Micro-nano-bubbles and their application in microalgae production: Wastewater treatment, carbon capture and microalgae separation

Microalgae is capable of fixing CO2 and utilizing nutrients from wastewater through photosynthesis, making it the most promising biotechnology for carbon capture. Efficient carbon capture is crucial for both microalgae cultivation processes and biomass conversion. Micro-nano-bubbles (MNBs) have the potential to enhance the CO2 solubility and carbon capture efficiency of microalgae due to their minuscule size, high gas-liquid mass transfer efficiency, and large electrostatic interactions. However, there is still a lack of comprehensive reviews to elucidate the potential applications of MNBs in microalgae production. Therefore, this review will systematically introduce the unique properties of MNBs and suitable generation methods for microalgae cultivation. In addition, the insights mechanisms into how MNBs improve the gas-liquid mass transfer and carbon capture efficiency during microalgae cultivation are illustrated. Moreover, potential applications of MNBs in microalgae cultivation, such as the synergistic effects of MNBs in the pretreatment of wastewater and microalgae separation, are highlighted and discussed in depth. Finally, future research directions for MNBs-coupled microalgae systems are outlined. This review is organized to provide readers with an understanding of relevant topics to advance the application of MNBs in the microalgae cultivation industry as well as in upstream and downstream industries.