Microwave-assisted inorganic salt pretreatment of sugarcane leaf waste: Effect on physiochemical structure and enzymatic saccharification

Evaluation of co-culture of cellulolytic fungi for enhanced cellulase and xylanase activity and saccharification of untreated lignocellulosic material

Bioethanol production from lignocellulosic materials is hindered by the high costs of pretreatment and the enzymes. The present study aimed to evaluate whether co-cultivation of four selected cellulolytic fungi yields higher cellulase and xylanase activities compared to the monocultures and to investigate whether the enzymes from the co-cultures yield higher saccharification on selected plant materials without thermo-chemical pretreatment. The fungal isolates, Trichoderma reesei F118, Penicillium javanicum FS7, Talaromyces sp. F113, and Talaromyces pinophilus FM9, were grown as monocultures and binary co-cultures under submerged conditions for 7 days. The cellulase and xylanase activities of the culture filtrates were measured, and the culture filtrates were employed for the saccharification of sugarcane leaves, Guinea grass leaves, and water hyacinth stems and leaves. Total reducing sugars and individual sugars released from each plant material were quantified. The co-culture of Talaromyces sp. F113 with Penicillium javanicum FS7 and of T. reesei F118 with T. pinophilus FM9 produced significantly higher cellulase activities compared to the corresponding monocultures whereas no effect was observed on xylanase activities. Overall, the highest amounts of total reducing sugars and individual sugars were obtained from Guinea grass leaves saccharified with the co-culture of T. reesei F118 with T. pinophilus FM9, yielding 63.5% saccharification. Guinea grass leaves were found to be the most susceptible to enzymatic saccharification without pre-treatment, while water hyacinth stems and leaves were the least. Accordingly, the study suggests that fungal co-cultivation could be a promising approach for the saccharification of lignocellulosic materials for bioethanol production.

Bioethanol Production from Characterized Pre-treated Sugarcane Trash and Jatropha Agrowastes

Low production costs and a potential feedstock supply make lignocellulosic ethanol (bioethanol) an important source of advanced biofuels. The physical and chemical preparation of this kind of lignocellulosic feedstock led to a high ethanol yield. In order to increase the yield of fermentable sugars, pretreatment is an essential process step that alters the lignocellulosic structure and improves its accessibility for the expensive hydrolytic enzymes. In this context, the chemical composition of sugarcane trash (dry leaves, green leaves, and tops) and jatropha (shell and seed cake) was determined to be mainly cellulose, hemicellulose, and lignin. Hydrogen peroxide and sodium hydroxide were applied in an attempt to facilitate the solubilization of lignin and hemicelluloses in five agrowastes. The extraction of hydrogen peroxide was much better than that of sodium hydroxide. A comparative study was done using SEM, EDXA, and FTIR to evaluate the difference between the two methods. The pretreated wastes were subjected to saccharification by commercial cellulases (30 IU/g substrate). The obtained glucose was fortified with nutrients and fermented statically by Saccharomyces cerevisiae F-307 for bioethanol production. The results revealed the bioethanol yields were 325.4, 310.8, 282.9, 302.4 and 264.0 mg ethanol/g treated agrowastes from green leaves of sugarcane, jatropha deolied seed cake, tops sugarcane, dry leaves of sugarcane, and jatropha shell, respectively. This study emphasizes the value of lignocellulosic agricultural waste as a resource for the production of biofuels as well as the significance of the extraction process.

Sustainable process for fractionation of lignin by the microwave-assisted chemical additive approach: Towards sugarcane leaf biorefinery and characterization

