(647g) Analysis of Air Scouring Effect in Flat Sheet Type MBR

MBR (Membrane Bioreactor) is a water treatment process to treat the sewage and the waste water. Membrane module is immersed in an activated sludge tank and filtrated by microfiltration membrane or ultrafiltration membrane. As compared with conventional process, activated sludge method, MBR has advantages of space saving and treated water quality, but inferior in much power consumption caused by the aeration for restraining the membrane fouling. Reduction of power consumption is the biggest challenge in MBR process. There are two methods to reduce aeration quantity, one is developing the low fouling membrane, and the other is increasing washing efficiency for membrane surface without increasing power consumption. To develop the method for increasing washing efficiency for membrane surface, it is important to understand the scouring effect for membrane surface caused by aerated bubbles. Several researches studied washing effect for membrane surface caused by aeration, but there are few researches focusing on quantifying the washing effect for membrane surface caused by aerated rising bubbles.  

This study is focused on analyzing the scouring effect of rising bubbles in flat sheet type MBR. The relationship between aerated bubbles and shear stress at the membrane surface was analyzed using PIV analysis. We prepared the tank which modeled the zone between adjacent membranes in flat sheet type MBR and filmed the motion of tracer particles around a rising bubble. Velocity distribution of liquid around a rising bubble was analyzed, and then shear rate and shear stress at the membrane surface was derived. It was confirmed that the aeration condition affect the shear stress at the membrane surface by using PIV analysis. And also, relationship between shear stress at the membrane surface and washing effect for membrane surface caused by aeration was studied in model experiment. From the experiment, it was studied what kind of shear stress, such as average and maximum, has more relation with the washing efficiency. These results showed that PIV analysis was a useful method to quantify the washing effect of rising bubbles restraining membrane fouling in MBR. Also it was confirmed that the increase of shear stress at the membrane surface could improve the detachment of foulants and washing efficiency for membrane surface.