稀酸和稀碱预处理对四种不同生物质资源制备还原糖的影响

本论文探讨了不同浓度的稀H_2SO_4和稀NaOH预处理对大豆秸秆、水稻秸秆、象草和狼尾草四种不同生物质酶解制备还原糖的影响。结果表明,大豆秸秆、水稻秸秆、象草和狼尾草具有较高的纤维素和半纤维素含量,是制备还原糖的理想原料。与稀H_2SO_4预处理相比,经稀NaOH预处理后的样品表现出较好的酶解性能。通过使用4%的NaOH对大豆秸秆和狼尾草进行预处理,还原糖产量分别为145.8 mg/mL和319.2 mg/mL。此外,以1%NaOH预处理后的水稻秸秆和象草为原料,可以分别获得385.2 mg/mL和231.6 mg/mL还原糖产量。     

Enzymatic Saccharification of Pretreated Wheat Straw by T. Reesei Cellulases and A. Niger β-Glucosidase

Three methods of wheat straw treatment (with NaOH, H₂O₂ and butylamine) and its subsequent saccharification by Trichoderma reesei cellulases and Aspergillus niger β-glucosidase are reported. The treatment of straw with NaOH for 1 h in the autoclave (120°C) caused a great loss of the hemicellulose content and a partial removal of lignin, provoking an increase of the cellulose content (from 24% to 69%) in the residue. When the straw was pre-treated with H₂O₂ at 25°C for 20 h, the relative content of cellulose in the straw increased (from 24% to 52%) due to the solubilisation of hemicellulose.

The effect of varying the hydrolysis parameters (enzyme and substrate concentration, temperature and pH) was studied in order to maximise the yield of sugars. Under the best conditions and after 48 h with a mixture of 2:1 (w/w) cellulase/β-glucosidase (with a concentration of 7 and 0.1 U ml^-1, respectively) the native, NaOH-treated and H₂O₂-treated straw material were degraded to reducing sugars for 28%, 89% and 97% respectively.     

Influence of different chemical pretreatments of elephant grass (<Emphasis Type="Italic">Pennisetum purpureum</Emphasis>, Schum.) used as a substrate for cellulase and xylanase production in submerged cultivation

This study evaluated the potential use of elephant grass biomass, a highly productive species, for cellulase and xylanase production by the cellulolytic mutant Penicillium echinulatum 9A02S1 in submerged cultivation, using untreated biomass, biomass pretreated with different concentrations of NaOH, H₂SO₄ or NH₄OH, or biomass pretreated with H₂O at 121 °C. For filter paper activity, all cultivation carried out with pretreated elephant grass under the evaluated conditions showed superior activity when compared with the control (untreated elephant grass). The activities of endoglucanases and β-glucosidases were higher in the cultivation prepared from pretreated samples than the control made with cellulose (Celuflok^®). Without pretreatment, elephant grass can be used for xylanase production, enabling similar activities to those obtained in the cultivation with cellulose, reducing the enzyme production cost. These results indicate that the pretreatment of elephant grass, especially when pretreated with H₂SO₄, may be used as a partial or total replacement for cellulose to cellulase production, and untreated elephant grass may be used for xylanase production.     

Mild alkaline pretreatment can achieve high hydrolytic and fermentation efficiencies for rice straw conversion to bioethanol

Abstract

Mild alkaline pretreatment was evaluated as a strategy for effective lignin removal and hydrolysis of rice straw. The pretreatment efficiency of different NaOH concentrations (0.5, 1.0, 1.5 or 2.0% w/w) was assessed. Rice straw (RS) pretreated with 1.5% NaOH achieved better sugar yield compared to other concentrations used. A cellulose conversion efficiency of 91% (45.84?mg/ml glucose release) was attained from 1.5% NaOH pretreated rice straw (PRS), whereas 1% NaOH pretreated rice straw yielded 35.10?mg/ml of glucose corresponding to a cellulose conversion efficiency of 73.81%. The ethanol production from 1% and 1.5% NaOH pretreated RS hydrolysates was similar at ～3.3% (w/v), corresponding to a fermentation efficiency of 86%. The non-detoxified hydrolysate was fermented using the novel yeast strain Saccharomyces cerevisiae RPP-03O without any additional supplementation of nutrients.     

