Effective mixing and aeration in a bioreactor with Taylor vortex flow

Abstract

In order to clarify the effects of the behaviors of the bubbles of aeration on the productivity of biomass, experiments including cultivation and computation were performed utilizing a bioreactor with a Taylor vortex flow in the annular gap of concentric cylinders. The shape of the inner cylinder and the position of the aeration were changed to vary the floating speed of the bubbles. The flow velocity was measured by Particle Image Velocimetry and the time taken for the floating of the bubbles from the lower wall to the upper surface of the suspension was also measured along with prediction by Large Eddy Simulations. The cultivation of cyanobacteria was also performed. Attaching spiral fins to the inner cylinder induces downward velocity in the region close to the outer cylinder, where a large-scale vortex replaces the original three vortical structures generated in the case of a simple circular inner cylinder. As a result, the time taken for the floating of the bubbles becomes longer when the aeration was performed at a position close to the outer cylinder. When cultivation was performed in these conditions, the cyanobacteria were found to have developed up to a high content and that their growth rate was also high. The present results indicate that the behaviors of the bubbles of aeration are related to the productivity of the biomass.