Doses Of Coagulants
It depends upon the following factors :
Turbidity Of Water: Greater the turbidity of water, more is coagulant required. The amount per liter varies from 0.03-0.13 gms or more of alum or iron.
Colour Of Water : It also affects the dose of coagulant.
pH Value: For alum, if the pH is lower than the optimum, the insoluble floc becomes soluble and the floc disappears. And if the pH Value is more than the optimum, the aluminum hydroxide ionizes into an aluminate which is both negative in electrical charge and soluble in water. For alum the best value of pH is 6-8, for iron salts 8-10.
Temperature Of Water: The amount of coagulant increases with lower temperature because of slower relation of floc formation.
Time Of Settlement: The dose increases with reduction in time of settlement.