FeCl3-catalyzed ethanol pretreatment of sugarcane bagasse boosts sugar yields with low enzyme loadings and short hydrolysis time

An integrated biorefinery strategy for Eucalyptus fractionation and co-producing glucose, furfural, and lignin based on deep eutectic solvent/cyclopentyl methyl ether system

A novel biphasic system containing water-soluble deep eutectic solvent (DES) and cyclopentyl methyl ether (CPME) was developed to treat Eucalyptus for furfural production, extracting lignin and enhancing cellulose enzymatic hydrolysis. Herein effect of DES type, water content in DES, temperature and time on furfural yield in water-soluble DES/CPME pretreatment process was firstly evaluated. A maximum furfural yield of 80.6 % was attained in 10 min at 150 °C with choline chloride (ChCl)/citric acid monohydrate (CAM)/CPME system containing 30 wt% water and 2.5 wt% SnCl4·5H2O, which was higher than that obtained from ChCl/CAM/CPME system without water (55.5 %) and H2O/CPME system (49.7 %). These results demonstrated that the water-soluble DES/CPME system was a powerful method enhancing the furfural production. Under the optimal pretreatment conditions, the delignification and glucose yield were reached to 72.7 % and 94.3 %, respectively. The extracted lignin showed low molecular weight and β-aryl-ether was obviously cleaved. Additionally, water-soluble DES/CPME pretreatment led to a significant removal of hemicelluloses (100.0 %) and lignin (72.7 %) and introduced morphological changes on cell walls, especially from the cell corner (CC) and secondary wall (SW) layers. Overall, this work proposed a practical one-step fractionation strategy for co-producing furfural, lignin and fermentable sugar, providing a way to biorefinery.

Enhancing ethylene glycol and ferric chloride pretreatment of rice straw by low-pressure carbon dioxide to improve enzymatic saccharification

Ethylene glycol and ferric chloride pretreatment assisted by low-pressure carbon dioxide (1 MPa CO₂) realized the targeted deconstruction of lignocelluloses at 170 °C for 5 min, achieving 98 % cellulose recovery with removal of 92 % lignin and 90 % hemicellulose. After the pretreatment, the formation of stable platform mono-phenol components would be with the destruction of the lignin-carbohydrate complexes structure, and the surface of rice straw became rough, with a less negative charge and higher specific surface area, while the enzyme adsorption rate increased by 8.1 times. Furthermore, the glucose yield of pretreated straw was remarkably increased by 5.6 times that of the untreated straw, reaching 91 % after hydrolyzed for 48 h. With Tween 80 added in concentrated solid (12 %) hydrolysis at low cellulase loading (3 FPU/g dry substrate), half of the hydrolysis time was shortened than that without Tween 80, with 45 % higher glucose yield.

Advances in organosolv modified components occurring during the organosolv pretreatment of lignocellulosic biomass

The valorization of organosolv pretreatment (OP) is a required approach to the industrialization of the current enzyme-mediated lignocellulosic biorefinery. Recent literature has demonstrated that the solvolysis happening in the OP can modify the soluble components into value-added active compounds, namely organosolv modified lignin (OML) and organosolv modified sugars (OMSs), in addition to protecting them against excessive degradation. Among them, the OML is coincidental with the "lignin-first" strategy that should render a highly reactive lignin enriched with β-O-4 linkages and less condensed structure by organosolv grafting, which is desirable for the transformation into phenolic compounds. The OMSs are valuable glycosidic compounds mainly synthesized by trans-glycosylation, which can find potential applications in cosmetics, foods, and healthcare. Therefore, a state-of-the-art OP holds a big promise of lowering the process cost by the valorization of these active compounds. Recent advances in organosolv modified components are reviewed, and perspectives are made for addressing future challenges.

