Autohydrolysis of Tropical Agricultural Residues by Compressed Liquid Hot Water Pretreatment

Pretreatment is an essential step in biorefineries for improving digestibility of recalcitrant agricultural feedstocks prior to enzymatic hydrolysis to composite sugars, which can be further converted to fuels and chemicals. In this study, autohydrolysis by compressed liquid hot water (LHW) pretreatment of various tropical agricultural residues including sugarcane bagasse (BG), rice straw (RS), corn stover (CS), and empty palm fruit bunch (EPFB) was investigated. It was found that LHW pretreatment at 200 °C for 5–20 min resulted in high levels of hemicellulose solubilization into the liquid phase and marked improvement on enzymatic digestibility of the solid cellulose-enriched residues. The maximal yields of glucose and pentose were 409.8–482.7 mg/g and 81.1–174.0 mg/g of pretreated substrates, respectively. Comparative analysis based on severity factor showed varying susceptibility of biomass to LHW in the order of BG> RS> CS> EPFB. Structural analysis revealed surface modification of the pretreated biomass along with an increase in crystallinity index. Overall, 75.7–82.3 % yield of glucose and 27.4–42.4 % yield of pentose from the dried native biomass was recovered in the pretreated solid residues, while 18.3–29.7 % of pentoses were recovered in the liquid phase with dehydration by-product concentration under the threshold for ethanologens. The results suggest the potential of LHW as an efficient pretreatment strategy for implementation in biorefineries operated using various seasonal agricultural feedstocks.     

Stimulatory Effect of Different Lignocellulosic Materials for Phenolic Compound Production and Antioxidant Activity from Inonotus obliquus in Submerged Fermentation

White-rot fungus Inonotus obliquus grown in submerged culture produces antioxidative phenolic compounds. In this study, addition of lignocellulosic materials into the liquid culture increased the production and antioxidant activity of extra- and intra-cellular phenolic compounds (EPC and IPC, respectively). The production of EPC and IPC was significantly enhanced by wheat straw (by 151.2 and 45.3 %), sugarcane bagasse (by 106.9 and 26.1 %), and rice straw (by 67.6 and 38.9 %). Both of the EPC and IPC extracts from the three substrates showed a higher hydroxyl and 1,1-diphenyl-2-picrylhydrazyl radical scavenging activity than those from the control medium. The highly active polyphenols such as tea catechins of epicatechin-3-gallate (ECG) and epigallocatechin-3-gallate (EGCG), and phelligridin G in the EPC extracts increased by 113.1, 75.0, and 86.3 % in the sugarcane bagasse medium. Davallialactone and inoscavin B in the EPC extracts were generated in large amounts in the lignocellulose media but not found in the control medium. The IPC extract from the wheat straw medium had the highest production of EGCG and ECG (17.6 and 18.1 mg/l). The different enhancement among the materials was attributed to the content and degradation rate of cellulose, hemicellulose, and lignin. The different antioxidant activity of the EPC and IPC extracts was related to their phenolic compositions.     

Cellulose nanocrystal extraction from rice straw using a chlorine-free bleaching process

Cellulose nanocrystals (CNCs) have attracted tremendous attention because of their excellent chemical and physical properties and due to their renewability and sustainability. This material can be extracted from agricultural by-products such as rice straw, banana tree, or bagasse. Rice straw was selected as the raw material in this study. Initially, a large amount of lignin must be removed by an alkaline process to obtain a slurry. Thereafter, a green bleaching process can be used to remove the remaining lignin in the slurry. An UV-emitting diode with 365 nm wavelength assisted the oxidation reaction of the H₂O₂ solution without the use of chlorine-containing chemical bleach. The reaction required only 2.5 h to obtain high-purity cellulose and successfully enhanced the yield. Transmission electron microscopy images showed that the CNCs from rice straw were?~?100 nm long and 10–15 nm wide. The crystalline index and degradation temperature of CNCs were 83.8% and 257 °C, respectively.

     

Fast pyrolysis of rice straw,sugarcane bagasse and coconut shell in an induction-heating reactor

With the application of induction heating, a fast pyrolysis was used for producing valuable products from rice straw, sugarcane bagasse and coconut shell in an externally heated fixed-bed reactor. The effect of process parameters such as pyrolysis temperature, heating rate and holding time on the yields of pyrolysis products and their chemical compositions were investigated. The maximum yield of ca. 50% on the pyrolysis liquid product could be obtained at the proper process conditions. The chemical characterization by elemental (CHNO), calorific, Fourier transform infrared (FT-IR) spectroscopy and gas chromatography/mass spectrometry (GC–MS) showed that the pyrolysis liquid products contain large amounts of water (>65 wt.%), and fewer contents of oxygenated hydrocarbons composing of carbonyl groups, resulting in low pH and low heating values. The results were very similar to bio-oils obtained from other biomass materials. The residual solid (char or charcoal) was also characterized in the present study.     

