Microalgae are a promising feedstock for biofuel production. Lipid content in microalgae could be enhanced under nutrient depletion. This work investigated the effect of the nutrient on lipid accumulation in Ankistrodesmus sp. culture. Batch cultures were carried out using fresh BG11 medium, and after the harvest, the medium was reused for the next culture; this method was repeated two times. The maximum lipid productivity of 29.75 mg L(-1) day(-1) was obtained from the culture with the second reuse medium. In continuous cultures, Ankistrodesmus sp. was cultured in both fresh and modified BG11 mediums. The modified BG11 medium was adjusted to resemble the content of the first reuse medium. As a comparison between batch and continuous cultures, it was proven that the productivity in the continuous culture was better than in the batch, where the achievable maximum biomass and lipid were 188.30 and 38.32 mg L(-1) day(-1). The maximum lipid content of 34.22% was obtained from the continuous culture at a dilution rate of 0.08 day(-1), whereas the maximum saturated and unsaturated fatty acid productivities of 79.96 and 104.54 mg L(-1) day(-1) were obtained at a dilution rate of 0.16 day(-1.)

Abstract-Ankistrodesmussp. was cultivated for the production of microalgal lipid. It was proven that batch culture provided a better biomass and lipid productivities than continuous cultures where the achievable maximum cell and lipid productivities were 279.80 and 87.10 mg L -1 d -1 . pH in the range from 6 to 8 was not found to give significant effects on growth and lipid production where the culture seemed to grow best at pH 8. Although the algal growth remained unaltered, lipid production could be enhanced when the culture was aerated with additional CO 2 . It was found that as much as 30% lipid could be enhanced when 5% by vol. of CO 2 was mixed with the air supply, i.e. lipid productivity increased from 87.10 to 104.43 mg L -1 d -1 . Analysis indicates that CO 2 helped promote the accumulation of palmitic acid which is the dominant lipid species.