Optimized bubbling strategy for improving microalgae growth of Chlorella vulgaris and subsequent valorization to lipids

Bubble size plays an important role in microalgae cultivation in bubble column bioreactor. Three bubbling strategies (millimeter bubbles, microbubbles, and multiscale bubbles) were compared in this study for enhancing microalgae growth of Chlorella vulgaris. A higher microalgae growth rate using microbubbles was observed in the initial growth phase; afterwards, millimeter bubbles exhibited better performance in the growth rate of Chlorella vulgaris. CO₂ mass transfer and gas–liquid mixing performance were evaluated, and highly variable between bubble sizes. Therefore, a multiscale bubble strategy was proposed, leading to an increase of 7.47% and 17.84% in biomass concentration compared with the sole use of microbubbles and millimeter bubbles, respectively. Finally, the potential of Chlorella vulgaris as the feedstock for biodiesel production and the performance characteristics of produced biodiesel were investigated. The multiscale bubble feeding method can simultaneously optimize mixing and mass transfer throughout the cultivation process and enhance the photosynthetic efficiency.