The microwave assisted pretreatment on sugarcane leaf (SCL) biomass for delignification was studied to enhance cellulose digestibility. In this work, microwave assisted with additives were used to delignification SCL for maximize sugar yield recovery. Single factorial and Central composite design (CCD) were employed to optimize the microwave assisted pretreatment conditions for improve delignification efficiency and the sugar yield recovery. The optimized pretreatment conditions were determined to be 4 min pre-treatment time, 500 W microwave power, 1.0 M Na2CO3 and 10 % biomass loading condition produce maximum reducing sugar yield (601 mg g-1) and glucose sugar yield (231 mg g-1) were achieved during saccharification. Pretreated biomass produced reducing sugar and glucose yields that were 4.5 and 4.1 times higher than those of untreated (native) SCL-N biomass, respectively. Additionally, the recyclability study of black liquor, obtained from optimized conditioned treatment of SCL-MSC (Microwave-assisted sodium carbonate pretreated SCL) resulted in considerable saccharification yield up to three pretreatment cycles. The 1H NMR and 13C NMR spectra studies illustrate that aromatic units present in SCL fractionated lignin samples. The variations of structure features and chemical compositions of the raw and pretreated SCL biomass were analyzed by SEM, XRD and XPS analysis. Overall, SCL-MSC pretreatment condition significantly delignification of SCL and led to the maximum sugar production optimized strategies pretreatment conditions was produced maximum amount of sugar, which is great potential for bio-refinery product development.

Surfactant assisted microwave irradiation pretreatment of corncob: Effect on hydrogen production capacity, energy consumption and physiochemical structure

The combination pretreatment strategy is an effective way to intensify photo-fermentative biohydrogen production (PFHP) process. In this study, the synergistic effects of microwave irradiation and surfactants on the hydrogen production performance, energy analysis and structural characteristics was evaluated. Results revealed that hydrogen production performance was improved after microwave irradiation pretreatment (MIP) and surfactants assisted microwave irradiation pretreatment (SMIP). SMIP group had a higher cumulative hydrogen yield (CHY) of 367.87 ± 6.481 mL compared with control group (223.26 ± 4.329 mL) and MIP group (303.66 ± 3.366 mL), which was an increase of 36.01% and 64.77%, respectively. Energy evaluation analysis showed that the energy ratio of SMIP (0.49) was higher than that of MIP (0.37) in the PFHP system, therefore, SMIP can save more energy. After SMIP, the corncob lignocellulose structure was greatly damaged, which was verified by SEM, FTIR, XRD and XPS analyses.

Role of Combined Na2HPO4 and ZnCl2 in the Unprecedented Catalysis of the Sequential Pretreatment of Sustainable Agricultural and Agro-Industrial Wastes in Boosting Bioethanol Production

Improper lignocellulosic waste disposal causes severe environmental pollution and health damage. Corn Stover (CS), agricultural, and aseptic packaging, Tetra Pak (TP) cartons, agro-industrial, are two examples of sustainable wastes that are rich in carbohydrate materials and may be used to produce valuable by-products. In addition, attempts were made to enhance cellulose fractionation and improve enzymatic saccharification. In this regard, these two wastes were efficiently employed as substrates for bioethanol production. This research demonstrates the effect of disodium hydrogen phosphate (Na₂HPO₄) and zinc chloride (ZnCl₂) (NZ) as a new catalyst on the development of the sequential pretreatment strategy in the noticeable enzymatic hydrolysis. Physico-chemical changes of the native and the pretreated sustainable wastes were evaluated by compositional analysis, scanning electron microscopy (SEM), X-ray diffractometry (XRD), Fourier transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA). These investigations showed major structural changes after the optimized sequential pretreatment. This pretreatment not only influences the delignification process, but also affects the functionalization of cellulose chemical structure. NZ released a higher glucose concentration (328.8 and 996.8 mg/dl) than that of ZnCl₂ (Z), which released 203.8 and 846.8 mg/dl from CS and TP, respectively. This work led to the production of about 500 mg/dl of ethanol, which is promising and a competitor to other studies. These findings contribute to increasing the versatility in the reuse of agricultural and agro-industrial wastes to promote interaction areas of pollution prevention, industrialization, and clean energy production, to attain the keys of sustainable development goals.

Biodegradation Potential of Bacillus sp. PAH-2 on PAHs for Oil-Contaminated Seawater

Microbial degradation is a useful tool for inhibiting or preventing polycyclic aromatic hydrocarbons (PAHs) widely distributed in marine environment after oil spill accidents. This study aimed to evaluate the potential and diversity of bacteria Bacillus sp. PAH-2 on Benzo (a) anthracene (BaA), Pyrene (Pyr), and Benzo (a) pyrene (BaP), their composite system, aromatic components system, and crude oil. The seven-day degradation rates against BaA, Pyr, and BaP were 20.6%, 12.83%, and 17.49%, respectively. Further degradation study of aromatic components demonstrated PAH-2 had a high degradation rate of substances with poor stability of molecular structure. In addition, the degradation of PAHs in crude oil suggested PAH-2 not only made good use of PAHs in such a more complex structure of pollutants but the saturated hydrocarbons in the crude oil also showed a good application potential.

