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Some Interesting Reverse Osmosis
and Water Facts
The process of osmosis was discovered by Abbe Nollet in 1748
Research on Reverse Osmosis began in the 1950's at the University of Florida
where Reid and Breton were able to demonstrate desalination properties of cellulose
acetate membrane.
First Spiral wound elements produced - 1967
First Thin Film Composite (TFC) membrane produced - 1977
Distribution of the Water on Earth
Total water equals 1,360,000,000 cubic km
Percentage of Total
| Oceans |
97.2 |
|
Icecaps and Glaciers
|
2.15 |
| Ground Water |
0.62 |
| Freshwater Lakes |
0.009 |
| Salt Lakes & Inland seas |
0.008 |
| Soil Moisture |
0.005 |
| Atmosphere |
0.001 |
| Rivers |
0.0001 |
| Total |
100% |
Worldwide rainfall equals 113,000 billion cubic meters per year.
The salinity of the open Oceans varies from 20,000 ppm to 40,000 ppm but the salinity
of a significant majority of the ocean area is between 34,000 to 36,000 ppm.
The ocean is in chemical equilibrium. This means the proportion and amounts
of dissolved salts per unit volume of ocean are nearly constant.
The Great Lakes contain nearly 5% of all the fresh water on Earth.
The average human body contains 10 gallons of water.
Some useful Reverse Osmosis Terms and Equations
Concentrate
Brine discharge or concentrate is Feed water minus the permeate. Salts are concentrated
in the stream flowing out of the membrane element.
Feed Water
This is the name applied to the filtered seawater stream that enters the membrane
element.
Osmotic Pressure
The force exerted by dissolved solids in solution. It can be approximated at 11psi
per 1000ppm (mg/L) of dissolved solids.
Permeate
Permeate or product is the water that passes (permeates) through the semi-permeable
membrane.
Permeate Recovery Rate
Recovery or conversion rate of feed water to product (permeate) is
defined by
R = 100% * (PR/FR)
R = recovery rate (in %)
PR = product water flow rate
FR = feed water flow rate.
Salt Rejection
Salt rejection is the percentage of salt that is excluded from the product water
(permeate).
SR = 100% - (CP/CF)
SR is the salt rejection (in %)
CP = the salt concentration in the permeate
CF=the mean salt concentration in feed
For a TFC Seawater membrane element salt rejection is typically 99.5% measured
at 800 psi, 35000 ppm NaCl @ 25°C (77°F). Under these conditions the permeate
TDS would measure approx. 175 ppm.
Temperature Correction Factor
The output of a TFC membrane is normalized at 25° C (77°F) As the temperature
goes down the out put is reduced. Conversely as the temperature goes up the output
is increased. The amount of change can be approximated by assuming a 2% difference
per degree F (from the normalized 77°F flow).
FC= FN * (1- (( 77-T)*.02))
FC = Corrected flow
FN = Normalized flow
