The two layer turbulence model combining mass transfer model and settling model was used to establish a mathematical model describing flowing, mixing and settling characteristics in rectangular primary settling tanks. The Semi Implicit Method for the Pressure Linked Equations (SIMPLE) method was used on pressure correction. The hybrid finite analytic method with staggered grid was used to solve this model. The simulation results obtained using the mathematical model were compared with the experimental data and simulation results available in literatures, and the results of comparison indicate that the profiles of the velocity field at Re=10900 and the recirculation length increasing with Reynolds number range from 2500 to 25000 in case of incoming flow coming from the bottom are in agreements with the experimental results and simulation results of Imam; the Flow Through Curve (FTC) obtained using the mathematical model are in good agreement with the curves based on experimental data and simulation results of Imam, and the accuracy of predicted FCT is higher than Imam’s results. Under the low Suspended Solids (SS
