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Line 26: − − ==See also== − *[[Filtration Manufactured Treatment Devices]] − *[[Media filters]] − *[[Pretreatment]] − *[[Oil and grit separators]]
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Filtration is the process by which stormwater [[Runoff volume control targets|runoff]] is conveyed through a filter medium to remove solid particles and associated pollutants. Several stormwater practices use filtration through sand or gravel media as the primary mechanism for treatment of urban runoff.
Filtration is the process by which stormwater [[Runoff volume control targets|runoff]] is conveyed through a filter medium to remove solid particles and associated pollutants. Several stormwater practices use filtration through sand or gravel media as the primary mechanism for treatment of urban runoff.
Stormwater passes through a filter based on the pressure difference on either side of the filter. In most stormwater treatment applications, the pressure difference is created by gravity (or hydraulic head). As the filter becomes [[clogging|clogged]], higher pressure is needed to drive stormwater through the filter, until a point is reached at which flow through the treatment system must be redirected to another flow path (usually a [[overflow|bypass]] within or upstream of the system).
Stormwater passes through a filter based on the pressure difference on either side of the filter. In most stormwater treatment applications, the pressure difference is created by gravity (or hydraulic head). As the filter becomes [[clogging|clogged]], higher pressure is needed to drive stormwater through the filter, until a point is reached at which flow through the treatment system must be redirected to another flow path (usually a [[overflow|bypass]] within or upstream of the system).
Stormwater treatment practices that use filtration include:
*[[Filtration Manufactured Treatment Devices]]
*[[Media filters]]
*[[Pretreatment]]
*[[Oil and grit separators]]
==Types of filtration==
==Types of filtration==
[[Permeable pavements]] can also be considered to be a type of filter. In this case, runoff and rainwater is filtered through the surface pores or granular media between the pavers, as well as through the bedding and base layers. Most of the [[sediment]] directed onto the pavements is trapped near the surface where it can be more easily accessed for cleaning. Since permeable pavements need to maintain a high rate of infiltration to avoid ponding, the area of impervious surface draining on to them should be no larger than the area of the permeable pavement itself.
[[Permeable pavements]] can also be considered to be a type of filter. In this case, runoff and rainwater is filtered through the surface pores or granular media between the pavers, as well as through the bedding and base layers. Most of the [[sediment]] directed onto the pavements is trapped near the surface where it can be more easily accessed for cleaning. Since permeable pavements need to maintain a high rate of infiltration to avoid ponding, the area of impervious surface draining on to them should be no larger than the area of the permeable pavement itself.