Instruct: Given a question, retrieve passages that can help answer the question.
Query: Where are septic tanks normally built?
A septic tank consists of one or more concrete or plastic tanks of between 4000 and 7500 liters (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 a manhole cover, and separated by a dividing wall with openings located about midway between the floor and roof of the tank.
A septic tank is part of a small scale sewage treatment system often referred to as a septic system. Septic systems are commonly used to treat wastewater from homes and small businesses in rural and suburban areas. It consists of the tank and a septic drain field. Waste water enters the tank where solids can settle and scum floats. Anaerobic digestion occurs on the settled solids, reducing the volume of solids. The water released by the system is normally absorbed by the drain field without needing any further treatment.
Effluent sewers also currently serve fewer people than septic systems, which also use septic tanks, but simply dispose of the effluent by draining it into a leach field. About one quarter of United States homes dispose of their wastewater with septic tanks. However, effluent sewers are being looked at as a sewage treatment solution in areas where gravity sewer systems are not well-suited or when the high capital cost to build a gravity system is prohibitive. Areas that are less than ideal for gravity systems include areas that are large, but extremely flat and areas that require long-distance pumping, such as where homes are widely spread out or when several small villages or towns connect their sewage systems so that a centralized plant can be built.
Australian scientists investigated the effect of additives in a wastewater treatment plant and a number of septic tanks. Their aim was to test the hypothesis that the additive reduces sludge volumes. They found significant reduction in pH levels at the wastewater treatment plant together with improved settlement of sludge but with a significant increase in organic matter (measured as biological oxygen demand). Their results for the septic tanks showed a homogenization of conditions in the tanks after application of septic tank additives, which they suggested was due to domination by a particular type of micro-organism. However, they found no reduction in suspended solids concentration in the effluent and concluded that there were not sufficient changes in sludge volume in the wastewater treatment plant or suspended solids in the septic tanks to indicate a clear benefit from the use of these kinds of additives in wastewater.
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 adjoining 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.[16]
The standard system is a tiled leach field combined with a septic tank. The basic idea is to provide a small system with primary sewage treatment. Sludge settles to the bottom of the septic tank, is partially reduced by anaerobic digestion, and fluid is dispersed in the leach field. The leach field is usually under a yard growing grass. Septic tanks can operate entirely by gravity, and if well managed, are reasonably safe.
A properly designed and normally operating septic system is odor-free and, besides periodic inspection and emptying of the septic tank, should last for decades with minimal maintenance.
Septic tanks have to be pumped periodically by a vacuum truck to eliminate non reducing solids. Failure to pump a septic tank can cause overflow that damages the leach field, and contaminates ground water. Septic tanks may also require some lifestyle changes, such as not using garbage disposals, minimizing fluids flushed into the tank, and minimizing nondigestible solids flushed into the tank. For example, septic safe toilet paper is recommended.
Weeping tile is used for the opposite reason in the septic drain fields for septic tanks. Clarified sewage from the septic tank is fed into weeping tiles buried shallowly in the drain field. The weeping tile spreads the liquid throughout the drain field.
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.
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.
Septic tanks also have a higher capital cost if they are being installed for new homes or if the existing septic tanks must be replaced. If there is a suitable septic tank in place, pumping the effluent from the tank is the lowest cost option for initial costs. Whether the septic tank is the lowest cost option over time depends on the cost of electricity in the area, how often the tank must be emptied and how much it costs to have the solids pumped out of the tank.
North of the GreenHAB is the underground septic tank and its outflow field. This area is a "No Drive - Foot Traffic Only Zone" as there is no record of where exactly the septic tank is buried. East of the GreenHab is an omnidirectional Jovian radio telescope.
The United States Environmental Protection Agency (USEPA) produced a fact sheet on the use of pit additives to improve the performance of septic tank treatment systems. The fact sheet concludes that bacteria and extracellular enzymes do not appear to significantly enhance normal biological decomposition processes in septic tanks. They go on to say that ‘some biological additives have been found to degrade or dissipate septic tank scum and sludge. However, whether this relatively minor benefit is derived without compromising long-term viability of the soil infiltration system has not been demonstrated conclusively’. They noted that some studies suggest that material degraded by additives in the tank actually adds to the suspended solids and other contaminants in the otherwise clarified septic tank effluent.
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. However, these additives—which are commonly based on "effective microorganisms"—are usually costly in the longer term and fail to live up to expectations.[13] It has been estimated that in the U.S. more than 1,200 septic system additives were available on the market in 2011.[14] However, very little peer-reviewed and replicated field research exists regarding the efficacy of these biological septic tank additives.[14]
While a properly maintained and located septic tank does not pose any more environmental problems than centralized municipal sewage treatment, certain problems can arise with septic tanks in unsuitable locations. Since septic systems require large drainfields, they are not suitable for densely built areas.
A septic tank is an underground chamber made of concrete, fiberglass or plastic through which domestic wastewater (sewage) flows for basic treatment.[1] Settling and anaerobic processes reduce solids and organics, but the treatment efficiency is only moderate (referred to as "primary treatment").[1] Septic tank systems are a type of simple onsite sewage facility (OSSF). 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. However, groundwater pollution may occur and can be a problem.
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.[10] 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.[11] Using water softeners - the brine discharge from water softeners may harm the bacteria responsible for breaking down the wastewater. Usually the brine is however sufficiently diluted with other wastewater that it does not adversely affect the septic system.[12]
Most residents of Manila discharge their wastewater into an estimated 2.2 million septic tanks. The concessionaires are obliged to empty these septic tanks. Manila Water operates 60 desludging trucks that empty septic tanks free of charge. The sludge is brought to two septage treatment plants. Maynilad also operates desludging trucks, but so far does not have a septage treatment plant.
Costs of emptying septic tanks. The cost of emptying septic tanks can be significant. Some people avoid using their septic tanks, because if they do the tank fills up more quickly and they must pay to empty it more often. They thus continue to pollute the surrounding environment, although they have sanitation facilities at home.
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.[26] 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.[26] 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.[26]
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.
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, added to which 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".
In the United States, the 2007 American Housing Survey indicated that about 20 percent of all households rely on septic tanks, [17] and that the overwhelming majority of systems are located in rural (50%) and suburban (47%) areas.[17] Indianapolis is one example of a large city where many of the city's neighborhoods still rely on separate septic systems.[18] In Europe, septic systems are generally limited to rural areas.
The term "septic" refers to the anaerobic bacterial environment that develops in the tank which 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.[3]