Reduced generation time and size of carbon dioxide bubbles in a volute aerator for improving Spirulina sp. growth

•A volute aerator was proposed to generate shear force through water centrifugation.•The volute aerator can break gas flow to promote liquid mixing and mass transfer.•The outlet bubble diameter and generation time decreased by 50.7% and 60.1%.•Mixing time reduced by 15.6% and mass transfer coefficient increased by 42.2%.•CO2 fixation rate by microalgae and biomass production increased by 26.6% and 50.7%. A novel volute aerator was proposed to generate shear force and break gas flow through water centrifugation to promote mass transfer for CO2 fixation with microalgae. The bubble evolution and gas-liquid mixing processes in volute aerator were numerically simulated. The bubble generation time and diameter were measured on a high-speed camera and assessed with level-set method. By optimizing gas inletpipe angle and water/gas inlet velocities of volute aerator, the bubble generation time decreased by 60.1% to 3.3 ms and outlet bubble diameter decreased by 50.7% to 1.8 mm, compared with traditional strip aerator. The corresponding gas-liquid mixing time reduced by 15.6% and mass transfer coefficient increased by 42.2%. The volute aerator was used as an alternative to traditional strip aerator to culture microalgae under high-purity CO2 condition, which promoted average growth rate and biomass production by 26.6% and 50.7%, respectively.