Processes for removing pollutants from stormwater runoff
Processes for removing pollutants from stormwater runoff. Source: Design of Urban Stormwater Controls.
Link to this table
| 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 |