Alkali-explosion pretreatment of straw and bagasse for enzymic hydrolysis

Sugarcane bagasse and wheat straw were subjected to alkali treatment at 200 degrees C for 5 min and at 3.45 MPa gas pressure (steam and nitrogen), followed by an explosive discharge through a defibrating nozzle, in an attempt to improve the rate and extent of digestibility. The treatment resulted in the solubilization of 40-45% of the components and in the production of a pulp that gave saccharification yields of 80 and 65% in 8 h for bagasse and wheat straw, respectively. By comparison, alkali steaming at 200 degrees C (1.72 MPa) for 5 min gave saccharification yields of only 58 and 52% in 48 h. The increase in temperature from 140 to 200 degrees C resulted in a gradual increase in in vitro organic matter digestibility (IVOMD) for both the substrates. Also, the extent of alkalinity during pretreatment appears to effect the reactivity of the final product towards enzymes. Pretreatment times ranging from 5 to 60 caused a progressive decline in the IVOMD of bagasse and wheat straw by the alkali explosion method and this was accompanied by a progressive decrease in pH values after explosion. In the alkali-steaming method, pretreatment time had no apparent effect with either substrate. An analysis of the alkali-exploded products showed that substantial amounts of hemicellulose and a small proportion of the lignin were solubilized. The percentage crystallinity of the cellulose did not alter in either substrate but there was a substantial reduction in the degree of polymerization. The superiority of the alkali-explosion pretreatment is attributed to the efficacy of fiber separation and disintegration; this increases the surface area and reduces the degree of polymerization.     

Effect of steam explosion on biodegradation of lignin in wheat straw

The effect of steam explosion pretreatment on biodegradation of lignin in wheat straw was studied in this paper. Through experiments and analysis, 0.8MPa operation pressure and 1:20 wheat straw to water ratio are optimum for destroying lignin and the maximum of lignin loss rate is 19.94%. After steam explosion pretreatment, the wheat straw was retted by Trametes versicolor for 40 days. Biodegradation rate of lignin was tested and the maximum of 55.40% lignin loss rate was found on day 30. During the whole process of both steam explosion pretreatment and biodegradation, 75.34% lignin was degraded, without steam explosion the biodegradation of raw material the degradation rate of lignin was 31.23% only. FT-IR spectroscopy, TGA and SEM were used for further validating the results of biodegradation.     

Characterization of enzymatic saccharification for acid-pretreated lignocellulosic materials with different lignin composition

The enzymatic saccharification of three different feedstocks, rice straw, bagasse and silvergrass, which had been pretreated with different dilute acid concentrations, was studied to verify how enzymatic saccharification was affected by the lignin composition of the raw materials. There was a quantitatively inverse correlation between lignin content and enzymatic digestibility after pretreatment with 1%, 2% and 4% sulfuric acid. The lignin accounted for about 18.8–21.8% of pretreated rice straw, which was less than the 23.1–26.5% of pretreated bagasse and the 21.5–24.1% of pretreated silvergrass. The maximum glucose yield achieved, under an enzyme loading 6.5 FPU g^?1 DM for 72 h, was close to 0.8 g glucose/g glucan from the enzymatic hydrolysis of the pretreated rice straw; this was twice that from bagasse and silvergrass. A decrease in initial rate of glucose production was observed in all cases when the raw materials underwent enzymatic saccharification with 4% sulfuric acid pretreatment. It is suggested that the higher acid concentration led to an inhibition of β-glucosidase activity. Fourier transform infrared (FTIR) spectroscopy further indicated the chemical properties of the rice straw and silvergrass become more hydrophilic after pretreatment using 2% of sulfuric acid, but the pretreated bagasse tended to become more hydrophobic. The hydrophilic nature of the pretreated solid residues may increase the inhibitive effects of lignin on the cellulase and this could become very important for raw materials such as silvergrass that contain more lignin.     

