Pre-treatment of sugarcane bagasse with aqueous ammonia-glycerol mixtures to enhance enzymatic saccharification and recovery of ammonia

Higher efficiency of vanadate iron in heterogeneous Fenton-like systems to pretreat sugarcane bagasse and its enzymatic saccharification

Pretreatment is crucial for effective enzymatic saccharification of lignocellulose such as sugarcane bagasse (SCB). In the present study, SCB was pretreated with five kinds of heterogeneous Fenton-like systems (HFSs), respectively, in which α-FeOOH, α-Fe2O3, Fe3O4, and FeS2 worked as four traditional heterogeneous Fenton-like catalysts (HFCs), while FeVO4 worked as a novel HFC. The enzymatic reducing sugar conversion rate was then compared among SCB after different heterogeneous Fenton-like pretreatments (HFPs), and the optimal HFS and pretreatment conditions were determined. The mechanism underlying the difference in saccharification efficiency was elucidated by analyzing the composition and morphology of SCB. Moreover, the ion dissolution characteristics, variation of pH and Eh values, H2O2 and hydroxyl radical (·OH) concentration of FeVO4 and α-Fe2O3 HFSs were compared. The results revealed that the sugar conversion rate of SCB pretreated with FeVO4 HFS reached up to 58.25%, which was obviously higher than that under other HFPs. In addition, the surface morphology and composition of the pretreated SCB with FeVO4 HFS were more conducive to enzymatic saccharification. Compared with α-Fe2O3, FeVO4 could utilize H2O2 more efficiently, since the dissolved Fe3+ and V5+ can both react with H2O2 to produce more ·OH, resulting in a higher hemicellulose and lignin removal rate and a higher enzymatic sugar conversion rate. It can be concluded that FeVO4 HFP is a promising approach for lignocellulose pretreatment.

Sustainable valorization of sugarcane residues: Efficient deconstruction strategies for fuels and chemicals production

The global climate crisis and the ongoing increase in fossil-based fuels have led to an alternative solution of using biomass for fuel production. Sugarcane bagasse (SCB) is an agricultural residue with a global production of more than 100 million metric tons and it has various applications in a biorefinery concept. This review brings forth the composition, life cycle assessment, and various pretreatments for the deconstruction techniques of SCB for the production of valuable products. The ongoing research in the production of biofuels, biogas, and electricity utilizing the bagasse was elucidated. SCB is used in the production of carboxymethyl cellulose, pigment, lactic acid, levulinic acid, and xylooligosaccharides and it has prospective in meeting the demand for global energy and environmental sustainability.

Pretreatment of sugarcane bagasse with acid catalyzed ethylene glycol-water to improve the cellulose enzymatic conversion

In this work, HCl catalyzed ethylene glycol-water pretreatment (HCl/EG-H₂O) of sugarcane bagasse (SCB) was explored with response surface methodology (RSM) and single factor analysis, which aim to investigate the influence of pretreatment variable on pretreated solid cellulose enzymatic conversion. The result showed that HCl/EG-H₂O pretreatment could selectively extract ∼89.9 % xylan and ∼61.2 % lignin in SCB, meanwhile maintain a relatively high cellulose retention (∼86.8 %). Pretreatment of SCB at 120 °C for 60 min with 1.00 % HCl and 90 % EG obtained the pretreated solid having maximum cellulose enzymatic conversion of 88.7 % under 10 FPU/g enzyme dosage, this enhancement of cellulose enzymatic conversion mainly attributed to structure change of SCB in pretreatment. The adding of enzymatic additives into the hydrolysis process could not only improve hydrolysis efficiency but also lower the enzyme dosage. Besides, the linear relationship between substrate characteristic parameters (such cellulose content, lignin removal rate etc.) and cellulose conversion were observed.

Glycerol organosolv pretreatment can unlock lignocellulosic biomass for production of fermentable sugars: Present situation and challenges

The complex structure of lignocellulosic biomass forms the recalcitrance to prevent the embedded holo-cellulosic sugars from undergoing the biodegradation. Therefore, a pretreatment is often required for an efficient enzymatic lignocellulosic hydrolysis. Recently, glycerol organosolv (GO) pretreatment is revealed potent in selective deconstruction of various lignocellulosic biomass and effective improvement of enzymatic hydrolysis. Evidently, the GO pretreatment is capable to modify the structure of dissolved components by glycerolysis, i.e., by trans-glycosylation onto glyceryl glycosides and by hydroxylation grafting onto glyceryl lignin. Such modifications tend to protect these main components against excessive degradation, which can be mainly responsible for the obviously less fermentation inhibitors arising in the GO pretreatment. This pretreatment can provide opportunities for valorization of emerging lignocellulosic biorefinery with production of value-added biochemicals. Recent advances in GO pretreatment of lignocellulosic biomass followed by enzymatic hydrolysis are reviewed, and perspectives are made for addressing remaining challenges.

