Hydrolysis Of Wood Research Articles

Enhanced Production of Xylitol from Poplar Wood Hydrolysates Through a Sustainable Process Using Immobilized New Strain Candida tropicalis UFMG BX 12-a.

A new strain, Candida tropicalis UFMG BX 12-a, was found to produce higher yields of xylitol on poplar wood hemicellulose hydrolysate. The hemicellulose hydrolysate liquor was detoxified using a novel method we developed, involving vacuum evaporation and solvent separation of inhibitors which made the hydrolysate free of toxins while retaining high concentrations of fermentable sugars. The effect of the detoxification method on the fermentation was also reported and compared to well-known methods reported in literature. In this study, the new strain C. tropicalis UFMG BX 12-a was used on the detoxified hydrolysate to produce xylitol. It was also compared to Candida guilliermondii FTI 20037, which has been reported to be one of the best strains for fermentative production of xylitol. To further improve the efficiency of the fermentation process, these strains were immobilized in calcium alginate beads. The yield (0.92gg-1) and productivity (0.88gL-1h-1) obtained by fermenting the wood hydrolysate detoxified by our new detoxification technique using an immobilized new Candida strain were found to be higher than the values reported in literature.

Improving the efficiency of the bioconversion of plant raw materials with mutant cellulases of Penicillium verruculosum

Plant biomass is the main type of organic material on Earth. The efficiency of biocatalytic conversion of plant raw materials determines the cost of their biotechnological processing to produce commercially valuable products such as organic alcohols and acids, carbohydrates, and hydrocarbons. New recombinant Penicillium canescens strains that produce not only their own enzyme complex but also heterologous cellulases (i.e., mutant and wild-type cellobiohydrolase I (CBH I) and endoglucanase II (EG II) of P. verruculosum) are constructed. Enzymatic agents (EAs) prepared on the basis of recombinant strains of P. canescens are found to be more active in the hydrolysis of crushed aspen wood. Yields of glucose and reducing sugars are observed 24–72 h after hydrolysis with EAs prepared in recombinant strains to be from 48 to 52 and 60 to 64%, respectively, higher than those for hydrolysis with EAs prepared in the initial recipient strain. The presence of N45A and N194A site-specific mutations introduced to reduce surface glycosilation thus results in a substantial increase in the yields of desired CBH I and EG II.

Development of Methods for Synthesis of Quality Hydrolyzates Based on the Integration of Catalytic Processes of Peroxide Delignification and Acid Hydrolysis of Birchwood

The traditional processes of catalytic acid hydrolysis of wood are low effective due to the low quality of the formed glucose solutions contaminated with admixtures that inhibit fermentation of glucose to ethanol. This is a particularly acute problem in hydrolysis of birchwood containing hemicelluloses in large proportions. In the present paper, quality glucose solutions are suggested to produce via sulfuric acid hydrolysis (80 % H 2 SO 4 , 25 °C) of cellulose products formed during catalytic peroxide delignification of birchwood. The composition of the cellulose products are established to affect considerably the content of glucose, xylose and admixtures (furfural, 5-hydroxymethylfurfural, levulinic acid) in glucose, which inhibit enzymatic synthesis of bioethanol. High yields of glucose (80.4–83.5 wt %) are achieved with cellulose products prepared by integrated processes of sulfuric acid hydrolysis of birchwood hemicelluloses and peroxide delignification of pre-hydrolyzed wood in the presence of catalysts 2 % H 2 SO 4 and 1 % TiO 2 . Concentrations of inhibitors of enzymatic processes are lower of the admissible levels in these hydrolyzates. The hydrolyzates with the maximal glucose content (86.4–88.5 wt %) and minimal concentration of inhibiting impurities are prepared by acid hydrolysis of cellulose products treated with 18 % NaOH. The hydrolyzate composition was studied using gas chromatography, HELC, chromatomass spectroscopy. IRS, XPS and chemical techniques were used for characterization of cellulose products.

Strategies for efficient and economical 2,3-butanediol production: new trends in this field.