Bioethanol Production from Lignocellulosic Biomass-Challenges and Solutions

Regarding the limited resources for fossil fuels and increasing global energy demands, greenhouse gas emissions, and climate change, there is a need to find alternative energy sources that are sustainable, environmentally friendly, renewable, and economically viable. In the last several decades, interest in second-generation bioethanol production from non-food lignocellulosic biomass in the form of organic residues rapidly increased because of its abundance, renewability, and low cost. Bioethanol production fits into the strategy of a circular economy and zero waste plans, and using ethanol as an alternative fuel gives the world economy a chance to become independent of the petrochemical industry, providing energy security and environmental safety. However, the conversion of biomass into ethanol is a challenging and multi-stage process because of the variation in the biochemical composition of biomass and the recalcitrance of lignin, the aromatic component of lignocellulose. Therefore, the commercial production of cellulosic ethanol has not yet become well-received commercially, being hampered by high research and production costs, and substantial effort is needed to make it more widespread and profitable. This review summarises the state of the art in bioethanol production from lignocellulosic biomass, highlights the most challenging steps of the process, including pretreatment stages required to fragment biomass components and further enzymatic hydrolysis and fermentation, presents the most recent technological advances to overcome the challenges and high costs, and discusses future perspectives of second-generation biorefineries.

Improve Enzymatic Hydrolysis of Lignocellulosic Biomass by Modifying Lignin Structure via Sulfite Pretreatment and Using Lignin Blockers

Even traditional pretreatments can partially remove or degrade lignin and hemicellulose from lignocellulosic biomass for enhancing its enzymatic digestibility, the remaining lignin in pretreated biomass still restricts its enzymatic hydrolysis by limiting cellulose accessibility and lignin-enzyme nonproductive interaction. Therefore, many pretreatments that can modify lignin structure in a unique way and approaches to block the lignin’s adverse impact have been proposed to directly improve the enzymatic digestibility of pretreated biomass. In this review, recent development in sulfite pretreatment that can transform the native lignin into lignosulfonate and subsequently enhance saccharification of pretreated biomass under certain conditions was summarized. In addition, we also reviewed the approaches of the addition of reactive agents to block the lignin’s reactive sites and limit the cellulase-enzyme adsorption during hydrolysis. It is our hope that this summary can provide a guideline for workers engaged in biorefining for the goal of reaching high enzymatic digestibility of lignocellulose.

Sugarcane bagasse into value-added products: a review

Strategic valorization of readily available sugarcane bagasse (SB) is very important for waste management and sustainable biorefinery. Conventional SB pretreatment methods are ineffective to meet the requirement for industrial adaptation. Several past studies have highlighted different pretreatment procedures which are lacking environmentally benign characteristics and effective SB bioconversion. This article provides an in-depth review of a variety of environmentally acceptable thermochemical and biological pretreatment techniques for SB. Advancements in the conversion processes such as pyrolysis, liquefaction, gasification, cogeneration, lignin conversion, and cellulose conversion via fermentation processes are critically reviewed for the formation of an extensive array of industrially relevant products such as biofuels, bioelectricity, bioplastics, bio adsorbents, and organic acids. This article would provide comprehensive insights into several crucial aspects of thermochemical and biological conversion processes, including systematic perceptions and scientific developments for value-added products from SB valorization. Moreover, it would lead to determining efficient pretreatment and/or conversion processes for sustainable development of industrial-scale sugarcane-based biorefinery.

Surfactant-assisted alkaline pretreatment and enzymatic hydrolysis of Miscanthus sinensis for enhancing sugar recovery with a reduced enzyme loading

Surfactants play a vital role in the delignification and saccharification of lignocellulosic biomass. A strategy for coupling surfactant-assisted alkaline pretreatment (SAP) with surfactant-assisted enzymatic hydrolysis (SEH) has been proposed for improving sugar recovery from a potential energy crop, Miscanthus sinensis. Poly (ethylene glycol) 2000 (PEG 2000) was found to be more efficient in SAP than in other tested surfactants. Compositional and structural analysis revealed that the SAP process with 1% of PEG 2000 produced more efficient lignin removal and microstructure disruption of the pretreated sample, thus indicating much higher reducing sugar yields of 544.4–601.2 mg/g compared to the samples that were untreated or pretreated by alkali alone. Moreover, SEH with 1% Tween 80, which could block the lignin-enzyme interactions, produced a substantial reduction of 33.3% in the enzyme loading to achieve a higher sugar recovery from the SAP sample.

