Fluent Simulation In Biological Aerated Filter Based On Stratified Biofilm

Biological aerated filter (BAF) which attracted a wide range of attention was oneof the most popular wastewater treatment process in nowadays. With thebiodegradation and physical filtration process by the biofim which attached on thefilter media, BAF could efficiently remove contaminants in wastewater. In this articlewe focused on the biodegradation process inside the BAF, and established amathematical model to simulating the process in Biostyr BAF.Considering the heterogeneous feature of the biofilm, a variable diffusioncoefficient which decreased along the thickness of biofilm was added to theDiffusion-Reaction equation, and a stratified-biofilm mathematical model had beenbuilt. We wrote a Matlab program to calculate the model and compared the differenceof substrate fluxes between stratified-biofilm model and homogeneous model. Modelparameters had been changed to analyze their effect on effectiveness factors and wefound the following rules. The effectiveness factors of the two models were bothreduced as the Thiele modulus() was increased and the difference of theeffectiveness factors between the two models got larger when the diffusivitygradient(δ) was increased and the substrate concentration (C) was reduced.Based on the local volume averaging method, we analyzed the multi-scalephenomena in BAF and derived the governing equations in bioilm-scale,representative elementary volume-scale (REV-scale) and reactor scale. The governingequations in REV-scale would be applied to Fluent simulation. With the Matlabprogram for stratified-biofilm, we simulated the biofilms reaction in five samplingports of Biostyr BAF and got piecewise functions for effectiveness factor. Thepiecewise functions had been combined with the solving method for homogenousbiofilm to obtain a pseudo-analytical model for stratified biofilm.Established a3-dimensional mesh model for Biostyr BAF in Gambit, and simulatedthe biofiltration process inside the BAF by Eulerian model in Fluent6.3. Numericalsimulation of COD and N N:4concentration distribution along the filter bed wereconsistent with the experiment values measured by Viotti. The verified mathematicalmodel had been used to predict the dissolved oxygen distribution along the bed height andthe effect of operating parameters such as hydraulic loading, inlet velocity and filter mediasize on Biostyr Biological aerated filter’s performance. As the oxygen consumption rate changed along the filter height, dissolved oxygen fraction in liquid phase increased at thebottom of the filter before decreased obviously in the middle of the filter bed, and thefraction rose to normal level at last. Hydraulic loading and media size both affected theremove rate of COD and N N:4in liquid phase. When the COD concentration was100mg/L and the N N:4concentration was7.2mg/L in the inlet, the remove rate becameworse when the inlet velocity increased and got better when the media size decreased.