Production of H2 from cellulose by rumen microorganisms: effects of inocula pre-treatment and enzymatic hydrolysis

H₂ production from cellulose, using rumen fluid as the inoculum, has been investigated in batch experiments. Methanogenic archaea were inhibited by acid pre-treatment, which also inhibited cellulolytic microorganisms, and in consequence, the conversion of cellulose to H₂. Positive results were observed only with the addition of cellulase. H₂ yields were 18.5 and 9.6 mmol H₂ g cellulose^?1 for reactors with 2 and 4 g cellulose l^?1 and cellulase, respectively. H₂ was primarily generated by the butyric acid pathway and this was followed by formation of acetic acid, ethanol and n-butanol. In reactors using 4 g cellulose l^?1 and cellulase, the accumulation of alcohols negatively affected the H₂ yield, which changed the fermentation pathways to solventogenesis. PCR–DGGE analysis showed changes in the microbial communities. The phylogenetic affiliations of the bands of DGGE were 99 % similar to Clostridium sp.     

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.     

Study of the Ultrastructure of <Emphasis Type="Italic">Eucalyptus globulus</Emphasis> Wood Substrates Subjected to Auto-Hydrolysis and Diluted Acid Hydrolysis Pre-treatments and Its Influence on Enzymatic Hydrolysis

Dilute acid hydrolysis (DAH) and auto-hydrolysis (AU) have demonstrated to be optimal pre-treatments for the generation of biofuels from wood. Recent studies have highlighted the importance of ensuring the accessibility of cellulose enzymes during the enzymatic hydrolysis (EH) of pre-treated materials. In this work, the microscopic and nanoscopic structures of Eucalyptus globulus samples pre-treated by AU and DAH were evaluated by different techniques to understand the effect of the ultrastructure of samples on the enzymatic conversion and cellulose accessibility for bioethanol production. Microscopic techniques revealed changes in the physical characteristics of pre-treated fibers, coalescence at microscopic level, and differences in the chemical distribution of lignocellulosic components depending on the severity and type of pre-treatment. The atomic force microscopy-based nanoscopic study of samples showed differences in the effect of the pre-treatments on the ultrastructure of samples, with DAH pre-treatment producing major changes in the secondary cell wall with respect to AU samples at comparable severities, and a positive effect of the DAH ultrastructure changes to increase the EH yield.     

Liquid hot water and alkaline pretreatment of soybean straw for improving cellulose digestibility

Soybean straw was pretreated with either liquid hot water (LHW) (170-210 °C for 3-10 min) or alkaline soaking (4-40 g NaOH/100 g dry straw) at room temperature to evaluate the effects on cellulose digestibility. Nearly 100% cellulose was recovered in pretreated solids for both pretreatment methods. For LHW pretreatment, xylan dissolution from the raw material increased with pretreatment temperature and time. Cellulose digestibility was correlated with xylan dissolution. A maximal glucose yield of 70.76%, corresponding to 80% xylan removal, was obtained with soybean straw pretreated at 210 °C for 10 min. NaOH soaking at ambient conditions removed xylan up to 46.37% and the subsequent glucose yield of pretreated solids reached up to 64.55%. Our results indicated LHW pretreatment was more effective than NaOH soaking for improving cellulose digestibility of soybean straw.     

Comparison between solid-state and powder-state alkali pretreatment on saccharification and fermentation for bioethanol production from rice straw

The efficacy of different concentrations of NaOH (0.25%, 0.50%, 0.75%, and 1.00%) for the pretreatment of rice straw in solid and powder state in enzymatic saccharification and fermentation for the production of bioethanol was evaluated. A greater amount of biomass was recovered through solid-state pretreatment (3.74 g) from 5 g of rice straw. The highest increase in the volume of rice straw powder as a result of swelling was observed with 1.00% NaOH pretreatment (48.07%), which was statistically identical to 0.75% NaOH pretreatment (32.31%). The surface of rice straw was disrupted by the 0.75% NaOH and 1.00% NaOH pretreated samples as observed using field-emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM). In Fourier-transform infrared (FT-IR) spectra, absorbance of hydroxyl groups at 1,050 cm^?1 due to the OH group of lignin was gradually decreased with the increase of NaOH concentration. The greatest amounts of glucose and ethanol were obtained in 1.00% NaOH solid-state pretreated and powder-state hydrolyzed samples (0.804 g g^?1 and 0.379 g g^?1, respectively), which was statistically similar to the use of 0.75% NaOH (0.763 g g^?1 and 0.358 g g^?1, respectively). Thus, solid-state pretreatment with 0.75% NaOH and powder-state hydrolysis appear to be suitable for fermentation and bioethanol production from rice straw.     

