Bubble rise velocity and bubble size in thickened waste activated sludge: Utilising electrical resistance tomography (ERT)

Abstract

Bubble columns are intensively used in many different industries as multiphase contactors. The gas phase properties in the bubble column significantly impact on the hydrodynamics of the column which effects on heat and mass transfer rates within the column. In this paper, electrical resistance tomography together with dynamic gas disengagement technique is used to determine the gas holdup and bubble rise velocity within the column at four different gas flow rates (1–7 L/min) and two different total solids concentrations of waste activated sludge (3% & 5.5%). For the first time, effective shear rate and bubble size are calculated based on the Herschel–Bulkley model. A linear relation was observed for the bubble rise velocity with stress imposed and between gas holdup and natural logarithm of stress imposed by gas injection.