Biotechnological advances in biomass pretreatment for bio-renewable production through nanotechnological intervention

Globally, the fossil fuel reserves are depleting rapidly and the escalating fuel prices as well as plethora of the pollutants released from the emission of burning fossil fuels cause global warming that massively disturb the ecological balance. Moreover, the unnecessary utilization of non-renewable energy sources is a genuine hazard to nature and economic stability, which demands an alternative renewable source of energy. The lignocellulosic biomass is the pillar of renewable sources of energy. Different conventional pretreatment methods of lignocellulosic feedstocks have employed for biofuel production. However, these pretreatments are associated with disadvantages such as high cost of chemical substances, high load of organic catalysts or mechanical equipment, time consuming, and production of toxic inhibitors causing the environmental pollution. Nanotechnology has shown the promised biorefinery results by overcoming the disadvantages associated with the conventional pretreatments. Recyclability of nanomaterials offers cost effective and economically viable biorefineries processes. Lignolytic and saccharolytic enzymes have immobilized onto/into the nanomaterials for the higher biocatalyst loading due to their inherent properties of high surface area to volume ratios. Nanobiocatalyst enhance the hydrolyzing process of pretreated biomass by their high penetration into the cell wall to disintegrate the complex carbohydrates for the release of high amounts of sugars towards biofuel and various by-products production. Different nanotechnological routes provide cost-effective bioenergy production from the rich repertoires of the forest and agricultural-based lignocellulosic biomass. In this article, a critical survey of diverse biomass pretreatment methods and the nanotechnological interventions for opening up the biomass structure has been carried out.

Surfactants in biorefineries: Role, challenges & perspectives

The use of lignocellulosic biomass (LCB) as feedstock has received increasing attention as an alternative to fossil-based refineries. Initial steps such as pretreatment and enzymatic hydrolysis are essential to breakdown the complex structure of LCB to make the sugar molecules available to obtain bioproducts by fermentation. However, these steps increase the cost of the bioproduct and often reduces its competitiveness against synthetic products. Currently, the use of surfactants has shown considerable potential to enhance lignocellulosic biomass processing. This review addresses the main mechanisms and role of surfactants as key molecules in various steps of biorefinery processes, viz., increasing the removal of lignin and hemicellulose during the pretreatments, increasing enzymatic stability and enhancing the accessibility of enzymes to the polymeric fractions, and improving the downstream process during fermentation. Further, technical advances, challenges in application of surfactants, and future perspectives to augment the production of several high value-added bioproducts have been discussed.

Direct production of 2, 5-Furandicarboxylicacid from raw biomass by manganese dioxide catalysis cooperated with ultrasonic-assisted diluted acid pretreatment

In recent years, 2, 5-furandicarboxylic acid (FDCA) has attracted much attention as the precursor of bio-polyester materials. A coupled process of ultrasonic-assisted dilute acid pretreatment and MnO₂ was designed in this study to directly produce FDCA from lignocellulosic biomass, which is different from the traditional preparation process. Moreover, the critical parameters in the process were analyzed and optimized by the response surface method. The yield of FDCA could reach 52.1% under the optimal conditions. The reaction mechanism indicated that heavy metal elements in lignocellulosic biomass could play the role of the Lewis acid catalyst to promote the formation of FDCA to a certain extent. With the increase of temperature, the heavy metals transfer in biomass from the solid phase to the liquid phase increased, but most of them remain in the former. Therefore, further purification and treatment measures are worthy of attention.