Inhibition of cellulose enzymatic hydrolysis by laccase‐derived compounds from phenols

The presence of inhibitors compounds after pretreatment of lignocellulosic materials affects the saccharification and fermentation steps in bioethanol production processes. Even though, external addition of laccases selectively removes the phenolic compounds from lignocellulosic prehydrolysates, when it is coupled to saccharification step, lower hydrolysis yields are attained. Vanillin, syringaldehyde and ferulic acid are phenolic compounds commonly found in wheat‐straw prehydrolysate after steam‐explosion pretreatment. These three phenolic compounds were used in this study to elucidate the inhibitory mechanisms of laccase‐derived compounds after laccase treatment. Reaction products derived from laccase oxidation of vanillin and syringaldehyde showed to be the strongest inhibitors. The presence of these products causes a decrement on enzymatic hydrolysis yield of a model cellulosic substrate (Sigmacell) of 46.6 and 32.6%, respectively at 24 h. Moreover, a decrease in more than 50% of cellulase and β‐glucosidase activities was observed in presence of laccase and vanillin. This effect was attributed to coupling reactions between phenoxyl radicals and enzymes. On the other hand, when the hydrolysis of Sigmacell was performed in presence of prehydrolysate from steam‐exploded wheat straw a significant inhibition on enzymatic hydrolysis was observed independently of laccase treatment. This result pointed out that the other components of wheat‐straw prehydrolysate are affecting the enzymatic hydrolysis to a higher extent than the possible laccase‐derived products. © 2015 American Institute of Chemical Engineers Biotechnol. Prog., 31:700–706, 2015     

Efficient conversion of wheat straw wastes into biohydrogen gas by cow dung compost

Efficient conversion of wheat straw wastes into biohydrogen gas by cow dung compost was reported for the first time. Batch tests were carried out to analyze influences of several environmental factors on biohydrogen production from wheat straw wastes. The performance of biohydrogen production using the raw wheat straw and HCl pretreated wheat straw was then compared in batch fermentation tests. The maximum cumulative hydrogen yield of 68.1 ml H2/g TVS was observed at 126.5 h, the value is about 136-fold as compared with that of raw wheat straw wastes. The maximum hydrogen production rate of 10.14 ml H2/g TVS h was obtained by a modified Gompertz equation. The hydrogen content in the biogas was 52.0% and there was no significant methane observed in this study. In addition, biodegradation characteristics of the substrate were also discussed. The experimental results showed that the pretreatment of the substrate plays a key role in the conversion of the wheat straw wastes into biohydrogen by the composts generating hydrogen.     

Ethanol from lignocellulosic materials by a simultaneous saccharification and fermentation process (SFS) with Kluyveromyces marxianus CECT 10875

Simultaneous saccharification and fermentation (SSF) process for ethanol production from various lignocellulosic woody (poplar and eucalyptus) and herbaceous (Sorghum sp. bagasse, wheat straw and Brassica carinata residue) materials has been assayed using the thermotolerant yeast strain Kluyveromyces marxianus CECT 10875. Biomass samples were previously treated in a steam explosion pilot plant to provide pretreated biomass with increased cellulose content relative to untreated materials and to enhance cellulase accessibility. SSF experiments were performed in laboratory conditions at 42 °C, 10% (w/v) substrate concentration and 15 FPU/g substrate of commercial cellulase. The results indicate that it is possible to reach SSF yields in the range of 50–72% of the maximum theoretical SSF yield, based on the glucose available in pretreated materials, in 72–82 h. Maximum ethanol contents from 16 to 19 g/l were obtained in fermentation media, depending on the material tested.     

Alkaline peroxide delignification of agricultural residues to enhance enzymatic saccharification

Approximately one-half of the lignin and most of the hemicellulose present in agricultural residues such as wheat straw and corn stover are solubilized when the residue is treated at 25 degrees C in an alkaline solution of hydrogen peroxide. The delignification reaction is most efficient when the ratio of hydrogen peroxide to substrate is at least 0.25 (w/w) and the pH is 11.5. The supernatant fraction from a given pretreatment, after addition of makeup peroxide and readjustment of the pH, can be recycled to treat at least six additional batches of substrate, resulting in a substantial concentration of hemicellulose and soluble lignin degradation products. Hydrolysis of the insoluble fraction with Trichoderma reesei cellulase after alkaline peroxide treatment yields glucose with almost 100% efficiency, based upon the cellulose content of the residue before treatment. These data indicate that alkaline peroxide pretreatment is a simple and efficient method for enhancing the enzymatic digestibility of lignocellulosic crop residues to levels approaching the theoretical maximum.     