蔗渣的热解与燃烧动力学特性研究

利用热重分析仪对蔗渣在不同升温速率下的热解、燃烧失重特性进行了研究。采用Friedman法对反应过程中可能存在的反应机理进行初步判断，蔗渣热解过程由其主要组分半纤维素、纤维素和木质素热解的三个独立的平行反应来描述，相应的反应活化能分别为203.92 kJ·mol-1、238.50 kJ·mol-1和77.11 kJ·mol-1； 蔗渣燃烧过程分为两段，第一段类似于其热解过程，第二段由木质素热解和残焦燃烧共同组成的连续反应，反应活化能为255.57 kJ·mol-1和159.11 kJ·mol-1。通过非线性回归法拟合获得的曲线与实验曲线基本一致，证实了蔗渣的热解、燃烧过程中存在着上述假定的反应机理。     

Thermal behaviour of lignins extracted from different raw materials

The thermal degradation of lignins extracted from bagasse, rice straw, corn stalk and cotton stalk, have been investigated using the techniques of thermogravimetric analysis (TG) and differential thermal analysis (DTA), between room temperature and 600°C. The actual pyrolysis of all samples starts above 200°C and is slow. The results calculated from TG curves indicated that the activation energy, Efor thermal degradation for different lignins lies in the range 7.949–8.087 kJ mol^?1. The DTA of all studied lignins showed an endothermic tendency around 100°C. In the active pyrolysis temperature range, thermal degradation occurred via two exothermic process at about 320 and 480°C, and a large endothermic pyrolysis region between 375 and 450°C. The first exothermic peak represents the main oxidation and decomposition reaction, the endothermic effect represents completion of the decomposition and the final exothermic peak represents charring.     

Adsorption performance and stability of the modified straws and their extracts of cellulose,lignin, and hemicellulose for Pb2+: pH effect

Adsorption performance and stability of the carboxyl groups modified straws and their extracts of cellulose, lignin, and hemicellulose for Pb²⁺ were investigated, and the optimum pH range for Pb²⁺ adsorption was determined by considering both the stability and capacity of the modified biosorbents for the first time. Results showed that adsorption capacity and stability of the straws and extracts were both improved significantly after modification. Adsorption capacities of the modified straws and extracts followed the order: modified hemicellulose > modified lignin, modified straw > modified cellulose, while stability of them followed the reverse order. In the optimum pH range from 4.0 to 5.0, modified rape and cotton straw showed better stability than the modified maize straw, and total organic carbon (TOC) values determined from the two modified straws and extracts were lower than 5.0 mg L⁻¹ even after adsorption for 30 days, which reached the drinking water standard in China.     

Solid state fermentation of plant residues for improved animal feed byPleurotus sp.

In laboratory-scale experiments, studies were made on the solid state fermentation of plant residues—rice straw and the upper soft portion of the stems of sarkanda (Saccharum munja)—by selected cultures of white-rot fungi,Pleurotus sajor-caju andPleurotus ostreatus. These cultures were selected after preliminary screening of their lignin-degrading capacities on lignin-agar medium. Their lignin degrading and (cellulose + hemicellulose) sparing, along with protein improving capacities, were studied for their potential application in animal feed production. A 100 g quantity of presoaked and sterilized residues was inoculated with wheat spawn of the two cultures and incubated at 25‡C. It was observed that, after 25 d, the crude protein contents (N × 6.25) of rice straw increased from 3 to 17.0% in the case of P.sajor-caju and to 19.2% in case of P. ostreatus. The percent removal values of cellulose, hemicellulose, and lignin were found to be as follows: 45.8, 16.8, and 47.1%, respectively, in the case ofP. sajor-caju and 56.5, 40.4, and 50%, respectively, in the case of P.ostreatus. After solid state fermentation of sarkanda for 25 d, its protein content increased from 3 to 12.8% in the case ofP. sajor-caju and to 14.5% in the case ofP. ostreatus. The percent removal of cellulose, hemicellulose, and lignin was found to be as follows: 31.2, 7.1, and 19%, respectively, in the case ofP. sajor-caju and 34.4, 7.1, and 14.3%, respectively, in the case ofP. ostreatus. The results obtained after solid state fermentation of the two residues by the mixed culture of these two basidiomycetes was also presented.     

