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{{Short description|Method for basic wastewater treatment (on-site)}} | |||
{| align=right | |||
{{About|a septic tank|the band of the same name|Septic Tank (band)}} | |||
|] | |||
{{Infobox sanitation technology | |||
|- | |||
| name = <!--{{PAGENAME}} by default--> | |||
|] | |||
| synonym = | |||
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| image = File:Septic tank Bolduc.jpg | |||
|]]] | |||
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| caption = A septic tank being installed in the ground | |||
| pronounce = | |||
| position = Collection and storage/treatment (on-site)<ref name="SSWM septic tanks">{{cite web|url=https://sswm.info/sanitation-systems/sanitation-technologies/septic-tank|title=Sanitation Systems – Sanitation Technologies – Septic Tank|website=SSWM|date=19 June 2018|access-date=31 October 2018}}</ref> | |||
| application = Household or neighborhood level (schools, hotels etc.)<ref name="SSWM septic tanks"/> | |||
| management = Household, public, shared (most common is household level)<ref name="SSWM septic tanks"/> | |||
| inputs = ], ], brownwater<ref name="SSWM septic tanks"/> | |||
| outputs = ], ]<ref name="SSWM septic tanks"/> | |||
| types = Single tank or multi-chamber septic tanks (potentially with baffles)<ref name="SSWM septic tanks"/> | |||
| construction cost = | |||
| maintenance = | |||
| environmental = ], ] e.g. during floods<ref name="SSWM septic tanks"/> | |||
| usage = | |||
}}A '''septic tank''' is an underground chamber made of concrete, fiberglass, or plastic through which domestic wastewater (]) flows for basic ].<ref name="tilley2">{{cite book|url=http://www.eawag.ch/en/department/sandec/publications/compendium/|title=Compendium of Sanitation Systems and Technologies|last2=Ulrich|first2=Lukas|last3=Lüthi|first3=Christoph|last4=Reymond|first4=Philippe|last5=Zurbrügg|first5=Chris|publisher=Swiss Federal Institute of Aquatic Science and Technology (Eawag)|year=2014|isbn=978-3906484570|edition=2nd|location=Duebendorf, Switzerland|chapter=Septic tanks|chapter-url=http://ecompendium.sswm.info/sanitation-technologies/septic-tank?group_code=s|last1=Tilley|first1=Elizabeth}}</ref> Settling and ] processes reduce solids and organics, but the treatment efficiency is only moderate (referred to as "primary treatment").<ref name="tilley2" /> Septic tank systems are a type of simple ]. They can be used in areas that are not connected to a ] system, such as rural areas. The treated liquid effluent is commonly disposed in a ], which provides further treatment. Nonetheless, ] may occur and is a problem. | |||
The term "septic" refers to the ] environment that develops in the tank that decomposes or mineralizes the waste discharged into the tank. Septic tanks can be coupled with other ] units such as ]s or aerobic systems involving artificially forced ].<ref>{{cite web | |||
A '''septic tank''', the key component of a '''septic system''', is a small scale ] system common in areas with no connection to main sewerage pipes provided by private corporations or local governments. (Other components, typically mandated and/or restricted by local governments, optionally include pumps, alarms, sand filters, and clarified liquid effluent disposal means such as drain fields, ponds, or ] beds.) Septic systems are a type of On-Site Sewage Facility (]). In ] approximately 25% of the population relies on septic tanks; this can include ] and small towns as well as ] areas. In Europe they are generally limited to rural areas only. | |||
|url = http://www.agwt.org/info/septicsystems.htm | |||
|title = Septic Systems for Waste Water Disposal | |||
The term "septic" refers to the ] environment that develops in the tank and which decomposes or mineralizes the waste discharged into the tank. Adding a supplemental bacterial agent to the tank will accelerate the digestion of solids in the tank. The alternative to a septic tank is to use an aerobic system involving artificial ].<ref>{{web cite | |||
|publisher = American Ground Water Trust | |||
| url = http://www.agwt.org/SepticSystems.htm | |||
|access-date = 2008-05-20 | |||
| title = Septic Systems for Waste Water Disposal | |||
|url-status = dead | |||
| publisher = American Ground Water Trust | |||
|archive-url = https://web.archive.org/web/20080517080933/http://www.agwt.org/info/septicsystems.htm | |||
| accessdate = 2006-07-11 | |||
|archive-date = 2008-05-17 | |||
}}</ref> | }}</ref> | ||
The rate of accumulation of sludge—also called ] or ]—is faster than the rate of decomposition.<ref name="tilley2" /> Therefore, the accumulated fecal sludge must be periodically removed, which is commonly done with a ].<ref name=nesc>{{cite web|title=What is a septic system? How do I maintain one?|url=http://www.nesc.wvu.edu/subpages/septic_defined.cfm|website=National Environmental Services Center|publisher=nesc|access-date=4 March 2015|archive-date=26 April 2016|archive-url=https://web.archive.org/web/20160426142538/http://www.nesc.wvu.edu/subpages/septic_defined.cfm|url-status=dead}}</ref> | |||
Periodic ] is required to remove the irreducible solids which settle and gradually fill the tank, reducing its efficiency. In most jurisdictions this maintenance is required by law, yet often not enforced. Those who ignore the requirement will eventually be faced with extremely costly repairs when solids escape the tank and destroy the clarified liquid effluent disposal means. A properly cared for system can last for decades and possibly a lifetime. | |||
{{TOC level|3}} | |||
==Description== | |||
The hose used to remove the waste solids from the septic tank to the truck's tank is called the "honey dipper". The trucks which carry the removed materials away are euphemistically called "]". | |||
] | |||
]]] | |||
A septic tank consists of one or more concrete or plastic tanks of between 4,500 and 7,500 litres (1,000 and 2,000 gallons); one end is connected to an inlet ] pipe and the other to a ]. Generally these pipe connections are made with a T pipe, allowing liquid to enter and exit without disturbing any crust on the surface.{{Citation needed|date=April 2024}} Today, the design of the tank usually incorporates two chambers, each equipped with an access opening and cover, and separated by a dividing wall with openings located about midway between the floor and roof of the tank. | |||
Wastewater enters the first chamber of the tank, allowing solids to settle and scum to float. The settled solids are anaerobically digested, reducing the volume of solids. The liquid component flows through the dividing wall into the second chamber, where further settlement takes place. One option for the effluent is the draining into the ], also referred to as a leach field, drain field or seepage field, depending upon locality. A ] is required prior to installation to ensure the porosity of the soil is adequate to serve as a drain field.<ref>Section H2 Building Regulations</ref><ref>{{cite web|last1=Gustafson|first1=David|last2=Machmeier|first2=Roger E.|title=How to run a percolation test|url=http://www.extension.umn.edu/environment/housing-technology/moisture-management/how-to-run-a-percolation-test/index.html|publisher=University of Minnesota|access-date=26 February 2016|archive-date=19 April 2016|archive-url=https://web.archive.org/web/20160419084621/http://www.extension.umn.edu/environment/housing-technology/moisture-management/how-to-run-a-percolation-test/index.html|url-status=dead}}</ref> | |||
==Description== | |||
A septic tank generally consists of a tank of between 1,000 and 1,500 gallons (4000 - 5500 litres) which is connected to an inlet wastewater pipe at one end and to a septic drain field at the other. These pipe connections are generally made via a T pipe which allows liquid entry and egress without disturbing any crust on the surface. Today the design of the tank usually incorporates two chambers (each of which is equipped with a manhole cover) which are separated by means of a dividing wall which has openings located about midway between the floor and roof of the tank. | |||
