Preparation and characterization of biopolyol via liquefaction of rice straw

Biopolyols were prepared by the liquefaction of rice straw under the mild condition. The optimum liquefaction effect was obtained at 5 : 1 volume ratio of PEG400 to DEG, 4 : 1 liquid–solid ratio, H₂SO₄ 3%, time 2.5 h, and reaction temperature120°C. Products were characterized by FTIR and gel permeation chromatograms (GPC) measurements. The hydroxyl value and weight-average molecular weight of the biopolyol produced based on the above optimal conditions were 260 mg KOH/g polyol and 420 g mol^–1, respectively. Biopolyol obtained is suitable for the preparation of rigid polyurethane foam. This study has certain significance for the high added value use of rice straw and reducing the production cost and improvement biodegradability of polyurethane foams.     

Kinetic Studies on the Product Inhibition of Enzymatic Lignocellulose Hydrolysis

In order to understand the product inhibition of enzymatic lignocellulose hydrolysis, the enzymatic hydrolysis of pretreated rice straw was carried out over an enzyme loading range of 2 to 30 FPU/g substrate, and the inhibition of enzymatic hydrolysis was analyzed kinetically based on the reducing sugars produced. It was shown that glucose, xylose, and arabinose were the main reducing sugar components contained in the hydrolysate. The mass ratio of glucose, xylose, and arabinose to the total reducing sugars was almost constant at 52.0?%, 29.7?% and 18.8?%, respectively, in the enzyme loading range. The reducing sugars exerted competitive inhibitory interferences to the enzymatic hydrolysis. Glucose, xylose, and arabinose had a dissociation constant of 1.24, 0.54 and 0.33?g/l, respectively. The inhibitory interferences by reducing sugars were superimposed on the enzymatic hydrolysis. The enzymatic hydrolysis could be improved by the removal of the produced reducing sugars from hydrolysate.     

Steam pretreatment of acid-sprayed and acid-soaked barley straw for production of ethanol

Barley is an abundant crop in Europe, which makes its straw residues an interesting cellulose source for ethanol production. Steam pretreatment of the straw followed by enzymatic hydrolysis converts the cellulose to fermentable sugars. Prior to pretreatment the material is impregnated with a catalyst, for example, H₂SO₄, to enhance enzymatic digestibility of the pretreated straw. Different impregnation techniques can be applied. In this study, soaking and spraying were investigated and compared at the same pretreatment condition in terms of overall yield of glucose and xylose. The overall yield includes the soluble sugars in the liquid from pretreatment, including soluble oligomers, and monomer sugars obtained in the enzymatic hydrolysis. The yields obtained differed for the impregnation techniques. Acid-soaked barley straw gave the highest overall yield of glucose, regardless of impregnation time (10 or 30 min) or acid concentration (0.2 or 1.0 wt%). For xylose, soaking gave the highest overall yield at 0.2 wt% H₂SO₄. An increase in acid concentration resulted in a decrease in xylose yield for both acid-soaked and acid-sprayed barley straw. Optimization of the pretreatment conditions for acid-sprayed barley straw was performed to obtain yields using spraying that were as high as those with soaking. For acid-sprayed barley straw the optimum pretreatment condition for glucose, 1.0 wt% H₂SO₄ and 220°C for 5 min, gave an overall glucose yield of 92% of theoretical based on the composition of the raw material. Pretreatment with 0.2wt% H₂SO₄ at 190°C for 5 min resulted in the highest overall xylose yield, 67% of theoretical based on the composition of the raw material.     

Fermentation of rice straw/chicken manure to carboxylic acids using a mixed culture of marine mesophilic micoorganisms

Countercurrent fermentation of rice straw and chicken manure to carboxylic acids was performed using a mixed culture of marine mesophilic microorganisms. To increase the digestibility of the biomass, rice straw, and chicken manure were pretreated with 0.1 g Ca(OH)₂/g biomass. Fermentation was performed for 80% rice straw and 20% chicken manure at various volatile solid loading rates (VSLR) and liquid residence times (LRT). The highest acid productivity of 1.69 g/(L·d) occurred at a total acid concentration of 32.4 g/L. The highest conversion (0.69 g VS digested/g VS fed) and yield (0.29 g total acids/g VS fed) were at a total acid concentration of 25 g/L. A Continuum Particle Distribution Model of the process predicted the experimental total acid concentration and conversion results with an average error of 6.41% and 6.15%, respectively. Results show how total acid concentrations, conversions, and yields vary with VSLR and LRT in the MixAlco process.     

