Aerobic Septic System Parts
Aerobic Septic System Parts
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FLOW BUFFERING
The septic tank also provides a buffering of flows between the house and the drainfield. Large surges from the household, such as toilet flushing or washing machine drainage, are dampered by the septic tank so that the flows leaving the tank and entering the drainfield are at substantially lower flow rates and extend over a longer period of time than the incoming surges.
THE MEANDER TANK
me-an-der intr. v. 1. To follow a winding and turning course, n. l.A circuitous journey...
As explained on page 7, retention time (how long water remains in the tank before exiting to the drainfield) is important in the functioning of the system. Dr. John H. Timothy Winneberger, a well-respected innovator in sewage disposal technology, invented a triple-compartment tank —which Peter Warshall (in Septic Tank Practices) named the meander tank.
The meander tank actually increases the velocity of liquid, but smooths out the flow and helps stop short-circuiting from the inlet to the outlet. Two partitions are built as shown, dividing the tank aerobic septic system parts into three rectangular chambers. Passage from one compartment to another is through slots too large to clog, and liquids traverse the tank's length three times, passing through one chamber, then the next two, before exiting to the drainfield. In the early model shown, the first chamber held about % of the liquid volume, the last about V9 of the liquid volume.
Note: Two-compartment meander tanks—easier to construct—are also built, with one longitudinal baffle.
The meander tank is considered by many engineers to be far more effective than conventional tanks, but the industry has not caught up with the vision. The meander tank is a better mousetrap, but no one is building it, at least not for homes. For commercial applications, engineer Michael D. Mitchell, of Northwest Septic, Inc., of Mt. Vernon, WA, has designed some very interesting meander tank configurations, intended, he says, to "minimize mixing while maximizing settling."
The meander tank,
a 3-compartment tank that increases retention time
if you need to build your own tank due to cost, remote site, etcv see mflcs
4A/D serr/c sysre/ws. ('seer. /tg&J
however, this is not a job for someone with no construction experience.
MICROBES IN SEPTIC TANKS DIGEST, DISSOLVE, AND GASIFY COMPLEX ORGANIC WASTES
In 1907, W. P. Dunbar conducted tests on the decomposition of vegetable and animal matter in septic tanks. He stated, "The author has investigated the subject by suspending in septic tanks a large number of solid organic substances, such as cooked vegetables, cabbages, turnips, potatoes, peas, beans, bread, various forms of cellulose, flesh in the form of dead bodies of animals, skinned and unskinned, various kinds of fat, bones, cartilage, etc., and has shown that many of these substances are almost completely dissolved in from three to four weeks. They first presented a swollen appearance, and increased in weight. The turnips had holes on the surface, which gradually became deeper. The edges of the cabbage leaves looked as though they had been bitten, and similar signs of decomposition were visible in the case of other substances. Of the skinned animals, the skeleton alone remained after a short time; with the unskinned animals the process lasted rather longer. At this stage I will only point out that the experiments were so arranged that no portion of the substances could be washed away; their disappearance was therefore due to solution and gasification."
-Principles of Sewage Treatment, W. P. Dunbar, Charles Griffin & Co., London, 1907
CHAPTER TWO
The Drainfield
WHERE DOES THE WASTEWATER GO AFTER IT LEAVES THE TANK?
Most commonly, wastewater goes to a drainfield, (also called leachfield or disposal field). It can also go to a mound (seep. 89), a seepage bed (seep. 24), or a seepage pit (seep. 25). The general and more technical term for all these methods of handling the wastewater from the tank is the soil absorption system. We will begin here with the most common type, the drainfield or leachfield.
WHAT THE DRAINFIELD DOES
Once sewage undergoes primary treatment in the septic tank, the clarified effluent flows to the drainfield, where it is discharged into the soil for final treatment and disposal.
Note: A typical drainfield consists of several relatively narrow and shallow gravel-filled trenches with a perforated pipe near the top of the gravel to distribute the wastewater throughout each trench. In most cases, drainfields will perform almost indefinitely if the system is designed, used, and maintained properly.
