Insights into the improvement of alkaline hydrogen peroxide (AHP) pretreatment on the enzymatic hydrolysis of corn stover: Chemical and microstructural analyses

Efficient production of xylobiose and xylotriose from corncob by mixed acids and xylanase hydrolysis

Propionic acid (PA) hydrolysis offers a potential pathway for industrial xylooligosaccharide (XOS) production owing to efficiency and simplicity of the process. However, the cost of XOS production needs to be reduced as PA is expensive. This work proposed a strategy of mixed acids hydrolysis, replacing 20% of PA with formic acid (FA), and combined with xylanase hydrolysis to reduce production costs and increase the production of XOS from corncob. The hydrolysis of corncob using mixed FA and PA in a mass ratio of 2:8 produced 61.8% XOS. Xylanase hydrolysis of corncob residue improved XOS yield to 73.1%. Among them, the X2 + X3 yield was as high as 50.6%. Economic evaluation showed that the combined process reduced the XOS production cost by 10.8% compared to PA hydrolysis. The strategy of using FA instead of 20% PA for hydrolysis and enzymatic hydrolysis, with high XOS and monosaccharide yields from corncob, has potential industrial promise.

Digestion of lignocellulosic biomass under an innovative pneu-mechanical system and optimization of process

In this study, an anaerobic pneumatic mechanical digester (PMD) was designed for the first time to investigate the impact of pneumatic agitator on increasing the bioethanol production and compared with a mechanical digester (MD). Fermentation was performed during an optimized pretreatment and hydrolysis process by RSM (Response Surface Method). Ultrasound optimized points (the time values, the acid concentration, and the biomass load) were 30 min, 1.95% v/v, and 6%, and hydrolysis was done within 45 min at the acid concentration of 2.04% v/v and temperature of 148.4 °C. The hydrolysis solutions were poured and the fermentation process took place within 20 days in the PMD and MD. The sampling sequence was every 5 days. According to the results, the PMD could produce bioethanol more than the MD by 27.94%. Besides, CO, H2S and O2 were measured through fermentation. In PMD, the amount of H2S and O2 was lower than the MD, but then the production of CO in the PMD was meaningfully higher. Finally, by the application of the PMD, the amount of harmful mixtures produced throughout the process can be controlled. It can be said that with the new method designed in this study, it is possible to take an important step in the biorefinery and use the biomass produced in nature in an economical and environmentally friendly way.

Different pre-treatments and kinetic models for bioethanol production from lignocellulosic biomass: A review

Lignocellulosic biomass is the generally explored substrate to produce bioethanol for environmental sustainability due to its availability in abundance. However, the complex network of cellulose-hemicellulose-lignin present in it makes its hydrolysis as a challenging task. To boost the effectiveness of conversion, biomass is pre-treated before enzymatic hydrolysis to alter or destroy its original composition. Enzymes like Cellulases are widely used for breaking down cellulose into fermentable sugars. Enzymatic hydrolysis is a complex process involving many influencing factors such as pH, temperature, substrate concentration. This review presents major four pre-treatment methods used for hydrolysing different substrates under varied reaction conditions along with their mechanism and limitations. A relative comparison of data analysis for most widely studied 10 kinetic models is briefly explained in terms of substrates used to get the brief insight about hydrolysis rates. The summary of pre-treatment methods and hydrolysis rates including cellulase enzyme kinetics will be the value addition for upcoming researchers for optimising the hydrolysis process.

Oxidative pretreatment of lignocellulosic biomass for enzymatic hydrolysis: Progress and challenges

Deconstruction of cell wall structure is important for biorefining of lignocellulose to produce various biofuels and chemicals. Oxidative delignification is an effective way to increase the enzymatic digestibility of cellulose. In this work, the current research progress on conventional oxidative pretreatment including wet oxidation, alkaline hydrogen peroxide, organic peracids, Fenton oxidation, and ozone oxidation were reviewed. Some recently developed novel technologies for coupling pretreatment and direct biomass-to-electricity conversion with recyclable oxidants were also introduced. The primary mechanism of oxidative pretreatment to enhance cellulose digestibility is delignification, especially in alkaline medium, thus eliminating the physical blocking and non-productive adsorption of enzymes by lignin. However, the cost of oxidative delignification as a pretreatment is still too expensive to be applied at large scale at present. Efforts should be made particularly to reduce the cost of oxidants, or explore valuable products to obtain more revenue.

