Sanitary sewer

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Sanitary sewer installation with PVC pipe. Sanitary sewers are sized to carry the amount of sewage generated by the collection area. These sewers are much smaller than combined sewers, which are designed to also carry surface runoff. Sansewer.jpg
Sanitary sewer installation with PVC pipe. Sanitary sewers are sized to carry the amount of sewage generated by the collection area. These sewers are much smaller than combined sewers, which are designed to also carry surface runoff.

A sanitary sewer is an underground pipe or tunnel system for transporting sewage from houses and commercial buildings (but not stormwater) to a sewage treatment plant or disposal.

Contents

Sanitary sewers are a type of gravity sewer and are part of an overall system called a "sewage system" or sewerage. Sanitary sewers serving industrial areas may also carry industrial wastewater. In municipalities served by sanitary sewers, separate storm drains may convey surface runoff directly to surface waters. An advantage of sanitary sewer systems is that they avoid combined sewer overflows. Sanitary sewers are typically much smaller in diameter than combined sewers which also transport urban runoff. Backups of raw sewage can occur if excessive stormwater inflow or groundwater infiltration occurs due to leaking joints, defective pipes etc. in aging infrastructure.

Purpose

Sewage treatment is less effective when sanitary waste is diluted with stormwater, and combined sewer overflows occur when runoff from heavy rainfall or snowmelt exceeds the hydraulic capacity of sewage treatment plants. [1] To overcome these disadvantages, some cities built separate sanitary sewers to collect only municipal wastewater and exclude stormwater runoff, which is collected in separate storm drains. The decision to build a combined sewer system or two separate systems is mainly based on the need for sewage treatment and the cost of providing treatment during heavy rain events. Many cities with combined sewer systems built their systems prior to installing sewage treatment plants, and have not subsequently replaced those sewer systems. [2]

Types

Conventional gravity sewers

Manhole access to sewer Working underground.jpg
Manhole access to sewer
Schematic of a conventional sanitary sewer to convey blackwater and greywater from households to a centralized sewage treatment facility. Schematic of the Conventional Gravity Sewer.jpg
Schematic of a conventional sanitary sewer to convey blackwater and greywater from households to a centralized sewage treatment facility.
A manhole cover for a sanitary sewer access point. Sewer cover.jpg
A manhole cover for a sanitary sewer access point.
View looking down into an open manhole showing two converging sanitary sewer lines. The larger line enters from the right and changes direction within the manhole to exit from the top of the photo. A smaller line enters from the bottom of the photo under the access steps. The concrete floor of the manhole has channels to minimize accumulation of solids. Manhole1.JPG
View looking down into an open manhole showing two converging sanitary sewer lines. The larger line enters from the right and changes direction within the manhole to exit from the top of the photo. A smaller line enters from the bottom of the photo under the access steps. The concrete floor of the manhole has channels to minimize accumulation of solids.
Interior of a large sanitary sewer viewed from an access manhole chamber. Orfice.jpg
Interior of a large sanitary sewer viewed from an access manhole chamber.

In the developed world, sewers are pipes from buildings to one or more levels of larger underground trunk mains, which transport the sewage to sewage treatment facilities. Vertical pipes, usually made of precast concrete, called manholes, connect the mains to the surface. Depending upon site application and use, these vertical pipes can be cylindrical, eccentric, or concentric. The manholes are used for access to the sewer pipes for inspection and maintenance, and as a means to vent sewer gases. They also facilitate vertical and horizontal angles in otherwise straight pipelines. [4]

Pipes conveying sewage from an individual building to a common gravity sewer line are called laterals. Branch sewers typically run under streets receiving laterals from buildings along that street and discharge by gravity into trunk sewers at manholes. Larger cities may have sewers called interceptors, receiving flow from multiple trunk sewers. [5] [6]

