A waste water plant may have to remove phosphorus (phosphate) from its wastewater prior to discharge to the River. The DNR may set an effluent standard as low as 0.1 mg P/L. You are to make some preliminary calculations about phosphorus removal by chemical precipitation. Use the following data to make your calculations.
Design average wet-weather flow (AWW) = 10 MGD
Total phosphorus concentration = 6 mg P/L
Alkalinity = 120 mg/L as CaCO3
pH = 6.9
Alum: $1/gallon; density = 11.1 lb/gallon; 42% active alum by weight
FeCl3: $1.10/gallon; density = 11.3 lb/gallon; 35% active FeCl3 by weight
(a) Calculate the annual costs ($/yr) of meeting the proposed effluent requirement of 0.1 mg P/L using alum to precipitate AlPO4(s). Assume the chemical formula for alum is Al2(SO4)3·18H2O (MW = 666).
(b) Assuming an interest rate of 6% and a design life of 20 years, calculate the net present worth of the annual costs determined in part (a).
(c) Calculate the annual costs ($/yr) of meeting the proposed effluent requirement of 0.1 mg P/L using FeCl3 to precipitate FePO4(s).