Enhanced removal of Cd2+ from water by AHP-pretreated biochar: Adsorption performance and mechanism

The sesame straw-derived biochar was successfully prepared via alkaline hydrogen peroxide (AHP) pretreatment in this study. Systematic experimental characterizations, 15 relevant batch and column adsorption models, combined with density functional theory (DFT) calculation were used to investigate the performances and micro-mechanisms of Cd²⁺ adsorption onto biochar. We found AHP-pretreatment could greatly improve the adsorption performance of biochar for Cd²⁺. The maximum Cd²⁺ adsorption capacity of AHP-pretreated biochar (87.13 mg g^-1) was much larger than that of unpretreated biochar. Cd²⁺ adsorption was mainly dominated by the chemisorption of the homogeneous surface monolayer. The hydroxyl and carboxyl groups on the surface of biochar provided preferential adsorption sites, and liquid film diffusion and intra-particle diffusion were two dominant rate-controlling steps. Our results showed that ion exchange, co-precipitation, surface complexation, and Cd²⁺-π interaction were the dominant adsorption mechanisms. Especially, DFT calculations well-identified that lone-pair electrons during complexation and π electrons during coordination were provided by oxygen-containing functional groups and aromatic rings, respectively. The experimental breakthrough curves fitted better with the theoretical value of the BJP model, compared to Thomas, Yoon-Nelson, and EXY models. Overall, our study provides a promising method for Cd²⁺ removal from wastewater and resource utilization of agricultural wastes.

Adsorption of basic fuchsin using soybean straw hydrolyzed by subcritical water

The valorization of agro-industrial residues can be improved through their full use, making the production of second-generation ethanol viable. In this scenario, hydrolyzed soybean straw generated from a subcritical water process was applied to the basic fuchsin adsorption. At pH eight, a high adsorption capacity was obtained. The mass test results showed that basic fuchsin's removal and adsorption capacity could be maximized with an adsorbent dosage of 0.9 g L-1. The linear driving force model was suitable for predicting the kinetic profile, and the kinetic curves showed that equilibrium was reached with only 30 min of contact time. Besides, the Langmuir model was the best to predict the adsorption isotherms. The thermodynamic parameters revealed a spontaneous and endothermic process. At 328 K, there is maximum adsorption capacity (72.9 mg g-1). Therefore, it can be stated that this material could be competitive in terms of adsorption capacity coupled with the idea of full use of waste.

Enhancing for Bagasse Enzymolysis via Intercrystalline Swelling of Cellulose Combined with Hydrolysis and Oxidation

To overcome the biological barriers formed by the lignin–carbohydrate complex for releasing fermentable sugars from cellulose by enzymolysis is both imperative and challenging. In this study, a strategy of intergranular swelling of cellulose combined with hydrolysis and oxidation was demonstrated. Pretreatment of the bagasse was evaluated by one bath treatment with phosphoric acid and hydrogen peroxide. The chemical composition, specific surface area (SSA), and pore size of bagasse before and after pretreatment were investigated, while the experiments on the adsorption equilibrium of cellulose to cellulase and reagent reuse were also performed. Scanning electron microscopy (SEM) and high-performance liquid chromatography (HPLC) were employed for microscopic morphology observations and glucose analysis, respectively. The results showed that pretreated bagasse was deconstructed into cellulose with a nanofibril network, most of the hemicellulose (~100%) and lignin (~98%) were removed, and the SSA and void were enlarged 11- and 5-fold, respectively. This simple, mild preprocessing method enhanced cellulose accessibility and reduced the biological barrier of the noncellulose component to improve the subsequent enzymolysis with a high glucose recovery (98.60%).

Effects of enzyme-assisted ultrasonic treatment to the properties of nanofibrils isolated from wheat straw

This study aimed to prepare cellulose nanofibrils (CNF) with tunable morphology and properties from wheat straw using enzyme-assisted ultrasonic treatment. The effects of different enzymatic hydrolysis duration on the morphology and the properties of the CNF were studied. The effects of different enzymatic hydrolysis duration on the morphology and the properties of the CNF were studied. AFM analysis showed that average height distribution for CNF-0 (without enzymatic pretreatment) decreased from 11.86 to 8.18 nm for CNF-4 (with the enzymatic hydrolysis duration of 4 h), while the crystallinity and water reserve value (WRV) for CNF-0 increased from 36 and 485% to 47 and 789% for CNF-4, respectively. The transmittance, wettability properties, and mechanical performances of CNF-based films were systematically studied. The results show that the film properties are highly dependent on the morphology of their corresponding CNF and can be effectively modulated by controlling the structural characteristics of CNF. The discoveries of this study provide an environment-friendly approach for the production of CNF with tunable morphology and fibril size, which can promote the production of cellulose-based nanomaterial as well as their related applications.