Bioconversion of wheat straw to ethanol: Chemical modification,enzymatic hydrolysis,and fermentation

Native wheat straw (WS) was pretreated with various concentrations of H₂SO₄ and NaOH followed by secondary treatments with ethylene diamine (EDA) and NH₄OH prior to enzymatic saccharification. Conversion of the cellulosic component to sugar varied with the chemical modification steps. Treatment solely with alkali yield 51–75% conversion, depending on temperature. Acid treatment at elevated tempeatures showed a substantial decrease in the hemicellulose component, whereas EDA-treated WS (acid pretreated) showed a 69–75% decrease in the lignin component. Acid-pretreated EDA-treated straw yielded a 98% conversion rate, followed by 83% for alkali–NH₄OH treated straws. In other experiments, WS was pretreated with varying concentration of H₂SO₄ or NaOh followed by NH₄OH treatment prior to enzymatic hydrolysis. Pretreatment of straw with 2% NaOH for 4 h coupled to enzymatic hydrolysis yield a 76% conversion of the cellulosic component. Acid–base combination pretreatment yielded only 43% conversions. A reactor column was subsequently used to measure modification–saccharification–fermentation for wheat straw conversion on a larger scale. Thirty percent conversions of wheat straw cellulosics to sugar were observed with subsequent fermentation to alcohol. The crude cellulase preparation yielded considerable quantities of xylose in addition to the glucose. Saccharified materials were fermented directly with actively proliferating proliferating yeast cells without concentration of the sugars.     

Synergism of cellulase,pectinase and xylanase on hydrolyzing differently pretreated sweet potato residues

Abstract

The synergism of cellulase (C), pectinase (P), and xylanase (X) for the saccharification of sweet potato residues (SPR) was investigated. The removal of starch from SPR was easily achieved by using amylase, but the cellulose conversion of de-starched SPR was relatively low, thus dilute H₂SO₄, NaOH, and H₂O₂ pretreatment was conducted to improve the enzymatic digestibility. The lignin content of NaOH pretreated SPR was the lowest, whereas H₂SO₄ pretreatment resulted in the lowest contents of hemicellulose and pectin. The combination of C, P, and X exhibited different sugar production patterns, C–P displayed synergistic action on glucose and galactose production from each type of SPR, C–X also exhibited synergistic effect on glucose production except when H₂SO₄ pretreated SPR was used, whereas no synergism between P–X on monosaccharide production was observed. The presence of synergism between cellulase and mixed accessory enzymes [C–(PX)] on glucose formation was determined by C–X, and the degree of synergism between C–P and C–(PX) on glucose production had a positive relationship with pectin content. The highest cellulose conversion of 96.2% was obtained from NaOH pretreated SPR using mixed enzymes comprising C, P, and X with the ratio of 8:1:1.     

Cellulose Fermentation: Effect of Substrate Pretreatment on Microbial Growth

The effects of chemical, physical, and enzymatic treatments of rice straw and sugarcane bagasse on the microbial digestibility of cellulose have been investigated. Treatment with 4% NaOH for 15 min at 100 C increased the digestibility of cellulose from 29.4 to 73%. Treatment with 5.2% NH₃ could increase digestibility to 57.0% Treatments with sulfuric acid and crude cellulase preparation solubilized cellulose but did not increase the digestibility. Grinding or high-pressure cooking of the substrate had little effect on increasing the digestibility of cellulosic substrates by the Cellulomonas species.     

Microbial Fermentation of Rice Straw: Nutritive Composition and In Vitro Digestibility of the Fermentation Products

Rice straw was fermented with Cellulomonas sp. and Alcaligenes faecalis. Microbial cells and undigested residue, as well as chemically treated (NaOH or NH₄OH) and untreated straws, were analyzed for nutrient composition and in vitro digestibility. In a typical fermentation, 75% of the rice straw substrate was digested, and 18.6% of the total substrate weight that disappeared was recovered as microbial protein. The microbial cell fraction was 37% protein and 5% crude fiber; the residue was 12% protein and 45% crude fiber. The microbial protein amino acid profile was similar to alfalfa, except for less cysteine. The microbial cells had more thiamine and less niacin than Torula yeast. In vitro digestibility of the microbial protein was 41.2 to 55%; that of cellulose was 52%.     