Septic tank effluent can also be conveyed to a secondary treatment, typically constructed wetlands. Constructed wetlands benefit from the good performance of septic tanks at removing solids, which avoids them getting clogged quickly. | |||
Wastewater enters the first chamber of the tank, allowing solids to settle and scum to float. The settled solids are anaerobically digested reducing the volume of solids. The liquid component flows through the dividing wall into the second chamber where further settlement takes place with the excess liquid then draining in a relatively clear condition from the outlet into the leach field, also referred to as a drain field, or seepage field, depending upon locality. | |||
Septic tank effluent can also be conveyed to a centralized treatment facility. | |||
]The remaining impurities decompose in the soil, and the water is eliminated through ] into the ], and eventually taken up through the ] system of ]s or added to the ]. A piping network, often constructed in a stone filled trench (see ]), distributes the wastewater throughout the field with multiple drainage holes in the network. The size of the ] is proportional to the volume of wastewater and inversely proportional to the porosity of the drainage field. The entire septic system can operate by gravity alone, or where topographic considerations require, with inclusion of a lift ]. | |||
The remaining impurities are trapped and eliminated in the ], with the excess water eliminated through ] into the soil, through ], and by uptake through the ] system of ]s and eventual ] or entering ] or ]. A piping network, often laid in a stone-filled trench (see ]), distributes the wastewater throughout the field with multiple drainage holes in the network. The size of the drain field is proportional to the volume of wastewater and inversely proportional to the porosity of the drainage field. The entire septic system can operate by gravity alone or, where topographic considerations require, with inclusion of a lift ]. | |||
An ] is a two stage septic system where the sludge is digested in a separate tank. This avoids mixing digested sludge with incoming sewage. Also some septic tank designs have a second stage where the ] from the anaerobic first stage is aerated, before it drains into the seepage field. | |||
Certain septic tank designs include ]s or other devices to increase the volume and velocity of outflow to the drainage field. These help to fill the drainage pipe more evenly and extend the drainage field life by preventing premature clogging or ]. | |||
Waste that is not decomposed by the anaerobic digestion eventually has to be removed from the septic tank or else the septic tank fills up and undecomposed wastewater discharges directly to the drainage field. Not only is this bad for the environment, but if the sludge overflows the septic tank into the leach field, it may clog the leach field piping requiring expensive repairs. | |||
An ] is a two-stage septic system where the sludge is digested in a separate tank. This avoids mixing digested sludge with incoming sewage. Also, some septic tank designs have a second stage where the ] from the anaerobic first stage is aerated before it drains into the seepage field. | |||
How often the septic tank has to be emptied depends on the volume of the tank relative to the input of solids, the amount of indigestible solids and the ambient temperature (as anaerobic digestion occurs more efficiently at higher temperatures). In general it is rare for a septic tank system to require emptying more than once a year, and by careful management many users can reduce emptying to every 3 to 5 years. When emptying a tank, only a small residue of sludge should be left in the tank. Anaerobic decomposition is rapidly re-started when the tank re-fills. | |||
A properly designed and normally operating septic system is |
A properly designed and normally operating septic system is odour-free. Besides periodic inspection and emptying, a septic tank should last for decades with minimal maintenance, with concrete, fibreglass, or plastic tanks lasting about 50 years.<ref>{{cite web |url=http://cecalaveras.ucdavis.edu/realp.htm |title=Septic Tanks: The Real Poop |publisher=University of California Extension |access-date=28 December 2015 |archive-url=https://web.archive.org/web/20090303040517/http://cecalaveras.ucdavis.edu/realp.htm |archive-date=3 March 2009}}</ref> | ||
==Emptying (desludging) == | |||
A well designed and maintained concrete, fiberglass or plastic tank should last about 50 years.<ref>{{web cite | |||
] | |||
| url = http://cecalaveras.ucdavis.edu/realp.htm | title = Septic Tanks: The Real Poop | publisher = University of California Extension | accessdate = 2006-07-11 }}</ref> | |||
{{Further|Fecal sludge management}} | |||
Waste that is not decomposed by the anaerobic digestion must eventually be removed from the septic tank. Otherwise the septic tank fills up and wastewater containing undecomposed material discharges directly to the drainage field. Not only is this detrimental for the environment but, if the sludge overflows the septic tank into the leach field, it may clog the leach field piping or decrease the soil porosity itself, requiring expensive repairs. | |||
When a septic tank is emptied, the accumulated sludge (], also known as ]<ref name=Arbogast2013>{{cite web |url=http://blogs.worldbank.org/water/why-fecal-sludge-management-serious-business |title=Why Fecal Sludge Management is Serious Business |last=Arbogast |first=Brian |date=November 18, 2013 |work=The Water Blog, ]}}</ref>) is pumped out of the tank by a ]. How often the septic tank must be emptied depends on the volume of the tank relative to the input of solids, the amount of indigestible solids, and the ambient temperature (because anaerobic digestion occurs more efficiently at higher temperatures), as well as usage, system characteristics and the requirements of the relevant authority. | |||
==Potential problems== | |||
Some health authorities require tanks to be emptied at prescribed intervals, while others leave it up to the decision of an inspector. Some systems require pumping every few years or sooner, while others may be able to go 10–20 years between pumpings. An older system with an undersize tank that is being used by a large family will require much more frequent pumping than a new system used by only a few people. Anaerobic decomposition is rapidly restarted when the tank is refilled. | |||
#Excessive dumping of cooking oils and grease can fill up the upper portion of the septic tank and can cause the inlet drains to block. Oils and grease are often difficult to degrade and can cause odor problems and difficulties with the periodic emptying. | |||
#Flushing non-biodegradable hygiene products such as sanitary towels and cotton buds will rapidly fill or clog a septic tank and these materials should not be disposed of in this way. | |||
#The use of ] for disposal of waste food can cause a rapid overload of the system and early failure. | |||
#Certain chemicals may damage the working of a septic tank, especially pesticides, herbicides, materials with high concentrations of bleach or caustic soda (lye) or any other inorganic materials such as paints, solvents etc. | |||
#Roots from trees and shrubbery growing above the tank or the drain field may clog and or rupture them. | |||
#Playgrounds and storage buildings may cause damage to a tank and the drainage field. In addition, covering the drainage field with an impervious surface, such as a driveway or parking area, will seriously affect its efficiency and possibly damage the tank and absorption system. | |||
#Excessive water entering the system will overload it and cause it to fail. Checking for plumbing leaks and practicing water conservation will help the system's operation. | |||
