Coagulation is when a chemical substance ( Organic, Inorganic or Blend ) is added to a colloidal suspension to cause its destabilisation by the reduction of forces that keep them apart. It involves the reduction or neutralisation of surface charges responsible for particle repulsions. This reduction in charge causes agglomeration creating lesser surface area and aids flocculation. Particles of larger size are then easier to settle and clarified effluent is obtained.