Effect of Ammoniated Fiber Explosion Combined with H2O2 Pretreatment on the Hydrogen Production Capacity of Herbaceous and Woody Waste

An appropriate pretreatment process is an important part of the preparation of biomass energy from agricultural and forestry waste. Compared to physical and chemical pretreatments alone, the combined ammoniated fiber explosion (AFEX) + hydrogen peroxide (H₂O₂) pretreatment process can significantly improve the lignin degradation rate and saccharification efficiency, thus improving the hydrogen production capacity during medium-temperature dark fermentation. This study showed that the combined pretreatment increased the saccharification efficiency of herbaceous, hardwood, and softwood biomass by 58.7, 39.5, and 20.6% and the corresponding gas production reached 145.49, 80.75, and 57.52 mL/g, respectively. In addition, X-ray diffraction, scanning electron microscopy, and Fourier-transform infrared spectroscopy showed that AFEX + H₂O₂ disrupted the structure of the feedstock and was more favorable for lignin removal. Soluble metabolites indicated that AFEX + H₂O₂ pretreatment enhanced the butyrate metabolic pathway of the substrate and biohydrogen generation and increased the levels of extracellular polymers and microbial community structure.

A Comparative Study of Various Pretreatment Approaches for Bio-Ethanol Production from Willow Sawdust, Using Co-Cultures and Mono-Cultures of Different Yeast Strains

The effect of different pretreatment approaches based on alkali (NaOH)/hydrogen peroxide (H₂O₂) on willow sawdust (WS) biomass, in terms of delignification efficiency, structural changes of lignocellulose and subsequent fermentation toward ethanol, was investigated. Bioethanol production was carried out using the conventional yeast Saccharomyces cerevisiae, as well as three non-conventional yeasts strains, i.e., Pichia stipitis, Pachysolen tannophilus, Wickerhamomyces anomalus X19, separately and in co-cultures. The experimental results showed that a two-stage pretreatment approach (NaOH (0.5% w/v) for 24 h and H₂O₂ (0.5% v/v) for 24 h) led to higher delignification (38.3 ± 0.1%) and saccharification efficiency (31.7 ± 0.3%) and higher ethanol concentration and yield. Monocultures of S. cerevisiae or W. anomalus X19 and co-cultures with P. stipitis exhibited ethanol yields in the range of 11.67 ± 0.21 to 13.81 ± 0.20 g/100 g total solids (TS). When WS was subjected to H₂O₂ (0.5% v/v) alone for 24 h, the lowest ethanol yields were observed for all yeast strains, due to the minor impact of this treatment on the main chemical and structural WS characteristics. In order to decide which is the best pretreatment approach, a detailed techno-economical assessment is needed, which will take into account the ethanol yields and the minimum processing cost.

Pretreatment Affects Profits From Xylanase During Enzymatic Saccharification of Corn Stover Through Changing the Interaction Between Lignin and Xylanase Protein

Effective pretreatment is vital to improve the biomass conversion efficiency, which often requires the addition of xylanase as an accessory enzyme to enhance enzymatic saccharification of corn stover. In this study, we investigated the effect of two sophisticated pretreatment methods including ammonium sulfite (AS) and steam explosion (SE) on the xylanase profits involved in enzymatic hydrolysis of corn stover. We further explored the interactions between lignin and xylanase Xyn10A protein. Our results showed that the conversion rates of glucan and xylan in corn stover by AS pretreatment were higher by Xyn10A supplementation than that by SE pretreatment. Compared with the lignin from SE pretreated corn stover, the lignin from AS pretreated corn stover had a lower Xyn10A initial adsorption velocity (13.56 vs. 10.89 mg g⁻¹ min⁻¹) and adsorption capacity (49.46 vs. 27.42 mg g⁻¹ of lignin) and weakened binding strength (310.6 vs. 215.9 L g⁻¹). Our study demonstrated the low absolute zeta potential and strong hydrophilicity of the lignin may partly account for relative weak interaction between xylanase protein and lignin from AS pretreated corn stover. In conclusion, our results suggested that AS pretreatment weakened the inhibition of lignin to enzyme, promoted the enzymatic hydrolysis of corn stover, and decreased the cost of enzyme in bioconversion.