Design and sizing of sanitary sewers considers the population to be served over the anticipated life of the sewer, per capita wastewater production, and flow peaking from timing of daily routines. Minimum sewer diameters are often specified to prevent blockage by solid materials flushed down toilets; gradients may be selected to maintain flow velocities generating sufficient turbulence to minimize solids deposition within the sewer. Commercial and industrial wastewater flows are also considered, but diversion of surface runoff to storm drains eliminates wet weather flow peaks of inefficient combined sewers. [7]

Force mains

A force main or rising main [8] is a pumped sewer that may be necessary where gravity sewers serve areas at lower elevations than the sewage treatment plant, or distant areas at similar elevations. A lift station is a sewer sump that lifts accumulated sewage to a higher elevation. They may also be used to prime an inverted siphon used to cross underneath rivers or other obstructions. The pump may discharge to another gravity sewer or directly to a treatment plant. [6] Force mains are typically constructed of welded steel or HDPE jointed to resist pressures within the pipe. Force mains are substantially different from pressure sewers which serve individual properties or groups of properties and provide a means of injecting sewage into a local gravity main.

Effluent sewer

Effluent sewer systems, also called septic tank effluent drainage (STED) or solids-free sewer (SFS) systems, have septic tanks that collect sewage from residences and businesses, and the effluent that comes out of the tank is sent to either a centralized sewage treatment plant or a distributed treatment system for further treatment. Most of the solids are removed by the septic tanks, so the treatment plant can be much smaller than a typical plant. In addition, because of the vast reduction in solid waste, a pumping system, rather than a gravity system, can be used to move the wastewater. The pipes have small diameters, typically 1.5 to 4 inches (4 to 10 cm). Because the waste stream is pressurized, they can be laid just below the ground surface along the land's contour.[ citation needed ]

Pressure sewer

Where it is impossible or impractical to discharge sewage from a property into a gravity sanitary sewer, a pressure sewer may provide an alternative means of connection. A macerator pump in a pumping well close to the property ejects sewage through a small diameter high pressure pipe into the nearest gravity sewer. [9]

Simplified sewer

Simplified sanitary sewers consist of small-diameter pipes, typically around 100 millimetres (4 in), often laid at fairly flat gradients (1 in 200). Although the investment cost for simplified sanitary sewers can be about half the cost of conventional sewers, the requirements for operation and maintenance are usually higher. Simplified sewers are most common in Brazil and other developing countries.[ citation needed ]

Vacuum sewer

In low-lying communities, wastewater is often conveyed by vacuum sewer. Pipelines range in size from pipes of 125 millimetres (4.9 in) in diameter up to 280 millimetres (11 in) in diameter. Vacuum sewer systems use differential atmospheric pressure to move the liquid to a central vacuum station. [10]

Maintenance

Stoneware sanitary sewer (bottom) submerged in trash and fecalia Kanalizacni pripojka, smer dum.jpg
Stoneware sanitary sewer (bottom) submerged in trash and fecalia

Sanitary sewer overflow can occur due to blocked or broken sewer lines, infiltration of excessive stormwater or malfunction of pumps. In these cases untreated sewage is discharged from a sanitary sewer into the environment prior to reaching sewage treatment facilities. To avoid such overflows, maintenance is required. Blockage prevention campaigns or regulations (e.g. requiring the use of grease interceptors by some customers) may also be necessary.

The maintenance requirements vary with the type of sanitary sewer. In general, all sewers deteriorate with age, but infiltration and inflow are problems unique to sanitary sewers, since both combined sewers and storm drains are sized to carry these contributions. Holding infiltration to acceptable levels requires a higher standard of maintenance than necessary for structural integrity considerations of combined sewers. [11] A comprehensive construction inspection program is required to prevent inappropriate connection of cellar, yard, and roof drains to sanitary sewers. [12] The probability of inappropriate connections is higher where combined sewers and sanitary sewers are found in close proximity, because construction personnel may not recognize the difference. Many older cities still use combined sewers while adjacent suburbs were built with separate sanitary sewers.

