Productivity improvement of microalgal biofuel using sodium bicarbonate($NaHCO_3$)

Abstract

Microalgae as a raw material for biofuel have remarkable strength, does not contribute to food shortages and is more productive than the second generation biofuels. In terms of biodiesel, the kind of renewable energy that can be used directly in existing engine system, the amount of lipid in microalgae quantify the productivity of the biodiesel. In order to overcome the incompatibility of high growth and high lipid content, additional step to accumulate lipid (called ‘lipid induction’) is encouraged after cultivation. In this study, the change of lipid contents in Chlorella vulgaris (UTEX-265) was investigated when sodium bicarbonate ($NaHCO_3$) was added as a lipid inducer, compared with nitrogen starvation as a representative lipid induction method. $NaHCO_3$ has the possibility to change on lipid content in C. vulgaris due to acting as salinity stress and an additional carbon source and a precursor of lipid. In order to analyze the lipid content of microalgae, Nile Red and Fatty Acid Methyl Ester (FAME) were measured. The Nile Red intensity, which is known to be related to the storage lipid content of microalgae, was higher as the added $NaHCO_3$ concentration increased. In the case of quantitative FAME analysis using gas chromatography, the highest increase was observed when 100mM $NaHCO_3$ was added, and the FAME content was 5% higher than nitrogen starvation, which was conventional lipid induction method. The Nile Red intensity and FAME content, which were complementary to each other, showed a similar tendency but showed a difference in the degree. Additional experiments to verify reproducibility showed a total lipid increase under 100mM $NaHCO_3$ greater than nitrogen starvation.