subject: Gravel Filter [print this page] The media is contained in a watertight vessel either below the surface of the ground or wholly or partially elevated in a containment vessel. Proper function requires
that influent to the filter be distributed over the media in frequent, cycled uniform doses. In order to achieve accurate dosing, these systems require a timed dosing with associated pump
chambers, electrical components, and distribution network. This frequent, cycled dosing provides a constantly wetted media. The effluent is collected in the bottom of the filter and
returned to the recirculating/mixing tank where it mixes with fresh septic tank effluent or a portion of the effluent is discharged to the soil dispersal component. Flow splitting mechanisms
are used to control recirculation, flow splitting and discharge to the soil dispersal component. The treated wastewater is discharged to an approved soil dispersal component, usually a
conventional sub-surface drainfield.
Recirculating Pressure Sand Filter are quite suitable for treating residential strength wastewater. The filter will be smaller in size than an intermittent sand filter, and therefore may be preferred for
this reason. The recirculating gravel filter is also not so susceptible to hydraulic and biological overloading as is an intermittent sand filter. This technology is used where size is a constraint
and where wastewater strength is moderately greater than what is typically generated in a single- family residence. Recirculating gravel filter effluent may be discharged to a soil profile
containing as little as 24 inches of vertical separation.
Influent Characteristics
Residential Wastewater: Recirculating gravel filters are quite suitable for treating residential strength wastewater. The filter will be smaller in size than an intermittent sand filter, and therefore may be preferred for this reason. The
recirculating gravel filter is also not so susceptible to hydraulic and biological overloading as is an intermittent Gravel Filter.
Pretreatment
If the wastewater is domestic in origin, settleable and floatable solid separation by a properly sized two-compartment septic tank with effluent baffle screening, or
equivalent wastewater sedimentation/initial treatment unit, will suffice.
If the wastewater is from a non-domestic source, pretreatment other than a septic tank may be required if the influent to the Gravel Filter is not within the allowable
limits for recirculating gravel filters.
Wastewater Distribution
Pressure distribution: Pressure distribution with timed dosing is required and must comply with the pressure distribution standards and guidance. This requirement applies to all pressure distribution related components.
Wastewater application to the filter bed:
The wastewater must be applied to the layer of drain rock atop the filter media, or sprayed upward against the top of gravelless chambers.
