Effect of acid pretreatment on different parts of corn stalk for second generation ethanol production

The Potential Valorization of Corn Stalks by Alkaline Sequential Fractionation to Obtain Papermaking Fibers, Hemicelluloses, and Lignin-A Comprehensive Mass Balance Approach

The current study deals with an examination of strategies for the sequential treatment of corn stalks (CSs) in an integrated manner aiming to obtain papermaking fibers and to recover both lignin and hemicelluloses (HCs). Several pathways of valorization were experimentally trialed, focusing on getting information from mass balance analysis in an attempt to reveal the potential outcomes in terms of pulp yield, chemical composition, and papermaking properties such as tensile and burst strength. The raw lignin amounts and purity as well as separated hemicelluloses were also characterized. In this work, pulp yields in the range of 44-50% were obtained from CSs, while lignin and hemicelluloses yielded maximum values of 10 g/100 g of CS and 6.2 g/100 g of CS, respectively. Other findings of mass balance analysis evidenced that besides the papermaking pulp, the lignin and HCs also have interesting output values. The recovered lignin yield values were shown to be less than 50% in general, meaning that even if 67 to 90% of it is removed from CSs, only about half is recovered. The removal rates of hemicelluloses were found to be in the range of approx. 30 to 60%. About 15 to 25% of the original HCs could be recovered, and polysaccharides-based products with 67 to 75% xylan content could be obtained. Some key opinions were developed regarding how the mass balance could turn as a result of the chosen CS valorization set-up. The determined antioxidant activity showed that both lignin and hemicelluloses had interesting values for IC50.

Construction of a synthetic microbial community based on multiomics linkage technology and analysis of the mechanism of lignocellulose degradation

The efficient degradation of lignocellulose is a bottleneck for its integrated utilization. This research performed species analysis and made functional predictions in various ecosystems using multiomics coupling to construct a core synthetic microbial community with efficient lignocellulose degradation function. The synthetic microbial community was employed to degrade corn straw via solid-state fermentation. The degradation mechanisms were resolved using proteomics. The optimum culture conditions included 10% inoculum level (w/v), 4% nitrogen source ratio and a fermentation time of 23 d. Under these conditions, the degradation rates of cellulose, hemicellulose, and lignin were 34.91%, 45.94%, and 23.34%, respectively. Proteomic analysis revealed that lignin 1,4-β-xylanase, β-xylosidase and endo-1,4-β-xylanase were closely related to lignocellulose degradation. The metabolic pathways involved in lignocellulose degradation and the functional roles of eight strains were obtained. The synthesis of a microbial community via multiomics linkage technology can effectively decompose lignocellulose, which is useful for their further utilization.

Enhanced fermentable sugar production in lignocellulosic biorefinery by exploring a novel corn stover and configuring high-solid pretreatment conditions

This study aimed to produce enhanced fermentable sugars from a novel stover system through the bioprocessing of its soluble sugars and insoluble carbohydrates. The pretreatment conditions were optimized for this high sugar-containing stover (HSS) to control inhibitor formation and obtain enhanced fermentable sugar concentrations. The optimum temperature, acid loading, and reaction time for the pretreatment were 155 °C, 0.5%, and 30 min, respectively, providing up to 97.15% sugar yield and 76.51 g/L total sugars at 10% solid-load. Sugar concentration further increased to 126.9 g/L at 20% solid-load, generating 3.89 g/L acetate, 0.92 g/L 5-hydroxymethyl furfural, 0.82 g/L furfural, and 3.75 g/L total phenolics as inhibitors. To determine the effects of soluble sugars in HSS on fermentable sugar yield and inhibitor formation, sugar-removed HSS was further studied under the optimum conditions. Although prior removal of sugars exhibited a reduction in inhibitor generation, it also decreased total fermentable sugar production to 115.45 g/L.

Comparison of Alkaline Sulfite Pretreatment and Acid Sulfite Pretreatment with Low Chemical Loading in Saccharification of Poplar

Sulfite pretreatment is a productive process for lignin dissolution in lignocelluloses and to reduce the hydrophobicity of lignin by sulfonation, thus promoting the hydrolyzability of the substrate. Previously, sulfite pretreatment needs high dosages of chemicals and thus results in the high cost of the pretreatment and the great pressure of environmental pollution. To overcome these problems, it was crucial to research whether alkaline sulfite pretreatment (ALS) and acid sulfite pretreatment (ACS) with low chemical loading could enhance the saccharification of poplar. In this work, the results indicated that with low loading of chemicals in sulfite pretreatment, ALS pretreatment (1.6% Na2SO3 and 0.5% NaOH) at 180 °C removed more lignin, resulted in lower hydrophobicity and higher cellulase adsorption capacity of poplar than ACS pretreatment (1.6% Na2SO3 and 0.5% H2SO4) at 180 °C. A satisfying glucose yield of 84.9% and a xylose yield of 76.0% were obtained from poplar after ALS pretreatment with 1.6% Na2SO3 and 0.5% NaOH at 180 °C for 1 h using 10 FPU cellulase/g dry matter, saving sodium sulfite by 60.0% compared to the loading of sulfite in traditional sulfite pretreatment. The strategy developed in this work reduced chemical loading and cellulase loading in alkali sulfite pretreatment for the saccharification of poplar.

`A critical review on current status and environmental sustainability of pre-treatment methods for bioethanol production from lignocellulose feedstocks

Lignocellulosic biomass resource has been widely used as a natural resource for the synthesis of biofuels and bio-based products through pre-treatment, saccharification and fermentation processes. In this review, we delve into the environmental implications of bioethanol production from the widely utilized lignocellulosic biomass resource. The focus of our study is the critical stage of pre-treatment in the synthesis process, which also includes saccharification and fermentation. By collecting scientific data from the available literature, we conducted a comprehensive life cycle analysis. Our findings revealed substantial differences in the environmental burdens associated with diverse pre-treatment methods used for lignocellulosic biomass. These results highlight the importance of selecting environmentally benign pre-treatment techniques to promote the sustainability of bioethanol production. Future research directions are suggested, emphasizing the optimization of pre-treatment processes to further mitigate their environmental impact.