Cellulolytic activities ofChaetomium globosum on different cellulosic substrates

The effect of cellulosic substrates on the production of extra-cellular cellulases and their cellulolytic activity inChaetomium globosum has been studied in shake flask cultures. Production of endoglucanase, exoglucanase and filter paper cellulase was highest with pure cellulose whereas -glucosidase was maximally induced by wheat straw. A suitable pretreatment for wheat straw was peracetic acid followed by NaOH and that of bagasse with NaOH for saccharification.

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Résumé On a étudié l'effet de substrats cellulosiques sur la production de cellulases extracellulaires et leur activité cellulolytique chezChaetomium globosum en culture en flacons agités. La production d'endoglucanase, d'exoglucanase et de cellulase type papier-filtre est maximum avec la cellulose pure tandis que la -glucosidase est induite de manière maximum par la paille de froment. La paille de froment est traitée de manière adéquate pour la saccharification par l'acide peracétique suivi de NaOH, la bagasse, par NaOH.

     

Fractionation of wheat and barley straw to access high-molecular-mass hemicelluloses prior to ethanol production

The cost efficiency of the biorefining process can be improved by extracting high-molecular-mass hemicelluloses from lignocellulosic biomass prior to ethanol production. These hemicelluloses can be used in several high-value-added applications and are likely to be important raw materials in the future. In this study, steam pretreatment in an alkaline environment was used to pretreat the lignocellulosic biomass for ethanol production and, at the same time, extract arabinoxylan with a high-molecular-mass. It was shown that 30% of the arabinoxylan in barley straw could be extracted with high-molecular-mass, without dissolving the cellulose. The cellulose in the solid fraction could then be hydrolysed with cellulase enzymes giving a cellulose conversion of about 80–90% after 72 h. For wheat straw, more than 40% of the arabinoxylan could be extracted with high-molecular-mass and the cellulose conversion of the solid residue after 72 h was about 70–85%. The high cellulose conversion of the pretreated wheat and barley straw shows that they can be used for ethanol production without further treatment. It is therefore concluded that it is possible to extract high-molecular-mass arabinoxylan simultaneously with the pretreatment of biomass for ethanol production in a single steam pretreatment step.     

纤维素酶降解小麦秸秆最适条件的研究及其动力学分析

以小麦秸秆为原料,通过正交实验对纤维素酶降解秸秆纤维的影响因素进行了研究。结果表明,影响小麦秸秆降解的因素依次为:酶量>酶解时间>料液比>反应温度,其最适条件是:加酶量为40u/g,酶解时间为10h,反应温度为40℃,料液比为1∶3,总糖含量达到43.24%。以米氏方程为基础,建立起最适酶解条件下总纤维素降解的动力学模型。     

Thermostable, alkalophilic and cellulase free xylanase production by Thermoactinomyces thalophilus subgroup C

Thermoactinomyces thalophilus produced cellulase free extracellular endo-1,4-beta-xylanase (EC 3.2.1.8) at 50 degrees C and pH 8.5. Maximum xylanase production was achieved in fermentation medium using birchwood xylan as substrate after 96 h of growth at 50 degrees C. Other agricultural substrates such as wheat bran, wheat straw, sugarcane bagasse and cornstover produced less xylanase. The crude enzyme preparation from mutant T. thalophilus P2 grown under optimised fermentation conditions showed no cellulase contamination and maximum xylanase activity of 42 U/ml at 65%deg;C and pH 8.5-9.0. This enzyme with initial xylanase activity of 42 U/ml was found thermostable up to 65 degrees C and retaining 50% of its activity after its incubation for 125 min at 65 degrees C.     

