Investigating the effects of substrate morphology and experimental conditions on the enzymatic hydrolysis of lignocellulosic biomass through modeling

Abstract

Background Understanding how the digestibility of lignocellulosic biomass is affected by its morphology is essential to design efficient processes for biomass deconstruction. In this study, we used a model based on a set of partial differential equations describing the evolution of the substrate morphology to investigate the interplay between experimental conditions and the physical characteristics of biomass particles as the reaction proceeds. Our model carefully considers the overall quantity of cellulase present in the hydrolysis mixture and explores its interplay with the available accessible cellulose surface. Results Exploring the effect of various experimental and structural parameters highlighted the significant role of internal mass transfer as the substrate size increases and/or the enzyme loading decreases. In such cases, diffusion of cellulases to the available cellulose surface limits the rate of glucose release. We notably see that increasing biomass loading, while keeping enzyme loading constant should be favored for both small- (R < 300 $$\mu m$$ μ m ) and middle-ranged (300 < R < 1000 $$\mu m$$ μ m ) substrates to enhance enzyme diffusion while minimizing the use of enzymes. In such cases, working at enzyme loadings exceeding the full coverage of the cellulose surface (i.e. eI>1) does not bring a significant benefit. For larger particles (R > 1000 $$\mu m$$ μ m ), increases in biomass loading do not offset the significant internal mass transfer limitations, but high enzyme loadings improve enzyme penetration by maintaining a high concentration gradient within the particle. We also confirm the well-known importance of cellulose accessibility, which increases with pretreatment. Conclusions Based on the developed model, we are able to propose several design criteria for deconstruction process. Importantly, we highlight the crucial role of adjusting the enzyme and biomass loading to the wood particle size and accessible cellulose surface to maintain a strong concentration gradient, while avoiding unnecessary excess in cellulase loading. Theory-based approaches that explicitly consider the entire lignocellulose particle structure can be used to clearly identify the relative importance of bottlenecks during the biomass deconstruction process, and serve as a framework to build on more detailed cellulase mechanisms.

Complete Cycle from Feedstock Miscanthus Giganteus to Target Product Bacterial Nanocellulose

“…This is a very important fact. The results obtained herein are in good agreement with the literature sources [15,16] that note an exceptional recalcitrance of Miscanthus to enzymatic hydrolysis [15], and the behavior of natural rather than model substrates during enzymatic hydrolysis is explained, most notably, by the morphology of the substrate [16].…”

Production of sugars from lignocellulosic biomass via biochemical and thermochemical routes

“…The structure of plant cell walls and the presence of hemicellulose and lignin impede the diffusion of cellulases to cellulose fibers. As a result, enzymatic hydrolysis of unmodified lignocellulosic biomass liberates little sugar even after days or weeks of treatment (Hatakka, 1983;Rohrbach and Luterbacher, 2021). The rate and yield of enzymatic hydrolysis can be greatly increased by removing lignin and hemicellulose, which is the goal of biomass pretreatments that are frequently employed prior to enzymatic hydrolysis.…”

Properties and Hydrolysis Behavior of Celluloses of Different Origin

“…So, the most significant factor affecting the cellulose hydrolysis behavior is the nature or origin of the cellulose itself. However, any single factor that completely explains enzy-matic hydrolysis tendencies cannot be discriminated by comparing celluloses of different origin [17,62].…”

“…The hydrolysis behavior of cellulose is governed by the chemical and physical features of the cellulose source. To the chemical features are related the composition and structure of cellulose, hemicelluloses, and lignin (for plant-based cellulose), while the accessible surface area, cellulose crystallinity, and degree of polymerization, pore volume, particle size, and the others refer to the physical features [16,17]. It has more recently been believed that the relationship between the enzymatic hydrolysis efficiency and the said factors has been well-established and well-proved, but the more studies have been conducted, the more controversial data have emerged.…”