subject: Sand Filter Media Specification [print this page] Sand Filter Media Specification Sand Filter Media Specification
Sand filter media are beds of granular material, or sand, drained from underneath so that pretreated wastewater can be treated, collected and distributed to the land application system. They are normally used to polish effluent from septic tanks or other treatment processes before it is distributed on the land.
All on-site systems are "no-discharge," meaning the wastewater must stay in the system and not leave the property.The wastewater cannot enter surface water, streams, ditches or any water resources. After the filtrate is collected by the sand filter's under drains, it is then disposed of by a soil absorption system. Intermittent sand filters provide biodegradation or decomposition of wastewater constituents by bringing the wastewater into close contact with a well developed aerobic biological community attached to the surfaces of the filter media. This process requires unsaturated downward flow of the effluent through a filter media which may be a mineral sand or equivalently sized crushed glass meeting one of the media.
The Sand filter 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 the influent to the filter be distributed over the media in controlled, uniform doses. In order to achieve accurate dosing, these systems require a timer controlled pump with associated pump tank, electrical components, and distribution network to deliver a minimum of 12 doses per day spread evenly over a 24 hour period.
The effluent is collected in the bottom of the sand filter and discharged either by gravity or pressure to a suitable disposal component, usually a sub-surface drainfield. This technology is used on sites with high groundwater levels and/or shallow soil conditions where treatment must be accomplished before disposal. Intermittent sand filters are also used as part of a mitigation strategy when horizontal separations are reduced. Media Specifications -- The filter media must meet either the Coarse Sand Media or the Sand Filter Media specifications for particle size gradation detailed in Appendix A. Filter media used in constructing a sand filter must be accompanied with a written certification from the supplier that the sand fully conforms to one of the media. Treated Wastewater (Filtrate) Collection and Discharge -- Filtrate may be collected and discharged from the bottom of the sand filter by either a gravity flow underdrain, or pumped from a pump basin. When sand filters are membrane-lined, gravity flow underdrains must exit through a boot. The boot and exit pipe must be watertight.
Sand filter media Filteration
Filtration is the last unit process in pretreatment of water
Water flows either by gravity or under pressure through a filter media like sand or anthracite
Suspended solids and flocs formed previously by coagulation and flocculation are retained on the filter surface
Once the pressure drop exceeds the set limit, the filer bed is cleaned by back washing the media by reversal of flow of water
