Comparative study of alkaline hydrogen peroxide and organosolv pretreatments of sugarcane bagasse to improve the overall sugar yield

Fungal behavior and recent developments in biopulping technology

Biological pretreatment of wood chips by fungi is a well-known approach prior to mechanical- or chemical pulp production. For this biological approach, a limited number of white-rot fungi with an ability to colonize and selectively degrade lignin are used to pretreat wood chips allowing the remaining cellulose to be processed for further applications. Biopulping is an environmentally friendly technology that can reduce the energy consumption of traditional pulping processes. Fungal pretreatment also reduces the pitch content in the wood chips and improves the pulp quality in terms of brightness, strength, and bleachability. The bleached biopulps are easier to refine compared to pulps produced by conventional methodology. In the last decades, biopulping has been scaled up with pilot trials towards industrial level, with optimization of several intermediate steps and improvement of economic feasibility. Nevertheless, fundamental knowledge on the biochemical mechanisms involved in biopulping is still lacking. Overall, biopulping technology has advanced rapidly during recent decades and pilot mill trials have been implemented. The use of fungi as pretreatment for pulp production is in line with modern circular economy strategies and can be implemented in existing production plants. In this review, we discuss some recent advances in biopulping technology, which can improve mechanical-, chemical-, and organosolv pulping processes along with their mechanisms.

Novel Double Cross-Linked Acrylic Acid/Bagasse Cellulose Porous Hydrogel for Controlled Release of Citral and Bacteriostatic Effects

In this study, double cross-linked acrylic acid/bagasse cellulose (AA/BC) porous hydrogels were first prepared using cold plasma (CP) technology instead of chemical initiators. The structure and properties of porous hydrogels, as well as the controlled release and bacteriostatic application as functional carriers, were investigated. Results showed that a novel double cross-linked hydrogel had been successfully synthesized by utilizing ^•OH and H⁺ produced during plasma discharge. The acrylic acid (AA) monomers were successfully grafted onto the main chains of bagasse cellulose (BC), forming a porous three-dimensional network structure. The AA/BC porous hydrogels showed excellent swelling levels and intelligent responses. The release of citral in hydrogel inclusion compounds embedded with citral was controlled by adjusting the pH, and the slow release period was about 2 days. The inclusion compounds presented strong bacteriostatic effects against Escherichia coli and Staphylococcus aureus, extending the shelf life of fruits for about 4 days. Therefore, it can be concluded that CP technology is considered to be an efficient and environmental-friendly initiation technology for preparing hydrogels. The potential application of hydrogel inclusion compounds in the food field is expanded.

Biosurfactant promoted enzymatic saccharification of alkali‑pretreated reed straw

The decrease of cellulase activity and unproductive adsorption of lignin are important obstructive factors for inefficient enzymatic hydrolysis. This paper applied five different kinds of biosurfactants including rhamnolipid, sophorolipid, chitin, tea saponin, and sodium lignosulfonate in the enzymatic hydrolysis process of alkali-pretreated reed straw (RS) to enhance the saccharification efficiency. When 8 g/L sophorolipid is added, the efficiency of enzymatic hydrolysis is 91.68 %, which is 30.65 % higher than that without using any biosurfactant. The efficiency of enzymatic hydrolysis can be further increased to 99.56 % when 7.5 g/L sophorolipid and 1.5 g/L tea saponin are added together. This is because the sophorolipid, rhamnolipid, and chitin can synergistically hamper the enzymatic inactivation during enzymatic hydrolysis, while tea saponin and sodium lignosulfonate can inhibit the non-productive adsorption of lignin. This work proposed a very effective method to improve the efficiency of enzymatic hydrolysis and reduce the dosage of the enzyme by adding biosurfactants.

