A novel magnet-driven rotary mixing aerator for carbon dioxide fixation and microalgae cultivation: Focusing on bubble behavior and cultivation performance

Abstract

A novel magnet-driven rotary mixing aerator (MDRMA) was proposed to reduce the diameter and rising rate of bubbles while improving CO₂ mass transfer during microalgae growth in a column photobioreactor. Visualization results showed that the bubble number density increased significantly with the increasing rotation rate of MDRMA. As the rotation rate increased from 0 to 300 r min^-1, the average bubble diameter decreased from 3.8 mm to 2.0 mm (47.4% reduction), while the corresponding average bubble rising rate decreased from 0.32 m s^-1 to 0.22 m s^-1 (31.3% reduction). Notably, when the rotation rate of MDRMA exceeded 300 r min^-1, a significant number of microbubbles with diameters below 0.5 mm were generated. When synthetic flue gas containing 12% CO₂ (v/v) was supplied for microalgae cultivation, a maximum biomass concentration of 1.75 g L^-1 was obtained with rotating MDRMA at 200 r min^-1, showing a 57.7% increase compared to the control aerated with a silicone tube aerator. Meanwhile, the pigment content reached 14.48 mg L^-1, 22.7% higher than that of the control.

Keywords: Bioreactor; Carbon fixation; Gas bubble; Magnet-driven rotary mixing aerator; Microalgae.