Discrete phase model representation of particulate matter (PM) for simulating PM separation by hydrodynamic unit operations

Modeling the separation of dilute particulate matter (PM) has been a topic of interest since the introduction of unit operations for clarification of rainfall-runoff. One consistent yet controversial issue is the representation of PM and PM separation mechanisms for treatment. While Newton's Law and surface overflow rate were utilized, many historical models represented PM as a lumped gravimetric index largely out of economy and lack of particle analysis methods. As a result such models did not provide information about particle fate in or through a unit operation. In this study, PM discrete phase modeling (DPM) and computational fluid dynamics (CFD) are applied to model PM fate as a function of particle size and flow rate in two common types of hydrodynamic separator (HS) units. The study examines the discretization requirements (as a discretization number, DN) and errors for particle size distributions (PSDs) that range from the common heterodisperse to a monodisperse PSD. PSDs are categorized based on granulometric indices. Results focus on ensuring modeling accuracy while examining the role of size dispersivity and overall PM fineness on DN requirements. The fate of common heterodisperse PSDs is accurately predicted for a DN of 16, whereas a single particle size index, commonly the d(50m), is limited to monodisperse PSDs in order to achieve similar accuracy.