Comparative Study of Green and Traditional Routes for Cellulose Extraction from a Sugarcane By-Product

Sugarcane bagasse (SCB) is the main residue of the sugarcane industry and a promising renewable and sustainable lignocellulosic material. The cellulose component of SCB, present at 40-50%, can be used to produce value-added products for various applications. Herein, we present a comprehensive and comparative study of green and traditional approaches for cellulose extraction from the by-product SCB. Green methods of extraction (deep eutectic solvents, organosolv, and hydrothermal processing) were compared to traditional methods (acid and alkaline hydrolyses). The impact of the treatments was evaluated by considering the extract yield, chemical profile, and structural properties. In addition, an evaluation of the sustainability aspects of the most promising cellulose extraction methods was performed. Among the proposed methods, autohydrolysis was the most promising approach in cellulose extraction, yielding 63.5% of a solid fraction with ca. 70% cellulose. The solid fraction showed a crystallinity index of 60.4% and typical cellulose functional groups. This approach was demonstrated to be environmentally friendly, as indicated by the green metrics assessed (E(nvironmental)-factor = 0.30 and Process Mass Intensity (PMI) = 20.5). Autohydrolysis was shown to be the most cost-effective and sustainable approach for the extraction of a cellulose-rich extract from SCB, which is extremely relevant for aiming the valorization of the most abundant by-product of the sugarcane industry.

Modification of cellulose from sugarcane (Saccharum officinarum) bagasse pulp by cold plasma: Dissolution, structure and surface chemistry analysis

Cellulose is a most abundant natural biopolymer, however, the strong hydrogen bonding system makes cellulose hard to dissolve, limiting its further applications. In this study, an innovative cold plasma (CP) technology was used to modify cellulose from sugarcane (Saccharum officinarum) bagasse pulp. Dissolution, structure, and surface chemistry of cellulose before and after CP treatment were investigated. Results showed that the dissolution rate of cellulose after different CP treatment time (3-12 min) and operating voltage (40-70 kV) was significantly improved. Roughness, even holes (CP treatment 9 min with 50 kV) and breakage (CP treatment 9 min with 70 kV) were observed on the surface. The crystallinity index decreased from 62.31% (control) to 60.88% (CP treatment 3 min with 50 kV). The hydrogen bonding force was weakened and the peak intensity of CO and CO stretching vibration groups were enhanced. Therefore, CP-modified cellulose may be applied more in future, such as biological films for food future packaging.

Optimization of alkali-treated poplar fiber saccharification using metal ions and surfactants

In this study, contrary to untreated poplar fiber, processing of alkali-treated poplar fiber was optimized for the enzymatic saccharification. Considering reducing sugar content as the evaluation index, pH, temperature, time, amount of enzyme, and rotational speed of shaker were standardized to optimize the sugar production by enzymatic hydrolysis. Using response surface methodology, the optimum technological condition of enzymatic hydrolysis was found to be utilizing 43 mg cellulase at 46 °C for 50 h. At this, the sugar conversion amount of NaOH or H₂O₂-NaOH pretreated poplar was 164.62 mg/g and 218.82 mg/g respectively. It was a corresponding increase of 446.73% or 626.75% than that of poplar fiber without a pretreatment. At a low concentration, metal ions and surfactants promoted the conversion of reducing sugar. Especially, 0.01 g/L Mn²⁺ and 0.50 g/L hexadecyl trimethyl ammonium bromide (CTAB) produced the best effect and increased the conversion rate of reducing sugar by 23.62% and 21.44% respectively. Also, the effect of the combination of metal ions and surfactants was better than that of a single accelerator. By improving the enzymatic process, these findings could enhance the utilization of poplar fiber for the production of reducing sugar.

Briquetting of sugarcane bagasse as a proper waste management technology in Vietnam

The present research describes an application of high-pressure briquetting technology to the waste management of sugarcane processing in Vietnam. The amount of generated sugarcane bagasse was monitored during sugarcane processing within the street juice production in Hue city, Vietnam. Generated sugarcane bagasse was subjected to fuel parameters analysis within its suitability for direct combustion. The obtained sugarcane bagasse was converted into bio-briquette fuel by a high-pressure briquetting press and its mechanical quality was determined. Results proved that the proportion of generated sugarcane bagasse from whole sugarcane stem mass was equal to 35.45%. This indicated generation of an abundant amount of sugarcane bagasse worldwide in general. Fuel parameters analysis proved high quality level of low ash content = 0.97% and high calorific values (gross calorific value = 18.35 MJ·kg^-1, net calorific value = 17.06 MJ·kg^-1), which indicated good suitability for direct combustion processes. Indicators of mechanical quality proved the following observations: mechanical durability = 99.29%, compressive strength = 150.82 N∙mm^-1 and bulk density = 1022.44 kg·m^-3, with all these indicators representing positive results. In general, the observed results indicated suitability of sugarcane bagasse valorization within the production of bio-briquette fuel by using high-pressure briquetting technology. Finally, analysis of such waste biomass proved its great potential for energy recovery, thus, the advantage of its valorization within the sustainable technologies.

