Optimization of sodium hydroxide pretreatment and enzymatic saccharification of spent rubberwood sawdust for glucose production
Large quantities of oyster mushroom spent medium (MSM) were disposed of as agricultural waste to the environment and thereby constituting environmental pollution. Economic reuse of the waste mushroom medium to produce glucose might be a viable solution instead of disposal. Therefore, the study wa...
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| Format: | Thesis |
| Language: | English |
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| Online Access: | http://dspace.unimap.edu.my:80/xmlui/bitstream/123456789/44112/1/p.1-24.pdf http://dspace.unimap.edu.my:80/xmlui/bitstream/123456789/44112/2/full%20text.pdf |
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| Summary: | Large quantities of oyster mushroom spent medium (MSM) were disposed of as
agricultural waste to the environment and thereby constituting environmental pollution.
Economic reuse of the waste mushroom medium to produce glucose might be a viable
solution instead of disposal. Therefore, the study was conducted to improve the added
value of mushroom spent medium as an alternative glucose source to the current
expensive sugar crops and starchy products. Firstly, the chemical characteristics, surface
morphology, and suitability of mushroom spent medium in comparison to rubber
sawdust (RSD) and growth medium (GM) were examined in order to investigate its
potential as a new glucose feedstock. The composition analysis proved that decreases in
lignocellulosic contents occurred after cultivation of Pleurotus sajor caju. The amount
of lignin, hemicelluloses, and cellulose in MSM showed lower values than those in RSD
and GM which were 22.40, 27.93, and 27.97% respectively. The surface morphology of
MSM appeared to be rough and broken and traces of hyphen on the fibre surface were
observed as a result from the mushroom cultivation process. RSD and FM had an even
and smooth flat surface, indicating a rigid and highly ordered surface structure.
Preliminary study on effectiveness and feasibility of the three pretreatment techniques
(autoclaving at 121°C, heating in water bath, soaking at room temperature) with
different NaOH concentration on RSD, GM, and MSM revealed the best result of 30.13
g glucose/100g dry substrate and 33.50% of hydrolysis weight decrease obtained from
MSM, which had been treated in water bath at 90°C for 2 h. The scanning electron
microscope (SEM) images of the corresponding MSM hydrolysate showed severe
disruptions of biomass structure, irregular cracks, and pores. One factor at a time
(OFAT) method was applied to screen the range of parameters in NaOH pretreatment
via heating in water bath and enzymatic saccharification. With known parameters’
range, the Response surface methodology (RSM) based on Box-Behnken Design (BBD)
was adopted to optimize the conditions of NaOH pretreatment via heating in water bath
method and enzymatic saccharification of MSM. The optimum conditions of MSM
pretreatment at substrate loading of 5.0% (w/v) were found to be NaOH concentration
of 2.63 M, reaction temperature of 92.26°C, and treatment time of 112.92 min with
maximum glucose yield of 34.55 g/100g dry substrate after 48 h of enzymatic
saccharification at constant enzyme loading of 67 FPU/g dry substrate and substrate
loading of 1.0% (w/v). The MSM hydrolysate obtained under optimal NaOH
pretreatment conditions were further used to optimize enzymatic saccharification
conditions at constant substrate loading of 1.0% (w/v). Under optimized conditions
(agitation rate of 150.74 rpm, enzyme loading of 94.92 FPU/g substrate, and hydrolysis
time of 56.89 h), a maximum glucose yield of 71.21 g/100 g dry substrate was achieved.
The Analysis of Variance (ANOVA) test revealed that the model and all independent
parameters were considered statistically significant at 95% for both optimization studies
using the second order polynomial equation. The model validation showed a good
agreement between experimental results and the predicted responses. Therefore the
models could be successfully used to identify the effective combinations of the three
different factors in both optimization studies for predicting the glucose yield from
MSM. |
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