wastewater treatment

{{Short description|Converting wastewater into an effluent for return to the water cycle}}

{{About|the treatment of any type of wastewater from a range of sources|treatment of wastewater from households or municipalities (domestic wastewater)|Sewage treatment}}

File:La Crosse wastewater treatment facility-2.jpg (a type of wastewater treatment plant) in La Crosse, Wisconsin]]

Wastewater treatment is a process which removes and eliminates contaminants from wastewater. It thus converts it into an effluent that can be returned to the water cycle. Once back in the water cycle, the effluent creates an acceptable impact on the environment. It is also possible to reuse it. This process is called water reclamation.{{Cite web|date=October 29, 2020|title=wastewater treatment {{!}} Process, History, Importance, Systems, & Technologies|url=https://www.britannica.com/technology/wastewater-treatment|access-date=2020-11-04|website=Encyclopedia Britannica|language=en}} The treatment process takes place in a wastewater treatment plant. There are several kinds of wastewater which are treated at the appropriate type of wastewater treatment plant. For domestic wastewater the treatment plant is called a Sewage Treatment. Municipal wastewater or sewage are other names for domestic wastewater. For industrial wastewater, treatment takes place in a separate Industrial wastewater treatment, or in a sewage treatment plant. In the latter case it usually follows pre-treatment. Further types of wastewater treatment plants include Agricultural wastewater treatment and leachate treatment plants.

One common process in wastewater treatment is phase separation, such as sedimentation. Biological and chemical processes such as oxidation are another example. Polishing is also an example. The main by-product from wastewater treatment plants is a type of sludge that is usually treated in the same or another wastewater treatment plant.{{cite book|title=Metcalf & Eddy Wastewater Engineering: Treatment and Reuse|publisher=McGraw-Hill|year=2003|isbn=0-07-112250-8 |edition=4th|location=New York}}{{rp|Ch.14}} Biogas can be another by-product if the process uses anaerobic treatment. Treated wastewater can be reused as reclaimed water.{{Cite journal |last1=Takman |first1=Maria |last2=Svahn |first2=Ola |last3=Paul |first3=Catherine |last4=Cimbritz |first4=Michael |last5=Blomqvist |first5=Stefan |last6=Struckmann Poulsen |first6=Jan |last7=Lund Nielsen |first7=Jeppe |last8=Davidsson |first8=Åsa |date=2023-10-15 |title=Assessing the potential of a membrane bioreactor and granular activated carbon process for wastewater reuse – A full-scale WWTP operated over one year in Scania, Sweden |journal=Science of the Total Environment |volume=895 |pages=165185 |doi=10.1016/j.scitotenv.2023.165185 |pmid=37385512 |bibcode= 2023ScTEn.89565185T|s2cid=259296091 |issn=0048-9697|doi-access=free }} The main purpose of wastewater treatment is for the treated wastewater to be able to be disposed or reused safely. However, before it is treated, the options for disposal or reuse must be considered so the correct treatment process is used on the wastewater.

The term "wastewater treatment" is often used to mean "sewage treatment".{{cite book |last1=Tchobanoglous |first1=George |url=https://books.google.com/books?id=_WV6CgAAQBAJ|title=Metcalf & Eddy Wastewater Engineering: Treatment and Reuse |last2=Burton |first2=Franklin L. |last3=Stensel |first3=H. David |publisher=McGraw-Hill|year=2003|isbn=978-0-07-112250-4|edition=4th}}

Types of treatment plants

Wastewater treatment plants may be distinguished by the type of wastewater to be treated. There are numerous processes that can be used to treat wastewater depending on the type and extent of contamination. The treatment steps include physical, chemical and biological treatment processes.{{Cite web |last=Salai |first=Ramasamy |date=1 May 2025 |title=Wastewater Treatment Plants and Processes – A Complete Guide |url=https://pervel.in/wastewater-treatment-plants-processes-a-complete-guide/ |access-date=1 June 2025 |website=Pervel.in |archive-url=https://web.archive.org/web/20250603163555/https://pervel.in/wastewater-treatment-plants-processes-a-complete-guide/ |archive-date=3 June 2025 |url-status=live}}

Types of wastewater treatment plants include:

= Sewage treatment plants =

File:Belebungsbecken - aeration tank (12359229313).jpg process at the wastewater treatment plant in Dresden-Kaditz, Germany]]

=Industrial wastewater treatment plants=

=Agricultural wastewater treatment plants=

= Leachate treatment plants =

Leachate treatment plants are used to treat leachate from landfills. Treatment options include: biological treatment, mechanical treatment by ultrafiltration, treatment with active carbon filters, electrochemical treatment including electrocoagulation by various proprietary technologies and reverse osmosis membrane filtration using disc tube module technology.{{cite web|date=2018-03-16|title=Landfills Effluent Guidelines|url=https://www.epa.gov/eg/landfills-effluent-guidelines|publisher=EPA}}

Unit processes

File:Surface-Aerated Basin.png

The unit processes involved in wastewater treatment include physical processes such as settlement or flotation and biological processes such oxidation or anaerobic treatment. Some wastewaters require specialized treatment methods. At the simplest level, treatment of most wastewaters is carried out through separation of solids from liquids, usually by sedimentation. By progressively converting dissolved material into solids, usually a biological floc or biofilm, which is then settled out or separated, an effluent stream of increasing purity is produced.{{page needed|date=December 2023}}{{cite report |url=https://www.epa.gov/npdes/npdes-resources |title=Primer for Municipal Waste water Treatment Systems|publisher=US Environmental Protection Agency (EPA) |location=Washington, DC |id=EPA 832-R-04-001 |year=2004}}.