Wheat straw components fractionation, with efficient delignification, by hydrothermal treatment followed by facilitated ethanol extraction

Lignocellulosic biomass fractionaion into its three major components is critically important for efficient feedstock utilization. The hydrothermal-ethanol method has broad application as its first step, hydrothermal treatment, provides high hemicellulose separation efficiency. However, it severely inhibits the delignification on the subsequent ethanol extraction. In this study, the second step, ethanol extraction, was facilitated by the addition of 3% NaOH and 3% H₂O₂, resulting in a significant improvement of lignin separation (by 48.2%). SEM, AFM, XPS, and XRD were used to characterize the surface composition of the remaining solids (crude cellulose) while the structure of isolated lignin was characterized by FT-IR, CP/MAS 13C NMR, GPC and TGA. The lignin samples isolated with both facilitated and non-facilitated ethanol extraction were compared to elucidate the lignin removal mechanism. The results showed that lignin degradation and crosslinking/polymerization occur in parallel during both the hydrothermal treatment and ethanol extraction.

Theoretical modeling and experimental validation of hydrodynamic cavitation reactor with a Venturi tube for sugarcane bagasse pretreatment

A hydrodynamic cavitation reactor with a Venturi tube was modeled through a computational fluid dynamics approach in order to evaluate the influence of pressure ratio, diameter and length of the throat zone. A cavitation reactor equipped with a Venturi tube was built in accordance with the computational modeling results. Hydrodynamic cavitation assisted alkaline pretreatment was performed to evaluate the influence of NaOH concentration (1-5%), the weight to volume percentage of solid in liquid (1-5%) and the reaction time (20-60 min.) in the lignin removal. The response surface methodology was used to optimize pretreatment parameters for maximum lignin removal. The optimal condition was 4.90% of NaOH and a solid weight percentage in liquid of 2.03% in 58.33 min, resulting in a maximum removal of 56.01% of lignin. Hydrodynamic cavitation can be easy to employ, an efficient and promissory pretreatment tool.

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.

Morphological changes of lignin during separation of wheat straw components by the hydrothermal-ethanol method

The separation efficiencies of wheat straw components by hydrothermal treatment and ethanol extraction have been compared. The results showed that the lignin removal rate by two-step hydrothermal-ethanol method was significantly lower than that of single-step ethanol extraction. Microscopic and adsorption studies (using SEM/AFM, XPS and pore structure analysis) showed that during the hydrothermal treatment a large lignin fraction migrated from the intercellular layer and cell wall and deposited on the fiber surface. Furthermore, the deposited lignin then spread on the fiber surface to form a lignin coating layer, which prevented its dissolution in ethanol. Without prior heating, i.e., upon a single step ethanol extraction, the massive lignin deposition was avoided, presumably due to its efficient dissolution hindering its tight binding with carbohydrate polymers on the fiber surface. Therefore, the lignin removal efficiency was drastically reduced as a result of hydrothermal treatment compared to ethanol extraction.

