Prediction of the circulation velocity in a membrane bioreactor

Abstract

In this study, the hydrodynamics of a pilot scale membrane bioreactor (MBR) with different configurations for air scouring were investigated experimentally and numerically. The results were analyzed with the aim to derive a correlation between the aeration flow rate and the circulation velocity in the reactor, as it is well known for airlift loop reactors without internals. To achieve a fouling reduction by air scour at a minimal energy input, an airlift loop configuration was chosen because higher cross flow velocities and therefore higher shear rates can be obtained on the membrane surface. The experimental investigations were carried out with water and air in a quasi 2-dimensional model with 2.1 m height, 1.2 m width and 0.1 m depth. The bubble distributions were optically analyzed by video imaging through the transparent walls of the tank. Numerical simulations were used to perform parameter studies by varying geometrical values or operating conditions (e.g. channel width, bubble diameter). A first approach to calculate the circulation velocity depending on the geometry of the flat sheet membrane module and the aeration intensity was derived.