Green approach to produce xylo-oligosaccharides and glucose by mechanical-hydrothermal pretreatment

A pretreatment method combining ball-milling, ultrasound, and hydrothermal treatment was developed to produce xylooligosaccharides (XOS) and glucose with a high yield from corn stover. Under optimal conditions, the yield of XOS reached 80.40%, and the functional XOS (X2-X4) took up to 26.97%. Small amount of inhibitors were formed during the hydrothermal process. Enzymatic hydrolysis of the hydrothermally pretreated residue gave 92.60% yield of glucose, leaving lignin as the final residue which accounted for 66.82% of native lignin. The correlations between the yield of glucose and the physio-chemical properties of corn stover, such as crystalline index, particle size, and the removal of xylan, were established to understand the recalcitrance removal during the pretreatment process. Results demonstrate that this combined pretreatment method is a green and effective process to selectively separate the hemicellulose fractions and improve both production of XOS and glucose yield.

Functional characterization of a GH62 family α-L-arabinofuranosidase from Eupenicillium parvum suitable for monosaccharification of corncob arabinoxylan in combination with key enzymes

Corncob rich in arabinoxylan is an important raw material widely used in bio-refinery. Complete saccharification of arabinoxylan depends on the synergism of different enzymes including α-L-arabinofuranosidase (ABF). This study aimed to investigate the functional characteristics of a new ABF EpABF62A belonging to glycoside hydrolase (GH) 62 family from the fungus Eupenicillium parvum, and to explore its potential in the saccharification of corncob arabinoxylan. The recombinant EpABF62A showed high activity against wheat arabinoxylan and rye arabinoxylan, with the optimal temperature of 55 °C and pH of 4.5. The protein contains an N-terminal cellulose-binding domain family 1 (CBM_1) domain, and displayed a 59.5% absorption rate to phosphoric acid swollen cellulose. Regioselectivity analysis indicated that the enzyme selectively removed α-1,2 or α-1,3 linked arabinofuranosyl residues on mono-substituted xylose residues on arabinoxylan. Corncob arabinoxylans (CAX1 or CAX2) with different (low or high) branching degrees were extracted from the raw material by alkaline hydrogen peroxide pretreatment and graded ethanol precipitation. Single EpABF62A removed 69.5% or 67.1% arabinose from CAX1 or CAX2, respectively. EpABF62A combined with a GH10 xylanase, a GH43 β-D-xylosidase and a GH67 α-glucuronidase released 75.0% or 64.5% xylose from CAX1 or CAX2, respectively. The addition of the four hemicellulases enhanced the saccharification the solid fraction of the pretreated corncob by the commercial cellulase Cellic® CTec2, and the conversion ratios of glucose, xylose and arabinose were up to 94.0%, 91.8% and 82.6%, respectively.

Biopolymer poly-hydroxyalkanoates (PHA) production from apple industrial waste residues: A review

Apple pomace, the residue which is left out after processing of apple serves as a potential carbon source for the production of biopolymer, PHA (poly-hydroxyalkanoates). It is rich in carbohydrates, fibers and polyphenols. Utilization of these waste resources has dual societal benefit-waste management and conversion of waste to an eco-friendly biopolymer. This will lower the overall economics of the process. A major limitation for the commercialization of biopolymer in comparison with petroleum derived polymer is the high cost. This article gives an overview of valorization of apple pomace for the production of biopolymer, various strategies adopted, limitations as well as future perspectives.

Co-production of functional xylo-oligosaccharides and fermentable sugars from corn stover through fast and facile ball mill-assisted alkaline peroxide pretreatment

The aim of this work was to develop a feasible ball mill-assisted alkaline peroxide pretreatment followed by stepwise hydrolysis to improve the yield of xylo-oligosaccharides (XOS) and fermentable sugars. The hydrogen peroxide charge, ball-milling time, and solid-to-liquid ratio affected the compositions, particle sizes, morphology, and crystallinity of the corn stover, directly improving the following hydrolytic efficiency. The optimal pretreatment was with 0.45 g/g (H₂O₂: substrate) and 1:3 solid-to-liquid ratio (w/v) for 1.0 h ball-milling, resulting in 84.29% delignification. Physicochemical properties of the pretreated samples were characterized and their correlations to the enzymatic hydrolysis were revealed. Compared with one-step cellulase hydrolysis, the two-step xylanase-cellulase hydrolysis of the pretreated corn stover showed significant advance in preparing XOS, producing 69.65% (on the base of xylan content in pretreated sample) of XOS, along with 20.55% xylose, 68.94% glucose, and 21.15% gluco-oligosaccharides. The yield of XOS was 2-7 times higher than those in previous studies.

