(16f) Study of Local Gas Holdup, and Specific Interfacial Area in a Split-Column Airlift Bioreactor for Culturing Microalgae/Cyanobacteria

Local gas hold-up (ε ) and interfacial area (a) at different axial locations of the riser
and downcomer of a split-column airlift bioreactor were investigated using sophisticated 4-
point optical probe. Such a type of a reactor has been found to outperform both bubble
column and draft-tube airlift bioreactors for culturing microalgae. The effect of superficial
gas velocity (0.3 – 2.8 cm/s) on both gas hold-up and interfacial area was studied using airwater
system. It was found that both the gas hold-up and interfacial area significantly
decrease from the top to the bottom of the downcomer for all superficial gas velocities while
their variation from the bottom to the top for the riser was found to be much less than that of
the downcomer at the same superficial gas velocities. It was found that the interfacial area of
the riser tends to increase by 35% from the bottom to the upper middle point of the column
(6.15 Z/D from the bottom), then declines by 10% at the top location (7.7 Z/D from the
bottom). Having obtained variable interfacial area (a) at different locations of both the riser
and the downcomer of the bioreactor, the local (KLa) consequently changes as a function of
location of the bioreactor and hence, needs to be investigated locally as opposed to the
current studies that have only measured and correlated the overall KLa.