High solids loading pretreatment: The core of lignocellulose biorefinery as an industrial technology - An overview

Adaptive evolution of Paecilomyces variotii enhanced the biodetoxification of high-titer inhibitors in pretreated lignocellulosic feedstock

High inhibitor concentrations in lignocellulose feedstock negatively affect the degradation rate of biodetoxification strains. This study designed two adaptive laboratory evolutions in solid substrate and liquid medium to boost the biodetoxification capacity of P. variotii to high titers of lignocellulose-derived inhibitors, resulting in two evolved strains AC70 and ZW70. The results showed that the evolutionary adaptation in liquid medium could better boost the acetic acid assimilation compared to that on solid substrate. Transcriptional analysis revealed that the evolved strains exhibited a significant upregulation of adh, acs, ach1, and ackA directly related to the initial steps of acetate and furan aldehydes metabolisms. ZW70 strain can effectively remove the high concentration inhibitors cocktail from the hydrolysates derived from pretreated wheat straw and furfural residues. The biodetoxified hydrolysates by ZW70 were successfully used for cellulose chiral L-lactic acid production with the titers of ∼110 g/L, which were over 20 % higher than that detoxified by parental strain.

Efficient extraction of lignin from moso bamboo by microwave-assisted ternary deep eutectic solvent pretreatment for enhanced enzymatic hydrolysis

Applications of deep eutectic solvent (DES) systems to separate lignocellulosic components are of interest to develop environmentally friendly processes and achieve efficient utilization of biomass. To enhance the performance of a binary neutral DES (glycerol:guanidine hydrochloride), various Lewis acids (e.g., AlCl3·6H2O, FeCl3·6H2O, etc.) were introduced to synthesize a series of ternary DES systems; these were coupled with microwave heating and applied to moso bamboo. Among the ternary DES systems evaluated, the FeCl3-based DES effectively removed lignin (81.17%) and xylan (85.42%), significantly improving enzymatic digestibility of the residual glucan and xylan (90.15% and 99.51%, respectively). Furthermore, 50.74% of the lignin, with high purity and a well-preserved structure, was recovered. A recyclability experiment showed that the pretreatment performance of the FeCl3-based DES was still basically maintained after five cycles. Overall, the microwave-assisted ternary DES pretreatment approach proposed in this study appears to be a promising option for sustainable biorefinery operations.

Life cycle assessment and techno-economic analysis of wood-based biorefineries for cellulosic ethanol production

Poplar is widely used in the paper industry and accompanied by abundant branches waste, which is potential feedstock for bioethanol production. Acid-chlorite pretreatment can selectively remove lignin, thereby significantly increasing enzymatic efficiency. Moreover, lignin residues valorization via gasification-syngas fermentation can achieve higher fuel yield. Herein, environmental and economic aspects were conducted to assess technological routes, which guides further process optimization. Life cycle assessment results show that wood-based biorefineries especially coupling scenarios have significant advantages in reducing global warming potential in contrast to fossil-based automotive fuels. Normalization results indicate that acidification potential surpasses other indicators as the primary impact category. In terms of economic feasibility, coupling scenarios present better investment prospects. Bioethanol yield is the most critical factor affecting market competitiveness. Minimum ethanol selling price below ethanol international market price is promising with higher-levels technology. Further work should be focused on technological breakthrough, consumable reduction or replacement.

Employing deep eutectic solvent synthesized by cetyltrimethylammonium bromide and ethylene glycol to advance enzymatic hydrolysis efficiency of rape straw

An efficient deep eutectic solvent (DES) was synthesized by cetyltrimethylammonium bromide (CTAB) and ethylene glycol (EG) and employed to treat rape straw (RS) for advancing enzymatic saccharification in this work. By optimizing the pretreatment parameters, the results displayed that the novel DES was strongly selective towards removing lignin and xylan while preserving cellulose. Under optimum conditions with 1:6 of CTAB: EG in DES, 180 °C and 80 min, the enzymatic hydrolysis efficiency of RS was enhanced by 46.0% due to the 62.2% of delignification and 53.2% of xylan removal during CTAB: EG pretreatment. In terms of the recalcitrant structure of RS, DES pretreatment caused the increment of cellulosic accessibility, reduction of hydrophobicity and surface area of lignin, and migration of cellulosic crystalline structure, which was associated with its enzymatic hydrolysis efficiency. Overall, this study presented an emerging method for the effective fractionation and valorization of lignocellulosic biomass within biorefinery technology.

Recent advances in biorefineries based on lignin extraction using deep eutectic solvents: A review

Considering the urgent need for alternative biorefinery schemes based on sustainable development, this review aims to summarize the state-of-the-art in the use of deep eutectic solvent pretreatment to fractionate lignocellulose, with a focus on lignin recovery. For that, the key parameters influencing the process are discussed, as well as various strategies to enhance this pretreatment efficiency are explored. Moreover, this review describes the challenges and opportunities associated with the valorization of extraction-derived streams and highlights recent advancements in solvent recovery techniques. Furthermore, the utilization of computational models for process design and optimization is introduced, as the initial attempts at the economic and environmental assessment of this lignocellulosic bioprocess based on deep eutectic solvents. Overall, this review offers a comprehensive perspective on the recent advances in this emerging field and serves as a foundation for further research on the potential integration of deep eutectic pretreatment in sustainable multi-product biorefinery schemes.

