Waut Broos

• 14 January 2025
• 4 p.m.
• ​Campus Drie Eiken- Building O, room d.O.01
• Promotor: prof. dr. prof. dr. Iris Cornet, prof. dr. Siegfried E. Vlaeminck & prof. dr. Jan Dries ​
• Faculty of Applied Engineering

Abstract

Lignocellulose-based biorefineries produce a significant amount of wastewater containing several phenolic compounds. Today, these wastewaters are mostly considered a burden. However, some microorganisms, e.g., Rhodotorula kratochvilovae and Cutaneotrichosporon oleaginosum can convert phenolics into valuable intracellular components, namely single-cell oil (SCO). This turns the waste stream into a raw material and an economic opportunity. However, valorising wastewater to SCO is challenging due to its low substrate concentration. Therefore, supplementation with a high-value carbon source is used in literature to obtain appreciable SCO titters. To date, the production of SCO from high-value carbon sources has proven to be economically unfeasible. As a result, this study explores the use of a repeated batch fermentation strategy to overcome the low substrate concentration. In a repeated batch, the cells are recycled for use in the next batch. Cell recycling and repeated feeding allow intracellular SCO to accumulate in the cells. This allows high SCO concentrations to be achieved from substrate-poor wastewaters. Three technologies can be used for cell recycling: centrifugation, membrane technology and immobilisation. However, each of these technologies has its drawbacks: centrifugation is energy-consuming and requires a significant investment, membrane technology is prone to fouling, and conventional immobilisation technologies make recovery of the intracellular product problematic.
Our hypothesis is that the design of a new reactor type, namely a reversible immobilised cell reactor (RICR), offers a possible solution. In this reactor, the cells are first immobilised on a suitable support, repeated batch fermentation occurs, and finally remobilised to recover the intracellular components. As a case study, the wastewater obtained from thermochemical pre-treatment of lignocellulose is investigated as a substrate for microbial oil production. This study aimed to design an economically feasible process for valorising this lignocellulosic wastewater.