Interaction between CO2-mass transfer, light availability, and hydrodynamic stress in the growth ofPhaeodactylum tricornutum in a concentric tube airlift photobioreactor

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Abstract
The microalga Phaeodactylum tricornutum was grown in a concentric tube airlift photobioreactor. A maximum specific growth rate of 0.023 h−1 was obtained using a superficial gas velocity around 0.055 m/s. Lower or higher gas flow rates limited the culture performance. To establish if the observed limitation was due to CO2 or to the photosynthetically active irradiance, characteristic times for mixing, mass transfer and CO2 consumption, and the photon flux absorbed by the culture were analyzed. The CO2-gradients in the culture were shown to be responsible for the limitation during the exponential growth phase, and both CO2 and light irradiance were limiting in the linear growth phase. The decrease in specific growth rate relative to the maximum was found to be related to the specific gas-liquid interfacial area, the length scale of the microeddies and the shear rate. © 1998 John Wiley & Sons, Inc. Biotechnol Bioeng 60: 317–325, 1998.