Pretreatment and enzymic saccharification of water hyacinth cellulose

Water hyacinth was pretreated, under variable conditions, with NaOH, alkaline H₂O₂, peracetic acid and sodium chlorite. Combined pretreatments included sodium chlorite with each of NaOH, alkaline H₂O₂ and peracetic acid. Combined pretreatment with 0.1% NaClO₂ for 1 h at 100 °C and peracetic acid at 100 °C for 15 min afforded the most promising sample. The recovered lignin, cellulose and hemicellulose of this sample was 2.56%, 96.69%, and 81.38%, respectively. The same sample, by cellulase hydrolysis showed the highest cellulose conversion (80.8%) and 90% saccharification using 200 FPU/g substrate. Some ambient factors affecting saccharification of pretreated water hyacinth were investigated. Enzymic saccharification after 6 h was about 50% of that at 48 h, indicating a slow hydrolysis rate by time. Addition of 8% glucose at the beginning of the enzymic hydrolysis decreased the saccharification to about its half while addition of 8% ethanol brought about complete inhibition of the enzyme. Addition of cellobiase to the reaction mixture increased cellulose conversion and saccharification by 10%.     

Ethanol production from rice straw using optimized aqueous-ammonia soaking pretreatment and simultaneous saccharification and fermentation processes

Rice straw was pretreated using aqueous-ammonia solution at moderate temperatures to enable production of the maximum amount of fermentable sugars from enzymatic hydrolysis. The effects of various operating variables including pretreatment temperature, pretreatment time, the concentration of ammonia and the solid-to-liquid ratio on the degree of lignin removal and the enzymatic digestibility were optimized using response surface methodology. The optimal reaction conditions, which resulted in an enzymatic digestibility of 71.1%, were found to be 69 °C, 10 h and an ammonia concentration of 21% (w/w). The effects of different commercial cellulases and the additional effect of a non-cellulolytic enzyme, xylanase, were also evaluated. Additionally, simultaneous saccharification and fermentation was conducted with rice straw to assess the ethanol production yield and productivity.     

Mild pretreatment of yellow poplar biomass using sequential dilute acid and enzymatically-generated peracetic acid to enhance cellulase accessibility

Biomass contains cellulose, xylan and lignin in a complex interwoven structure that hinders enzymatic hydrolysis of the cellulose. To separate these components in yellow poplar biomass, we sequentially pretreated with dilute sulfuric acid and enzymatically-generated peracetic acid. In the first step, the dilute acid with microwave heating (140°C, 5 min) hydrolyzed 90% of xylan. The xylose yield in hydrolysate after dilute acid pretreatment was 83.1%. In the second step, peracetic acid (60°C, 6 h) removed up to 80% of lignin. This sequential pretreatment fractionated biomass into xylan and lignin, leaving a solid residue enriched in cellulose (~80%). The sequential pretreatment enhanced enzymatic digestibility of the cellulase by removal of the other components in biomass. The glucose yield after enzymatic hydrolysis was 90.5% at a low cellulase loading (5 FPU/g of glucan), which is 1.6 and 18 times higher than for dilute acid-pretreated biomass and raw biomass, respectively. This novel sequential pretreatment with dilute acid and peracetic acid efficiently separates the three major components of yellow poplar biomass, and reduces the amount of cellulase needed.     

Thermo-mechanical extrusion pretreatment for conversion of soybean hulls to fermentable sugars

Thermo-mechanical extrusion pretreatment for lignocellulosic biomass was investigated using soybean hulls as the substrate. The enzyme cocktail used to hydrolyze pretreated soybean hulls to fermentable sugars was optimized using response surface methodology (RSM). Structural changes in substrate and sugar yields from thermo-mechanical processing were compared with two traditional pretreatment methods that utilized dilute acid (1% sulfuric acid) and alkali (1% sodium hydroxide). Extrusion processing parameters (barrel temperature, in-barrel moisture, screw speed) and processing aids (starch, ethylene glycol) were studied with respect to reducing sugar and glucose yields. The conditions resulting in the highest cellulose to glucose conversion (95%) were screw speed 350 rpm, maximum barrel temperature 80 °C and in-barrel moisture content 40% wb. Compared with untreated soybean hulls, glucose yield from enzymatic hydrolysis of soybean hulls increased by 69.6%, 128.7% and 132.2%, respectively, when pretreated with dilute acid, alkali and extrusion.     

