Hydrodynamic and mass transfer characterization of an internally illuminated airlift photobioreactor for growing Spirulina platensis

Abstract

Abstract The dimensions of the of a photobioreactor play a major role in its hydrodynamic and mass transfer characteristics that also affect its growth performance. In this study, a bench-scale airlift photobioreactor (PBR) was designed and fabricated to have a riser-to-diameter ratio (Ar/Ad) equal to 0.42 and an aspect ratio (H/D) equal to 1.53. These dimension ratios are different from typical values wherein most airlift photobioreactors are designed to have Ar/Ad of at least 1.0 and H/D of at least 2.0. It was hypothesized, based on the results of Hwang and Cheng [1], the fabricated PBR in this study will have better hydrodynamic and mass transfer characteristics such as lesser mixing time, better liquid circulation and lesser gas entrainment that may lead to better growth performance. Due to the different dimension ratios from other studies, characterization of the PBR and testing of its performance are required. The hydrodynamic and mass transfer characteristics of the fabricated airlift photobioreactor in this study were measured at varying superficial gas velocities (UGR) from 0.0017 ms−1 to 0.0124 ms−1. The growth parameters of the Spirulina platensis were then tested at different aeration rates to relate the hydrodynamic and mass transfer characteristics to the photobioreactor performance. This study has proven that a photobioreactor that is designed and operated to have the best hydrodynamic and mass transfer characteristics will have the best growth performance at the same light intensity and initial optical density.