2D modeling of rectangular primary settling tanks - Verification of mathematical model and numerical method

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 < 150-200 mg/L) concentration, the influence of solid phase to the fluid phase could be ignored, the mathematical model could be used to predict the remove efficiency, and the results are in good agreements with other predicted values available in literatures. The flow field changes when the incoming flow coming from the middle part of the inlet, there are two vortices in the inlet region in this case, and the predicted results were verified by comparing with Adams and Rodi's work. It is therefore concluded that the mathematical model and HFAM approach can be used to simulate the turbulent flow, mass transfer and settling process in rectangular primary settling tanks with low SS concentration wastewater.