For decades, when sanitary sewer pipes cracked or experienced other damage, the only option was an expensive excavation, removal and replacement of the damaged pipe, typically requiring street repavement afterwards. In the mid-1950s a unit was invented where two units at each end with a special cement mixture in between was pulled from one manhole cover to the next, coating the pipe with the cement under high pressure, which then cured rapidly, sealing all cracks and breaks in the pipe. [13] Today, a similar method using epoxy resin is used by some municipalities to re-line aging or damaged pipes, effectively creating a "pipe in a pipe". These methods may be unsuitable for locations where the full diameter of the original pipe is required to carry expected flows, and may be an unwise investment if greater wastewater flows may be anticipated from population growth, increased water use, or new service connections within the expected service life of the repair.

Another popular method for replacing aged or damaged lines is called pipe bursting, where a new pipe, typically PVC or ABS plastic, is drawn through the old pipe behind an "expander head" that breaks apart the old pipe as the new one is drawn through behind it.

These methods are most suitable for trunk sewers, since repair of lines with lateral connections is complicated by making provisions to receive lateral flows without accepting undesirable infiltration from inadequately sealed junctions.

Ventilation

Some sewers have tall vent pipes to release foul gases well up away from people. Common names for these pipes are stink pipe, stink pole, stench pipe and sewer ventilation pipe. [14]

History

Old brick sanitary sewer from second half of the 19th century. Prague, New Town Kanalizacni pripojka, rekonstrukce (001).jpg
Old brick sanitary sewer from second half of the 19th century. Prague, New Town

Sanitary sewers evolved from combined sewers built where water was plentiful. Animal feces accumulated on city streets while animal-powered transport moved people and goods. Accumulations of animal feces encouraged dumping chamber pots into streets where night soil collection was impractical. [15] Combined sewers were built to use surface runoff to flush waste off streets and move it underground to places distant from populated areas. Sewage treatment became necessary as population expanded, but increased volumes and pumping capacity required for treatment of diluted waste from combined sewers is more expensive than treating undiluted sewage. [16]

Communities that have urbanized in the mid-20th century or later generally have built separate systems for sewage (sanitary sewers) and stormwater, because precipitation causes widely varying flows, reducing sewage treatment plant efficiency. [17]

In the UK, the term "foul sewer" was also in use for a sanitary sewer.

See also

Related Research Articles

<span class="mw-page-title-main">Stormwater</span> Water that originates during precipitation events and snow/ice melt

Stormwater, also written storm water, is water that originates from precipitation (storm), including heavy rain and meltwater from hail and snow. Stormwater can soak into the soil (infiltrate) and become groundwater, be stored on depressed land surface in ponds and puddles, evaporate back into the atmosphere, or contribute to surface runoff. Most runoff is conveyed directly as surface water to nearby streams, rivers or other large water bodies without treatment.

<span class="mw-page-title-main">Sewerage</span> Infrastructure that conveys sewage or surface runoff using sewers

Sewerage is the infrastructure that conveys sewage or surface runoff using sewers. It encompasses components such as receiving drains, manholes, pumping stations, storm overflows, and screening chambers of the combined sewer or sanitary sewer. Sewerage ends at the entry to a sewage treatment plant or at the point of discharge into the environment. It is the system of pipes, chambers, manholes or inspection chamber, etc. that conveys the sewage or storm water.

<span class="mw-page-title-main">Storm drain</span> Infrastructure for draining excess rain and ground water from impervious surfaces

A storm drain, storm sewer, surface water drain/sewer, or stormwater drain is infrastructure designed to drain excess rain and ground water from impervious surfaces such as paved streets, car parks, parking lots, footpaths, sidewalks, and roofs. Storm drains vary in design from small residential dry wells to large municipal systems.

Sewage disposal regulation and administration describes the governance of sewage treatment and disposal.

<span class="mw-page-title-main">Combined sewer</span> Sewage collection system of pipes and tunnels designed to also collect surface runoff

A combined sewer is a type of gravity sewer with a system of pipes, tunnels, pump stations etc. to transport sewage and urban runoff together to a sewage treatment plant or disposal site. This means that during rain events, the sewage gets diluted, resulting in higher flowrates at the treatment site. Uncontaminated stormwater simply dilutes sewage, but runoff may dissolve or suspend virtually anything it contacts on roofs, streets, and storage yards. As rainfall travels over roofs and the ground, it may pick up various contaminants including soil particles and other sediment, heavy metals, organic compounds, animal waste, and oil and grease. Combined sewers may also receive dry weather drainage from landscape irrigation, construction dewatering, and washing buildings and sidewalks.

