Enhanced photo bio-reaction by multiscale bubbles.

Highlights • Microbubbles can improve mass transfer and photo bio-reaction. • The scale effect between bubbles and microalgae was studied. • A multiscale bubble combination intake method was proposed. • Multiscale bubbles can provide dual-intensification function. • The multiscale bubbles method can enhance the growth efficiency of Chlorella. Abstract Based on experimental and computational fluid dynamics simulations, the scale effect between the bubbles and the algae for different sizes in the culture process were investigated in a photobioreactor column under single and combined gas intake conditions, including factors such as the bubble distribution, gas holdup and mass transfer coefficient of different scale bubbles (500 μm microbubbles and 5 mm bubbles). In general, microbubbles could improve mass transfer and photo bio-reaction. For microalgae cultures with large particle sizes or high biomass concentration, the mixing ability of microbubbles was weakened, and therefore, the culture efficiency decreased. However, this can be improved by using millimeter bubbles with the strong turbulent characteristic. Therefore, a multiscale bubble combination intake method was proposed. This method can significantly strengthen both the multiphase mixture and mass transfer processes and was beneficial to improving the growth efficiency of Chlorella. [ABSTRACT FROM AUTHOR]