Flocculation

IUPAC definition^[1]

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]

In colloidal chemistry, flocculation is a process by which colloidal particles come out of suspension to sediment in the form of floc 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 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.^{[clarification needed]}

YouTube Encyclopedic

1/5
Views:
692 490
143 016
77 606
8 446
14 194

Transcription

Let's do a small experiment Would you rather drink this water, or this water? Well, of course you would choose the water on the left Unfortunately, some people in other parts of the world have no choice at all Did you know that small floating particles in drinking water can make you sick? Imagine we have a super powerful microscope and we can zoom into the water. ZOOM! What will we find? What are these small, floating particles, and how do they float? These particles are of two types: inorganic (like clay, silt, and mineral oxides) and organic (such as algae, protozoa, and bacteria). The bacteria, once ingested by humans, can sometimes be fatal. All of these small particles are able to float, because they are not heavy enough to settle to the bottom by gravity. Suspended particles that are too light and small to settle are called colloids. When looked at together, these colloids cause a state of cloudiness or haziness, known as turbidity. The more cloudy a fluid looks, the more turbid it is. Here we see four beakers of water with increasing levels of turbidity, from left to right. There is a relation between turbidity and the risk of getting a disease. Science shows that the more turbid the drinking water is, the higher the risk of getting sick is. Now why is this? This is because toxic compounds can adsorb, that is, stick to the surface of the suspended colloids. The more colloids there are, the more toxic the water can become. These toxic materials and bacteria can cause cholera, salmonellosis, hepatitis A, dysentery, and e-coli infection. These illnesses effect and kill millions of people a year, and are especially dangerous to children, whose weak immune systems cannot provide an adequate defense. Fortunately, we can do something about this! One of the very practical ways to clean this turbid water is called flocculation Flocculation is the process in which colloids aggregate, or come together to form larger particles called flocks, by the addition of a chemical called a flocculant. Typical flocculants include Alum and Ferrix, because they work well with high turbidity fluid mixtures Now, let's demonstrate how flocculation works. First, we'll need to go out and collect some muddy water from the Charles River Here are two beakers filled with the same amount of muddy Charles River water On the left is our control, which will remain untouched, and on the right, we'll add 3mL of prepared flocculant solution Then we'll stir for two minutes, and wait Wow! What just happened? The colloids in the turbid water on the left may never settle whereas, with the addition of just a little bit of flocculant the water on the right became clear. In order to make this water potable, it will require skimming and filtration and maybe some additional treatment If you're wondering what's going on, let's explain how this flocculant business works. Almost all colloids have negatively charged surfaces This means that positive ions, or charged particles in water will attract to the colloid surface, forming a first layer. Recall how like poles of a magnet will repel, while opposite poles will attract. The same occurs with colloids in water. A diffuse layer, made up of a mix of positive and negative ions will then surround the first forming what is called a double layer. This double layer provides a repulsive force which prevents two colloids from sticking to each other. Once the flocculant is added, it adheres to the surfaces of the particles, compressing the double layer, and allowing the colloids to stick to each other and form "flocks" These flocks are now heavy enough to settle to the bottom by gravity. Given how effective flocculation is, many countries around the world use this method for cleaning their water supplies. Did you know that Singapore, for instance, produces drinking water from sewer water using a number of methods, including flocculation? As the global population increases and freshwater resources become more and more scarce flocculation is one tool that can supply clean, healthy, and tasty drinking water worldwide.

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 mixing 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 SO²⁻
₄ + 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 speeds, mixing intensity, mixing 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]

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]

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

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

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 primarily 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 insolubable 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

4x speed video of floc settling after adding flocculant polymers during a jar test.

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. Typical treatment processes consist of grates, coagulation, flocculation, sedimentation, granular filtration and disinfection.^[16] As the demand for eco-friendly solutions in the flocculation process continues to grow, biopolymers are emerging as a highly promising solution. Among these, chitosan stands out for its exceptional properties, making it a top contender in this environmentally-conscious endeavor.^[17] 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.^[18]

Deflocculation

Deflocculation is the exact opposite of flocculation, also 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.^[19] 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".^[19]

Deflocculation can be a problem in wastewater treatment plants as it commonly causes sludge settling problems and deterioration of the effluent quality.

