Two membrane systems are under consideration for treating cooling tower blowdown to reduce its volume. A low-pressure seawater reverse osmosis (SWRO) system will operate at 500 psi and pro­duce 720,000 gallons of permeate per day. It will have a fixed cost of $465 per day and an operating cost of $485 per day. A higher-pressure SWRO system operating at 800 psi will produce 950,000 gallons per day at a cost of $1280 per day. The fixed cost of the high-pressure SWRO system will be only $328 per day because fewer membranes will be required. How many gallons of blowdown water will require treatment each day for the two systems to break even?

What will be an ideal response?


Let x = gallons per day to breakeven

-465 - (485/720,000)x = -328 - (1280/950,000)x
0.00067376x = 137
x = 203,336 gallons per day

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