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영어

Botryococcus braunii was cultivated with ambient air containing 10% CO2 and flue gas. With flue gas, the biomass and lipid productivity for B. braunii were 77 mg L-1 d-1 and 21 mg L-1 d-1, respectively, which were higher than those with 10% CO2. Oleic acid, a main component of biodiesel, occupied 55% among the fatty acids in B. braunii. The photosynthetic parameter Ik, which is the irradiance at the onset of light saturation, was relatively higher for B. braunii, meaning it could be cultivated under a high light intensity. Therefore, the present results suggest that B. braunii is appropriate for producing biodiesel, due to its high lipid content and oleic acid proportion. The specific growth rate of B. braunii reached a constant of 0.177 d-1 during
cultivation with an initial nitrate feed of 3.66 mM. The maximum lipid productivity of 19 mg L-1 d-1was achieved at 0.37 mM nitrate. Fatty acid composition changed with nitrogen concentration. Under nitrogen limitation, the fatty acid composition of the B. braunii changed with increase in oleic acid content. Oleic acid content (86 % of total fatty acids) was higher in nitrogen limited culture than in nitrogen sufficiency culture condition (69 % of total FA). Delta-9 desaturase (desC) gene encodes an ACP-desaturase involved in the synthesis of the oleic acid. The expression level of desC measured by qRT-PCR showed a 2.6-fold increase in nitrogen-limited cells than that of nitrogen-sufficient cells. This coincides with the time when the cells reached nitrogen-starvation conditions i.e., after day 4. Biodiesel containing higher concentration of oleic acid has better properties such as anti-oxidation and cold flow property. Photosynthetic capacity based on O2 evolution rate per cell or chl-a was increased with decreased nitrate concentration. The factors for harvest by flocculation of B. braunii were investigated. The most significant factors were determined as FeCl3 concentration, bioflocculant percentage, and the time for slow mixing. When the biomass of B. braunii was 1.1 g L-1, the optimum harvesting condition were 0.57 mM FeCl3, 0.87% bioflocculant, and slow mixing for 180 sec. Additionally, 10 mM CaCl2 and rapid mixing for 60 sec. were basically needed for bioflocculation.