= Phase separation =

File:Bundesarchiv Bild 183-1984-1002-002, Güstrow, Zuckerwerk, Klärwerk.jpgs are widely used for wastewater treatment.]]

Phase separation transfers impurities into a non-aqueous phase. Phase separation may occur at intermediate points in a treatment sequence to remove solids generated during oxidation or polishing. Grease and oil may be recovered for fuel or saponification. Solids often require dewatering of sludge in a wastewater treatment plant. Disposal options for dried solids vary with the type and concentration of impurities removed from water.Ajay Kumar Mishra Smart Materials for Waste Water Applications, Wiley-Scrivener 2016 {{ISBN|111904118X}} https://onlinelibrary.wiley.com/doi/book/10.1002/9781119041214

File:Vorklärung - primary settling tank (12359073495).jpg

==Sedimentation==

{{Further|Sedimentation (water treatment)|Sewage treatment#Primary treatment}}

Solids such as stones, grit, and sand may be removed from wastewater by gravity when density differences are sufficient to overcome dispersion by turbulence. This is typically achieved using a grit channel designed to produce an optimum flow rate that allows grit to settle and other less-dense solids to be carried forward to the next treatment stage. Gravity separation of solids is the primary treatment of sewage, where the unit process is called "primary settling tanks" or "primary sedimentation tanks".{{Citation|title=Chapter 16 - Gravity Separation|date=2016-01-01|url=http://www.sciencedirect.com/science/article/pii/B9780444635891000162|work=Mineral Processing Design and Operations (Second Edition)|pages=563–628|editor-last=Gupta|editor-first=Ashok|place=Amsterdam|publisher=Elsevier|doi=10.1016/B978-0-444-63589-1.00016-2|language=en|isbn=978-0-444-63589-1|access-date=2020-11-30|editor2-last=Yan|editor2-first=Denis|url-access=subscription}} It is also widely used for the treatment of other types of wastewater. Solids that are denser than water will accumulate at the bottom of quiescent settling basins. More complex clarifiers also have skimmers to simultaneously remove floating grease such as soap scum and solids such as feathers, wood chips, or condoms. Containers like the API oil-water separator are specifically designed to separate non-polar liquids.{{Cite book|last=Weber|first=Walter J.|url=https://www.worldcat.org/oclc/389818|title=Physicochemical processes for water quality control|date=1972|publisher=Wiley-Interscience|isbn=0-471-92435-0|location=New York|oclc=389818}}{{rp|111–138}}

= Biological and chemical processes =

==Oxidation==

Oxidation reduces the biochemical oxygen demand of wastewater, and may reduce the toxicity of some impurities. Secondary treatment converts organic compounds into carbon dioxide, water, and biosolids through oxidation and reduction reactions.{{Cite journal|last=BERGENDAHL|first=JOHN|title=Applications of Advanced Oxidation for Wastewater Treatment|url=https://web.wpi.edu/Images/CMS/NEABC/wastewatersummary.pdf|url-status=live|archive-url=https://web.archive.org/web/20170829045706/https://web.wpi.edu/Images/CMS/NEABC/wastewatersummary.pdf|archive-date=2017-08-29|journal=Dept. Of Civil & Environmental Engineering, WPI}} Chemical oxidation is widely used for disinfection.{{Cite web |title=Water Disinfection - an overview {{!}} ScienceDirect Topics |url=https://www.sciencedirect.com/topics/chemical-engineering/water-disinfection#:~:text=The%20most%20widely%20used%20disinfectants,efficient%20in%20inactivating%20most%20microbes. |access-date=2023-03-02 |website=www.sciencedirect.com}}

===Biochemical oxidation (secondary treatment)===

===Chemical oxidation===

Advanced oxidation processes are used to remove some persistent organic pollutants and concentrations remaining after biochemical oxidation.{{rp|363–408}} Disinfection by chemical oxidation kills bacteria and microbial pathogens by adding hydroxyl radicals such as ozone, chlorine or hypochlorite to wastewater.{{rp|1220}} These hydroxyl radical then break down complex compounds in the organic pollutants into simple compounds such as water, carbon dioxide, and salts.{{Cite journal|last1=Deng|first1=Yang|last2=Zhao|first2=Renzun|date=2015-09-01|title=Advanced Oxidation Processes (AOPs) in Wastewater Treatment|journal=Current Pollution Reports|language=en|volume=1|issue=3|pages=167–176|doi=10.1007/s40726-015-0015-z|bibcode=2015CPolR...1..167D |issn=2198-6592|doi-access=free}}

== Anaerobic treatment ==

Anaerobic wastewater treatment processes (for example UASB, EGSB) are also widely applied in the treatment of industrial wastewaters and biological sludge.

=Polishing=

Polishing refers to treatments made in further advanced treatment steps after the above methods (also called "fourth stage" treatment). These treatments may also be used independently for some industrial wastewater. Chemical reduction or pH adjustment minimizes chemical reactivity of wastewater following chemical oxidation.{{rp|439}} Carbon filtering removes remaining contaminants and impurities by chemical absorption onto activated carbon.{{rp|1138}} Filtration through sand (calcium carbonate) or fabric filters is the most common method used in municipal wastewater treatment.

References

External links

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Category:Sanitation

Category:Water pollution

Category:Environmental engineering