Biomass and lipid productivity of Neochloris oleoabundans under alkaline–saline conditions

• N. oleoabundans biomass production costs more light energy at high pH.
• Fatty acid content of N. oleoabundans was two-fold higher at high pH.
• Fatty acid yield on light energy was highest at high pH with nitrogen starvation.

We explored the effect of pH and nitrogen supply on the biomass and fatty acid productivities of the microalga Neochloris oleoabundans cultivated in saline medium under continuous light. During light-limited and nitrogen-replete conditions, the maximal volumetric biomass productivity was 0.98 gDW L− 1 d− 1 at pH 8.2 and 0.47 gDW L− 1 d− 1 at pH 10. Apparently microalgal growth costs more energy at high pH, resulting in lower biomass productivities. With the fatty acid content being 2-fold higher at pH 10 (8% versus 15% w/w), the maximal volumetric fatty acid productivity was 75.2 mgFA L− 1 d− 1 at pH 8.2 and 66.6 mgFA L− 1 d− 1 at pH 10. When high pH was combined with nitrogen depletion, fatty acids accumulated up to 29% (w/w), leading to the highest fatty acid productivity observed in this study (112.4 mgFA L− 1 d− 1). These findings stimulate further development of a two-stage process for optimal overall lipid productivity.