Valorization of Miscanthus × giganteus by γ-Valerolactone/H2O/FeCl3 system toward efficient conversion of cellulose and hemicelluloses

γ-Valerolactone (GVL), a biomass-derived green chemical, offers an environmentally responsible solvent for conversion of lignocellulose to high value-added chemicals. Herein, we report a two-step process for directly producing cellulosic residual, furfural and lignin from Miscanthus × giganteus (M. × giganteus) bypassing the isolation of xylose, which exhibits promising advantage in energy reduction. The optimized pretreatment (100 mM FeCl₃ at 160 °C for 60 min) induced significant xylan removal (98.4%), resulting in rugged fibre surface, thus leading to the peak cellulose conversion of 99.3%. Furfural yield in the second step reached to 76.6% after 100 mM FeCl₃ catalyzed GVL/H₂O treatment at 180 °C for 10 min without addition of any chemical. The extracted lignin showed representative structure (such as β-O-4', β-β' linkages) and medium molecular weight (4275.5 g/mol). 79.6% of furfural can be recovered by distillation. This study proposes a systematic and energy efficient approach for maximizing biomass utilization.

Effect of acclimatized paddy soil microorganisms using swine wastewater on degradation of rice straw

Rice straw (RS) is one of abundant agricultural waste for biogas production in China. However, the low carbon-methane conversion rate limits its wide application due to the low degradation rate of RS during fermentation. This study investigated the effect of acclimatized paddy soil microorganisms using swine wastewater on degradation of RS before anaerobic digestion. The total organic carbon, reducing sugar and NH₄⁺-N content of paddy soil + RS + swine wastewater (PRS) (653.50 mg/L) was higher than that of other groups after 19 days. The carboxymethyl cellulose activity (4.01 IU), cellulose/lignin ratio (5.25) and the degradation rate of lignin (51.96%) in PRS were higher than those of other groups. The Firmicutes (21.02%), Chloroflexi (12.48%), Proteobacteria (20.92%), and Bacteroidetes (25.78%) were the main fermentation phyla in PRS during acclimatization. These results indicated that the acclimatized paddy soil microorganisms using swine wastewater (SW) could degrade RS more efficiently.

Investigation of choline chloride-formic acid pretreatment and Tween 80 to enhance sugarcane bagasse enzymatic hydrolysis

In this study, a pretreatment that consisting of choline chloride (ChCl) and formic acid (FA) were performed to improve sugarcane bagasse (SCB) enzymatic hydrolysis. Results showed that the ChCl-FA pretreatment exhibited an extraordinary ability to selectively extract hemicellulose (~95.6%) and degrade a large number of lignin (~72.6%) at 110 °C for 120 min, which enhanced the enzymatic hydrolysis of pretreated SCB. Besides, the impact of various additives on pretreated substrate enzymatic hydrolysis confirmed that Tween 80 was the best enzymatic additive, which could significantly improve the glucose produced from pretreated SCB and remarkably reduce the hydrolysis time (from 72 h to 48 h) and enzyme dosage (from 20 FPU/g pretreated solid to 10 FPU/g pretreated solid). In summary, the coupling of ChCl-FA pretreatment and Tween 80 exhibited a promising way to enhance the sugar release from SCB.

Current developments and challenges of green technologies for the valorization of liquid, solid, and gaseous wastes from sugarcane ethanol production

The sugarcane industry is one of the largest in the world and processes huge volumes of biomass, especially for ethanol and sugar production. These processes also generate several environmentally harmful solid, liquid, and gaseous wastes. Part of these wastes is reused, but with low-added value technologies, while a large unused fraction continues to impact the environment. In this review, the classic waste reuse routes are outlined, and promising green and circular technologies that can positively impact this sector are discussed. To remain competitive and reduce its environmental impact, the sugarcane industry must embrace technologies for bagasse fractionation and pyrolysis, microalgae cultivation for both CO₂ recovery and vinasse treatment, CO₂ chemical fixation, energy generation through the anaerobic digestion of vinasse, and genetically improved fermentation yeast strains. Considering the technological maturity, the anaerobic digestion of vinasse emerges as an important solution in the short term. However, the greatest environmental opportunity is to use the pure CO₂ from fermentation. The other opportunities still require continued research to reach technological maturity. Intensifying the processes, the exploration of driving-change technologies, and the integration of wastes through biorefinery processes can lead to a more sustainable sugarcane processing industry.

