Two-phase flow modelling for oxygen renewal estimation in vertical flow filter: luxury or necessity?

摘要

Scientists and practitioners exhibit an increasing interest on effluent transfer and degradationnmodelling in Vertical Flow Sand Filters (VFSF) and Vertical Flow Constructed Wetland (VFCW).nModelling software used to this purpose is mainly monophasic: in the unsaturated zone, onlynwater flow is taken into account and air phase influence is assumed to be negligible.nIn hydrology, many studies have point out the limitations of this assumption in order to quantifynair phase movement but little has been done in the modelling of vertical flow filter. Despite itsncomplexity, two-phase flow modelling allows to overcome these difficulties. In this work,nwe describe the complex air and water flows in the particular case of vertical flow filter fednintermittently using both numerical and experimental results. Complete different behaviournis observed depending on ponding occurs or not. If it does, flow is clearly influenced by airnentrapment which is responsible of a reduction of the infiltration speed and of the drainagenof a part of the water kept at the interface between the sand and the drainage layer. Finally,nwe study the dependency of oxygen income by convection on hydraulic load and comparennumerical results with experimental results obtained on oxygen consumption.