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Continuous Deflective Separation: An Integrated Technology for Removal of Storm-Water Gross Pollutants Utilizing Special Flow Mechanics

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Continuous Deflective Separation (CDS) is an innovative technology capable of separating solids from liquids. In general a CDS unit could separate the followings loads from a storm-water system: suspended solids, bed loads, floating solids, free oil & grease.

Field studies have verified removal efficiencies for gross solids to be greater than 95%, with particulate phosphorous removal of greater than 30%, and TSS removals greater than 70%.

The heart of the CDS system is a cylindrical fine screen that effects solids separation using indirect filtration. The filtration is carried out in a uniquely balanced hydraulic system that allows screening separation without blinding the screen. A strong tangential velocity around the inside of the cylindrical screen is maintained to wash the screen, while a small secondary hydraulic head is maintained across the screen that drives the screened water through it.

The high removal rates are made possible by special flow patterns that develop and are maintained inside the CDS units. The hydraulic flow pattern create the ideal environment for the above mentioned materials to be captured in different parts of the flow path depending on the gross pollutant physical characteristics.

Flow mechanics in CDS units are unique, and as a result, different materials are captured by different parts of the unit.

Once water enters the screen chamber, it takes on a strong three-dimensional spiral vortical flow path as it moves downward along the screen.

The hydraulic condition along the screen is not uniform; consequently, the flow through the screen is also non-uniform. Different amounts of flow pass through different areas of the screen depending on the local hydraulic condition.

Theoretically, the flow path inside the screen chamber can be identified, as a number of different layers, which depending on local conditions, will vary in size. In general these can be classified as a turbulent boundary layer at the screen face, a stagnant core at the center, and a shear layer in between.

When a solid particle enters the CDS inlet, it is pushed strongly by the inlet currents into the unit. Depending on the size and specific gravity of the solid particle it will drop suddenly into the sump if the size is big and the specific gravity is large, such as bed load.

Buoyant solids float on the surface. These light particles may pass through the screen aperture opening if first they get to the right streamlines, which lead, through the screen opening and second if their physical size is smaller than the screen opening.

Suspended particles on the other hand will spin and travel more through the spiral and vortical paths while they slowly move to the center of the near stagnant core where they can slowly settle.

Free oil and grease can be separated through application of oil sorbents to CDS unit separation chamber. The sorbent binds the O & G until it is removed during unit cleanout.
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Document Type: Research Article

Publication date: 01 January 2000

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