In the present work, a 4-point optical probe was applied to a photo-bioreactor to assess bubble dynamics. All experiments were performed in 14 cm diameter column operated in the bubbly regime. Air was used as a gas phase and a strain of cyanobacteria, Synechocystis PCC 6803 is selected as a type of algae. The experiments were performed at different optical density of the culture ranging from 0.03 to 2. Local gas hold-up and bubble frequency were reduced slightly as optical density of the culture increases. The bubble velocity and bubble chord length increases with the increase in optical density. The gas-liquid interfacial area is reduced as the optical density of the culture increased; this indicates possible mass transfer limitations in cultures with high optical density. The effect of optical density on volumetric mass transfer coefficient is also studied in this work.

Key Words: Slurry bubble column, Gas hold-up, Bubble velocity, Gas-liquid interfacial area, Volumetric mass transfer coefficient.