Structural Insights into Rice Straw Pretreated by Hot-Compressed Water in Relation to Enzymatic Hydrolysis

Pretreatment-induced structural alteration is critical in influencing the rate and extent of enzymatic saccharification of lignocellulosic biomass. The present work has investigated structural features of rice straw pretreated by hot-compressed water (HCW) from 140 to 240 °C for 10 or 30 min and enzymatic hydrolysis profiles of pretreated rice straw. Compositional profiles of pretreated rice straw were examined to offer the basis for structural changes. The wide-angle X-ray diffraction analysis revealed possible modification in crystalline microstructure of cellulose and the severity-dependent variation of crystallinity. The specific surface area (SSA) of pretreated samples was able to achieve more than 10-fold of that of the raw material and was in linear relationship with the removal of acetyl groups and xylan. The glucose yield by enzymatic hydrolysis of pretreated materials correlated linearly with the SSA increase and the dissolution of acetyl and xylan. A quantitatively intrinsic relationship was suggested to exist between enzymatic hydrolysis and the extraction of hemicellulose components in hydrothermally treated rice straw, and SSA was considered one important structural parameter signaling the efficiency of enzymatic digestibility in HCW-treated materials in which hemicellulose removal and lignin redistribution happened.     

Structure of Alkali Lignins Fractionated from Ricinus communis and Bagasse. 1. Chemical Constituents

Fractionation of alkali lignins of the soda and sulfate pulping processes of Ricinus communis and bagasse was carried out by using successive equal concentrations of the alkaline reagent. Soda lignins were soluble in organic solvents, while the sulfate ones were sparingly soluble. Thus, two fractions of the sulfate lignins, soluble and insoluble, could be obtained from acetone. The different alkali lignin fractions were subjected to elemental and functional group analyses. For both Ricinus communis and bagasse, the carbon content of the fractions of the various types of lignin is in the order: soluble sulfate > soda > insoluble sulfate, while the methoxy is in the order: soda > soluble sulfate > insoluble sulfate. The phenolic OH content, as well as OH/C₉ of soda lignins of bagasse, are lower than those of soluble sulfate lignins. For Ricinus communis, the phenolic OH content and OH/C₉ is higher for some of the fractions (first three stages of cooking) of soda lignin than the corresponding fractions of kraft (sulfate) lignin, while the reverse takes place for the other fractions. For the same type of lignin, the fractions showed changes in their carbon, methoxyl, and phenolic OH contents. The change may be regular, i.e., increase or decrease with the order of stage of cooking, or irregular. Molecular weights of the different alkali lignins which are soluble in organic solvents ranged between 750 and 840.     

Xylan hydrolysis in zinc chloride solution

Xylan is the major component of hemicellulose, which consists of up to one-third of the lignocellulosic biomass. When the zinc chloride solution was used as a pretreatment agent to facilitate cellulose hydrolysis, hemicellulose was hydrolyzed during the pretreatment stage. In this study, xylan was used as a model to study the hydrolysis of hemicellulose in zinc chloride solution. The degradation of xylose that is released from xylan was reduced by the formation of zinc-xylose complex. The xylose yield was >90% (w/w) at 70°C. The yield and rate of hydrolysis were a function of temperature and the concentration of zinc chloride. The ratio of zinc chloride can be decreased from 9 to 1.3 (w/w). At this ratio, 76% of xylose yield was obtained. When wheat straw was pretreated with a concentrated zinc chloride solution, the hemicellulose hydrolysate contained only xylose and trace amounts of arabinose and oligosaccharides. With this approach, the hemicellulose hydrolysate can be separated from cellulose residue, which would be hydrolyzed subsequently to glucose by acid or enzymes to produce glucose. This production scheme provided a method to produce glucose and xylose in different streams, which can be fermented in separated fermenters.     

Pretreatment of bagasse by UCT-Solvent for the enzymatic hydrolysis

A thermochemical pretreatment of bagasse for the enzymatic hydrolysis has been carried out, in which pretreatment bagasse was autoclaved with binary solvent, composed of Water and organic solvent having upper critical temperature (UCT) on the mutual solubility curve. The pretreatment was named “UCT-solvent pretreatment.” The hydrophobic decomposition products from lignin and hemicellulose, that dissolved in organic phase at room temperature, could be easily separated from the solid and sugars in the aqueous phase. By using UCT-solvent instead of only water, the sugar recoveries from bagasse through the pretreatment and the enzymatic hydrolysis were much improved. There exists an optimal mixing ratio between organic solvent and water to maximize the effect of the pretreatment for enzymatic hydrolysis. The optimal ratio can be explained by the competitive effect between the ability of water as a reagent for the hydrolysis and the ability of solvent for the extraction of the decomposition product, and furthermore by the competitive effect between affinities of the solvent to hydrophilic hemicellulose and hydrophobic lignin. Decomposition of hemicellulose at lower temperature than 190°C was decreased, and hence the degradation of xylose during the pretreatment decreased. These favorable effects of UCT-solvent pretreatment are significantly attributed to the formation of the homogeneous single phase of organic solvent and water at high temperature and the phase separation at room temperature.     