A sustainable woody biomass biorefinery

Woody biomass is renewable only if sustainable production is imposed. An optimum and sustainable biomass stand production rate is found to be one with the incremental growth rate at harvest equal to the average overall growth rate. Utilization of woody biomass leads to a sustainable economy. Woody biomass is comprised of at least four components: extractives, hemicellulose, lignin and cellulose. While extractives and hemicellulose are least resistant to chemical and thermal degradation, cellulose is most resistant to chemical, thermal, and biological attack. The difference or heterogeneity in reactivity leads to the recalcitrance of woody biomass at conversion. A selection of processes is presented together as a biorefinery based on incremental sequential deconstruction, fractionation/conversion of woody biomass to achieve efficient separation of major components. A preference is given to a biorefinery absent of pretreatment and detoxification process that produce waste byproducts. While numerous biorefinery approaches are known, a focused review on the integrated studies of water-based biorefinery processes is presented. Hot-water extraction is the first process step to extract value from woody biomass while improving the quality of the remaining solid material. This first step removes extractives and hemicellulose fractions from woody biomass. While extractives and hemicellulose are largely removed in the extraction liquor, cellulose and lignin largely remain in the residual woody structure. Xylo-oligomers, aromatics and acetic acid in the hardwood extract are the major components having the greatest potential value for development. Higher temperature and longer residence time lead to higher mass removal. While high temperature (>200°C) can lead to nearly total dissolution, the amount of sugars present in the extraction liquor decreases rapidly with temperature. Dilute acid hydrolysis of concentrated wood extracts renders the wood extract with monomeric sugars. At higher acid concentration and higher temperature the hydrolysis produced more xylose monomers in a comparatively shorter period of reaction time. Xylose is the most abundant monomeric sugar in the hydrolysate. The other comparatively small amounts of monomeric sugars include arabinose, glucose, rhamnose, mannose and galactose. Acetic acid, formic acid, furfural, HMF and other byproducts are inevitably generated during the acid hydrolysis process. Short reaction time is preferred for the hydrolysis of hot-water wood extracts. Acid hydrolysis presents a perfect opportunity for the removal or separation of aromatic materials from the wood extract/hydrolysate. The hot-water wood extract hydrolysate, after solid-removal, can be purified by Nano-membrane filtration to yield a fermentable sugar stream. Fermentation products such as ethanol can be produced from the sugar stream without a detoxification step.     

Optimization of microwave-assisted FeCl3 pretreatment conditions of rice straw and utilization of Trichoderma viride and Bacillus pumilus for production of reducing sugars

In this study, Box-Behnken design (BBD) and response surface methodology (RSM) were used to optimize microwave-assisted FeCl₃ pretreatment conditions of rice straw with respect to FeCl₃ concentration, microwave intensity, irradiation time and substrate concentration. When rice straw was pretreated at the optimal conditions of FeCl₃ concentration, 0.14 mol/L; microwave intensity, 160 °C; irradiation time, 19 min; substrate concentration, 109 g/L; and inoculated with Trichoderma viride and Bacillus pumilus, the production of reducing sugars was 6.62 g/L. This yield was 2.9 times higher than that obtained with untreated rice straw. The microorganisms degraded 37.8% of pretreated rice straw after 72 h. The structural characteristic analyses suggest that microwave-assisted FeCl₃ pretreatment damaged the silicified waxy surface of rice straw, disrupted almost all the ether linkages between lignin and carbohydrates, and removed lignin.     

