Sewerage

Last updated
Map of London sewer network, late 19th century Bazellgette Sewer Network EN.svg
Map of London sewer network, late 19th century

Sewerage (or sewage system) is the infrastructure that conveys sewage or surface runoff (stormwater, meltwater, rainwater) 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.

Contents

In many cities, sewage (municipal wastewater or municipal sewage) is carried together with stormwater, in a combined sewer system, to a sewage treatment plant. In some urban areas, sewage is carried separately in sanitary sewers and runoff from streets is carried in storm drains. Access to these systems, for maintenance purposes, is typically through a manhole. During high precipitation periods a sewer system may experience a combined sewer overflow event or a sanitary sewer overflow event, which forces untreated sewage to flow directly to receiving waters. This can pose a serious threat to public health and the surrounding environment.

The system of sewers is called sewerage or sewerage system in British English and sewage system or sewer system in American English. [1]

History

It was probably the need to get rid of foul smells rather than an understanding of the health hazards of human waste that led to the first proper sewage systems. Most settlements grew next to natural waterways into which waste from latrines was readily channeled, but the emergence of major cities exposed the inadequacy of this approach. Early civilizations like the Babylonians dug cesspits below floor level in their houses and created crude drainage systems for removing storm water. But it was not until 2000 BC in the Indus valley civilization that networks of precisely made brick-lined sewage drains were constructed along the streets to convey waste from homes. [2] Toilets in homes on the street side were connected directly to these street sewers and were flushed manually with clean water. Centuries later, major cities such as Rome and Constantinople built increasingly complex networked sewer systems, some of which are still in use. It was after the construction of the sewer systems that people realized the reduction of health hazards. [3]

Components and types

Map of Seattle sewer districts, 1894 Seattle sewer districts, 1894.jpg
Map of Seattle sewer districts, 1894

The main part of such a system is made up of large pipes (i.e. the sewers, or "sanitary sewers") that convey the sewage from the point of production to the point of treatment or discharge.

Sewers under construction in Ystad, Sweden Avlopp - Ystad-2018.jpg
Sewers under construction in Ystad, Sweden

Types of sanitary sewer systems that all usually are gravity sewers include:

Sanitary sewers not relying solely on gravity include:

Where a sewerage system has not been installed, sewage may be collected from homes by pipes into septic tanks or cesspits, where it may be treated or collected in vehicles and taken for treatment or disposal (a process known as fecal sludge management).

Maintenance and rehabilitation

Severe constraints are applied to sewerage, which may result in premature deterioration. These include root intrusion, joint displacement, cracks, and hole formations that lead to a significant volume of leakage with an overall risk for the environment and public health. For example, it is estimated that 500 million m3 of contaminated water per year can leak into soil and ground-water in Germany. [4] The rehabilitation and replacement of damaged sewers is very costly. Annual rehabilitation costs for Los Angeles County are about €400 million, [5] and in Germany, these costs are estimated to be €100 million. [6]

Vacuuming debris from a sewer line CES utilities 120627-F-CC568-041.jpg
Vacuuming debris from a sewer line

Hydrogen sulfide (H2S) is indirectly responsible for biogenic sulfide corrosion and consequently, sewers need rehabilitation work. Various repair options are available to owners over a large range of costs and potential durability. One option is the application of a cementitious material based on calcium aluminate cement, after a cleaning of the corroded structure to remove loose material and contaminants in order to expose a sound, rough and clean substrate. Depending on the concrete condition and contamination, the cleaning can range from simple high pressure jet water cleaning (200 bar) up to real hydro-demolition (2000 bars).

One method to ensure sound concrete is exposed is to verify that the surface pH is superior to 10.

As for any concrete repair, the state-of-the-art rules must be followed. After this cleaning step, the cementitious material is applied to the saturated-surface-dry substrate using either:

Challenges

Building a sewer in newly filled land on former tideflats in Seattle, 1910. Seattle - Lander Street sewer construction, 1910 (48250199862).gif
Building a sewer in newly filled land on former tideflats in Seattle, 1910.

Water table

Sewer system infrastructure often reduces the water table in areas, especially in densely populated areas where rainwater (from house roofs) is directly piped into the system, as opposed to being allowed to be absorbed by the soil. In certain areas it has resulted in a significant lowering of the water table. In the example of Belgium, a lowering of the water table by 100 meters has been the result. [7] [8] The freshwater that is accumulated by the system is then piped to the sea. In areas where this is a concern, vacuum sewers may be used instead, due to the shallow excavation that is possible for them.

Lack of infrastructure

In many low-income countries, sewage may in some cases drain directly into receiving water bodies without the existence of sewerage systems. This can cause water pollution. Pathogens can cause a variety of illnesses. Some chemicals pose risks even at very low concentrations and can remain a threat for long periods of time because of bioaccumulation in animal or human tissue.

