Sanitary sewer overflow: Difference between revisions

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{{Short description|Discharge of untreated sewage}}

: ''Not to be confused with [[Combined sewer#Combined sewer overflows (CSOs)|combined sewer overflow (CSO)]]''

{{distinguish|Combined sewer overflow}}
[[File:Sewer overflow RI EPA.jpg|thumb|right|A [[sanitary manhole|manhole]] cover unable to contain a sanitary sewer overflow]]

'''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'''. ItCauses isof primarilysanitary meaningfulsewer inoverflows include: Blockage of sewer lines, [[developedinfiltration/Inflow]] countriesof excessive [[stormwater]] into sewer lines during heavy [[rainfall]], whichmalfunction haveof extensive[[pumping treatmentstation]] facilities.lifts Frequentor causeselectrical [[power failure]], broken sewer lines. Prevention of SSOsuch spillsoverflow include:events involves regular maintenance and timely upgrades of infrastructure.

SSOs can cause [[gastrointestinal illness]]es ([[waterborne diseases]]), beach closures and restrictions on fish and [[shellfish]] consumption.

* 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.

=== United States= ==

SSOs can cause [[gastrointestinal illness]]es, beach closures and restrictions on fish and shellfish consumption.

The [[U.S. Environmental Protection Agency]] (EPA) estimates that at least 23,000 to 75,000 SSO events occur in the United States each year.<ref>{{cite web |url=https://www.epa.gov/npdes/sanitary-sewer-overflows-ssos |title=Sanitary Sewer Overflows |author=<!--Staff writer(s); no by-line.--> |date=2015-11-16 |access-date=2023-02-17 |website=National Pollutant Discharge Elimination System |publisher=U.S. Environmental Protection Agency (EPA) |___location=Washington, D.C.}}</ref> EPA estimated that upgrading every municipal treatment and collection system to reduce the frequency of overflow events to no more than once every five years would cost about $88 billion as of 2004.<ref name="EPA-RTC">{{cite report |date=August 2004 |title=Report to Congress: Impacts and Control of CSOs and SSOs |url=https://www.epa.gov/npdes/2004-npdes-cso-report-congress |access-date=2023-02-17 |publisher=EPA |id=EPA-833-R-04-001}}</ref> This cost would be in addition to approximately $10 billion already invested. Although the volume of untreated sewage discharged to the environment is less than 0.01 percent of all treated sewage in the United States, the total volume amounts to several billion gallons per annum and accounts for thousands of cases of gastrointestinal illness each year.<ref name="EPA-RTC" />{{rp|Ch. 6}}

=== Worldwide perspective= ==

==Magnitude of the problem==

Developed countries such as the [[United States]], [[Canada]], most [[Western Europe]]an nations (e.g. [[Italy]] and [[France]]), [[Australia]], [[Singapore]], [[South Korea]] and [[Japan]] are struggling with public health problems of SSO prevention. However, the magnitude of the problem is much greater in most developing countries.

===United States===

The [[U.S. Environmental Protection Agency]] (EPA) estimates that at least 23,000 to 75,000 SSO events occur in the United States each year.<ref>{{cite web |url=https://www.epa.gov/npdes/sanitary-sewer-overflows-ssos |title=Sanitary Sewer Overflows |author=<!--Staff writer(s); no by-line.--> |date=2015-11-16 |website=National Pollutant Discharge Elimination System |publisher=U.S. Environmental Protection Agency (EPA) |___location=Washington, D.C.}}</ref> EPA estimated that upgrading every municipal treatment and collection system to reduce the frequency of overflow events to no more than once every five years would cost about $88 billion as of 2004.<ref name="EPA-RTC">{{cite report |date=August 2004 |title=Report to Congress: Impacts and Control of CSOs and SSOs |url=https://www.epa.gov/npdes/2004-npdes-cso-report-congress |publisher=EPA |id=EPA-833-R-04-001}}</ref> This cost would be in addition to approximately $10 billion already invested. Although the volume of untreated sewage discharged to the environment is less than 0.01 percent of all treated sewage in the United States, the total volume amounts to several billion gallons per annum and accounts for thousands of cases of gastrointestinal illness each year.<ref name="EPA-RTC" />{{rp|Ch. 6}}

===Worldwide perspective===

Developed European countries and Japan have similar or somewhat larger percentages of SSO events compared to the U.S.{{citation needed|date=June 2015}}

In [[developing countries]], most wastewater is still not treated when discharged into the environment. The [[People's Republic of China]] discharged about 55 percent of all sewage without treatment of any type, as of 2001.<ref>"[[World Bank]] Supports China's Wastewater Treatment", ''The People’s Daily'', November 30, 2001, Beijing</ref> In a relatively developed [[Middle East]]ern country such as [[Iran]], the majority of [[Tehran]]'s population has totally untreated sewage injected to the city’scity's groundwater.<ref>Massoud Tajrishy and Ahmad Abrishamchi, "Integrated Approach to Water and Wastewater Management for [[Tehran]], [[Iran]]", [[Water Conservation]], Reuse, and Recycling: Proceedings of the Iranian-American Workshop, National Academies Press (2005)</ref> In [[Venezuela]], a below-average country in [[South America]] with respect to wastewater treatment, 97 percent of the country’scountry's sewage is discharged untreated into the environment.<ref>Appropriate Technology for Sewage Pollution Control in the Wider [[Caribbean]] Region, Caribbean Environment Programme Technical Report #40 1998</ref>

In many countries there are obligations to measure and report SSO occurrence using real-time [[telemetry]] to warn the public, bathers and shellfishery operators.{{citation needed|date=June 2016}}

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===Engineering aspects===

[[Image:Aparissewer.jpg|thumb|230px|Sanitary sewer line in [[Paris]] more than two meters in diameter.]]

