Editing Flocculation (section)

== Applications ==
=== Surface chemistry ===
In [[colloid chemistry]], flocculation refers to the process by which fine [[particulate]]s are caused to clump together into a floc. The floc may then float to the top of the liquid (creaming), [[settling|settle]] to the bottom of the liquid ([[sedimentation]]), or be readily [[filtration|filtered]] from the liquid. Flocculation behavior of soil colloids is closely related to freshwater quality. High dispersibility of soil colloids not only directly causes turbidity of the surrounding water but it also induces [[eutrophication]] due to the adsorption of nutritional substances in rivers and lakes and even boats under the sea.

=== Physical chemistry ===
For [[emulsion]]s, flocculation describes clustering of individual dispersed droplets together, whereby the individual droplets do not lose their identity.<ref>Adamson A.W. and Gast A.P. (1997) "Physical Chemistry of Surfaces", John Wiley and Sons.</ref> Flocculation is thus the initial step leading to further ageing of the emulsion (droplet coalescence and the ultimate separation of the phases). Flocculation is used in mineral dressing,<ref>Investigation of laws of selective flocculation of coals with synthetic latexes / P. V. Sergeev, V. S. Biletskyy // ICCS’97. 7–12 September 1997, Essen, Germany. V. 1.  pp. 503–506.</ref> but can be also used in the design of physical properties of food and pharmaceutical products. <ref>{{Cite journal|last1=Fuhrmann|first1=Philipp L.|last2=Sala|first2=Guido|last3=Stieger|first3=Markus|last4=Scholten|first4=Elke|date=2019-08-01|title=Clustering of oil droplets in o/w emulsions: Controlling cluster size and interaction strength|journal=Food Research International|volume=122|pages=537–547|doi=10.1016/j.foodres.2019.04.027|pmid=31229109|issn=0963-9969|doi-access=free}}</ref>

=== Medical diagnostics ===
In a [[medical laboratory]], flocculation is the core principle used in various diagnostic tests, for example the [[rapid plasma reagin]] test.<ref>{{Cite journal |last1=Arora |first1=Satyam |last2=Doda |first2=Veena |last3=Rani |first3=Sunita |last4=Kotwal |first4=Urvershi |date=2015 |title=Rapid plasma reagin test: High false positivity or important marker of high risk behavior |journal=Asian Journal of Transfusion Science |volume=9 |issue=1 |pages=109 |doi=10.4103/0973-6247.150979 |issn=0973-6247 |pmc=4339923 |pmid=25722593 |doi-access=free }}</ref>
{{seealso|Porges-Meier reaction}}

=== Civil engineering/earth sciences ===
In [[civil engineering]], and in the [[earth sciences]], flocculation is a condition in which [[clay]]s, polymers or other small charged particles become attached and form a fragile [[structure]], a floc. In dispersed clay [[Slurry|slurries]],
flocculation occurs after mechanical agitation ceases and the dispersed clay platelets spontaneously form flocs because of attractions between negative face charges and positive edge charges.

=== Biology ===
{{See also|Yeast flocculation#Process}}
Flocculation is used in [[biotechnology]] applications in conjunction with [[microfiltration]] to improve the efficiency of biological feeds. The addition of synthetic flocculants to the [[bioreactor]] can increase the average particle size making microfiltration more efficient. When flocculants are not added, cakes form and accumulate causing low cell viability. Positively charged flocculants work better than negatively charged ones since the cells are generally negatively charged.<ref>{{Cite journal|title = Flocculation of biological cells: Experiment vs. theory|journal = AIChE Journal|date = 2003-07-01|issn = 1547-5905|pages = 1687–1701|volume = 49|issue = 7|doi = 10.1002/aic.690490709|first1 = Binbing|last1 = Han|first2 = S.|last2 = Akeprathumchai|first3 = S. R.|last3 = Wickramasinghe|first4 = X.|last4 = Qian| bibcode=2003AIChE..49.1687H }}</ref>