2,3-Butanediol (2,3-BD) is a promising bulk chemical with a potentially wide range of applications e.g., in the manufacture of printing inks, perfumes, synthetic rubber, fumigants, antifreeze agents, fuel additives, foodstuffs and pharmaceuticals. Its high heating value and ability to increase the octane number of fuels make 2,3-BD a promising drop-in fuel. It can also be converted to methyl-ethyl ketone (MEK), which is considered an effective liquid fuel additive. After combination with MEK and hydrogenation reaction, 2,3-BD can be converted to octane, which is used to produce high-quality aviation fuel. Currently 2,3-BD is mainly produced on an industrial scale by chemical methods. However, microbiological production of 2,3-BD offers a less expensive and more environmentally friendly alternative to traditional synthesis. This alcohol is generated from hexoses and pentoses mainly by bacterial strains of the genera Klebsiella, Bacillus, Serratia, and Enterobacter, which can convert waste products (such as glycerol and agricultural residues) and excess biomass (such as wood hydrolysates) to 2,3-BD. Recently, a significant improvement in microbial production has been achieved by the screening of efficient natural microbial strains, the application of alternative cost-effective substrates, and the genetic improvement of microbial producers. Furthermore, Klebsiella strains, which are regarded the most efficient natural 2,3-BD producers, have been subjected to genetic modifications aiming at the removal of pathogenic factors and the development of avirulent strains that could be used for the safe production of the diol. This review summarizes existing knowledge and experience concerning various strategies for efficient and economical microbial production of 2,3-BD.

Single-stage and two-stage anaerobic digestion of extruded lignocellulosic biomass

This study investigated in single-stage and two-stage batches, the anaerobic digestibility of hydrolysates obtained from poplar wood biomass pretreated using the twin screw extrusion (TSE) process. The TSE process produced two distinct sugar-rich streams i.e. the liquid and solid streams. The liquid streams showed significantly higher hydrogen production potential and rates, comparable methane production potential and yields, but higher methane production rates than the solid streams in the single-stage BMP tests. This study revealed that the two-stage process for separate acidogenic and methanogenic processes, maximized both COD removal efficiencies and energy recovery as well as enhanced the overall process efficiency. Energy yields of 11.6kJ/gCODfeedstock and 9.8kJ/gCODfeedstock were obtained from the liquid and solid streams respectively in the two-stage anaerobic digestion process compared with 8.7kJ/gCODfeedstock and 8.3kJ/gCODfeedstock obtained in the single stage BMP process which are a 33% and 18% increase respectively. Feedstock COD removal efficiency was enhanced in the second-stage BMP process after acidification by 16% and 14% for the liquid and solid streams respectively compared to the single-stage BMP process. This work demonstrated the overall potential of poplar wood hydrolysates for sequential hydrogen and methane production.

Saccharification of lignocellulosic biomasses via ionic liquid pretreatment

The current work focuses on the pretreatment efficiency of ILs combined with heat for woody biomass consisting of spruce, birch and pine as well as winter wheat straw. The latter was investigated as a comparison and with the aim to enhance its digestibility during enzymatic hydrolysis whereby the influence of IL-treatment to cellulose resistance for hydrolysis was investigated. Considering the wood species, the most common and industrially important wood species in Northern Europe were chosen in the present work and the goal was to obtain fermentable sugars and their degradation product, i.e. 5-hydroxymethylfurfural (5-HMF), which is known valuable platform chemical. Further, the differences in the yields of IL-obtainable carbohydrates between these species were studied. The highest sugar yields were obtained to glucose in the case of spruce and arabinose in the case of pine sapwood, 12.07 and 7.72mmol/L, respectively. The highest 5-HMF yield was obtained for spruce heartwood (9.18mmol/L) with longer treatment time, such as 100h. However, regarding woody biomass, the present work was focused more on the study and analysis of the IL-containing liquid part, wood hydrolysate, after IL-treatment aiming to answer the analysis challenges related to this fraction.

Green Semi-IPN Hydrogels by Direct Utilization of Crude Wood Hydrolysates

Crude and unmodified acetylated galactoglucomannan containing wood hydrolysate (WH) was directly incorporated into a semi-interpenetrating network (semi-IPN) composed of up to 60% renewable polymers. Semi-IPNs were produced by a facile and green synthetic pathway through cross-linking modified carboxymethylcellulose in the presence of at least 30%(w/w) WH, via free radical copolymerization with acrylic acid and N,N′-methylenebis(acrylamide). FTIR verified the presence of WH interlaced with CMC in the semi-IPN, and the highly porous microscopic structure of the networks was confirmed by SEM. The gelation process of these networks was monitored in situ, and their individual “gel point” (the G′-G″ crossover) was determined by in situ rheological measurements. Semi-IPN hydrogels with various swelling ratios (Q = 20–225) were obtained within 2.8–20 min of a cross-linking reaction.

