Physical Modeling of Particulate Matter Washout from a Hydrodynamic Separator

Abstract

A hydrodynamic separator (HS) is commonly used as a preliminary unit operation for separation of coarser particulate matter (PM) and PM-associated constituents transported by urban rainfall-runoff. Although the small spatial footprint of an HS is advantageous for integration into sewer (storm or combined) or drainage systems, the small footprint also concentrates flow energy. In many HS units, where PM sludge is not isolated or in units that are not maintained (cleaned), washout of previously separated PM sludge can result in a net export of PM. This study analyzes PM washout from a baffled HS as a function of steady-flow rates and particle-size distributions (PSDs) guided by a physical modeling framework utilized for scour certification. The HS hydraulic signature is determined through velocity measurements and a residence time distribution (RTD) analysis. As a function of surface overflow rate (SOR), the predeposited PM washout rate ranges from 0.4 to