at-grade, free-access filters are composed of coarse sand
covered with peastone to grade.
Recirculating media filters treat wastewater by recirculating
effluent that has passed through the filter bed back to a separate
recirculation tank. Effluent passing through the recirculating
filter is collected in an underdrain pipe. The effluent is
then directed to a recirculating device that directs the effluent
either to the recirculation tank or to final treatment and
dispersal, depending on the effluent level in the tank.This
mixing commonly occurs in a recirculation tank, but in some
technologies it happens in the headworks (inlet end) of the
septic tank. A programmable timer controls the amount of wastewater
recirculated to the filter bed surface. Filtrate from the media
filter can be split so that a portion returns back to the recirculation
tank and a portion goes out for final treatment and dispersal.