Co-catalysis of magnesium chloride and ferrous chloride for xylo-oligosaccharides and glucose production from sugarcane bagasse

Inorganic salt treatment is a novel, high-yield, and environmentally friendly approach for the production of xylo-oligosaccharides from Sugarcane bagasse with degree of polymerization of 2-5. A xylo-oligosaccharides yield of 53.79% was obtained with 0.1 M MgCl₂ treatment at 180 °C/10 min, and 41.89% with 0.1 M FeCl₂ treatment at 140 °C/30 min. The xylo-oligosaccharides yield from the co-catalysis of 0.05 M FeCl₂ + 0.05 M MgCl₂ reached 54.68% (29.34% xylobiose and 20.94% xylotriose) at 140 °C/30 min. The co-catalysis not only effectively improved the xylobiose and xylotriose contents but also increased the total yield of xylo-oligosaccharides under mild reaction conditions. Additionally, the glucose yield observed from the solid residue after inorganic salt treatment was 71.62% by enzymatic hydrolysis. Mg²⁺ and Fe²⁺ are essential for good human health without separation from the system, therefore, the inorganic salt treatment can be potentially applied in the co-production of xylo-oligosaccharides and glucose.

A finalized determinant for complete lignocellulose enzymatic saccharification potential to maximize bioethanol production in bioenergy Miscanthus

BACKGROUND

Miscanthus is a leading bioenergy crop with enormous lignocellulose production potential for biofuels and chemicals. However, lignocellulose recalcitrance leads to biomass process difficulty for an efficient bioethanol production. Hence, it becomes essential to identify the integrative impact of lignocellulose recalcitrant factors on cellulose accessibility for biomass enzymatic hydrolysis. In this study, we analyzed four typical pairs of Miscanthus accessions that showed distinct cell wall compositions and sorted out three major factors that affected biomass saccharification for maximum bioethanol production.

RESULTS

Among the three optimal (i.e., liquid hot water, H₂SO₄ and NaOH) pretreatments performed, mild alkali pretreatment (4% NaOH at 50 °C) led to almost complete biomass saccharification when 1% Tween-80 was co-supplied into enzymatic hydrolysis in the desirable Miscanthus accessions. Consequently, the highest bioethanol yields were obtained at 19% (% dry matter) from yeast fermentation, with much higher sugar-ethanol conversion rates by 94-98%, compared to the other Miscanthus species subjected to stronger pretreatments as reported in previous studies. By comparison, three optimized pretreatments distinctively extracted wall polymers and specifically altered polymer features and inter-linkage styles, but the alkali pretreatment caused much increased biomass porosity than that of the other pretreatments. Based on integrative analyses, excellent equations were generated to precisely estimate hexoses and ethanol yields under various pretreatments and a hypothetical model was proposed to outline an integrative impact on biomass saccharification and bioethanol production subjective to a predominate factor (CR stain) of biomass porosity and four additional minor factors (DY stain, cellulose DP, hemicellulose X/A, lignin G-monomer).

CONCLUSION

Using four pairs of Miscanthus samples with distinct cell wall composition and varied biomass saccharification, this study has determined three main factors of lignocellulose recalcitrance that could be significantly reduced for much-increased biomass porosity upon optimal pretreatments. It has also established a novel standard that should be applicable to judge any types of biomass process technology for high biofuel production in distinct lignocellulose substrates. Hence, this study provides a potential strategy for precise genetic modification of lignocellulose in all bioenergy crops.

Enhancing enzymatic digestibility of waste wheat straw by presoaking to reduce the ash-influencing effect on autohydrolysis

BACKGROUND

The acid buffering capacity of high free ash in waste wheat straw (WWS) has been revealed to be a significant hindrance on the efficiency of autohydrolysis pretreatment. Previous researches have mainly relied on washing to eliminate the influence of ash, and the underlying mechanism of the ash influencing was not extensively investigated. Presently, studies have found that cations can destroy the acid buffering capacity of ash through cation exchange. Herein, different cations were applied to presoak WWS with the aim to overcome the negative effects of ash on autohydrolysis efficiency, further improving its enzymatic digestibility.

RESULTS

Results showed that cations can be adsorbed on the surface of the material by electrostatic adsorption to change the acid buffering capacity of WWS. The acid buffering capacity of 120 mM Fe²⁺ presoaked WWS is reduced from 226.3 mmol/pH-kg of original WWS to 79.3 mmol/pH-kg. This reduced the autohydrolysis pretreatment medium pH from 5.7 to 3.8 and promoted the removal of xylan from 61.7 to 83.7%. In addition, the enzymatic digestibility of WWS was enhanced from 49.7 to 86.3% by presoaking with 120 mM Fe²⁺ solution. The relationship between enzymatic accessibility and hydrophobicity with enzymatic digestibility of the autohydrolyzed WWS was analyzed.