Cellulosic and hemicellulosic fractions of sugarcane bagasse: Potential, challenges and future perspective

Sugarcane bagasse is a rich source of cellulose (32-45%), hemicellulose (20-32%) and lignin (17-32%), 1.0-9.0% ash and some extractives. Huge amount of the generation of sugarcane bagasse has been a great challenge to industries and environment at global level for many years. Though cellulosic and hemicellulosic fractions in bagasse makes it a potential raw substrate for the production of value-added products at large scale, the presence of lignin hampers its saccharification which further leads to low yields of the value-added products. Therefore, an appropriate pretreatment strategy is of utmost importance that effectively solubilizes the lignin that exposes cellulose and hemicellulose for enzymatic action. Pretreatment also reduces the biomass recalcitrance i.e., cellulose crystallinity, structural complexity of cell wall and lignification for its effective utilization in biorefinery. Sugarcane bagasse served as nutrient medium for the cultivation of diverse microorganisms for the production of industrially important metabolites including enzymes, reducing sugars, prebiotic, organic acids and biofuels. Sugarcane bagasse has been utilized in the generation of electricity, syngas and as biosorbant in the bioremediation of heavy metals. Furthermore, the ash generated from bagasse is an excellent source for the synthesis of high strength and light weight bricks and tiles. Present review describes the utility of sugarcane bagasse as sustainable and renewable lignocellulosic substrate for the production of industrially important multifarious value-added products.

Current state-of-the-art in ethanol production from lignocellulosic feedstocks

The renewable lignocellulosic biomass is a sustainable feedstock for the production of bioethanol, which shows the potential to replace fossil fuels. Due to the recalcitrant structure of plant cell wall made of cellulose, hemicellulose, and lignin, the biomass conversion process requires the use of efficient pretreatment process before enzymatic hydrolysis and fermentation to degrade the crystallinity of cellulose fibres and to remove lignin from biomass. Proper pretreatment techniques, economical production of cellulolytic enzymes, and effective fermentation of glucose and xylose in the presence of inhibitors are key challenges for the viable production of bioethanol. Although new strains capable of fermenting xylose are being designed, they are often not resistant to toxic compounds in hydrolysates. This paper provides an in-depth review of lignocellulosic bioethanol production via biochemical route, focusing on the most widely used pretreatment technologies and key operational conditions of enzymatic hydrolysis and fermentation considering sugar/ethanol yields. In addition, this review examines the relevant detoxification strategies for the removal of toxic substances and the importance of immobilization. The review also indicates potential usage of engineered microorganisms to improve glucose and xylose fermentation, cellulolytic enzymes production, and response to stress conditions.

Sustainability of sugarcane lignocellulosic biomass pretreatment for the production of bioethanol

The sustainability of a biofuel is severely affected by the technological route of its production. Chemical pretreatment can be considered the traditional method of decomposition of the lignocellulose into its mono and oligomeric units, which can be further bioconverted to ethanol. The evaluation of the recent advances in chemical pretreatments of sugarcane bagasse, especially diluted acids, alkaline, organosolv and ionic liquids, identified the critical points for sustainability. In this context, chemicals recovery and reutilization or their substitution by green solvents, heat and electricity generation through bioenergy, reutilization of water from evaporators, vinasse concentration and the upgrading of lignin were discussed as strategic routes for developing sustainable chemical-based lignocellulose pretreatment. The advances in the technologies that allow greater fractionation of lignocellulosic biomass should be focused on the minimization of the use of natural resources, effluent generation and energy expenditure.

