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Sanitary sewer overflow

Sanitary sewer overflow

Overview

Sanitary sewer overflow (SSO) is a condition whereby untreated sewage
Sewage
Sewage is water-carried waste, in solution or suspension, that is intended to be removed from a community. Also known as wastewater, it is more than 99% water and is characterized by volume or rate of flow, physical condition, chemical constituents and the bacteriological organisms that it contains...

 is discharged into the environment prior to reaching treatment facilities thereby escaping wastewater treatment
Wastewater Treatment
Wastewater treatment may refer to:* Sewage treatment* Industrial wastewater treatment...

. When caused by rainfall it is also known as wet weather overflow. It is primarily meaningful in developed countries, which have extensive sewage treatment facilities. The main causes of SSO are:
  • Infiltration
    Infiltration (hydrology)
    Infiltration is the process by which water on the ground surface enters the soil. Infiltration rate in soil science is a measure of the rate at which soil is able to absorb rainfall or irrigation. It is measured in inches per hour or millimeters per hour. The rate decreases as the soil becomes...

     of excessive stormwater
    Stormwater
    Stormwater is water that originates during precipitation events. It may also be used to apply to water that originates with snowmelt that enters the stormwater system...

     into sewer
    Sanitary sewer
    A sanitary 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...

     lines during heavy rainfall
  • Rupture or blockage of sewerage
    Sanitary sewer
    A sanitary 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...

     lines
  • Malfunction of pumping station
    Pumping station
    Pumping stations are facilities including pumps and equipment for pumping fluids from one place to another. They are used for a variety of infrastructure systems, such as the supply of water to canals, the drainage of low-lying land, and the removal of sewage to processing sites.A pumping station...

     lifts or electrical power failure
  • Human operator error at treatment plant facilities.


SSO is distinct from a combined sewer overflow (CSO), a similar problem of untreated sewage discharges, but which occurs only in a municipal system specifically designed with a combined sewer.

Since medieval times rulers have been aware of the impact of raw sewage improperly discharged to the environment.
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Encyclopedia

Sanitary sewer overflow (SSO) is a condition whereby untreated sewage
Sewage
Sewage is water-carried waste, in solution or suspension, that is intended to be removed from a community. Also known as wastewater, it is more than 99% water and is characterized by volume or rate of flow, physical condition, chemical constituents and the bacteriological organisms that it contains...

 is discharged into the environment prior to reaching treatment facilities thereby escaping wastewater treatment
Wastewater Treatment
Wastewater treatment may refer to:* Sewage treatment* Industrial wastewater treatment...

. When caused by rainfall it is also known as wet weather overflow. It is primarily meaningful in developed countries, which have extensive sewage treatment facilities. The main causes of SSO are:
  • Infiltration
    Infiltration (hydrology)
    Infiltration is the process by which water on the ground surface enters the soil. Infiltration rate in soil science is a measure of the rate at which soil is able to absorb rainfall or irrigation. It is measured in inches per hour or millimeters per hour. The rate decreases as the soil becomes...

     of excessive stormwater
    Stormwater
    Stormwater is water that originates during precipitation events. It may also be used to apply to water that originates with snowmelt that enters the stormwater system...

     into sewer
    Sanitary sewer
    A sanitary 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...

     lines during heavy rainfall
  • Rupture or blockage of sewerage
    Sanitary sewer
    A sanitary 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...

     lines
  • Malfunction of pumping station
    Pumping station
    Pumping stations are facilities including pumps and equipment for pumping fluids from one place to another. They are used for a variety of infrastructure systems, such as the supply of water to canals, the drainage of low-lying land, and the removal of sewage to processing sites.A pumping station...

     lifts or electrical power failure
  • Human operator error at treatment plant facilities.


SSO is distinct from a combined sewer overflow (CSO), a similar problem of untreated sewage discharges, but which occurs only in a municipal system specifically designed with a combined sewer.