#If the system is damaged or malfunctions, contact your local health or environmental authority before attempting any repairs. Improper repair can result in costly mistakes and potential health hazards. | |||
An empty tank may be damaged by hydrostatic pressure causing the tank to partially "float" out of the ground, especially in flood situations or very wet ground conditions.<ref>{{cite web |title=Septic Systems - What to Do after the Flood |url=https://www.epa.gov/ground-water-and-drinking-water/septic-systems-what-do-after-flood |website=] |date=18 November 2015 |access-date=14 August 2018}}</ref> | |||
==Environmental issues== | |||
Another option is "scheduled desludging" of septic tanks which has been initiated in several Asian countries including the Philippines, Malaysia, Vietnam, Indonesia, and India.<ref name=":5">{{Cite journal|last1=Mehta|first1=Meera|last2=Mehta|first2=Dinesh|last3=Yadav|first3=Upasana|date=2019|title=Citywide Inclusive Sanitation Through Scheduled Desludging Services: Emerging Experience From India|journal=Frontiers in Environmental Science|volume=7|page=188|doi=10.3389/fenvs.2019.00188|issn=2296-665X|doi-access=free}}</ref> In this process, every property is covered along a defined route and the property occupiers are informed in advance about desludging that will take place. | |||
Some pollutants, especially ]s, under the anaerobic conditions of septic tanks, are reduced to ], a ] and ] gas. Likewise, ]s and ] are reduced to ]. Because of the anaerobic conditions, ] processes take place, which ultimately generate ] and ], both of which are known greenhouse gases. | |||
==Maintenance== | |||
The fermentation processes cause the contents of a septic tank to be anoxic with a low redox potential, which keeps ] in a soluble and thus mobilized form. Because phosphate can be the limiting nutrient for plant growth in many ecosystems, the discharge from a septic tank into the environment can trigger prolific plant growth including algal blooms which can also include blooms of potentially toxic ]. | |||
The maintenance of a septic system is often the responsibility of the resident or property owner. Some forms of abuse or neglect include the following: | |||
Soil capacity to retain phosphorus is large compared with the load through a normal residential septic tank. An exception occurs when septic drain fields are located in sandy or coarser soils on property adjoining a water body. Because of limited particle surface area, these soils can become saturated with phosphate. Phosphate will progress beyond the treatment area, posing a threat of eutrophication to surface waters.<ref>{{cite web | url = http://cru.cahe.wsu.edu/CEPublications/eb1475/eb1475.html | author = Craig G. Cogger | publisher = College of Agriculture and Home Economics, Pullman, Washington | title = eb1475 Septic System Waste Treatment in Soil | accessdate = 2006-07-11}}</ref> | |||
=== User's actions === | |||
In areas with high population density, groundwater pollution levels often exceed acceptable limits. Some small towns are facing the costs of building a very expensive centralized wastewater treatment system because of this problem, owing to the high cost of extended collection systems. Too often, the efficient and economical alternative of a properly designed decentralized wastewater treatment plant is not considered. | |||
* Excessive disposal of cooking oils and grease can cause the inlet drains to block. Oils and grease are often difficult to degrade and can cause odor problems and difficulties with the periodic emptying. | |||
* Flushing non-biodegradable waste items down the toilet such as ], ] or ] and ]s can cause a septic tank to clog and fill rapidly, so these materials should not be disposed of in that manner. The same applies when the toilet is connected to a ] rather than a septic tank. | |||
* Using the toilet for disposal of ] can cause a rapid overload of the system with solids and contribute to failure.<ref name="homeowner2">{{cite web |title=What can make my system fail? |url=http://www3.epa.gov/npdes/pubs/homeowner_guide_long_customize.pdf |website=United States Environmental Protection Agency |publisher=EPA |access-date=28 December 2015}}</ref> | |||
* Certain chemicals may damage the components of a septic tank or kill the bacteria needed in the septic tank for the system to operate properly, such as ]s, ]s, materials with high concentrations of ] or ] (lye),{{citation needed|date=July 2016}} or any other inorganic materials such as paints or solvents.<ref>{{cite web|last1=Roberts|first1=Mark|title=Septic Tanks – The Guide|url=https://septicleanse.com/septic-tanks/|publisher=Septicleanse|access-date=18 July 2016|date=9 March 2016}}</ref> | |||
* Using ] – the brine discharge from water softeners may harm the bacteria responsible for breaking down the wastewater. Usually, however, the brine is sufficiently diluted with other wastewater that it does not adversely affect the septic system.<ref>{{cite web |url=https://www.hockingcountyhealthdepartment.com/pdf/water-softener-fact-sheet.pdf |title=water-softener-fact-sheet |work=www.hockingcountyhealthdepartment.com |access-date=18 October 2022}}</ref> | |||
=== Other factors === | |||
To slow pollution, building moratoriums and limits on the splitting of property are often imposed. Ensuring existing septic tanks are functioning properly is also helpful for a limited time, but it is not the solution. Once polluted, groundwater is very slow to clean - thus urgent action is appropriate. | |||
* Roots from trees and shrubbery protruding above the tank or drainfield may clog and/or rupture them. Trees that are directly within the vicinity of a concrete septic tank have the potential to penetrate the tank as the system ages and the concrete begins to develop cracks and small leaks. Tree roots can cause serious flow problems due to plugging and blockage of drain pipes, and the trees themselves tend to expand extremely vigorously due to the ready supply of nutrients from the septic system. | |||
* Playgrounds and storage buildings may cause damage to a tank and the drainage field. In addition, covering the drainage field with an impermeable surface, such as a driveway or parking area, will seriously affect its efficiency and possibly damage the tank and absorption system. | |||
* Excessive water entering the system may overload it and cause it to fail. | |||
* Very high rainfall, rapid ], and ]ing from rivers or the sea can all prevent a drain field from operating, and can cause flow to back up, interfering with the normal operation of the tank. High winter ]s can also result in ] flowing back into the septic tank. | |||
* Over time, ]s develop on the pipes of the drainage field, which can lead to blockage. Such a failure can be referred to as "biomat failure". | |||
=== Septic tank additives === | |||
The common expression ''the grass is always greener over the septic tank'' (which is also the title of an ] book) is technically incorrect. The grass is greener over the '''leach field''', which is better watered and has more nutrients than the surrounding land. However, it is not unusual to find better growth over the septic tank itself as well, particularly the end nearer the leach field. | |||
{{Further|Pit additive}} | |||
Septic tank additives have been promoted by some manufacturers with the aim to improve the effluent quality from septic tanks, reduce sludge build-up and to reduce odors. These additives—which are commonly based on "]"—are usually costly in the longer term and fail to live up to expectations.<ref name=":0">Foxon, K., Still, D. (2012). Water Research Commission (WRC), University of Kwazulu-Natal, Partners in Development (PiD), South Africa</ref> It has been estimated that in the U.S. more than 1,200 septic system additives were available on the market in 2011.<ref name="Pradhan" /> Very little peer-reviewed and replicated field research exists regarding the efficacy of these biological septic tank additives.<ref name="Pradhan">S. Pradhan, Michael T. Hoover, G.H. Clark, ], C. Cobb, J. Strock (2011) {{Webarchive|url=https://web.archive.org/web/20160304112606/http://www.soil.ncsu.edu/publications/septic/JEH12.11_Feature_Impacts_of_Biological_Additives_Part_2.pdf |date=2016-03-04 }}, ''Journal of Environmental Health'', Volume 74, Number 5, p. 22–28</ref> | |||
