1) Objective: The
objective of pretreatment clarification is to remove suspended solids and
colloidal particles in water.
2) Method: The
method involves retention of cooling water in settling tanks and dosing
chemicals to expedite settling of suspended particles. The settling tank in
engineering language is called ‘Clarifier’.
§ The
settling tank or clarifier is basically fabricated of structural steel, usually
circular in shape with bottom made of concrete.
§ The
dosing chemical consists of coagulant and lime.
The settled sludge is removed periodically. The
sludge handling system consists of sludge pumps, sludge thickener and belt
press.
Many a times, the clarifier is fabricated to
serve water-softening purposes also. The system is known as clarifier-softener
that in addition to removing suspended solids & silica also removes
hardness. The water softening using ion-exchange principle is described below.
Coagulation: The destabilization and
initial aggregation of finely divided suspended solids by the addition of a
polyelectrolyte or a biological process.
Flocculation: Gentle stirring or agitation
to accelerate the agglomeration of particles to enhance sedimentation or
flotation.
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