Mass Transfer And Hydrodynamics In A Split-Column Airlift Photobioreactor

Abstract

Overall gas-liquid mass transfer coefficients of oxygen gas (KLa) at different axiallocations of the riser and downcomer of a split-column Airlift Photobioreactor wereinvestigated 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 wasused to measure local interfacial area (a) and other bubble dynamics parameters for both theriser and the downcomer of a split-column airlift photobioreactor. Having both overall masstransfer (KLa) and interfacial area (a) measured at different locations, local oxygen masstransfer coefficient (KL) can be determined for each location along the riser and thedowncomer of the airlift bioreactor. Effects of different operating conditions (0.3 – 2.8 cm/ssuperficial gas velocity) on both mass transfer and bubble dynamics of the riser and thedowncomer have been investigated for air-water system. It was found that both local masstransfer and gas-liquid interfacial area are considerably varying from the bottom to the top ofthe riser and the downcomer of the bioreactor. It was found that local mass transfer coefficientvaries 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 inthe downcomer section of the column is very different from that of the riser, as it was noticedthat insignificant mass transfer takes place at the lower part of the downcomer. The results ofmass transfer and bubble dynamics in the riser and the downcomer of the studied conditionswill be presented and discussed.