Modification of Rice Straw for Heavy Metal Ion Adsorbents by Microwave Heating

Summary: Cellulose in rice straw was chemically modified by phosphorylation using conventional heating or microwave heating. Rice straw pretreated by NaOH solution gave the highest phosphorus content when it was phosphorylated using microwave heating at 450 watt (7.07%P, ion exchange capacity 2.60 meq/g). The 3 hour-reaction in oil bath yielded the modified rice straw with lower of phosphorus content (6.32%P) and higher ion exchange capacity (2.99 meq/g) than that of microwave heating. The feasibility of the modified rice straw as cation sorbents for removing heavy metal was investigated. Cd²⁺, Cr³⁺ and Pb²⁺ were used as sorbates. In sorption test of 40 ppm with 2.0 g/L of the modified rice straw, both modified rice straws could adsorb metal ions faster than the commercial ion exchange resin (dowax) at the time less than 60 min. The modified rice straw prepared by microwave heating (A-MCW2) could remove 90% of Cd²⁺ and Cr³⁺ in 60 minutes and remove 99% of Pb²⁺ after 30 min.     

Microwave Pretreatment of Substrates for Cellulase Production by Solid-State Fermentation

The agricultural residues, wheat bran and rice hulls, were used as substrates for cellulase production with Trichoderma sp 3.2942 by solid-state fermentation. Microwave irradiation was employed to pretreat the substrates in order to increase the susceptibility. Although the highest cellulase yield was obtained by the substrates pretreated by 450 W microwave for 3 min, pretreatment time and microwave power had no significant effect on cellulase production. The initial reducing sugar content (RSC) of substrates was decreased by microwave irradiation, but more reducing sugars were produced in later fermentation. Alkali pretreatment combined with microwave pretreatment (APCMP) of rice hulls could significantly increase cellulase yields and reducing sugar. The maximum filter paper activity, carboximethylcellulase (CMC)ase, and RSC were increased by 35.2%, 21.4%, and 13%, respectively, compared with those of untreated rice hulls. The fermented residues could produce more cellulase and reducing sugars than fresh rice hulls after they were treated by APCMP. The increased accessibility of the substrates by microwave pretreatment was mainly achieved by rupture of the rigid structure of rice hulls. However, for alkali pretreatment and APCMP, delignification and removal of ash played very important roles for increasing the acceptability of substrates.     

Optimizing ammonia pressurization/depressurization processing conditions to enhance enzymatic susceptibility of dwarf elephant grass

An ammonia pressurization/depressurization process was investigated to evaluate the potential of producing reducing sugars from dwarf elephant grass, a warm-season forage. Moisture, temperature, and ammonia loading affected sugar yield (p<0.0001). At optimal conditions, ammonia processing solubilized 50.9% of the hemicellulose and raised the sugar yield (percentage of theoretical) from 18 to 83%. Glucose and xylose production were increased 3.2-and 8.2-fold, respectively. The mild processing conditions of the ammonia treatment (90–100°C, 5 min), the low enzyme loading (2 international filter paper units/g), and the short hydrolysis time (24 h), greatly enhance the potential of using for ages to produce sugars valuable for several applications.     

