A plug flow model without axial dispersion was utilized to evaluate the mass transfer coefficient in Scenedesmus microalgae culture grown in a split airlift photobioreactor. The local volumetric mass transfer coefficient and the local interfacial area also were calculated at various gas velocity (1.0, 2.0 and 2.8 cm s–1). In the riser and the downcomer section, the local volumetric mass transfer coefficients were dominated by interfacial area and gas holdup values, and were favored by lower optical densities (ODs) and higher values of superficial gas velocities of microalgae cultures. The OD effects on the liquid side and the local volumetric mass transfer coefficient were analyzed over the growth period divided into three zones: Zone I, for OD ≤0.08; Zone II, OD between 0.08 and 0.19; and Zone III, OD between 0.19 and 0.30. Although the local volumetric mass transfer coefficient was constant axially in the riser, it decreased axially on moving through the downcomer. The estimated local volumetric mass transfer coefficient was found always to be higher than that estimated from the available correlations. © 2020 Society of Chemical Industry (SCI)