Characterization of split cylinder airlift photobioreactors for efficient microalgae cultivation

Abstract

An extensive characterization of photobioreactors (PBRs) must be made in order to optimize their operational conditions, operate design improvements and perform scale-up. In this work, a hydrodynamic characterization of liquid and gas phases was performed, as well as the determination of the mass transfer coefficient of three different PBRs (bubble column – BC – and two Split Cylinder Airlift Photobioreactors – SCAPBRs – featuring two different riser-to-downcomer cross sectional area ratios: SCAPBR 75 and SCAPBR 50). The effect of these parameters on biomass productivity was also evaluated. The developed SCAPBRs proved to be extremely suitable for microalgae cultivation. The design of the PBR, particularly the designed gas sparger, allowed meeting the needs of microalgae in terms of mixing and mass transfer (efficient supply and removal of CO2 and O2, respectively). SCAPBR 50 (with a superficial gas velocity of 0.0044 m s−1) showed, among the tested PBRs, the highest value of biomass volumetric productivity (0.75 g L−1 d−1). This result is probably due to a higher PBR illuminated surface area, and a more regular flow pattern between the illuminated and dark zones verified in SCAPBR 50, which allows exposing cells to regular light–dark periods.