Flocculation: Difference between revisions
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{{redirect|Flocculent|the galaxy type|Flocculent spiral galaxy}} | {{redirect|Flocculent|the galaxy type|Flocculent spiral galaxy}} | ||
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|title =[[International Union of Pure and Applied Chemistry|IUPAC]] definition<ref | |title =[[International Union of Pure and Applied Chemistry|IUPAC]] definition<ref>{{cite journal |last1=Slomkowski |first1=Stanislaw |last2=Alemán |first2=José V. |last3=Gilbert |first3=Robert G. |last4=Hess |first4=Michael |last5=Horie |first5=Kazuyuki |last6=Jones |first6=Richard G. |last7=Kubisa |first7=Przemyslaw |last8=Meisel |first8=Ingrid |last9=Mormann |first9=Werner |last10=Penczek |first10=Stanisław |last11=Stepto |first11=Robert F. T. |title=Terminology of polymers and polymerization processes in dispersed systems (IUPAC Recommendations 2011) |journal=Pure and Applied Chemistry |date=2011 |volume=83 |issue=12 |pages=2229–2259 |doi=10.1351/PAC-REC-10-06-03 }}</ref> | ||
|width = 33% | |width = 33% | ||
|quote = '''Flocculation (in polymer science)''': Reversible formation of aggregates in which the particles are not in physical contact. | |quote = '''Flocculation (in polymer science)''': Reversible formation of aggregates in which the particles are not in physical contact. | ||
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=== Jar test === | === Jar test === | ||
The process by which the dosage and choice of flocculant are selected is called a jar test. The equipment used for jar testing consists of one or more beakers, each equipped with a paddle mixer. After the addition of flocculants, rapid mixing takes place, followed by slow mixing and later the sedimentation process. Samples can then be taken from the aqueous phase in each beaker. <ref>{{cite book |author=<!--Staff writer(s); no by-line.--> |date=2011-06-01 |title=Operational Control of Coagulation and Filtration Processes (M37): AWWA Manual of Practice |url= https://engage.awwa.org/PersonifyEbusiness/Store/Product-Details/productId/6726|publisher= American Water Works Association|isbn=978-1583218013}}</ref> | The process by which the dosage and choice of flocculant are selected is called a jar test. The equipment used for jar testing consists of one or more beakers, each equipped with a paddle mixer. After the addition of flocculants, rapid mixing takes place, followed by slow mixing and later the sedimentation process. Samples can then be taken from the aqueous phase in each beaker.<ref>{{cite book |author=<!--Staff writer(s); no by-line.--> |date=2011-06-01 |title=Operational Control of Coagulation and Filtration Processes (M37): AWWA Manual of Practice |url= https://engage.awwa.org/PersonifyEbusiness/Store/Product-Details/productId/6726|publisher= American Water Works Association|isbn=978-1583218013}}</ref> | ||
== Mechanisms == | == Mechanisms == | ||
| Line 41: | Line 41: | ||
=== Physical chemistry === | === Physical chemistry === | ||
For [[emulsion]]s, flocculation describes clustering of individual dispersed droplets together, whereby the individual droplets do not lose their identity.<ref>Adamson | For [[emulsion]]s, flocculation describes clustering of individual dispersed droplets together, whereby the individual droplets do not lose their identity.<ref>{{cite book |last1=Adamson |first1=Arthur W. |last2=Gast |first2=Alice P. |title=Physical Chemistry of Surfaces |date=1997 |publisher=Wiley |isbn=978-0-471-14873-9 }}{{pn|date=July 2025}}</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>{{cite conference |last1=Sergeev |first1=P. V. |last2=Biletskyi |first2=V. S. |title=Investigation of laws of selective flocculation of coals with synthetic latexes |date=1997 |conference=9th International Conference on Coal Science (ICCS-9) and Exhibition |url=https://www.osti.gov/etdeweb/biblio/360716 }}</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 |title=Clustering of oil droplets in o/w emulsions: Controlling cluster size and interaction strength |journal=Food Research International |date=August 2019 |volume=122 |pages=537–547 |doi=10.1016/j.foodres.2019.04.027 |pmid=31229109 |doi-access=free }}</ref> | ||
