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sanitary_sewer
Snippet from Wikipedia: Sanitary sewer

A sanitary sewer or foul sewer is an underground pipe or tunnel system for transporting sewage from houses and commercial buildings (but not stormwater) to treatment facilities or disposal. Sanitary sewers are part of an overall system called a sewage system or sewerage.

Sewage may be treated to control water pollution before discharge to surface waters. Sanitary sewers serving industrial areas also carry industrial wastewater.

Separate sanitary sewer systems are designed to transport sewage alone. In municipalities served by sanitary sewers, separate storm drains may convey surface runoff directly to surface waters. Sanitary sewers are distinguished from combined sewers, which combine sewage with stormwater runoff in one pipe. Sanitary sewer systems are beneficial because they avoid combined sewer overflows.

. The few sanitary sewers large enough for a man to stand erect typically carry flows that would sweep him off his feet.]]

for a sanitary sewer access point.]]

A sanitary sewer (also called a foul sewer) is a separate underground carriage system specifically for transporting sewage from houses and commercial buildings to treatment or disposal. Sanitary sewers serving industrial areas also carry industrial wastewater. The 'system of sewers' is called sewerage.

History

Animal feces were plentiful 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.<ref>

</ref> The earliest sewers were designed to carry street runoff away from inhabited areas and into surface waterways without treatment. Indoor plumbing was often drained to combined sewers through the 19th century. Sewage treatment facilities built for combined sewers become ineffective during periods of precipitation or snowmelt.<ref name=“EPARTC”>U.S. Environmental Protection Agency (EPA), Washington, D.C. (2004)."Report to Congress: Impacts and Control of CSOs and SSOs." August 2004. Document No. EPA-833-R-04-001.</ref> Cities were built with sanitary sewers operated separately and independently of storm drains carrying the runoff of rain after wagons and carriages powered by internal combustion engines reduced the advantages of treating street runoff; but many cities built prior to the twentieth century have not replaced combined sewer infrastructure.<ref>Metcalf & Eddy, Inc. (1972). Wastewater Engineering. (New York: McGraw–Hill.) p.119.</ref>

Nomenclature

In the developed world, sewers are usually pipelines that begin with connecting pipes from buildings to one or more levels of larger underground trunk mains, which transport the sewage to sewage treatment facilities. Vertical pipes, called manholes, connect the mains to the surface. 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. Sewers are generally gravity powered, though pumps may be used if necessary. The most commonly used sanitary pipe is SDR-35 (standard dimension ratio), with smaller sized laterals interconnected within a larger sized main.

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. A lift station is a gravity sewer sump with a pump to lift accumulated sewage to a higher elevation. The pump may discharge to another gravity sewer at that location or may discharge through a pressurized force main to some distant location.<ref name=“asce”>American Society of Civil Engineers and Water Pollution Control Federation Design and Construction of Sanitary and Storm Sewers (1969) pp.2&288</ref>

Maintenance

All sewers deteriorate with age, but infiltration/inflow is a problem 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.<ref name=“hammer”>Hammer, Mark J. Water and Waste-Water Technology (1975) John Wiley & Sons ISBN 0-471-34726-4 p.442</ref> A comprehensive construction inspection program is required to prevent inappropriate connection of cellar, yard, and roof drains to sanitary sewers.<ref name=“steel”>Steel, E.W. and McGhee, Terence J. Water Supply and Sewerage (1979) McGraw-Hill ISBN 0-07-060929-2 p.22</ref> 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 got cracks or other damage, the only choice was the expensive operation of digging up the damaged pipe and replacing it, usually requiring the street to be repaved 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 dried at a fast rate, sealing all cracks and breaks in the pipe. <ref> "Sewer Sealing Machine Patches Cracks Underground." Popular Mechanics, April 1956, p. 86.</ref>

Simplified sewers

Simplified sanitary sewers consist of small-diameter pipes (typically 100&nbsp;mm or about 4&nbsp;inches), often laid at fairly flat gradients (1 in 200). The investment cost for sanitary sewers can be about half the costs of conventional sewers. However, the requirements for operation and maintenance are usually higher. Simplified sewers are most common in Brazil and are also used in a number of other developing countries.

See also

References

Environmental engineering Sewerage infrastructure Water pollution

sanitary_sewer.txt · Last modified: 2020/03/12 18:38 (external edit)