Co-fermentation of alfalfa juice and hardwood hydrolysate for butanol production in combined biorefinery systems

In this study, a new fermentation medium combining a flocculated hemicellulosic wood hydrolysate (FHWH), rich in carbohydrates, obtained from a pulp and paper mill and an alfalfa juice, rich in nitrogen was used to produce butanol by Clostridium acetobutylicum ATCC 842. It was demonstrated that pH control enhances solvent production. The culture containing the two renewable biomass resources resulted in the production of 3.80g/L of acetone-butanol-ethanol (ABE) with a productivity of 0.03g/Lh and a yield of 0.14g/g. The obtained results demonstrated that the proposed combination can be used as a new fermentation medium for ABE production. However, the complexity of the medium induced an inhibitory effect and a decrease in the production of ABE, compared to the fermentation of FHWH and yeast extract.

Synergistic effect of white-rot fungi and alkaline pretreatments for improving enzymatic hydrolysis of poplar wood

White-rot fungi pretreatment is one of the most environment-friendly pretreatment methods because of low chemical and energy requirement. However, apart from time consuming, white-rot fungi treatment results in inefficient delignification and humin formation, both of which inhibit subsequent enzymatic hydrolysis. Combined alkaline treatment for partial depolymerization of residual lignin and dissolution of humin is an efficient option for the conversion of white-rot pretreated samples. In the work presented, combined treatments increased the enzymatic digestibility to 89.3%, compared with 10.6% for untreated sample and 12.9% for solely white-rot treated samples. Highest digestibility of cellulose was achieved after 8 weeks of white-rot treatment and alkaline treatment at 120°C, whereas sugar yield was highest from sole alkaline treatment at 160°C. The efficient conversion can be ascribed to synergistic interaction between white-rot and alkaline treatments, resulting in increased enzymatic accessibility of cellulose. Therefore, white-rot fungi treatment is a green process that can efficiently decrease energy consumption, and in combination with alkaline treatment is highly effective in promoting sugar conversion.

Separation of hemicellulose-derived saccharides from wood hydrolysate by lime and ion exchange resin

A combined process of lime treatment and mixed bed ion exchange was proposed to separate hemicellulose-derived saccharides (HDS) from prehydrolysis liquor (PHL) of lignocellulose as value added products. The optimization of lime treatment achieved up to 44.2% removal of non-saccharide organic compounds (NSOC), mainly colloidal substances, with negligible HDS degradation at 0.5% lime level and subsequent neutralization by phosphoric acid. The residual NSOC and calcium ions in lime-treated PHL were eliminated by mixed bed ion exchange. The breakthrough curves of HDS and NSOC showed selective retention toward NSOC, leading to 75% HDS recovery with 95% purity at 17 bed volumes of exchange capacity. In addition, macroporous resin showed higher exchange capacity than gel resin as indicated by the triple processing volume. The remarkable selectivity of the combined process suggested the feasibility for HDS separation from PHL.

Bioethanol production from alkaline hydrogen peroxide pretreated Populus deltoides wood using hydrolytic enzymes of Bacillus stratosphericus N12(M) and Bacillus altitudinis Kd1(M) under different modes of separate hydrolysis and fermentation by monoculture and co-culture combinations of ethanologens

An integrated approach was studied for in-house cellulase and xylanase production, from novel hyper hydrolytic enzyme producers and enzymatic hydrolysis of pretreated Populus deltoides wood into bioethanol. A xylanase producer Bacillus altitudinis Kd1 (M) and cellulase producerBacillus stratosphericus N12 (M) was isolated from soil. Optimization of process parameters led to an optimal xylanase activity of 96.25 IU at 300C and pH 5.5 and cellulase activity of 5.98 IU at 300C and pH 8.0. The NaOH+H2O2 pretreated biomass was hydrolysed using cellulase and xylanase producing 12.45 mg/g of reducing sugars. Further fermentation of lignocellulosic hydrolysate was performed using different yeasts viz. Saccharomyces cerevisiae I, Saccharomyces cerevisiae II, Pichia stipitis, Candida shehatae and Zymomonas mobilis and maximum 11.10 g/l ethanol yield achieved with co-culture of S. cerevisiae II + P. stipitis with fermentation efficiency of 43.52% under method IV of SHF. The results have significant implications and further applications regarding production of fuel ethanol from agricultural lignocellulosic waste.

