Sand filter septic design details:

This document discusses design and use of septic media filters using sand. When using a septic media filter system, effluent treatment is by both actual filtration and ultimately by a biochemical process as the filter "matures" and includes its own biomass. This is particularly true of sand-bed filter septic systems which also often use a recirculating sand bed design to move septic effluent multiple passes through the sand filter system.

Septic Media Filters Using Sand

The septic tank which receives waste from the building should have either two compartments, or two tanks in series are used.

A gas baffle on the tank outlet is recommended (NY State Wastewater Treatment Standards) to reduce the chances of a periodic bolus of gas forming in the bottom of the tank and forcing solids into the sand media.

When a sand filter system is used, effluent is periodically distributed out of the septic tank and over the surface of a constructed bed of sand through a network of perforated pipes. Collector pipes below the sand pick up effluent after it has filtered through and been treated by (the biomat formed on) the sand filter.

Effluent dosing is by pressure-fed perforated lines of 1.5" to 3" diameter, or by siphon dosing using a 3" to 4" diameter effluent line. New York requires that the system is dosed at least three times daily. Dosing should not exceed 1.15 gallons/day/sq. ft. of media area.

Various texts cite the critical importance of selecting the proper sand for a septic media filter. New York's standard specifies a sand grain size of 0.25 to 1.0 mm; if nitrification is required (which may be specified by the local health department), the grain size is larger, 0.5mm to 1.0 mm., and all sand is passed through a 1/4" sieve and must be uniform to a coefficient of 4.0.

The effluent collector pipes below the sand bed discharge the treated effluent to an absorption system such as a drain field placed below the original ground level or possibly into a raised bed or mound system. The raised bed or mound receiving the treated effluent may itself be constructed of sand or other fill material with a percolation rate of not faster than 5 minutes per inch.

Typical sand filter construction (NY State Wastewater Standards) involves an excavated bed area which is filled in layers of material as follows (bottom up):

1. Collector pipe system set in gravel sized 3/4" to 1.5" aggregate.
2. 4" of aggregate above the collector pipes
3. 3" of crushed stone or clean gravel sized 1/8 to 1/4" atop the aggregate.
4. 24" of approved sand. Jantrania points out that a geotextile fabric should not be placed below the sand and atop the gravel. Though some installers think that's a great idea to keep the sand out of the gravel, he points out that the fabric is likely to clog and lead to early sand filter bed failure.
5. Distribution pipes placed in a layer of aggregate providing 4" or more across the whole surface of the sand filter and with aggregate of at least 2" underneath and above the distribution pipes.
6. A geotextile, 2" of hay or straw, or untreated building paper is placed atop the bed to keep soil fines out of the filter.
7. 6" to 12" of topsoil is placed atop the sand filter bed system, mounded to encourage surface water runoff to drain off of the system. The topsoil is seeded to grass.

Sand filter problems: keep deep rooting plants, surface runoff, and heavy traffic (that could compact the media) off of the system. Don't block air movement over the surface of the system with buildings or plantings.

Sand Filter Septic Research

• Also seeReferences or Citations
• Spychala, M., and R. Blazejewski. "Sand filter clogging by septic tank effluent." Water science and technology 48, no. 11-12 (2004): 153-159.
  Abstract:
  The aim of this study was to characterise conditions and factors affecting fine sand clogging by septic tank effluent on the basis of physical modelling. The physical model consisted of 12 sand columns dosed with sewage from one household (5 persons), preliminary treated in a septic tank. Hydraulic loadings of the sand filters were equal to 82 mm/d.
  
  The mean discharge from sand columns, measured as the effluent volume collected during 10 minutes, decreased significantly over the experiment period from 34 cm3/min in August 2000 to 20 cm3/min in August 2001 at the same temperature of about 20°C.
  
  First the columns clogged almost completely after 480 days in December 2001, however six columns had remained unclogged till the end of the experiment (March 2002). The temperature had a significant impact on hydraulic conductivity. A vertical distribution of accumulated mass and biomass was investigated in partly clogged sand. Microscopic survey of the clogging layer showed a presence of live micro-organisms, residuals of dead micro-organisms, particularly pieces of small animal armour and many fibres. These particles accelerated the accumulation of solids in the upper clogging layer.
  
  The study indicated that temperature impact on the filter hydraulic conductivity was more significant for biological activity, than for sewage viscosity.

Septic Media Filter System Articles

• MEDIA FILTER SEPTIC SYSTEMS - home
  • BAT MEDIA SEPTIC PLANTS
  • DOSING CONTROL for SEPTIC MEDIA SYSTEMS
  • FOAM CUBE SEPTIC MEDIA FILTERS
  • PEAT SEPTIC MEDIA FILTERS
  • POD SEPTIC SYSTEMS
  • RUCK® SEPTIC MEDIA FILTER SYSTEMS
  • SAND FILTER SEPTIC DESIGN SPECIFICATIONS
  • SAND SEPTIC MEDIA FILTERS
  • SANDY SOIL SEPTIC DESIGNS
  • SEPTIC MEDIA FILTER CAPACITY & MAINTENANCE
  • SEPTIC MEDIA FILTER SOURCE LIST
  • SEPTIC MEDIA FILTER SYSTEM OPERATION
  • SINGLE PASS vs RECIRCULATING SEPTIC MEDIA FILTER DESIGNS
  • TEXTILE SEPTIC MEDIA FILTERS
  • TYPES of SEPTIC MEDIA FILTER MATERIALS

...

Continue reading  at SEPTIC MEDIA FILTER CAPACITY & MAINTENANCE or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Sandy Soil Septic System Articles

• AEROBIC SEPTIC SYSTEMS, ATUs - home
• SEPTIC CONSULTANTS, DESIGNERS, ENGINEERS
• BAT MEDIA SEPTIC PLANTS
• BED the SEWER LINE in SAND
• MEDIA FILTER SEPTIC SYSTEMS - home
• SAND BED SEPTIC SYSTEMS
• SAND SEPTIC MEDIA FILTERS
• SAND FILTER SEPTIC DESIGN SPECIFICATIONS
• SANDY SOIL SEPTIC DESIGNS
• SEPTIC MEDIA FILTER CAPACITY & MAINTENANCE
• SEPTIC MEDIA FILTER SOURCE LIST
• SEPTIC MEDIA FILTER SYSTEM OPERATION
• SEPTIC SYSTEM DESIGN ALTERNATIVES - home
• SEPTIC SYSTEM DESIGN BASICS - home
• ALTERNATIVE DESIGN SEPTIC SYSTEM SUPPLIERS
• TYPES OF SEPTIC SYSTEMS - master list

Suggested citation for this web page

SAND SEPTIC MEDIA FILTERS at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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INDEX to RELATED ARTICLES: ARTICLE INDEX to SEPTIC SYSTEMS

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Citations & References

In addition to any citations in the article above, a full list is available on request.

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