CFD Model of PM Sedimentation and Resuspension in Urban Water Clarification

Abstract

Unit operations (UO) for urban water clarification are commonly implemented for management of particulate matter (PM), PM-associated chemicals, and microbial species, primarily through sedimentation. In this study, an Eulerian-equilibrium Eulerian computational fluid dynamics (CFD) model is developed to simulate the transport and fate of dilute PM suspensions in UO clarification systems. PM sedimentation and resuspension are considered with PM bed boundary conditions. For these simulations, two Robin boundary conditions are proposed for the capacity-limited resuspension (no-flux condition) of the PM bed layer and nonequilibrium sedimentation conditions. The applicability of the numerical model to PM transport is tested through four case-study databases including two laboratory flumes and two full-scale commercial UO systems designed for PM sedimentation. The numerical implementation of the proposed model is based on an open-source C++ framework. The detailed numerical structure of the model is given. For PM sedimentation with no resuspension, the numerical and physical models of PM separation are in excellent agreement for these systems. For PM resuspension, numerical and physical models of eluted PM concentration as a function of hydraulic stress (flow rate) and PM gradation are in good agreement. The numerical and mechanistic robustness of the proposed model represents an improvement compared with a representative Lagrangian particle method of previous studies. The proposed model can be implemented for design iterations and regulatory certification of UO clarification systems.