Isolation, characterization, and validation of oleaginous, multi-trophic, and haloalkaline-tolerant microalgae for two-stage cultivation

Mass outdoor cultivation of microalgae for biofuels and co-products faces challenges of low lipid productivity, contamination, inefficient CO2 supply, and difficulties in harvesting. A two-stage cultivation process was developed to address these challenges. This involves culturing microalgae in a fermentor heterotrophically or photobioreactor mixotrophically as first-stage to rapidly obtain high cell densities for inoculating a phototrophic open-pond culture featuring high levels of NaHCO3, pH, and salinity as second-stage. A microalgae that is tolerant of these phototrophic conditions, can use organic carbon, and can prolifically produce oil is key to the success of such a two-stage process. Two oleaginous, haloalkaline-tolerant, and multi-trophic green microalgae from soda lakes were isolated, identified, and compared in this study using a multi-instrument approach as candidates for such process. A model triacylglyceride (TAG) was developed for rapid, non-destructive lipid quantitation using liquid-state 1H NMR. A two-stage cultivation system and a high pH-mediated auto-flocculation method were tested on the selected strain ALP2 with a 1 L fermentor and 40 L open-tank. In unoptimized conditions, the stain achieved a final biomass concentration of 0.978 g DCW/L, lipid content of 39.78% DCW, and auto-flocculation harvesting efficiency of 64.1%.