Screening of freshwater oleaginous microalgae from South China and its cultivation characteristics in energy grass digestate

Abstract

Microalgae biodiesel attracts considerable attention from energy organizations around the world. Lack of high oil-producing oleaginous microalgae is considered as one of the main bottlenecks for large-scale production of microalgae biodiesel. To address this issue, a nitrogen limitation-based method for screening oleaginous microalgae using 24-well plates was developed in the present study. Thirty microalgae strains collected from a subtropical freshwater system of South China were selected and cultivated in bubbling column photobioreactors, with lipid yields as the endpoints. The dry weight (DW) of seven strains exceeded 6.0 g L−1 and total lipid contents of 10 strains were over 40% DW. Coelastrella sp. GN12 was further evaluated as it had the highest lipid yield (4.94 g L−1) and abundant triacylglycerol (95% total lipid). This strain was cultured in various digestates from mono-digested energy grass diluted with BG-11. A ratio of 25% energy grass digestate: BG-11 (v: v) (designated as EG25) and a pure unsterilized energy grass digestate (designated as EG100U) were the most effective at growth and oil accumulation (with total lipid content > 50% DW). Total nitrogen removal rates of EG25 and EG100U were 73% and 57%, respectively, and the strain was even more effective at removing total phosphorus (96% and 94%, respectively). Therefore, energy grass digestate can be used as a substitute medium for GN12, transforming waste into valuable energy sources and achieving the benefits of resource recycling and clean energy production.