Outdoor Photoautotrophic Cultivation of Chlorella sp. TISTR 8990 in Nitrogen- and Phosphorus-Minimal Media for Lipid Accumulation

Abstract

The nitrogen/phosphorus pool available during phases of microalgal growth plays an important role in obtaining higher biomass and lipid accumulation. The current study was based upon the optimization of the microalga, Chlorella sp. TISTR 8990 using a photoautotrophic culture in an open 6 L drinking water bottle with a total working volume of 4 L and continuous sparging with 1% (v/v) CO2 mixed air at a flow rate of 0.67 volume per liquid volume per minute. The effects were investigated of nitrogen (0, 258.5, 317.0 and 475.5 mg.L-1 KNO3 at fixed 1 g.L-1 KH2PO4) and phosphorus (0, 19.4, 38.8 and 58.2 mg.L-1 KH2PO4 at fixed 2 g.L-1 KNO3) concentrations on the biomass and lipid production. The results showed that 258.5 mg.L-1 KNO3 and 38.8 mg.L-1 KH2PO4 maximized the cell concentrations after 144 hr of cultivation at 473.7 and 455.0 mg.L-1, respectively. On the other hand, 31% and 22% lipid contents were obtained in the basal medium with 475.5 mg.L-1 KNO3 and 38.8.mg.L-1 KH2PO4, respectively. The biomass concentration and lipid content were highest in the nitrogen-minimal medium, but at different initial concentrations of KNO3 (258.5 and 475.5 mg.L-1 KNO3, respectively). In addition, palmitic acid (C16:0), linoleic acid (C18:2) and linolenic acid (C18:3) were mostly found in the microalgal oil obtained from all treatments. It was concluded that KNO3 and KH2PO4 in the basal media assisted in producing the optimal microalgal growth and lipid accumulation in cells. However, the nitrogen-minimal medium showed potential for lipid production on the basis of the lipid content. In addition, the biodiesel quality specified using the saponification number, iodine value and cetane number were calculated from the fatty acid methyl ester composition. It was also found that fatty acids derived from the nitrogen-minimal medium are a higher potential source for biodiesel production than those from the phosphorus-minimal medium.