High solid loading enzymatic hydrolysis of acetic acid-peroxide/acetic acid pretreated poplar and cellulase recycling

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.

A critical assessment on scalable technologies using high solids loadings in lignocellulose biorefinery: challenges and solutions

The pretreatment and the enzymatic saccharification are the key steps in the extraction of fermentable sugars for further valorization of lignocellulosic biomass (LCB) to biofuels and value-added products via biochemical and/or chemical conversion routes. Due to low density and high-water absorption capacity of LCB, the large volume of water is required for its processing. Integration of pretreatment, saccharification, and co-fermentation has succeeded and well-reported in the literature. However, there are only few reports on extraction of fermentable sugars from LCB with high biomass loading (>10% Total solids-TS) feasible to industrial reality. Furthermore, the development of enzymatic cocktails can overcome technology hurdles with high biomass loading. Hence, a better understanding of constraints involved in the development of technology with high biomass loading can result in an economical and efficient yield of fermentable sugars for the production of biofuels and bio-chemicals with viable titer, rate, and yield (TRY) at industrial scale. The present review aims to provide a critical assessment on the production of fermentable sugars from lignocelluloses with high solid biomass loading. The impact of inhibitors produced during both pretreatment and saccharification has been elucidated. Moreover, the limitations imposed by high solid loading on efficient mass transfer during saccharification process have been elaborated.

Production of Extracellular Enzymes by Lentinula edodes Strains in Solid-State Fermentation on Lignocellulosic Biomass Sterilized by Physical and Chemical Methods

Two methods of sterilization of lignocellulosic biomass were performed in this study. Eucalypt waste (EW) supplemented with rice bran (RB) was added in the proportions 80:20 and 90:10 in dry weight. The compositions were sterilized by physical method (autoclaving) and by chemical method (H2O2). The production of extracellular enzymes by Lentinula edodes strains was compared within the two methods. Inactivation of catalase present in RB was achieved with 250 mM H2O2. The use of H2O2, when compared by physical method, favored high production of hydrolytic enzymes such as endoglucanase (1,600 IU/kg), twofold higher, β-glucosidase (1,000 IU/kg), fivefold higher, xylanase (55,000 IU/kg), threefold higher and β-xylosidase (225 IU/kg), similar results. Oxidative enzymes, MnP and laccase, were produced within a different profile between strains, with shorter times for laccase (2,200 IU/kg) by SJC in 45 days and MnP (2,000 IU/kg) by CCB-514 in 30 days. High production of extracellular enzymes is achieved by the use of the chemical method of sterilization of lignocellulosic biomass; in addition to no energy consumption, this process is carried out in a shorter execution time when compared to the physical process. The use of H2O2 in sterilization does not produce toxic compounds from the degradation of hemicellulose and cellulose such as furfural and hydroxy-methyl-furfural that cause inhibition of microorganisms and enzymes.

Efficient production of high concentration monosaccharides and ethanol from poplar wood after delignification and deacetylation

Efficient enzymatic hydrolysis is required for production of high concentration monosaccharides and ethanol. The lignin and acetyl group in poplar can limit the enzymatic hydrolysis. However, the effect of delignification combined with deacetylation on the saccharification of poplar for high concentration monosaccharides was not clear. Herein, hydrogen peroxide-acetic acid (HPAA) was used for delignification and sodium hydroxide was used for deacetylation to enhance the hydrolyzability of poplar. Delignification with 60% HPAA at 80 °C could remove 81.9% lignin. Acetyl group was completely removed with 0.5% NaOH at 60 °C. After saccharification, 318.1 g/L monosaccharides were obtained with a poplar loading of 35% (w/v). After simultaneous saccharification and fermentation, 114.9 g/L bioethanol was gained from delignified and deacetylated poplar. Those results showed the highest monosaccharides and ethanol concentrations in reported research. This developed strategy with relatively low temperature could effectively improve the production of high concentration monosaccharide and ethanol from poplar.

Combination of surfactants and enzyme cocktails for enhancing woody biomass saccharification and bioethanol production from lab-scale to pilot-scale

Converting woody biomass to bioethanol might be more affordable, environmentally friendly, and efficient for making biofuel commercially feasible, but it would still need a significant optimization process and expand pilot-scale research. A combination of commercial low enzymes loading at 10 FPU/g glucan and compound additives utilizing Tween 80, PEG8000 and sophorolipid applied from lab-scale to pilot-scale have been studied in this work at economically viable dosages for enhancing bioethanol production. In lab-scale saccharification and fermentation, pretreated poplar at a high solid loading of 20% yielded the highest ethanol titers of 30.96 g/L and theoretical ethanol yield of 92.79%. Additionally, pilot-scale operation was used to investigate the bioethanol amplification, a final volume of 33 m³ which yielded the greatest ethanol amount of 599.6 kg from poplar wood while gaining on-site value-added production of hemicellulosic and cellobiose liquor 1122 kg and lignin residues 2292 kg.

Advances and perspectives on mass transfer and enzymatic hydrolysis in the enzyme-mediated lignocellulosic biorefinery: A review

Enzymatic hydrolysis is a critical process for the cellulase-mediated lignocellulosic biorefinery to produce sugar syrups that can be converted into a whole range of biofuels and biochemicals. Such a process operating at high-solid loadings (i.e., scarcely any free water or roughly ≥ 15% solids, w/w) is considered more economically feasible, as it can generate a high sugar concentration at low operation and capital costs. However, this approach remains restricted and incurs "high-solid effects", ultimately causing the lower hydrolysis yields with increasing solid loadings. The lack of available water leads to a highly viscous system with impaired mixing that exhibits strong transfer resistance and reaction limitation imposed on enzyme action. Evidently, high-solid enzymatic hydrolysis involves multi-scale mass transfer and multi-phase enzyme reaction, and thus requires a synergistic perspective of transfer and biotransformation to assess the interactions among water, biomass components, and cellulase enzymes. Porous particle characteristics of biomass and its interface properties determine the water form and distribution state surrounding the particles, which are summarized in this review aiming to identify the water-driven multi-scale/multi-phase bioprocesses. Further aided by the cognition of rheological behavior of biomass slurry, solute transfer theories, and enzyme kinetics, the coupling effects of flow-transfer-reaction are revealed under high-solid conditions. Based on the above basic features, this review lucidly explains the causes of high-solid hydrolysis hindrances, highlights the mismatched issues between transfer and reaction, and more importantly, presents the advanced strategies for transfer and reaction enhancements from the viewpoint of process optimization, reactor design, as well as enzyme/auxiliary additive customization.

Optimized production of xylooligosaccharides from poplar: A biorefinery strategy with sequential acetic acid/sodium acetate hydrolysis followed by xylanase hydrolysis

The preparation of xylooligosaccharides (XOS) from lignocelluloses by organic acid hydrolysis has the advantages of high efficiency and simplicity, but reducing the production of by-products, especially xylose, is a prerequisite for commercial preparation of XOS using organic acid. In this work, to reduce the production of by-products, the acetic acid/sodium acetate conjugate system (AC/SA) was used to prepare XOS from poplar. Under the optimal conditions (0.15 M AC/SA, molar ratio of 3.0, 175 °C, 60 min), the maximum XOS yield was 33.6% with a low xylose/XOS ratio of 0.19. Xylanase hydrolysis effectively converted XOS with DP above 6 in the AC/SA hydrolysate to X2-X6 with little xylose produced. The XOS yield increased to 42.1%, with a xylose/XOS ratio was only 0.17. This work shows that AC/SA in combination with xylanase hydrolysis of poplar successfully achieved high XOS yield with low by-products yields without the extraction of xylan from the substrate.