==Environmental concerns== | |||
=="Septic tank" in slang== | |||
] | |||
In ] (common in Britain and ]) "septic tank" or, more commonly, simply "septic" or "]" is used as a ] ], based on a rhyme for "]". The pejorative nature of the term is further underlined by its referral to a container for storing human waste. See also "Sherman Tank" (= wank). | |||
] | |||
While a properly maintained and located septic tank poses no higher amount of environmental problems than centralized municipal sewage treatment,<ref name="betterenviro">{{cite web |last1=Arnold |first1=Rory |title=Sewer vs septic system: which is better for the environment? |url=https://www.earth.com/news/sewer-septic-system-environment/ |website=Earth.com |access-date=16 October 2020}}</ref> certain problems could arise with a septic tank in an unsuitable location, and septic tank failures are typically more expensive to fix or replace than municipal sewer.<ref name="betterenviro"/> Since septic systems require large ], they are unsuitable for densely built areas. | |||
=== Odor, gas emissions and carbon footprint === | |||
In an episode of the British panel show "]", ] mentioned the ] "listerine", from a mouthwash whose antiseptic properties made it suitable for rhyming slang use to refer to anti-Americans. | |||
Some constituents of wastewater, especially ]s, under the anaerobic conditions of septic tanks, are reduced to ], a ] and ] gas. ]s and ] can be reduced to ]. Because of the anaerobic conditions, ] and methanogenesis processes take place, which may generate ] and/or ]. Both carbon dioxide and methane are greenhouse gases, with methane having a global warming potential about 25 times larger than carbon dioxide. This makes septic tanks potential greenhouse gas emitters. The same methane can be burnt to produce energy for local usage.<ref>{{Cite journal |last1=Boiocchi |first1=Riccardo |last2=Mainardis |first2=Matia |last3=Rada |first3=Elena Cristina |last4=Ragazzi |first4=Marco |last5=Salvati |first5=Silvana Carla |date=January 2023 |title=Carbon Footprint and Energy Recovery Potential of Primary Wastewater Treatment in Decentralized Areas: A Critical Review on Septic and Imhoff Tanks |journal=Energies |language=en |volume=16 |issue=24 |pages=7938 |doi=10.3390/en16247938 |doi-access=free |issn=1996-1073|hdl=11390/1267670 |hdl-access=free }}</ref> | |||
=== Nutrients in the effluent === | |||
The term is a euphemism originally referring to a horse drawn wagon carrying a tank of liquid manure or sewage. Today a tanker truck equipped with a ] pump to empty septic and conservancy tanks is also euphemistically known as a "honey sucker". | |||
Septic tanks by themselves are ineffective at removing ] compounds that have potential to cause ] in waterways into which affected water from a septic system finds its way. This can be remedied by using a nitrogen-reducing technology,<ref name="Vcenter">{{cite web |url=http://www.epa.gov/etv/pubs/600s07004.pdf |title=Residential nutrient reduction |access-date=2010-12-22 |url-status=bot: unknown |archive-url=https://web.archive.org/web/20110602060154/http://www.epa.gov/etv/pubs/600s07004.pdf |archive-date=June 2, 2011 }}</ref> such as hybrid constructed wetlands, or by simply ensuring that the leach field is properly sited to prevent direct entry of effluent into bodies of water.{{Citation needed|date=December 2014}} | |||
The fermentation processes cause the contents of a septic tank to be anaerobic with a low ] potential, which keeps ] in a soluble and, thus, mobilized form. Phosphates discharged from a septic tank into the environment can trigger prolific plant growth including algal blooms, which can also include blooms of potentially toxic ]. | |||
==See also== | |||
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*] (Percolation testing for the capacity of soil to absorb water) | |||
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The soil's capacity to retain phosphorus is usually large enough to handle the load through a normal residential septic tank. An exception occurs when ]s are located in sandy or coarser soils on property adjacent to a water body. Because of limited particle surface area, these soils can become saturated with phosphates. Phosphates will progress beyond the treatment area, posing a threat of ] to surface waters.<ref>{{cite web | url = http://cru.cahe.wsu.edu/CEPublications/eb1475/eb1475.html | author = Craig G. Cogger | publisher = College of Agriculture and Home Economics, Pullman, Washington | title = eb1475 Septic System Waste Treatment in Soil | access-date = 2006-07-11 | url-status = dead | archive-url = https://web.archive.org/web/20060823033140/http://cru.cahe.wsu.edu/CEPublications/eb1475/eb1475.html | archive-date = 2006-08-23 }}</ref> | |||
==External links== | |||
=== Pathogens === | |||
* | |||
* | |||
Diseases extremely dangerous to human contact such as ] and other ] are often reported following failures of septic tanks.<ref name="wellwater">{{cite news |last1=Dare |first1=Don |title=Residents' well water contaminated by septic failure at Bean Station slaughterhouse |url=https://www.wate.com/investigations/residents-well-water-contaminated-by-septic-failure-at-bean-station-slaughterhouse-2/ |access-date=February 8, 2021 |work=] |date=March 21, 2018}}</ref> | |||
* | |||
* | |||
A properly functioning septic system, on the other hand, provides significant reduction of pathogens compared to direct discharge due to settling (in the tank) and soil absorption (in the drain field). ]s of 4–8 for coliform bacteria, 0–2 for viruses are achieved in the effluent. Parasitic worm eggs are also removed. Additional filters may be added to improve removal performance although they will need to be replaced periodically.<ref>{{cite journal|url=https://www.waterpathogens.org/book/septic-systems |title=Septic Systems | Global Water Pathogen Project |doi=10.1016/j.watres.2008.06.014 |publisher=Waterpathogens.org |date=2019-02-08 |pmid=18718625 |accessdate=2022-08-07|last1=Vinnerås |first1=B. |last2=Nordin |first2=A. |last3=Niwagaba |first3=C. |last4=Nyberg |first4=K. |journal=Water Research |volume=42 |issue=15 |pages=4067–4074 }}</ref> | |||
* | |||
* USEPA's ], Morgantown, West Virginia, USA (http://www.epa.gov/owm/mab/smcomm/nsfc.htm) | |||
=== Groundwater pollution === | |||
In areas with high population density, ] beyond acceptable limits may occur. Some small towns experience the costs of building very expensive centralized wastewater treatment systems because of this problem, due to the high cost of extended collection systems. To reduce residential development that might increase the demand to construct an expensive centralized sewerage system, building moratoriums and limitations on the ] of property are often imposed. Ensuring existing septic tanks are functioning properly can also be helpful for a limited time, but becomes less effective as a primary remediation strategy as population density increases. | |||
=== Surface water pollution === | |||
In areas adjacent to water bodies with fish or ] intended for human consumption, improperly maintained and failing septic systems contribute to pollution levels that can force harvest restrictions and/or commercial or recreational harvest closures. | |||
== Use == | |||
] | |||