Two-stage pretreatment of rice straw using aqueous ammonia and dilute acid

Liberation of fermentable sugars from recalcitrant lignocellulosic biomass is one of the key challenges in production of cellulosic ethanol. Here we developed a two-stage pretreatment process using aqueous ammonia and dilute sulfuric acid in a percolation mode to improve production of fermentable sugars from rice straw. Aqueous NH? was used in the first stage which removed lignin selectively but left most of cellulose (97%) and hemicellulose (77%). Dilute acid was applied in the second stage which removed most of hemicellulose, partially disrupted the crystalline structure of cellulose, and thus enhanced enzymatic digestibility of cellulose in the solids remaining. Under the optimal pretreatment conditions, the enzymatic hydrolysis yields of the two-stage treated samples were 96.9% and 90.8% with enzyme loadings of 60 and 15FPU/g of glucan, respectively. The overall sugar conversions of cellulose and hemicellulose into glucose and xylose by enzymatic and acid hydrolysis reached 89.0% and 71.7%, respectively.     

Comparing the Recalcitrance of Eucalyptus, Pine, and Switchgrass Using Ionic Liquid and Dilute Acid Pretreatments

Pine, eucalyptus, and switchgrass were evaluated for the production of fermentable sugars via ionic liquid and dilute acid pretreatments and subsequent enzymatic hydrolysis. The results show that among the three feedstocks, switchgrass has the highest sugar yields and faster hydrolysis rates for both pretreatment technologies by achieving 48 % (dilute acid) and 96 % (ionic liquid) sugar yields after 24 h. Of the two wood species, eucalyptus has a higher and faster sugar recovery after ionic liquid pretreatment than pine (93 vs. 62 % in 24 h) under 160 °C for 3 h with [C₂mim][OAc]. Pretreatment of pine and eucalyptus is observed to be ineffective under 1.2 % dilute acid condition and 160 °C for 15 min, indicating that further enhancement of reaction temperature or acid concentration is necessary to increase the digestibility of pretreated materials. Raman spectroscopy data show that the extent of lignin depolymerization that occurs during pretreatment also varies for the three different feedstocks. Under similar hemicellulose removal conditions, lignin removal in ionic liquid pretreatment can help improve cellulose conversion. This finding may help explain the observed variation in the saccharification yields and kinetics. These results indicate that ionic liquid pretreatment not only improved saccharification over dilute acid for all three feedstocks but also better dealt with the differences among them, suggesting better tolerance to feedstock variability.     

Production of sugars from wood using high-pressure hydrogen chloride

Saturating wood particles with HCl gas under pressure was found to be an effective pretreatment prior to subjecting wood to dilute acid hydrolysis. Pretreament is necessary to release sugars from wood because of the tight lattice structure of cellulose. The HCl gas makes the cellulose more susceptible to subsequent acid hydrolysis and the glucose yield is doubled when dilute acid hydrolysis is preceded by HCl saturation at high pressure. The saturation was most effectively performed in a fluidized bed reactor, with pure HCl gas fluidizing an equal volume of ground wood plus inert particles. The fluidized bed effectively dissipated the large amount of heat released upon HCl absorption into the wood. Batch reaction times of 1 h at 315 psia gave glucose yields of 80 degrees and xylose yields of 95 degrees after dilute acid hydrolysis. A model was developed which proposed gas diffusing through the solid as limiting the reaction rate and this was found to effectively describe the HCl-wood reaction in the fluidized bed. The HCl was found to form a stable adduct with the lignin residue in the wood, in a ratio of 3.33 mole of lignin monomer. The adduct was broken upon the addition of water.     

Comparison of Dilute Acid and Sulfite Pretreatment for Enzymatic Saccharification of Earlywood and Latewood of Douglas fir

This study applied dilute acid (DA) and sulfite pretreatment to overcome the recalcitrance of lignocelluloses (SPORL) to deconstruct earlywood and latewood cell walls of Douglas fir for fermentable sugars production through subsequent enzymatic hydrolysis. DA pretreatment removed almost all the hemicelluloses, while SPORL at initial pH?=?4.5 (SP-B) removed significant amount of lignin between 20 and 25 %. But both are not sufficient for effective enzymatic saccharification. SPORL at low initial pH?=?2 (SP-AB) combines the advantage of both DA and SPORL-B to achieve approximately 90 % hemicellulose removal and delignification of 10–20 %. As a result, SP-AB effectively removed recalcitrance and thereby significantly improved enzymatic saccharification compared with DA and SP-B. Results also showed that earlywood with significantly lower density produced less saccharification after DA pretreatment, suggesting that wood density does not contribute to recalcitrance. The thick cell wall of latewood did not limit chemical penetration in pretreatments. The high lignin content of earlywood limited the effectiveness of DA pretreatment for enzymatic saccharification, while hemicellulose limits the effectiveness of high pH pretreatment of SP-B. The higher hemicellulose content in the earlywood and latewood of heartwood reduced saccharification relative to the corresponding earlywood and latewood in the sapwood using DA and SP-AB.     