Biochemical properties of cellulolytic and xylanolytic enzymes from Sporotrichum thermophile and their utility in bioethanol production using rice straw

Production of cellulolytic and xylanolytic enzymes by Sporotrichum thermophile was enhanced using response surface methodology in solid-state fermentation (SSF) using wheat straw and cotton oil cake. Cellulolytic and xylanolytic enzymes were partially purified by ammonium sulfate precipitation followed by ion exchange and gel filtration chromatographic techniques. Xylanase of S. thermophile is neutral xylanase displaying optimal activity at 60 °C with K_m and V_max values of 0.2 mg/mL and 238.05 µmole/min, respectively. All cellulases produced by the thermophilic mold showed optimal activity at pH 5.0 and 60 °C with K_m values of 0.312 mg/mL, 0.113 mg/mL, and 0.285 mM for carboxymethyl cellulase (CMCase), filter paper cellulase (FPase), and β-glucosidase, respectively and while V_max values were 181.81, 138.88, and 66.67 µmole/min, respectively. The presence of various metal ions (Ca²⁺ and Co²⁺), chemical reagent (glutaraldehyde), and surfactants (Tween 80 and Triton X-100) significantly improved the activities of all enzymes. All the enzymes showed high storage stability under low temperature (-20 and 4 °C) conditions. Cellulolytic and xylanolytic enzymes resulted in enhanced liberation of reducing sugars (356.34 mg/g) by hydrolyzing both cellulosic and hemicellulosic fractions of ammonia-pretreated rice straw as compared to other pretreatment methods used in the study. Fermentation of enzymatic hydrolysate resulted in the formation of 28.88 and 27.18 g/L of bioethanol in separate hydrolysis and fermentation (SHF) process by Saccharomyces cerevisiae and Pichia stipitis, respectively. Therefore, cellulolytic and xylanolytic enzymes of S. thermophile exhibited ideal properties of biocatalysts useful in the saccharification of cellulosic and hemicellulosic fractions of rice straw for the production of bioethanol.

Biomass Fractionation and Lignin Fractionation towards Lignin Valorization

Lignin, as the most abundant aromatic biopolymer in nature, has attracted great attention due to the complexity and richness of its functional groups for value-added applications. The yield of production of lignin and the reactivity of prepared lignin are very important to guarantee the study and development of lignin-based chemicals and materials. Various fractionation techniques have been developed to obtain high yield and relatively high-purity lignin as well as carbohydrates (hemicelluloses and celluloses) and to reduce the condensed and degraded nature of conventional biorefinery lignin. Herein, novel and efficient biomass fractionation and lignin fractionation towards lignin valorization are summarized and discussed.

Evaluation of Ammonia Pretreatment for Enzymatic Hydrolysis of Sugarcane Bagasse to Recover Xylooligosaccharides

Sugarcane bagasse is a useful biomass resource. In the present study, we examined the efficacy of ammonia pretreatment for selective release of hemicellulose from bagasse. Pretreatment of bagasse with aqueous ammonia resulted in significant loss of xylan. In contrast, pretreatment of bagasse with anhydrous ammonia resulted in almost no xylan loss. Aqueous ammonia or anhydrous ammonia-pretreated bagasse was then subjected to enzymatic digestion with a xylanase from the glycoside hydrolase (GH) family 10 or a xylanase from the GH family 11. The hydrolysis rate of xylan in bagasse pretreated with aqueous ammonia was approximately 50 %. In contrast, in the anhydrous ammonia-treated bagasse, xylan hydrolysis was > 80 %. These results suggested that anhydrous ammonia pretreatment would be an effective method for preparation of sugarcane bagasse for enzymatic hydrolysis to recover xylooligosaccharides.

Recent advances on ammonia-based pretreatments of lignocellulosic biomass

Ammonia-based pretreatments have been extensively studied in the last decade as one of the leading pretreatment technologies for lignocellulose biorefining. Here, we discuss the key features and compare performances of several leading ammonia-based pretreatments (e.g., soaking in aqueous ammonia or SAA, ammonia recycled percolation or ARP, ammonia fiber expansion or AFEX, and extractive ammonia or EA). We provide detailed insight into the distinct physicochemical mechanisms employed during ammonia-based pretreatments and its impact on downstream bioprocesses (e.g., enzymatic saccharification); such as modification of cellulose crystallinity, lignin/hemicellulose structure, and other ultrastructural changes such as cell wall porosity. Lastly, a brief overview of process technoeconomics and environmental impacts are discussed, along with recommendations for future areas of research on ammonia-based pretreatments.

Pretreatment of Pennisetum sinese silages with ferulic acid esterase-producing lactic acid bacteria and cellulase at two dry matter contents: Fermentation characteristics, carbohydrates composition and enzymatic saccharification

The impact of Lactobacillus plantarum A1 producing ferulic acid esterase and Acremonium cellulase on Pennisetum sinese silages was investigated at two dry matter contents by studying the ensiling characteristics, lignocellulosic degradation and enzymatic saccharification properties. The P. sinese was treated with nothing (control), Acremonium cellulase (AC), L. plantarum A1 (Lp) and AC + Lp and ensiled for 60 d. All additive treatments effectively preserved P. sinese and promoted the degradation of lignocellulose in comparison with control. Pretreatment with AC exhibited better effects in degradation of lignocellulose and enhancing enzymatic saccharification of P. sinese silage with low dry matter content (L-DM), while AC + Lp performed better in lignocellulose degradation in silages with high dry matter content (H-DM). Application of Lp exhibited a better performance in reducing the concentration of acid detergent lignin in treated silages. In addition, Lp enhanced enzymatic saccharification at 72 h in H-DM silage relative to other treatments.