In the ], the 2008 American Housing Survey indicated that about 20 percent of all households rely on septic tanks,<ref name="AHS2007">{{cite web |title=American Housing Survey for the United States: 2007 |url=https://www.census.gov/content/dam/Census/library/publications/2008/demo/h150-07.pdf |website=American Housing Survey |publisher=U.S. Department of Housing and Urban Development |access-date=2018-08-08 |page=6}}</ref> and that the overwhelming majority of systems are located in ] (50%) and ]an (47%) areas.<ref name="AHS2007" |page=17,28,39/> ] is one example of a large city where many of the city's neighborhoods still rely on separate septic systems.<ref>{{cite web|url=http://www.citizensenergygroup.com/STEP|title=Septic Tank Elimination Program|publisher=Citizens Energy Group|access-date=2016-02-16}}</ref> In Europe, septic systems are generally limited to rural areas.{{citation needed|date=August 2018}} | |||
==Regulations== | |||
=== European Union === | |||
In the ] the ] standard provides the general requirements for packaged and site assembled treatment plants used for domestic wastewater treatment. | |||
Part 1 (]) is for septic tanks that are prefabricated or factory manufactured and made of ], ], ], ], ] or ]. Part 4 (]) regulates septic tanks that are assembled on site from prefabricated kits, generally of concrete construction. Certified septic tanks of both types must pass a standardized hydraulic test to assess their ability to retain suspended solids within the system. Additionally, their structural adequacy in relevant ground conditions is assessed in terms of water-tightness, treatment efficiency, and structural behaviour.<ref>Santala, E. . Finnish Environment Institute.</ref> | |||
==== France ==== | |||
In ], about 4 million households (or 20% of the population) are using on-site wastewater disposal systems (''l’assainissement non collectif''),<ref>{{cite web|url=https://www.assainissement-non-collectif.developpement-durable.gouv.fr/publication-dispositifs-de-traitement-agrees-a772.html|title=Portail interministériel sur l'assainissement non collectif|first= |last= |date=13 December 2018|website=www.assainissement-non-collectif.developpement-durable.gouv.fr |access-date=18 October 2022}}</ref> including septic tanks (''fosse septique''). The legal framework for regulating the construction and maintenance of septic systems was introduced in 1992 and updated in 2009 and 2012 with the intent to establish the technical requirements applicable to individual sewerage systems.<ref>{{cite web|url=http://www.legifrance.gouv.fr/affichTexte.do;jsessionid=87BFC4F3E89500EDF54382AC22342262.tpdila21v_2?cidTexte=JORFTEXT000025743299&dateTexte=20150527|title=Arrêté du 7 mars 2012 modifiant l'arrêté du 7 septembre 2009 fixant les prescriptions techniques applicables aux installations d'assainissement non collectif recevant une charge brute de pollution organique inférieure ou égale à 1,2 kg/j de DBO5 – Legifrance|work=legifrance.gouv.fr|access-date=7 September 2015}}</ref> Septic tanks in France are subject to inspection by SPANC (''Service Public d’Assainissement Non Collectif''), a professional body appointed by the respective local authorities to enforce wastewater collection laws, at least once in four years. Following the introduction of EN 12566, the discharge of effluent directly into ditches or watercourses is prohibited, unless the effluent meets prescribed standards.<ref>{{cite web|url=http://www.thegoodlifefrance.com/fosse-septique-france-rules-and-requirements/|title=Fosse Septique France|work=The Good Life France|date=20 July 2012|access-date=7 September 2015}}</ref> | |||
==== Ireland ==== | |||
According to the ], 27.5% of Irish households (i.e. about 440,000 households), with the majority in rural areas, use an individual septic tank.<ref>{{cite web|url=https://www.cso.ie/en/census/census2011reports/census2011profile4theroofoverourheads-housinginireland/|title=Census 2011 Profile 4 The Roof over our Heads – Housing in Ireland |publisher= CSO – Central Statistics Office|website=www.cso.ie}}</ref> | |||
Following a ] judgment made against ] in 2009 that deemed the country non-compliant with the ] in relation to domestic wastewaters disposed of in the countryside, the Water Services (Amendment) Act 2012 was passed in order to regulate wastewater discharges from domestic sources that are not connected to the public sewer network and to provide arrangements for registration and inspection of existing individual domestic wastewater treatment systems.<ref> {{Webarchive|url=https://web.archive.org/web/20150924001320/http://www.environ.ie/en/Legislation/Environment/Water/FileDownLoad,29427,en.pdf |date=2015-09-24 }}, Department of the Environment, Community and Local Government, Ireland.</ref><ref>, Judgment of the Court (Second Chamber) of 29 October 2009. Commission of the European Communities v Ireland. Failure of a Member State to fulfil obligations – Directive 75/442/EEC – Waste – Domestic waste waters discharged through septic tanks in the countryside – Waste not covered by other legislation – Failure to transpose.</ref> | |||
Additionally, a code of practice has been developed by the ] to regulate the planning and construction of new septic tanks, secondary treatment systems, septic drain fields and filter systems.<ref name="EPA_CodeOfPractice"> {{Webarchive|url=https://web.archive.org/web/20120625121859/http://www.epa.ie/downloads/advice/water/wastewater/code%20of%20practice%20for%20single%20houses/#d.en.27967 |date=2012-06-25 }}, 2010. Environmental Protection Agency, Ireland.</ref> Direct discharge of septic tank effluent into groundwater is prohibited in Ireland, while the indirect discharge via unsaturated subsoil into groundwater, e.g. by means of a septic drain field, or the direct discharge into surface water is permissible in accordance with a Water Pollution Act license.<ref name="EPA_CodeOfPractice" /> Registered septic tanks must be desludged by an authorized contractor at least once a year; the removed fecal sludge is disposed of, either to a managed municipal wastewater treatment facility or to agriculture provided that nutrient management regulations are met.<ref name="EPA_CodeOfPractice" /> | |||
=== United Kingdom === | |||
Since 2015, only certain property owners in ] and ] with septic tanks or small packaged sewage treatment systems need to register their systems, and either apply for a permit or qualify for an exemption with the ].<ref>Standard Note SN06059 (2014). , House of Commons Library</ref> Permits need to be granted to systems that discharge more than a certain volume of effluent in a given time or that discharge effluent directly into sensitive areas (e.g., some groundwater protection zones).<ref>{{cite web|url=https://www.gov.uk/permits-you-need-for-septic-tanks/permits|title=Septic tanks and treatment plants: permits and general binding rules|work=www.gov.uk|access-date=7 September 2015}}</ref> In general, permits are not granted for new septic tanks that discharge directly into surface waters. A septic tank discharging into a watercourse must be replaced or upgraded by 1 January 2020 to a Sewage Treatment Plant (also called an ]), or sooner if the property is sold before this date, or if the Environment Agency (EA) finds that it is causing pollution. | |||
In ], the ] must give permission for all wastewater discharges where it is proposed that the discharge will go to a waterway or soil infiltration system. The discharge consent will outline conditions relating to the quality and quantity of the discharge in order to ensure the receiving waterway or the underground aquifer can absorb the discharge.<ref>Department of the Environment (Northern Ireland) {{webarchive|url=https://web.archive.org/web/20150613041745/http://www.doeni.gov.uk/niea/water-home/regulation_of_discharges_industrial/septictanks.htm |date=2015-06-13 }}</ref> | |||
The Water Environment Regulations 2011 regulate the registration of septic tank systems in ]. Proof of registration is required when new properties are being developed or existing properties change ownership.<ref>Scottish Environment Protection Agency (SEPA) </ref> | |||
=== Australia === | |||
