Bioreactor and Bioprocess Design Issues in Enzymatic Hydrolysis of Lignocellulosic Biomass

Abstract

Saccharification of lignocellulosic biomass is a fundamental step in the biorefinery of second generation feedstock. The physicochemical and enzymatic processes for the depolymerization of biomass into simple sugars has been achieved through numerous studies in several disciplines. The present review discusses the development of technologies for enzymatic saccharification in industrial processes. The kinetics of cellulolytic enzymes involved in polysaccharide hydrolysis has been discussed as the starting point for the design of the most promising bioreactor configurations. The main process configurations—proposed so far—for biomass saccharification have been analyzed. Attention was paid to bioreactor configurations, operating modes and possible integrations of this operation within the biorefinery. The focus is on minimizing the effects of product inhibition on enzymes, maximizing yields and concentration of sugars in the hydrolysate, and reducing the impact of enzyme cost on the whole process. The last part of the review is focused on an emerging process based on the catalytic action of laccase applied to lignin depolymerization as an alternative to the consolidated physicochemical pretreatments. The laccases-based oxidative process has been discussed in terms of characteristics that can affect the development of a bioreactor unit where laccases or a laccase-mediator system can be used for biomass delignification.

Fungal Laccases: The Forefront of Enzymes for Sustainability

“…Decrease of up to 87.8% of lignin content; increase of 9% of bioethanol production [142] Decrease of up to 81.2% of lignin content; production of up to 500 mg/g of fermentable sugars [143] T. versicolor Pretreatment of coffee bean processing waste for composting Increase in total plate count values [144] A purified LC from Trichoderma asperellum was used to pretreat sweet sorgum stover [136]. Thanks to its high stability at high temperatures and low pH, the authors were able to remove of up to 77% of lignin and obtain a 3.26-fold increase in biohydrogen production, proving that this LC could represent an important tool to be used in biofuels conversion.…”

“…Therefore, the implementation of the use of an LC for the pretreatment of the vegetable biomass is feasible. Nonetheless, to save costs, reduce the environmental impact, and maximize yields, it requires a careful analysis of technical solutions that enable the design of a single reactor to perform delignification, saccharification, and fermentation in a continuous or sequential mode [144]. Eventually, it is important to study the delignification kinetic and the enzyme stability/activity/adsorption to the lignocellulosic material in a bioreactor to obtain reproducible and satisfactory results also when material with different lignin/cellulose/hemicellulose ratio is used.…”

Simultaneous Enzymatic Cellulose Hydrolysis and Product Separation in a Radial-Flow Membrane Bioreactor

“…MBRs of different configurations have been tested for the enhancement of enzymatic hydrolysis of cellulose from different sources. The use of ultrafiltration membranes allowed a continuous selective permeation of the small product molecules while retaining the active enzymes inside the reaction for multiple cycles [ 14 ]. Separate reaction and separation units were tested to enhance enzymatic hydrolysis of pretreated microcrystalline cellulose at 50 °C.…”

A Simple Techno-Economic Assessment for Scaling-Up the Enzymatic Hydrolysis of MSW Pulp

“…Further benefits may be seen with comparatively low reactor down-times, greater space-time yields, and optimized energy consumption (Rao et al, 2009). Other TEA studies have compared the costbenefit of the batch, fed-batch, and continuous enzymatic systems, but none have performed this analysis with an MSWderived pulp lignocellulosic feedstock (Argo and Keshwani, 2019;Olivieri et al, 2021).…”