Residual level of dimethachlon in rice‐paddy field system and cooked rice determined by gas chromatography with electron capture detector

In this study, a modified quick, easy, cheap, effective, rugged and safe method coupled with gas chromatography with electron capture detection was established to determine dimethachlon residues in paddy soil, rice husk, rice straw, brown rice and cooked rice. The limits of quantification of dimethachlon were 0.01 mg/kg for paddy soil, brown rice and cooked rice and 0.02 mg/kg for rice straw and rice husk. The mean recoveries were in the range 78.59–104.7% with relative standard deviation values of <10% for dimethachlon in the five matrices. For field experiments, the final residues of dimethachlon in paddy soil were < 0.05 mg/kg and were < 1.21 mg/kg in rice straw from six sites. The final residues of dimethachlon in the brown rice at 21, 28 and 35 days after spraying from six sites were 0.08–7.58 mg/kg, and 0.16–30.1 mg/kg in rice husk. Our six test sites covered the main rice–producing areas of China. The routine rice cooking process of a Chinese family could apparently increase the removal of dimethachlon in rice compared with brown rice, and the reduction ratios were > 96%.     

Integrated processes for use of pulps and lignins obtained from sugarcane bagasse and straw

Sugarcane bagasse and straw can be converted into pulps, oils, controlled-release formulations, chelating agents, and composites. This article reviews bagasse and straw conversion efforts in Brazil. Laboratory-scale processes were developed aiming at the integral use of these biomass byproducts. Organosolv pulping and oxidation of lignin are the most promising processes for the rational use of sugarcane residues. Fungal pretreatment and spectroscopic characterization are also discussed.     

Lime pretreatment of crop residues bagasse and wheat straw

Lime (calcium hydroxide) was used as a pretreatment agent to enhance the enzymatic digestibility of two common crop residues: bagasse and wheat straw. A systematic study of pretreatment conditions suggested that for short pretreatment times (1–3 h), high temperatures (85-135°C) were required to achieve high sugar yields, whereas for long pretreatment times (e.g., 24 h), low temperatures (50–65°C) were effective. The recommended lime loading is 0.1 g Ca(OH)₂/g dry biomass. Water loading had little effect on the digestibility. Under the recommended conditions, the 3-d reducing sugar yield of the pretreated bagasse increased from 153 to 659 mg Eq glucose/g dry biomass, and that of the pretreated wheat straw increased from 65 to 650 mg Eq glucose/g dry biomass. A material balance study on bagasse showed that the biomass yield after lime pretreatment is 93.6%. No glucan or xylan was removed from bagasse by the pretreatment, whereas 14% of lignin became solubilized. A lime recovery study showed that 86% of added calcium was removed from the pretreated bagasse by ten washings and could be recovered by carbonating the wash water with CO₂ at pH 9.5.     

Oxidation in Acidic Medium of Lignins from Agricultural Residues

Agricultural residues as sugarcane straw and bagasse are burned in boilers for generation of energy in sugar and alcohol industries. However, excess of those by-products could be used to obtain products with higher value. Pulping process generates cellulosic pulps and lignin. The lignin could be oxidized and applied in effluent treatments for heavy metal removal. Oxidized lignin presents very strong chelating properties. Lignins from sugarcane straw and bagasse were obtained by ethanol–water pulping. Oxidation of lignins was carried out using acetic acid and Co/Mn/Br catalytical system at 50, 80, and 115 °C for 5 h. Kinetics of the reaction was accomplished by measuring the UV-visible region. Activation energy was calculated for lignins from sugarcane straw and bagasse (34.2 and 23.4 kJ mol⁻¹, respectively). The first value indicates higher cross-linked formation. Fourier-transformed infrared spectroscopy data of samples collected during oxidation are very similar. Principal component analysis applied to spectra shows only slight structure modifications in lignins after oxidation reaction.     