In Australia, septic tank design and installation requirements are regulated by State Governments, through Departments of Health and Environmental Protection Agencies. Regulation may include Codes of Practice<ref>{{cite web|url=http://www.sahealth.sa.gov.au/wps/wcm/connect/ba6ead0048f0d8ab828287f25a3eb7d6/2013SAHealth_On-site_Wastewater_Systems_Code_April.pdf?MOD=AJPERES&CACHEID=ba6ead0048f0d8ab828287f25a3eb7d6&CACHE=NONE|title=On-site Wastewater Systems Code|date=April 2013|website=SA Health|publisher=SA Health, Government of South Australia|access-date=11 February 2017}}</ref><ref>{{cite web|url=http://www.epa.vic.gov.au/~/media/Publications/891%204.pdf|title=Code of practice - onsite wastewater management|date=July 2016|publisher=EPA Victoria|access-date=11 February 2017|archive-date=10 April 2017|archive-url=https://web.archive.org/web/20170410232234/http://www.epa.vic.gov.au/~/media/Publications/891%204.pdf|url-status=dead}}</ref> and Legislation.<ref>{{cite web|url=http://www.slp.wa.gov.au/statutes/regs.nsf/3b7e5f26432801b348256ec3002c128c/40d2c1afd926a7b448256704000fdd55/$FILE/Health%20(Treatment%20of%20Sewage%20and%20Disposal%20of%20Effluent%20and%20Liquid%20Waste)%20Regulations%201974.PDF|title=Health (Treatment of Sewage and Disposal of Effluent and Liquid Waste) Regulations 1974|date=7 October 2005|publisher=Government of Western Australia}}</ref> Regulatory requirements for the design and installation of septic tanks commonly references Australian Standards (1547 and 1546). Capacity requirements for septic tanks may be outlined within Codes of Practice, and can vary between states. | |||
Mainly because of water leaching from the effluent drains of a lot of closely spaced septic systems,<ref>{{cite web |title=How to Solve The Biggest Problems With Septic Tanks and Systems |url=https://commercial-environmental.coerco.com.au/industry-updates/how-to-solve-the-biggest-problems-with-septic-tanks-and-systems |publisher=Coerco |access-date=2021-05-11}}</ref> many council districts (e.g. ]) have banned septic systems, and require them to be replaced with much more expensive small-scale ] systems that actively pump air into the tank, producing an aerobic environment.{{citation needed|date=May 2017}} Septic systems have to be replaced as part of any new building applications, regardless of how well the old system performed.{{citation needed|date=May 2017}} | |||
=== United States === | |||
According to the ], in the United States it is the home owners' responsibility to maintain their septic systems.<ref name="homeowner">{{cite web|url=http://www3.epa.gov/npdes/pubs/homeowner_guide_long_customize.pdf|title=A Homeowner's Guide to Septic Systems|website=United States Environmental Protection Agency|publisher=EPA|access-date=28 December 2015}}</ref> Anyone who ignores this requirement will eventually experience costly repairs when solids escape the tank and clog the clarified liquid effluent disposal system. | |||
In ], for example, a "shellfish protection district" or "clean water district" is a geographic service area designated by a county to protect water quality and tideland resources. The district provides a mechanism to generate local funds for water quality services to control non-point sources of pollution, such as septic system maintenance. The district also serves as an educational resource, calling attention to the pollution sources that threaten shellfish growing waters.<ref>{{cite web|url=http://www.psparchives.com/publications/our_work/misc/Fact_sheets/shellfish_protection_dist_05.pdf|title=Shellfish - Marine|author=Beatrice|work=Marine|access-date=7 September 2015|archive-date=15 January 2014|archive-url=https://web.archive.org/web/20140115031728/http://www.psparchives.com/publications/our_work/misc/Fact_sheets/shellfish_protection_dist_05.pdf|url-status=dead}}</ref> | |||
== Slang usage == | |||
The term "septic tank", or more usually "septic", is used in some parts of Britain as a slang term to refer to Americans,<ref>{{cite web |title=Online slang dictionary |url=http://onlineslangdictionary.com/meaning-definition-of/septic-tank}}</ref> from Cockney ] septic tank equalling yank.<ref>{{cite web |title=Collins Dictionary |url=https://www.collinsdictionary.com/us/dictionary/english/yank}}</ref> This is sometimes further shortened to "seppo" by Australians .<ref>{{cite web |title=Macquarie Dictionary |date=25 October 2023 |url=https://www.macquariedictionary.com.au/resources/aus/word/map/search/word/seppo/Australia/}}</ref> | |||
== See also == | |||
* ] | |||
* ] | |||
* ] | |||
* ] | |||
* ] | |||
==References== | |||
{{reflist|30em}} | |||
==External links== | |||
* | |||
{{Wastewater}} | |||
== References == | |||
{{Pollution}} | |||
<references/> | |||
{{Authority control}} | |||
] | |||
] | |||
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Latest revision as of 10:39, 25 December 2024
Method for basic wastewater treatment (on-site) This article is about a septic tank. For the band of the same name, see Septic Tank (band).Septic tank | |
---|---|
A septic tank being installed in the ground | |
Position in sanitation chain | Collection and storage/treatment (on-site) |
Application level | Household or neighborhood level (schools, hotels etc.) |
Management level | Household, public, shared (most common is household level) |
Inputs | blackwater (waste), greywater, brownwater |
Outputs | Fecal sludge, effluent |
Types | Single tank or multi-chamber septic tanks (potentially with baffles) |
Environmental concerns | Groundwater pollution, water pollution e.g. during floods |
A septic tank is an underground chamber made of concrete, fiberglass, or plastic through which domestic wastewater (sewage) flows for basic sewage treatment. Settling and anaerobic digestion processes reduce solids and organics, but the treatment efficiency is only moderate (referred to as "primary treatment"). Septic tank systems are a type of simple onsite sewage facility. They can be used in areas that are not connected to a sewerage system, such as rural areas. The treated liquid effluent is commonly disposed in a septic drain field, which provides further treatment. Nonetheless, groundwater pollution may occur and is a problem.
The term "septic" refers to the anaerobic bacterial environment that develops in the tank that decomposes or mineralizes the waste discharged into the tank. Septic tanks can be coupled with other onsite wastewater treatment units such as biofilters or aerobic systems involving artificially forced aeration.
The rate of accumulation of sludge—also called septage or fecal sludge—is faster than the rate of decomposition. Therefore, the accumulated fecal sludge must be periodically removed, which is commonly done with a vacuum truck.
Description
A septic tank consists of one or more concrete or plastic tanks of between 4,500 and 7,500 litres (1,000 and 2,000 gallons); one end is connected to an inlet wastewater pipe and the other to a septic drain field. Generally these pipe connections are made with a T pipe, allowing liquid to enter and exit without disturbing any crust on the surface. Today, the design of the tank usually incorporates two chambers, each equipped with an access opening and cover, and separated by a dividing wall with openings located about midway between the floor and roof of the tank.
Wastewater enters the first chamber of the tank, allowing solids to settle and scum to float. The settled solids are anaerobically digested, reducing the volume of solids. The liquid component flows through the dividing wall into the second chamber, where further settlement takes place. One option for the effluent is the draining into the septic drain field, also referred to as a leach field, drain field or seepage field, depending upon locality. A percolation test is required prior to installation to ensure the porosity of the soil is adequate to serve as a drain field.
Septic tank effluent can also be conveyed to a secondary treatment, typically constructed wetlands. Constructed wetlands benefit from the good performance of septic tanks at removing solids, which avoids them getting clogged quickly.
Septic tank effluent can also be conveyed to a centralized treatment facility.
