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{{Short description|Liquid waste or sewage discharged into a river or the sea}}
[[File:Discharge pipe.jpg|thumb|right|[[Wastewater]] dischargeis considered effluent as it is released to surface water.]]
'''Effluent''' is an outflowing of water or gas to a natural body of water, from a structure such as a [[wastewater treatment plant]], [[Sewerage|sewer pipe]], or industrial outfall. Effluent, in engineering, is the stream exiting a [[chemical reactor]].<ref>Scott Fogler, ''Elements of Chemical Reaction Engineering'', page 43</ref>
'''Effluent''' is [[wastewater]] from sewers or industrial outfalls that flows directly into [[surface water]]s, either untreated or after being [[Wastewater treatment|treated]] 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]]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>
 
==Background Definition ==
Effluent is defined by the [[United States Environmental Protection Agency]] (EPA) as "wastewater - treatedwastewater–treated or untreated - thatuntreated–that flows out of a treatment plant, sewer, or industrial outfall. Generally refers to wastes discharged into surface waters".<ref>{{cite web |urlname=http://www.epa.gov/OCEPAterms/eterms.html |title=Terms of Environment Beginning With "E"EPA effluent |publisher=United States Environmental Protection Agency |accessdate=2010-06-09 |date=2006-10-03}}<defn"/ref> 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 |title=AskOxford: effluent |work=Ask Oxford.com |publisher=Oxford University Press |year=2010}}{{dead link|accessdatedate=2010September 2022|bot=medic}}{{cbignore|bot=medic}}</ref> Wastewater is not usually described as effluent while being [[recycle]]d, re-06used, or treated until it is released to surface water. Wastewater [[Percolation|percolated]] or [[Injection well|injected]] into [[groundwater]] may not be described as effluent if [[soil]] is assumed to perform treatment by [[filtration]] or [[ion exchange]];<ref>{{cite book |last=Rich |first=Linville G. |title =Low-09Maintenance 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]], [[lava tube]]s, [[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]] in ancient [[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 [[Spring (hydrology)|springs]].<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]], such as the outflow from a [[sewage treatment]] facility or the [[wastewater]] discharge from industrial facilities. An effluent [[sump pump]], for instance, pumps waste from toilets installed below a main sewage line.
Effluent in the artificial sense is in general considered to be [[water pollution]], such as the outflow from a [[sewage treatment]] facility or an [[Industrial wastewater treatment|industrial wastewater]] discharge. An effluent [[sump pump]], for instance, pumps waste from toilets installed below a main sewage line. In the context of [[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]] in [[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]] 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]].<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]] practice, effluent is the stream exiting a [[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>
In the context of [[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]] in [[biofilters]].
 
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>
In the context of a [[thermal power station]], the output of the cooling system may be referred to as the effluent cooling water, which is noticeably warmer than the environment. Effluent only refers to liquid discharge.
 
== Treatment ==
In [[sugar beet]] processing, effluent is often settled in water tanks that allow the mud-contaminated water to settle. The mud sinks to the bottom, leaving the top section of water clear, free to be pumped back into the river or be reused in the process again.
{{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]]) is processed at a [[Sewage treatment|sewage treatment plant]]. For industrial wastewater, treatment either takes place in a separate [[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]] and [[leachate]] treatment plants.
 
Treating wastewater efficiently is challenging, but improved technology allows for enhanced removal of specific materials, increased [[Water reuse|re-use of water]], 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 |url=https://www.sciencedirect.com/science/article/pii/B9780081000250000107 |title=Twort's Water Supply (Seventh Edition) |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. |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]] requires all direct effluent discharges to surface waters to be regulated with permits under the [[Clean Water Act#Point sources|National Pollutant Discharge Elimination System]] (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 [[Wastewater treatment|treatment technologies]] 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]]", 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]]
*[[Effluent guidelines]] (U.S. wastewater regulations)
*[[Effluent limitation]]
*[[Industrial wastewater treatment]]
*[[Wastewater]]
*[[Stormwater]]
*[[Surface runoff]]
 
==References==
{{reflistReflist}}
 
{{Rivers, streams and springs}}
 
[[Category:Environmental science]]
[[Category:Environmental engineering]]
[[Category:Water pollution]]
 
[[pl:Ścieki]]
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