<span class="mw-page-title-main">First flush</span> Initial surface runoff of a rainstorm

First flush is the initial surface runoff of a rainstorm. During this phase, water pollution entering storm drains in areas with high proportions of impervious surfaces is typically more concentrated compared to the remainder of the storm. Consequently, these high concentrations of urban runoff result in high levels of pollutants discharged from storm sewers to surface waters.

<span class="mw-page-title-main">Sanitary sewer overflow</span> Discharge of untreated sewage

Sanitary sewer overflow (SSO) is a condition in which untreated sewage is discharged from a sanitary sewer into the environment prior to reaching sewage treatment facilities. When caused by rainfall it is also known as wet weather overflow. Causes of sanitary sewer overflows include: Blockage of sewer lines, infiltration/Inflow of excessive stormwater into sewer lines during heavy rainfall, malfunction of pumping station lifts or electrical power failure, broken sewer lines. Prevention of such overflow events involves regular maintenance and timely upgrades of infrastructure.

Dallas Water Utilities (DWU) is the water and wastewater service operated by the City of Dallas, Texas, in the United States. DWU is a non-profit City of Dallas department that provides services to the city and 31 nearby communities, employs approximately 1450 people, and consists of 26 programs. DWU's budget is completely funded through the rates charged for water and wastewater services provided to customers. Rates are based on the cost of providing the services. The department does not receive any tax revenues. Primary authority and rules for the department are listed in Chapter 49Archived 2006-10-04 at the Wayback Machine of the Dallas City Code.

<span class="mw-page-title-main">Vacuum sewer</span> Method of transporting sewage from its source to a sewage treatment plant

A vacuum sewer or pneumatic sewer system is a method of transporting sewage from its source to a sewage treatment plant. It maintains a partial vacuum, with an air pressure below atmospheric pressure inside the pipe network and vacuum station collection vessel. Valves open and reseal automatically when the system is used, so differential pressure can be maintained without expending much energy pumping. A single central vacuum station can collect the wastewater of several thousand individual homes, depending on terrain and the local situation.

<span class="mw-page-title-main">Simplified sewerage</span> Type of small-bore sewerage system

Simplified sewerage, also called small-bore sewerage, is a sewer system that collects all household wastewater in small-diameter pipes laid at fairly flat gradients. Simplified sewers are laid in the front yard or under the pavement (sidewalk) or - if feasible - inside the back yard, rather than in the centre of the road as with conventional sewerage. It is suitable for existing unplanned low-income areas, as well as new housing estates with a regular layout. It allows for a more flexible design. With simplified sewerage it is crucial to have management arrangements in place to remove blockages, which are more frequent than with conventional sewers. It has been estimated that simplified sewerage reduces investment costs by up to 50% compared to conventional sewerage.

<span class="mw-page-title-main">Sewage treatment</span> Process of removing contaminants from municipal wastewater

Sewage treatment is a type of wastewater treatment which aims to remove contaminants from sewage to produce an effluent that is suitable to discharge to the surrounding environment or an intended reuse application, thereby preventing water pollution from raw sewage discharges. Sewage contains wastewater from households and businesses and possibly pre-treated industrial wastewater. There are a high number of sewage treatment processes to choose from. These can range from decentralized systems to large centralized systems involving a network of pipes and pump stations which convey the sewage to a treatment plant. For cities that have a combined sewer, the sewers will also carry urban runoff (stormwater) to the sewage treatment plant. Sewage treatment often involves two main stages, called primary and secondary treatment, while advanced treatment also incorporates a tertiary treatment stage with polishing processes and nutrient removal. Secondary treatment can reduce organic matter from sewage,  using aerobic or anaerobic biological processes. A so-called quarternary treatment step can also be added for the removal of organic micropollutants, such as pharmaceuticals. This has been implemented in full-scale for example in Sweden.