Seawater-based biorefineries: A strategy to reduce the water footprint in the conversion of lignocellulosic biomass

Biorefineries are an essential step towards implementing a circular economy in the long term. They are based on renewable raw materials and must be designed holistically, recovering building blocks from being converted into several products. Lignocellulosic biomass is considered a critical pillar for a biologically based economy and a high value-added feedstock. The separation of the structural complexity that makes up the biomass allows the development of different product flows. Chemical, physical, and biological processes are evaluated for fractionation, hydrolysis, and fermentation processes in biorefineries; however, the volume of freshwater used affects water safety and increases the economic costs. Non-potable-resources-based technologies for biomass bioconversion are essential for biorefineries to become environmentally and economically sustainable systems. Studies are being carried out to substitute freshwater with seawater to reduce the water footprint. Accordingly, this review addresses a comprehensive discussion about seawater-based biorefineries focusing on lignocellulosic biomass conversion in biofuel and value-added products.

Insight into the recent advances of microwave pretreatment technologies for the conversion of lignocellulosic biomass into sustainable biofuel

The utilization of renewable lignocellulosic biomasses for bioenergy synthesis is believed to facilitate competitive commercialization and realize affordable clean energy sources in the future. Among the pathways for biomass pretreatment methods that enhance the efficiency of the whole biofuel production process, the combined microwave irradiation and physicochemical approach is found to provide many economic and environmental benefits. Several studies on microwave-based pretreatment technologies for biomass conversion have been conducted in recent years. Although some reviews are available, most did not comprehensively analyze microwave-physicochemical pretreatment techniques for biomass conversion. The study of these techniques is crucial for sustainable biofuel generation. Therefore, the biomass pretreatment process that combines the physicochemical method with microwave-assisted irradiation is reviewed in this paper. The effects of this pretreatment process on lignocellulosic structure and the ratio of achieved components were also discussed in detail. Pretreatment processes for biomass conversion were substantially affected by temperature, irradiation time, initial feedstock components, catalyst loading, and microwave power. Consequently, neoteric technologies utilizing high efficiency-based green and sustainable solutions should receive further focus. In addition, methodologies for quantifying and evaluating effects and relevant trade-offs should be develop to facilitate the take-off of the biofuel industry with clean and sustainable goals.

Preparation of Furfural From Xylose Catalyzed by Diimidazole Hexafluorophosphate in Microwave

In this work, functionalized alkyl imidazolium hexafluorophosphate ILs were synthesized and characterized; then, they were applied in the conversion of xylose to furfural under the microwave method. The results showed that when C_nMF was used as a catalyst, an acidic environment was provided to promote the formation of furfural. In addition, the heating method, the solvent, and the different structures of cations in the ionic liquid influenced their catalytic activity. In an aqueous solution, the yield of furfural obtained using the microwave method was better than that of the conventional heating method, and the catalytic activity of diimidazole hexafluorophosphate was better than that of monoimidazole. Meanwhile, for the diimidazole hexafluorophosphate, the change of the carbon chain length between the imidazole rings also slightly influenced the yield. Finally, the optimal yield of 49.76% was obtained at 205°C for 8 min using 3,3′-methylenebis(1-methyl-1H-imidazol-3-ium), C₁MF, as a catalyst. Mechanistic studies suggested that the catalytic activity of C₁MF was mainly due to the combined effect of POF_n (OH)_3-n and imidazole ring. Without a doubt, the catalytic activity of C₁MF was still available after five cycles, which not only showed its excellent catalytic activity in catalyzing the xylose to prepare the biomass platform compound furfural but also could promote the application of functionalized ionic liquids.

