| Author: | Chan, Ka Lai |
| Title: | Construction of a numerical platform for enzymatic saccharification and multi-sugars fermentation for simulation of whole slurry biorefinery |
| Advisors: | Leu, Shao-yuan (CEE) |
| Degree: | Ph.D. |
| Year: | 2021 |
| Subject: | Biomass conversion Biomass energy Lignocellulose -- Biotechnology Hong Kong Polytechnic University -- Dissertations |
| Department: | Department of Civil and Environmental Engineering |
| Pages: | xv, 164 pages : color illustrations |
| Language: | English |
| Abstract: | This dissertation constructed a numerical platform to incorporate the dynamic interaction among enzyme adsorption, cellulose hydrolysis, cell growth and utilization in bioconversion processes of lignocellulosic biomass in biorefinery. Enzymatic hydrolysis is a heterogeneous reaction involving the dynamic interaction between enzyme complex and solid substrates. The dynamic enzyme adsorption was modeled based on the Langmuir isotherm and first order kinetic reaction of to simulate the equilibrium enzyme concentration during the hydrolysis process. A first order model with fractal kinetic and product inhibition was applied to describe cellulose hydrolysis for various pretreated substrates. Cell growth of microorganism was defined by Monod kinetic with both substrates and product inhibition terms. Utilization rate of both single and mixed sugars in batch and continues fermentation was described by the cell growth and product formation. To quantify the impacts of lignin properties to enzymatic hydrolysis, various types of lignin were isolated from the pretreated substrates of the single/two-staged organosolv pretreatments using 1,4-butanediol and dilute sulfuric acid. The impacts of condensed lignin and high phenolic hydroxyl group generated after acid-first process; the beneficial structures of organosolv associated functional groups to effective adsorption of cellulase to cellulose, were simulated. Suspended pretreated by-products or functional additives are common impurities in the hydrolysate, causing different effects to hydrolysis that need to be quantified by mathematical model. Bovine Serum Albumin (BSA) and lysozyme were applied as model additives to enzyme adsorption and cellulose hydrolysis. Addition of BSA and lysozyme improved the hydrolysis performance by reducing the non-productive adsorption of enzyme onto the surface of lignin and other impurities. The kinetic model revealed that the hydrolysis rate coefficient increased but the fractal exponent decreased with the addition of BSA and lysozyme. Addition of lysozyme exhibited a better hydrolysis performance, which confirmed by the larger hydrolysis rate coefficient and the smaller fractal exponent. The feasibility of co-fermentation process featuring with a cell recycling unit (CF/CR) was studied for mixed sugar utilization to produce lactic acid. The fermentation model was applied clarify the cell metabolism through kinetic analysis under the carbon catabolite repression (CCR) in co-fermentation. The model successfully simulated the transition of sugar consumption, cell growth, and lactic acid production among the batch, continuous process, and the continuous process with cell recycling. Cell retention time played a critical role in the pentose and hexose consumption, cell decay, and lactic acid production in the whole process, which was characterized by stead-state expression of the model parameters. |
| Rights: | All rights reserved |
| Access: | open access |
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