# Effluent

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{{Short description|Liquid waste or sewage discharged into a river or the sea}}
[[File:Discharge pipe.jpg|thumb|right|[Wastewater](/source/Wastewater) is considered effluent as it is released to surface water.]]
'''Effluent''' is [wastewater](/source/wastewater) from sewers or industrial outfalls that flows directly into [surface water](/source/surface_water)s, either untreated or after being [treated](/source/Wastewater_treatment) at a facility.<ref name="EPA effluent defn">{{cite web |title=Terms of Environment |url=https://nepis.epa.gov/Exe/ZyPURL.cgi?Dockey=40000807.txt |date=February 1993 |publisher=United States Environmental Protection Agency (EPA) |location=Washington, D.C. |page=10 |id=EPA 175-B-93-001}}</ref> The term has slightly different meanings in certain contexts, and may contain various [pollutant](/source/pollutant)s depending on the source.<ref name="WWD-effluent">{{cite magazine |last=Tuser |first=Cristina |title=What is Effluent? |url=https://www.wwdmag.com/wastewater-treatment/wastewater-treatment/article/10939353/what-is-effluent |date=2021-10-27 |magazine=Water & Wastes Digest |publisher=Endeavor Business Media, LLC}}</ref>

== Definition ==
Effluent is defined by the [United States Environmental Protection Agency](/source/United_States_Environmental_Protection_Agency) (EPA) as "wastewater–treated or untreated–that flows out of a treatment plant, sewer, or industrial outfall. Generally refers to wastes discharged into surface waters".<ref name="EPA effluent defn"/> The ''Compact Oxford English Dictionary'' defines effluent as "liquid waste or sewage discharged into a river or the sea".<ref>{{cite web |url=http://www.askoxford.com/concise_oed/effluent?view=uk |archive-url=https://archive.today/20120718034729/http://www.askoxford.com/concise_oed/effluent?view=uk |url-status=dead |archive-date=July 18, 2012 |title=AskOxford: effluent |work=Ask Oxford.com |publisher=Oxford University Press |year=2010}}</ref>  Wastewater is not usually described as effluent while being [recycle](/source/recycle)d, re-used, or treated until it is released to surface water.  Wastewater [percolated](/source/Percolation) or [injected](/source/Injection_well) into [groundwater](/source/groundwater) may not be described as effluent if [soil](/source/soil) is assumed to perform treatment by [filtration](/source/filtration) or [ion exchange](/source/ion_exchange);<ref>{{cite book |last=Rich |first=Linville G. |title =Low-Maintenance Mechanically Simple Wastewater Treatment Systems |publisher =McGraw-Hill Book Company |date =1980 |location =New York |pages =181–186 |isbn =0-07-052252-9}}</ref> although concealed flow through fractured [bedrock](/source/bedrock), [lava tube](/source/lava_tube)s, [limestone cave](/source/limestone_cave)s,<ref>{{cite book |last1=Linsley |first1=Ray K. |last2=Franzini |first2=Joseph B. |title =Water-Resources Engineering |publisher =McGraw-Hill Book Company |edition =Second |date =1972 |location =New York |pages =84 & 85 |isbn =0-07-037959-9}}</ref> or [gravel](/source/gravel) in ancient [stream channel](/source/stream_channel)s<ref>{{cite book |last=Harr |first=M.E. |title =Groundwater and Seepage |publisher =McGraw-Hill Book Company |date=1962 |location=New York |page=26 |isbn=0-07-026740-5}}</ref> may allow relatively untreated wastewater to emerge as [springs](/source/Spring_(hydrology)).<ref>{{cite book |last1=Steel |first1=E.W. |last2=McGhee |first2=Terence J.|title=Water Supply and Sewerage |publisher=McGraw-Hill Book Company |edition =Fifth |date=1979 |location=New York |pages=81–82 |isbn=0-07-060929-2}}</ref>

