Advancing microalgae culturing via bubble dynamics, mass transfer, and dynamic growth investigations

The major hindrances to large scale cultivation of microalgae are the problems associated with the design, operation, and scale-up of airlift photobioreactors (PBRs), due to a lack of a comprehensive understanding of the gas-liquid interaction process in real microalgae cultures. Thus, the overall objective of this work is to advance the fundamental understanding of microalgae culturing via gas holdup, bubble dynamics, mass transfer, and dynamic growth investigations. First, a four-point optical fiber probe technique was employed to study the local gas holdup, and bubble dynamics properties such as bubble passage frequency, chord length and bubble velocity distribution, and interfacial area in an air-water system in a split airlift PBR at superficial gas velocities between 0.3-2.8 cm/s. These properties were then studied in green fresh-water microalgae, Scenedesmus, grown inside the PBR, and their variation with a change in the optical density and rheology of the medium due to microalgae growth was also studied. For mass transfer investigation, the significance and development of a new approach to calculate the liquid side and the local volumetric mass transfer coefficient was established in an air-water system. This new approach was then applied to estimate the local mass transfer coefficient in the Scenedesmus culture, as it grew in optical density. Finally, a separate-effects experiment was developed to estimate the dynamic growth kinetics parameters of microalgae Scenedesmus, by measuring its growth rate and fluorescence in a tubular airlift PBR --Abstract, page iv