A Counter-Current Acid Leaching Process for the Remediation of Contaminated Soils from a Small-Arms Shooting Range

The objective of this research was to use a counter-current leaching process (CCLP) with leachate treatment to develop a remediation process for contaminated soils at a small-arms shooting range (SASR). The soil contaminant concentrations were 245 mg Cu kg^?1, 3,368 mg Pb kg^?1, 73 mg Sb kg^?1, and 177 mg Zn kg^?1. The CCLP includes three acid leaching steps (1M H₂SO₄ + 4M NaCl, t = 1 h, T = 20°C, soil suspension = 100 g L^?1), followed by one water rinsing step (1 h). Seven counter-current remediation cycles were completed, and the average resulting metal removals were 93.2 ± 3.5% of Cu, 91.5 ± 5.7% of Pb, 82.2 ± 10.9% of Sb, and 30.0 ± 11.4% of Zn. The metal leaching performances decreased with the number of completed cycles. Soil treated with the CCLP with leachate treatment process met the USEPA threshold criteria of 5 mg Pb L^?1 in the TCLP leachate. The CCLP allows a decrease of the water use by 32.9 m³ t^?1 and the chemicals’ consumption by approximately 2,650 kg H₂SO₄, 6,014 kg NaCl, and 1,150 kg NaOH per ton of treated soil, in comparison to standard leaching processes. This corresponds to 78%, 69%, 83%, and 67% of reduction, respectively.     

Effect of dilute acid pretreatment on the saccharification and fermentation of rye straw

This research shows the effect of dilute acid pretreatment with various sulfuric acid concentrations (0.5–2.0% [wt/vol]) on enzymatic saccharification and fermentation yield of rye straw. After pretreatment, solids of rye straw were suspended in Na citrate buffer or post-pretreatment liquids (prehydrolysates) containing sugars liberated after hemicellulose hydrolysis. Saccharification was conducted using enzymes dosage of 15 or 25 FPU/g cellulose. Cellulose saccharification rate after rye straw pretreatment was enhanced by performing enzymatic hydrolysis in sodium citrate buffer in comparison with hemicellulose prehydrolysate. The maximum cellulose saccharification rate (69%) was reached in sodium citrate buffer (biomass pretreated with 2.0% [wt/vol] H₂SO₄). Lignocellulosic complex of rye straw after pretreatment was subjected to separate hydrolysis and fermentation (SHF) or separate hydrolysis and co-fermentation (SHCF). The SHF processes conducted in the sodium citrate buffer using monoculture of Saccharomyces cerevisiae (Ethanol Red) were more efficient compared to hemicellulose prehydrolysate in respect with ethanol yields. Maximum fermentation efficiency of SHF processes obtained after rye straw pretreatment at 1.5% [wt/vol] H₂SO₄ and saccharification using enzymes dosage of 25 FPU/g in sodium citrate buffer, achieving 40.6% of theoretical yield. However, SHCF process using cocultures of pentose-fermenting yeast, after pretreatment of raw material at 1.5% [wt/vol] H₂SO₄ and hydrolysis using enzymes dosage of 25 FPU/g, resulted in the highest ethanol yield among studied methods, achieving 9.4 g/L of ethanol, corresponding to 55% of theoretical yield.     

Identification of Newly Isolated Talaromyces pinophilus and Statistical Optimization of β-Glucosidase Production Under Solid-State Fermentation

Fungi able to degrade agriculture wastes were isolated from different soil samples, rice straw, and compost; these isolates were screened for their ability to produce β-glucosidase. The most active fungal isolate was identified as Talaromyces pinophilus strain EMOO 13-3. The Plackett–Burman design is used for identifying the significant variables that influence β-glucosidase production under solid-state fermentation. Fifteen variables were examined for their significances on the production of β-glucosidase in 20 experimental runs. Among the variables screened, moisture content, Tween 80, and (NH₄)₂SO₄ had significant effects on β-glucosidase production with confidence levels above 90% (p < 0.1). The optimal levels of these variables were further optimized using Box–Behnken statical design. As a result, the maximal β-glucosidase activity is 3648.519 U g^?1, which is achieved at the following fermentation conditions: substrate amount 0.5 (g/250 mL flask), NaNO₃ 0.5 (%), KH₂PO₄ 0.3 (%), KCl 0.02 (%), MgSO₄ · 7H₂O 0.01 (%), CaCl₂ 0.01 (%), yeast extract 0.07 (%), FeSO₄ · 7H₂O 0.0002 (%), Tween 80 0.02 (%), (NH₄)₂SO₄ 0.3 (%), pH 6.5, temperature 25°C, moisture content 1 (mL/g dry substrate), inoculum size 0.5 (mL/g dry substrate), and incubation period 5 days.     

Structure and saccharification of rice straw pretreated with sulfur trioxide micro-thermal explosion collaborative dilutes alkali

In this paper, a sulfur trioxide collaborative dilutes alkali method has been developed to pre-treat rice straw and it has been studied that the pre-treated rice straw structure affected the saccharification of the rice straw hydrolyzed by cellulose enzymatic hydrolysis. The results show that the reaction of the sulfur trioxide with rice straw resulted in the internal micro-thermal explosion, and the saccharification rate was 91% based on the pretreated rice straw with sulfur trioxide for 4h following 1% w/v NaOH treatment for 7h at 50°C.     