Differential effects of inorganic salts on cellulase kinetics in enzymatic saccharification of cellulose and lignocellulosic biomass

Inorganic salt pretreatment of lignocellulosic biomass has proven to be an efficient way to increase the efficiency of enzymatic saccharification. However, it is not clear that this improvement is the result of modification of the lignocellulosic substrate after pretreatment, or removal of inhibitor, or enhancement of cellulase or a combination of these events. Therefore, this study aimed to analyze the effects of inorganic salts on kinetics of cellulase enzymes (celluclast 1.5L and accellerase 1500). Two substrates rich in cellulose content [carboxymethylcellulose (CMC), avicel (AV)] and lignocellulose substrate [sugarcane bagasse (SB)] were considered. The enzymatic saccharification was carried with and without the addition of inorganic salts (NaCl and KCl) at 0.5 M and 1.0 M concentration. The kinetic parameters, K_m and V_m, were determined to mechanically understand the pattern of inhibition and enhancement of inorganic salts on enzymatic saccharification. The kinetics parameters of celluclast 1.5L and accellerase 1500 for hydrolysis of CMC and AV with NaCl showed uncompetitive inhibition. Whereas, influences of KCl on both cellulase were differentiated to function in inhibition or enhancement modes when challenged with different substrates. On the other hand, enzymatic hydrolysis efficiencies of SB using both cellulases were enhanced under addition of NaCl and KCl, by increasing V_m of celluclast 1.5L from 0.303 to 0.635 mg/mL min (0.5 M KCl) and accellerase 1500 from 0.383 to 0.719 mg/mL min (1.0 M NaCl). The details of kinetic analysis in this work revealed the mechanism of inorganic salts on cellulase kinetics to be involved in substrate modification and removal of inhibitor.

Cellulose Recovery from Agri-Food Residues by Effective Cavitational Treatments

Residual biomass from agri-food production chain and forestry are available in huge amounts for further valorisation processes. Delignification is usually the crucial step in the production of biofuels by fermentation as well as in the conversion of cellulose into high added-value compounds. High-intensity ultrasound (US) and hydrodynamic cavitation (HC) have been widely exploited as effective pretreatment techniques for biomass conversion and in particular for cellulose recovery. Due to their peculiar mechanisms, cavitational treatments promote an effective lignocellulosic matrix dismantling with delignification at low temperature (35–50 °C). Cavitation also promotes cellulose decrystallization due to a partial depolymerization. The aim of this review is to highlight recent advances in US and HC-assisted delignification and further cellulose recovery and valorisation.

Two-Step Saccharification of the Xylan Portion of Sugarcane Waste by Recombinant Xylanolytic Enzymes for Enhanced Xylose Production

Sugarcane bagasse (SB) and sugarcane trash (SCT) containing 30% hemicellulose content are the waste from the sugarcane industry. Hemicellulose being heterogeneous, more complex, and less abundant than cellulose remains less explored. The optimized conditions for the pretreatment of SB and SCT for maximizing the delignification are soaking in aqueous ammonia (SAA), 18.5 wt %, followed by heating at 70 °C for 14 h. The optimization of hydrolysis of SAA pretreated (ptd) SB and SCT by the Box-Behnken design in the first step of saccharification by xylanase (CtXyn11A) and α-l-arabinofuranosidase (PsGH43_12) resulted in the total reducing sugar (TRS) yield of xylooligosaccharides (TRS_(XOS)) of 93.2 mg/g ptd SB and 85.1 mg/g ptd SCT, respectively. The second step of saccharification by xylosidase (BoGH43) gave the TRS yield of 164.7 mg/g ptd SB and 147.2 mg/g ptd SCT. The high-performance liquid chromatography analysis of hydrolysate obtained after the second step of saccharification showed 69.6% xylan-to-xylose conversion for SB and 64.1% for SCT. This study demonstrated the optimization of the pretreatment method and of the enzymatic saccharification by recombinant xylanolytic enzymes, resulting in the efficient saccharification of ptd hemicellulose to TRS by giving 73.5% conversion for SB and 71.1% for SCT. These optimized conditions for the pretreatment and saccharification of sugarcane waste can also be used at a large scale.