<span class="mw-page-title-main">Sewage</span> Wastewater that is produced by a community of people

Sewage is a type of wastewater that is produced by a community of people. It is typically transported through a sewer system. Sewage consists of wastewater discharged from residences and from commercial, institutional and public facilities that exist in the locality. Sub-types of sewage are greywater and blackwater. Sewage also contains soaps and detergents. Food waste may be present from dishwashing, and food quantities may be increased where garbage disposal units are used. In regions where toilet paper is used rather than bidets, that paper is also added to the sewage. Sewage contains macro-pollutants and micro-pollutants, and may also incorporate some municipal solid waste and pollutants from industrial wastewater.

<span class="mw-page-title-main">Effluent sewer</span>

Effluent sewer systems, also called septic tank effluent gravity (STEG), solids-free sewer (SFS), or septic tank effluent drainage (STED) systems, have septic tanks that collect sewage from residences and businesses, and the liquid fraction of sewage that comes out of the tank is conveyed to a downstream receiving body such as either a centralized sewage treatment plant or a distributed treatment system for further treatment or disposal away from the community generating the sewage. Most of the solids are removed by the interceptor tanks, so the treatment plant can be much smaller than a typical plant and any pumping for the supernatant can be simpler without grinders.

Infiltration/Inflow is the process of groundwater, or water from sources other than domestic wastewater, entering sanitary sewers. I/I causes dilution in sanitary sewers, which decreases the efficiency of treatment, and may cause sewage volumes to exceed design capacity. Although inflow is technically different from infiltration, it may be difficult to determine which is causing dilution problems in inaccessible sewers. The United States Environmental Protection Agency defines the term infiltration/inflow as combined contributions from both.

<span class="mw-page-title-main">Philadelphia Water Department</span>

The Philadelphia Water Department is the public water utility for the City of Philadelphia. PWD provides integrated potable water, wastewater, and stormwater services for Philadelphia and some communities in Bucks, Delaware and Montgomery counties. PWD is a municipal agency of the City of Philadelphia, and is seated in rented space at the Jefferson Tower in the Market East area of Center City, Philadelphia.

<span class="mw-page-title-main">Great Lakes Water Authority</span>

The Great Lakes Water Authority (GLWA) is a regional water authority in the U.S. state of Michigan. It provides drinking water treatment, drinking water distribution, wastewater collection, and wastewater treatment services for the Southeast Michigan communities, including Wayne, Oakland, and Macomb counties, among others. GLWA overlays a majority of the water and sewer assets which were formerly operated and maintained by the Detroit Water Sewer District (DWSD) prior to the bankruptcy of the City of Detroit, Michigan.

<span class="mw-page-title-main">Gravity sewer</span> Conduit which removes wastewater by use of gravity

A gravity sewer is a conduit utilizing the energy resulting from a difference in elevation to remove unwanted water. The term sewer implies removal of sewage or surface runoff rather than water intended for use; and the term gravity excludes water movement induced through force mains or vacuum sewers. Most sewers are gravity sewers because gravity offers reliable water movement with no energy costs wherever grades are favorable. Gravity sewers may drain to sumps where pumping is required to either force sewage to a distant location or lift sewage to a higher elevation for entry into another gravity sewer, and lift stations are often required to lift sewage into sewage treatment plants. Gravity sewers can be either sanitary sewers, combined sewers, storm sewers or effluent sewers.

Ever since Chicago was incorporated as a city in 1837, it has faced multiple issues concerning water quality to accommodate its growing size, driven by the city's ideal geography and accessibility to one of the largest bodies of fresh water, the Great Lakes. The City of Chicago has implemented multiple proposals and plans such as the Master Drainage Plan and Tunnel and Reservoir Plan to combat the increasing water quality issue and move in a more environmentally friendly direction. These plans will construct spillways to temporarily store overfilling sewage or stormwater and clean it before releasing it. However, it wasn't until 2015 that Chicago began to treat sewage and stormwater runoff, thus finally shedding its title as the last major city not to treat its sewage before being discharged into its waterways.

