What is coagulation?
Colloids are extremely stable substances and contain extremely small particles (0.00001mm) which have electrical forces which repel each other.
These particles are normally of negative charge. In order to destabilise the colloid a compound of positive charge is introduced which reduces these charges and so the particles tend to collide and form larger particles, called a pin floc.
The stage of coagulation can be summed up as colloid destabilisation by charge neutralisation. As it is a charge neutralisation process care should be taken to not overdose the coagulant as it will take the process too far and result in a positively charged colloid. As coagulation is a contact process a high rate of mixing is required. The process takes between 60 and 90 seconds to occur normally.
Coagulants are normally low to medium molecular weight with high electronic charges. Coagulants come in organic form such as polyamines, polydadamacs and tannins. Inorganic ones are normally iron or aluminium based.