Lignocellulose particle size and rheological properties changes in periodic peristalsis enzymatic hydrolysis at high solids

Rheological investigation of complex lignocellulosic suspensions during hydrolysis using pure and cocktail of enzymes

Enzymatic hydrolysis of lignocellulosic materials at high dry matter content is of crucial interest in bioindustry, and namely for biorefinery. Physical limitations linked to high concentrations must be understood and surpassed. This study used online and in-situ measurements to examine the rheological properties of different cellulosic suspensions and its evolution during enzymatic hydrolysis. Semi-dilute conditions were used to introduce non-Newtonian rheological behaviors while limiting complexity. For all suspensions, the relationship between shear-thinning behavior versus substrate concentration was modeled. During enzymatic digestion using single and cocktails of cellulolytic activities, the evolution in shear-thinning properties was finely quantified. The viscosity-time relationship during hydrolysis was accurately described through first-order kinetics, and a unique, dimensionless representation was obtained. The critical concentrations indicating a shift from diluted to concentrated regime and the viscosity reduction kinetics that were identified should provide a strong foundation for defining an optimal substrate feed rate for fed-batch and continuous processes.

Role of in situ surfactant modification of lignin structure and surface properties during glycerol pretreatment in modulating cellulase-lignin binding affinities

Surfactants are effective agents for enhancing lignocellulosic pretreatment, synergistically modifying lignin with polyols to improve substrate hydrolyzability while achieving comparable delignification. However, the mechanisms underlying the multiple modifications from dual in situ surfactant/polyols grafting that passivate lignin-cellulase interactions and their core affecting factors remain unclear. Following the previously developed polyethylene glycol (PEG) and Triton-assisted pretreatment, the intrinsic correlation among lignin structures, physical barriers, and cellulase interactions was analyzed in this study. The surfactant grafting onto lignin can significantly decrease non-productive cellulase adsorption by 5-59 % compared to the initial glycerol-modified lignin. Structurally, the changes in lignin aliphatic -OH (r > 0.93), H-OH (r > 0.98), and G-OH (r > 0.74) showed strong correlations with cellulase adsorption; the -COOH and C=O were not well-valiadted for assessing the non-productive interaction. Physically, surfactant modification also induced changes in lignin surface structure, with variations in specific surface area, pore size, and pore volume showing positive correlations (r > 0.71). The structurally modified lignin had a relatively strong affinity for exo-glucanase and β-glucosidase in enzyme cocktails, while it reduced the irreversible adsorption of lignin onto cellulases (up to 97 % of total adsorbed protein). The secondary structure of desorbed cellulases underwent obvious changes independent of lignin structural modifications, with lowering β-sheet content and increasing random coil content. Based on molecular forces, surfactant modification lowered the binding free energy of cellulases by 60.3-86.5 %, and the reduction in H-bonding interaction was predominant. This study provides mechanistic insights for constructing lignin-modified pretreatments to enhance the substrate hydrolyzability.

Quantitative correlation analysis between particle liquefaction and saccharification through dynamic changes of slurry rheological behavior and particle characteristics during high-solid enzymatic hydrolysis of sugarcane bagasse

This study identified the intrinsic relationships among slurry rheology, particle characteristics, and lignocellulosic liquefaction/saccharification based on correlation analysis and principal component analysis during the hydrolysis of sugarcane bagasse pretreated by deep eutectic solvents (DES) and mechanical milling (MM). The DES-MM pretreated lignocellulosic slurry (20% solids) exhibited high apparent viscosity of 1.4 × 104 Pa·s and shear stress of 929.0 Pa under steady state. Glucose production had a negative linear correlation with slurry viscosity (R2, 0.69-0.97), whereas its correlation with yield stress (R2, 0.85-0.98) depended on the particle liquefaction rate. The availability of free water provided a major contribution to improving slurry rheology. However, the size reduction of submillimeter particles and the changes in particle hydrophilicity during liquefaction were not significantly correlated with rheological changes. Various interrelated particle characteristics and rheological changes were integrated into two simple principal variables to predict glucose production with a high R2 of 0.96.

