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Flocculation, in the field of Chemistry, is a process wherein colloids come out of suspension 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 in a liquid and not actually dissolved in a Solution. In the flocculated system, there is no formation of a cake, since all the flocs are in the suspension.

Coagulation and flocculation are important processes in water treatment with coagulation to destabilize particles through chemical reaction between coagulant and colloids, and flocculation to transport the destabilized particles that will cause collisions with floc.

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.

Basically, coagulation is a process of addition coagulant to destabilize a stabilized charged particle. Meanwhile, flocculation is a mixing technique that promotes agglomeration and makes particles settling down. The most common used coagulant is alum, Al2(SO4)3•14H2O.

The chemical reaction involved:

Al2(SO4)3•14H2O → 2Al(OH)3(s) + 6H+ + 3SO42- + 8H2O

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, and mixing time. The product of the mixing intensity and mixing time is used to describe flocculation process.

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.

Physical chemistry
For emulsions, flocculation describes clustering of individual dispersed droplets together, whereby the individual droplets do not lose their identity. Flocculation is thus the initial step leading to further aging of the emulsion (droplet coalescence and the ultimate separation of the phases).(1993) Flocculation is used in mineral dressing

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.

In civil engineering, which related to domestic water supply measurement of turbidity is very important as some water treatment process can affected by turbidity (WHO, 2011). High turbidity of raw water from stream or river can block filters during the process of water treatment. For example; filtration,coagulation, flocculation and sedimentation are part of water treatment processes designed to remove turbidity.

Biology
Flocculation is an important process in many different fields of science and biology is not an exception. In Biotechnology applications flocculation is used in conjunction with Microfiltration to improve the efficiency of biological feeds. If left untreated, cakes form and accumulate and that proves to be highly undesirable as it causes low cell viability. Research has shown that the addition of synthetic flocculants can increase the average particle size making the microfiltration more efficient. More detailed, the flocculant is added to the Bioreactor. Positively charged flocculants are regarded as more successful than negatively charged ones since the cells are generally negatively charged themselves.

Cheese industry
In the Dairy industry flocculation is widely employed to measure the progress of Curd formation while in the initial stages of making many cheeses to determine how long the curds must set. The reaction involving the Rennet micelles are modeled by Smoluchowski kinetics. During the renneting of milk the micelles can approach one another and flocculate, a process that involves Hydrolysis of molecules and macropeptides.

It is also worth mentioning that in flocculation is used during cheese wastewater treatment. Three different coagulants are mainly used:
 * 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 at the end of the fermentation. Subsequently the yeast can be collected from the bottom (Lager fermentation) or the top (ale fermentation)of the fermenter in order to be used for the next fermentation. It is not to be confused with sedimentation in colloidal dispersions as the mechanisms are different even though they appear to be pretty similar.

Water treatment process
Designing a water treatment plant is a very important and complex process. It requires consideration of a number of factors, such as the water chemistry, operating components, filter media and/or membrane systems. A typical water treatment plant is shown in Figure 1 and consists of grates, coagulation, flocculation, sedimentation, granular filtration and disinfection as the most important processes in water treatment.

Flocculation and sedimentation are widely employed in the purification of drinking water as well as sewage treatment, storm-water treatment and treatment of other industrial wastewater streams.

Jar test
The purpose of this test is to select types of coagulant (alum) and also to estimate the optimal dose needed in removing the charged particles that occurred in raw water. Jar test is an experiment to understand the processes of coagulatioan, flocculation and sedimentation (AWWA, 2011).

Jar test apparatus consists of six batch beakers, and equipped with a paddle mixer for each beaker. In a standard practice, jar test involving of rapid mixing, then follow by slow mixing and later with sedimentation process.

Deflocculation
Deflocculation is the exact opposite of flocculation. Usually in higher pH ranges in addition to low ionic strengths of soil solutions and domination of alkali metal cations the soil colloidal particles can be dispersed. The additive that prevents the colloids from forming flocs is called a deflocculant. 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. A deflocculated suspension shows zero or very low yield value".

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