Two-staged acid hydrolysis on ethylene glycol pretreated degraded oil palm empty fruit bunch for sugar based substrate recovery

Ethylene glycol in the presence of sodium hydroxide was utilised as pretreatment for effective delignification and reduced the recalcitrance of lignocellulosic biomass which ramified the exposure of cellulose. Two-staged acid hydrolysis was also investigated which demonstrated its synergistic efficiency by minimising the deficiency of single stage acid hydrolysis. The operating parameters including acid concentration, temperature, residence time and cellulose loading for two-staged acid hydrolysis were studied by using ethylene glycol delignified degraded oil palm empty fruit bunch (DEFB) to recover the sugar based substrates for potential biofuels and other bio-chemicals production. In this study, stage I 45 wt% acid at 65 °C for 30 min coupled with high cellulose loading 21.25 w/v% and 12 wt% acid at 100 °C for 120 min was able to release a total of 89.8% optimum sugar yield with minimal formation of degradation products including 0.058 g/L furfural, 0.0251 g/L hydroxymethylfurfural and 0.200 g/L phenolic compounds.

Complete recovery of cellulose from rice straw pretreated with ethylene glycol and aluminum chloride for enzymatic hydrolysis

Rice straw was pretreated with ethylene glycol (EG) and AlCl₃ for enzymatic hydrolysis. EG-AlCl₃ pretreatment had an extremely good selectivity for component fractionation, resulting in 88% delignification and 90% hemicellulose removal, with 100% cellulose recovered or 76% (w/w) cellulose content in solid residue at 150 °C with 0.055 mol/L AlCl₃. The pretreated residue (5%, w/v) presented a higher enzymatic hydrolysis rate (glucose yield increased 2 times to 94%) for 24 h at cellulase loading of 10 FPU/g. The hydrolysis behavior was correlated with the composition and structure of substrates characterized by SEM, FT-IR, BET, XRD and TGA. The enzyme adsorption ability of pretreated straw was 12-folds that for the original sample. EG-AlCl₃ solution was further cycled for 3 times with 100% cellulose recovery but only 29% lignin removal due to the loss of AlCl₃. EG-AlCl₃ pretreatment is an efficient method with little loss of cellulose for lignocelluloses.

Sugarcane Bagasse Hydrolysis Enhancement by Microwave-Assisted Sulfolane Pretreatment

Sugarcane bagasse is the major by-product of the sugarcane industry and, due to its abundant availability, it has been extensively studied for lignocellulosic bioconversion in the production of bioethanol and other value-added commercial products. In the study presented herein, a combined pretreatment using sulfolane, TiO2 and alkali microwave irradiation (MW-A) was assessed for the dissolution of lignin prior to enzymatic saccharification of holocellulose. Total reducing sugars (TRS) and saccharinic acid yields were investigated. The increase in NaOH concentration up to 5% and in temperature from 120 °C to 140 °C were found to have a positive influence on both yields. While increasing the reaction time from 5 to 60 min only led to an increase in TRS yield <2%, a reaction time of 30 min almost doubled the saccharinic acids production. TRS yields and saccharinic acid production were approximately 5% and 33% higher when the sulfolane-TiO2 reaction medium was used, as compared to MW-A in water, reaching up to 64.8% and 15.24 g/L of saccharinic acids, respectively. The proposed MW-A pretreatment may hold promise for industrial applications, given the good TRS yields obtained, and the associated enzyme and time/energy savings. The use of sulfolane-TiO2 reaction medium is encouraged if saccharinic acids are to be recovered too.

Degradation of bamboo lignocellulose by bamboo snout beetle Cyrtotrachelus buqueti in vivo and vitro: efficiency and mechanism

BACKGROUND

As an important biomass raw material, the lignocellulose in bamboo is of significant value in energy conversion. The conversion of bamboo lignocellulose into fermentable reducing sugar, i.e. the degradation of bamboo lignocellulose, is an important step in lignocellulose conversion. However, little research has focussed on excavating the enzymes and microbes that are related to the degradation of bamboo lignocellulose, which is important for its utilisation. This study used Cyrtotrachelus buqueti (bamboo snout beetle) to evaluate the efficiency of bamboo lignocellulose degradation.

