The Whole Process CFD Numerical Simulation of Flow Field and Suspended Solids Distribution in a Full-Scale High-Rate Clarifier

To further reduce the contents of phosphorus and suspended solids (SS) in the effluent, the high-rate clarifier is adopted by some wastewater treatment plants (WWTPs) to upgrade their processes. However, due to the complex phosphorus species and unclear hydraulic characteristics after the addition of the high-rate clarifier, the removal efficiencies of total phosphorus and the optimization strategies of SS removal remain unclear. The high-rate clarifiers are mainly composed of the mixing zone and the settling zone. Only the hydraulic characteristics of the mixing zone have been studied. It is necessary to focus on the hydrodynamics of the settling zone to understand the sedimentation process and pollutant removal mechanism in depth. Therefore, this study focused on the whole process of high-rate clarifier of the Wuhan Nantaizi Lake WWTP in China. The distributions of flow velocity and SS in the full-scale high-rate clarifier were simultaneously simulated by the solid-liquid two-phase whole process computational fluid dynamics (CFD) model which was established in this study. The simulated results of the developed CFD model were in good agreement with the experimental data obtained in the high-rate clarifier. The normalized standard error was less than 7.66%. The overall flow velocities in the settling tank were much smaller than that in the reaction tank. After the fluid passed through the diversion effect of the overflow wall and the under-through channel, the overall kinetic energy loss was relatively large. Meanwhile, the residence time of fluid in the settling tank was longer than that in the reaction tank. The sludge sedimentation happened at the edge of the settling tank due to the vertical angle between the plug-flow fluid and the outlet. The successful construction of the CFD model could lay the foundation for the next step of the high-rate clarifier optimization operation and research on pollutant removal.