Re-circulating Sand Filters
Re-Circulating Sand Filters
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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 within the drain field 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, including suspended solids so it minimizes the likelihood of the drainage field to become clogged.
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.
Re-Circulating Sand Filters |
Recirculating Sand Filters
The recirculating sand filter (RSF) concept was introduced in the late 1960s and early 70s by public health engineers from Illinois who were experimenting with sand filter designs. An RSF system is a modified version of the single-pass open sand filter. It was designed to alleviate the odor problems associated with open sand filters. The odors were eliminated through recirculation, which increases the oxygen contend in the effluent that is distributed on the filter bed.
Wastewater treated in a RSF contains more oxygen that eliminates odors. "The final sand filter effluent also is of a higher quality. Recirculating sand filter media is somewhat coarser than other sand filter media and therefore is less prone to clogging. Hydraulic loading rates typically are two to three times higher than ISF's meaning that less land area is generally needed to treat the same amount of wastewater.
Recirculating Sand Filters |
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