Alkaline-assisted screw press pretreatment affecting enzymatic hydrolysis of wheat straw

Bioprocess and Biosystems Engineering - Screw press processing of biomass can be considered as a suitable mechanically based pretreatment for biofuel production since it disrupts the structure of...     

Enhanced enzymatic hydrolysis of wheat straw by aqueous glycerol pretreatment

Considering the practical technology-economy of glycerol processing from oleochemicals industry, the ensuing work was proposed to further explore the atmospheric aqueous glycerol autocatalytic organosolv pretreatment (AAGAOP) to improve the enzymatic hydrolysis of lignocellulosic biomass. With the liquid-solid ratio of 20 g g(-1) at 220 degrees C for 3h, the AAGAOP enabled wheat straw to remove approximately 70% hemicelluloses and approximately 65% lignin, with approximately 98% cellulose retention. The pretreated fiber was achieved with approximately 90% of the enzymatic hydrolysis yield after 48 h. At oven-drying, dehydration was likely to cause the hornification of fiber, which was responsible for the low enzymatic hydrolysis of dried fiber. With SEM observations, the AAGAOP disrupted wheat straw into thin and fine fibrils, with a small average size and more surface area. The AAGAOP technique, as a novel strategy, enhanced the enzymatic hydrolysis of lignocellulosic biomass by removing the chemically compositional barrier and altering the physically structural impediment.     

Effect of compounds released during pretreatment of wheat straw on microbial growth and enzymatic hydrolysis rates

In the process of producing ethanol from lignocellulosic materials such as wheat straw, compounds that can act inhibitory to enzymatic hydrolysis and to cellular growth may be generated during the pretreatment. Ethanol production was evaluated on pretreated wheat straw hydrolysate using four different recombinant Saccharomyces cerevisiae strains, CPB.CR4, CPB.CB4, F12, and FLX. The fermentation performance of the four S. cerevisiae strains was tested in hydrolysate of wheat straw that has been pretreated at high dry matter content (220 g/L dry matter). The results clearly showed that F12 was the most robust strain, whereas the other three strains were strongly inhibited when the fraction of hydrolysate in the fermentation medium was higher than 60% (v/v). Furthermore, the impact of different lignin derivatives commonly found in the hydrolysate of pretreated wheat straw, was tested on two different enzyme mixtures, a mixture of Celluclast 1.5 L FG and Novozym 188 (3:1) and one crude enzyme preparation produced from Penicillium brasilianum IBT 20888. From all the potential inhibiting compounds that were tested, formic acid had the most severe influence on the hydrolysis rate resulting in a complete inactivation of the two enzyme mixtures.     

Effect of pretreatment and enzymatic hydrolysis of wheat straw on cell wall composition, hydrophobicity and cellulase adsorption

The present study aimed to determine the impact of cell wall composition and lignin content on enzyme adsorption and degradability. Thioacidolysis analysis of residual lignins in wheat straw after steam-explosion or organosolv pretreatment revealed an increase in lignin condensation degree of 27% and 33%, respectively. Surface hydrophobicity assessed through wettability tests decreased after the pretreatments (contact angle decrease of 20-50%), but increased with enzymatic conversion (30% maximum contact angle increase) and correlatively to lignin content. Adsorption of the three major cellulases Cel7A, Cel6A and Cel7B from Trichoderma reesei decreased with increasing hydrolysis time, down to 7%, 31% and 70% on the sample with the highest lignin content, respectively. The fraction of unspecifically bound enzymes was dependent both on the enzyme and the lignin content. Adsorption and specific activity were shown to be inversely proportional to lignin content and hydrophobicity, suggesting that lignin is one of the factors restricting enzymatic hydrolysis.     