Effect of nano-metal doped calcium peroxide on biomass pretreatment and green hydrogen production from rice straw

In this study, calcium peroxide was modified and doped with metal-based nanoparticles (NP) to enhance the efficiency of pretreatment and biohydrogen generation from RS. The findings revealed that the addition of MnO2-CaO2 NPs (at a dosage of 0.02 g/g TS of RS) had a synergistic effect on the breakdown of biomass and the production of biohydrogen. This enhancement resulted in a maximum hydrogen yield (HY) of 58 mL/g TS, accompanied by increased concentrations of acetic acid (2117 mg/L) and butyric acid (1325 mg/L). In contrast, RS that underwent pretreatment without the use of chemicals or NP exhibited a lower HY of 28 mL/g TS, along with the lowest concentrations of acetic acid (1062 mg/L) and butyric acid (697 mg/L). The outcome showed that supplementation of NP stimulated the pretreatment of RS and improved the formation of acetic and butyric acid through the regulation of metabolic pathways during acidogenic fermentation.

Synthesis of bifunctional thermal response promoters for improved high-solids enzymatic hydrolysis of corncob residues

The enzymatic hydrolysis cost of lignocellulose can be reduced by improving enzymatic hydrolysis and recycling cellulase by adding additives. A series of copolymers P(SSS-co-SPE) (PSSPs) were synthesized using sodium p-styrene sulfonate (SSS) and sulfobetaine (SPE) as monomers. PSSP exhibited upper critical solution temperature response. PSSP with high molar ratio of SSS displayed more significant improved hydrolysis performance. When 10.0 g/L PSSP5 was added to the hydrolysis system of corncob residues, and substrate enzymatic digestibility at 72 h (SED@72 h) increased by 1.4 times. PSSP with high molecular weight and moderate molar ratio of SSS, had significant temperature response, enhanced hydrolysis, and recovering cellulase properties. For high-solids hydrolysis of corncob residues, SED@48 h increased by 1.2 times with adding 4.0 g/L of PSSP3. Meanwhile, 50% of cellulase amount was saved at the room temperature. This work provides a new idea for reducing the hydrolysis cost of lignocellulose-based sugar platform technology.

Enhancing cellulosic digestibility of wheat straw by adding sodium lignosulfonate and sodium hydroxide to hydrothermal pretreatment

Surfactant-assisted pretreatment has been widely reported to improve the enzymatic hydrolysis of lignocellulose by promoting removal of xylan and lignin. Hence, this work innovatively proposed the use of sodium lignosulfonate (SL) as an additive of alkaline pretreatment (AP), and evaluated its influence on the cellulosic digestibility of wheat straw (WS). The results displayed that the maximum of 72-h cellulosic digestibility could reach 83.5% as 15 g/L SL was introduced to the AP process (SAP), while the cellulosic digestibility of hydrothermal and alkaline pretreated WS was only 63.6% and 70.2%, respectively. These increments were subsequently attributed to the improvement of 6.5% xylan and 26.8% lignin accelerated by SAP, resulting in positive changes in structural characteristics such as accessibility, specific surface area, and cellulosic crystalline structure. The utilization of lignin-based surfactants in pretreatment has realized the economic feasibility of lignocellulosic biorefining and broadened the application prospect of surfactants.

Simultaneous and rate-coordinated conversion of lignocellulose derived glucose, xylose, arabinose, mannose, and galactose into D-lactic acid production facilitates D-lactide synthesis

D-lactide is the precursor of poly(D-lactide) (PDLA) or stereo-complex with poly(L-lactide) (PLLA). Lignocellulosic biomass provides the essential feedstock option to synthesize D-lactic acid and D-lactide. The residual sugars in D-lactic acid fermentation broth significantly blocks the D-lactide synthesis. This study showed a simultaneous and rate-coordinated conversion of lignocellulose derived glucose, xylose, arabinose, mannose, and galactose into D-lactic acid by adaptively evolved Pediococcus acidilactici ZY271 by simultaneous saccharification and co-fermentation (SSCF) of wheat straw. The produced D-lactic acid achieved minimum residual sugars (∼1.7 g/L), high chirality (∼99.1%) and high titer (∼128 g/L). A dry acid pretreatment eliminated the wastewater stream generation and the biodetoxification by fungus Amorphotheca resinae ZN1 removed the inhibitors from the pretreatment. The removal of the sugar residues and inhibitor impurities in D-lactic acid production from lignocellulose strongly facilitated the D-lactide synthesis. This study filled the gap in cellulosic D-lactide production from lignocellulose-derived D-lactic acid.