Investigating microalgae behaviour via experimentation in micro-scale photobioreactors

Microalgae are photosynthetic microorganisms with significant ecological and industrial relevance, playing a crucial role in global photosynthesis and offering sustainable solutions across various sectors. Since the mid-20th century, industrial interest in microalgae has grown considerably; however, challenges in scaling up and optimising cultivation processes still persist. Emerging biofilm-based systems present a promising alternative, reducing the energy-intensive harvesting steps and offering higher biomass productivities. However, these systems are still in the early stages of development and require further research to optimise their design and functionality. Mathematical models are a key tool for optimising microalgae cultivation systems, yet data collection is often slow and costly. Micro-scale technologies help accelerate this process but often come with operational issues. To address these challenges, this PhD thesis focuses on improving cultivation methods using micro- and milli-scale platforms to enhance data collection and modelling. Two novel photobioreactors were designed: a milli-photobioreactor to study suspended cultures, and a microfluidic set-up to examine biofilm communities. Experiments with the green alga Tetradesmus obliquus revealed that acclimation to light and temperature significantly affects biomass production and must be accounted for in mathematical models. The microfluidic set-up was used to analyse biofilm growth, showing that the diatom Phaodactylum tricornutum was better suited for biofilm systems, forming denser biofilms under higher light intensity. Novel non-invasive techniques like dissolved oxygen monitoring and reflectance spectra measurements were introduced for biofilm monitoring, showing potential for future biomass production applications.