Engineering Economy 7th Edition by Leland Blank ,Anthony Tarquin

Exercise 47

Different membrane systems are under consideration for treating 3 million gallons per day (MGD) of cooling tower blowdown water to reduce its volume. Option 1 is a low-pressure seawater reverse osmosis (SWRO) system that will operate at 500 psi with a fixed cost of $465 per day and an operating cost of $0.67 per 1000 gallons. A second option is a higher-pressure SWRO system offered by vendor X that operates at 800 psi and will have a lower fixed cost of $328 per day (because of fewer membranes); however, its operating cost will be $1.35 per 1000 gallons. A third option is also a high-pressure SWRO system from vendor Y, who claims that its system will have a lower operating cost of $1.28 per 1000 gallons and the same fixed cost as that of vendor X. Determine if the selection of a low- or high-pressure system is dependent on the lower operating cost offered by vendor Y.