Enhancing Waste Biorefineries by Using Diverse Waste Streams and Cell Immobilisation Techniques

Abstract

Sustainable waste management has received increasing research and industrial attention to cope with ongoing waste generation and environmental problems and fulfil the principles of a circular economy. There is a growing demand to introduce novel bioprocesses in waste biorefineries to improve the bioprocess performance. As part of this goal, the research work reported in this thesis was conducted to demonstrate the application of the cell immobilisation approach in waste biorefinery strategies to valorise food waste via different microorganisms.

Distinct factors influencing the valorisation potentials of food waste were first investigated to provide insights into real biorefinery applications. The characteristics of the food wastes and their corresponding hydrolysates differed based on their origins, and both the origins and storage conditions of food wastes were found to affect downstream microbial fermentation. Possible inhibitors that could account for the different performances of food waste hydrolysates, such as food additives and fatty acids, were identified using untargeted metabolite analysis.

To get comprehensive understandings of food waste biorefinery using cell immobilisation technique, three microbes targeting on different value-added products were selected to verify the performance. For recombinant protein production, the yeast Yarrowia lipolytica was able to achieve highest lipase titre of 28,957 UI/mL and productivity of 142 U/mL/h using defined medium in an in-situ fibrous bed bioreactor (isFBB) compared with other fermentation modes in classical bioreactors, and improved lipase productivity of 266 UI/mL/h was obtained when applied food waste hydrolysate as the culture medium. The bacterium Lactobacillus casei Shirota was examined to improve the production efficiency of lactic acid using a combination of food waste hydrolysate, the cell immobilisation approach, and seashell waste, which showed promising results with enhanced lactic acid productivity of 1.90 g/L/h and glucose uptake rate of 3.41 g/L/h when shell waste was applied to replace commercial base as the acid neutraliser. Lastly, the cultivation of microalga Euglena gracilis, by utilisation of a food waste hydrolysate medium coupled with cell immobilisation cultivation, resulted in a high productivity of microalgal polysaccharide of 1.77 g/L/day. Through the insights obtained from these research work, a waste biorefinery strategy for efficient and green valorisation of food waste was successfully developed. The studies presented in this thesis could promote the commercialisation of waste-based products and contribute to the sustainable development of a green and circular economy.

Date of Award	31 Aug 2023
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Sze Ki Carol LIN (Supervisor)