Enhanced productivity of microalgae by the designed vertical flow in a small-scale cultivation system

Abstract

Microalgae are one of the most promising renewable energy sources, which utilize carbon dioxide, water and sunlight only in order to produce valuable bio-product. Different from other biomass, microalgae have advantages of high biomass productivity and no adverse effect on food supply. Light intensity, one of the major factors in the cultivation of microalgae, decreases with the depth of medium. Therefore, vertical mixing is necessary to expose more algal cells to sunlight. It is important as vertical mixing determines the probability by which cells are exposed to light. In this study, we demonstrated the effect of vertical mixing on algal cell growth by employing a structure in a small-scale experiment. Experiments were performed in a beaker incubator using a delta wing, modified delta wing, and a rotor design for vertical flow. On Day 8, the dry cell weight (DCW) was 0.53 g/L for delta wing (vertical velocity = 0.00577 m/s), 0.55 g/L for modified delta wing (vertical velocity = 0.00589 m/s), and rotor showed 0.87 g/L of DCW (Vertical velocity = 0.0076 m/s). DCW was 0.44 g/L for the control beaker incubator with the vertical flow of 0.0053 m/s. These correspond to 12%, 25.0%, and 56.6% increase in volumetric biomass productivity for delta wing, modified delta wing, and rotor, respectively, as compared to the control. Numerical simulation was performed for the rotor and the control beaker incubators using computational fluid dynamic (CFD) software, ANSYS CFX 18.0.