Improvement of the Efficiency of Bioconversion of Plant Materials under the Action of Mutant Strains of Cellulases Penicillium verruculosum

Plant biomasses are the predominant organic material on Earth. The efficiency of biocatalytic conversion of the plant materials is determined by the cost of their biotechnological processing to valuable commercial products (organic alcohols and acids, carbohydrates and hycrocarbons). The obtained recombinant strains Penicillium canescens produce, apart from their own enzymatic complex, heterological cellulases (mutant and non-mutant cellobiohydrolase I (CBHI) and endoglucanase II (EGII) P. verruculosum ). Enzymatic agents (EA) prepared from recombinant strains P. canescens were more active to hydrolysis of crushed aspen wood. The yields of glucose and reducing sugars after 24–72 hour hydrolysis under the action of EA prepared from the recombinant strains were higher by на 48–52 % and 60–64 %, respectively, than under the action of EA prepared from the initial strainrecipient. Thus, introduction of site-specific mutations N45A and N194A for partial inhibition of the surface glycosilation led to a considerable increase in the yields of target CBHI and EGII.

Study of the solubility and composition of welded wood material at progressive welding times

The solubility in water and carbohydrates/lignin composition after hydrolysis of wood welded by linear friction welding was studied. Welded beech (WB) and welded spruce (WS) were analyzed at welding times (Wt) of 1, 1.5, 2, 2.5, 3 s, and 2, 4, 6, 8, 10, 12 s, respectively. Scratched welded material was first extracted in water, dried, cryo-milled, and then hydrolyzed with sulfuric acid. Maximal percentages of solids dissolved in water were 17.7 and 10 for WB and WS and 2.2 and 1.4 for un-welded beech and spruce, respectively. Among water extracts, lignin, mono-oligosaccharides, acetic acid, vanillin, furfural, 5 hydroxymethylfurfural (5HMF), and syringaldehyde were quantified. Maximal percentages of water soluble lignin in WB and WS were 5 and 3.6, respectively; molecular weight and polydispersity were also determined. Regarding carbohydrates in the water extracts, a maximum of 1.4 % oligosaccharides in WB and 1 % monosaccharides in WS were detected. After hydrolysis, an increase in the amount of Klason lignin and a progressive diminution of some sugars take place at consecutive Wt of WB and WS. This study allows explaining to a good extent the behavior of welded joints face to liquid water. Moreover, the degradation of certain wood components is clearly presented.

How chip size impacts steam pretreatment effectiveness for biological conversion of poplar wood into fermentable sugars.

BackgroundWoody biomass is highly recalcitrant to enzymatic sugar release and often requires significant size reduction and severe pretreatments to achieve economically viable sugar yields in biological production of sustainable fuels and chemicals. However, because mechanical size reduction of woody biomass can consume significant amounts of energy, it is desirable to minimize size reduction and instead pretreat larger wood chips prior to biological conversion. To date, however, most laboratory research has been performed on materials that are significantly smaller than applicable in a commercial setting. As a result, there is a limited understanding of the effects that larger biomass particle size has on the effectiveness of steam explosion pretreatment and subsequent enzymatic hydrolysis of wood chips.ResultsTo address these concerns, novel downscaled analysis and high throughput pretreatment and hydrolysis (HTPH) were applied to examine whether differences exist in the composition and digestibility within a single pretreated wood chip due to heterogeneous pretreatment across its thickness. Heat transfer modeling, Simons’ stain testing, magnetic resonance imaging (MRI), and scanning electron microscopy (SEM) were applied to probe the effects of pretreatment within and between pretreated wood samples to shed light on potential causes of variation, pointing to enzyme accessibility (i.e., pore size) distribution being a key factor dictating enzyme digestibility in these samples. Application of these techniques demonstrated that the effectiveness of pretreatment of Populus tremuloides can vary substantially over the chip thickness at short pretreatment times, resulting in spatial digestibility effects and overall lower sugar yields in subsequent enzymatic hydrolysis.ConclusionsThese results indicate that rapid decompression pretreatments (e.g., steam explosion) that specifically alter accessibility at lower temperature conditions are well suited for larger wood chips due to the non-uniformity in temperature and digestibility profiles that can result from high temperature and short pretreatment times. Furthermore, this study also demonstrated that wood chips were hydrated primarily through the natural pore structure during pretreatment, suggesting that preserving the natural grain and transport systems in wood during storage and chipping processes could likely promote pretreatment efficacy and uniformity.