=== Medical diagnostics === | === Medical diagnostics === | ||
In a [[medical laboratory]], flocculation is the core principle used in various diagnostic tests, for example the [[rapid plasma reagin]] test.<ref>{{ | 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 |title=Rapid plasma reagin test: High false positivity or important marker of high risk behavior |journal=Asian Journal of Transfusion Science |date=2015 |volume=9 |issue=1 |pages=109 |doi=10.4103/0973-6247.150979 |pmid=25722593 |pmc=4339923 |doi-access=free }}</ref> | ||
{{seealso|Porges-Meier reaction}} | {{seealso|Porges-Meier reaction}} | ||
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=== Biology === | === Biology === | ||
{{See also|Yeast flocculation#Process}} | {{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>{{ | 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 |last1=Han |first1=Binbing |last2=Akeprathumchai |first2=S. |last3=Wickramasinghe |first3=S. R. |last4=Qian |first4=X. |title=Flocculation of biological cells: Experiment vs. theory |journal=AIChE Journal |date=July 2003 |volume=49 |issue=7 |pages=1687–1701 |doi=10.1002/aic.690490709 |bibcode=2003AIChE..49.1687H }}</ref> | ||
=== Cheese industry === | === Cheese industry === | ||
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|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> | |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>{{ | Flocculation is also used during cheese [[wastewater treatment]]. Three different coagulants are mainly used:<ref>{{cite journal |last1=Rivas |first1=Javier |last2=Prazeres |first2=Ana R. |last3=Carvalho |first3=Fatima |last4=Beltrán |first4=Fernando |title=Treatment of Cheese Whey Wastewater: Combined Coagulation−Flocculation and Aerobic Biodegradation |journal=Journal of Agricultural and Food Chemistry |date=14 July 2010 |volume=58 |issue=13 |pages=7871–7877 |doi=10.1021/jf100602j |pmid=20557068 |bibcode=2010JAFC...58.7871R |hdl=20.500.12207/540 |hdl-access=free }}</ref> | ||
* FeSO<sub>4</sub> ([[iron(II) sulfate]]) | * FeSO<sub>4</sub> ([[iron(II) sulfate]]) | ||
* Al<sub>2</sub>(SO<sub>4</sub>)<sub>3</sub> ([[aluminium sulfate]]) | * Al<sub>2</sub>(SO<sub>4</sub>)<sub>3</sub> ([[aluminium sulfate]]) | ||
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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. | 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>{{ | [[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}}{{self-published inline|date=July 2025}}</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 |last1=Jin |first1=Yu-Lai |last2=Alex Speers |first2=R. |title=Flocculation of Saccharomyces cerevisiae |journal=Food Research International |date=August 1998 |volume=31 |issue=6–7 |pages=421–440 |doi=10.1016/S0963-9969(99)00021-6 }}</ref> | ||
=== Water treatment process === | === 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]] | [[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. | 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> | 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}}{{self-published inline|date=July 2025}}</ref> | ||