The remaining impurities are trapped and eliminated in the soil, with the excess water eliminated through percolation into the soil, through evaporation, and by uptake through the root system of plants and eventual transpiration or entering groundwater or surface water. A piping network, often laid in a stone-filled trench (see weeping tile), distributes the wastewater throughout the field with multiple drainage holes in the network. The size of the drain field is proportional to the volume of wastewater and inversely proportional to the porosity of the drainage field. The entire septic system can operate by gravity alone or, where topographic considerations require, with inclusion of a lift pump.
Certain septic tank designs include siphons or other devices to increase the volume and velocity of outflow to the drainage field. These help to fill the drainage pipe more evenly and extend the drainage field life by preventing premature clogging or bioclogging.
An Imhoff tank is a two-stage septic system where the sludge is digested in a separate tank. This avoids mixing digested sludge with incoming sewage. Also, some septic tank designs have a second stage where the effluent from the anaerobic first stage is aerated before it drains into the seepage field.
A properly designed and normally operating septic system is odour-free. Besides periodic inspection and emptying, a septic tank should last for decades with minimal maintenance, with concrete, fibreglass, or plastic tanks lasting about 50 years.
Emptying (desludging)
Further information: Fecal sludge managementWaste that is not decomposed by the anaerobic digestion must eventually be removed from the septic tank. Otherwise the septic tank fills up and wastewater containing undecomposed material discharges directly to the drainage field. Not only is this detrimental for the environment but, if the sludge overflows the septic tank into the leach field, it may clog the leach field piping or decrease the soil porosity itself, requiring expensive repairs.
When a septic tank is emptied, the accumulated sludge (septage, also known as fecal sludge) is pumped out of the tank by a vacuum truck. How often the septic tank must be emptied depends on the volume of the tank relative to the input of solids, the amount of indigestible solids, and the ambient temperature (because anaerobic digestion occurs more efficiently at higher temperatures), as well as usage, system characteristics and the requirements of the relevant authority.
Some health authorities require tanks to be emptied at prescribed intervals, while others leave it up to the decision of an inspector. Some systems require pumping every few years or sooner, while others may be able to go 10–20 years between pumpings. An older system with an undersize tank that is being used by a large family will require much more frequent pumping than a new system used by only a few people. Anaerobic decomposition is rapidly restarted when the tank is refilled.
An empty tank may be damaged by hydrostatic pressure causing the tank to partially "float" out of the ground, especially in flood situations or very wet ground conditions.
Another option is "scheduled desludging" of septic tanks which has been initiated in several Asian countries including the Philippines, Malaysia, Vietnam, Indonesia, and India. In this process, every property is covered along a defined route and the property occupiers are informed in advance about desludging that will take place.
Maintenance
The maintenance of a septic system is often the responsibility of the resident or property owner. Some forms of abuse or neglect include the following:
User's actions
- Excessive disposal of cooking oils and grease can cause the inlet drains to block. Oils and grease are often difficult to degrade and can cause odor problems and difficulties with the periodic emptying.
- Flushing non-biodegradable waste items down the toilet such as cigarette butts, cotton buds/swabs or menstrual hygiene products and condoms can cause a septic tank to clog and fill rapidly, so these materials should not be disposed of in that manner. The same applies when the toilet is connected to a sewer rather than a septic tank.
- Using the toilet for disposal of food waste can cause a rapid overload of the system with solids and contribute to failure.
- Certain chemicals may damage the components of a septic tank or kill the bacteria needed in the septic tank for the system to operate properly, such as pesticides, herbicides, materials with high concentrations of bleach or caustic soda (lye), or any other inorganic materials such as paints or solvents.
- Using water softeners – the brine discharge from water softeners may harm the bacteria responsible for breaking down the wastewater. Usually, however, the brine is sufficiently diluted with other wastewater that it does not adversely affect the septic system.
Other factors
- Roots from trees and shrubbery protruding above the tank or drainfield may clog and/or rupture them. Trees that are directly within the vicinity of a concrete septic tank have the potential to penetrate the tank as the system ages and the concrete begins to develop cracks and small leaks. Tree roots can cause serious flow problems due to plugging and blockage of drain pipes, and the trees themselves tend to expand extremely vigorously due to the ready supply of nutrients from the septic system.
- Playgrounds and storage buildings may cause damage to a tank and the drainage field. In addition, covering the drainage field with an impermeable surface, such as a driveway or parking area, will seriously affect its efficiency and possibly damage the tank and absorption system.
- Excessive water entering the system may overload it and cause it to fail.
- Very high rainfall, rapid snowmelt, and flooding from rivers or the sea can all prevent a drain field from operating, and can cause flow to back up, interfering with the normal operation of the tank. High winter water tables can also result in groundwater flowing back into the septic tank.
- Over time, biofilms develop on the pipes of the drainage field, which can lead to blockage. Such a failure can be referred to as "biomat failure".
Septic tank additives
Further information: Pit additiveSeptic tank additives have been promoted by some manufacturers with the aim to improve the effluent quality from septic tanks, reduce sludge build-up and to reduce odors. These additives—which are commonly based on "effective microorganisms"—are usually costly in the longer term and fail to live up to expectations. It has been estimated that in the U.S. more than 1,200 septic system additives were available on the market in 2011. Very little peer-reviewed and replicated field research exists regarding the efficacy of these biological septic tank additives.
Environmental concerns
While a properly maintained and located septic tank poses no higher amount of environmental problems than centralized municipal sewage treatment, certain problems could arise with a septic tank in an unsuitable location, and septic tank failures are typically more expensive to fix or replace than municipal sewer. Since septic systems require large drainfields, they are unsuitable for densely built areas.
Odor, gas emissions and carbon footprint
Some constituents of wastewater, especially sulfates, under the anaerobic conditions of septic tanks, are reduced to hydrogen sulfide, a pungent and toxic gas. Nitrates and organic nitrogen compounds can be reduced to ammonia. Because of the anaerobic conditions, fermentation and methanogenesis processes take place, which may generate carbon dioxide and/or methane. Both carbon dioxide and methane are greenhouse gases, with methane having a global warming potential about 25 times larger than carbon dioxide. This makes septic tanks potential greenhouse gas emitters. The same methane can be burnt to produce energy for local usage.
Nutrients in the effluent
Septic tanks by themselves are ineffective at removing nitrogen compounds that have potential to cause algal blooms in waterways into which affected water from a septic system finds its way. This can be remedied by using a nitrogen-reducing technology, such as hybrid constructed wetlands, or by simply ensuring that the leach field is properly sited to prevent direct entry of effluent into bodies of water.
The fermentation processes cause the contents of a septic tank to be anaerobic with a low redox potential, which keeps phosphates in a soluble and, thus, mobilized form. Phosphates discharged from a septic tank into the environment can trigger prolific plant growth including algal blooms, which can also include blooms of potentially toxic cyanobacteria.
The soil's capacity to retain phosphorus is usually large enough to handle the load through a normal residential septic tank. An exception occurs when septic drain fields are located in sandy or coarser soils on property adjacent to a water body. Because of limited particle surface area, these soils can become saturated with phosphates. Phosphates will progress beyond the treatment area, posing a threat of eutrophication to surface waters.
Pathogens
Diseases extremely dangerous to human contact such as E. coli and other coliform bacteria are often reported following failures of septic tanks.
A properly functioning septic system, on the other hand, provides significant reduction of pathogens compared to direct discharge due to settling (in the tank) and soil absorption (in the drain field). Log reductions of 4–8 for coliform bacteria, 0–2 for viruses are achieved in the effluent. Parasitic worm eggs are also removed. Additional filters may be added to improve removal performance although they will need to be replaced periodically.
