Different types of bubbly flows in a confined channel with the aim of limiting microalgae biofilm development – Part II: study of the development and removal of microalgae biofilm
Abstract
This study aims at investigating the role of bubbles passage to prevent biofouling in thin-gap bubble column photobioreactors (PBRs) where the biomass concentration is important and the reactor thickness is low. Different types of gas sparging are tested in a square channel with a cross-section of 4x4 mm2 mimicking a thin-gap bubble column PBR.
Firstly, it is shown that it is very difficult to detach the biofilm once it has adhered to the wall:only the bubbling conditions with high wall shear rate fluctuations are able to detach part of the superficial layers of the biofilm, but no effect is observed on the detachment of the conditioning layer.
Secondly, bubbling generating either high shear rate fluctuations, or high mean shear stress are tested to assess their ability to delay biofilm development: both accentuate biofilm adhesion, showing that the biofilm may be compacted by highly confined bubbles.
Thus, small bubbles whose diameter (1.4 mm) is smaller than the side of the square channel are investigated, allowing bubbles oscillations and a 3D hydrodynamics around the bubble. This bubbling, which creates the most important shear rate fluctuations, is the most adapted to limit the development of biofilm in thin-gap PBR.