Enhanced growth and hydrocarbon production of Botryococcus braunii KMITL 2 by optimum carbon dioxide concentration and concentration-dependent effects on its biochemical composition and biodiesel properties

The purposes of this study were to find the optimum level of supplementing CO₂ for increasing the biomass and hydrocarbon production of B. braunii KMITL 2 (A race) and to determine the effects of CO₂ level on CO₂ fixation and biodiesel properties. The experimental results showed that the alga supplemented with 10% CO₂ produced the highest biomass (1.48±0.02gL^-1) and CO₂ fixation rate (100.43±1.42mgL^-1d^-1) that were 2.7 and 5.3 times higher than the control (0.04% CO₂). The gravimetric hydrocarbon content (36.82±3.39%) and hydrocarbon titer (0.35±0.03gL^-1) of the alga supplemented with 5% CO₂ were 1.6 and 2.7 times higher than the control. Cultivation of this strain under 5% CO₂ gave the highest hydrocarbon yield and good biodiesel properties with the lowest iodine value and a higher CN value than the ASTM D6751 and EN 14214 fuel standards.