Studies on laccase mediated conversion of lignin from ginseng residues for the production of sugars

The purpose of this study was to determine the production of sugars from ginseng residues treated with laccase. Laccase was used to degrade lignin from ginseng residues in order to increase the yield of sugars. Reaction conditions, including solid loading, pH, enzyme concentration, incubation temperature, and incubation time, were investigated and optimized. The results showed that the optimum conditions were 20% of solid loading (w/v), pH 7, 300 IU/ml, temperature of 40 °C and incubation time of 6 h. The minimum residual lignin obtained was 59.89%. The results also showed that 56.58% sugars including 12.04% water soluble polysaccharides (WSP), 16.24% water insoluble polysaccharides (WIP) and 5.08% reducing sugar were afforded from delignify substance. Chemical characters of these sugars were analyzed. Pretreat of laccase delignification for sugars production is expected to be applied to other herbal residues.

Critical overview of biomass feedstocks as sustainable substrates for the production of polyhydroxybutyrate (PHB)

Polyhydroxybutyrates (PHBs) are a class of biopolymers produced by different microbial species and are biodegradable and biocompatible in nature as opposed to petrochemically derived plastics. PHBs have advanced applications in medical sector, packaging industries, nanotechnology and agriculture, among others. PHB is produced using various feedstocks such as glycerol, dairy wastes, agro-industrial wastes, food industry waste and sugars. Current focus on PHB research has been primarily on reducing the cost of production and, on downstream processing to isolate PHB from cells. Recent advancements to improve the productivity and quality of PHB include genetic modification of producer strain and modification of PHB by blending to develop desirable properties suited to diversified applications. Selection of feedstock plays a critical role in determining the economic feasibility and sustainability of the process. This review provides a bird's eye view of the suitability of different waste resources for producing polyhydroxybutyrate; providing state-of the art information and analysis.

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.

The utilization of seawater for the hydrolysis of macroalgae and subsequent bioethanol fermentation

A novel seawater-based pretreatment process was developed to improve the hydrolysis yield of brown (Laminaria digitata), green (Ulva linza) and red (Porphyra umbilicalis) macroalgae. Pre-treated with 5% sulphuric acid at 121 °C, 15 minutes, L. digitata, U. linza and P. umbilicalis liberated 64.63 ± 0.30%, 69.19 ± 0.11% and 63.03 ± 0.04% sugar in seawater compared with 52.82 ± 0.16%, 45.93 ± 0.37% and 48.60 ± 0.07% in reverse-osmosis water, respectively. Low hydrolysis yields (2.6-11.7%) were observed in alkali and hydrothermal pretreatment of macroalgae, although seawater led to relatively higher yields. SEM images of hydrolyzed macroalgae showed that reverse-osmosis water caused contortions in the remaining cell walls following acid and hydrothermal pre-treatments in the L. digitata and U. linza samples. Fed-batch fermentations using concentrated green seaweed hydrolysates and seawater with marine yeast Wickerhamomyces anomalus M15 produced 48.24 ± 0.01 g/L ethanol with an overall yield of 0.329 g/g available sugars. Overall, using seawater in hydrolysis of seaweed increased sugar hydrolysis yield and subsequent bioethanol production.

Microwave-assisted cascade exploitation of giant reed (Arundo donax L.) to xylose and levulinic acid catalysed by ferric chloride

The present work aimed to investigate and optimize the selective exploitation of hemicellulose and cellulose fractions of the energy crop Arundo donax L. (giant reed), to give xylose and levulinic acid, respectively. In order to improve the sustainability of this process, a microwave-assisted hydrolysis in the presence of FeCl₃ was implemented using as substrate the raw biomass without any pretreatment process. The effects of the hydrolysis reaction conditions, such as temperature, reaction time, salt amount and biomass loading, on giant reed exploitation were investigated. In the first step, under the optimized conditions (150 °C, 2.5 min and 1.6 wt% FeCl₃), the xylose yield reached 98.2 mol%. In the second step, under the best conditions (190 °C, 30 min and 2.4 wt% FeCl₃), the levulinic acid yield was 57.6 mol%. This novel cascade approach ensured an extensive exploitation of giant reed polysaccharides working in the respect of Green Chemistry principles.