Features correlated to improved enzymatic digestibility of corn stover subjected to alkaline hydrogen peroxide pretreatment

As one of the leading pretreatment approaches, alkaline hydrogen peroxide (AHP) pretreatment can enhance the enzymatic digestibility of lignocellulose significantly. In this study, the glucan conversion of AHP pretreated corn stover (CS) without and with water-wash were 28.4% and 50.0% higher than that of raw material, respectively. In order to systematically understand its mechanism, analyses of the features of AHP pretreated and raw CS, such as specific surface area, crystallinity, zeta potential, water holding capacity and swelling capacity and others were performed. The weight-average molecular weight (Mw) of the sugars in the hydrolysate and the particle size distribution of the hydrolysis residue were also analyzed. These results explained why AHP-CS was more conducive to enzymatic hydrolysis. The deeper reason was that the removal of lignin and the destruction of hydrogen bonds within cellulose and hemicellulose increased the accessibility of cellulose and reduced the non-productive adsorption of cellulase, which significantly improved the enzymatic digestibility.

Effect of Pretreatments on the Enzymatic Hydrolysis of High-Yield Bamboo Chemo-Mechanical Pulp by Changing the Surface Lignin Content

Hydrogen peroxide chemo-mechanical pulp (APMP), sulfonated chemo-mechanical pulp (SCMP), and chemical thermomechanical pulp (CTMP) were used as raw materials to explore the effects of hydrogen peroxide (HP), Fenton pretreatment (FP), and ethanol pretreatment (EP) on the enzymatic hydrolysis of high-yield bamboo mechanical pulp (HBMP). The surface lignin distribution and contents of different HBMPs were determined using confocal laser scanning microscopy (CLSM) and X-ray photoelectron spectroscopy (XPS). The correlation between the surface lignin and the enzymatic hydrolysis of HBMP was also investigated. The residue of enzymatic hydrolysis was used to adsorb methylene blue (MB). The results showed that the cracks and fine fibers on the surface of APMP, SCMP, and CTMP increased after FP, when compared to HP and EP. The total removal content of hemicellulose and lignin in SCMP after FP was higher than with HP and EP. Compared to SCMP, the crystallinity increased by 15.4%, and the surface lignin content of Fenton-pretreated SCMP decreased by 11.7%. The enzymatic hydrolysis efficiency of HBMP after FP was higher than with HP and EP. The highest enzymatic hydrolysis of Fenton-pretreated SCMP was 49.5%, which was higher than the enzymatic hydrolysis of Fenton-pretreated APMP and CTMP. The removal rate of MB reached 94.7% after the adsorption of the enzymatic hydrolysis residue of SCMP. This work provides an effective approach for a high value-added utilization of high-yield bamboo pulp.

Effect of sulfuric acid on production of xylooligosaccharides and monosaccharides from hydrogen peroxide-acetic acid-pretreated poplar

Lignin is one of the main obstacles for enzymatic hydrolysis, which can be selectively removed by hydrogen peroxide-acetic acid pretreatment (HPAC). In this work, the effects of sulfuric acid concentration on chemical composition, structural features, physical properties and enzymatic digestibility of HPAC pretreated poplar were investigated. The increased H₂SO₄ dosage enhanced the lignin removal of HPAC-pretreated poplar, resulting in the increased accessibility and decreased hydrophobicity. A satisfying glucose yield (91.84%) was obtained from HPAC pretreated poplar (100 mM H₂SO₄) at 5 FPU/g DM of cellulase loading with the addition of xylanase (30 U/g DM) and Tween 80 (3 g/L). The increment of H₂SO₄ concentration promoted the yield of xylooligosaccharides from 0.69% to 20.45% and monosaccharides from 5.76% to 92.89% respectively by two-step enzymatic hydrolysis. This work demonstrated that HPAC pretreatment played a critical role in efficient utilization of poplar carbohydrates by enzymatic hydrolysis.

One-pot fractionation of corn stover with peracetic acid and maleic acid

Lignocellulose fractionation is a primary treatment to enhance cellulose accessibility and multi-component use. Herein, the development of a one-step fractionation is reported for cellulose enrichment from corn stover using a low concentration of peracetic acid combined with maleic acid (PAM). The effects of pretreatment parameters on the contents of cellulose, hemicellulose, and lignin were investigated. After cooking for 1 h at 130 °C with 1.5 wt% peracetic acid and 3 wt% maleic acid, 86.83% of corn stover cellulose remained in the solid residue while 88.21% of hemicellulose and 87.77% of lignin dissolved into the aqueous liquid. Hemicellulose was primarily hydrolyzed into xylose with 84.58% recovered during the PAM process. The cellulose-rich residue was enzymatically hydrolyzed with a glucose yield of 89.65%, which was two to three times that of untreated substrate. Generally, the proposed process offers a promising approach for efficient fractionation of lignocellulose under mild and environmental-friendly conditions.

