Hydrodynamic Analysis and Evaluation of a Novel Air Stirred Tank Reactor (ASTR) for Microalgae Production

Abstract

Aerobic and anaerobic microorganisms are responsible for the production of high-quality goods and services in virtually every major industry on earth. There are a variety of scales and methods by which these microorganisms are cultured, allowing for a vast diversity of cell culture systems. There are several common themes that are shared between all types of cultivation systems; for example, each culturing method requires a vessel to contain liquid media, dissolved nutrients are also required in accordance with the biological requirements of the chosen organism, and some method of mixing is required to distribute nutrients evenly throughout the media. The latter of these becomes challenging as the scale of the reactor system increases. It becomes difficult to adequately distribute dissolved gases to the entirety of the reactor due primarily to the characteristic hydrodynamics of the reactor type and the solubility of the particular gases in liquid media. At low impeller velocities, for instance, eddy formation hinders adequate mixing by creating resistance to the desired flow pattern within the reactor. As such, it has been noted by several groups that mass transfer is inherently low at slower mixture velocities. This study attempts to alleviate the maldistribution of nutrients and improve dissolved-gas mass transfer to the microorganisms by optimizing the hydrodynamics of a cylindrical bioreactor using a novel type of mixing impeller.