Modeling of pretreatment condition of extrusion-pretreated prairie cordgrass and corn stover with poly (oxyethylen)20 sorbitan monolaurate.
ABSTRACT Extrusion processing has shown potential to be used as a pretreatment method for second-generation bioethanol production. Furthermore, surfactants have been shown to reduce enzyme deactivation and increase the efficiency of hydrolysis. Therefore, a sequential pretreatment technique was developed for corn stover (CS) and prairie cordgrass (PCG) in which a single screw extruder was used for the first pretreatment according to a previously optimized condition using 70-180 °C for feed, barrel, and die zones with 65-155 rpm screw speed. The second pretreatment was optimized in this study at 45-55 °C, 1-4 h, 0.15-0.6 g Tween 20/g glucan according to response surface methodology. Optimization of surfactant pretreatment facilitated the estimation of interaction and higher-order effects for major factors involved in surfactant treatment (temperature, time, surfactant loading). Using 8.6 FPU/g glucan cellulase, the optimum conditions found by fitting appropriate quadratic models to the data increased glucose and xylose yield by 27.5 and 33% for CS and by 21.5 and 27% for PCG, respectively. Tween 20 concentrations and pretreatment temperature were the most significant factors affecting sugar yield (p value <0.05). Studies of SDS concentration at and beyond critical micelle concentration (5.2-100 mM) demonstrated a decrease in sugar yield compared to control.
SourceAvailable from: Bishnu Karki[Show abstract] [Hide abstract]
ABSTRACT: Fed-batch, solid state, simultaneous saccharification and fermentation (SSF) was evaluated as an approach to reduce enzyme use in converting cellulose to ethanol, and to maximize ethanol titer. Kraft pulp, an intermediate in paper production, was used to represent a fractionated cellulose feedstock. Following a literature survey, average dosages were determined as 34 FPU of cellulase (Celluclast 1.5L) and 135 CBU of β-glucosidase (Novozyme 188) per gram glucan, and were set as 100% dosages. Initially, submerged fed-batch SSF trials were conducted in a traditional bioreactor using enzyme dosages of 17, 33, 67, and 133%, with a final solids loading rate (SLR) of 14%. Ethanol production was similar (77.3-83.4% of theoretical yield) for trials with 33-133% enzyme dosages, but fell to 36% of theoretical at 17% enzyme dosage. Fed-batch saccharification and fed-batch SSF were then performed in a solid state bioreactor, achieving a 34.8% SLR. This reduced the initial 133% enzyme dosage to 19%. In saccharification trials the glucose yield was only 35% of theoretical (103.6 g/L), due to feedback inhibition of enzymes. Companion SSF trials achieved an ethanol yield of only 20% of theoretical (30.1 g/L ethanol). While some ethanol was lost due to evaporation, yeast inhibition by low water activity was presumed to be the primary limitation. Performance at lower solid loading rates were evaluated, and even diluted the fermented slurry and conducted a secondary fermentation. These trials suggest that enzyme inactivation via irreversible binding may be the primary limitation, instead of low water activity or nutrient limitation
[Show abstract] [Hide abstract]
ABSTRACT: Enzymatic hydrolysis of lignocellulosic biomass is limited by rapid cellulase deactivation, consequently requiring large amounts of enzyme to maintain acceptable biomass conversion. In this study, a new approach to improve lignocellulose hydrolysis was investigated. Performing enzymatic hydrolysis of corn stover (CS) in the presence of polymeric–surfactant micelles (PMs) was demonstrated to improve hydrolysis yield to a greater extent than using only surfactant micelles. Application of 2 % (w/w) of polyethylene glycol (PEG 6000) with casein, Tween-20, and Triton X-100 at levels above the critical micelle concentrations increased the hydrolysis yield of CS containing high-bound lignin (extrusion-pretreated) by up to 87.8, 11.7, and 7.5 %, respectively. These PMs were not effective during enzymatic hydrolysis of biomass lacking lignin (Avicel) or alkali-pretreated CS (7.2 % lignin). The main reasons for the enhanced cellulase activity observed due to PEG-casein, PEG-Tween, and PEG-Triton were enhanced cellulase solubilization; reformation of α-helix substructure; and combination of induced cellulase solubilization, α-helix reformation, and chemical changes in the microstructure of biomass, respectively. Deformation of the cellulase substructure during hydrolysis of biomass and its subsequent reformation in the presence of surfactants were shown in this study for the first time. Chemical changes in the microstructure of biomass (e.g., lignin side changes, C–O bonds, and amorphous cellulose) were found to be another potential reason for the effectiveness of surfactants when they are incubated at above 6 g/L for 72 h with biomass.BioEnergy Research 03/2014; 7(1). DOI:10.1007/s12155-013-9379-3 · 3.40 Impact Factor
[Show abstract] [Hide abstract]
ABSTRACT: An enzyme producing micro-organism, which can directly saccharify rice straw that has only been crushed without undergoing the current acid or alkaline pretreatment, was found. From the homology with the ITS, 28S rDNA sequence, the strain named A592-4B was identified as Penicillium oxalicum. Activities of the A592-4B enzymes and commercial enzyme preparations were compared by Novozymes Cellic CTec2 and Genencore GC220. In the present experimental condition, activity of A592-4B enzymes was 2.6 times higher than that of CTec2 for degrading milled rice straw. Furthermore, even when a quarter amount of A592-4B enzyme was applied to the rice straw, the conversion rate was still higher than that by CTec2. By utilizing A592-4B enzymes, improved lignocellulose degradation yields can be achieved without pre-treatment of the substrates; thus, contributing to cost reduction as well as reducing environmental burden.Bioscience Biotechnology and Biochemistry 01/2015; DOI:10.1080/09168451.2014.993913 · 1.21 Impact Factor