Consideration of inclined mixers embedded inside a photobioreactor for microalgae cultivation using computational fluid dynamic and particle image velocimetry measurement

Microalgae have been introduced as one of the most promising alternative resource to substitute fossil fuels. Photobioreactors (PBR) are essential apparatus that facilitate cultivation of microalgae. In this study, a new PBR is designed and constructed based on internal mixing of microalgae to increase biomass productivity. The proposed PBR is equipped with hollow tubes which are simultaneously served as static mixer and internal light source to the culture. A PBR with the same geometry and without internal mixers is used as control PBR to evaluate the performance of this new system. The hydrodynamics inside both systems are simulated using 3D computational fluid dynamics (CFD). According to simulation results, the proposed PBR with static mixers has better performance in terms of fluid circulation, gas volume fraction and turbulency compared to the control system. Algal growth in the proposed PBR and the control system are compared through experimental cultivation tests. Microalgae cultured in the proposed PBR has higher growth rate compared to microalgae cultured in the control PBR at the same light intensity. According to experimental results, maximum biomass concentration in the proposed PBR is 100% higher than that in the control one which could be due to the better circulation of culture inside the proposed PBR. Analysis of the biomass obtained from both PBRs shows similar composition and heating value. However, the other properties of these samples such as volatile matter content, ash content and fixed carbon content are slightly different.