Incoming water contains 2.5 mg/L as a substance of natural alkalinity (HCO₃^-). The flow rate is 9.5 ML/day).

(a) What feed rate is required if the alum dose is 7 mg/L and is available with 87% purity.

(b) What is the annual cost of alum if it is available at $234 per Megagram (Mg). 

 Ans: 

(a) Given that purity, P = 87% = 0.87 

(b) Annual quantity cost of alum   

 Amount of alum needed per year = 76.4 Kg/day *365 day/year 

    = 27886 Kg/year = 27.886 Mg/year {1000 kg = 1 Mg)

      Alum cost = 27.886*$234   = $6,525/year.