According to the IUPAC definition, flocculation is “a process of contact and adhesion whereby the particles of a dispersion form larger-size clusters”. 

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. While coagulation neutralizes the charges on the particles, flocculation enables them to bind together, making them bigger, so that they can be more easily separated from the liquid.

An Ancient narrative on Use of Coagulant for treating water has history around 2000 BC when the Egyptians used almonds, smeared around vessels, to treat river water

The coagulant is properly dispersed to promote particle collisions with rapid mixing. The metal coagulant such as hydrolysis products formed within 0.01 to 1.0 seconds tend to be the most effective for destabilization – this is why adjustment of pH and post-dosing of more coagulant is rarely effective after the initial coagulant addition. 

Types of coagulants :Organic and inorganic are two types of coagulants that are used in water and wastewater treatment.. 

Inorganic coagulants include:

• Aluminum coagulants – e.g. aluminum sulphate, aluminum chloride and sodium aluminate
• Iron coagulants – e.g. ferric sulphate, ferrous sulphate, ferric chloride and ferric chloride sulphate

Organic coagulants include:

• Polyamines
• Polydiallyldimethylammonium chloride (Poly DADMACs)
• Polytannate

 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.  

Inorganic coagulants :

Both aluminum and iron coagulants have been proven to be very effective at removing most suspended solids. They offer a number of advantages:

• Enable highly charged ions to give a high charge density to neutralise suspended particles, which allows hydrated inorganic hydroxides to form and produce short polymer chains that enhance microfloc formation and heavy floc
• Capable of removing a portion of the organic precursors which may combine with chlorine to form disinfection by-products
• Low unit cost and widespread availability 

They have some disadvantages:

• They create large volumes of floc, rich in metal, which must be disposed of in an environmentally appropriate manner, which can add significant cost to disposal
• They operate at lower pH range consequently needs use of acid resistant 
• Aluminum sulphate and chloride, ferric sulphate and chloride and ferrous sulphate due to acidic nature lower ph. Sodium aluminate, on the other hand, will add alkalinity and raise pH.