== Description ==
Effluent in the artificial sense is in general considered to be [water pollution](/source/water_pollution), such as the outflow from a [sewage treatment](/source/sewage_treatment) facility or an [industrial wastewater](/source/Industrial_wastewater_treatment) discharge. An effluent [sump pump](/source/sump_pump), for instance, pumps waste from toilets installed below a main sewage line. In the context of [waste water treatment plants](/source/waste_water_treatment_plants), effluent that has been treated is sometimes called ''secondary effluent'', or ''treated effluent''. This cleaner effluent is then used to feed the [bacteria](/source/bacteria) in [biofilters](/source/biofilters).<ref>{{Cite book |title=Wastewater engineering: Treatment and reuse |date=2003 |publisher=McGraw-Hill |author=George Tchobanoglous |author2=Franklin L. Burton |author3=H. David Stensel |isbn=0-07-041878-0|edition=4th |location=Boston |oclc=48053912}}</ref>

In the context of a [thermal power station](/source/thermal_power_station) and other industrial facilities, the output of the cooling system may be referred to as the effluent cooling water, which is noticeably warmer than the environment and is called [thermal pollution](/source/thermal_pollution).<ref name="Laws-aquatic">{{cite book |url=https://books.google.com/books?id=V5D2DQAAQBAJ |title=Aquatic Pollution<nowiki>:</nowiki> An Introductory Text |last=Laws |first=Edward A. |date=2017 |publisher=John Wiley & Sons |isbn=978-1-119-30450-0 |edition=4th |location=Hoboken, NJ}}</ref>{{rp|375}} In [chemical engineering](/source/chemical_engineering) practice, effluent is the stream exiting a [chemical reactor](/source/chemical_reactor).<ref>{{cite book |last=Fogler |first=H. Scott |title=Elements of Chemical Reaction Engineering |date=2006 |publisher=Prentice Hall |isbn=978-0-13-127839-4 |location=Hoboken, NJ |page=43}}</ref>

Effluent may carry pollutants such as fats, oils and greases; solvents, detergents and other chemicals; heavy metal; other solids; and food waste.<ref name="WWD-effluent"/> Possible sources include a wide range of manufacturing industries, mining industries, oil and gas extraction, and service industries.<ref name="EPA EG categories">{{Cite web |title=Industrial Effluent Guidelines |url=https://www.epa.gov/eg/industrial-effluent-guidelines |date=2022-11-07 |publisher=EPA}}</ref>

== Treatment ==
{{Main|Wastewater treatment}}
There are several kinds of wastewater which are treated at the appropriate type of treatment plant. Domestic wastewater (also called municipal wastewater or [sewage](/source/sewage)) is processed at a [sewage treatment plant](/source/Sewage_treatment). For industrial wastewater, treatment either takes place in a separate [industrial wastewater treatment](/source/industrial_wastewater_treatment) facility, or in a sewage treatment plant (usually after some form of pre-treatment). Other types of wastewater treatment plants include [agricultural wastewater treatment](/source/agricultural_wastewater_treatment) and [leachate](/source/leachate) treatment plants.

Treating wastewater efficiently is challenging, but improved technology allows for enhanced removal of specific materials, increased [re-use of water](/source/Water_reuse), and energy production from waste.<ref name="WWD-effluent"/><ref name="Brandt">{{Cite book |last1=Brandt |first1=Malcolm J. |chapter=Chapter 10. Specialized and Advanced Water Treatment Processes |date=2017-01-01 |chapter-url=https://www.sciencedirect.com/science/article/pii/B9780081000250000107 |title=Twort's Water Supply |pages=407–473 |editor-last=Brandt |editor-first=Malcolm J. |location=Boston |publisher=Butterworth-Heinemann |doi=10.1016/b978-0-08-100025-0.00010-7 |isbn=978-0-08-100025-0 |last2=Johnson |first2=K. Michael |last3=Elphinston |first3=Andrew J. |last4=Ratnayaka |first4=Don D. |edition=Seventh |editor2-last=Johnson |editor2-first=K. Michael |editor3-last=Elphinston |editor3-first=Andrew J. |editor4-last=Ratnayaka |editor4-first=Don D.}}</ref><ref name="Jegatheesan">{{cite encyclopedia |last1=Jegatheesan |first1=V. |last2=Shu |first2=L. |last3=Visvanathan |first3=C. |title=Aquaculture Effluent: Impacts and Remedies for Protecting the Environment and Human Health |encyclopedia=Encyclopedia of Environmental Health |year=2011 |publisher=Elsevier |doi=10.1016/b978-0-444-52272-6.00340-8 |isbn=978-0-444-52272-6 |page=123}}</ref><ref>{{Cite book |author=ProQuest LLC |title=Energy from Toxic Organic Water for Head and Power Generation |date=2018 |publisher=Woodhead Publishing |isbn=978-0-08-102529-1 |oclc=1096233045}}</ref>