Addressing two major limitations in high-solids enzymatic hydrolysis by an ordered polyethylene glycol pre-incubated strategy: Rheological properties and lignin adsorption for enzyme

High-solids enzymatic hydrolysis for biomass has currently received considerable interest. However, the solid effect during the process limits its economic feasibility. This work presented an ordered polyethylene glycol (PEG) pre-incubated strategy for enhancing the auxiliary effect of PEG in a high-solids enzymatic hydrolysis system. The substrate and enzyme were separately pre-incubated with PEG in this strategy. The ordered PEG pre-incubated strategies yielded a maximum glucose concentration of 166.6 g/L from 32 % (w/v) pretreated corncob with an enzymatic yield of 94.1 % by 72 h hydrolysis. Using this method, PEG not only lessened the lignin adsorption to cellulase but also altered particle rheological characteristics in the high-solids enzymatic hydrolysis system as a viscosity modifier. This study offered a new insight into the mechanism behind the PEG synergistic effect and would make it possible to achieve efficient high-solids loading hydrolysis in the commercial manufacture of cellulosic ethanol.

High Concentration of Fermentable Sugars Prepared from Steam Exploded Lignocellulose in Periodic Peristalsis Integrated Fed-Batch Enzymatic Hydrolysis

High concentrations of fermentable sugars are a demand for economical bioethanol production. A single process strategy cannot comprehensively solve the limiting factors in high-solid enzymatic hydrolysis. The multiple intensification strategies in this study achieved the goal of preparing high-concentration fermentable sugars of corn stalk with high solid loading and low enzyme loading. First, steam explosion pretreatment enhanced the hydrophilicity of substrates and enzymatic accessibility. Second, periodic peristalsis was used to improve the mass transfer efficiency and short the liquefaction time. Additionally, fed-batch feeding and enzyme reduced the enzyme loading. Ultimately, the intensification strategies above showed that the highest fermentable sugar content was 313.8 g/L with a solids loading as much as 50% (w/w) and enzyme loading as low as 12.5 FPU/g DM. Thus, these multiple intensification strategies were promising in the high-solid enzymatic hydrolysis of steam-exploded lignocellulose.

Advances and Challenges in Biocatalysts Application for High Solid-Loading of Biomass for 2nd Generation Bio-Ethanol Production

Growth in population and thereby increased industrialization to meet its requirement, has elevated significantly the demand for energy resources. Depletion of fossil fuel and environmental sustainability issues encouraged the exploration of alternative renewable eco-friendly fuel resources. Among major alternative fuels, bio-ethanol produced from lignocellulosic biomass is the most popular one. Lignocellulosic biomass is the most abundant renewable resource which is ubiquitous on our planet. All the plant biomass is lignocellulosic which is composed of cellulose, hemicellulose and lignin, intricately linked to each other. Filamentous fungi are known to secrete a plethora of biomass hydrolyzing enzymes. Mostly these enzymes are inducible, hence the fungi secrete them economically which causes challenges in their hyperproduction. Biomass’s complicated structure also throws challenges for which pre-treatments of biomass are necessary to make the biomass amorphous to be accessible for the enzymes to act on it. The enzymatic hydrolysis of biomass is the most sustainable way for fermentable sugar generation to convert into ethanol. To have sufficient ethanol concentration in the broth for efficient distillation, high solid loading ~<20% of biomass is desirable and is the crux of the whole technology. High solid loading offers several benefits including a high concentration of sugars in broth, low equipment sizing, saving cost on infrastructure, etc. Along with the benefits, several challenges also emerged simultaneously, like issues of mass transfer, low reaction rate due to water constrains in, high inhibitor concentration, non-productive binding of enzyme lignin, etc. This article will give an insight into the challenges for cellulase action on cellulosic biomass at a high solid loading of biomass and its probable solutions.