Selective extraction of hemicelluloses from spruce using switchable ionic liquids

Switchable ionic liquids (SILs) made from alcohols, either hexanol or butanol, and CO₂ together with an amidine (1,8-diazabicyclo-[5.4.0]-undec-7-ene (DBU)) were investigated as dissolution/fractionation solvents for wood material. Both native spruce (Picea abies), and pre-extracted spruce were treated with either butanol SIL (SIL1) or hexanol SIL (SIL2) for 5 days at 55 °C under normal pressure. The SILs were formed by bubbling CO₂ through an equimolar mixture of either 1-hexanol or 1-butanol and DBU. The viscosity of the mixture increased from 7.1 mPa s to 2980 mPa s for SIL2 and 5.1 to 1600 mPa s for SIL1. Melting points of the SILs 1 and 2 were at 8 and 14 °C, respectively. After the treatment time (5 days), the undissolved fraction contained 38 wt.% less hemicelluloses compared to native spruce. There was an increase in the glucose content of the milled spruce treated with both SILs, since the milling step reduced the cellulose crystallinity of the wood and facilitated an easier SIL access into the wood. The solvents were very neutral in terms of lignin removal. Consequently, only about 2% of the lignin was removed from native wood. Moreover, a priori removal of the wood extractives did not influence the lignin removal.     

Biodegradation of lignin-carbohydrate complexes

Covalent lignin-carbohydrate (LC) linkages exist in lignocellulose from wood and groups herbaceous plants. In wood, they consist of ester and ether linkages through sugar hydroxyl to the -carbanol of phenylpropane subunits in lignin. In grasses, ferulic and p-coumaric acids are esterified to hemicelluloses and lignin, respectively. Hemicelluloses also contain substitutents and side groups that restrict enzymatic attack. Watersoluble lignin-carbohydrate complexes (LCCs) often precipitate during digestion with polysaccharidases, and the residual sugars are more diverse than the bulk hemicellulose. A number of microbial esterases and hemicellulose polysaccharidases including acetyl xylan esterase, ferulic acid esterase, and p-coumaric esterase attack hemicellulose side chains. Accessory hemicellulases include -l-arabinofuranosidase and -methyl-glucuranosidase. Both of these side chains are involved in LC bonds. -Glucosidase will attach sugar residues to lignin degradation products and when carbohydrate is attached to lignin, lignin peroxidase will depolymerize the lignin more readily.Abbreviations APPL acid precipitable polymeric lignin - CBQase cellobioquinone oxidoreductase - LC lignincarbohydrate - LCC(s) lignin-carbohydrate complex - DHP Dehydrogenative polymerisate - DMSO dimethylsulfoxide - DP degree of polymerisation - MWEL milled wood enzyme lignin - MWL milled wood lignin (not digested with carbohydrases)     

Structural and physico-chemical characterization of hemicelluloses from ultrasound-assisted extractions of partially delignified fast-growing poplar wood through organic solvent and alkaline solutions