Effect of ozonolysis pretreatment on enzymatic digestibility of wheat and rye straw

Wheat and rye straws were pretreated with ozone to increase the enzymatic hydrolysis extent of potentially fermentable sugars. Through a 2(5-1) factorial design, this work studies the influence of five operating parameters (moisture content, particle size, ozone concentration, type of biomass and air/ozone flow rate) on ozonization pretreatment of straw in a fixed bed reactor under room conditions. The acid insoluble lignin content of the biomass was reduced in all experiments involving hemicellulose degradation. Near negligible losses of cellulose were observed. Enzymatic hydrolysis yields of up to 88.6% and 57% were obtained compared to 29% and 16% in non-ozonated wheat and rye straw respectively. Moisture content and type of biomass showed the most significant effects on ozonolysis. Additionally, ozonolysis experiments in basic medium with sodium hydroxide evidenced a reduction in solubilization and/or degradation of lignin and reliable cellulose and hemicellulose degradation.     

Organosolv pretreatment by crude glycerol from oleochemicals industry for enzymatic hydrolysis of wheat straw

In order to defray the cost of biodiesel production, the ensuing work was to further investigate utilization of the crude glycerol (CG) from oleochemicals industry in the atmospheric autocatalytic organosolv pretreatment (AAOP) to enhance enzymatic hydrolysis.

The AAOP–CG enabled wheat straw to achieve with reasonable enzymatic hydrolysis yields, reaching 75% for the wet substrate and 63% for the dried. Lipophilic compounds from the CG formed pitch deposition on the fiber, which was responsible for low delignification (30%) and also troublesome in practical operation. Pitch deposits itself had no significant role on enzymatic hydrolysis. A striking finding of the lignin recondensation and/or lignin–carbohydrate complex helped explain why dried pretreated wheat straw had a low enzymatic hydrolysis yield. The CG was suitable for the AAOP to enhance enzymatic hydrolysis of lignocellulosic biomass. But it was advisable to remove lipophilic compounds from crude glycerol before utilization.     

Correlating the effect of pretreatment on the enzymatic hydrolysis of straw

Avicell, Alkali-treated straw cellulose (ATSC), and wheat straw were ball-milled to reduce crystallinity; wheat straw was delignified by hot (120 degrees C) sodium hydroxide solutions of various concentrations. The physically and chemically pretreated cellulosic materials were hydrolyzed by the cellulases of Fusarium oxysporum strain F3. Enzymic hydrolysis data were fitted by the hyperbolic correlation of Holtzapple, which involves two kinetic parameters, the maximum conversion (X(max)), and the enzymic hydrolysis time corresponding to 50% of X(max) (t(1/2)). An empirical correlation between X(max) and cellulose crystallinity, lignin content, and degree of delignification has been found under our experimental conditions. Complete cellulose hydrolysis is shown to be possible at less than 60% crystallinity indices or less than 10% lignin content.     

Kinetic model of enzymatic hydrolysis of steam-exploded wheat straw

The hydrolysis kinetics of steam-exploded wheat straw treated with cellulase NS 50013 enzyme complex in combination with β-glucosidase NS 50010 is studied. The time dependence of the reducing sugars amount is followed at varying the temperature value and the amount of the enzyme introduced. The activation energy determined on the ground of the rate temperature dependence stays unchanged in the course of the process. The preexponential factor decreases with the increase of the degree of hydrolysis and is responsible for the process rate decrease. A new expression for the dependence of degree of hydrolysis of one of carbohydrate polymers (cellulose) in wheat straw on the time, the enzyme concentration and the temperature is obtained. It is of practical importance as well because it provides estimation of the degree of hydrolysis required at predetermined values of the temperature, the enzyme concentration and the time used. The expression can be used for control of the enzyme hydrolysis of cellulose in the wheat straw.     

Economic evaluation of enzymatic hydrolysis of phenol-pretreated wheat straw

Experimental data from the enzymatic hydrolysis of phenol-pretreated Swedish wheat straw have been used to evaluate the cost fractions of capital and utility, enzyme, and raw material. Two different raw material prices and varying enzyme prices have been used. The evaluation is based on an empirical model for the enzymatic hydrolysis and a computer program where utility and equipment, enzyme, and raw material prices can be varied. The optimal residence time for the enzymatic hydrolysis is in the range of 70-110 h. A fed-batch procedure with substrate concentrations higher than 10% oven-dried material (ODM) and enzyme concentrations in the range (6-10) . 10(6) FPU/ton ODM should be used.     