Production of xylanase under solid-state fermentation by <Emphasis Type="Italic">Aspergillus tubingensis</Emphasis> JP-1 and its application

The production of extracellular xylanase by a locally isolated strain of Aspergillus tubingensis JP-1 was studied under solid-state fermentation. Among the various agro residues used wheat straw was found to be the best for high yield of xylanase with poor cellulase production. The influence of various parameters such as initial pH, moisture, moistening agents, nitrogen sources, additives, surfactants and pretreatment of substrates were investigated. The production of the xylanase reached a peak in 8 days using untreated wheat straw with modified MS medium, pH 6.0 at 1:5 moisture level at 30 °C. Under optimized conditions yield as high as 6,887 ± 16 U/g of untreated wheat straw was achieved. Crude xylanase was used for enzymatic saccharification of agro-residues like wheat straw, rice bran, wheat bran, sugarcane bagasse and industrial paper pulp. Dilute alkali (1 N NaOH) and acid (1 N H₂SO₄) pretreatment were found to be beneficial for the efficient enzymatic hydrolysis of wheat straw. Dilute alkali and acid-pretreated wheat straw yielded 688 and 543 mg/g reducing sugar, respectively. Yield of 726 mg/g reducing sugar was obtained from paper pulp after 48 h of incubation.     

The pretreatment effect on wheat straw saccharification

Enzymatic hydrolysis of cellulose is potentially an attractive method for converting cellulose into glucose which can then be used as a chemical feed or as a growth substrate for a number of microorganisms to produce microbial products. An enzymatic hydrolysis of wheat straw with cellulase preparation “Trichocease” was made. The wheat straw used was pretreated mechanically and with NaOH. A procedure of pretreatment was investigated in 26 variants. The dynamics of enzymatic hydrolysis was studied. An assay of this dynamics based on the amount of reducing sugars formed during the cellulase reaction and depending upon enzyme and substrate concentration and time of action was carried out.     

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.     

Enhanced cellulase production from Trichoderma reesei QM 9414 on physically treated wheat straw

Summary Trichoderma reesei QM 9414 was grown on wheat straw as the sole carbon source. The straw was pretreated by physical and chemical methods. The particle size of straw was less than 0.177 mm. Growth of T. reesei QM 9414 was maximal with alkali-pretreated straw whereas cellulase production was optimal when physically pretreated straw was used as substrate. Cellulase yields expressed as IU enzyme activity/g cellulose present in the cultures were considerably higher when alkali pretreatment of wheat straw was omitted. Cellulase yields of 666 IU/g cellulose for filter paper activity (FPA) are the highest described for cultures of T. reesei QM 9414 carried out in analogous conditions. Crystallinity index of the cellulose contained in wheat straw increased slightly after alkali pretreatment. This increase did not decrease cellulose accessibility to the fungus. Delignification of wheat straw was not necessary to achieve the best cellulase production.     

Bioethanol production from ammonia percolated wheat straw

This study examined the effectiveness of ammonia percolation pretreatment of wheat straw for ethanol production. Ground wheat straw at a 10% (w/v) loading was pretreated with a 15% (v/v) ammonia solution. The experiments were performed at treatment temperature of 50∼170°C and residence time of 10∼150 min. The solids treated with the ammonia solution showed high lignin degradation and sugar availability. The pretreated wheat straw was hydrolyzed by a cellulase complex (NS50013) and β-glucosidase (NS50010) at 45°C. After saccharification, Saccharomyces cerevisiae was added for fermentation. The incubator was rotated at 120 rpm at 35°C. As a result of the pretreatment, the delignification efficiency was > 70% (170°C, 30 min) and temperature was found to be a significant factor in the removal of lignin than the reaction time. In addition, the saccharification results showed an enzymatic digestibility of > 90% when 40 FPU/g cellulose was used. The ethanol concentration reached 24.15 g/L in 24 h. This paper reports a total process for bioethanol production from agricultural biomass and an efficient pretreatment of lignocellulosic material.     

