Microalgae have been widely studied as one of the best sources of biomass for biodiesel production. Microalgae biodiesel production economic efficiency should be considered. Floating plastic PBRs advantage is relatively low cost compared with tubular photobioreactors, vertical glass cylinders, raceway ponds and flat photobioreactors. Moreover, microalgae ocean culture system has a lot of advantage. First of all, we performed microalgae seasonal (spring, summer and fall) cultivation utilizing floating plastic photobioreactors in Wando’s offshore, Korea to confirm the potential of microalgae cultivation in the ocean. Microalgae species is Dunaliella tertiolecta LB999.. The highest biomass productivity was achieved in the summer by optimal seawater temperature (0.11 g/L/d). However, the biomass productivities in spring and fall were 0.005 g/L/d and 0.02 g/L/d, respectively, by low seawater temperature. As a result, we confirmed the possibility of microalgae cultivation in the ocean. Ocean culture biomass productivities were lower than lab scale.
To overcome low biomass productivity and low temperature stress, In this study, we examined to develop the culture system of marine microalgae in the ocean. Furthermore, Tetraselmis sp. KCTC12236BP grow well in low temperature. It isolated in Gang-hwa, Incheon, Korea. We were used marine photo-bioreactor (MPBR). Repeated batch culture was applied. Culture medium used in this experiment is 3-fold concentrated f/2 medium suspended in natural seawater. NaHCO3 4 g/L was added as an carbon source. Working volume was 15 L. Natural seawater obtained from west sea, Korea. Culture was inoculated at fresh cell weight 0.1 g/L. Culture environmental condition at average light intensity 708 μE/m/s, average temperature 20.2℃ and water temperature 11.7℃. Nitrate depletion when 50% of culture medium was harvested. Then 3-fold concentrated f/2 medium suspended in natural seawater. NaHCO3 4 g/L was added. As a result, average biomass productivity was 0.36 g/L/day. Average FAME productivity was 3 mg/L/day. Repeated batch culture biomass productivity has increased more than 2.9 times batch culture.