Reverse osmosis

[Ncpfluke12]

Does anybody know how energy efficient reverse osmosis is? Wondering what the most energy efficient way of separating salt and water is and reverse osmosis was suggested by a lot of people. Just wondering if anyone had exact figures on what it takes to get 1 gallon of clean water. Thanks

[Acme]

Does anybody know how energy efficient reverse osmosis is? Wondering what the most energy efficient way of separating salt and water is and reverse osmosis was suggested by a lot of people. Just wondering if anyone had exact figures on what it takes to get 1 gallon of clean water. Thanks

Since reverse osmosis requires pressurized water, an exact figure on the energy used would depend on the specific pump setup used. This Wiki article mentions a pressure of 600-1200psi for desalinization.:

Reverse osmosis

This process requires that a high pressure be exerted on the high concentration side of the membrane, usually 217 bar (30250 psi) for fresh and brackish water, and 4082 bar (6001200 psi) for seawater, which has around 27 bar (390 psi)[6] natural osmotic pressure that must be overcome. ...

Here's a 1200 psi pump setup. PumpTec 80346 Water Otter 1200 psi Pressure Washer Pump

 

Specifications:

14.3 amp 120 volt motor

2.2 gallons per minute

 

Calculate:

14.3 amps * 120 volts = 1,716 watts = 1.7kilowatts

1.7kw * 10cents per kw hour = 17 cents per hour

17 cents per hr / 60 minutes = .28 cents per minute

.28 cents per minute / 2.2 gallons per minute = 0.12 cents per gallon

 

1.7kwhr/60 min= .0283kwhr per minute/2.2gpm=0.01287kwhr per gallon=46332joules per gallon

Edited September 30, 2015 by Acme

[dirtyamerica]

To get 1 gallon of clean water (or "permeate") it will require 1.33 gallons of "feed" water. Typical reverse osmosis units run at a 75% recovery rate (or how much clean water you make). You need a certain amount of water going to waste (called concentrate) to remove the impurities that are left behind. A proper set-up like this will also prevent the membranes from scaling up.

 

ROs are more effective if you are using water that has already been clarified, filtered and degasified.