=== Cheese industry ===
Flocculation is widely employed to measure the progress of [[curd]] formation in the initial stages of [[cheese]] making to determine how long the curds must set.<ref name="fox2" /> The reaction involving the [[rennet]] [[micelle]]s are modeled by [[Einstein relation (kinetic theory)|Smoluchowski kinetics]].<ref name="fox2">{{Cite book
|last = Fox |first = Patrick F. |title = Cheese Volume 1: Chemistry, Physics, and Microbiology |edition = 2nd |publisher = Aspen Publishers |year = 1999 |location = [[Gaithersburg, Maryland]]|pages = 144–150|isbn = 978-0-8342-1378-4}}</ref> During the renneting of milk the micelles can approach one another and flocculate, a process that involves [[hydrolysis]] of molecules and macropeptides.<ref>{{Cite book|title = Cheese - Chemistry, Physics and Microbiology|last = Fox|first = Patrick F.|publisher = Elsevier|year = 2004|isbn = 978-0-12-263653-0|pages = 72|edition = 3rd}}</ref>

Flocculation is also used during cheese [[wastewater treatment]]. Three different coagulants are mainly used:<ref>{{Cite journal |title = Treatment of Cheese Whey Wastewater: Combined Coagulation−Flocculation and Aerobic Biodegradation |journal = Journal of Agricultural and Food Chemistry |date = 2010-07-14 |issn = 0021-8561 |pages = 7871–7877 |volume = 58 |issue = 13 |doi = 10.1021/jf100602j |first1 = Javier|last1 = Rivas |first2 = Ana R. |last2 = Prazeres |first3 = Fatima |last3 = Carvalho |first4 = Fernando |last4 = Beltrán |pmid=20557068 |bibcode = 2010JAFC...58.7871R |hdl=20.500.12207/540 |hdl-access = free}}</ref>
* FeSO<sub>4</sub> ([[iron(II) sulfate]])
* Al<sub>2</sub>(SO<sub>4</sub>)<sub>3</sub> ([[aluminium sulfate]])
* FeCl<sub>3</sub> ([[iron(III) chloride]])

=== Brewing ===
{{main|Yeast flocculation}}
In the brewing industry flocculation has a different meaning. It is a very important process in [[fermentation]] during the production of beer where cells form macroscopic flocs. These flocs cause the yeast to sediment or rise to the top of a fermentation at the end of the fermentation. Subsequently, the yeast can be collected (cropped) from the top ([[ale]] fermentation) or the bottom ([[lager]] fermentation) of the fermenter in order to be reused for the next fermentation.

[[Yeast flocculation]] is partially determined by the calcium concentration, often in the 50-100ppm range.<ref>{{cite web|last1=Brungard |first1 =Martin|title=Water Knowledge|url=https://sites.google.com/site/brunwater/water-knowledge|website=Bru'n Water|date = 20 February 2018}}</ref>  Calcium salts can be added to cause flocculation, or the process can be reversed by removing calcium by adding [[phosphate]] to form insoluble calcium phosphate, adding excess [[sulfate]] to form insoluble calcium sulfate, or adding [[EDTA]] to [[chelate]] the calcium ions. While it appears similar to sedimentation in colloidal dispersions, the mechanisms are different.<ref>{{Cite journal|title = Flocculation in Saccharomyces cerevisiae |journal=Food Res. Int.|date = 1999|pages =421–440|volume = 31|first1 = Y-L.|last1 = Jin |first2 = R.A..|last2 = Speers|issue=6–7 |doi=10.1016/S0963-9969(99)00021-6 }}</ref>

