The molar ratio of aluminum to phosphorus in the precipitation reaction is 1:1 which is equivalent to a weight ratio of 0.87:1.0 . Since alum contains 9% Al 9.7 kg of coagulant is theoretically required to precipitate 1 kg of P.
The reaction is complex because of secondary reactions with colloidal solids and alkalinity. Therefore, the theoretical quantity should be confirmed in the field.