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.

Carbon dioxide anion radical as a tool to enhance lignin valorization

Lignin is particularly recalcitrant for valorization via the existing pretreatment methods due to its complex cross-linking polymeric network. The aim of this study is to develop a novel integrated pretreatment strategy to exploit the potential of lignocellulosic biomass as resource for production of biofuels and aromatic chemicals. In this regard, a novel UV/TiO₂/HCOOH reaction was proposed to systematically generate hydroxyl radical (OH) and carbon dioxide radical anion (CO₂^-) to depolymerize lignin. Usage of 2,3-dihydrobenzofuran as a simple probe molecule showed cleavage β-O-4 linkage occurred via H abstraction mechanism. The addition of methyl viologen as CO₂^- scavengers proved the presence of CO₂^- in this UV/TiO₂/HCOOH reaction. Lignin and wheat straw were used to investigate the effect of different parameters, including formic acid concentration and TiO₂ dosage, on the efficiency of the reaction. At optimized conditions, the highest phenolic concentrations attained were 173.431 and 66.802 mg/g lignin and wheat straw, respectively. A cycle test was designed with the aim to favor the complete consumption of formic acid through more pretreatment cycles for producing the highest possible Total Phenolic Compounds (TPC) in the liquid phase. After the third consecutive cycle, 103.651 ± 5.964 mg-TPC/g, was obtained. Meanwhile it was found the remaining wheat straw solid fibers used for biogas production, showed 11.0% increase biogas production and increased degradation rate compared to the untreated wheat straw.

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.

Development of artificial neural network tools for predicting sugar yields from inorganic salt-based pretreatment of lignocellulosic biomass

This study developed two Artificial Neural Network (ANN) tools for predicting sugar yields from inorganic salt-based pretreatment of lignocellulosic biomass. Pretreatment data from 90 experimental runs with 8 different input conditions were used to develop a microwave-based and a steam-based model. Both models exhibited high coefficients of determination (R²) of 0.97. Knowledge extraction revealed reducing sugar yields from the steam- and microwave-based models exhibited high sensitivity to both salt and alkali concentration. These models may be employed as initial screening tools in lignocellulosic bioprocesses, thereby potentially enhancing the economic and productivity of lignocellulosic-based bioprocesses.

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.

Effects of ferric chloride pretreatment and surfactants on the sugar production from sugarcane bagasse

An efficient pretreatment with various concentrations of FeCl₃ (0.005-0.2 mol/L) was developed to extract hemicellulose in sugarcane bagasse and enhance the enzymatic hydrolysis of cellulose in pretreated solids. It was found that 0.025 mol/L FeCl₃ pretreated substrate yielded a high glucose yield of 80.1% during enzymatic hydrolysis. Then the characterization of raw material and pretreated solids was carried out to better understand how hemicellulose removal affected subsequent enzymatic hydrolysis. In addition, Tween 80 and Bovine Serum Albumin (BSA) were added to promote enzymatic hydrolysis of pretreated substrate. Together with that obtained from pretreatment, the highest glucose yield reached 97.7% with addition of Tween 80, meanwhile, a reduction of 50% loading of enzyme yielded the same level of glucose. However, the increased yields with additives decreased gradually as the hydrolysis time was extended. Furthermore, the enhancement mechanisms of Tween 80 and BSA were determined.

Recent progress in homogeneous Lewis acid catalysts for the transformation of hemicellulose and cellulose into valuable chemicals, fuels, and nanocellulose

The evolution from petroleum-based products to the bio-based era by using renewable resources is one of the main research challenges in the coming years. Lignocellulosic biomass, consisting of inedible plant material, has emerged as a potential alternative for the production of biofuels, biochemicals, and nanocellulose-based advanced materials. The lignocellulosic biomass, which consists mainly of carbohydrate-based polysaccharides (hemicellulose and cellulose), is a green intermediate for the synthesis of bio-based products. In recent years, the re-engineering of biomass into a variety of commodity chemicals and liquid fuels by using Lewis acid catalysts has attracted much attention. Much research has been focused on developing new chemical strategies for the valorization of different biomass components. Homogeneous Lewis acid catalysts seem to be one of the most promising catalysts due to their astonishing features such as being less corrosive to equipment and being friendlier to the environment, as well as having the ability to disrupt the bonding system effectively and having high selectivity. Thus, these catalysts have emerged as important tools for the highly selective transformation of biomass components into valuable chemicals and fuels. This review provides an insightful overview of the most important recent developments in homogeneous Lewis acid catalysis toward the production and upgrading of biomass. The chemical valorization of the main components of lignocellulosic biomass (hemicellulose and cellulose), the reaction conditions, and process mechanisms are reviewed.