=== Water treatment process ===
[[File:The coagulation and filtration processes at a drinking water treatment plant. (14868618507).jpg|thumb|Coagulation-flocculation process in a water treatment system]]
Flocculation and [[sedimentation (water treatment)|sedimentation]] are widely employed in the [[water purification|purification]] of [[drinking water]] as well as in [[sewage treatment]], storm-water treatment and treatment of industrial wastewater streams. 
For drinking water, typical treatment processes consist of grates, coagulation, flocculation, sedimentation, granular filtration and disinfection.<ref>{{Cite web |url = http://app.knovel.com/hotlink/toc/id:kpWTPME003/water-treatment-process/water-treatment-process |title=Water Treatment Process Monitoring and Evaluation |date=2014-04-17 |access-date=2015-10-14 |website = Knovel |publisher = American Water Works Association (AWWA) |last = Beverly |first = Richard P}}</ref> The coagulation and flocculation steps are similar, causing particles to aggregate and fall out of solution, but may use different chemicals or physical movement of water.<ref name="Engelhardt" /> A variety of salts may be added to adjust the pH and act as [[clarifying agent]]s, depending on the water chemistry. These include [[sodium hydroxide]], [[calcium hydroxide]], [[aluminum sulfate]], [[aluminum oxide]], [[ferric sulfate]], [[ferric chloride]], [[sodium aluminate]], with flocculant aids [[polyaluminum chloride]], [[polyferric chloride]].<ref name="Engelhardt" />  A variety of [[cationic]], [[anionic]], and [[non-ionic]] [[polymer]]s are also used, typically with a [[molecular weight]] below 500,000.<ref name="Engelhardt" /> [[Polydiallyldimethyl ammonium chloride]] (polyDADMAC) and epiDMA (a [[copolymer]] of [[epichlorohydrin]] and [[dimethylamine]]) are common choices, though these can produce carcinogenic [[nitrosamine]]s.<ref name="Engelhardt" /> Sand, powerdered [[activated carbon]], and clay may also be used as [[nucleating agents]]; in some cases, these are re-used after extraction.<ref name="Engelhardt">{{cite web |title=Coagulation, Flocculation and Clarification of Drinking Water |author=Terry L. Engelhardt |date=April 2010 |url=https://sswm.info/sites/default/files/reference_attachments/ENGELHARDT%202010%20Coagulation%20Flocculation%20and%20Clarification.pdf}}</ref>

Biopolymers, especially, [[chitosan]], are increasingly popular as environmentally friendly flocculants.<ref>{{Cite journal |last1=Lamanna |first1=Leonardo |last2=Giacoia |first2=Gabriele |last3=Friuli |first3=Marco |last4=Leone |first4=Gabriella |last5=Carlucci |first5=Nicola |last6=Russo |first6=Fabrizio |last7=Sannino |first7=Alessandro |last8=Demitri |first8=Christian |date=2023-06-13 |title=Oil–Water Emulsion Flocculation through Chitosan Desolubilization Driven by pH Variation |journal=ACS Omega |language=en |volume=8 |issue=23 |pages=20708–20713 |doi=10.1021/acsomega.3c01257 |issn=2470-1343 |pmc=10268613 |pmid=37332801}}</ref> Chitosan is not only biodegradable but also exhibits a unique ability to bind with a wide range of contaminants, including heavy metals and organic pollutants, effectively removing them from water sources.<ref>{{Cite journal |last1=Pal |first1=Preeti |last2=Pal |first2=Anjali |last3=Nakashima |first3=Kazunori |last4=Yadav |first4=Brijesh Kumar |date=2021-03-01 |title=Applications of chitosan in environmental remediation: A review |url=https://www.sciencedirect.com/science/article/pii/S0045653520331313 |journal=Chemosphere |volume=266 |pages=128934 |doi=10.1016/j.chemosphere.2020.128934 |pmid=33246700 |bibcode=2021Chmsp.26628934P |issn=0045-6535|url-access=subscription }}</ref> 

Flocculation provides promising results for removing fine particles and treating stormwater runoff from transportation construction projects, but are not used by most state departments of transportation in the U.S. This may be due to regulative restrictions or insufficient guidance for [[soil]] sampling requirements in light of changing soil characteristics. States that must achieve a numeric turbidity limit are more inclined to use flocculants to ensure the appropriate level of treatment.<ref>{{Cite journal |last=Kazaz |first=Billur |date=July 2021 |title=State-of-the-Practice Review on the Use of Flocculants for Construction Stormwater Management in the United States |url=https://journals.sagepub.com/doi/10.1177/0361198121995192 |journal=Transportation Research Record |volume=2675 |issue=7 |pages=248–258 |doi=10.1177/0361198121995192 |via=Sage|url-access=subscription }}</ref>