Study of supercritical carbon dioxide pretreatment processes on green coconut fiber to enhance enzymatic hydrolysis of cellulose

Green coconut fiber was treated by supercritical CO₂ with the aim to enhance hydrolysis of its enzymatic cellulose. To this end, different static conditions of CO₂ contact times (3 and 5 h) and polarity modifiers (NaOH, NaHSO₄, ethanol) were evaluated at 20 MPa, 70 °C and 1 h of dynamic extraction followed by fast depressurization. After supercritical CO₂ exposition, SEM images showed fiber damage and FTIR spectra showed decreases of phenolic and wax contents, including a reduction in the degree of the hydrogen bond established between lignin and cellulose. Despite the apparent delignification, supercritical CO₂ did not enhance cellulose enzymatic hydrolyses. Fiber exposed to supercritical CO₂ (5 h) demonstrated that the highest sugar content (540.9 μmol glucose likely limited supercritical CO₂ delignification; however, green coconut in natura can be an innovative substrate for fermentation in alcohol production.

Pretreatment of corn stover via sodium hydroxide-urea solutions to improve the glucose yield

Because of the abundance and renewability of lignocellulosic biomass, lignocellulose-derived biofuels and chemicals are promising alternatives to fossil resources. In this study, we developed a strategy for pretreating lignocellulose (corn stover) using a sodium hydroxide-urea solution (SUs) and evaluated changes in the efficiency and structure. The results showed that treatment with 6% NaOH/12% urea at 80 °C for 20 min gave a glucose yield of 0.54 g/g corn stover. Recycling of the NaOH/urea was also explored, and the average glucose yield over four pretreatment cycles was 0.44 g/g corn stover. The structural characteristics of corn stover were investigated by scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy and gas chromatography-mass spectrometry. Compared with untreated corn stover, NaOH/urea-pretreated corn stover had more micropores, mesopores, and macropores, higher crystallinity, and a higher cellulose content. This pretreatment process is economical and efficient and has good application prospects for lignocellulose biorefinery.

Combinations of alkaline hydrogen peroxide and lithium chloride/N,N-dimethylacetamide pretreatments of corn stalk for improved biomethanation

The purpose of this study was to improve methane generation from corn stalk (CS) through alkaline hydrogen peroxide and lithium chloride/N,N-dimethylacetamide (AHP-LiCl/DMAc) pretreatment. Changes in the structures of treated and untreated CSs were investigated, and biomass components, including cellulose, hemicellulose and lignin, were analysed. Our findings revealed that AHP-LiCl/DMAc pretreatment improved accumulative methane yield by forceful delignification and effectively destroyed the structure of cellulose. The AHP-LiCl/DMAc-treated group had a maximum methane yield of 318.6 ± 17.85 mL/g volatile solid, which was 40.08% and 10.10% higher than the maximum methane yields of the untreated and AHP-treated group, respectively. This result showed enhanced cellulose dissolution by the ionic solvent of LiCl/DMAc and improved enzymatic saccharification in fermentative bacteria without structural modifications. The AHP-LiCl/DMAc treated group had higher glucose level, acetate followed by biomethanation process. Furthermore, the decrease in crystallinity indexes for AHP-LiCl/DMAc treated group was reported. Overall, this investigation proved a promising pretreatment approach for enhancing the degradation of CS into reducing sugars and improving methane generation.

Enhanced lignin removal and enzymolysis efficiency of grass waste by hydrogen peroxide synergized dilute alkali pretreatment

Pretreatment process plays a key role in biofuel production from lignocellulosic feedstocks. A study on dilute NaOH pretreatment supplemented with H₂O₂ under mild condition was conducted to overcome the recalcitrance of grass waste (GW). The optimized process could selectively increase lignin removal (73.2%), resulting in high overall recovery of holocellulose (73.8%) as well as high enzymolysis efficiency (83.5%) compared to H₂O₂ or NaOH pretreatment. The analyses by Scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR) revealed that supplementary H₂O₂ disrupted the structure of GW to facilitate the removal of lignin by NaOH, and exhibited synergistic effect on lignin removal and enzymolysis with dilute NaOH. Moreover, high titer of ethanol (100.7 g/L) was achieved by SSCF on 30% (w/v) pretreated GW loading. The present study suggests that the established synergistic pretreatment is a simple, efficient, and promising process for GW biorefinery.