A pressure sewer provides a method of discharging sewage from properties into a conventional gravity sewer or directly to a sewage treatment plant. Pressure sewers are typically used where properties are located below the level of the nearest gravity sewer or are located on difficult terrain.

<span class="mw-page-title-main">Sanitary manhole</span> An access point to an underground sanitary sewer system

A sanitary manhole is a manhole that is used as an access point for maintenance and inspection of an underground sanitary sewer system. Sanitary manholes are sometimes used as vents to prevent the buildup of pressurized sewage gas. Additionally, they are used for debris removal, and application of chemicals such as degreaser and insecticide.

References

  1. ↑ Report to Congress: Impacts and Control of CSOs and SSOs (Report). Washington, D.C.: U.S. Environmental Protection Agency (EPA). August 2004. p. ES-2. EPA-833-R-04-001.
  2. ↑ Metcalf & Eddy, Inc. (1972). Wastewater Engineering: collection, treatment, disposal. New York: McGraw–Hill. p. 119. ISBN   9780070416765.
  3. ↑ Tilley, E., Ulrich, L., Lüthi, C., Reymond, Ph., Zurbrügg, C. (2014) Compendium of Sanitation Systems and Technologies (2nd Revised Edition). Swiss Federal Institute of Aquatic Science and Technology (Eawag), Duebendorf, Switzerland. ISBN   978-3-906484-57-0.
  4. ↑ "Acu-Sewer Pressure Pipe for Sewer Mains". Acu-Tech Piping Systems. Retrieved 2018-10-03.
  5. ↑ Lee, C.C., ed. (2005). Environmental Engineering Dictionary (4th ed.). Lanham, MD: Government Institutes. p. 423. ISBN   9780865878488.
  6. 1 2 Design and Construction of Sanitary and Storm Sewers. New York: American Society of Civil Engineers and Water Pollution Control Federation. 1969. pp. 2, 288.
  7. ↑ Tyler, Richard G. (1959). "Section 9". Civil Engineering Handbook (4th ed.). New York: McGraw-Hill. pp. 1–24.
  8. ↑ "Design and Construction Guidance for foul and surface water sewers offered for adoption under the Code for adoption agreements for water and sewerage companies operating wholly or mainly in England ("the Code")" (PDF). Water UK. March 2020. p. 6. Retrieved 18 January 2022.
  9. ↑ Stauffer, Beat; Spuhler, Dorothee. "Pressurised Sewers". Sustainable Sanitation and Water Management Toolbox. Retrieved 18 January 2022.
  10. ↑ Wastewater Treatment/Disposal for Small Communities: Manual (Report). EPA. 1992. pp. 84–88. EPA 625/R-95/005.
  11. ↑ Hammer, Mark J. Water and Waste-Water Technology (1975) John Wiley & Sons ISBN   0-471-34726-4 p.442
  12. ↑ Steel, E.W.; McGhee, Terence J. (1979). Water Supply and Sewerage (5th ed.). New York: McGraw-Hill. p.  22. ISBN   0-07-060929-2.
  13. ↑ "Sewer Sealing Machine Patches Cracks Underground." Popular Mechanics, April 1956, p. 86.
  14. ↑ Lloyd, Chris (2008-07-16). "Is this just the tip of the stink pole?". The Northern Echo. Darlington, UK.
  15. ↑ Bellis, Mary (2018-03-31). "The History of Plumbing". Archived from the original on 2017-10-14. Retrieved 2018-05-14. Alt URL
  16. ↑ Steel, E.W.; McGhee, Terence J. (1979). Water Supply and Sewerage (5th ed.). New York: McGraw-Hill. p.  318. ISBN   0-07-060929-2.
  17. ↑ Burrian, Steven J.; et al. (1999). The Historical Development of Wet-Weather Flow Management (Report). Cincinnati, OH: EPA National Risk Management Research Laboratory. EPA/600/JA-99/275.
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