A green and sustainable approach on statistical optimization of laccase mediated delignification of sugarcane tops for enhanced saccharification

Bioethanol production from lignocellulosic biomass is a promising approach towards finding an alternative for transportation fuels that is driven by the prerequisite to lessen our dependency on fossil fuels, increase energy security and mitigate greenhouse gas emission. Recalcitrance of lignocellulosic biomass is a major hindrance in bioethanol production. Hence, an efficient pretreatment method is necessary for degradation of lignin and providing accessibility of holocellulose for hydrolysis. In an attempt to overcome this bottleneck, laccase mediated delignification of sugarcane tops was studied using central composite design (CCD) based on response surface methodology (RSM). The effect of different process parameters such as temperature, pH, solid loading, enzyme titre and incubation time were evaluated. It was observed that under optimum conditions of pH 7, solid loading of 21% (w/v), enzyme titre of 430.3 IU/mL, temperature of 40 °C and incubation of 6 h, maximum delignification of 79.1% was achieved. Compositional analysis, energy density measurement and water retention capacity of the biomass was also conducted along with GC-MS analysis for identification of low molecular compounds formed during delignification. Structural characterization of the biomass before and after pretreatment process were analysed by Scanning Electron Microscopy (SEM), Fourier-Transform Infra-Red Spectroscopy (FTIR) and X-Ray Diffraction Spectroscopy (XRD) that further substantiated the delignification of sugarcane tops.

Synergistic effects of metal salt and ionic liquid on the pretreatment of sugarcane bagasse for enhanced enzymatic hydrolysis

High cost of ionic liquids (ILs) restricts the industrial application of IL-mediated lignocellulose pretreatment. In this study, a simple and economic technology for the pretreatment of natural lignocellulose was developed. The delignification capacity of aqueous choline ornithine ([Cho][Orn]) and hemicellulose-removal capacity of metal salt FeCl₂ were combined. The changes of morphological structure and composition indicated a synergistic interaction of [Cho][Orn] and FeCl₂ in the pretreatment process. The delignification and hemicellulose-removal capacity of aqueous [Cho][Orn]_50% solution was significantly improved in the presence of FeCl₂ by 28% and 53%, respectively. The combination use of FeCl₂ and [Cho][Orn] made it possible to save the amount of IL used for pretreatment in half. Enhancement effect of metal salts on the IL-pretreatment efficiency was proved.

Optimization of a novel sequential alkalic and metal salt pretreatment for enhanced delignification and enzymatic saccharification of corn cobs

This study presents a sequential sodium phosphate dodecahydrate (Na₃PO₄·12H₂O) and zinc chloride (ZnCl₂) pretreatment to enhance delignification and enzymatic saccharification of corn cobs. The effects of process parameters of Na₃PO₄·12H₂O concentration (5-15%), ZnCl₂ concentration (1-5%) and solid to liquid ratio (5-15%) on reducing sugar yield from corn cobs were investigated. The sequential pretreatment model was developed and optimized with a high coefficient of determination value (0.94). Maximum reducing sugar yield of 1.10±0.01g/g was obtained with 14.02% Na₃PO₄·12H₂O, 3.65% ZnCl₂ and 5% solid to liquid ratio. Scanning electron microscopy (SEM) and Fourier Transform Infrared analysis (FTIR) showed major lignocellulosic structural changes after the optimized sequential pretreatment with 63.61% delignification. In addition, a 10-fold increase in the sugar yield was observed compared to previous reports on the same substrate. This sequential pretreatment strategy was efficient for enhancing enzymatic saccharification of corn cobs.