Experimental and Modeling Studies of Fermentative Butanol Production from Lignocellulosic Sugars

Abstract

The primary focus of the work performed and summarized in this thesis was to understand and improve anaerobic fermentation of lignocellulosic sugars for butanol production by Clostridia. Experimental studies form the basis for systematic data collection for modeling. The secondary focus of the thesis was to develop a model for fermentative butanol production from lignocelluosic sugars. The tertiary focus was to investigate all fermentation variables and performance indicators with exploration of the interdependencies. This thesis accommodated these focuses.

First, fermentation variables including typical operating conditions and performance indicators were identified by collecting literature data. Exploratory data analysis of the variables provided a holistic overview of the process to demonstrate their significance and interconnectedness.

Initial fermentation experiments were done with different lignocellulosic sugar ratios at different scales i.e. serum flaks and microbioreactors. Results showed that sugar ratio had a profound impact on the fermentation kinetics, and serum flask setup was more beneficial in terms of stability of operation and sample collection.

Next, the effect of different pre-growth conditions on fermentation performance was explored by using different sugar ratios. Culture pre-grown on xylose as the sole sugar shows a better performance than culture pre-grown on a mixture of glucose and xylose in bench-scale bioreactors, and this strategy was used in the next experiments.

A model for Clostridial growth on mixtures of lignocellulosic sugars was developed first, which included the noncompetitive inhibition between them. By using this growth model, fermentative butanol production from lignocellulosic sugars was modelled. The model was validated with extra experimental data, and a sensitivity analysis was performed to gain better understanding of the model parameters.