Ethanol production from steam-explosion pretreated wheat straw

Bioconversion of cereal straw to bioethanol is becoming an attractive alternative to conventional fuel ethanol production from grains. In this work, the best operational conditions for steam-explosion pretreatment of wheat straw for ethanol production by a simultaneous saccharification and fermentation process were studied, using diluted acid [H₂SO₄ 0.9% (w/w)] and water as preimpregnation agents. Acid-or water-impregnated biomass was steam-exploded at different temperatures (160–200°C) and residence times (5, 10, and 20 min). Composition of solid and filtrate obtained after pretreatment, enzymatic digestibility and ethanol production of pretreated wheat straw at different experimental conditions was analyzed. The best pretreatment conditions to obtain high conversion yield to ethanol (approx 80% of theoretical) of cellulose-rich residue after steam-explosion were 190°C and 10 min or 200°C and 5 min, in acid-impregnated straw. However, 180°C for 10 min in acid-impregnated biomass provided the highest ethanol yield referred to raw material (140 L/t wheat straw), and sugars recovery yield in the filtrate (300 g/kg wheat straw).     

Impact of sulfuric acid pretreatment of durian peel on the production of fermentable sugar and ethanol

After harvesting season, large amounts of durian peels were produced and uselessly disposed of by combustion or landfilling leading to environmental pollution and human health hazards. Proper management of these wastes is necessary to reduce not only an environmental problem but also to create value-added products. Herein, we optimized sulfuric acid pretreatment to promote enzymatic saccharification of durian peels and convert fermentable sugars to bioethanol. Three pretreatment parameters were optimized based on Response Surface Methodology (RSM), including acid concentration (0.5%–3.5%), temperature (60–140 ​°C), and time (20–100 ​min). At optimal pretreatment condition using 2.75% H₂SO₄, at 127.14 ​°C for 74.13 ​min, 0.53 ​g/g-biomass of reducing sugars were produced, which is 1.88 folds higher than the untreated durian peel. The pretreatment liquor and biomass hydrolysate were analyzed by Gas Chromatograph-Mass spectrometer (GC-MS), and fermentation inhibitors, i.e. acetic acid, furfural, and furan methanol, were identified in those fractions. Due to pretreatment at the optimal condition, a higher yield of reducing sugar was observed, and the production of ethanol from the pretreated biomass was 5.70 ​g/L (equivalent to 87.43% of theoretical yields). These findings demonstrated the potential of using durian waste in the biorefinery concept to achieve a concept of the green economy.     

Pretreatment of Rice Straw by a Hot-Compressed Water Process for Enzymatic Hydrolysis

Hot-compressed water (HCW) is among several cost-effective pretreatment processes of lignocellulosic biomass for enzymatic hydrolysis. The present work investigated the characteristics of HCW pretreatment of rice straw including sugar production and inhibitor formation in the liquid fraction and enzymatic hydrolysis of pretreated material. Pretreatment was carried out at a temperature ranging from 140 to 240 °C for 10 or 30 min. Soluble oligosaccharides were found to constitute almost all the components of total sugars in the liquid fraction. The maximal production of total glucose at 180 °C and below accounted for 4.4–4.9% of glucan in raw material. Total xylose production peaked at 180 °C, accounting for 43.3% of xylan in raw material for 10-min pretreatment and 29.8% for 30-min pretreatment. The production of acetic acid increased at higher temperatures and longer treatment time, indicating more significant disruption of lignocellulosic structure, and furfural production achieved the maximum (2.8 mg/ml) at 200 °C for both 10-min and 30-min processes. The glucose yield by enzymatic hydrolysis of pretreated rice straw was no less than 85% at 180 °C and above for 30-min pretreatment and at 200 °C and above for 10-min pretreatment. Considering sugar recovery, inhibitor formation, and process severity, it is recommended that a temperature of 180 °C for a time of 30 min can be the most efficient process for HCW pretreatment of rice straw.     