Investigation of alkaline hydrogen peroxide pretreatment to enhance enzymatic hydrolysis and phenolic compounds of oil palm trunk

Alkaline hydrogen peroxide (AHP) as a pretreatment effectively enhances the increasing enzymatic digestibility of oil palm trunk (OPT) for conversion to biofuels and bioproducts in the biorefinery processes. The effect of hydrogen peroxide concentration (1-5%), temperature (50-90 °C), and time (30-90 min) were studied to find out the optimum condition for the removal of lignin. The optimum condition attained at 70 °C, 30 min, and 3% H₂O₂ g /g of biomass not only increased the cellulose content from 38.67% in raw material to 73.96% but also removed lignin and hemicellulose up to 50% and 57.12%, respectively. The AHP-treated fibers subjected to enzyme hydrolysis showed significant improvement in glucose concentration that increased from 11.77 (± 0.84) g/L (raw material) to 46.15 (± 0.32) g/L with 59.82% enzyme digestibility at 96 h. Scanning electron microscopy (SEM) and Fourier transformation infrared (FT-IR) were employed to analyze the morphology and structural changes of untreated and AHP-treated fibers. SEM results showed disruption of the intact OPT structure resulting in increase of enzyme accessibility to cellulose. The FT-IR identified changes in peaks which indicated structural transformation and dissolution of both lignin and hemicellulose molecules caused by AHP treatment. The black liquor obtained from AHP treatment contained about 5.13 mg gallic acid equivalent (GAE)/g of dry sample of total phenolic content (TPC) and an antioxidant activity of 59.80% and 65.51% inhibitions of DPPH and ABTS assays, respectively. Hence, it is a sustainable approach to utilize waste for the recovery of multiple value-added products during pretreatment process.

Multi-perspective analyses of rice straw modification by Pleurotus ostreatus and effects on biomethane production

Multi-perspective analyses were carried out to investigate the effect of rice straw modification for 45 days by P. ostreatus on biomethane of production. The results showed that rice straw modified for 25 days achieved the highest biomethane yield of 269 mL·g^-1 VS, which was a 26.9% improvement compared with non-modified rice straw. The multi-perspective analyses demonstrated that the improvement resulted from fungal enzymatic reactions, which led to changes in the physicochemical properties of rice straw. The porosity, surface area, acetyl group abundance, degree of polymerization, and lignin degradation selectivity of rice straw modified for 25 days were optimal for enzyme adsorption. Compared with non-modified rice straw, the adsorption of cellulase and xylanase on rice straw modified for 25 days was increased by 18.8% and 58.1%, respectively, which facilitated biomethane production. The study indicated that P. ostreatus is effective for improving biomethane production from rice straw.

Lignocellulosic Biomass: Understanding Recalcitrance and Predicting Hydrolysis

Lignocellulosic biomass (LB) is an abundant and renewable resource from plants mainly composed of polysaccharides (cellulose and hemicelluloses) and an aromatic polymer (lignin). LB has a high potential as an alternative to fossil resources to produce second-generation biofuels and biosourced chemicals and materials without compromising global food security. One of the major limitations to LB valorisation is its recalcitrance to enzymatic hydrolysis caused by the heterogeneous multi-scale structure of plant cell walls. Factors affecting LB recalcitrance are strongly interconnected and difficult to dissociate. They can be divided into structural factors (cellulose specific surface area, cellulose crystallinity, degree of polymerization, pore size and volume) and chemical factors (composition and content in lignin, hemicelluloses, acetyl groups). Goal of this review is to propose an up-to-date survey of the relative impact of chemical and structural factors on biomass recalcitrance and of the most advanced techniques to evaluate these factors. Also, recent spectral and water-related measurements accurately predicting hydrolysis are presented. Overall, combination of relevant factors and specific measurements gathering simultaneously structural and chemical information should help to develop robust and efficient LB conversion processes into bioproducts.