CONCLUSIONS

The results showed that the acid buffering capacity of the high free ash was detrimental for the autohydrolysis efficiency of WWS. After WWS was presoaked with different cations, the acid buffering capacity of ash was weakened by cation exchange and electrostatic adsorption, which improved the autohydrolysis efficiency. The results expound that the enzymatic digestibility of WWS can be enhanced through presoaking to reduce the ash-influencing effect on autohydrolysis.

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.

Enhanced enzymatic hydrolysis of cellulose from waste paper fibers by cationic polymers addition

Cationic polymers (cationic polyacrylamide (CPAM), polyethyleneimine (PEI) or cationic starch (CS)) were used to enhance the enzymatic hydrolysis of waste paper fibers (WPFs) at 15% (w/w) solids concentration. Results showed that 0.05 g/L PEI, CPAM and CS resulted in 72.5%, 65.9% and 59.7% conversion of WPFs, increased by 15.4%, 8.8% and 2.6%, respectively, compared with control (57.1%). PEI was shown to have a larger effect than CPAM and CS, and generate a total sugar concentration of 73.9 g/L. Improvement in hydrolysis with cationic polymer addition is attributed to increased cellulase adsorption on cellulose through electrostatic attraction, rather than enhancement of cellulase activity. A patching/ bridging mechanism of cationic polymer enhancement of cellulose adsorption in cellulose is hypothesized. PEI exhibited maximum cellulose binding for polymers examined and appears to promote binding through a patching mechanism. CPAM and CS adsorbed a relatively low cellulase through bridging mechanism. In addition, enzyme loading could be reduced by addition of cationic polymers to obtain the same glucose yield, especially when PEI was used.

Influence of size reduction treatments on sugar recovery from Norway spruce for butanol production

This study investigated whether the effectiveness of pretreatment is limited by a size reduction of Norway spruce wood in biobutanol production. The spruce was milled, chipped, and mashed for hydrogen peroxide-acetic acid (HPAC) and dilute acid (DA) pretreatment. Sugar recoveries from chipped and mashed spruce after enzymatic hydrolysis were higher than from milled spruce, and the recoveries were not correlated with the spruce fiber length. HPAC pretreatment resulted in almost 100% glucose and 88% total reducing sugars recoveries from chipped spruce, which were apparently higher than DA pretreatment, demonstrating greater effectiveness of HPAC pretreatment on sugar production. The butanol and ABE yield from chipped spruce were 126.5 and 201.2 g/kg pretreated spruce, respectively. The yields decreased with decreasing particle size due to biomass loss in the pretreatment. The results suggested that Norway spruce chipped to a 20 mm length is applicable to the production of platform sugars for butanol fermentation.

Improving enzymatic hydrolysis efficiency of wheat straw through sequential autohydrolysis and alkaline post-extraction

In this work, a two-step pretreatment process of wheat straw was established by combining autohydrolysis pretreatment and alkaline post-extraction. The results showed that employing alkaline post-extraction to autohydrolyzed wheat straw could significantly improve its enzymatic hydrolysis efficiency from 36.0% to 83.7%. Alkaline post-extraction lead to the changes of the structure characteristics of autohydrolyzed wheat straw. Associations between enzymatic hydrolysis efficiency and structure characteristics were also studied. The results showed that the factors of structure characteristics such as delignification, xylan removal yield, crystallinity, accessibility and hydrophobicity are positively related to enzymatic hydrolysis efficiency within a certain range for alkaline post-extracted wheat straw. The results demonstrated that autohydrolysis coupled with alkaline post-extraction is an effective and promising method to gain fermentable sugars from biomass.