One organic and three alkaline hemicellulosic fractions were isolated by an ultrasound-assisted extraction which partially delignified the fast-growing poplar wood. Successive treatments were conducted with dimethyl sulfoxide under ultrasonic irradiation at 570 W, 25 °C for 30 min, 70% ethanol containing 1% NaOH, 3% NaOH and 6% NaOH at 75 °C for 3 h, respectively. The four hemicellulosic fractions obtained were comparatively studied by sugar analysis, alkaline nitrobenzene oxidation of bound lignin, GPC, FT-IR, 1D and 2D NMR spectroscopy as well as TGA and DTA. The results showed that the ultrasonic treatment and sequential extractions with three different concentrations of NaOH led to a release of 75.5% of the original hemicelluloses and 96.2% of the lignin. All four purified hemicellulose fractions contained relatively low amounts of associated lignin, ranging between 0.96 and 3.10%. In addition, the hemicellulosic fraction H₄ isolated with 6% NaOH is formed by a linear backbone of four (β-1 → 4)-xylopyranosyl residues and at least one of the xylose residues is monosubstituted at C-2 by a 4-O-methylglucuronic acid, giving a typical ratio of 4-O-methyl glucuronic acid to Xyl of 1 to 4.     

Simplified process for ethanol production from sugarcane bagasse using hydrolysate-resistant Escherichia coli strain MM160

Hexose and pentose sugars from phosphoric acid pretreated sugarcane bagasse were co-fermented to ethanol in a single vessel (SScF), eliminating process steps for solid-liquid separation and sugar cleanup. An initial liquefaction step (L) with cellulase was included to improve mixing and saccharification (L + SScF), analogous to a corn ethanol process. Fermentation was enabled by the development of a hydrolysate-resistant mutant of Escherichia coli LY180, designated MM160. Strain MM160 was more resistant than the parent to inhibitors (furfural, 5-hydroxymethylfurfural, and acetate) formed during pretreatment. Bagasse slurries containing 10% and 14% dry weight (fiber plus solubles) were tested using pretreatment temperatures of 160-190 °C (1% phosphoric acid, 10 min). Enzymatic saccharification and inhibitor production both increased with pretreatment temperature. The highest titer (30 g/L ethanol) and yield (0.21 g ethanol/g bagasse dry weight) were obtained after incubation for 122 h using 14% dry weight slurries of pretreated bagasse (180 °C).     

Pretreatment of waste newspaper using ethylene glycol for bioethanol production

Pretreatment using ethylene glycol was investigated to enhance the enzyme digestibility of wastepaper. The pretreatment was conducted over a wide range of conditions including sulfuric acid concentrations of 1.3 ∼ 4.7%, temperatures of 143.2 ∼ 176.7°C and reaction time of 1.6 ∼ 18.4 min. The optimum conditions were around 2% sulfuric acid, 150°C and 15 min. At these conditions, 60 and 75% of hemicellulose and lignin, respectively, were removed while cellulose remained intact. Additionally, an enzyme digestibility of 94% was achieved. From the substrate dissolution analysis, the dissolution yield was strongly related to the enzymatic digestibility and the removal of cellulose, hemicellulose and lignin. Also, the dissolution yield was directly related to the severity parameter, which provides a quantitative prediction of the intensity of a reaction. Recycling and re-use of ethylene glycol were also studied. Ethylene glycol could be recycled and re-used at least four times without significantly lowering the pretreatment performance.     

Reducing agents improve enzymatic hydrolysis of cellulosic substrates in the presence of pretreatment liquid

Enzymatic hydrolysis of pretreated lignocellulosic substrates has emerged as an interesting option to produce sugars that can be converted to liquid biofuels and other commodities using microbial biocatalysts. Lignocellulosic substrates are pretreated to make them more accessible to cellulolytic enzymes, but the pretreatment liquid partially inhibits subsequent enzymatic hydrolysis. The presence of pretreatment liquid from Norway spruce resulted in a 63% decrease in the enzymatic saccharification of Avicel compared to when the reaction was performed in a buffered aqueous solution. The addition of 15 mM of a reducing agent (hydrogen sulfite, dithionite, or dithiothreitol) to reaction mixtures with the pretreatment liquid resulted in up to 54% improvement of the saccharification efficiency. When the reducing agents were added to reaction mixtures without pretreatment liquid, there was a 13-39% decrease in saccharification efficiency. In the presence of pretreatment liquid, the addition of 15 mM dithionite to Avicel, α-cellulose or filter cake of pretreated spruce wood resulted in improvements between 25 and 33%. Positive effects (6-17%) of reducing agents were also observed in experiments with carboxymethyl cellulose and 2-hydroxyethyl cellulose. The approach to add reducing agents appears useful for facilitating the utilization of enzymes to convert cellulosic substrates in industrial processes.     