CONSTRUCTION OF DRAINFIELD
The typical drainfield trench is a level excavation, rectangular in cross section, with a level bottom. Trenches are typically 1 to 3 feet wide, 2 to 3 feet deep, and usually no more than 100 feet long. The trench is partially filled with a bed of clean gravel (%- to 2Vi-inch diameter) to within 1 or 2 feet of ground surface. A single line of perforated pipe, 3 to 4 inches in diameter, is installed level (no slope) on top of the gravel and covered with an additional 2 or 3 inches of gravel.
the main job of the drainfield is to purify and disperse the effluent flowing out of the septic tank.
Cross section — typical drainfield. For an EPA diagram showing the pathway of air to the soil in a drainfield, seep. 159 in the Appendix.
The gravel is covered with a semipermeable geotextile fabric and the remaining 1 to 2 feet of the trench is backfilled with soil up to the ground surface. The fabric barrier keeps the backfill soil out of the gravel and prevents the fine soil particles from clogging the pores of the gravel. (Before the advent of geotextile fabric, a layer of straw or hay or untreated building paper was used for the soil-gravel barrier.)
A NOTE ABOUT DRAINFIELD DESIGNS
The size, design, and location of a drainfield for a given home depend on a variety of factors, such as local soil characteristics, the amount of wastewater flow, ground slope, and depth to groundwater or bedrock. The objective is to distribute the effluent into an area with an adequate depth of suitably permeable, unsaturated soil. The drainfield also should be located as far as possible from drinking-water wells, streams, lakes, steep hillsides, road-cuts, property lines, etc.
Specific design criteria are provided by local building or sewer codes and often vary from one locality to the next. Local health departments often require a permit before allowing any work on a drainfield and frequently can offer helpful advice. A comprehensive presentation of the many and various local design rules is beyond the scope of this book. Rather, our intent is to provide a basic understanding of what the drainfield is and how it works.
FLOW BUFFERING
The septic tank also provides a buffering of flows between the house and the drainfield. Large surges from the household, such as toilet flushing or washing machine drainage, are dampered by the septic tank so that the flows leaving the tank and entering the drainfield are at substantially lower flow rates and extend over a longer period of time than the incoming surges.
THE MEANDER TANK
me-an-der intr. v. 1. To follow a winding and turning course, n. l.A circuitous journey...
As explained on page 7, retention time (how long water remains in the tank before exiting to the drainfield) is important in the functioning of the system. Dr. John H. Timothy Winneberger, a well-respected innovator in sewage disposal technology, invented a triple-compartment tank —which Peter Warshall (in Septic Tank Practices) named the meander tank.
The meander tank actually increases the velocity of liquid, but smooths out the flow and helps stop short-circuiting from the inlet to the outlet. Two partitions are built as shown, dividing the tank aerobic septic system parts into three rectangular chambers. Passage from one compartment to another is through slots too large to clog, and liquids traverse the tank's length three times, passing through one chamber, then the next two, before exiting to the drainfield. In the early model shown, the first chamber held about % of the liquid volume, the last about V9 of the liquid volume.
Note: Two-compartment meander tanks—easier to construct—are also built, with one longitudinal baffle.
The meander tank is considered by many engineers to be far more effective than conventional tanks, but the industry has not caught up with the vision. The meander tank is a better mousetrap, but no one is building it, at least not for homes. For commercial applications, engineer Michael D. Mitchell, of Northwest Septic, Inc., of Mt. Vernon, WA, has designed some very interesting meander tank configurations, intended, he says, to "minimize mixing while maximizing settling."
The meander tank,
a 3-compartment tank that increases retention time
if you need to build your own tank due to cost, remote site, etcv see mflcs
4A/D serr/c sysre/ws. ('seer. /tg&J
however, this is not a job for someone with no construction experience.