Combining sestc engineered A. niger with sestc engineered S. cerevisiae to produce rice straw ethanol via step-by-step and in situ saccharification and fermentation

The development of agricultural residue ethanol has a profound effect on the environment protection and energy supply. To increase the production efficiency of straw ethanol and reduce operation progress, the single-enzyme-system-three-cellulase gene (sestc) engineered Aspergillus niger and sestc engineered Saccharomyces cerevisiae were combined to produce ethanol using the pretreated rice straw as the substrate. The present results showed that both the step-by-step and in situ saccharification and fermentation can effectively produce ethanol using rice straw as the carbon substrate. The conversion rates of ethanol were 12.76 and 14.56 g per 1 kg of treated rice straw, respectively, via step-by-step and in situ processes. In situ process has higher ethanol conversion efficiency of rice straw and fewer operation processes as compared with step-by-step process. Therefore, in situ saccharification and fermentation is a more economical and effective pathway to convert rice straw into ethanol. This study provides a reference to the conversion of lignocellulosic residues into ethanol with a combination of two kinds of sestc engineered strains.

Single and binary adsorption of heavy metal ions from aqueous solutions using sugarcane cellulose-based adsorbent

A high efficient and eco-friendly sugarcane cellulose-based adsorbent was prepared in an attempt to remove Pb²⁺, Cu²⁺ and Zn²⁺ from aqueous solutions. The effects of initial concentration of heavy metal ions and temperature on the adsorption capacity of the bioadsorbent were investigated. The adsorption isotherms showed that the adsorption of Pb²⁺, Cu²⁺ and Zn²⁺ followed the Langmuir model and the maximum adsorptions were as high as 558.9, 446.2 and 363.3mg·g^-1, respectively, in single component system. The binary component system was better described with the competitive Langmuir isotherm model. The three dimensional sorption surface of binary component system demonstrated that the presence of Pb²⁺ decreased the sorption of Cu²⁺, but the adsorption amount of other metal ions was not affected. The result from SEM-EDAX revealed that the adsorption of metal ions on bioadsorbent was mainly driven by coordination, ion exchange and electrostatic association.

Enhancement of ethanol production from green liquor-ethanol-pretreated sugarcane bagasse by glucose-xylose cofermentation at high solid loadings with mixed Saccharomyces cerevisiae strains

BACKGROUND

Efficient cofermentation of glucose and xylose is necessary for economically feasible bioethanol production from lignocellulosic biomass. Here, we demonstrate pretreatment of sugarcane bagasse (SCB) with green liquor (GL) combined with ethanol (GL-Ethanol) by adding different GL amounts. The common Saccharomyces cerevisiae (CSC) and thermophilic S. cerevisiae (TSC) strains were used and different yeast cell mass ratios (CSC to TSC) were compared. The simultaneous saccharification and cofermentation (SSF/SSCF) process was performed by 5-20% (w/v) dry substrate (DS) solid loadings to determine optimal conditions for the co-consumption of glucose and xylose.

RESULTS

Compared to previous studies that tested fermentation of glucose using only the CSC, we obtained higher ethanol yield and concentration (92.80% and 23.22 g/L) with 1.5 mL GL/g-DS GL-Ethanol-pretreated SCB at 5% (w/v) solid loading and a CSC-to-TSC yeast cell mass ratio of 1:2 (w/w). Using 10% (w/v) solid loading under the same conditions, the ethanol concentration increased to 42.53 g/L but the ethanol yield decreased to 84.99%. In addition, an increase in the solid loading up to a certain point led to an increase in the ethanol concentration from 1.5 mL GL/g-DS-pretreated SCB. The highest ethanol concentration (68.24 g/L) was obtained with 15% (w/v) solid loading, using a CSC-to-TSC yeast cell mass ratio of 1:3 (w/w).

CONCLUSIONS

GL-Ethanol pretreatment is a promising pretreatment method for improving both glucan and xylan conversion efficiencies of SCB. There was a competitive relationship between the two yeast strains, and the glucose and xylose utilization ability of the TSC was better than that of the CSC. Ethanol concentration was obviously increased at high solid loading, but the yield decreased as a result of an increase in the viscosity and inhibitor levels in the fermentation system. Finally, the SSCF of GL-Ethanol-pretreated SCB with mixed S. cerevisiae strains increased ethanol concentration and was an effective conversion process for ethanol production at high solid loading.