Regulations

In many European countries, citizens are obliged to connect their home sanitation to the national sewerage where possible. This has resulted in large percentages of the population being connected. For example, the Netherlands have 99% of the population connected to the system, and 1% has an individual sewage disposal system or treatment system, e.g.,  septic tank. Others have slightly lower (although still substantial) percentages; e.g., 96% for Germany.

Current approaches to sewage management may include handling surface runoff separately from sewage, handling greywater separately from blackwater (flush toilets), and coping better with abnormal events (such as peaks stormwater volumes from extreme weather).

See also

Related Research Articles

<span class="mw-page-title-main">Sanitary sewer</span> Underground pipe for transporting sewage

A sanitary sewer is an underground pipe or tunnel system for transporting sewage from houses and commercial buildings to a sewage treatment plant or disposal.

<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.

<span class="mw-page-title-main">London sewer system</span> English infrastructure system

The London sewer system is part of the water infrastructure serving London, England. The modern system was developed during the late 19th century, and as London has grown the system has been expanded. It is currently owned and operated by Thames Water and serves almost all of Greater London.

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

<span class="mw-page-title-main">Milwaukee Metropolitan Sewerage District</span>

The Milwaukee Metropolitan Sewerage District (MMSD) is a regional government agency that provides water reclamation and flood management services for about 1.1 million people in 28 communities in the Greater Milwaukee Area. A recipient of the U.S. Water Prize and many other awards, the District has a record of 98.4 percent, since 1994, for capturing and cleaning wastewater from 28 communities in a 411-square-mile (1,060 km2) area. The national goal is 85 percent of all the rain and wastewater that enters their sewer systems.

<span class="mw-page-title-main">District of Columbia Water and Sewer Authority</span> Water authority of Washington, D.C.

The District of Columbia Water and Sewer Authority(DC Water) provides drinking water, sewage collection, and sewage treatment for Washington, D.C. The utility also provides wholesale wastewater treatment services to several adjoining municipalities in Maryland and Virginia, and maintains more than 9,000 public fire hydrants in Washington, D.C.

<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">Sewage farm</span>

Sewage farms use sewage for irrigation and fertilizing agricultural land. The practice is common in warm, arid climates where irrigation is valuable while sources of fresh water are scarce. Suspended solids may be converted to humus by microbes and bacteria in order to supply nitrogen, phosphorus and other plant nutrients for crop growth. Many industrialized nations use conventional sewage treatment plants nowadays instead of sewage farms. These reduce vector and odor problems; but sewage farming remains a low-cost option for some developing countries. Sewage farming should not be confused with sewage disposal through infiltration basins or subsurface drains.

<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.

Biogenic sulfide corrosion is a bacterially mediated process of forming hydrogen sulfide gas and the subsequent conversion to sulfuric acid that attacks concrete and steel within wastewater environments. The hydrogen sulfide gas is biochemically oxidized in the presence of moisture to form sulfuric acid. The effect of sulfuric acid on concrete and steel surfaces exposed to severe wastewater environments can be devastating. In the USA alone, corrosion is causing sewer asset losses estimated at $14 billion per year. This cost is expected to increase as the aging infrastructure continues to fail.

<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">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">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">East Side Big Pipe</span>

The East Side Big Pipe is a large sewer line and tunnel in Portland in the U.S. state of Oregon. It is part of a combined sewer system of pipes, sumps, drains, pumps, and other infrastructure that transports sewage and stormwater run-off to the city's Columbia Boulevard Wastewater Treatment Plant. The East Side Big Pipe project, begun in 2006 and finished in 2011, was the largest of a 20-year series of projects designed to nearly eliminate combined sewer overflows (CSO)s into the Willamette River and the Columbia Slough. The combined projects were completed on time, and they reduced CSOs into the river by 94 percent and into the slough by more than 99 percent.

<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.

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. ↑ "sewerage – definition of sewerage in English from the Oxford dictionary". Oxforddictionaries.com. Archived from the original on 2015-09-24. Retrieved 2015-09-04.
  2. ↑ George, A.R. (2015). "On Babylonian Lavatories and Sewers". Iraq. 77: 75–106. doi:10.1017/irq.2015.9. ISSN   0021-0889. JSTOR   26426051. S2CID   162653122.
  3. ↑ 1001 Inventions that changed the World. Hachette India.
  4. ↑ Kaempfer, W., Berndt, M., 2009. Estimation of service life of concrete pipes in sewer networks. Durability of building materials and components, 8, 36-45.
  5. ↑ Sydney, R., Esfandi, E., Surapaneni, S., 1996. Control concrete sewer corrosion via the crown spray process. Water Environment Research, 68 (3), 338-347.
  6. ↑ Kaempfer, W., Berndt, M., 1998. Polymer modified mortar with high resistance to acid corrosion by biogenic sulphuric acid. In: Proceedings of the IX ICPIC Congress, Bologna, Italy, pp. 681–687
  7. ↑ "Beleid tegen watertekort dringt zich op". deredactie.be. 28 January 2015.
  8. ↑ "Publicaties — Vlaamse Milieumaatschappij" (PDF). vmm.be.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.