Alkaline
pretreatment has been commonly used for bioconversion
of lignocellulose into fuel ethanol due to its gentle condition. However,
the large quantity of water consumption and wastewater generation
from the pretreatment and washing steps have been two bottleneck problems
for the practical application of alkaline pretreatment. In order to
save water consumption and reduce wastewater generation, black liquor
(BL) generated in the sodium hydroxide (NaOH) pretreatment process
was recycled for pretreating sugarcane bagasse (SCB), and the BL-NaOH-treated
SCB without being washed was directly enzymatically hydrolyzed and
fermented. After 120-h fed-batch enzymatic hydrolysis with the addition
of 20 FPU cellulase/g cellulose and 2.51 μL Tween80/mL hydrolytic
slurry, the maximum glucose concentration and enzymatic hydrolysis
efficiency achieved 99.95 g/L and 71.02%, respectively. After 36-h
fermentation with the domesticated Saccharomyces cerevisiae, the ethanol production reached 44.53 g/L, which amounted to 87.35%
of theoretical ethanol yield. Compared with other water-saving and
wastewater-reducing alkaline pretreatments, this technology saved
more than 20% water consumption and reduced over 20% wastewater discharge.
It provides a promising applied technology for cellulosic ethanol
production.
Reduction
in the adsorption of cellulase onto lignin has been thought
to be the common reason for the improvement of enzymatic hydrolysis
of lignocellulose (EHLC) by a nonionic surfactant (NIS). Few research
studies have focused on the relationship between lignocellulosic features
and NIS for improving EHLC. This study investigated the impact of
Tween20 on the enzymatic hydrolysis and enzyme adsorption of acid-treated
and alkali-treated sugarcane bagasse (SCB), cypress, and Pterocarpus soyauxii (PS) with and without being
ground. After addition of Tween20, the adsorption of cellulase onto
unground and ground alkali-treated SCB increased, and the unground
acid-treated SCB exhibited little change in adsorption cellulase,
while other unground and ground, treated samples showed decreased cellulase adsorption. Tween20 could
improve the enzymatic hydrolysis of acid-treated SCB, while it had
little influence on the enzymatic hydrolysis of other treated materials.
After being ground, both cellulase adsorption and enzymatic hydrolysis
of treated lignocelluloses increased, and Tween20 could enhance the
enzymatic hydrolysis of acid-treated materials while hardly affected
the enzymatic hydrolysis of alkali-treated materials. This indicated
that the promotion effect of Tween20 on enzymatic hydrolysis of treated
lignocellulose could not be mainly ascribed to the hindrance of Tween20
to cellulase adsorption on lignin but was related to the lignocellulosic
features such as hemicellulose removal and surface morphology changes.
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