Biopolymers, especially, [[chitosan]], are increasingly popular as environmentally friendly flocculants.<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 |title=Oil–Water Emulsion Flocculation through Chitosan Desolubilization Driven by pH Variation |journal=ACS Omega |date=13 June 2023 |volume=8 |issue=23 |pages=20708–20713 |doi=10.1021/acsomega.3c01257 |pmid=37332801 |pmc=10268613 }}</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 |title=Applications of chitosan in environmental remediation: A review |journal=Chemosphere |date=March 2021 |volume=266 |article-number=128934 |doi=10.1016/j.chemosphere.2020.128934 |pmid=33246700 |bibcode=2021Chmsp.26628934P }}</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>{{ | 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 |last1=Kazaz |first1=Billur |last2=Perez |first2=Michael A. |last3=Donald |first3=Wesley N. |title=State-of-the-Practice Review on the Use of Flocculants for Construction Stormwater Management in the United States |journal=Transportation Research Record: Journal of the Transportation Research Board |date=July 2021 |volume=2675 |issue=7 |pages=248–258 |doi=10.1177/0361198121995192 }}</ref> | ||
== Deflocculation == | == Deflocculation == | ||
{{Main|Peptization}} | {{Main|Peptization}} | ||
Deflocculation is the opposite of flocculation, sometimes known as [[peptization]]. [[Sodium silicate]] (Na<sub>2</sub>SiO<sub>3</sub>) is a typical example. Usually, in higher [[pH]] ranges, in addition to low [[ionic strength]] of solutions and domination of monovalent metal [[cation]]s, the [[colloid]]al particles can be dispersed.<ref name="Deflocculation">{{ | Deflocculation is the opposite of flocculation, sometimes known as [[peptization]]. [[Sodium silicate]] (Na<sub>2</sub>SiO<sub>3</sub>) is a typical example. Usually, in higher [[pH]] ranges, in addition to low [[ionic strength]] of solutions and domination of monovalent metal [[cation]]s, the [[colloid]]al particles can be dispersed.<ref name="Deflocculation">{{cite book |title=Encyclopedic Dictionary of Polymers |chapter=Deflocculation |date=2007 |page=265 |doi=10.1007/978-0-387-30160-0_3313 |isbn=978-0-387-31021-3 |editor1-first=Jan W. |editor1-last=Gooch }}</ref> | ||
The additive that prevents the colloids from forming flocs is called a deflocculant. For deflocculation imparted through electrostatic barriers, the efficacy of a deflocculant can be gauged in terms of [[zeta potential]]. According to the Encyclopedic Dictionary of Polymers deflocculation is ''"''a state or condition of a dispersion of a solid in a liquid in which each solid particle remains independent and unassociated with adjacent particles (much like [[Emulsion|emulsifier]]). A deflocculated suspension shows zero or very low yield value".<ref name="Deflocculation"/> | The additive that prevents the colloids from forming flocs is called a deflocculant. For deflocculation imparted through electrostatic barriers, the efficacy of a deflocculant can be gauged in terms of [[zeta potential]]. According to the Encyclopedic Dictionary of Polymers deflocculation is ''"''a state or condition of a dispersion of a solid in a liquid in which each solid particle remains independent and unassociated with adjacent particles (much like [[Emulsion|emulsifier]]). A deflocculated suspension shows zero or very low yield value".<ref name="Deflocculation"/> | ||
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* John Gregory (2006), ''Particles in water: properties and processes'', Taylor & Francis, {{ISBN|1-58716-085-4}} | * John Gregory (2006), ''Particles in water: properties and processes'', Taylor & Francis, {{ISBN|1-58716-085-4}} | ||
* John C. Crittenden, R. Rhodes Trussell, David W. Hand, Kerry J. Howe, George Tchobanoglous (2012), ''MWH's water treatment: principles and design, third edition'', John Wiley & Sons, {{ISBN|978-0-470-40539-0}} | * John C. Crittenden, R. Rhodes Trussell, David W. Hand, Kerry J. Howe, George Tchobanoglous (2012), ''MWH's water treatment: principles and design, third edition'', John Wiley & Sons, {{ISBN|978-0-470-40539-0}} | ||
* {{cite journal |last1=Thomas |first1=D.N. |last2=Judd |first2=S.J. |last3=Fawcett |first3=N. |title=Flocculation modelling: a review |journal=Water Research |date=May 1999 |volume=33 |issue=7 |pages=1579–1592 |doi=10.1016/S0043-1354(98)00392-3 |bibcode=1999WatRe..33.1579T }} | |||
