Urban Drainage Clarifier Load-Response as a Function of Flow, Unsteadiness, and Baffling
Publication: Journal of Environmental Engineering
Volume 144, Issue 3
Abstract
A major function of clarifiers (basins or tanks) for urban drainage (stormwater or wastewater) is separation of particulate matter (PM) and PM-associated constituents. Clarifier response is often indexed to geometric parameters of surface area (SA) or length to width (L/W) ratio. Yet in urban areas, clarifier geometry is constrained by infrastructure and alternative opportunity land uses. As a result, retrofitting clarifiers with baffles is considered to improve hydraulic and PM separation response. While most studies evaluate such response based on steady flow, stormwater unit operations (UO) are subject to highly unsteady flows. This study examines baffle configuration [direction and flow tortuosity () as an analog for L/W], flow rate, and hydrograph unsteadiness () on hydraulic response through the Morrill index (MI), volumetric efficiency (VE), and N-tanks-in-series (N) metrics. Results are generated from physical and computational fluid dynamics (CFD) models for clarifier designs with and without baffles. For clarifiers without baffles, but of differing cross-sectional geometries, VE and N increased while MI decreased with increasing flow rate. Clarifiers with baffles produced an asymptotic relationship between N and the Péclet number (P). The MI and N trends were a function of and . For a fixed SA, a higher baffle number (higher ) generated greater PM separation. Although there is not a singular hydraulic response for clarifiers as a function of ; increasing does confer a more consistent, reproducible response.
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Published In
Journal of Environmental Engineering
Volume 144 • Issue 3 • March 2018
Copyright
©2017 American Society of Civil Engineers.
History
Received: Jul 20, 2016
Accepted: Jun 7, 2017
Published online: Dec 20, 2017
Published in print: Mar 1, 2018
Discussion open until: May 20, 2018
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