Effect of hydrogen peroxide pretreatment on the structural features and the enzymatic hydrolysis of rice straw

Assessment was made to evaluate the effect of hydrogen peroxide pretreatment on the change of the structural features and the enzymatic hydrolysis of rice straw. Changes in the lignin content, weight loss, accessibility for Cadoxen, water holding capacity, and crystallinity of straw were measured during pretreatment to express the modification of the lignocellulosic structure of straw. The rates and the extents of enzymatic hydrolysis, cellulase adsorption, and cellobiose accumulation in the initial stage of hydrolysis were determined to study the pretreatment effect on hydrolysis. Pretreatment at 60 degrees C for 5 h in a solution with 1% (w/w) H(2)O(2) and NaOH resulted in 60% delignification, 40% weight loss, a fivefold increase in the accessibility for Cadoxen, an one times increase in the water-holding capacity, and only a slight decrease in crystallinity as compared with that of the untreated straw. Improvement on the pretreatment effect could be made by increasing the initial alkalinity and the pretreatment temperature of hydrogen peroxide solution. A saturated improvement on the structural features was found when the weight ratio of hydrogen peroxide to straw was above 0.25 g H(2)O(2)/g straw in an alkaline H(2)O(2) solution with 1% (w/w) NaOH at 32 degrees C. The initial rates and extents of hydrolysis, cellulase adsorption, and cellobiose accumulation in hydrolysis were enhanced in accordance with the improved structural features of straw pretreated. A four times increase in the extent of the enzymatic hydrolysis of straw for 24 h was attributed to the alkaline hydrogen peroxide pretreatment.     

Improving enzymatic hydrolysis of wheat straw using ionic liquid 1-ethyl-3-methyl imidazolium diethyl phosphate pretreatment

This study aims to establish a cellulose pretreatment process using ionic liquids (ILs) for efficient enzymatic hydrolysis. The IL 1-ethyl-3-methyl imidazolium diethyl phosphate ([EMIM]DEP) was selected in view of its low viscous and the potential of accelerating enzymatic hydrolysis, and it could be recyclable. The yield of reducing sugars from wheat straw pretreated with this IL at 130 °C for 30 min reached 54.8% after being enzymatically hydrolyzed for 12 h. Wheat straw regenerated were hydrolyzed more easily than that treated with water. The fermentability of the hydrolyzates, obtained after enzymatic saccharification of the regenerated wheat straw, was evaluated using Saccharomyces cerevisiae. This microbe could ferment glucose efficiently, and the ethanol production was 0.43 g/g glucose within 26 h. In conclusion, the IL [EMIM]DEP shows promise as pretreatment solvent for wheat straw, although its cost should be reduced and in-depth exploration of this subject is needed.     

The enzymatic hydrolysis and fermentation of pretreated wheat straw to ethanol

Autohydrolysis and ethanol-alkali pulping were used as pretreatment methods of wheat straw for its subsequent saccharification by Trichoderma reesei cellulase. The basic hydrolysis parameters, i.e., reaction time, pH, temperature, and enzyme and substrate concentration, were optimized to maximize sugar yields from ethanol-alkali modified straw. Thus, a 93% conversion of 2.5% straw material to sugar syrup containing 73% glucose was reached in 48 h using 40 filter paper units/g hydrolyzed substrate. The pretreated wheat straw was then fermented to ethanol at 43 degrees C in the simultaneous saccharification and fermentation (SSF) process using T. reesei cellulase and Kluyveromyces fragilis cells. From 10% (w/v) of chemically treated straw (dry matter), 2.4% (w/v) ethanol was obtained after 48 h. When the T. reesei cellulase system was supplemented with beta-glucosidase from Aspergillus niger, the ethanol yield in the SSF process increased to 3% (w/v) and the reaction time was shortened to 24 h.     

