Problem Set 4 Solution

# Problem Set 4 Solution - will force water from areas of...

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Chemical Engineering 140 September 16, 2009 Problem Set #4 17. 4.2 F& R 18. 6.8 19. 7.1 20. 7.12 (Problem 7.12 does not include problems 7.13 and 7.14) 21. To provide fresh water in arid areas, seawater can be desalinated by reverse osmosis (RO). As the population of California rises and more years of draught occur, there is active consideration of building reverse-osmosis desalination units along the coast (such as San Diego county). The current cost of desalination by reverse osmosis is listed as around \$ 3.50 / 1000 gal 1 . a. Explain how desalination by reverse osmosis works and why is it expensive. b. Assume that all water for crop irrigation in California is supplied by RO desalination. How much would this cost expressed as a fraction of the current Sate budget? 1. www.livescience.com/environment/070625_desalination_membranes.html ).

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21 (5 Points) How Reverse Osmosis works Reverse Osmosis forces the water to go against the solute concentration gradient. So, this
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Unformatted text preview: will force water from areas of high solute concentration to areas of low solute concentration. This makes sense in purifying water since you do not want to be drinking any type of solute, just the water. Essentially, you are forcing the water away from the solutes (things you do not want to drink) by forcing it to go against its concentration gradient (thus the term Reverse osmosis). (2 points) Why expnsive? 1. Membranes are expensive, the unit itself is costly and you will need lot of water to get small amount of water with 90% purity. (1 point) (2 points) Different answer possible. Numbers for state budget and agriculture water (1 point) showing fraction (1 point) State Budget: 14 Billion Water : 2 Trillion gal Cost of irrigating= 3.5 \$/1000 gal *2 Trillion gal gal=6 Billion Fraction=6/14=0.42...
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