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y <br /> 11-4 MULTIPASS (RECIRCULATING) PACKED-BED FILTERS 739 <br /> E <br /> Recirculating Underdraln pipe <br /> Treated effluent <br /> granular <br /> 14 medium filter Flow splitter <br /> Distribution To reuse or disposal <br /> system ——__ <br /> 1' Effluent pump <br /> Divided <br /> Septic tank t r <br /> t t recirculation tank <br /> pay Dosing pump <br /> r t t Recirculation <br /> t — chamber <br /> Wastewater <br /> Effluent fitter vault <br /> FIGURE 11-17 <br /> Schematic flow diagram for a recirculating granular medium filter. <br /> greatly reduced or eliminated and higher loading rates are possible. A schematic <br /> flow diagram for a modern recirculating granular medium filter is presented .in <br /> Fig. 11-17: As shown in Fig. 11-17, the recirculating granular medium filter re- <br /> quires the use of an additional.tank as compared to the ISF Additional details on the <br /> design and application of RSFs may be found in Piluk and Peters (1994)_ <br /> Types of Applications <br /> w <br /> Recirculating sand and fine-gravel filters are used to treat septic tank effluent from t° <br /> individual homes, clusters of homes,lnstitutions,'and small communities with flows <br /> up to 1.0 Mgal/d(3785... <br /> n3/d).They have also been used to nitrify pond effluent prior <br /> to discharge to constructed wetlands.RPBFs have also been used to treat septic tank <br /> effluent prior to UV disinfection and water reuse (see Chap. 12). <br /> Individual systems. In Anne Arundel County, Maryland, RGFs have been <br /> used extensively for individual family residences (Piluk and Peters, 1994; Piluk, <br /> 1996---97). Typical examples are shown in Fig. 11-18. An innovation that has been <br /> developed in the application of these systems is the precasting of the concrete en- <br /> closure for the RGF and the addition of the piping and filter medium at the location ` <br /> where the tank is constructed(see Fig. l I-19).The completed unit is delivered to the <br /> construction site ready to be booked up to'the septic tank and the disposal system. <br /> Stonehurst development. Stonehurst is a 47-lot subdivision located near the <br /> City of Martinez in Contra Costa County,California, approximately 25 miles east of' . <br /> San Francisco.The subdivision is located in a hilly, rural area without a wastewater <br /> collection system. An overall view of the rolling terrain is as shown previously in <br />