Dilute-acid hydrolysis of sugarcane bagasse at varying conditions

Sugarcane bagasse, a byproduct of the cane sugar industry, is an abundant source of hemicellulose that could be hydrolyzed to yield a fermentation feedstock for the production of fuel ethanol and chemicals. The effects of sulfuric acid concentration, temperature, time, and dry matter concentration on hemicellulose hydrolysis were studied with a 20-L batch hydrolysis reactor using a statistical experimental design. Even at less severe conditions considerable amounts (>29%) of the hemicellulose fraction could be extracted. The percentage of soluble oligosaccharides becomes very low in experiments with high yields in monosaccharides, which indicates that the cellulose fraction is only slightly affected. For the sugar yields, acid concentration appears to be the most important parameter, while for the formation of sugar degradation products, temperature shows the highest impact. It could be demonstrated that the dry matter concentration in the reaction slurry has a negative effect on the xylose yield that can be compensated by higher concentrations of sulfuric acid owing to a positive interaction between acid concentration and dry matter contents.     

Effect of various environmental factors on the adsorption of U(VI) onto biochar derived from rice straw

Herein, we used biochar pyrolyzed from rice straw to adsorb uranium (U) from aqueous solutions. The adsorption of U(VI) on biochar was strongly dependent on pH but independent on ionic strength. HA/FA enhanced the sorption at pH <6.8 while inhibited the sorption at pH >6.8. The sorption reached equilibrium within 3 h, which was not mediated by pH. The adsorption process was spontaneous and endothermic, and enhanced at higher temperature. However, the influence of temperature was negligible at low initial U(VI) concentrations. Therefore, biochar derived from rice straw may be a promising adsorbent for the removal of U(VI).

     

Toxicity evaluation of single and mixed antifouling biocides measured with acute toxicity bioassays

Antifouling biocides used in boat paints were analyzed with a battery of toxicity bioassays to evaluate the toxic effects of these compounds on Vibrio fischeri, Daphnia magna and Selenastrum capricornotum. The antifoulants tested were Irgarol 1051, Kathon 5287, chlorothalonil, diuron, dichlofluanid, 2-thiocyanomethylthiobenzothiazole (TCMTB) and tributyltin (TBT). In most cases, the sensitivity of the organisms towards the toxicants followed the order: S. capricornotum > D. magna > V. fischeri. Toxicity by concentration level had the following order: TBT=Kathon 5287>chlorothalonil>Irgarol 1051>diuron>dichlofluanid>TCMTB for S. capricornotum. For D. magna (48 h test), the toxicity order of compounds was TBT>Kathon 5287>chlorothalonil>TCMTB>dichlofluanid>Irgarol 1051>diuron. For V. fischeri (30 min test), the compound toxicity had the following order: Kathon 5287>TBT>TCMTB>dichlofluanid>Irgarol 1051>chlorothalonil.Degradation products of Irgarol 1051 and diuron were also tested. Degradation product of Irgarol 1051 was found to be less toxic to the crustacean and the microalga but more toxic to the bacterium. Degradation products of diuron were less toxic to the microalga in comparison with the bacterium. For mixtures of compound, toxicities were additive in only 33% of the cases and 21% of mixtures were less toxic than expected based on the sum of concentrations of toxicants (antagonistic effect). Synergistic enhancements of toxicity were observed for a majority (46%) of the mixtures.The average reproducibility of the EC₅₀ and LOEC measurements was 27, 24 and 28%, respectively, in the V. fischeri, S. capricornotum and D. magna bioassays. For single compound, the reproducibility of EC₅₀ was better than ±20% for a vast majority of the measurements with the V. fischeri system, thus agreeing closely with the reported reproducibility values for this relatively well-known assay.     

Two-step preparation and thermal characterization of cationic 2-hydroxypropyltrimethylammonium chloride hemicellulose polymers from sugarcane bagasse

Cationic sugarcane bagasse hemicellulose derivatives with a relatively low degree of substitution (0.01-0.54) containing quaternary ammonium groups were prepared by etherification with 3-chloro-2-hydroxypropyltrimethylammonium chloride or preferably with 2,3-epoxypropyltrimethylammonium chloride using sodium hydroxide as a catalyst in aqueous solution. The extent of etherification was measured by yield percentage and degree of substitution (DS). The DS values of the products could be controlled by adjusting the molar ratio of etherifying agent to anhydroxylose units in hemicelluloses and the molar ratio of sodium hydroxide to etherifying reagent. In comparison, the etherified hemicellulose preparations were characterized by both degradative methods such as thermal analysis, and non-degradative techniques such as gel permeation chromatography (GPC), Fourier transform infrared (FT-IR), and ¹³C nuclear magnetic resonance (NMR) spectroscopy. It was found that a significant degradation of the hemicellulose polymers occurred during etherification under the alkaline conditions used. The thermal stability of the etherified hemicelluloses was lower than that of the unmodified hemicellulose polymers.