Gravitational Settling Velocity Regimes for Heterodisperse Urban Drainage Particulate Matter

Abstract

Gravitational settling regimes, most commonly discrete (Type I) or flocculent (Type II) can be hindered (Type III) in unmaintained urban drainage appurtenances. In coastal zones or in areas with deicing salt applications, high salinity may influence particulate matter (PM) settling. This study examines settling of PM with a heterodisperse particle size distribution (PSD); typical of urban runoff. For Type I settling at low concentration ( ∼0.1 g/L ) , Newton’s and logarithmic matching models each predict measured settling velocity ( Vs ) for PM from 2–4,750 μm . For Type I Vs in runoff, PM diameter dominates the influence of PM density, fluid temperature and salinity parameter ranges. Integrating Type I Vs across a common heterodisperse PSD for regulatory testing, a physically validated computational fluid dynamics model of a baffled hydrodynamic separator (HS) illustrates the influence of Vs parameters as PM diameter⪢PM density>temperature≈salinity . Event-based PM separation by a screened HS loaded by u...