Biochemical Conversion of Torrefied Norway Spruce After Pretreatment with Acid or Ionic Liquid

The chemical effects of torrefaction and the possibility to combine torrefaction with biochemical conversion were explored in experiments with five preparations of wood of Norway spruce that had been torrefied using different degrees of severity. Compositional analysis and analyses using solid-state CP/MAS 13C NMR, Fourier-transform infrared (FTIR) spectroscopy, and Py-GC/MS showed small gradual changes, such as decreased hemicellulosic content and increased Klason lignin value, for torrefaction conditions in the range from 260 °C and 8 min up to 310 °C and 8 min. The most severe torrefaction conditions (310 °C, 25 min) resulted in substantial loss of glucan and further increase of the Klason lignin value, which was attributed to conversion of carbohydrate to pseudo-lignin. Even mild torrefaction conditions led to decreased susceptibility to enzymatic hydrolysis of cellulose, a state which was not changed by pretreatment with sulfuric acid. Pretreatment with the ionic liquid (IL) 1-butyl-3-methylimidazolium acetate overcame the additional recalcitrance caused by torrefaction, and the glucose yields after 72 h of enzymatic hydrolysis of wood torrefied at 260 °C for 8 min and at 285 °C for 16.5 min were as high as that of IL-pretreated non-torrefied spruce wood. Compared to IL-pretreated non-torrefied reference wood, the glucose production rates after 2 h of enzymatic hydrolysis of IL-pretreated wood torrefied at 260 °C for 8 min and at 285 °C for 16.5 min were 63 and 40 % higher, respectively. The findings offer increased understanding of the effects of torrefaction and indicate that mild torrefaction is compatible with biochemical conversion after pretreatment with alternative solvents that disrupt pseudo-lignin-containing lignocellulose.

Production of optically pure l-lactic acid from lignocellulosic hydrolysate by using a newly isolated and d-lactate dehydrogenase gene-deficient Lactobacillus paracasei strain

The use of lignocellulosic feedstock for lactic acid production with a difficulty is that the release of inhibitory compounds during the pretreatment process which inhibit the growth of microorganism. Thus we report a novel lactic acid bacterium, Lactobacillus paracasei 7BL, that has a high tolerance to inhibitors and produced optically pure l-lactic acid after the interruption of ldhD gene. The strain 7BL fermented glucose efficiently and showed high titer of l-lactic acid (215g/l) by fed-batch strategy. In addition, 99g/l of l-lactic acid with high yield (0.96g/g) and productivity (2.25–3.23g/l/h) was obtained by using non-detoxified wood hydrolysate. Rice straw hydrolysate without detoxification was also tested and yielded a productivity rate as high as 5.27g/l/h. Therefore, L. paracasei 7BL represents a potential method of l-lactic acid production from lignocellulosic biomass and has attractive application for industries.

N-linked glycosylation of recombinant cellobiohydrolase I (Cel7A) from Penicillium verruculosum and its effect on the enzyme activity.