Comparative evaluations of cellulosic raw materials for second generation bioethanol production

Aims: To evaluate sugar recoveries and fermentabilities of eight lignocellulosic raw materials following mild acid pretreatment and enzyme hydrolysis using a recombinant strain of Zymomonas mobilis. Methods and Results: Dilute acid pretreatment (2% H₂SO₄) with 10% (w/v) substrate loading was performed at 134°C for 60 min followed by enzyme hydrolysis at 60°C. The results demonstrated that hydrolysis of herbaceous raw materials resulted in higher sugar recoveries (up to 60–75%) than the woody sources (<50%). Fermentation studies with recombinant Z. mobilis ZM4 (pZB5) demonstrated that final ethanol concentrations and yields were also higher for the herbaceous hydrolysates. Significant reduction in growth rates and specific rates of sugar uptake and ethanol production occurred for all hydrolysates, with the greatest reductions evident for woody hydrolysates. Further studies on optimization of enzyme hydrolysis established that higher sugar recoveries were achieved at 50°C compared to 60°C following acid pretreatment. Conclusions: Of the various raw materials evaluated, the highest ethanol yields and productivities were achieved with wheat straw and sugarcane bagasse hydrolysates. Sorghum straw, sugarcane tops and Arundo donax hydrolysates were similar in their characteristics, while fermentation of woody hydrolysates (oil mallee, pine and eucalyptus) resulted in relatively low ethanol concentrations and productivities. The concentrations of a range of inhibitory compounds likely to have influence the fermentation kinetics were determined in the various hydrolysates. Significance and Impact of the Study: The study focuses on lignocellulosic materials available for second generation ethanol fermentations designed to use renewable agricultural/forestry biomass rather than food‐based resources. From the results, it is evident that relatively good sugar and ethanol yields can be achieved from some herbaceous raw materials (e.g. sugarcane bagasse and sorghum straw), while much lower yields were obtained from woody biomass.     

Cellulase and hemicellulase production by Cellulomonas flavigena NIAB 441

Summary Cellulomonas flavigena (strain NIAB 441) produced cellulase and hemicellulase activities when grown on Leptochloa fusca L. Kunth (Kallar grass), found to be the best inducer for enzyme production. The enzyme possessed the potential to saccharify bagasse, Kallar grass straw, wheat straw, carboxymethyl cellulose (CMC) and xylan to reducing sugars.     

碱与微波联合处理蔗渣对里氏木霉发酵产纤维素酶的影响

以蔗渣为原料,采用碱和微波辐射联合处理后用于里氏木霉纤维素酶的液态发酵。采用单因素试验与正交试验确定了最佳的处理条件为:0.30 mol/L的NaOH溶液浸泡,微波功率160 W,处理5 min。在此条件下得到的单位能耗的酶活净增值最高。后续发酵结束后,酶活较未经处理的蔗渣发酵后所得酶活有显著提高。其中,β-葡萄糖苷酶活、滤纸酶(FPase)活、羧甲基纤维素酶(CMCase)活分别提高了81.3%,88.2%,154.5%。     

The effect of addition of different amounts and types of organic materials on soil physical properties and yield of wheat

A field experiment was conducted to investigate the influences of 0, 5, 10, 15 Mg ha^–1 of wheat (Triticum aestivum) straw, composted sugarcane bagasse residue and farmyard manure on soil physical properties and yield of winter wheat. The experimental design was a split plot with four replicates. The considered physical properties, 1 year after organic matter addition, included aggregate stability, infiltration rate, water retention curve and dry bulk density. Wheat yield and chemical characteristics of wheat grains were measured. Application of organic materials significantly increased wheat yield and increased aggregate stability, infiltration rate, water retained at less than –100 kPa, and decreased soil bulk density. The effectiveness of different organic materials, farmyard manure, composted bagasse and wheat straw, on improving the soil physical properties was similar. Wheat grain and stubble yield progressively increased as the rate of the organic materials increased. The effectiveness of composted bagasse, farmyard manure and wheat straw on improving wheat grain yield was 22, 14 and 3%, and wheat stubble yield was 26, 17 and 4% over the control.