Abstract:

Overall gas-liquid mass transfer coefficients of oxygen gas (KLa) at different axial locations of the riser and downcomer of a split-column Airlift Photobioreactor were investigated using FOXY Fiber Optic oxygen sensor supported by NeoFox viewer software. The effect of bubble dynamics on mass transfer was considered. A 4-point optical probe was used to measure local interfacial area (a) and other bubble dynamics parameters for both the riser and the downcomer of a split-column airlift photobioreactor. Having both overall mass transfer (KLa) and interfacial area (a) measured at different locations, local oxygen mass transfer coefficient (KL) can be determined for each location along the riser and the downcomer of the airlift bioreactor. Effects of different operating conditions (0.3 – 2.8 cm/s superficial gas velocity) on both mass transfer and bubble dynamics of the riser and the downcomer have been investigated for air-water system. It was found that both local mass transfer and gas-liquid interfacial area are considerably varying from the bottom to the top of the riser and the downcomer of the bioreactor. It was found that local mass transfer coefficient varies by 100% from the bottom to the top of the riser at low superficial gas velocity (1 cm/s) and by 30% at relatively high velocities (2-2.8 cm/s). The Trend of the variation of the KLa in the downcomer section of the column is very different from that of the riser, as it was noticed that insignificant mass transfer takes place at the lower part of the downcomer. The results of mass transfer and bubble dynamics in the riser and the downcomer of the studied conditions will be presented and discussed.

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