History


Since medieval times rulers have been aware of the impact of raw sewage improperly discharged to the environment. Before treatment systems existed in 16th century England
England
England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...

, King Henry VIII
Henry VIII of England
Henry VIII was King of England from 21 April 1509 until his death. He was Lord, and later King, of Ireland, as well as continuing the nominal claim by the English monarchs to the Kingdom of France...

 decreed that sewage troughs should be kept flowing so that they would not stagnate in London
London
London is the capital city of :England and the :United Kingdom, the largest metropolitan area in the United Kingdom, and the largest urban zone in the European Union by most measures. Located on the River Thames, London has been a major settlement for two millennia, its history going back to its...

 prior to reaching the River Thames
River Thames
The River Thames flows through southern England. It is the longest river entirely in England and the second longest in the United Kingdom. While it is best known because its lower reaches flow through central London, the river flows alongside several other towns and cities, including Oxford,...

 (London sewer system). It was not until the 19th century when America and parts of Europe developed wastewater treatment, that the concept of SSO materialized; however, communities were merely happy to have wastewater treatment systems, and did not complain greatly about overflows until the dawning of 20th century environmental awareness in the 1960s. At that time the USA began recognizing locations and frequencies of SSOs in a systematic way. Local governments heard complaints of citizens, beach closure protocols were systematised and the U.S. Environmental Protection Agency
United States Environmental Protection Agency
The U.S. Environmental Protection Agency is an agency of the federal government of the United States charged with protecting human health and the environment, by writing and enforcing regulations based on laws passed by Congress...

 (EPA) began detailed engineering analyses for major cities across the country. After passage of the U.S. Clean Water Act
Clean Water Act
The Clean Water Act is the primary federal law in the United States governing water pollution. Commonly abbreviated as the CWA, the act established the goals of eliminating releases of high amounts of toxic substances into water, eliminating additional water pollution by 1985, and ensuring that...

 in 1972, the 1980s saw spending of billions of dollars on system upgrading (although most funds during this period were spent on upgrades to secondary treatment rather than addressing SSO problems). In the 1990s Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...

, the UK and a number of other European countries began earnest investigation of some of their countries’ overflow issues.

Magnitude of the problem


EPA estimates that about 40,000 SSO events occur in the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...

 each year. The Agency estimated that to upgrade every municipal treatment and collection system to reduce overflow events to no more frequently than every five years, would cost about 88 billion dollars as of 2004. This cost would be in addition to approximately ten billion dollars already invested. Although the volume of untreated sewage discharged to the environment is less than .01 percent of all treated sewage in the US, the total volume amounts to several billion US gallons per annum and accounts for thousands of cases of gastrointestinal illness each year. Advanced European countries and Japan have similar or somewhat larger percentages of SSO events.

Engineering aspects


By far the most prevalent cause of Sanitary Sewer Overflow stems from heavy rainfall events which can cause massive infiltration of stormwater
Stormwater
Stormwater is water that originates during precipitation events. It may also be used to apply to water that originates with snowmelt that enters the stormwater system...

 into sewerage lines. The combined flow of wastewater and stormwater exceeds the capacity of the sewer system and is released into local waterways to prevent flooding in homes, businesses and streets. This circumstance is most prevalent in older cities whose subsurface infrastructure is quite old; Paris
Paris
Paris is the capital and largest city in France, situated on the river Seine, in northern France, at the heart of the Île-de-France region...

, London
London
London is the capital city of :England and the :United Kingdom, the largest metropolitan area in the United Kingdom, and the largest urban zone in the European Union by most measures. Located on the River Thames, London has been a major settlement for two millennia, its history going back to its...

, Stockholm
Stockholm
Stockholm is the capital and the largest city of Sweden and constitutes the most populated urban area in Scandinavia. Stockholm is the most populous city in Sweden, with a population of 851,155 in the municipality , 1.37 million in the urban area , and around 2.1 million in the metropolitan area...

