Photo-bioreactor design for microalgae: A review from the aspect of CO2 transfer and conversion.

Photobioreactor (PBR) is the most critical equipment for microalgal photosynthetic fixation of CO2. It provides suitable environmental conditions, such as CO2, light and nutrients, for microalgal growth. As the major carbon source for microalgae, CO2 gas is pumped into PBR with the formation of bubbles and formed gas-liquid flow. The gas-liquid flow affects CO2 and nutrients transmission as well as microalgae cells distribution in PBR, thereby affecting the biochemical reaction of microalgae. While the migration and transport of biochemical reaction products affect the two-phase flow, phase distribution and flow resistance in the PBR in return, thus affecting the transport of light and nutrients. Therefore, microalgal photosynthetic rate is determined synthetically by two-phase flow and the transport of CO2, light and nutrients in PBR. Deep understanding of gas-liquid two-phase flow, energy and mass transfer coupling with microalgal growth in PBR is the cornerstone for the design of an efficient microalgae PBR.