Intermittent Sand Filter: ***Pictures Below***
A sand filter type system usually has four basic parts to the system. You will have a septic tank to collect all the incoming sewage from the house and allow proper retention time to settle solids then from the septic tank effluent (wastewater) will gravity flow to the pump tank. You will most likely find either a effluent filter in the outlet of the septic tank or a pump mesh screen around the effluent pump. The pump tank will will have a series of liquid level floats and effluent pump and a control panel outside that controls the dosing to the sand filter.
A intermittent sand filter provides decomposition of wastewater constituents by bringing the wastewater into close contact with well developed aerobic biological community attached to the surfaces of the filter media (certified ASTM-33 sand). This process requires unsaturated downward flow of the effluent (wastewater) through the filter media. This filter media is contained in a watertight vessel made of concrete or a PVC lined pit. Proper function requires that the influent from the pump chamber (after septic tank) be distributed over the filter media in controlled, uniform doses. The only accurate way to ensure proper dosing is to install a quality time-dose control panel. This panel will include (among other items) a timer which controls how often the pump will deliver effluent to the sand filter.
The contained vessel will have a several layers of media. Within the contained sand filter vessel you will most likely have a layer of drain rock at the bottom near the under-drain, a layer of 24" of ASTM-33 certified sand, approximately 9" of drain rock near the surface and a series of laterals (PVC pipes) connected to the manifold which effluent gets delivered from the pump chamber. The laterals have a series of evenly spaced holes (orifices) throughout the length and usually long turn 90 degree elbows at each end for maintenance, cleaning, and testing. Usually, the laterals & drain rock will have approximately 12" of good topsoil covering the vessel which allows good air exchange within the system. PVC monitoring ports are likely installed at or above grade level in several locations within the contained vessel to monitor the liquid level in the sand filter.
After the effluent gets treated (filtered) through the sand filter media, it will either flow downward into a slotted or perforated pipe with gravity drains into a disposal area (drain field) or the effluent inside the sand filter will flow into a pump well that is installed within the sand filter itself. If a pump well is installed within the sand filter, that "treated" filtered effluent will get pumped to the final disposal area (drain field).
Below are some basic pictures of some types of intermittent sand filters:
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