Energy conversion analysis of microalgal lipid production under different culture modes

•Microalgal growth and lipid production in various culture modes were investigated.•The algae can accumulate biomass and lipids in aerobic and anaerobic conditions.•Maximum total lipid content of 51.3wt.% was obtained in mixotrophic aerobic mode.•Mixotrophic aerobic cells gave the highest energy conversion efficiency of 45.7%. Growth and lipid production performance of Scenedesmus sp. under different culture modes were investigated. Under heterotrophic aerobic mode, algal biomass concentration and total lipid content reached 3.42gL−1 and 43.0wt.%, which were much higher than those in autotrophic aerobic mode (0.55gL−1/20.2wt.%). The applied light exposure of 7.0Wm−2 was beneficial to biomass and lipid accumulation. Mixotrophic aerobic mode produced the highest biomass concentration of 3.84gL−1. The biomass was rich in lipids (51.3wt.%) and low in proteins (17.9wt.%) and carbohydrates (10.3wt.%). However, lower algal biomass concentration (2.93gL−1) and total lipid content (36.1wt.%) were obtained in mixotrophic anaerobic mode. Mixotrophic aerobic mode gave the maximum heat value conversion efficiency of 45.7%. These results indicate that mixotrophic aerobic cultivation was a promising culture mode for lipid production by Scenedesmus sp.