Combining nitrogen starvation with sufficient phosphorus supply for enhanced biodiesel productivity of Chlorella vulgaris fed on acetate

Heterotrophic cultivation of microalgae is attracting more attention due to its high production efficiency. In this study, Chlorella vulgaris was cultivated heterotrophically with acetate in batch systems. The effects of nitrogen deficiency and different phosphorus supply levels on biodiesel production were investigated. It was found that C. vulgaris can assimilate acetate and accumulate fatty acids simultaneously. The highest FAME (Fatty acid methyl ester) content (56%) of algae was obtained in nitrogen deficient media. Interestingly, the productivity of fatty acids under nitrogen starved conditions was three times greater than that under nitrogen sufficient conditions. Moreover, FAME productivity was further enhanced to 66 mg L^-1·d^-1 by a sufficient phosphorus supply but there was no effect caused by phosphorus limitation. Furthermore, the conversion yields of acetate consumed to fatty acids produced (Chemical oxygen demand (COD)-based) in nitrogen starved media were also three times higher than those in nitrogen sufficient media. FAME productivity of C. vulgaris under nitrogen starvation was not improved by controlling the pH at stable values (7.5, 8.0, and 8.5), and even decreased when pH was controlled at 7.0 and 9.0.