Re-circulating Sand Filters Improved on-site wastewater treatment and disposal technology  In many areas of the country, builders and homeowners rely predominantly on conventional septic tank-soil absorption systems for sewage disposal, even though less than a third of the land area in the United States is suitable for them. Septic-tank use in unsuitable land may lead to soil clogging and system failure. These problems may be reduced through improved on-site wastewater treatment and disposal technologies, such as the on-site re-circulating sand filter (RSF) system. The RSF system uses a sand filter to reduce pollutants, thereby minimizing the amount of waste deposited in the final soil disposal area.
With an RSF, effluent from a septic tank flows to a re-circulation tank where it is pumped to a filter. The sand filter consists of coarse sand or similar media that encourages biological growth. The filter media allows the wastewater to mix with air, as it slowly passes through the structure, giving the bacteria and other organisms time to digest the pollutants (which they consider food). Approximately 1/4 of the filtrate collected in the piping is diverted to the final soil disposal area while the remainder is returned to the re-circulation tank where it mixes with liquid waste received from the septic tank. By passing the effluent through the filter several times, the microbes eat more food, and thereby remove more pollutants, than they would in a single pass. The pollutant-removal processes in RSFs are complex. The pollutant parameters commonly analyzed in wastewater treatment systems are nitrogen, biochemical oxygen demand (BOD), total suspended solids (TSS), fecal coliform (FC), and phosphorous. RSF systems have been shown to produce effluent that is clear, odorless, and with pollutant concentrations much lower than conventional septic tank effluent. Typically, the effluent is low in nitrogen, TSS and BOD. Fecal concentrations are also reduced; however, FC concentrations are still well above the acceptable effluent standards found at municipal wastewater treatment plants. Overall, current costs of RSF systems are higher than conventional septic tank/leech field systems. Several barriers to the acceptance of RSFs are aesthetics, affordability, regulatory, competition from other types of alternative treatment systems, and long term maintenance. 
RSFs can be assembled and purchased from local septic tank manufacturers or through a national distributor.
The costs of an RSF system vary considerably due to design variations, local labor, and material costs. They are typically $3-$8K more than traditional on-site treatment systems.
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Information on state and county standards and their implications for individual systems may be obtained from the state, the environmental health office or your local health department.
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The typical RSF includes a septic tank with two compartments, a re-circulation tank, a pump, a sand filter, and a drainfield. Effluent flows from the septic tank to the re-circulation tank, where it is pumped to the sand filter. Effluent passes through the sand filter, where it is biologically treated, and then flows to a flow diverter. Some of the treated effluent is discharged to the drain field, and some goes back to the re-circulation tank.
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RSF systems have been shown to produce pollutant concentrations much lower than conventional septic tank effluent. The improved effluent quality is reported to increase soil absorption and reduce soil clogging, reducing the potential for system failure. RSFs have several advantages over single-pass sand filters. They are smaller, minimize or eliminate odors, are capable of treating higher-strength wastes, and are more effective at removing nitrogen. Potentially, RSFs offer environmental benefits by reducing harmful pollutants in wastewater effluent. The most important benefit of RSF technology is that they permit advanced on-site treatment and disposal on environmentally sensitive sites, and on soils that are typically considered marginal or unacceptable for conventional septic systems. The costs of an RSF system vary considerably due to design variations, local labor, and material costs. They are typically $3-$8K more than traditional on-site treatment systems. | 
