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The overlap between the diffuse layers of two approaching particles results in a repulsive double layer interaction potential, which leads to particle stabilization. When salt is added to the suspension, the electrical double layer repulsion is screened, and van der Waals attraction become dominant and induce fast aggregation.
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.
Curdling is the breaking of an emulsion or colloid into large parts of different composition through the physio-chemical processes of flocculation, creaming, and coalescence. [1] Curdling is purposeful in the production of cheese curd and tofu ; undesirable in the production of a sauce , cheese fondue or a custard .
Particles finer than 0.1 μm (10 −7 m) in water remain continuously in motion due to electrostatic charge (often negative) which causes them to repel each other. [citation needed] Once their electrostatic charge is neutralized by the use of a coagulant chemical, the finer particles start to collide and agglomerate (collect together) under the influence of Van der Waals forces.
Flocculation occurs when there is an attractive force between the droplets, so they form flocs, like bunches of grapes. This process can be desired, if controlled in its extent, to tune physical properties of emulsions such as their flow behaviour. [ 14 ]
Coagulation is a chemical process that involves neutralization of charge whereas flocculation is a physical process and does not involve neutralization of charge. The coagulation-flocculation process can be used as a preliminary or intermediary step between other water or wastewater treatment processes like filtration and sedimentation .
For example, coagulation can be used to describe irreversible, permanent aggregation where the forces holding the particles together are stronger than any external forces caused by stirring or mixing. Flocculation can be used to describe reversible aggregation involving weaker attractive forces, and the aggregate is usually called a floc.
This enzyme is responsible for the coagulation of the milk proteins to produce curds. Cheese produced this way is neither vegetarian nor kosher. Coagulation can also be achieved using acids, but this method yields lower-quality cheddar. The two key components of natural rennet are chymosin and bovine pepsin. Extracts from plants such as nettles ...