Consolidated bioprocessing of plant biomass to polyhydroxyalkanoate by co-culture of Streptomyces sp. SirexAA-E and Priestia megaterium

Polyhydroxyalkanoate (PHA) production from plant biomass is an ideal way to realize sustainable PHA-based bioplastic. The present study demonstrated consolidated bioconversion of plant biomass to PHA by co-culturing two specialized bacteria, cellulolytic Streptomyces sp. SirexAA-E and PHA producing Priestia megaterium. In monoculture, S. sp. SirexAA-E does not produce PHA, while P. megaterium did not grow on plant polysaccharides. The co-culture showed poly(3-hydroxybutyrate) (PHB) production using purified polysaccharides, including cellulose, xylan, mannan and their combinations, and plant biomass (Miscanthus, corn stalk and corn leaves) as sole carbon sources, confirmed by GC-MS. The co-culture inoculated with 1:4 (v/v) ratio of S. sp. SirexAA-E to P. megaterium produced 40 mg PHB/g Miscanthus using 0.5% biomass loading. Realtime PCR showed ∼85% S. sp. SirexAA-E and ∼15% P. megaterium in the co-culture. Thus, this study provides a concept of proof for one-pot bioconversion of plant biomass into PHB without separate saccharification processes.

Effect of acidic pretreatment on the microstructural arrangement and anaerobic digestion of Arachis hypogea shells; and process parameters optimization using response surface methodology

Enzymatic hydrolysis of lignocellulose feedstocks has been observed as the rate-limiting stage during anaerobic digestion. This necessitated the need for pretreatment before anaerobic digestion for an effective and efficient process. Therefore, this study investigated the impact of acidic pretreatment on Arachis hypogea shells, and different conditions of H₂SO₄ concentration, exposure time, and autoclave temperature were considered. The substrates were digested for 35 days at a mesophilic temperature to assess the impact of pretreatment on the microstructural organization of the substrate. For the purpose of examining the interactive correlations between the input parameters, response surface methodology (RSM) was used. The result reveals that acidic pretreatment has the strength to disrupt the recalcitrance features of Arachis hypogea shells and make them accessible for microorganisms' activities during anaerobic digestion. In this context, H₂SO₄ with 0.5% v. v^-1 for 15 min at an autoclave temperature of 90 °C increases the cumulative biogas and methane released by 13 and 178%, respectively. The model's coefficient of determination (R²) demonstrated that RSM could model the process. Therefore, acidic pretreatment poses a novel means of total energy recovery from lignocellulose feedstock and can be investigated at the industrial scale.

Review of chemical pretreatment of lignocellulosic biomass using low-liquid and low-chemical catalysts for effective bioconversion

Chemical pretreatment of lignocellulosic biomass (LCB) is essential for effective biological conversion in subsequent steps to produce biofuels or biochemicals. For effective pretreatment, high lignin content and its recalcitrant nature of LCB are major factors influencing bioconversion, especially lignin is known to be effectively solubilized by alkaline, organic, and deep eutectic solvents, ionic liquids, while hemicellulose is effectively dissolved by various acid catalysts and organic solvents. Depending on the pretreatment method/catalyst used, different pretreatment process scheme should be applied with different amounts of catalyst and water inputs to achieve a satisfactory effect. In addition, the amount of processing water required in the following processes such as washing, catalyst recovery, and conditioning after pretreatment is critical factor for scale-up (commercialization). In this review, the amount of catalyst and/or water used, and the effect of pretreatment, properties of the products, and recovery of liquid are also discussed.

Effects of Inorganic Passivators on Gas Production and Heavy Metal Passivation Performance during Anaerobic Digestion of Pig Manure and Corn Straw

The treatment of livestock manure caused by the expansion of the breeding industry in China has attracted wide attention. Heavy metals in pig manure can pollute soil and water and even transfer to crops, posing harm to humans through the food chain. In this study, corn straw was selected as the additive and introduced into the anaerobic digestion. Sepiolite (SE), ferric oxide (Fe₂O₃), attapulgite (AT) and ferric sulfate (FeSO₄) were used as passivators to compare the effects of these inorganic passivators on gas production and passivation of heavy metals during the process of the anaerobic digestion. When the dry mass ratio of pig manure to straw is 8:2, the gas production efficiency is optimal. SE, AT and ferric sulfate have a much stronger ability to improve gas production performance than Fe₂O₃. The total gas production increased by 10.34%, 6.62% and 4.56%, and the average methane production concentration increased by 0.7%, 0.3% and 0.4%, respectively. The influence of SE, AT and ferric sulfate on the passivation of heavy metals is much better than Fe₂O₃, and the fractions in biological effective forms of Cu and Zn reduced by 41.87 and 19.32%, respectively. The anaerobic digestion of mixed materials is conducive to the gas production and the passivation of heavy metals. Therefore, SE, AT and ferric sulfate are selected as composite passivators, and the optimal ratio of inorganic composite passivators i: AT 7.5 g/L, ferric sulfate 5 g/L and SE 7.5 g/L, according to the results of orthogonal experiments. This study can provide a theoretical basis for the safe application of biogas fertilizers.

