When calculating antiscalant dosage, inhibition of all scales must be considered. Potentials scales that can form are:
Calcium carbonate
Calcium phosphate
Calcium fluoride
Calcium sulfate
Barium sulfate
Strontium sulfate
metal hydroxides (iron, aluminum)
Silicate scales
Calcium hardness alone cannot be used to determine scaling tendency, as it must combine with an anion to form a scale. In order to calculate the antiscalant dosage, a comprehensive water analysis must be performed that contains the following parameters:
Cations:
Ca, Mg, Ba, Sr, Fe, Al, Mn, Na
Anions:
Alkalinity, SO4, F, PO4, SiO2
Other Required Information:
Feed water pH (measured upon collection at site), Feed water Temperature (measured upon collection at site), %Recovery, Membrane Salt Rejection (available on membrane cut sheet), and system configuration (# stages, # Pressure Vessels/stage)
Once all the above information is available, the scaling potential can be calculated by your antiscalant supplier, and the appropriate antiscalant can be selected with a corresponding dosage.