Butanol production from sweet sorghum bagasse with high solids content: Part I—comparison of liquid hot water pretreatment with dilute sulfuric acid

In these studies, we pretreated sweet sorghum bagasse (SSB) using liquid hot water (LHW) or dilute H₂SO₄ (2 g L^?1) at 190°C for zero min (as soon as temperature reached 190°C, cooling was started) to reduce generation of sugar degradation fermentation inhibiting products such as furfural and hydroxymethyl furfural (HMF). The solids loading were 250–300 g L^?1. This was followed by enzymatic hydrolysis. After hydrolysis, 89.0 g L^?1 sugars, 7.60 g L^?1 acetic acid, 0.33 g L^?1 furfural, and 0.07 g L^?1 HMF were released. This pretreatment and hydrolysis resulted in the release of 57.9% sugars. This was followed by second hydrolysis of the fibrous biomass which resulted in the release of 43.64 g L^?1 additional sugars, 2.40 g L^?1 acetic acid, zero g L^?1 furfural, and zero g L^?1 HMF. In both the hydrolyzates, 86.3% sugars present in SSB were released. Fermentation of the hydrolyzate I resulted in poor acetone‐butanol‐ethanol (ABE) fermentation. However, fermentation of the hydrolyzate II was successful and produced 13.43 g L^?1 ABE of which butanol was the main product. Use of 2 g L^?1 H₂SO₄ as a pretreatment medium followed by enzymatic hydrolysis resulted in the release of 100.6–93.8% (w/w) sugars from 250 to 300 g L^?1 SSB, respectively. LHW or dilute H₂SO₄ were used to economize production of cellulosic sugars from SSB. © 2018 American Institute of Chemical Engineers Biotechnol. Prog., 34:960–966, 2018     

Cellulosic Butanol (ABE) Biofuel Production from Sweet Sorghum Bagasse (SSB): Impact of Hot Water Pretreatment and Solid Loadings on Fermentation Employing <Emphasis Type="Italic">Clostridium beijerinckii</Emphasis> P260

A novel butanol fermentation process was developed in which sweet sorghum bagasse (SSB) was pretreated using liquid hot water (LHW) pretreatment technique followed by enzymatic hydrolysis and butanol (acetone butanol ethanol (ABE)) fermentation. A pretreatment temperature of 200 °C resulted in the generation of a hydrolyzate that inhibited butanol fermentation. When SSB pretreatment temperature was decreased to 190 °C (0-min holding time), the hydrolyzate was successfully fermented without inhibition and an ABE productivity of 0.51 g L^?1 h^?1 was achieved which is comparable to the 0.49 g L^?1 h^?1 observed in the control fermentation where glucose was used as a feedstock. These results are based on the use of 86 g L^?1 SSB solid loadings in the pretreatment reactors. We were also able to increase SSB solid loadings from 120 to 200 g L^?1 in the pretreatment step (190 °C) followed by hydrolysis and butanol fermentation. As pretreatment solid loadings increased, ABE yield remained in the range of 0.38–0.46. In these studies, a maximum ABE concentration of 16.88 g L^?1 was achieved. Using the LHW pretreatment technique, 88.40–96.00 % of polymeric sugars (cellulose + hemicellulose) were released in the SSB hydrolyzate. The LHW pretreatment technique does not require chemical additions and is environmentally friendly, and the hydrolyzate can be used successfully for butanol fermentation.     

The polythiophene molecular segment as a sensor model for H<Subscript>2</Subscript>O,HCN, NH<Subscript>3</Subscript>, SO<Subscript>3</Subscript>, and H<Subscript>2</Subscript>S: a density functional theory study

Studying the interaction of some atmospheric gases (H₂O, HCN, NH₃, SO₃ and H₂S) with 3PT oligomers is important in the development of polymeric sensors for gas detection. In the present study, we studied the relaxed geometries, interaction energies, charge analysis, HOMO–LUMO orbital analysis, and UV–vis spectra of all interacted systems using first-principles density functional theory (DFT). All these analyses indicated the potential of polythiophene as an inexpensive polymeric sensor for the analytes mentioned. Interaction energy values of ?19.90, ?19.66, ?14.01, ?8.70, and ?4.76 kJ mol^?1 were achieved for adsorption of SO₃, H₂O, NH₃, HCN, and H₂S on 3PT, respectively. Consequently, clarification of their physical parameters became the major focus of this study.