== Pollution control regulation ==
=== United States effluent guidelines ===
In the United States, the [Clean Water Act](/source/Clean_Water_Act) requires all direct effluent discharges to surface waters to be regulated with permits under the [National Pollutant Discharge Elimination System](/source/Clean_Water_Act) (NPDES).<ref>{{cite web |date=2021-10-11 |title=NPDES Permit Limits |url=https://www.epa.gov/npdes/npdes-permit-limits |website=National Pollutant Discharge Elimination System |publisher=EPA}}</ref><ref name="EPA-learn">{{Cite web |title=Learn about Effluent Guidelines |url=https://www.epa.gov/eg/learn-about-effluent-guidelines |date=2022-09-09 |publisher=EPA}}</ref> Indirect dischargers–facilities which send their wastewater to municipal sewage treatment plants–may be subject to pretreatment requirements.<ref name="EPA-pretreatment">{{cite web |title=National Pretreatment Program Overview |url=https://www.epa.gov/npdes/national-pretreatment-program-overview |date=2022-10-03 |website=NPDES |publisher=EPA}}</ref> NPDES permits require discharging facilities to limit or treat effluent to the levels that result from using the most effective [treatment technologies](/source/Wastewater_treatment) possible at a practical cost to mitigate the effects of discharges on the receiving waters.<ref name="EPA-learn" /> EPA has published technology-based regulations, called "[effluent guidelines](/source/effluent_guidelines)", for 59 industrial categories.<ref name="EPA EG categories"/> The agency reviews the standards annually, conducts research on various categories, and makes revisions as appropriate.<ref name="EPA-learn" /> Noncompliance with these standards and all other conditions in the permits is punishable by law.<ref>{{Cite web |title=Effluent Guidelines Implementation & Compliance |url=https://www.epa.gov/eg/effluent-guidelines-implementation-compliance |date=2022-09-09 |publisher=EPA}}</ref> Each year, effluent guidelines regulations prevent billions of pounds of contaminants from being released into bodies of water.<ref>{{Cite web |title=Effluent Guidelines Plan |url=https://www.epa.gov/eg/effluent-guidelines-plan |date=2022-11-18 |publisher=EPA}}</ref>

EPA regulations require effluent limitations to be expressed as mass-based limits (rather than concentration-based limits) in the permits, so that discharging facilities will not use dilution as a substitute for treatment. In cases where setting mass-based limits are infeasible, the permit authority must set conditions in the permit that prohibit dilution.<ref>EPA. "Calculating NPDES permit conditions." ''Code of Federal Regulations'', {{CodeFedReg|40|122|45|f}}</ref>

=== United States sewage treatment standards ===
The U.S. "Secondary Treatment Regulation" is the national standard for municipal sewage treatment plants.<ref>EPA. "Secondary Treatment Regulation." Code of Federal Regulations, {{USCFR|40|133}}</ref>

==See also==
{{Portal|Water}}
{{wiktionary}}
*[Agricultural wastewater treatment](/source/Agricultural_wastewater_treatment)
*[Effluent guidelines](/source/Effluent_guidelines) (U.S. wastewater regulations)
*[Effluent limitation](/source/Effluent_limitation)
*[Industrial wastewater treatment](/source/Industrial_wastewater_treatment)
*[Stormwater](/source/Stormwater)
*[Surface runoff](/source/Surface_runoff)

==References==
{{Reflist}}

{{Rivers, streams and springs}}

Category:Environmental science
Category:Environmental engineering
Category:Water pollution

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Adapted from the Wikipedia article [Effluent](https://en.wikipedia.org/wiki/Effluent) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Effluent?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.