Process Engineering Aspects of Vertical Column Photobioreactors for Mass Production of Microalgae

Microalgae cultivation can be made sustainable on a large-scale by lowering the costs associated with closed photobioreactors (PBRs). It can be achieved through the appropriate design of closed PBRs to achieve maximum productivity. The cultivation of microalgae is very sensitive to temperature, pH, shear stress, irradiance, and operating conditions of the PBR. The understanding of design parameters is a prerequisite for scale-up of gas-sparged vertical column PBRs. The hydrodynamics of gas-sparged vertical column PBRs play a very critical role in the optimum production of microalgae and avoiding the carbon loss (unabsorbed CO2 out of total supplied). In this article, the effects of design parameters on microalgae productivity in various vertical column PBRs, i.e., flat panel, bubble column, and airlift (draft tube) column, are critically reviewed. The microalgae production in PBRs is essentially a three-phase operation. Hence, the hydrodynamic aspects of two-and three-phase flow in the vertical column PBR are emphasized with respect to its scale-up prospect. The flow regimes and CFD modeling aspects of gas-sparged PBRs are also covered in this review.