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Treatment Technology: Recirculating sand filter
These 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.

For more information on recirculating filters:
Web Links:These media filters have been studied under various URI-lead projects, as well as by other onsite treatment testing facilities. The results of URI, NEOWTC projects can be found in various technical publications which will be online soon at www.uri.edu/ce/wq/OWT/research/
Copyright 2006 URI Water Quality Program