Raw water often contains impurities like sand, silt, gravels, organic
substances and microorganisms. Large and heavy particles such as sand, silt,
gravel, etc. readily settle out of water during presedimentation process.
However, the settling velocity of colloidal particles and organism, ranging
in size 0.01 to 1 micrometer, is so low that their removal by sedimentation
is not possible. Also, due to the size of the colloidal particles, the force
of attraction between particles is considerably less than the repelling
forces of the electrical charge.
Coagulation is the process of destabilizing colloidal particles and reducing
the forces, which tend to keep the colloidal particles apart so that particle
growth can occur because of particle collisions. Coagulant is a chemical
added to destabilize the colloidal particles and help floc formation.
The coagulation process is accomplished by rapid mixing to evenly disperse
the chemical coagulant. Napier Reid designs and manufactures wide range of
mixers to suit the process and client's requirement.