Aerobic Sludge Granulation: A Computational Fluid Dynamics Study of Fluid Flow Patterns in Bubble Column Reactors

The flow patterns of bioreactors are influenced by superficial gas velocity (SGV), substrate types, and concentration, which in turn affect the properties of aerobic granular sludge (AGS). This study used three-dimensional computational fluid dynamics to simulate the flow pattern in the bubble column reactor under the SGV of 1.2-5.0 cm/s and reactor ratio of height to diameter (H/D ratio) of 120/6, different substrate types, and concentration. The SGV was more significant to the flow pattern. The flow pattern transformed from single-cell circulation to small-scale vortices with the increase of SGV. Five sequencing batch reactors were employed to cultivate the AGS with an SGV ranging from 1.0 to 5.0 cm/s and an H/D ratio of 120/6. The mature AGS was performed under the SGV of 2.0-5.0 cm/s. The combination of simulation and experiment showed that the flow pattern of transverse rotation was a vital factor in the formation of AGS with an SGV of 1.2 cm/s. The flow pattern of multiple spiral vortices was necessary for the stability of AGS, with an SGV of 2.0-5.0 cm/s. The substrate types and concentration influenced the liquid viscosity and then affected the diameter, properties, and formation time of AGS.