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Description:
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Lignocellulose is a promising and valuable alternative energy source . Native
lignocellulosic biomass has limited accessibility to cellulase enzyme due to structural
features ; therefore , pretreatment is an essential prerequisite to make biomass accessible
and reactive by altering its structural features .
The effects of substrate concentration , addition of cellobiase , enzyme loading ,
and structural features on biomass digestibility were explored . The addition of
supplemental cellobiase to the enzyme complex greatly increased the initial rate and
ultimate extent of biomass hydrolysis by converting the strong inhibitor , cellobiose , to
glucose . A low substrate concentration (10 g /L ) was employed to prevent end -product
inhibition by cellobiose and glucose . The rate and extent of biomass hydrolysis
significantly depend on enzyme loading and structural features resulting from
pretreatment , thus the hydrolysis and pretreatment processes are intimately coupled
because of structural features .
Model lignocelluloses with various structural features were hydrolyzed with a
variety of cellulase loadings for 1 , 6 , and 72 h . Glucan , xylan , and total sugar
conversions at 1 , 6 , and 72 h were linearly proportional to the logarithm of cellulase
loadings from approximately 10 % to 90 % conversion , indicating that the simplified
HCH -1 model is valid for predicting lignocellulose digestibility . Carbohydrate
conversions at a given time versus the natural logarithm of cellulase loadings were
plotted to obtain the slopes and intercepts which were correlated to structural features (lignin content , acetyl content , cellulose crystallinity , and carbohydrate content ) by both
parametric and nonparametric regression models .
The predictive ability of the models was evaluated by a variety of biomass (corn
stover , bagasse , and rice straw ) treated with lime , dilute acid , ammonia fiber explosion
(AFEX ) , and aqueous ammonia . The measured slopes , intercepts , and carbohydrate
conversions at 1 , 6 , and 72 h were compared to the values predicted by the parametric
and nonparametric models . The smaller mean square error (MSE ) in the parametric
models indicates more satisfactorily predictive ability than the nonparametric models .
The agreement between the measured and predicted values shows that lignin content ,
acetyl content , and cellulose crystallinity are key factors that determine biomass
digestibility , and that biomass digestibility can be predicted over a wide range of
cellulase loadings using the simplified HCH -1 model . |