Fluid dynamics modelling and process optimization of a flashing-light photobioreactor for enhancing microalgae cultivation

This thesis was written in collaboration with the Technical University of Dresden and the Marigan Bio Extracts GmbH company for the development of an innovative photobioreactor (PBR) for microalgae cultivation. The peculiarity of the project is the application of the Forced Flash- ing Effect (FFE) for enhancing algal photoefficiency, reducing algal stress due to high light intensity, and reducing energy consumption. Moreover, the PBR is designed to be a module in a bigger plant, thus allowing flexibility in scaling up or down. At the present moment, the project is still at a laboratory-scale level. During the first run of the laboratory-scale PBR, several biological and structural issues were identified, thus precluding the possibility of further runs. Issues related to the inlet and outlet geometry were also assessed with the ANSYS Fluent software. Using computational fluid dynamics simulations, the proposed geometry of the pilot plant inlet and outlet was examined too, and a critical recirculation region was located. With the same software, some alternative geometries were proposed and analyzed. Experimental campaigns were conducted to identify the best microalgae strain-medium combination to use inside the laboratory scale PBR and obtain data from different cultivation systems to compare the PBR performances. Results indicate that significant work is needed to operate the reactor effectively, and modifications are needed on the lighting apparatus, on the dome placement, and on the cooling system. The laboratory-scale plant is also characterized by a too large dark-to-light volume ratio, which negatively affects algal growth. Such design improvements are necessary before moving from the laboratory-scale plant to the pilot plant.