Effect of hydrodynamics and mass transfer processes on biomass production of Synechococcus HS-9 cultivated using rectangular airlift photobioreactors with baffles

Synechococcus HS-9 is being recognized as one of the potential strains for biodiesel production due to its high levels of fatty acid methyl ester (FAME), which are around 70-78%. The first stage in producing microalgae biodiesel involves the biomass production process through a photobioreactor cultivation process. In addition to microalgae strains, the optimization of the photobioreactor's performance is essential for producing high biomass. In this case, biotic factors (microalgae inoculum) and abiotic factors (nutrients, temperature, light, pH, carbon dioxide (CO₂), fluid flow, hydrodynamic processes, and mass transfer processes) are being regulated and optimized in the photobioreactor, which is influencing the growth rate of microalgae. The main objective of this study is examining the effect of hydrodynamics and mass transfer processes using the Rectangular Airlift Photobioreactor with Baffles (RAPBR-Bs) to increase the growth of Synechococcus HS-9 during the cultivation process. The study is consisting of two main parts: collecting bubble photography and video, and the cultivation process of Synechococcus HS-9. During the cultivation of Synechococcus HS-9, hydrodynamics, mass transfer, optical density (OD), and biomass weight data are being measured. The research results indicate that hydrodynamic parameters, including bubble properties such as bubble velocity (0.0064 m/s), bubble diameter (720 μm), non-dimensional numbers (Re 4.51; Eo 0.0126; Mo 8.87 × 10^-12; We 6.85 × 10^-5), superficial gas velocity (0.0008 m/s), bubble rise velocity (0.117 m/s), gas holdup (0.0072), and the mass transfer process (k_La O₂ (oxygen) 0.114 s^-1; k_La CO₂ 0.099 s^-1) in RAPBR-Bs are influencing and contributing to the growth of Synechococcus HS-9 during cultivation. The study found that Synechococcus HS-9 cultivated in RAPBR-Bs exhibited significant growth because the mixing and aeration processes are optimal. An optimal aeration process enhances the mass transfer coefficient, which in turn improves the overall mass transfer capacity of the RAPBR-Bs. The results are showing that the hydrodynamic and mass transfer properties of these RAPBR-Bs are being more efficient than those that are reported for other PBRs. Optimal conditions for Synechococcus HS-9 cultivation are occurring at day 13, as it is reaching the late exponential phase. The weight of the cultivated Synechococcus HS-9 biomass is 3.226 g.