Sewers that were built in the early stages of urbanization were usually built before [[sewage treatment]] was implemented.<ref>''See'' [[History of water supply and sanitation]].</ref> Early sewers were simple drainage systems to remove [[surface runoff]] with any waste material it might contain. These drainage systems became [[combined sewers]] when sewage from kitchens, baths, and toilets was added; and the discharge became offensive. Early sewage treatment plants were built to treat the sewage during dry weather; but it was infeasible to treat the larger volume of mixed sewage and precipitation runoff from combined sewers during wet weather. SanitarySome sewers werecities built sanitary sewers to keep sewage from being mixed with surface runoff so the sewage could be efficiently treated during both wet and dry weather.<ref>{{cite book |last=Okun |first=Daniel A. |authorlink = |title =Sewage Treatment Plant Design |publisher =[[American Society of Civil Engineers]] and Water Pollution Control Federation |volumedate =1959 |editionpage =6 |date}}</ref> (About 860 communities in the U.S. continue to use combined sewers.<ref>{{cite web |url=1959https://www.epa.gov/npdes/combined-sewer-overflow-frequent-questions |___locationtitle=Combined Sewer Overflow Frequent Questions |author=<!--Staff writer(s); no by-line.--> |pagedate=2017-12-20 |access-date=6 |isbnwebsite=National Pollutant Discharge Elimination System |publisher=EPA}}</ref>)

===Blockages===

Decentralized failures in dry weather mainly occur from collection sewer line blockages, which can arise from a [[debris]] clog or tree root intrusion into the line itself. Approximately half of SSOs in the United States are caused by blockage.<ref name="EPA-RTC"/>{{rp|p. 4–26}} [[Brown grease|Grease]] is the blocking agent in approximately half of U.S. SSOs attributed to blockage, and solid debris is the blocking agent for another 25 percent. [[Root]]s are a contributing factor in approximately one-quarter of United States SSOs attributed to blockage. Grease deposits are caused by cooking fats liquified with hot water for discharge to sanitary sewers. These fats congeal as solid deposits in the cooler sewer. Solid debris includes soiled clothing, [[diaper]]s, and [[sanitary napkin]]s flushed down the toilet rather than being put in a waste bin.<ref name="EPA-RTC"/>{{rp|p. 4–28}}

Many U.S. municipalities require restaurants and food processing businesses to use [[grease interceptor]]s and regulate the disposal of fats, oil and grease in the sewer system.<ref>For example, the [[Washington Suburban Sanitary Commission]] (WSSC) in Maryland, U.S.: {{cite web |title=Fats, Oils, & Grease |url=https://www.wsscwater.com/fog |website=Special Wastewater Discharge Requirements |date=2023-12-29 |publisher=WSSC |___location=Laurel, MD}}</ref>

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 pipes, and the central treatment plant has no way of communicating with all the lines, unless expensive monitoring equipment has been installed. Companies in the UK have widely deployed bulk dielectric [[transducer]]s suspended in the sewers to detect high levels and to report the events back over fixed wireless data networks. In certain locations this practice has permitted the reduction of pollution events by up to 60 percent.{{citation needed|date=June 2016}}

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==Mitigation techniques==

{{Further|Combined sewer#Mitigation of CSOs}}

The concept of SSO containment valves has been pioneered in the UK and they are installed to mitigate dry spills, by correlating rainfall data with SSO spill activity.{{citation needed|date=June 2016}}

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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]], [[Henry VIII of England|King Henry VIII]] decreed that sewage troughs should be kept flowing so that they would not stagnate in [[London]] prior to reaching the [[River Thames]] ([[London sewer system]]).{{citation needed|date=June 2016}}

In the 19th century, sewage treatment plants were first developed and installed in the U.S. and parts of Europe, and the concept of SSO was identified. However, SSOs were not recognized as a widespread environmental problem until the rise of environmental awareness in the 1960s. Around that time government agencies in the U.S. began identifying locations and frequencies of SSOs in a systematic way. Local governments heard complaints of citizens, and beach closure protocols were systematised to reduce risks to public health.

After passage of the [[Clean Water Act]] in 1972, the U.S. spent billions of dollars on upgrades to sewage treatment plants, with some associated repairs and improvements to the associated collection systems, where the overflows occur. EPA continues to provide funding for low-interest loans to communities for addressing SSO problems, through the [[Clean Water State Revolving Fund]].<ref>{{cite web |url=https://www.epa.gov/npdes/sanitary-sewer-overflow-sso-frequent-questions |title=Sanitary Sewer Overflow (SSO) Frequent Questions |author=<!--Staff writer(s); no by-line.--> |date=2015-11-16 |access-date= |publisher=EPA}}</ref>

In the 1990s [[Japan]], the [[UK]] and a number of other European countries began earnest investigation of some of their countries’ overflow issues.{{citation needed|date=June 2016}}

==See also==

* [[Fatberg]] (sewer blockage)

* [[Water pollution]]