What’s Happening Inside My High Performance Biofiltration System?
An appropriately designed and manufactured high performance biofiltration system combines the benefits of natural biofiltration with the reliable and predictable performance of an engineered system. Each high performance biofiltration system utilizes a multifaceted approach including physical, chemical and biological processes to capture, immobilize and treat harmful pollutants, while also encouraging low impact development practices by treating smaller drainage areas at the source. Plants and organics facilitate a sustainable biological cycle through regeneration of hydraulic function and pollutant removal capacity through decomposition, degradation and uptake of captured pollutants.
There are two major time scales at play, intra-storm (during storms) and inter-storm (between storms), and all treatment process do not occur simultaneously. Inter-storm processes take place with the water and pollutants remaining in the treatment media, and while not the primary removal mechanism, are significant for retention of captured pollutants and media sustainability to make adsorption sites available for intra-storm processes. The pollutant removal occurs as a result of natural processes that directly correlate to the media composition and the plant-soil-microbe complex that develops over time. The table below attempts to summarize the bevy of complex processes that occur within a high performance biofiltration system that results in meeting your Water Quality Goals.
|
Process |
Type |
Time |
Description |
|
Passive Filtration & Infiltration |
Physical |
Intra-storm |
Pollutants are captured within the pores of the mulch and media through straining, impaction and interception |
|
Sedimentation |
Physical |
Intra-storm |
Ponded water on the surface lowers velocity and promotes particle settling |
|
Physical Absorption |
Physical |
Intra-storm |
Particles and water are incorporated into the bulk of the media |
|
Physical Adsorption |
Physical |
Intra-storm |
Material is amassed to the surface of the media via electrostatic forces |
|
Diffusion |
Physical |
Inter-storm |
Water moves from higher concentration to lower within the media, pulling surface pollutants into the interstitial pores of the media |
|
Volatilization |
Physical |
Inter-storm |
VOC’s are captured by the media and vaporized via evaporation, transpiration, or degradation by microbes |
|
Soil Processes |
Physical |
Intra-storm Inter-storm |
Physical changes within the media such as wetting and drying, root penetration, root expansion and contraction, microbial activity, introduction of larger organisms, and introduction of organic matter from stormwater and plant material maintain hydraulic and pollutant removal properties of the media |
|
Chemical Adsorption |
Chemical |
Intra-storm |
Reactive filtration through chemical interactions that bind and transform pollutants |
|
Cation Exchange |
Chemical |
Intra-storm |
Pollutants with exchangeable positive ions are bound to the media (clay and organic matter) through the replacement of a charged media ion and a charged pollutant ion in solution |
|
Precipitation |
Chemical |
Intra-storm |
Nutrients and other molecules in the stormwater runoff react with compounds in the media (often Al and Fe) to form new, insoluble particles |
|
Evapotranspiration |
Biological |
Intra-storm Inter-storm |
Plants take in water through their roots and transpire it into the atmosphere |
|
Phytoremediation |
Biological |
Intra-storm Inter-storm |
Heavy metals, VOCs and other dissolved pollutants can be taken up by the plant and stored or released to the atmosphere through bioaccumulation, degradation or other means to render contaminants harmless, reducing concentrations of pollutants in media and regenerating pollutant removal capacity |
|
Biological Absorption |
Biological |
Intra-storm Inter-storm |
Pollutants adhere onto and are transformed and/or sequestered by bacteria cell walls, fungi and plant roots |
|
Mineralization, Nitrification & Denitrification |
Biological |
Inter-storm |
Microbes biodegrade pollutants into less toxic forms and transform nitrogen compounds (ammonia, ammonium, nitrates, nitrites) via complex processes into atmospheric nitrogen (N2). Nitrogen compounds can also be assimilated and used by the plant |