OPTIMUM PHOTOBIOREACTOR DESIGN TO IMPROVE MICROALGAE PRODUCTIVITY USING CFD

Biodiesel production is a global green technology to produce renewable energy. Among the many raw materials for biodiesel production, microalgae are promising source with higher growth rate and oil lipid comparing to the crop including soybean and corn. Microalgae are typically cultivated mainly in the raceway pond or photobio¬reactor (PBR). The PBR system is more attractive in Korea because it can artificially control internal culture conditions such as temperature, light intensity, carbon dioxide concentration, and nutrients over unstable outside weather conditions. To optimize the design of PBR with bubble injection, a quantitative evaluation of mixing efficiency in PBR is highly needed to compare and upgrade the PBRs. Therefore the microalgae productivity (MP) was estimated by the model interlocking between hydrodynamics and algae growth model according to environmental conditions. The process of the MP calculation for PBR designs contains 1) a particle tracking methods using a com¬putational fluid dynamics (CFD) after a PIV (particle image velocimetry) validation and 2) a connecting with microalgal growth model considering light intensity from the illuminating surface area. Various PBR designs were simulated with bubble injection, internal baffle guiding internal fluid flow, and PBR types. And the MPs for each PBR were quantitatively compared. Finally, the P_8415 plate PBR with eight bubble injections and baffle (4 cm from the illuminating area, 1 cm upper, and 5 cm lower gaps) showed a maximum MP by 88.0% of increment compared to the basic PBR. Culture experiments were conducted to validate the MP comparison between the basic and upgraded 20 L PBRs using Chlorella vulgaris, and N8 culture medium. The results showed that the cell concentrations in the upgraded PBR were increased by 59.4 ~ 144% (88.6% in the average) during five culture experiments compared to the basic PBR.