Optimizing Dilute-Acid Pretreatment of Rapeseed Straw for Extraction of Hemicellulose

Biological conversion of biomass into fuels and chemicals requires hydrolysis of the polysaccharide fraction into monomeric sugars prior to fermentation. Hydrolysis can be performed enzymatically or with mineral acids. In this study, dilute sulfuric acid was used as a catalyst for the pretreatment of rapeseed straw. The purpose of this study is to optimize the pretreatment process in a 15-mL bomb tube reactor and investigate the effects of the acid concentration, temperature, and reaction time. These parameters influence hemicellulose removal and production of sugars (xylose, glucose, and arabinose) in the hydrolyzate as well as the formation of by-products (furfural, 5-hydroxymethylfurfural, and acetic acid). Statistical analysis was based on a model composition corresponding to a 3³ orthogonal factorial design and employed the response surface methodology to optimize the pretreatment conditions, aiming to attain maximum xylan, mannan, and galactan (XMG) extraction from hemicellulose of rapeseed straw. The obtained optimum conditions were: H₂SO₄ concentration of 1.76% and temperature of 152.6 °C with a reaction time of 21 min. Under these optimal conditions, 85.5% of the total sugar was recovered after acid hydrolysis (78.9% XMG and 6.6% glucan). The hydrolyzate contained 1.60 g/L glucose, 0.61 g/L arabinose, 10.49 g/L xylose, mannose, and galactose, 0.39 g/L cellobiose, 0.94 g/L fructose, 0.02 g/L 1,6-anhydro-glucose, 1.17 g/L formic acid, 2.94 g/L acetic acid, 0.04 g/L levulinic acid, 0.04 g/L 5-hydroxymethylfurfural, and 0.98 g/L furfural.     

Production of 5-Hydroxymethylfurfural and Furfural from Lignocellulosic Biomass in Water-Tetrahydrofuran Media with Sodium Bisulfate

5-Hydroxymethylfurfural (HMF) and furfural (FF), two bio-based platform chemicals, were produced from various raw lignocellulosic materials (corncob, corn stover, wheat straw, rice straw and sugarcane bagasse) in a water-tetrahydrofuran media by using NaHSO₄ as catalyst. The in fluences of reaction temperature (160-200 oC), reaction time (30-120 min), solvent volume ratio, feedstock concentration (2.4wt%-11.1wt%) and catalyst dosage were studied. The highest HMF and FF yields obtained from corncob were 47mol% and 56mol% under condition of 190 oC, 90 min, 10/1 of THF/H₂O. Besides, the lignin in the raw biomass wasalso depolymerized into organosolv lignin.     

Hybrid SSF/SHF Processing of SO<Subscript>2</Subscript> Pretreated Wheat Straw—Tuning Co-fermentation by Yeast Inoculum Size and Hydrolysis Time

Wheat straw is one of the main agricultural residues of interest for bioethanol production. This work examines conversion of steam-pretreated wheat straw (using SO₂ as a catalyst) in a hybrid process consisting of a short enzymatic prehydrolysis step and a subsequent simultaneous saccharification and fermentation (SSF) step with a xylose-fermenting strain of Saccharomyces cerevisiae. A successful process requires a balanced design of reaction time and temperature in the prehydrolysis step and yeast inoculum size and temperature in the SSF step. The pretreated material obtained after steam pretreatment at 210 °C for 5 min using 2.5 % SO₂ (based on moisture content) showed a very good enzymatic digestibility at 45 °C but clearly lower at 30 °C. Furthermore, the pretreatment liquid was found to be rather inhibitory to the yeast, partly due to a furfural content of more than 3 g/L. The effect of varying the yeast inoculum size in this medium was assessed, and at a yeast inoculum size of 4 g/L, a complete conversion of glucose and a 90 % conversion of xylose were obtained within 50 h. An ethanol yield (based on the glucan and xylan in the pretreated material) of 0.39 g/g was achieved for a process with this yeast inoculum size in a hybrid process (10 % water-insoluble solid (WIS)) with 4 h prehydrolysis time and a total process time of 96 h. The obtained xylose conversion was 95 %. A longer prehydrolysis time or a lower yeast inoculum size resulted in incomplete xylose conversion.     