Comparative study on the hydrogenolysis performance of solid residues from different bamboo pretreatments

Both alkaline organosolv and formaldehyde stabilization pretreatment can yield high-quality lignin by preventing condensation. For the hydrogenolysis of the pretreated solid residues, the highest yield of C2-C4 chemicals was 66.8% under alkaline organosolv pretreatment for 60 min. Specifically, the crimped fibers and residual lignin and hemicellulose increased the surface roughness of the residue by 40.6%, the crystallinity index decreased to 44.4%, and the crystal size was reduced to 2.15 nm, which in turn promoted hydrogenolysis of the residue. However, the increase of crystallinity and crystal size and the decrease in surface roughness of the formaldehyde stabilization pretreatment residue greatly hindered the conversion of polysaccharides. In addition, residual formaldehyde on the residue may also inhibit catalyst activity. Overall, this study provides novel perspectives on the full utilization of biomass, as well as new insights into the conversion of polysaccharides.

Separation of Lignocellulose and Preparation of Xylose from Miscanthus lutarioriparius with a Formic Acid Method

Efficient component separation technology is one of the key ways to improve the efficiency of lignocellulose bioconversion. In this study, the formic acid method was used to separate the components of lignocellulose from Miscanthus lutarioriparius, hemicellulose was degraded into xylose simultaneously, and the composition and structure of the separated components were analyzed. Then, xylose was further purified with activated carbon for decolorization and resins for the removal of formic acid and other monosaccharide impurities. The results showed that formic acid could effectively separate the cellulose, hemicellulose, and lignin of lignocellulose with recoveries of 91.7%, 80.2%, and 85.3%, respectively. Structural analyses revealed that the cellulose and lignin underwent different degrees of formylation during the formic acid treatment, yet their primary structures remained intact, and the crystallinity of cellulose increased significantly. By GC–MS and HPLC analysis, xylose was the main component of hemicellulose extract, accounting for 74.90%. The activated carbon treatment decolorized the xylose extract more than 93.66% and gave a xylose recovery of 88.58%. D301 resin could effectively remove more than 99% of the formic acid residue in xylose. The xylose extract was further purified by removing arabinose and other monosaccharide impurities with Dowex 50wx4 resin, which increased the purity to 95%. The results demonstrated that the formic acid method is an effective method to separate lignocellulose and prepare xylose, and it has broad application prospects in the field of bio-refining lignocellulose resources such as Miscanthus lutarioriparius

Fast pyrolysis of torrefied holocellulose for producing long-chain ether precursors in a fluidized bed

Combining torrefaction with fast pyrolysis is an achievable route for producing long-chain ether precursors. The results of structural characterization for native and torrefied holocellulose indicated that with increasing torrefaction temperature, the crystallinity index (CrI) decreased slightly and then sharply increased; hydroxyls, O-acetyl branches, ether bond and β-1,4-glycosidic bond were eliminated but carbonyls increased. Maximum mass loss rate and apparent activation energy increased after torrefaction. With an increase in torrefaction temperature, gaseous yield continuously dropped, and liquid product yield climbed to the highest point of 49.04% for holocellulose torrefied at 240 °C (240CS). Torrefaction was unfavorable for the production of small-molecule gases. The bio-oil analysis demonstrated that the yield of acetic acid decreased from 6.35% to 1.43% with torrefaction temperature increasing from 105 °C to 260 °C. Significantly, yields of targeted compounds were dramatically improved after torrefaction, and 240CS afforded the maximum carbon yield of 14.79%.

Ultrastructural change in lignocellulosic biomass during hydrothermal pretreatment

In recent years, visualization and characterization of lignocellulose at different scales elucidate the modifications of its ultrastructural and chemical features during hydrothermal pretreatment which include degradation and dissolving of hemicelluloses, swelling and partial hydrolysis of cellulose, melting and redepositing a part of lignin in the surface. As a result, cell walls are swollen, deformed and de-laminated from the adjacent layer, lead to a range of revealed droplets that appear on and within cell walls. Moreover, the certain extent morphological changes significantly promote the downstream processing steps, especially for enzymatic hydrolysis and anaerobic fermentation to bioethanol by increasing the contact area with enzymes. However, the formation of pseudo-lignin hinders the accessibility of cellulase to cellulose, which decreases the efficiency of enzymatic hydrolysis. This review is intended to bridge the gap between the microstructure studies and value-added applications of lignocellulose while inspiring more research prospects to enhance the hydrothermal pretreatment process.

Effects of post-washing on pretreated biomass and hydrolysis of the mixture of acetic acid and sodium hydroxide pretreated biomass and their mixed filtrate

Effects of post-washing [one-volume water (I-VW) or double-volume water (Ⅱ-VW)] on pretreated hemp and poplar biomass and enzymatic hydrolysis of the mixture of HOAc and NaOH pretreated biomass and their mixed filtrate were investigated. Compared to I-VW, Ⅱ-VW increased 3.76-6.80% of glucan content in NaOH pretreated biomass, diminished lignin recondensation, and heightened cellulose-related FTIR peak intensities, crystallinity index, and lignin removal. The pH of mixed filtrate was around 4.80, precipitating the NaOH soluble lignin partially. Although Ⅱ-VW showed lower lignin recoveries than I-VW, their FTIR characteristics were equivalent to the commercial alkali lignin. Enzymatic hydrolysis at solid loadings of 2.5-10% (w/v) demonstrated that I-VW and Ⅱ-VW had marginal variations in sugar concentration and conversion efficiency, indicating that I-VW is sufficient for post-washing pretreated biomass. Glucose concentration exhibited a quadratic correlation with solid loading and hemp biomass reached the maximum glucose (43.88 g/L) and total sugar (57.08 g/L) concentrations with I-VW.