白酒丢糟的多酶复配降解制备可发酵性糖

为有效利用纤维质原料制备可发酵性糖生产燃料酒精,通过NaOH-过氧乙酸预处理白酒丢糟,经质量分数2%NaOH和体积分数6%过氧乙酸处理后,白酒丢糟中木质素去除率达66.13%~77.02%,总纤维素回收率78.04%~90.73%。对处理后的白酒丢糟进行多酶复配糖化降解,通过均匀设计实验确定白酒丢糟酶降解的数学模型,得出总糖降解率与各酶添加量之间的回归关系,在最优条件下白酒丢糟降解率为(0.432 8±0.013 5)g/g。     

Impact of fly ash pretreatment on aerobic treatment of thermomechanical pulping spent liquor

This study investigated the impact of biomass‐based fly ash (FA) pretreatment on the biodegradability of a thermomechanical pulping spent liquor (TMPL) in an aerobic system. In this study, FA was mixed with TMPL under the conditions of 6 wt.% based on TMPL, 25°C and 10 h, which removed a part of recalcitrant organic materials and resulted in 68.0, 40.0, 60.1, 81.2 and 48.3% reductions in chemical oxygen demand (COD), biochemical oxygen demand (BOD), total organic carbon (TOC), lignin and sugar, respectively. FA‐pretreated TMPL pressate (FA‐TMPL) was biologically treated in an aerobic system of sequencing batch reactor (SBR). The performance of the biological treatment with and without FA pretreatment was studied in two parallel SBRs over three months. The combination of FA and biological treatments removed 97.3% of COD, 98.3% of BOD, 96.3% of lignin, 99.5% of sugar, and 98.1% of TOC. Without FA pretreatment, the biological system removed 87.3% of COD, 89% of BOD, 81.6% of lignin, 98.6% of sugars, and 90.5% of TOC. The results also confirmed that the settling ability of sludge, which was indicated as a sludge volume index, was reduced from 109.3 mL/g to 53.5 mL/g. In addition, the advantages of using FA pretreatment in aerobic systems were discussed in detail. © 2017 American Institute of Chemical Engineers Biotechnol. Prog., 34:370–378, 2018     

Dilute sulfuric acid cycle spray flow-through pretreatment of corn stover for enhancement of sugar recovery

A cycle spray flow-through reactor was designed and used to pretreat corn stover in dilute sulfuric acid medium. The dilute sulfuric acid cycle spray flow-through (DCF) process enhanced xylose sugar yields and cellulose digestibility while increasing the removal of lignin. Within the DCF system, the xylose sugar yields of 90–93% could be achieved for corn stover pretreated with 2% (w/v) dilute sulfuric acid at 95 °C during the optimal reaction time (90 min). The remaining solid residue exhibited enzymatic digestibility of 90–95% with cellulase loading of 60 FPU/g glucan that was due to the effective lignin removal (70–75%) in this process. Compared with flow-through and compress-hot water pretreatment process, the DCF method produces a higher sugar concentration and higher xylose monomer yield. The novel DCF process provides a feasible approach for lignocellulosic material pretreatment.     

Optimization of processing conditions for the pretreatment of wheat straw using aqueous ionic liquid

Pretreatment of wheat straw with the aqueous ionic liquid, 1-ethyl-3-methylimidazolium acetate, was optimized to maximize fermentable sugars recovery. The optimization process employed a central composite design, where the investigated variables were temperature (130-170 °C), time (0.5-5.5 h) and ionic liquid concentration (0-100%). All the tested variables were identified to have significant effects (p < 0.05) on fermentable sugars recovery. The optimum pretreatment conditions were 158 °C, an ionic liquid concentration of 49.5% (w/w), and a duration of 3.6 h. Cellulose and xylan digestibility generally increased with increasing temperature, time and ionic liquid concentration; but, the carbohydrates recovered in the washed solids following pretreatment decreased. Thus, the final optimum conditions for maximizing fermentable sugars from the starting biomass were a compromise between greater digestibility and minimal carbohydrates loss during pretreatment.