Cellobiohydrolase I from Penicillium verruculosum (PvCel7A) has four potential N-glycosylation sites at its catalytic module: Asn45, Asn194, Asn388, and Asn430. In order to investigate how the N-glycosylation influences the activity and other properties of the enzyme, the wild type (wt) PvCel7A and its mutant forms, carrying Asn to Ala substitutions, were cloned into Penicillium canescens PCA10 (niaD-) strain, a fungal host for production of heterologous proteins. The rPvCel7A-wt and N45A, N194A, N388A mutants were successfully expressed and purified for characterization, whereas the expression of N430A mutant was not achieved. The MALDI-TOF mass spectrometry fingerprinting of peptides, obtained as a result of digestion of rPvCel7A forms with specific proteases, showed that the N-linked glycans represent variable high-mannose oligosaccharides and the products of their sequential enzymatic trimming, according to the formula (Man)0-13 (GlcNAc)2 , or a single GlcNAc residue. Mutations had no notable effect on pH-optimum of PvCel7A activity and enzyme thermostability. However, the mutations influenced both the enzyme adsorption ability on Avicel and its activity against natural and synthetic substrates. In particular, the N45A mutation led to a significant increase in the rate of Avicel and milled aspen wood hydrolysis, while the substrate digestion rates in the case of N194A and N388A mutants were notably lower relative to rPvCel7A-wt. These data, together with data of 3D structural modeling of the PvCel7A catalytic module, indicate that the N-linked glycans are an important part of the processive catalytic machinery of PvCel7A.

Separation and purification of hemicellulose-derived saccharides from wood hydrolysate by combined process

Prehydrolysis of wood biomass prior to kraft cooking provides a stream containing hemicellulose-derived saccharides (HDSs) but also undesired non-saccharide compounds (NSCs) that were resulted from lignin depolymerization and carbohydrate degradation. In this study, a combined process consisting of lime treatment, resin adsorption, and gel filtration was developed to separate HDSs from NSCs. The macro-lignin impurities that accounted for 32.2% of NSCs were removed by lime treatment at 1.2% dosage with negligible HDSs loss. The majority of NSCs, lignin-derived phenolics, were eliminated by mixed bed ion exchange resin, elevating NSCs removal to 94.0%. The remaining NSCs, furfural and hydroxymethylfurfural, were excluded from HDSs by gel filtration. Chemical composition analysis showed that xylooligosaccharides (XOS) with the degree of depolymerization from 2 to 6 accounted for 28% of the total purified HDSs.

Algae-Mediated Valorization of Industrial Waste Streams

Abstract Pulp and paper mills have an abundance of underutilized waste wood with the potential for use as feedstock for the production of algae biomass. Enzymatic hydrolysates originating from pine softwood, southern hardwoods, and northern hardwoods pretreated using a proprietary process were tested for their ability to support heterotrophic growth of microalgae. Focusing on Hawaiian Chlorella and Scenedesmus species, growth varied with each type of wood hydrolysate, depending on the pentose (C5) and hexose (C6) sugar composition as well as process residuals such as organic acids and alcohols. Both species were able to utilize pentose sugars. A 1.6-fold higher biomass productivity, of 2.87 g/L/day in batch culture, was obtained on a medium with Bleached Southern Pine (BSP) hydrolysate than with the equivalent C5 and C6 model sugars alone, suggesting enhanced growth stimulation on wood hydrolysates compared to purified sugar streams. Biomass yield per gram of sugar consumed ranged from 0.45:1 in BSP hydro...

Butanol Fermentation by Clostridium saccharobutylicum Based on Poplar Wood

As a potential source of liquid fuels, lignocellulosic material is an alternative to plant-derived starch and sugar, which are urgently needed to meet global demands for food. The utilization of wood as feedstock for bioconversion to biobutanol fuel not only could reduce production costs, but also could increase raw material supply. However, little is known about biobutanol fermentation based on lignocellulosic material from wood. In this paper, biobutanol fermentation from poplar wood hydrolysates by Clostridium saccharobutylicum was investigated under three different conditions. The desired biobutanol and ABE yields reached 6.98 and 9.64 g/L, respectively, and 69.8 g biobutanol and 96.4 g ABE per kg of poplar wood were achieved. Fermentation of hydrolysates with no additives and with extra mixed carbon sources to biobutanol was also studied. The predicted results were confirmed: in the former, the production of biobutanol and ABE were 4.88 and 6.63 g/L, respectively; in the latter, the biobutanol and ABE yields reached 7.28 and 10.18 g/L, respectively. The results indicated that poplar wood is a potential renewable raw material suitable for biobutanol production, and that Clostridium saccharobutylicum BAA-117 is a promising biobutanol producer for such conversion.