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. (C) 2020 Elsevier Ltd. All rights reserved.