that
the pretreatment parameters played a crucial role in the trend of the glucose and xylose
yield from enzymatic hydrolysis of SPB. The results of glucose and xylose yield from
MSA pretreatment and enzymatic hydrolysis of SPB were selected to develop a hybrid
PSO–ANN model. The hybrid PSO–ANN model showed a higher regression
coefficient (R2) for the estimation and the experimental values of glucose and xylose
at 0.9939 and 0.9479, respectively. Meanwhile, R2 values of the RSM model were only
0.8901 and 0.8439 for glucose and xylose, respectively.
This study concluded that the SPB has the potentials to be developed as future
fermentable sugars source and the microwave-assisted pretreatment would be a
possible route to enhance the release of these sugars. |
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