RESULTS

RNA sequencing was conducted to sequence the transcriptome of the insect before and after feeding on bamboo shoots. The expression levels of genes encoding several carbohydrate-active enzymes, such as endoglucanase (evgtrinloc27093t1 and evgtrinloc16407t0) and laccase (evgtrinloc15173t0 and evgtrinloc11252t0), were found to be upregulated after feeding. Faecal component analysis showed that the degradation efficiencies of cellulose, hemicellulose and lignin were 61.82%, 87.65% and 69.05%, respectively. After 6 days of co-culture with crude enzymes in vitro, the degradation efficiencies of cellulose, hemicellulose and lignin in bamboo shoot particles (BSPs) were 24.98%, 37.52% and 26.67%, respectively. These results indicated that lignocellulosic enzymes and related enzymes within the insect itself co-degraded bamboo lignocellulose. These finding can potentially be used for the pre-treatment and enzymatic hydrolysis of bamboo lignocellulose.

CONCLUSION

Our results showed that intestinal digestive enzymes from C. buqueti degraded bamboo shoot lignocellulose both in vivo and in vitro. In addition, the expression levels of many carbohydrate-active enzyme (CAZyme) genes were upregulated in the transcriptome, including those for cellulase, xylanase and ligninase genes. Therefore, we proposed a scheme for applying the lignocellulolytic enzymes from C. buqueti to degrade bamboo lignocellulose using genetic, enzymatic and fermentation engineering techniques to overexpress the lignocellulolytic enzymes genes in vitro and obtain large quantities of enzymes that could efficiently degrade bamboo lignocellulose and be used for lignocellulose bioconversion.

Combined dilute hydrochloric acid and alkaline wet oxidation pretreatment to improve sugar recovery of corn stover

Two-stage dilute hydrochloric acid (DA)/aqueous ammonia wet oxidation (AWO) pretreatment was used to recover the sugars of corn stover. The morphology characterizations of samples were detected by SEM, BET and SXT. The results showed that DA-AWO process demonstrated a positive effect on sugar recovery compared to AWO-DA. 82.8% of xylan was recovered in the first stage of DA-AWO process at 120 °C for 40 min with 1 wt% HCl. The second stage was performed under relative mild reaction conditions (130 °C, 12.6 wt% ammonium hydroxide, 3.0 MPa O₂, 40 min), and 86.1% lignin could be removed. 71.5% of glucan was achieved with a low enzyme dosage (3 FPU·g^-1) in the following enzymatic hydrolysis. DA-AWO pretreatment was effective due to its sufficient hydrolysis of hemicellulose in the first stage and remarkably removal of the lignin in the second stage, resulting in high sugar recovery with a low enzyme dosage.

Evaluation of the action of Tween 20 non-ionic surfactant during enzymatic hydrolysis of lignocellulose: Pretreatment, hydrolysis conditions and lignin structure

The aim of this work was to study the effects of pretreatment process, hydrolysis condition and structural features of lignin on the improving action of surfactants (Tween 20) for enzymatic hydrolysis of pretreated wheat straw, and further to interpret the relation of these factors with the non-productive adsorption of cellulases on lignin. Tween 20 seemed to be more greatly improve cellulose conversion under harsher conditions. The surfactant showed more significant improvement for acid-pretreated substrates than oxidative-pretreated substrates. Highly-condensed lignin and phenolic hydroxyl groups showed much stronger adsorption ability to cellulases, while Tween 20 could well block the lignin-cellulase interactions recovering cellulose hydrolyzability. It was proposed that pretreatments altered lignin structures, resulting in the change of surface properties thus further impacting the lignin-cellulase interactions. Addition of Tween 20 could modify lignin surface properties to change its hydrophobicity, hydrogen bonding ability and surface charges, thus reducing the non-productive adsorption of proteins.

