Transient elution of particulate matter from hydrodynamic unit operations as a function of computational parameters and runoff hydrograph unsteadiness

While computational fluid dynamics (CFD) is utilized to simulate particulate matter (PM) separation and particle size distributions (PSDs) from unit operations, the role of computational parameters and runoff hydrograph unsteadiness to simulate intra-event elution of PM has not been examined. An Euler–Lagrangian CFD model is utilized to simulate discrete (Type I) separation of PM by a common hydrodynamic unit operation subject to unsteady runoff events and a hetero-disperse PM gradation. Utilizing a baffled hydrodynamic separator (HS) this study illustrates the potential of a CFD model to predict PM elution as a function of runoff hydrograph unsteadiness. The study hypothesizes that accurate simulation of unit behavior as a function of unsteadiness is dependent on mesh size (MS), time step (TS) and PSD discretization number (DN). Full-scale physical model and CFD results are compared. Intra-event results demonstrate that MS, TS and DN parameters significantly influence prediction of transient PM elution, PSDs and computational effort. Results demonstrate that each parameter generates error for transient PM elution as influenced by the unsteadiness level. In contrast, TS, MS and DN selection each have a statistically significantly smaller influence on event-based PM mass balances and PSDs.

► An Euler–Lagrangian CFD model is developed to simulate PM fate in a hydrodynamic unit operation subject to transient flow and hetero-disperse PM.
► Simulation of unit behavior as a function of unsteadiness is dependent on mesh size (MS), time step (TS) and PSD discretization number (DN).
► CFD and full-scale physical model results are compared and model error is significantly influenced by the level of hydrograph unsteadiness.