Modulation of macro and micronutrients to enhance lipid production by Scenedesmus abundans in a flat-panel photobioreactor under outdoor natural sunlight

The present study investigates the effect of macro- and micronutrients on photoautotrophic lipid production from Scenedesmus abundans. An optimized lipid medium has been formulated using one-at-a-time variation of macronutrients and a study of micronutrient interactions. Both single-stage and two-stage strategies were used for simultaneous production of lipid and exopolysaccharide (EPS) in medium-scale photobioreactors (PBRs) using the optimized lipid medium. In the single-stage cultivation 32% fatty acid methyl ester (FAME, biodiesel) was achieved, whereas only 12.6% FAME was observed in two-stage PBR. A FAME titer of 1.16 g/L with overall FAME productivity of 32 mg/L/day and 280 mg/L EPS was achieved using the single-stage strategy. Further, under diurnal natural sunlight and outdoor conditions, a FAME content of 46%, with 1.28 g/L of FAME and 27 mg/L/day FAME productivity, and 155 mg/L EPS were achieved using the single-stage strategy in 2 L medium-scale flat-panel PBRs. Apart from high biodiesel and EPS production, this microalgal strain also has the ability to carry out natural autoflocculation with high efficiency. The strain could be exploited for high lipid content under outdoor cultivation without photoinhibition.