Levels and risk assessment of polycyclic aromatic hydrocarbons in wood vinegars from pyrolysis of biomass

A method quantifying 16 polycyclic aromatic hydrocarbons (PAHs) in wood vinegars (WVs) obtained from slow pyrolysis of biomass with ultrasonic-assisted liquid-liquid extraction/gas chromatography-mass spectrometry (USALLE/GC-MS) was established. The recovery range was 83-128%, and the relative standard deviations (RSD%) were less than 15% except naphthalene, acenaphthylene and acenaphthene. Acenaphthylene, acenaphthene, fluorene, anthracene, phenanthrene, fluoranthene, and pyrene were observed in all samples and the other 9 compounds, including benzopyrene (B[a]P), were not detected. The concentration of ∑PAHs referred to the sum total of 7 PAHs mentioned above was 22.0-498.3 μg L^-1. The PAHs concentration increased with the increasing pyrolysis temperature in bamboo willow WV, pinus sylvestris WV, and corncob WV, while it increased initially, and then decreased with a maximum at 550 °C in rice husk WV. The ∑PAHs concentration increased with a higher heating rate in the white pine WV, while rice husk WV and cornstalk WV showed the opposite trend. The varied condensed aromatic ring number showed that 3-ring PAHs relatively were the main component in all kind WVs. 3-ring PAHs increased with increasing temperatures, while 4-ring PAHs showed an opposite trend in sawdust WV and corncob WVs. A higher cellulose content in sawdust enhanced the reaction of lignin leading to a higher concentration of PAHs than that in straws and leaves. Calculations of the toxicity equivalents of PAHs in WVs indicated that anthracene was the most toxic among the PAHs, and the pinus sylvestris WV had the highest risk of ∑PAHs toxicity in all WVs.

Agricultural bio-waste for removal of organic and inorganic contaminants from waste diesel engine oil

Corncob, an agricultural bio-waste, was used as adsorbent to remove organic and inorganic contaminants in waste lubricating oil (WLO) from diesel engine. To improve its adsorption capacity, corncob was modified with mixed solution of nitric acid, Hexadecyl trimethyl ammonium bromide and ethanol. Characterization results showed the crystallinity index of corncob enhanced 12%, which would be ascribed to the disruption of the dense lignin-carbohydrates structure in lignocellulose biomass by modification. The surface of modified corncob became smoother and porous. The adsorption results showed modified corncob had better removal rates to contaminants than raw corncob. For WLO with 80,000 km mileage, the removal rates to Fe, Al, Cu were enhanced from 19%, 6.4%, 48-27%, 27%, 53%, while that for oxide, sulphate, aromates, soot and insoluble resins were enhanced 1.7, 1.2, 3.0, 1.7 and 1.7 times. The reduction rate of total acid number to WLO with 40,000, 60,000, 80,000 km were enhanced 16%, 9%, 12% by modified corncob, respectively. The optimal adsorption condition was explored as adsorbing 60 min at 90 °C with 2% adsorbent. Corncob, with the advantages of low cost, good biodegradability and high adsorption capacity, could be used as alternative to conventional adsorbent for WLO.

Production of cellulose nanofibrils and films from elephant grass using deep eutectic solvents and a solid acid catalyst

A new strategy was developed to produce cellulose nanofibrils (CNFs) and films from raw elephant grass using deep eutectic solvents and a recyclable spent coffee-derived solid acid (SC-SO₃H) catalyst with assistance of ultrasonic disintegration and a suction filtration film forming method. The effects of a solid acid and reused solid acid were comprehensively studied by comparing with catalyst-free conditions and using sulfuric acid as the catalyst. The CNF fibers obtained from this novel SC-SO₃H catalyst method showed the longest fiber length. The corresponding films achieved the strongest tensile strength of 79.8 MPa and the elongation at break of 13.6%, and best thermostability. In addition, the performance of CNFs and films prepared by the fourth recovered SC-SO₃H-4 catalyst was close to that obtained with the first use. The SC-SO₃H could be reused by a simple decantation method, meaning this novel method has the potential for green and sustainable preparation of CNFs and films.

A new strategy was developed to produce cellulose nanofibrils and films from elephant grass using deep eutectic solvents and a recyclable solid acid catalyst with assistance of ultrasonic disintegration and a suction filtration film forming method.

Synthesis of a Stable Solid Acid Catalyst from Chloromethyl Polystyrene through a Simple Sulfonation for Pretreatment of Lignocellulose in Aqueous Solution

A stable solid acid catalyst, SCPR140-1, was synthesized from chloromethyl polystyrene resin (CPR) and used for catalytic pretreatment of corncob in aqueous solution. Under the optimized pretreatment condition, 73.07 % of xylose was directly obtained, and the enzymatic digestibility of treated residue reached up to 94.65 %, indicating that the SCPR140-1 had high selectivity for xylose production and effectively deconstructed the structure of corncob. The -CH₂ Cl group of CPR was substituted by -SO₃ H through the sulfonation, and the -SO₃ H was stably bound on the catalyst during the pretreatment process. Compared with other similar reports, the SCPR140-1 was not only synthesized through a simpler process but also had a more stable catalytic activity during multiple recycling runs.

Catalytic fast pyrolysis of enzymatic hydrolysis lignin over Lewis-acid catalyst niobium pentoxide and mechanism study

Lewis-acid catalyst Nb₂O₅ is first applied in catalytic fast pyrolysis (CFP) of enzymatic hydrolysis lignin (EHL) to produce aromatic hydrocarbons (AHs) that can be used as alternative liquid fuels. The catalyst exhibits a good talent to convert lignin into AHs with quite little polycyclic aromatic hydrocarbons (PAHs) formation. The yield of AHs reaches 11.2 wt% and monocyclic aromatic hydrocarbons (MAHs) takes up 94% under the optimized condition (Catalyst to Lignin ratio 9:1, 650 °C). No coke is generated during the reactions. The reaction sequence is proposed and verified by model compound reactions. Furthermore, DFT calculations are performed to understand the mechanisms of limitation of PAHs or char/coke formation and the efficient deoxygenation ability over catalyst. Nb₂O₅ with Lewis acid sites is proved to be a promising catalyst for the production of AHs from lignin. This work provides a new idea on choice of catalysts for CFP of lignin in future.