Wheat Straw Autohydrolysis: Process Optimization and Products Characterization

Wheat straw was subjected to autohydrolysis treatments in order to selectively hydrolyze the hemicellulose fraction. The effects of temperature (150–240°C) and non-isothermal reaction time on the composition of both liquid and solid phases were evaluated and interpreted using the severity factor (log R ₀). The operational conditions leading to the maximum recovery of hemicellulose-derived sugars were established for log R ₀?=?3.96 and correspond to 64% of the original (arabino)xylan with 80% of sugars as xylooligosaccharides. Under these conditions, a solubilization of 58% xylan, 83% arabinan, and 98% acetyl groups occurred. Glucan was mainly retained in the solid phase (maximum solubilization 16%), which enables an enrichment of the solid phase to contain up to 61% glucan. Delignification was not extensive, being utmost 15%. The yields of soluble products, including sugars, acetic acid, and degradation compounds, such as, furfural, 5-hydroxymethylfurfural furfural obtained suggest the fitness of liquid stream for fermentation purposes or to obtain xylooligosaccharides with potential applications in food, pharmaceutical, and cosmetic industries.     

Protein Extraction and Enzymatic Hydrolysis of Ammonia-Treated Cassava Leaves (Manihot esculenta Crantz)

In the present work, cassava leaves were treated with 0.5 kg ammonia/kg dry matter at 78 °C and 30% moisture content in a 2-kg reactor. Protein extraction was carried out with a calcium hydroxide solution (pH 10) for 30 min at several temperatures (30 °C, 45 °C, 60 °C, 75 °C, and 90 °C) and solid/liquid ratios (1:10 and 1:15) in a thermostatized bath. Soluble protein content of the extracts was determined by Lowry’s method. Dry substrate concentrations of 5%, 7.5%, and 10% and enzyme doses of 2 and 5 IU/g dry matter were used for the enzymatic hydrolysis in an orbital incubator at 50 °C and 100 rpm. Both cellulase and xylanase were used. Reducing sugars produced were determined with the dinitrosalicylic acid method. The highest protein extraction yield for the ammonia-treated leaves was 29.10%, which was 50% higher than with the untreated leaves (20%), and was obtained at 90 °C with a 1:10 solid/liquid ratio. The concentrate had a protein content of 36.35% and the amino acid profile was suitable for swine and poultry. The highest sugar yield was 54.72% with respect to theoretical and was obtained with 5% solids and an enzyme dose of 5 IU/g dry matter. This yield was 3.4 times higher than the yield of the untreated leaves (16.13%). These results indicate that cassava leaves have a great potential for animal feeding and ethanol production. Both protein extraction and sugar yields may be enhanced by optimizing the ammonia treatment.     

Pretreatment of Rice Straw by Proton Beam Irradiation for Efficient Enzyme Digestibility

Biomass was pretreated with proton beam irradiation (PBI) in order to enhance enzyme digestibility. Rice straw and soaking in aqueous ammonia (SAA)-treated rice straw were treated with 1-25 kGy doses of PBI at a beam energy of 45 MeV. The optimal doses of PBI for efficient sugar recovery were 15 and 3 kGy for rice straw and SAA-treated rice straw, respectively. When PBI was applied to rice straw at 15 kGy, the glucose conversion reached 68% of the theoretical maximum at 72 h. When 3 kGy of PBI was applied to SAA-treated rice straw, approximately 90% of the theoretical glucose conversion was obtained at 12 h compared to a 89% conversion at 48 h. After 2 h of enzymatic saccharification, the initial reaction rates of raw rice straw pretreated with 15 kGy of PBI and SAA-treated rice straw pretreated with 3 kGy of PBI were 1.4?×?10?? and 9.7?×?10?? g L?1 s?1, respectively. Further, the results of X-ray diffractometry support the effect of PBI on sugar recovery, whereas scanning electron microscopy images revealed a more rugged rice straw surface.     

Optimizing ammonia processing conditions to enhance susceptibility of legumes to fiber hydrolysis

A warm-season legume, Florigraze rhizoma peanut (FRP), was used as the source of fiber to produce sugars. FRP was subjected to several ammonia-processing conditions using temperature, biomass moisture content, and ammonia loading as process variables during a 5-min treatment. A cellulase loading of 2 FPU/g DM and 24 h incubation were used to produce the sugars. Total sugar yield was 3.34-fold higher in the optimal treatment (1.5 g ammonia/g DM-60%-90°C) compared to untreated and was 65.3% of theoretical. Cellulose and hemicellulose conversions increased from 30 and 15.5% in untreated FRP to 78 and 34% in treated FRP.     

