Photoautotrophic outdoor two-stage cultivation for oleaginous microalgae Scenedesmus obtusus XJ-15.

In this study, Scenedesmus obtusus XJ-15 was firstly selected from seven strains microalgae (Chlorophyta, Scenedesmaceae) and then cultivated using a two-stage strategy, which composed of fast cell growth in stage I and followed by lipid induction in stage II in 5-L flasks outdoors. In stage I, the biomass productivity was increased from 139.4 to 212.1 mg L(-1) d(-1). In stage II, lipid content was increased from 26.1% to 47.7% by adding NaCl into the culture. This two-stage process was also realized in an 140-L photobioreactor outdoors, with a biomass productivity of 86.5 mg L(-1) d(-1) and CO2 fixation rate of 170.0 mg L(-1) d(-1) in the first stage, and high lipid content of 42.1% in the second stage. With such a culture strategy, the overall lipid productivity was improved and better biodiesel quality was obtained. These results suggested the photoautotrophic two-stage system was not only feasible but also effective.