Processes for removing pollutants from stormwater runoff

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	Separation of gross pollutants from water by straining through large openings	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