Effect of p-TsOH pretreatment on separation of bagasse components and preparation of nanocellulose filaments

The efficient separation of bagasse components was achieved by p-toluenesulfonic acid (p-TsOH) pretreatment. The effects of p-TsOH dosage, reaction temperature and reaction time on cellulose, hemicellulose and lignin contents were studied. Eighty-five per cent of lignin was dissolved, whereas the cellulose loss was minimal (less than 8.1%). Cellulose-rich water-insoluble residual solids were obtained. The degree of polymerization of cellulose decreased slightly, but the crystallinity index (CrI) increased from 52.0% to 68.1%. It indicated that the highly efficient delignification of bagasse was achieved by p-TsOH pretreatment. The nanocellulose filaments (CNFs) were produced by the treated samples. The physico-chemical properties of CNFs were characterized by transmission electron microscopy and thermogravimetric analysis. The results show that the CNFs have smaller average size and higher thermal stability. It provides a new method for CNFs.

Progress in the development of alkali and metal salt catalysed lignocellulosic pretreatment regimes: Potential for bioethanol production

Lignocellulosic biomass (LCB) is well suited to address present day energy and environmental concerns, since it is abundant, environmentally benign and sustainable. However, the commercial application of LCB has been limited by its recalcitrant structure. To date, several biomass pretreatment systems have been developed to address this major bottleneck but have shown to be toxic and costly. Alkali and metal salt pretreatment regimes have emerged as promising non-toxic and low-cost treatments. This paper examines the progress made in lignocellulosic pretreatment using alkali and metal salts. The reaction mechanism of alkali and metal chloride salts on lignocellulosic biomass degradation are reviewed. The effect of salt pretreatment on lignin removal, hemicellulose solubilization, cellulose crystallinity, and physical structural changes are also presented. In addition, the enzymatic digestibility and inhibitor profile from salt pretreated lignocellulosic biomass are discussed. Furthermore, the challenges and future prospects on lignocellulosic pretreatment and bioethanol production are highlighted.

Enhancement of biogas production from rape straw using different co-pretreatment techniques and anaerobic co-digestion with cattle manure

The present study investigated the possibility of valorizing rape straw through anaerobic digestion and the possibility of improving biomethane yield by pretreatment with H₂SO₄, combined H₂SO₄ with steam explosion (SE) and SE combined with superfine grinding (SFG). To evaluate the pretreatment method efficiency, several analytical techniques were applied. Additionally, the performance of co-digesting of cattle manure (CM) with pretreated rape straw (PRS) at different ratios was evaluated. The results showed that combined pretreatment could dissolve the lignocellulosic fiber structure, which positively stimulated methane yield. The highest cumulative CH₄ yield (CMY) of 305.7 mLg^-1VS was achieved by combined SE at 180 °C for 5 min with SFG, which was 77.84% higher than the untreated. The CMY was further improved by 11.4-59% higher than the control (CM) using co-digestion. This study confirmed that, under optimal parameters of AD, pretreatment with SEG180 could significantly boost the CMY from co-digestion of CM and PRS.

Alkaline organosolv pretreatment of different sorghum stem parts for enhancing the total reducing sugar yields and p-coumaric acid release

BACKGROUND

The sorghum stem can be divided into the pith and rind parts with obvious differences in cell type and chemical composition, thus arising the different recalcitrance to enzyme hydrolysis and demand for different pretreatment conditions. The introduction of organic solvents in the pretreatment can reduce over-degradation of cellulose and hemicellulose, but significance of organic solvent addition in pretreatment of different parts of sorghum stem is still unclear. Valorization of each component is critical for economy of sorghum biorefinery. Therefore, in this study, NaOH-ethanol pretreatment condition for different parts of the sorghum stem was optimized to maximize p-coumaric acid release and total reducing sugar recovery.

RESULT

Ethanol addition improved p-coumaric acid release and delignification efficiency, but significantly reduced hemicellulose deconstruction in NaOH-ethanol pretreatment. Optimization using the response surface methodology revealed that the pith, rind and whole stem require different NaOH-ethanol pretreatment conditions for maximal p-coumaric acid release and xylan preservation. By respective optimal NaOH-ethanol pretreatment, the p-coumaric acid release yields reached 94.07%, 97.24% and 95.05% from pith, rind and whole stem, which increased by 8.16%, 8.38% and 8.39% compared to those of NaOH-pretreated samples. The xylan recoveries of pith, rind and whole stem reached 76.80%, 88.46% and 85.01%, respectively, which increased by 47.75%, 15.11% and 35.97% compared to NaOH pretreatment. Adding xylanase significantly enhanced the enzymatic saccharification of pretreated residues. The total reducing sugar yields after respective optimal NaOH-ethanol pretreatment and enzymatic hydrolysis reached 84.06%, 82.29% and 84.09% for pith, rind and whole stem, respectively, which increased by 29.56%, 23.67% and 25.56% compared to those of NaOH-pretreated samples. Considering the separation cost of the different stem parts, whole sorghum stem can be directly used as feedstock in industrial biorefinery.

CONCLUSION

These results indicated that NaOH-ethanol is effective for the efficient fractionation and pretreatment of sorghum biomass. This work will help to understand the differences of different parts of sorghum stem under NaOH-ethanol pretreatment, thereby improving the full-component utilization of sorghum stem.

Bioethanol production from sesame (Sesamum indicum L.) plant residue by combined physical, microbial and chemical pretreatments

This study explored the potential of sesame (Sesamum indicum L.) plant residue (SPR) for bioethanol production. Three particle sizes, including 400, 850 and 1300 µm of SPR, were subjected to microbial degradation by Phanerochaete chrysosporium followed by 1% H₂SO₄ pretreatments. FTIR and HPLC analyses showed that the combined pretreatment which begins with microbial followed up by acid degraded SPR in the finest particle size (400 µm) resulted in the maximum contents of reducing sugars (370.23 mg·g^-1). Kinetics studies of the pretreatment process also confirmed the maximized rate of hemicellulose and lignin reduction with reducing sugars production. The logistic model had better fitness as compared to the modified Gompertz model to predict bioethanol production. SPR gave a maximum of 1.90 g·L^-1 bioethanol yield after 60 h of fermentation using Saccharomyces cerevisiae. This study is the first report on bioethanol production from SPR, which proposed its suitability for sustainable energy production.