Effect of pretreatment severity on xylan solubility and enzymatic breakdown of the remaining cellulose from wheat straw

The effect of process conditions used for wheat straw pretreatments on the liquor- and residue-composition was studied. Hereto, the pretreatment conditions were expressed in a 'combined severity R(0)(')-factor'. The higher the combined severity factor (R(0)(')) the more xylan was released from the wheat straw, but the more xylan decomposed and furfural formation occurred. The percentage of residual xylan present after pretreatment appeared to be a good indicator concerning cellulose degradability or bio-ethanol production. Namely, cellulose degradation by using commercial enzymes was higher at higher severities corresponding to a lower amount of residual xylan. The xylan release and degradation was studied in more detail by using HPSEC and MALDI-TOF mass spectrometry. The more severe the treatment the more (acetylated) xylose oligomers with a DP lower than nine were analysed. The presence of (acetylated) xylans with a DP of 9-25 increased slightly from low to medium severity. The quantification of the DP-distribution of the (acetylated) xylans released proved to be a good tool to predict cellulose degradability.     

Organosolvent pretreatment and enzymatic hydrolysis of rice straw for the production of bioethanol

The present study investigates the operational conditions for organosolvent pretreatment and hydrolysis of rice straw. Among the different organic acids and organic solvents tested, acetone was found to be most effective based on the fermentable sugar yield. Optimization of process parameters for acetone pretreatment were carried out. The structural changes before and after pretreatment were investigated by scanning electron microscopy, X-ray diffraction and Fourier transform infrared (FTIR) analysis. The X-ray diffraction profile showed that the degree of crystallinity was higher for acetone pretreated biomass than that of the native. FTIR spectrum also exhibited significant difference between the native and pretreated samples. Under optimum pretreatment conditions 0.458 g of reducing sugar was produced per gram of pretreated biomass with a fermentation efficiency of 39%. Optimization of process parameters for hydrolysis such as biomass loading, enzyme loading, surfactant concentration and incubation time was done using Box–Benhken design. The results indicate that acetone pretreated rice straw can be used as a good feed stock for bioethanol production.     

Enhanced enzymatic hydrolysis of rapeseed straw by popping pretreatment for bioethanol production

The objective of this study was to find a pretreatment process that enhances enzymatic conversion of biomass to sugars. Rapeseed straw was pretreated by two processes: a wet process involving wet milling plus a popping treatment, and a dry process involving popping plus dry milling. The effects of the pretreatments were studied both in terms of structural and compositional changes and change in susceptibility to enzymatic hydrolysis. After application of the wet and dry processes, the amounts of cellulose and xylose in the straw were 37-38% and 14-15%, respectively, compared to 31% and 12% in untreated counterparts. In enzymatic hydrolysis performance, the wet process presented the best glucose yield, with a 93.1% conversion, while the dry process yielded 69.6%, and the un-pretreated process yielded <20%. Electron microscopic studies of the straw also showed a relative increase in susceptibility to enzymatic hydrolysis with pretreatment.     

Improved enzymatic hydrolysis yield of rice straw using electron beam irradiation pretreatment

Rice straw was irradiated using an electron beam at currents and then hydrolyzed with cellulase and beta-glucosidase to produce glucose. The pretreatment by electron beam irradiation (EBI) was found to significantly increase the enzyme digestibility of rice straw. Specifically, when rice straw that was pretreated by EBI at 80 kGy at 0.12 mA and 1 MeV was hydrolyzed with 60 FPU of cellulase and 30 CBU of beta-glucosidase, the glucose yield after 132 h of hydrolysis was 52.1% of theoretical maximum. This value was significantly higher than the 22.6% that was obtained when untreated rice straw was used. In addition, SEM analysis of pretreated rice straw revealed that EBI caused apparent damage to the surface of the rice straw. Furthermore, EBI pretreatment was found to increase the crystalline portion of the rice straw. Finally, the crystallinity and enzyme digestibility were found to be strongly correlated between rice straw samples that were pretreated by EBI under different conditions.