References

^ Slomkowski, Stanislaw; Alemán, José V.; Gilbert, Robert G.; Hess, Michael; Horie, Kazuyuki; Jones, Richard G.; Kubisa, Przemyslaw; Meisel, Ingrid; Mormann, Werner; Penczek, Stanisław; Stepto, Robert F. T. (2011). "Terminology of polymers and polymerization processes in dispersed systems (IUPAC Recommendations 2011)" (PDF). Pure and Applied Chemistry. 83 (12): 2229–2259. doi:10.1351/PAC-REC-10-06-03. S2CID 96812603. Archived from the original (PDF) on 2013-10-20. Retrieved 2013-07-27.
^ Richard G. Jones; Edward S. Wilks; W. Val Metanomski; Jaroslav Kahovec; Michael Hess; Robert Stepto; Tatsuki Kitayama, eds. (2009). Compendium of Polymer Terminology and Nomenclature (IUPAC Recommendations 2008) "The Purple Book" (2nd ed.). RSC Publishing. ISBN 978-0-85404-491-7.
^ IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version: (2006–) "flocculation". doi:10.1351/goldbook.F02429
^ Hubbard, Arthur T. (2004). Encyclopedia of Surface and Colloid Science. CRC Press. p. 4230. ISBN 978-0-8247-0759-0. Retrieved 2007-11-13.
^ Operational Control of Coagulation and Filtration Processes (M37): AWWA Manual of Practice. American Water Works Association. 2011-06-01. ISBN 978-1583218013.
^ Adamson A.W. and Gast A.P. (1997) "Physical Chemistry of Surfaces", John Wiley and Sons.
^ 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.
^ Fuhrmann, Philipp L.; Sala, Guido; Stieger, Markus; Scholten, Elke (2019-08-01). "Clustering of oil droplets in o/w emulsions: Controlling cluster size and interaction strength". Food Research International. 122: 537–547. doi:10.1016/j.foodres.2019.04.027. ISSN 0963-9969. PMID 31229109.
^ Arora, Satyam; Doda, Veena; Rani, Sunita; Kotwal, Urvershi (2015). "Rapid plasma reagin test: High false positivity or important marker of high risk behavior". Asian Journal of Transfusion Science. 9 (1): 109. doi:10.4103/0973-6247.150979. ISSN 0973-6247. PMC 4339923. PMID 25722593.
^ Han, Binbing; Akeprathumchai, S.; Wickramasinghe, S. R.; Qian, X. (2003-07-01). "Flocculation of biological cells: Experiment vs. theory". AIChE Journal. 49 (7): 1687–1701. Bibcode:2003AIChE..49.1687H. doi:10.1002/aic.690490709. ISSN 1547-5905.
^ ^a ^b Fox, Patrick F. (1999). Cheese Volume 1: Chemistry, Physics, and Microbiology (2nd ed.). Gaithersburg, Maryland: Aspen Publishers. pp. 144–150. ISBN 978-0-8342-1378-4.
^ Fox, Patrick F. (2004). Cheese - Chemistry, Physics and Microbiology (3rd ed.). Elsevier. p. 72. ISBN 978-0-12-263653-0.
^ Rivas, Javier; Prazeres, Ana R.; Carvalho, Fatima; Beltrán, Fernando (2010-07-14). "Treatment of Cheese Whey Wastewater: Combined Coagulation−Flocculation and Aerobic Biodegradation". Journal of Agricultural and Food Chemistry. 58 (13): 7871–7877. doi:10.1021/jf100602j. hdl:20.500.12207/540. ISSN 0021-8561. PMID 20557068.
^ Brungard, Martin (20 February 2018). "Water Knowledge". Bru'n Water.
^ Jin, Y-L.; Speers, R.A.. (1999). "Flocculation in Saccharomyces cerevisiae". Food Res. Int. 31 (6–7): 421–440. doi:10.1016/S0963-9969(99)00021-6.
^ Beverly, Richard P (2014-04-17). "Water Treatment Process Monitoring and Evaluation". Knovel. American Water Works Association (AWWA). Retrieved October 14, 2015.
^ Lamanna, Leonardo; Giacoia, Gabriele; Friuli, Marco; Leone, Gabriella; Carlucci, Nicola; Russo, Fabrizio; Sannino, Alessandro; Demitri, Christian (2023-06-13). "Oil–Water Emulsion Flocculation through Chitosan Desolubilization Driven by pH Variation". ACS Omega. 8 (23): 20708–20713. doi:10.1021/acsomega.3c01257. ISSN 2470-1343. PMC 10268613. PMID 37332801.
^ Pal, Preeti; Pal, Anjali; Nakashima, Kazunori; Yadav, Brijesh Kumar (2021-03-01). "Applications of chitosan in environmental remediation: A review". Chemosphere. 266: 128934. Bibcode:2021Chmsp.26628934P. doi:10.1016/j.chemosphere.2020.128934. ISSN 0045-6535. PMID 33246700.
^ ^a ^b Gooch, Jan W., ed. (2007-01-01). "Deflocculation". Encyclopedic Dictionary of Polymers. Springer New York. p. 265. doi:10.1007/978-0-387-30160-0_3313. ISBN 978-0-387-31021-3.

v t e Separation processes
Processes	Absorption Acid–base extraction Adsorption Chromatography Cross-flow filtration Crystallization Cyclonic separation Decantation Dialysis Dissolved air flotation Distillation Drying Electrochromatography Electrofiltration Extraction Filtration Flocculation Froth flotation Gravity separation Leaching Liquid–liquid extraction Electroextraction Microfiltration Osmosis Precipitation Recrystallization Reverse osmosis Sedimentation Solid-phase extraction Sublimation Ultrafiltration
Devices	API oil–water separator Belt filter Centrifuge Depth filter Electrostatic precipitator Evaporator Filter press Fractionating column Leachate Mixer-settler Protein skimmer Rapid sand filter Rotary vacuum-drum filter Scrubber Spinning cone Still Sublimation apparatus Vacuum ceramic filter
Multiphase systems	Aqueous two-phase system Azeotrope Eutectic
Concepts	Unit operation

From Wikipedia, the free encyclopedia