Ethanol production from residual lignocellulosic fibers generated through the steam treatment of whole sorghum biomass

Cellulosic ethanol could play a major role in the upcoming circular-economy once the process complexity, low carbohydrate extraction yields and high costs are resolved. To this purpose, different steam-treatment severity factors were employed on whole sweet sorghum biomass, followed by the delignification and hydrolysis of resulted lignocellulose fibers. A modified ASTM International (American Society for Testing and Material) standard cellulose hydrolysis approach as well as a newly developed SACH (Sulfuric Acid Cellulose Hydrolysis) process were used, recovering up to 24.3 wt% of cellulosic carbohydrates. This amounted to a total extractable and constitutive carbohydrate recovery of 51.7 wt% (dry basis) when a mild steam-treatment of whole sorghum biomass and the SACH cellulose hydrolysis were employed. An ethanol potential of 6378 L/ha/year was determined, comparable to values obtained from biomass such as sugarcane in warmer climates, supporting thus the opportunity of implementing this novel approach on a wider scale.

High-solid pretreatment of rice straw at cold temperature using NaOH/Urea for enhanced enzymatic conversion and hydrogen production

A high-solid loading pretreatment using NaOH/Urea solution at -12 °C was proposed to pretreat rice straw (RS) for enhanced saccharify and hydrogen production. Results shown NaOH/Urea pretreatment exhibited excellent pretreatment performance at solid loading ranged from 10% to 100% (w/v) with an average reducing sugar conversion of 80.22% was obtained which was 31.89% higher than that untreated RS. Upon fermentation of 100% solid loading pretreated hydrolysate, the H₂ yield of 72.5 mL/g-pretreated RS was calculated based on substrate consumption, which enabled 49.5% higher reducing sugar transfer to H₂ through material balance. FTIR and XRD analysis further demonstrated that the cold NaOH/Urea pretreatment at 100% (w/v) could effectively disrupt the lignin structure and decrease the cellulose crystallinity. The present study suggested a high solid loading pretreatment with NaOH/Urea at cold temperature could be a valuable alternative for better techno-economic of the lignocelluloses - to - sugars - to H₂ routes.

Mechanical pretreatment of lignocelluloses for enhanced biogas production: Methane yield prediction from biomass structural components

In this study, mechanical pretreatment was applied to six different lignocelluloses in two different treatment phases and the prediction of their methane yield was done from biomass chemical composition. Physicochemical, proximate and microbial analyses were carried out on both pretreated and untreated biomass using standard methods. Mechanical pretreatments caused the breakdown of structural materials in all the used biomass which was characterized by reduction of the lagging time during anaerobic digestion and the subsequent increase in methane yield up to 22%. The different loading rate of biomass had no effect on the overall methane yield increase. Both single and multiple linear regressions models were used in order to correlate the chemical composition of the biomass with their methane potentials and a fairly high correlation (R² = 0.63) was obtained. The study also showed that the pretreatments are economically feasible. Therefore, its further application to other biomass is encouraged.

Bioethanol production from sugarcane leaf waste: Effect of various optimized pretreatments and fermentation conditions on process kinetics

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Bioethanol kinetics was investigated under SSA-F, SSA-U, MSA-F and MSA-U conditions.

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Monod, logistic and modified Gompertz models gave R² > 0.97.

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SSA-U pretreated SLW produced 25% more bioethanol than MSA-U.

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No difference was observed between filtered and unfiltered enzymatic hydrolysate.

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SLW residue showed a suitable protein and fat content for animal feed.

This study examines the kinetics of S. cerevisiae BY4743 growth and bioethanol production from sugarcane leaf waste (SLW), utilizing two different optimized pretreatment regimes; under two fermentation modes: steam salt-alkali filtered enzymatic hydrolysate (SSA-F), steam salt-alkali unfiltered (SSA-U), microwave salt-alkali filtered (MSA-F) and microwave salt-alkali unfiltered (MSA-U). The kinetic coefficients were determined by fitting the Monod, modified Gompertz and logistic models to the experimental data with high coefficients of determination R² > 0.97. A maximum specific growth rate (μ_max) of 0.153 h⁻¹ was obtained under SSA-F and SSA-U whereas, 0.150 h⁻¹ was observed with MSA-F and MSA-U. SSA-U gave a potential maximum bioethanol concentration (P_m) of 31.06 g/L compared to 30.49, 23.26 and 21.79 g/L for SSA-F, MSA-F and MSA-U respectively. An insignificant difference was observed in the μ_max and P_m for the filtered and unfiltered enzymatic hydrolysate for both SSA and MSA pretreatments, thus potentially reducing a unit operation. These findings provide significant insights for process scale up.

Alkaline organosolv pretreatment of corn stover for enhancing the enzymatic digestibility

In the present study, a sodium hydroxide-methanol solution (SMs) pretreatment of corn stover was described to overcome biomass recalcitrance for the first time. Effects of sodium hydroxide loading, solid-to-liquid ratio, processing time and temperature on enzymatic saccharification were studied in detail. The SMs pretreatment could significantly enhance the enzyme accessibility of corn stover, minimize the degradation of sugar polymers, and decrease the energy consumption. 97.5% glucan and 83.5% xylan were preserved in the regenerated corn stover under the optimal condition. Subsequent enzymatic digestibilities of glucan and xylan reached 97.2% and 80.3%, respectively. The enzyme susceptibility of the regenerated samples was explained by their physical and chemical characteristics. This strategy provides a promising alternative for better techno-economic of the lignocelluloses-to-sugars routes.