MICROBES IN SEPTIC TANKS DIGEST, DISSOLVE, AND GASIFY COMPLEX ORGANIC WASTES
In 1907, W. P. Dunbar conducted tests on the decomposition of vegetable and animal matter in septic tanks. He stated, "The author has investigated the subject by suspending in septic tanks a large number of solid organic substances, such as cooked vegetables, cabbages, turnips, potatoes, peas, beans, bread, various forms of cellulose, flesh in the form of dead bodies of animals, skinned and unskinned, various kinds of fat, bones, cartilage, etc., and has shown that many of these substances are almost completely dissolved in from three to four weeks. They first presented a swollen appearance, and increased in weight. The turnips had holes on the surface, which gradually became deeper. The edges of the cabbage leaves looked as though they had been bitten, and similar signs of decomposition were visible in the case of other substances. Of the skinned animals, the skeleton alone remained after a short time; with the unskinned animals the process lasted rather longer. At this stage I will only point out that the experiments were so arranged that no portion of the substances could be washed away; their disappearance was therefore due to solution and gasification."
-Principles of Sewage Treatment, W. P. Dunbar, Charles Griffin & Co., London, 1907
CHAPTER TWO
The Drainfield
WHERE DOES THE WASTEWATER GO AFTER IT LEAVES THE TANK?
Most commonly, wastewater goes to a drainfield, (also called leachfield or disposal field). It can also go to a mound (seep. 89), a seepage bed (seep. 24), or a seepage pit (seep. 25). The general and more technical term for all these methods of handling the wastewater from the tank is the soil absorption system. We will begin here with the most common type, the drainfield or leachfield.
WHAT THE DRAINFIELD DOES
Once sewage undergoes primary treatment in the septic tank, the clarified effluent flows to the drainfield, where it is discharged into the soil for final treatment and disposal.
Note: A typical drainfield consists of several relatively narrow and shallow gravel-filled trenches with a perforated pipe near the top of the gravel to distribute the wastewater throughout each trench. In most cases, drainfields will perform almost indefinitely if the system is designed, used, and maintained properly.
CONSTRUCTION OF DRAINFIELD
The typical drainfield trench is a level excavation, rectangular in cross section, with a level bottom. Trenches are typically 1 to 3 feet wide, 2 to 3 feet deep, and usually no more than 100 feet long. The trench is partially filled with a bed of clean gravel (%- to 2Vi-inch diameter) to within 1 or 2 feet of ground surface. A single line of perforated pipe, 3 to 4 inches in diameter, is installed level (no slope) on top of the gravel and covered with an additional 2 or 3 inches of gravel.
the main job of the drainfield is to purify and disperse the effluent flowing out of the septic tank.
Cross section — typical drainfield. For an EPA diagram showing the pathway of air to the soil in a drainfield, seep. 159 in the Appendix.
The gravel is covered with a semipermeable geotextile fabric and the remaining 1 to 2 feet of the trench is backfilled with soil up to the ground surface. The fabric barrier keeps the backfill soil out of the gravel and prevents the fine soil particles from clogging the pores of the gravel. (Before the advent of geotextile fabric, a layer of straw or hay or untreated building paper was used for the soil-gravel barrier.)
A NOTE ABOUT DRAINFIELD DESIGNS
The size, design, and location of a drainfield for a given home depend on a variety of factors, such as local soil characteristics, the amount of wastewater flow, ground slope, and depth to groundwater or bedrock. The objective is to distribute the effluent into an area with an adequate depth of suitably permeable, unsaturated soil. The drainfield also should be located as far as possible from drinking-water wells, streams, lakes, steep hillsides, road-cuts, property lines, etc.
Specific design criteria are provided by local building or sewer codes and often vary from one locality to the next. Local health departments often require a permit before allowing any work on a drainfield and frequently can offer helpful advice. A comprehensive presentation of the many and various local design rules is beyond the scope of this book. Rather, our intent is to provide a basic understanding of what the drainfield is and how it works.