Groundwater pollution
In areas with high population density, groundwater pollution beyond acceptable limits may occur. Some small towns experience the costs of building very expensive centralized wastewater treatment systems because of this problem, due to the high cost of extended collection systems. To reduce residential development that might increase the demand to construct an expensive centralized sewerage system, building moratoriums and limitations on the subdivision of property are often imposed. Ensuring existing septic tanks are functioning properly can also be helpful for a limited time, but becomes less effective as a primary remediation strategy as population density increases.
Surface water pollution
In areas adjacent to water bodies with fish or shellfish intended for human consumption, improperly maintained and failing septic systems contribute to pollution levels that can force harvest restrictions and/or commercial or recreational harvest closures.
Use
In the United States, the 2008 American Housing Survey indicated that about 20 percent of all households rely on septic tanks, and that the overwhelming majority of systems are located in rural (50%) and suburban (47%) areas. Indianapolis is one example of a large city where many of the city's neighborhoods still rely on separate septic systems. In Europe, septic systems are generally limited to rural areas.
Regulations
European Union
In the European Union the EN 12566 standard provides the general requirements for packaged and site assembled treatment plants used for domestic wastewater treatment.
Part 1 (EN 12566-1) is for septic tanks that are prefabricated or factory manufactured and made of polyethylene, glass reinforced polyester, polypropylene, PVC-U, steel or concrete. Part 4 (EN 12566-4) regulates septic tanks that are assembled on site from prefabricated kits, generally of concrete construction. Certified septic tanks of both types must pass a standardized hydraulic test to assess their ability to retain suspended solids within the system. Additionally, their structural adequacy in relevant ground conditions is assessed in terms of water-tightness, treatment efficiency, and structural behaviour.
France
In France, about 4 million households (or 20% of the population) are using on-site wastewater disposal systems (l’assainissement non collectif), including septic tanks (fosse septique). The legal framework for regulating the construction and maintenance of septic systems was introduced in 1992 and updated in 2009 and 2012 with the intent to establish the technical requirements applicable to individual sewerage systems. Septic tanks in France are subject to inspection by SPANC (Service Public d’Assainissement Non Collectif), a professional body appointed by the respective local authorities to enforce wastewater collection laws, at least once in four years. Following the introduction of EN 12566, the discharge of effluent directly into ditches or watercourses is prohibited, unless the effluent meets prescribed standards.
Ireland
According to the Census of Ireland 2011, 27.5% of Irish households (i.e. about 440,000 households), with the majority in rural areas, use an individual septic tank.
Following a European Court of Justice judgment made against Ireland in 2009 that deemed the country non-compliant with the Waste Framework Directive in relation to domestic wastewaters disposed of in the countryside, the Water Services (Amendment) Act 2012 was passed in order to regulate wastewater discharges from domestic sources that are not connected to the public sewer network and to provide arrangements for registration and inspection of existing individual domestic wastewater treatment systems.
Additionally, a code of practice has been developed by the Environmental Protection Agency to regulate the planning and construction of new septic tanks, secondary treatment systems, septic drain fields and filter systems. Direct discharge of septic tank effluent into groundwater is prohibited in Ireland, while the indirect discharge via unsaturated subsoil into groundwater, e.g. by means of a septic drain field, or the direct discharge into surface water is permissible in accordance with a Water Pollution Act license. Registered septic tanks must be desludged by an authorized contractor at least once a year; the removed fecal sludge is disposed of, either to a managed municipal wastewater treatment facility or to agriculture provided that nutrient management regulations are met.
United Kingdom
Since 2015, only certain property owners in England and Wales with septic tanks or small packaged sewage treatment systems need to register their systems, and either apply for a permit or qualify for an exemption with the Environment Agency. Permits need to be granted to systems that discharge more than a certain volume of effluent in a given time or that discharge effluent directly into sensitive areas (e.g., some groundwater protection zones). In general, permits are not granted for new septic tanks that discharge directly into surface waters. A septic tank discharging into a watercourse must be replaced or upgraded by 1 January 2020 to a Sewage Treatment Plant (also called an Onsite sewage facility), or sooner if the property is sold before this date, or if the Environment Agency (EA) finds that it is causing pollution.
In Northern Ireland, the Department of the Environment must give permission for all wastewater discharges where it is proposed that the discharge will go to a waterway or soil infiltration system. The discharge consent will outline conditions relating to the quality and quantity of the discharge in order to ensure the receiving waterway or the underground aquifer can absorb the discharge.
The Water Environment Regulations 2011 regulate the registration of septic tank systems in Scotland. Proof of registration is required when new properties are being developed or existing properties change ownership.
Australia
In Australia, septic tank design and installation requirements are regulated by State Governments, through Departments of Health and Environmental Protection Agencies. Regulation may include Codes of Practice and Legislation. Regulatory requirements for the design and installation of septic tanks commonly references Australian Standards (1547 and 1546). Capacity requirements for septic tanks may be outlined within Codes of Practice, and can vary between states.
Mainly because of water leaching from the effluent drains of a lot of closely spaced septic systems, many council districts (e.g. Sunshine Coast, Queensland) have banned septic systems, and require them to be replaced with much more expensive small-scale sewage treatment systems that actively pump air into the tank, producing an aerobic environment. Septic systems have to be replaced as part of any new building applications, regardless of how well the old system performed.
United States
According to the US Environmental Protection Agency, in the United States it is the home owners' responsibility to maintain their septic systems. Anyone who ignores this requirement will eventually experience costly repairs when solids escape the tank and clog the clarified liquid effluent disposal system.
In Washington, for example, a "shellfish protection district" or "clean water district" is a geographic service area designated by a county to protect water quality and tideland resources. The district provides a mechanism to generate local funds for water quality services to control non-point sources of pollution, such as septic system maintenance. The district also serves as an educational resource, calling attention to the pollution sources that threaten shellfish growing waters.
Slang usage
The term "septic tank", or more usually "septic", is used in some parts of Britain as a slang term to refer to Americans, from Cockney rhyming slang septic tank equalling yank. This is sometimes further shortened to "seppo" by Australians .
See also
References
- ^ "Sanitation Systems – Sanitation Technologies – Septic Tank". SSWM. 19 June 2018. Retrieved 31 October 2018.
- ^ Tilley, Elizabeth; Ulrich, Lukas; Lüthi, Christoph; Reymond, Philippe; Zurbrügg, Chris (2014). "Septic tanks". Compendium of Sanitation Systems and Technologies (2nd ed.). Duebendorf, Switzerland: Swiss Federal Institute of Aquatic Science and Technology (Eawag). ISBN 978-3906484570.
- "Septic Systems for Waste Water Disposal". American Ground Water Trust. Archived from the original on 2008-05-17. Retrieved 2008-05-20.
- "What is a septic system? How do I maintain one?". National Environmental Services Center. nesc. Archived from the original on 26 April 2016. Retrieved 4 March 2015.
- Section H2 Building Regulations
- Gustafson, David; Machmeier, Roger E. "How to run a percolation test". University of Minnesota. Archived from the original on 19 April 2016. Retrieved 26 February 2016.
- "Septic Tanks: The Real Poop". University of California Extension. Archived from the original on 3 March 2009. Retrieved 28 December 2015.
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