Production of lipids with Microchloropsis salina in open thin-layer cascade photobioreactors

Microalgal biomass is considered as the most promising feedstock for sustainable production of liquid fuels. Lipid production with Microchloropsis salina was studied in open thin-layer cascade (TLC) photobioreactors with a surface area of 8 m² applying a physically simulated Mediterranean summer climate. High lipid concentrations of up to 6.6 g L^-1 with 46% (w w^-1) total lipids in dry cell mass were achieved in two-phase batch processes applying a nitrogen limitation. The two-phase batch process was transferred into a continuously operated reactor cascade of two TLC photobioreactors. Microchloropsis salina cells were produced continuously in the first photobioreactor, whereas continuous lipid production was enabled in the second, nitrogen-limited TLC photobioreactor resulting in continuous production of 3.0 g L^-1 lipids with a high overall lipid space-time-yield of 0.2 g L^-1 d^-1. The control of alkalinity to about 10 mM resulted in high CO₂ conversion efficiencies of 84-87%.