Comparison and intrinsic correlation analysis based on composition, microstructure and enzymatic hydrolysis of corn stover after different types of pretreatments

Pretreatment is a key step in the energy utilization of lignocellulosic biomass. Different types of pretreatments (ultrafine grinding pretreatment, alkaline hydroxide peroxide pretreatment, dilute acid pretreatment, and ammonia fiber expansion pretreatment) were conducted on corn stover. The lignocellulosic composition, microstructural parameters, and glucose yield of differently pretreated corn stover were characterized and compared. Then qualitative and quantitative correlation analyses of the parameters were carried out to explore the correlations among the composition, microstructure properties, and enzymatic hydrolysis efficacy of corn stover after different types of pretreatments and identify the main properties affecting enzymatic hydrolysis. Qualitative correlation analysis found that cellulose content, specific surface area, pore volume, enzyme-accessible pore volume, and surface area of cellulose had significant positive correlations with glucose yield. The results of quantitative correlation analysis were GY = 15.01 × cellulose content-339.05, GY = 13.06 × SSA + 172.35, GY = 7226.27 × PV + 129.14, GY = 8628.61 × EAPV + 125.61, and GY = 1.18 × SAC-287.21.

Consolidated bioprocessing performance of bacterial consortium EMSD5 on hemicellulose for isopropanol production

Consolidated bioprocessing (CBP) of lignocellulose by bacterial consortium for isopropanol production is considered as the most promising strategy. However, low utilization of xylan caused by the complex sidechain structure remains inhibit the conversion of full-biomass. In this study, isopropanol production from different lignocelluloses by the consortium EMSD5 through CBP was performed. A total of 7.00 g/L of isopropanol was obtained from corncob by optimizing fermentation conditions. Isopropanol production by EMSD5 was mainly based on utilizing xylan in corncob and isopropanol titer was increased by 47.71% and reached up to 8.39 g/L using arabinoxylan compared with linear xylan. The analysis of community structures and the isolation of key strain confirmed the enrichment of the isopropanol producer, Clostridium beijierinckii, in the bacterial community when it was incubated with corn glucuronoarabinoxylan and the cooperation between C. beijerinckii and lignocellulose degraders. The unique features of EMSD5 could lead to large-scale isopropanol production using lignocellulose.

Two-stage alkali-oxygen pretreatment capable of improving biomass saccharification for bioethanol production and enabling lignin valorization via adsorbents for heavy metal ions under the biorefinery concept

Converting lignin into value-added products in current lignocellulosic biorefineries has been challenging, which in turn restricts the commercialization of many lignocellulosic biorefineries. In this work, a two-stage alkali-oxygen assisted liquid hot water pretreatment (AlkOx) was proposed as the first step of biorefinery. This alkali-oxygen pretreatment facilitated biomass fractionation by solubilizing majority of lignin in water-soluble fraction, while remaining most of cellulose and hemicellulose in water-insoluble fraction. As a result, biomass saccharification was significantly improved by selective removal and oxidative modification of lignin through alkali-oxygen pretreatment. Moreover, lignin residues from both pretreatment hydrolysate and enzymatic hydrolysate were shown to be favorable adsorbents for Pb(II) ions, with adsorption capacity of 263.16 and 90.91 mg/g, respectively. Results demonstrated that this integrated process could not only improve biomass saccharification but also enable lignin valorization, which encouraged the holistic utilization of lignin residues as part of an integrated biorefinery.

Effects of Corn Stover Pretreated with NaOH and CaO on Anaerobic Co-Digestion of Swine Manure and Corn Stover

: In this study, effects of pretreatment of corn stover (CS) with sodium hydroxide (NaOH) combined with calcium oxide (CaO) on anaerobic co-digestion of swine manure and CS for biogas production were investigated. Different pretreated-CSs were prepared by adding different doses of NaOH and CaO to CS: Treat-CSA (0.10 g NaOH/g CS), Treat-CSB((0.075 g NaOH + 0.05 g CaO)/g CS), Treat-CSC ((0.05 g NaOH + 0.05 g CaO)/g CS), and Treat-CSD ((0.025 g NaOH + 0.1 g CaO)/g CS). Lignin removal rate, biomass recovery, reduced sugar, methane yield, DT80 (digestion time when biogas achieved 80% of the total biogas), composition of residues, and cost-efficiency were measured to characterize CS after pretreatment and to evaluate the performance of co-digestors fed with swine manure and differently-pretreated CS. The results showed that Treat-CSB showed an excellent lignin removal efficiency and biomass recovery, resulting in the highest methane yield in its co-digestion with swine manure. Since the net benefit of Treat-CSB was calculated to be the highest (i.e., $1.89/ton total solids), therefore, we believe the co-digestion of Treat-CSB and swine manure for biogas production be an effective valorization option for the wastes.