The present study compares typical measurements of bubble dynamics obtained with a 4-point optical probe over the same range of superficial gas velocity in the same size gas-liquid contactor in two different systems. The classical bubble column (BC) arrangement employed air bubbled through water. The photo-bioreactor (PBR) used a growing algae in appropriate culture solution. Local gas holdup distribution across the vessel was monitored, as well as the local distribution of bubble velocity, bubble chord length, bubble frequency and interfacial area per unit volume for both systems. It was observed these parameters were significantly different in the photo-bioreactor. This information coupled with the tracer absorption studies with oxygen provided the needed information to evaluate the gas liquid volumetric mass transfer coefficients from an appropriate model for both systems. The development of such a model is described. It was concluded that the difference in hydrodynamics of the two systems was due to difference in physicochemical properties. (C) 2017 Elsevier Ltd. All rights reserved.