Chemical precipitation and coagulation

CHEMICAL PRECIPITATION AND COAGULATION

• Chemical precipitation refers to removal of dissolved ions from water by addition of certain chemicals which precipitate the impurities by changing their liquid phase to the solid phase.
• Coagulation refers to a technique in water treatment applied before sedimentation and filtration to enhance the ability of a treatment process to remove particles.
• It involves the addition of a chemical followed by rapid mixing to dissolve the chemical and distribute it evenly in the water
• The purpose of coagulation is to destabilise the particles and enable them to become attached to other particles so that they might be removed in subsequent processes
• Coagulation and flocculation occur in successive steps, allowing particle collision and growth of floc.
• The main chemicals used for flocculation are Aliminium Sulphate (Al2(SO4)3.7H2O) or Alum and Poly Aluminium Chloride (PAC or liquid alum), Alum Potash and Iron salts (Ferric chloride or Ferric Sulphate)