Bubble Performance Study before and after Detachment in a Membrane Bioreactor
In the membrane filtration system of the Membrane Bioreactor, air bubbles are generated in the Membrane Bioreactor tank to scour the surface of the hollow fiber membranes by creating shear forces and vibrations to prevent fouling, known as air scouring process. The generation and formation characteristics of the air bubbles have a significant impact on the performance of the overall MBR system. In this paper, experimental studies were performed to investigate the bubble formation characteristics before and after detachment. Before detachment, based on the correlation between horizontal diameter and vertical diameter, two stages are identified, namely bound expansion stage and acceleration expansion. In the bound expansion stage, the bubble rises at a constant speed, while expands uniformly. In the acceleration expansion stage, the bubbles still rising at a constant speed, while expands speed gradually slows down. The higher the air inlet velocity, the shorter the bound expansion stage. After detachment, the bubble rising behavior is observed to be classified into three regions. In the first and third region, the bubble rising speed is constant, while in the second region, the bubble rising unsteadily. At detachment time, the bubble size in the horizontal direction does not change with air inlet speed, while increase slightly in the vertical direction.