Valorization of bamboo by γ-valerolactone/acid/water to produce digestible cellulose, degraded sugars and lignin

A novel pretreatment process was developed to achieve valorization of bamboo components into digestible cellulose, degraded sugars and lignin. In this case, bamboo was pretreated with 60% γ-valerolactone (GVL)/40% water containing 0.05mol/L H₂SO₄, yielding solid fraction rich in cellulose. The resulting liquor was further treated with the addition of NaCl and ultrasound, resulting in water phase rich in degraded sugars and GVL phase containing lignin, which was easy to recover. Results showed that the enzymatic hydrolysis was enhanced by 6.7-fold after treatment as compared to the control. The degraded sugars released in water phase contained monosaccharides (70.72-160.47g/kg) together with oligo- and polysaccharides (46.4-181.85g/kg). The lignin obtained had high purity, low molecular weight (1820-2970gmol^-1) and low polydispersity (1.93-1.98). The present study creates a novel pretreatment process for the conversion of Gramineae biomass into useful feedstocks with potential applications in the fields of fuels, chemicals and polymers.

Biological pretreatment of sugarcane bagasse with basidiomycetes producing varied patterns of biodegradation

This work evaluated sugarcane bagasse pretreatment with wood-decay fungi, producing varied patterns of biodegradation. The overall mass balance of sugars released after pretreatment and enzymatic hydrolysis indicated that a selective white-rot was necessary to provide glucose yields similar to the ones observed from leading physico-chemical pretreatment technologies. The selective white-rot Ceriporiopsis subvermispora was selective for lignin degradation in the lignocellulosic material, preserved most of the glucan fraction, and increased the cellulose digestibility of biotreated material. Glucose mass balances indicated that of the potential glucose of untreated bagasse, 47% was recovered as sugar-rich syrup after C. subvermispora biotreatment for 60days followed by enzymatic digestion of the pretreated material.

Saccharification of microalgae biomass obtained from wastewater treatment by enzymatic hydrolysis. Effect of alkaline-peroxide pretreatment

An enzymatic method for the carbohydrate hydrolysis of different microalgae biomass cultivated in domestic (DWB) and pig manure (PMWB) wastewaters, at different storage conditions (fresh, freeze-dried and reconstituted), was evaluated. The DWB provided sugars yields between 40 and 63%, although low xylose yields (< 23.5%). Approximately 2% of this biomass was converted to byproducts as succinic, acetic and formic acids. For PMWB, a high fraction of the sugars (up to 87%) was extracted, but mainly converted into acetic, butyric and formic acids, which was attributed to the bacterial action. In addition, the performance of an alkaline-peroxide pretreatment, conducted for 1h, 50°C and H2O2 concentrations from 1 to 7.5% (w/w), was essayed. The hydrolysis of pretreated microalgae supported a wide range of sugars extraction for DWB (55-90%), and 100% for PMWB. Nevertheless, a large fraction of these sugars (∼30% for DWB and 100% for PMWB) was transformed to byproducts.

Deconstruction of lignin linked p-coumarates, ferulates and xylan by NaOH enhances the enzymatic conversion of glucan

Thermo-assisted NaOH pretreatment to deconstruct xylan and lignin in sugar cane bagasse (SCB) is poorly understood. Hence, in this research it is was aimed to study the effect of NaOH pretreatment on the insoluble remaining lignin structures. Hereto, SCB milled fibres were pretreated using different dosages of NaOH at different temperatures and residence times. Of untreated SCB about 63% of the lignin compounds were assigned as p-coumarates and ferulates, analysed by pyrolysis-GC/MS as 4-vinyl phenol and 4-vinyl guaiacol, and designated as non-core lignin (NCL) compounds. More severe NaOH pretreatments resulted in lower xylan and lower lignin recoveries in the insoluble residues. Especially, the relative abundance of NCL decreased and this decrease followed a linear trend with the decrease in xylan. Core lignin compounds, analysed as phenol, guaiacol and syringol, accumulated in the residues. The decrease in residual xylan and NCL correlated positively with the enzymatic hydrolysis of the residual glucan.