Effect of additions on ensiling and microbial community of senesced wheat straw

Crop residues collected during or after grain harvest are available once per year and must be stored for extended periods. The combination of air, high moisture, and high microbial loads leads to shrinkage during storage and risk of spontaneous ignition. Ensiling is a wet preservation method that could be used to store these residues stably. To economically adapt ensiling to biomass that is harvested after it has senesced, the need for nutrient, moisture, and microbial additions must be determined. We tested the ensiling of senesced wheat straw in sealed columns for 83 d. The straw was inoculated with Lactobacillus plantarum and amended with several levels of water and free sugars. The ability to stabilize the straw polysaccharides was strongly influenced by both moisture and free sugars. Without the addition of sugar, the pH increased from 5.2 to as much as 9.1, depending on moisture level, and losses of 22% of the cellulose and 21% of the hemicellulose were observed. By contrast, when sufficient sugars were added and interstitial water was maintained, a final pH of 4.0 was attainable, with correspondingly low (<5%) losses of cellulose and hemicellulose. The results show that ensiling should be considered a promising method for stable storage of wet biorefinery feedstocks.     

Microbial Lipid Production from Enzymatic Hydrolysate of Pecan Nutshell Pretreated by Combined Pretreatment

Biodiesel is a fuel composed of monoalkyl esters of long-chain fatty acids derived from renewable biomass sources. In this study, biomass waste pecan nutshell (PS) was attempted to be converted into microbial oil. For effective utilization of PS, sequential pretreatment with ethylene glycol–H₂SO₄–water (78:2:20, wt:wt:wt) at 130 °C for 30 min and aqueous ammonia (25 wt%) at 50 °C for 24 h was used to enhance its enzymatic saccharification. Significant linear correlation was obtained about delignification-saccharification (R ² = 0.9507). SEM and FTIR results indicated that combination pretreatment could effectively remove lignin and xylan in PS for promoting its enzymatic saccharification. After 72 h, the reducing sugars from the hydrolysis of 50 g/L pretreated PS by combination pretreatment could be obtained at 73.6% yield. Using the recovered PS hydrolysates containing 20 g/L glucose as carbon source, microbial lipids produced from the PS hydrolysates by Rhodococcus opacus ACCC41043. Four fatty acids including palmitic acid (C16:0; 23.1%), palmitoleic acid (C16:1; 22.4%), stearic acid (C18:0; 15.3%), and oleic acid (C18:1; 23.9%) were distributed in total fatty acids. In conclusion, this strategy has potential application in the future.     

Determination of RH‐5849 and indoxacarb in rice straw,rice husk,brown rice and soil using liquid chromatography–tandem triple quadrupole mass spectrometry following extraction with QuEChERS method

A fast and simple analytical method was developed for the simultaneous determination of RH‐5849 and indoxacarb in soil, rice straw, rice husk and brown rice. QuEChERS (quick, easy, cheap, effective, rugged and safe) method was used for extraction, and liquid chromatography with tandem triple quadrupole mass spectrometry was used for quantification. The matrix‐matched calibration plots were linear in the range between 25 and 5000 μg/L for soil, rice straw, rice husk and brown rice samples. All determination coefficients (R²) were ≥0.9962. The limits of detection and quantification were 1.5 and 5 μg/kg, respectively. Recoveries at three fortification levels ranged between 79.5 and 97.9% with relative standard deviations <11%. The developed method was validated and applied for the analysis of dissipation study samples. For field experiments, the half‐lives of RH‐5849 and indoxacarb in rice straw were 11.93 and 5.83 days, respectively. The method was demonstrated to be reliable for the routine monitoring of RH‐5849 and indoxacarb in rice samples. Copyright © 2016 John Wiley & Sons, Ltd.