Medium screening and optimization for photoautotrophic culture of Chlorella pyrenoidosa with high lipid productivity indoors and outdoors

•Medium screening for Chlorella cultivation was carried out indoors and outdoors.•The outdoor results of medium screening were different from those indoor.•F-Si medium is the optimum both under indoor and outdoor conditions.•The selected medium was optimized under outdoor conditions.•The optimized medium results in higher productivities both indoors and outdoors.

Medium screening and optimization is one of the most important preconditions for photoautotrophic cultivation of microalgae. Although, it has been widely conducted indoors, little work performed outdoors. There are enormous differences between indoor and outdoor conditions, especially for light intensity, temperature and their diurnal or annual fluctuations, which would greatly influence microalgae growth. No data shows whether the differences would lead to different results on medium screening and optimization. In present study, medium screening for the photoautotrophic cultivation of Chlorella pyrenoidosa was carried out indoors and outdoors firstly, and then the selected medium was optimized. The results showed that F-Si medium is the optimum both under indoor and outdoor conditions. Based on F-Si medium, nutrients were optimized as follows: NaNO3 500 mg l−1, NaH2PO4·2H2O 7.7 mg l−1 and FeCl3·6H2O 6.30 mg l−1. With the optimized medium, the biomass, lipid content and productivity were all significantly higher both indoors and outdoors.