Numerical investigation of the aeration process in the MBR system equipped with a flat sheet membrane module

Abstract

This PhD study is devoted to numerically quantify the hydrodynamic characteristics in FS modules, such as shear stress distribution on the membrane surface and flow field distribution in membrane channels, under different operational and configurational conditions, so that it can provide some hints for the design and the operation of FS membrane modules. For this, interDyMFoam with the volume of fluid (VOF) method for modeling gas-liquid two-phase flow and the self-developed solver (interSolidFoam) coupled with the sludge models for modeling quasi gas-liquid-solid three-phase flow are adopted to simulate the ascent of single bubble and bubble swarms in FS membrane channels with the liquid medium of water and activated sludge, respectively. The critical parameters of the aeration process in FS modules, such as airflow rate, bubble size, superimposed liquid velocity, membrane channel depth, and MLSS concentration, are investigated in numerical models, and their effects are examined fundamentally. The models are validated against the experimental data from the literature in terms of bubble terminal rise velocity, and a good agreement is obtained between them. Numerical results reveal that the best performance is achieved at the narrowest membrane gap distance investigated, where the maximum shear stress is obtained under the same operational conditions. Therefore, it is recommended that the smallest membrane channel of 6 mm should be applied to the FS membrane modules for better membrane fouling control. Besides, the operational parameters affect the hydrodynamics in the FS membrane module significantly. Among all of the varied parameters, MLSS concentration, namely the rheology of non-Newtonian fluid, affects the bubble ascent behavior most. Airflow rate and superimposed liquid velocity are the parameters that have the most substantial influence regarding areaweighted shear stress, where a generally rising trend is observed with an increase in superimposed liquid velocity or an increase in airflow rate.