Effect of pretreatments on corn stalk chemical properties for biogas production purposes

Different pretreatments were evaluated on corn stalk (Zea mays) applied as a lignocellulosic source in anaerobic co-digestion with swine manure, using sulfuric acid (H₂SO₄) and hydrogen peroxide (H₂O₂) for biogas production purposes. Using H₂SO₄ we achieved a 75.1% removal of the hemicellulose fraction, in low acid concentrations (0.75% v.v^-1). However, this technique inhibited the co-digestion process. Pretreatment with 12% of H₂O₂ (pH 11.5) increased the cellulose fraction by 73.4% and reduced the lignin content by 71.6%. This pretreatment is recommended for biogas production, as it increased the final volume of biogas by 22% and reduced the digestion time by one third. So, a promising alternative was obtained in order to facilitate the anaerobic digestion of the carbohydrates present in this biomass.

The effects of fibrolytic enzymes, cellulolytic fungi and bacteria on the fermentation characteristics, structural carbohydrates degradation, and enzymatic conversion yields of Pennisetum sinese silage

Biological inoculants were tested on Pennisetum sinese for their effects on fermentation characteristics, structural carbohydrates degradation, and enzymatic conversion yields. Pennisetum sinese was ensiled without additive, Lactobacillus plantarum (Lp), Trichoderma reesei (Tr), fibrolytic enzymes (E), and Enterococcus faecium (Y83) for 90 days. Y83 silages had higher LA and lower AA, ammonia-N and DM loss as compared to E and Tr silages. Tr and E had superior effects for degrading lignocellulose while Y83 had intermediate effects. The first-order exponential decay models (R² = 0.928-0.998) predicted nonstructural carbohydrates kinetics and demonstrated high water soluble carbohydrate (g/kg DM) preservation potential in Y83 (21.40), followed by Tr (18.94) and E (16.74). Addition of Y83 improved the conversion efficiency of P. sinese silage than Tr and E, indicated by higher glucose and total reducing sugars yield (22.49 and 36.89 w/w % DM, respectively). In conclusion, Y83 can be exploited for the ensiling lignocellulosic biomass before grass processing.

Enhanced enzymatic saccharification of sugarcane bagasse pretreated by sodium methoxide with glycerol

Sodium methoxide (CH₃ONa) with glycerol pretreatment (CWGP) was performed to improve the enzymatic digestibility of sugarcane bagasse (SCB). Response surface methodology was utilized to optimize the CWGP parameters for pretreating SCB from the perspective of total fermentable sugar yield (TFSY) and total fermentable sugar concentration (TFSC). Under the optimal CWGP conditions, 0.5666g/g of TFSY (0.82% CH₃ONa, 1.11h, 150°C) and 17.75g/L of TFSC (0.87% CH₃ONa, 1.38h, 149.27°C) were achieved, corresponding to delignification of 79.05% and 79.34%, respectively. Compared the pretreatment using glycerol or CH₃ONa alone, the CWGP has significant synergies to enhance the enzymatic efficiency of SCB. The physical and chemical characteristics of untreated and pretreated SCBs were analyzed using FT-IR, XRD, and SEM, and the results suggest that CWGP significantly increased the susceptibility of the substrates to enzymatic digestibility. Ultimately, CWGP might be a prospective candidate for the pretreatment process of enzyme-based lignocellulosic biorefineries.

Treatment of different parts of corn stover for high yield and lower polydispersity lignin extraction with high-boiling alkaline solvent

The influence of different parts of corn stover on lignin extraction was investigated. Five kinds of lignin were isolated by the high boiling point solvent extraction from the whole corn stover and four different parts including leaf, husk, bark and pith. The optimal condition was obtained: 6.25 g/L NaOH, 140 °C, 1 h and 60% (v/v) 1,4-butanediol. The extracted lignins were then characterized. FT-IR analysis revealed that all of the lignins were typically herbaceous. The lignin extracted from husk contained more S unit. Gel permeation chromatography analysis showed that it was necessary to separate corn stover into different parts to obtain low polydispersity lignin. The SEM and FT-IR analysis proved that the lignin dissolution was related to the tightness structure presenting a positive correlation with hydrogen bond index.

Investigating desorption during ethanol elution to improve the quality and antioxidant activity of xylo-oligosaccharides from corn stalk

As the most representative of lignocellulosic materials, corn stalk (CS) will be a great candidate to produce xylo-oligosaccharides (XOS). Owing to the high impurity content of the XOS produced by directly enzymatic hydrolysis of xylan extracted from CS, subsequent refining steps are essential. The present study was aimed to investigate desorption during ethanol elution to improve the quality and antioxidant activity of XOS from CS. The desorption was systematically investigated after optimizing the elution conditions. The results showed that it had an elution watershed when the volume ratio was 2:1. More interestingly, XOS had a obvious priorities of desorption during ethanol gradient elution. The highest purity of XOS was 98.12% from 30% ethanol eluate. Antioxidant activity assay showed that the highest radical scavenging activity of XOS was 89.89% obtained from 70% ethanol eluate at a concentration of 3 mg/mL, which could be used in antioxidant food, feed additives.

Pretreatment of wheat straw leads to structural changes and improved enzymatic hydrolysis

Wheat straw (WS) is a potential biomass for production of monomeric sugars. However, the enzymatic hydrolysis ratio of cellulose in WS is relatively low due to the presence of lignin and hemicellulose. To enhance the enzymatic conversion of WS, we tested the impact of three different pretreatments, e.g. sulfuric acid (H₂SO₄), sodium hydroxide (NaOH), and hot water pretreatments to the enzymatic digestions. Among the three pretreatments, the highest cellulose conversion rate was obtained with the 4% NaOH pretreatment at 121 °C (87.2%). In addition, NaOH pretreatment was mainly effective in removing lignin, whereas the H₂SO₄ pretreatment efficiently removed hemicellulose. To investigate results of pretreated process for enhancement of enzyme-hydolysis to the WS, we used scanning electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy to analyze structural changes of raw and treated materials. The structural analysis indicated that after H₂SO₄ and NaOH pretreatments, most of the amorphous cellulose and partial crystalline cellulose were hydrolyzed during enzymatic hydrolysis. The findings of the present study indicate that WS could be ideal materials for production of monomeric sugars with proper pretreatments and effective enzymatic base hydrolysis.