, New York
New York
New York is a state in the Northeastern region of the United States. It is the nation's third most populous state. New York is bordered by New Jersey and Pennsylvania to the south, and by Connecticut, Massachusetts and Vermont to the east...

, Washington, DC, and Oakland, California
Oakland, California
Oakland is a major West Coast port city on San Francisco Bay in the U.S. state of California. It is the eighth-largest city in the state with a 2010 population of 390,724...

 are typical examples of such locations. Inflow into the sanitary lines can be caused by tree root rupture of subsurface lines or by mechanical fracture due to age and overpressure from trucks and buildings above.

Other modes of system failure can include power outage which may disable lift station pumps or parts of the treatment plant operations themselves; in fact, any mechanical system failure within a treatment plant can create a circumstance leading to overflow: breakdown of rotating arms of trickling filter
Trickling filter
A trickling filter consists of a fixed bed of rocks, lava, coke, gravel, slag, polyurethane foam, sphagnum peat moss, ceramic, or plastic media over which sewage or other wastewater flows downward and causes a layer of microbial slime to grow, covering the bed of media...

s, jamming of line gates, clogging of filters or grates etc. Furthermore, some forms of human error
Human Error
Human Error is the stage name of Rafał Kuczynski , a polish electronic musician, working mostly in the ambient music genre, produced only with a computer...

 can infrequently lead to diversion of sewage and result in an overflow event.

Decentralized failures in dry weather mainly occur from collection sewer line blockages, which can arise from a debris
Debris
Debris is rubble, wreckage, ruins, litter and discarded garbage/refuse/trash, scattered remains of something destroyed, or, in geology, large rock fragments left by a melting glacier etc. The singular form of debris is debris...

 clog, line rupture or tree root intrusion into the line itself. One of the main problems of a decentralized line failure is the difficulty of defining the location of overflow, since a typical urban system contains thousands of miles of collection pipage, and the central treatment plant has no way of communicating with all the lines, unless expensive monitoring equipment has been installed.

Human health and ecological consequences


Human health impacts include significant numbers of gastrointestinal illness each year, although death from one overflow event is uncommon. Additional human impacts include beach
Beach
A beach is a geological landform along the shoreline of an ocean, sea, lake or river. It usually consists of loose particles which are often composed of rock, such as sand, gravel, shingle, pebbles or cobblestones...

 closures, swimming restrictions and prohibition against consumption of certain aquatic animals (particularly certain molluscs) after overflow events. Ecological consequences include fish kill
Fish kill
The term fish kill, known also as fish die-off and as fish mortality, is a localized die-off of fish populations which may also be associated with more generalised mortality of aquatic life...

s, harm to plankton
Plankton
Plankton are any drifting organisms that inhabit the pelagic zone of oceans, seas, or bodies of fresh water. That is, plankton are defined by their ecological niche rather than phylogenetic or taxonomic classification...

 and other aquatic microflora and microfauna. Turbidity increase and dissolved oxygen decrease in receiving waters can lead to accentuated effects beyond the obvious pathogen
Pathogen
A pathogen gignomai "I give birth to") or infectious agent — colloquially, a germ — is a microbe or microorganism such as a virus, bacterium, prion, or fungus that causes disease in its animal or plant host...

ic induced damage to aquatic ecosystem
Ecosystem
An ecosystem is a biological environment consisting of all the organisms living in a particular area, as well as all the nonliving , physical components of the environment with which the organisms interact, such as air, soil, water and sunlight....

s. It is possible that higher life forms such as marine mammals can be affected since certain seals and sea lions are known to experience peaks in pathogenic harm.