* {{cite journal |last1=Watanabe |first1=Yoshimasa |title=Flocculation and me |journal=Water Research |date=May 2017 |volume=114 |pages=88–103 |doi=10.1016/j.watres.2016.12.035 |pmid=28229952 |bibcode=2017WatRe.114...88W }} | |||
* {{cite journal |last1=Gregory |first1=John |last2=O'Melia |first2=Charles R. |title=Fundamentals of flocculation |journal=Critical Reviews in Environmental Control |date=January 1989 |volume=19 |issue=3 |pages=185–230 |doi=10.1080/10643388909388365 |bibcode=1989CRvEC..19..185G }} | |||
* {{cite journal |last1=Brostow |first1=Witold |last2=Pal |first2=Sagar |last3=Singh |first3=Ram P. |title=A model of flocculation |journal=Materials Letters |date=September 2007 |volume=61 |issue=22 |pages=4381–4384 |doi=10.1016/j.matlet.2007.02.007 |bibcode=2007MatL...61.4381B }} | |||
* {{cite journal |last1=Camp |first1=Thomas R. |title=Flocculation and Flocculation Basins |journal=Transactions of the American Society of Civil Engineers |date=January 1955 |volume=120 |issue=1 |pages=1–16 |doi=10.1061/TACEAT.0007139 }} | |||
{{Separation processes}} | {{Separation processes}} | ||
Latest revision as of 20:02, 30 October 2025
Template:Short description Script error: No such module "redirect hatnote".
<templatestyles src="Template:Quote_box/styles.css" />
Flocculation (in polymer science): Reversible formation of aggregates in which the particles are not in physical contact.
Agglomeration (except in polymer science)
Coagulation (except in polymer science)
Flocculation (except in polymer science)
Process of contact and adhesion whereby dispersed molecules or particles are held together by weak physical interactions ultimately leading to phase separation by the formation of precipitates of larger than colloidal size.
- In contrast to aggregation, agglomeration is a reversible process.
- The definition proposed here is recommended for distinguishing agglomeration from aggregation. The particles that comprise agglomerates can be dispersed again.
- This quotation is from the Purple Book (Compendium of Polymer Terminology and Nomenclature: IUPAC Recommendations, 2008).[2]
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In colloidal chemistry, flocculation is a process by which colloidal particles come out of suspension to sediment in the form of Template:Linktext or flake, either spontaneously or due to the addition of a clarifying agent. The action differs from precipitation in that, prior to flocculation, colloids are merely suspended, under the form of a stable dispersion (where the internal phase (solid) is dispersed throughout the external phase (fluid) through mechanical agitation) and are not truly dissolved in solution.
Coagulation and flocculation are important processes in fermentation and water treatment with coagulation aimed to destabilize and aggregate particles through chemical interactions between the coagulant and colloids, and flocculation to sediment the destabilized particles by causing their aggregation into floc.Script error: No such module "Unsubst".
Term definition
According to the IUPAC definition, flocculation is "a process of contact and adhesion whereby the particles of a dispersion form larger-size clusters". Flocculation is synonymous with agglomeration and coagulation/coalescence.[3][4]
Basically, coagulation is a process of addition of coagulant to destabilize a stabilized charged particle. Meanwhile, flocculation is a technique that promotes agglomeration and assists in the settling of particles. The most common used coagulant is alum, Al2(SO4)3·14H2O.
The chemical reaction involved:
- Al2(SO4)3 · 14 H2O → 2 Al(OH)3(s) + 6 H+ + 3 Template:Chem/link + 8 H2O
During flocculation, gentle mixing accelerates the rate of particle collision, and the destabilized particles are further aggregated and enmeshed into larger precipitates. Flocculation is affected by several parameters, including mixing shear and intensity, time and pH. The product of the mixing intensity and mixing time is used to describe flocculation processes.
