Sanitary sewer overflow: Difference between revisions

Revision as of 21:13, 9 September 2015

Revision as of 21:16, 9 September 2015

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EPA. [http://cfpub.epa.gov/npdes/cso/cpolicy_report2004.cfm "Report to Congress: Impacts and Control of CSOs and SSOs"], Executive Summary. August 2004. Document No. EPA-833-R-04-001.</ref> 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 0.01% of all treated sewage in the United States, the total volume amounts to several billion U.S. gallons per annum and accounts for thousands of cases of gastrointestinal illness each year.<ref name="EPA-RTC" />{{rp|Ch. 6}} Advanced European countries and Japan have similar or somewhat larger percentages of SSO events.<ref>{{cite web|url=http://septiczone.com/global-sso-events |title=A Worldwide View Of Sanitary Sewer Overflow |accessdate=19 July 2009}}</ref>{{Failed verification|date=June 2015}}

==Engineering aspectsCauses ==

===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 practicedimplemented. 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 offensive 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. Sanitary sewers were built 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 |volume = |edition = |date =1959 |___location = |page =6 |isbn =}}</ref>

==Blockage=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="EPARTC"/>{{rp|p. 4–26}} [[Brown grease|Grease]] is the blocking agent in approximately half of United States 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 into toilets. <ref name="EPARTC"/>{{rp|p. 4–28}}

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Dry weather blockage is less likely within combined sewers; because combined sewers designed for the additional volume of surface runoff are so much larger than sanitary sewers. Combined sewer storm water regulators may be vulnerable to blockage by debris, but overflow from such blockage typically enters the diversion [[outfall]] to avoid flooding private or public property.

===Infiltration/inflow===

Approximately one-quarter of United States SSOs occur during heavy [[rainfall]] events, which can cause inflow of [[stormwater]] into sanitary sewers through damage, improper connections, or flooding buildings and lift stations in low-lying areas of the collection system. The combined flow of sewage and stormwater exceeds the capacity of the sanitary sewer system and sewage is released into homes, businesses and streets.<ref name="EPARTC"/>{{rp|p. 4–26}} This circumstance is most prevalent in older cities whose subsurface infrastructure is quite old; [[Paris]], [[London]], [[Stockholm]],<ref>Monica Spendilow, ''Impeller Magazine'', ITT Flygt AB, SE-174 87 Sundbyberg, Sweden (2004)</ref> [[New York]], [[Washington, DC]], and [[Oakland, California]]<ref>''Environmental Impact Statement for the [[East Bay Municipal Utility District]] Wet Weather Overflow Project'', Earth Metrics Incorporated, prepared for the U.S. EPA and East Bay Municipal Utility District, Oakland, Ca. (1985)</ref> 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.

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Historically, one of the biggest causes of SSO operation is the overloading of the sewer during storms and there has been a call to reduce the amount of water entering sewers by introducing SuDS.

==Malfunction=Malfunctions===

Another mode of system failure can include [[power outage]]s, which may disable lift station pumps and cause sewage overflow from the lift station wet well. Lift station mechanical or power failure causes approximately ten percent of United States SSOs. This type of discharge is uncommon from combined sewers, because the combined volume of sewage and storm water discourages use of lift stations. Broken sewer lines are responsible for approximately ten percent of United States SSOs.<ref name="EPARTC"/>{{rp|p. 4–27}}

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Human health impacts include significant numbers of [[gastrointestinal]] illness each year, although death from one overflow event is uncommon. Additional human impacts include [[beach]] closures, [[human swimming|swimming]] restrictions and prohibition of the consumption of certain aquatic animals (particularly certain [[mollusc]]s) after overflow events. Ecological consequences include [[fish kill]]s, harm to [[plankton]] and other aquatic microflora and microfauna. Turbidity increase and dissolved oxygen decrease in receiving waters can lead to accentuated effects beyond the obvious [[pathogen]]ic induced damage to aquatic [[ecosystem]]s. It is possible that higher life forms such as [[marine mammal]]s can be affected since certain seals and [[sea lion]]s are known to experience peaks in pathogenic harm.<ref>Johnson, S. P., Jang, S., Gulland, F.M.D., Miller, M., Casper, D., Lawrence, J., Herrera, J., [http://www.jwildlifedis.org/cgi/reprint/39/1/136.pdf "Characterization and clinical manifestations of Arcanobacterium phocae infections in marine mammals stranded along the central California coast"], ''Journal of Wildlife Diseases'', 39:136-144 (2003).</ref>

===Worldwide perspective===

In [[developing countries]], most wastewater is still not treated properly but discharged into the environment. Even a country such as the [[People's Republic of China]] discharged in 2001 about 55 percent of all sewage without treatment of any type.<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’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’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>