Optimization study on the hydrogen peroxide pretreatment and production of bioethanol from seaweed Ulva prolifera biomass

The seaweed Ulva prolifera, distributed in inter-tidal zones worldwide, contains a large percentage of cellulosic materials. The technical feasibility of using U. prolifera residue (UPR) obtained after extraction of polysaccharides as a renewable energy resource was investigated. An environment-friendly and economical pretreatment process was conducted using hydrogen peroxide. The hydrogen peroxide pretreatment improved the efficiency of enzymatic hydrolysis. The resulting yield of reducing sugar reached a maximum of 0.42g/g UPR under the optimal pretreatment condition (hydrogen peroxide 0.2%, 50°C, pH 4.0, 12h). The rate of conversion of reducing sugar in the concentrated hydrolysates to bioethanol reached 31.4% by Saccharomyces cerevisiae fermentation, which corresponds to 61.7% of the theoretical maximum yield. Compared with other reported traditional processes on Ulva biomass, the reducing sugar and bioethanol yield are substantially higher. Thus, hydrogen peroxide pretreatment is an effective enhancement of the process of bioethanol production from the seaweed U. prolifera.

Comparative study of different alcoholate pretreatments for enhanced enzymatic hydrolysis of sugarcane bagasse

Pretreatment of sugarcane bagasse (SCB) with alcoholates, sodium methoxide (CH3ONa), potassium methoxide (CH3OK) and sodium ethoxide (C2H5ONa), was investigated. Analyses of lignocellulose composition and enzymatic saccharification indicated that C2H5ONa showed the highest enzymatic efficiency of 102.1%. The response surface optimization of C2H5ONa pretreatment showed that under optimal conditions (4% of C2H5ONa, 121°C, 1h), 65.4% of lignin was removed and the enzymatic efficiency reached 105.2%. Hydrolysis of SCB with cellulases and xylanase at a ratio of 4:1 showed the strongest synergism with reducing sugar production of 21g/L and conversion rates of cellulose and xylan reaching 110.4% and 94.5%, respectively. These results indicated that C2H5ONa is a promising alkali to pretreat SCB and the synergism between cellulases and xylanase has a significant effect on enzymatic saccharification of the pretreated SCB.

A biotechnological process efficiently co-produces two high value-added products, glucose and xylooligosaccharides, from sugarcane bagasse

In this study, a co-production of two high value-added products, glucose and xylooligosaccharides (XOS), was investigated by utilizing sugarcane bagasse (SB) within a multi-product bio-refinery framework optimized by Box-Behnken design-based response surface methodology. The developed process resulted in a maximum cellulose conversion of xylan-removed SB, 98.69±1.30%, and a maximum extracted SB xylan conversion into XOS (xylobiose and xylotriose) of 57.36±0.79% that was the highest SB xylan conversion reported in the literature, employing cellulase from Penicillium oxalicum EU2106 and recombinant endo-β-1,4-xylanase in Pichia pastoris. Consequently, a mass balance analysis showed that the maximum yields of glucose and XOS were 34.43±0.32g and 5.96±0.09 g per 100 g raw SB. Overall, this described process may be a preferred option for the comprehensive utilization of SB.

Recent advances in alcohol and organic acid fractionation of lignocellulosic biomass

Organosolv fractionation is a promising process to separate lignocellulosic biomass for the preparation of multiply products including biofuels, chemicals, and materials. This review presents the state of art of different processes applying alcohols and organic acids to treat lignocellulosic biomass for the production of ethanol, lignin, xylose, etc. The major organosolv technologies using ethanol, formic acid, and acetic acid, are intensively introduced and discussed in depth. In addition, the structural modifications of the major components of lignocelluloses, the technical processes, and the applications of the products were also summarized. The object of the review is to provide recent information in the field of organosolv process for the integrated biorefinery. The perspectives of the challenge and opportunity related to this topic are also presented.

Comparative study of simultaneous saccharification and fermentation byproducts from sugarcane bagasse using steam explosion, alkaline hydrogen peroxide and organosolv pretreatments

Most of the hemicelluloses were removed and more acetyl groups were generated after steam pretreatment, and a high acetic acid concentration was observed during SSF.