Processes for removing pollutants from stormwater runoff. Source: Design of Urban Stormwater Controls.
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Process Category Process Mechanism Definition Primary Pollutant
Hydraulic / Volume Management Attenuation Temporary detention of water for the purpose of controlling the rate of outflow Peak flow
Infiltration / runoff reduction Water flowing into soils which does not become stormwater runoff Runoff volume
Evaporation Water returning to atmosphere from water surfaces Runoff volume
Transpiration Water returning to atmosphere through plant metabolism Runoff volume
Physical Screening Separation of gross pollutants from water by straining through large openings Gross pollutants, vegetation
Sedimentation Process by which solids are removed from the water column by settling Heavy suspended solids
Filtration Sedimentation and physical retention of smaller particles passing through media Suspended solids
Flotation Separation of oil/grease and litter upward through the water column through buoyancy Oil/grease, litter, vegetation
Laminar separation Movement of water through non-turbulent conditions to effectively separate particles Oil/grease
Swirl concentration Movement of water to the center of a hydraulic vortex and of particles to the outer edges of the vortex via inertia and gravitational force Suspended solids
Biological Plant metabolism Uptake of nutrients from the water by plants for the purpose of metabolism Phosphorus, dissolved
Pathogen die-off Die-off of pathogens by natural methods Pathogens
Nitrification / denitrification Process of nitrogen removal by bacteria that results in nitrogen release to atmosphere as a gas Nitrogen
Chemical Precipitation Joining of two inorganic dissolved pollutants into a heavier particle that can be settled or filtered Dissolved inorganic pollutants
Coagulation Joining of small particles of one pollutant into a heavier particle that can be settled or filtered Colloidal solids
Absorption Pollutant penetrating into the molecular level of the media Dissolved pollutants
Adsorption Attachment of a pollutant to the surfaces of a media Dissolved pollutants
Ion Exchange Capture of a dissolved pollutant, typically heavy metals, in a media through the exchange of ions between the media and the pollutant Heavy metals
Other Thermal / temperature control Cooling of water that has been heated through contact with pavements and other surfaces Temperature

This page was last edited on 4 August 2022, at 19:36.