Jar test
The process by which the dosage and choice of flocculant are selected is called a jar test. The equipment used for jar testing consists of one or more beakers, each equipped with a paddle mixer. After the addition of flocculants, rapid mixing takes place, followed by slow mixing and later the sedimentation process. Samples can then be taken from the aqueous phase in each beaker.[5]
Mechanisms
One mechanism for flocculation is coacervation.
Applications
Surface chemistry
In colloid chemistry, flocculation refers to the process by which fine particulates are caused to clump together into a floc. The floc may then float to the top of the liquid (creaming), settle to the bottom of the liquid (sedimentation), or be readily 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 emulsions, flocculation describes clustering of individual dispersed droplets together, whereby the individual droplets do not lose their identity.[6] 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,[7] but can be also used in the design of physical properties of food and pharmaceutical products.[8]
Medical diagnostics
In a medical laboratory, flocculation is the core principle used in various diagnostic tests, for example the rapid plasma reagin test.[9] Script error: No such module "Labelled list hatnote".
Civil engineering/earth sciences
In civil engineering, and in the earth sciences, flocculation is a condition in which clays, polymers or other small charged particles become attached and form a fragile structure, a floc. In dispersed clay 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
Script error: No such module "Labelled list hatnote". 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.[10]
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.[11] The reaction involving the rennet micelles are modeled by Smoluchowski kinetics.[11] During the renneting of milk the micelles can approach one another and flocculate, a process that involves hydrolysis of molecules and macropeptides.[12]
Flocculation is also used during cheese wastewater treatment. Three different coagulants are mainly used:[13]
- FeSO4 (iron(II) sulfate)
- Al2(SO4)3 (aluminium sulfate)
- FeCl3 (iron(III) chloride)
Brewing
Script error: No such module "Labelled list hatnote". 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.[14] 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.[15]
Water treatment process
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Flocculation and sedimentation are widely employed in the 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.[16] 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.[17] A variety of salts may be added to adjust the pH and act as clarifying agents, 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.[17] A variety of cationic, anionic, and non-ionic polymers are also used, typically with a molecular weight below 500,000.[17] Polydiallyldimethyl ammonium chloride (polyDADMAC) and epiDMA (a copolymer of epichlorohydrin and dimethylamine) are common choices, though these can produce carcinogenic nitrosamines.[17] Sand, powerdered activated carbon, and clay may also be used as nucleating agents; in some cases, these are re-used after extraction.[17]
Biopolymers, especially, chitosan, are increasingly popular as environmentally friendly flocculants.[18] 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.[19]
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.[20]
Deflocculation
Script error: No such module "Labelled list hatnote". Deflocculation is the opposite of flocculation, sometimes known as peptization. Sodium silicate (Na2SiO3) is a typical example. Usually, in higher pH ranges, in addition to low ionic strength of solutions and domination of monovalent metal cations, the colloidal particles can be dispersed.[21] The additive that prevents the colloids from forming flocs is called a deflocculant. For deflocculation imparted through electrostatic barriers, the efficacy of a deflocculant can be gauged in terms of zeta potential. According to the Encyclopedic Dictionary of Polymers deflocculation is "a state or condition of a dispersion of a solid in a liquid in which each solid particle remains independent and unassociated with adjacent particles (much like emulsifier). A deflocculated suspension shows zero or very low yield value".[21]
Deflocculation can be a problem in wastewater treatment plants, as it commonly causes problems with sludge settling and deterioration of the effluent quality.
See also
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References
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- ↑ IUPAC, Compendium of Chemical Terminology, 5th ed. (the "Gold Book") (2025). Online version: (2006–) "flocculation". Script error: No such module "CS1 identifiers".Script error: No such module "TemplatePar".
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Further reading
- John Gregory (2006), Particles in water: properties and processes, Taylor & Francis, Template:ISBN
- John C. Crittenden, R. Rhodes Trussell, David W. Hand, Kerry J. Howe, George Tchobanoglous (2012), MWH's water treatment: principles and design, third edition, John Wiley & Sons, Template:ISBN
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