Acetyl-assisted autohydrolysis of sugarcane bagasse for the production of xylo-oligosaccharides without additional chemicals

The aim of this work was to study acetyl-assisted autohydrolysis of sugarcane bagasse for the production of xylo-oligosaccharides without additional chemicals. A xylo-oligosaccharide yield of 50.35% was obtained in 10 min through sugarcane bagasse autohydrolysis at 200 °C; this yield was 49.64% after acetyl-assisted autohydrolysis of a 65:35 mixture of sugarcane bagasse/white birch at 160 °C for 100 min. The yield of xylo-oligosaccharides was close to that obtained at 180 °C/40 min and 200 °C/10 min through the autohydrolysis of sugarcane bagasse. Compared to sugarcane bagasse alone, the xylo-oligosaccharide (degree of polymerization 2-5) yield from the acetyl-assisted autohydrolysis at 200 °C for 10 min was 52.99%. In addition, the yield of glucose from the solid residue following autohydrolysis pretreatment was 96.87% after 72 h of enzymatic hydrolysis. These results demonstrate that acetyl-assisted autohydrolysis is a promising method for the production of xylo-oligosaccharides.

Influence of sulfur dioxide-ethanol-water pretreatment on the physicochemical properties and enzymatic digestibility of bamboo residues

SO₂-ethanol-water (SEW) is a promising pretreatment for improving enzymatic digestibility of biomass through simultaneously removing hemicellulose and lignin. In this work, SEW pretreatment was performed at different cooking times (10 min-60 min) and different SO₂ concentrations (0.5%-2%) to produce pretreated bamboo residues for enzymatic hydrolysis. Meanwhile, physicochemical features of the residual cellulose and lignin were analyzed to better understand how SEW improves enzymatic digestibility. Under optimized SEW pretreatment condition (1% SO₂ concentration, 150 °C, 60 min), 81.7% of xylan and 80.3% of lignin were solubilized, along with 89.1% of cellulose preserved in pretreated solid. A good enzymatic digestibility (80.4%) was achieved at optimum SEW condition. Several compelling correlations (R² > 0.7) were observable between enzymatic digestibility and physicochemical features, demonstrating the importance of SEW pretreatment abilities of hemicellulose and lignin removal, reducing cellulose's degree of polymerization, and improving the amount of sulfonyl groups imparted to the original lignin structure.

Enhancing enzymatic saccharification of sugarcane bagasse by combinatorial pretreatment and Tween 80

BACKGROUND

The recalcitrant structure of lignocellulosic biomass made it challenging for their bioconversion into biofuels and biochemicals. Pretreatment was required to deconstruct the intact structure by the removal of hemicellulose/lignin, improving the cellulose accessibility of enzyme. Combinatorial pretreatments with liquid hot water/H₂SO₄ and ethanol/NaOH of sugarcane bagasse were developed to improve enzymatic hydrolysis under mild conditions.

RESULTS

After one-step 60% ethanol containing 0.5% NaOH pretreatment with solid to liquid ratio of 1/10, the glucose yield after hydrolysis for 72 h with enzyme dosage of 20 FPU/g substrate was enhanced by 41% and 205% compared to that of NaOH or 60% ethanol pretreated solids, respectively. This improvement was correlated with the removal of hemicellulose and lignin. However, using combinatorial pretreatments with 1% H₂SO₄ followed by 60% ethanol containing 0.5% NaOH, the highest glucose yield with Tween 80 reached 76%, representing 84.5% of theoretical glucose in pretreated substrate. While retaining similar glucose yield, the addition of Tween 80 capacitated either a reduction of enzyme loading by 50% or shortening hydrolysis time to 24 h. However, the enhancement with the addition of Tween 80 decreased as hydrolysis time was extended.

CONCLUSIONS

This study demonstrated that a combinatorial pretreatment with 1% H₂SO₄ followed by 60% ethanol containing 0.5% NaOH had significant effects on improving the enzymatic hydrolysis of sugarcane bagasse. The addition of Tween 80 enabled reducing the enzyme loading or shortening the hydrolysis time. This study provided an economically feasible and mild process for the generation of glucose, which will be subsequently converted to bioethanol and biochemicals.