Worldwide perspective


It is difficult to visualize the issue of SSO in perspective, since underdeveloped countries discharge most of the sewage they create as effluent into the environment. Even a highly industrialized country such as the People's Republic of China
People's Republic of China
China , officially the People's Republic of China , is the most populous country in the world, with over 1.3 billion citizens. Located in East Asia, the country covers approximately 9.6 million square kilometres...

 discharges about 55 percent of all sewage without treatment of any type. In a relatively developed Middle East
Middle East
The Middle East is a region that encompasses Western Asia and Northern Africa. It is often used as a synonym for Near East, in opposition to Far East...

ern country such as Iran
Iran
Iran , officially the Islamic Republic of Iran , is a country in Southern and Western Asia. The name "Iran" has been in use natively since the Sassanian era and came into use internationally in 1935, before which the country was known to the Western world as Persia...

, the majority of Tehran
Tehran
Tehran , sometimes spelled Teheran, is the capital of Iran and Tehran Province. With an estimated population of 8,429,807; it is also Iran's largest urban area and city, one of the largest cities in Western Asia, and is the world's 19th largest city.In the 20th century, Tehran was subject to...

's population has totally untreated sewage injected to the city’s groundwater. In Venezuela
Venezuela
Venezuela , officially called the Bolivarian Republic of Venezuela , is a tropical country on the northern coast of South America. It borders Colombia to the west, Guyana to the east, and Brazil to the south...

, a below average country in South America
South America
South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...

 with respect to wastewater treatment, 97 percent of the country’s sewage
Sewage
Sewage is water-carried waste, in solution or suspension, that is intended to be removed from a community. Also known as wastewater, it is more than 99% water and is characterized by volume or rate of flow, physical condition, chemical constituents and the bacteriological organisms that it contains...

 is discharged raw into the environment. Most of sub-Saharan Africa
Sub-Saharan Africa
Sub-Saharan Africa as a geographical term refers to the area of the African continent which lies south of the Sahara. A political definition of Sub-Saharan Africa, instead, covers all African countries which are fully or partially located south of the Sahara...

 is without wastewater treatment, contributing to the excessive infant
Infant
A newborn or baby is the very young offspring of a human or other mammal. A newborn is an infant who is within hours, days, or up to a few weeks from birth. In medical contexts, newborn or neonate refers to an infant in the first 28 days after birth...

 death rates in that region.

While developed countries such as the US, Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...

, most Western Europe
Western Europe
Western Europe is a loose term for the collection of countries in the western most region of the European continents, though this definition is context-dependent and carries cultural and political connotations. One definition describes Western Europe as a geographic entity—the region lying in the...

an states, Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...

 and Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...

 are considered to be struggling with a public health problem of SSO prevention, the underdeveloped countries of the world discharge approximately 20,000 times the amount of raw sewage into the environment as those advanced countries collectively, approximately (the equivalent of) 100 trillion US gallons (380 km³) of untreated sewage per annum. This dichotomy of expenditure and public health
Public health
Public health is "the science and art of preventing disease, prolonging life and promoting health through the organized efforts and informed choices of society, organizations, public and private, communities and individuals" . It is concerned with threats to health based on population health...

 benefit is arguably the greatest disparity between developed and underdeveloped nations as of the year 2006.

See also

  • Combined sewer
  • Intestinal parasite
    Intestinal parasite
    Intestinal parasites are parasites that populate the gastro-intestinal tract in humans and other animals. They can live throughout the body, but most prefer the intestinal wall. Means of exposure include: ingestion of undercooked meat, drinking infected water, and skin absorption...

  • Sanitary sewer
    Sanitary sewer
    A sanitary 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...

  • Sewage treatment
    Sewage treatment
    Sewage treatment, or domestic wastewater treatment, is the process of removing contaminants from wastewater and household sewage, both runoff and domestic. It includes physical, chemical, and biological processes to remove physical, chemical and biological contaminants...

  • Water crisis
    Water crisis
    Water crisis is a general term used to describe a situation where the available water within a region is less than the region's demand. The term has been used to describe the availability of potable water in a variety of regions by the United Nations and other world organizations...

  • Water pollution
    Water pollution
    Water pollution is the contamination of water bodies . Water pollution occurs when pollutants are discharged directly or indirectly into water bodies without adequate treatment to remove harmful compounds....


External links