Feasibility of polyethylene composites reinforced by distillers dried fibers with solubles (DDFS) after different generations of ethanol fermentation

In order to effectively evaluate the distillers dried fibers with solubles (DDFS) obtained from biorefinery processes, sorghum distiller (SD), cassava distiller (CD) and corn cob distiller (CCD) residuals from different generation bioethanol plants were used as the reinforcing phase for polyethylene composites. The mechanical performances and the physical properties of the polyethylene/DDFS composites were evaluated. The results showed that the CCD reinforced specimen offered the best mechanical performances, with a flexural strength of 21.8 ± 2.2 MPa and a tensile strength of 39.7 ± 3.2 MPa. After multigelation, the retention ratios of the rupture modulus and the elasticity modulus of the CCD reinforced specimen reached 88.7 ± 6.7% and 84.1 ± 2.7%, while after 2000 h of xenon lamp weathering they reached 96.2 ± 4.7% and 82 ± 1.8%, respectively. Hybridizing the biorefinery process with the process of composites production was feasible.

Flowchart of the process for prepares polyethylene/DDFS composites. Solid residuals after 1 G, 1.5 G and 2 G SSF bioethanol plants were used as the reinforcement.

Improvement of cellulolytic enzyme production and performance by rational designing expression regulatory network and enzyme system composition

Filamentous fungi are considered as the most efficient producers expressing lignocellulose-degrading enzymes. Penicillium oxalicum strains possess extraordinary fungal lignocellulolytic enzyme systems and can efficiently utilize plant biomass. In recent years, the regulatory aspects of production of hydrolytic enzymes by P. oxalicum have been well established. This review aims to discuss the recent developments for the production of lignocellulolytic enzymes by P. oxalicum. The main cellulolytic transcription factors mediating the complex transcriptional-regulatory network are highlighted. The genome-wide identification of cellulolytic transcription factors, the cascade regulation network for cellulolytic gene expression, and the synergistic and dose-controlled regulation by cellulolytic regulators are discussed. A cellulase regulatory network sensitive to inducers in intracellular environments, the cross-talk of regulation of lignocellulose-degrading enzyme and amylase, and accessory enzymes are also demonstrated. Finally, strategies for the metabolic engineering of P. oxalicum, which show promising applications in the enzymatic hydrolysis for biochemical production, are established.

Potential of Brachiaria mutica (Para grass) for bioethanol production from Loktak Lake

The aim of present study was to evaluate feasibility of using the Para grass as feedstock for production of bioethanol. Process involved the pretreatment with dilute acid or alkali and followed by enzymatic saccharification with commercial cellulase. Maximum sugar release of 696mg/g was obtained from 10% biomass loading and 0.5% w/v of alkali whereas in the case of acid pretreatment maximum sugar of 660mg/g was obtained from 20% biomass loading and 2% w/v acid loading. Results showed that Para grass utilization as a biorefinery feedstock can be a potential strategy to address the sustainable utilization of this invasive grass thereby keeping its population in check in the Loktak Lake.

Pretreatment of corn stover by solid acid for d-lactic acid fermentation

Solid acid is a new acid that is safe and green, which has been widely used in the fields of acid pickling. In this study, we adopted solid acid to pretreat corn stover and used the pretreated corn stover in the fermentation of d-lactic acid. Finally, we obtained optimal conditions for the pretreatment of corn stover by solid acid: digestion temperature of 120°C, digestion time of 80min, and solid acid concentration of 1.5%. Then adding cellulase of 30FPU/g, the conversion rate of glucose reached 71.06% after enzymatic hydrolysis for 72h. In addition, the changes of corn stover structure after pretreatment were further represented by using scanning electron microscope (SEM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). At the same time, we used the pretreated corn stover as fermentation substrate and Lactobacillus. delbrueckii sp. bulgaricus as the starting strain to produce d-lactic acid. The yield reached 18g/L, with the optical purity being 99%e.e. This research has provided a new way to comprehensively utilizae corn stover.

Green synthesis of bacterial cellulose via acetic acid pre-hydrolysis liquor of agricultural corn stalk used as carbon source

Herein, bacterial cellulose (BC) was synthesized by acetobacter xylinum via organic acid pre-hydrolysis liquor of agricultural corn stalk used as carbon source. Acetic acid was applied to pretreat the corn stalk, then, the prehydrolysate was detoxified by sequential steps of activated carbon and ion exchange resin treatment prior to use as carbon source to cultivate acetobacter xylinum. Moreover, the recovery of acetic acid was achieved for facilitating the reduction of cost. The results revealed that the combination method of detoxification treatment was very effective for synthesis of BC, yield could be up to 2.86g/L. SEM analysis showed that the diameter size of BC between 20 and 70mm. In summary, the process that bacterial cellulose was biosynthesized via prehydrolysate from agricultural corn stalk used as carbon source is feasible, and the ability to recover organic acid make it economical, sustainable and green, which fits well into the biorefinery concept.

Enhanced fuel ethanol production from rice straw hydrolysate by an inhibitor-tolerant mutant strain of Scheffersomyces stipitis

A novel process for bioethanol production from lignocellulosic biomass using an inhibitor-tolerant mutant strain of Scheffersomyces stipitis and cell-recycling continuous fermentation.