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Reverse Osmosis Information

Ionic Solutes

 

Typical ionic rejection for reverse osmosis membranes @ 225 psi.

 
CATIONS
MATERIAL   SYMBOL  % REJECTION CTA  % REJECTION TFC
SODIUM  Na+ 90 - 93 99
CALCIUM  Ca+2  94 - 97 99
MAGNESIUM  Mg+2 96 - 98 99
POTASSIUM K+ 87 - 94 98
IRON  Fe+2  I95 - 98 99
MANGANESE  Mn+2  95 - 98 99
ALUMINUM  Al+3  98 - 99 99
AMMONIUM NH4+ 86 - 92 97
COPPER  Cu+2  98 - 99 99
NICKEL Ni+2  98 - 99 99
ZINC Zn+2  98 - 99 99
STRONTIUM  Sr+2  98 - 99  
CADMIUM  Cd+2  96 - 98 99
SILVER Ag 93 - 98 98
MERCURY  Hg+2  96 - 98 98
BARIUM  Ba+2  96 - 98 >99
CHROMIUM  Cr+3  96 - 99 99
LEAD  Pb+2  96 - 98 99
 

ANIONS

MATERIAL    SYMBOL  % REJECTION CTA  % REJECTION TFC
       
CHLORIDE Cl 87 - 93 99
BICARBONATE  HCO3- 90 - 95 98
NITRATE  NO3 60 - 75 97
FLUORIDE  F 87 - 93 98
SILICATE  SiO2-2 85 - 90 98
PHOSPHATE PO4-3  98 - 99 99
CHROMATE  CrO4-2  86 - 92 99
CYANIDE  Cn 86 - 92 95
SULFITE  SO3-2  96 - 98  
THIOSULFATE  S2O3-2  98 - 99 99
FERROCYANIDE  Fe(Cn)6-3  98 - 99 97
BROMIDE  Br 87 - 93 98
BORATE  B4O2-2  30 - 50 <50
SULFATE  SO4-2   98 - 99 99
ARSENIC  As-3  A94 - 96 99
SELENIUM  Se-2  94 - 96  99

 

Organic compounds such as Benzene, EDB, Trichloroethane, TCE, DBCP, THMs, Dichloroethylene, etc. are removed, but the % rejection is much lower, 50-80% typically for TFCs. Most organic compounds with molecular weights greater than 200 are highly rejected by both types of membrane. Materials, including some of the above compounds, that attack the membrane material will eventually destroy any rejecting ability of the active layer. The membrane will behave much more like a microfilter than reverse osmosis membrane. In the most severe cases with CTA membranes, the membrane can disappear entirely. Consult water treatment professionals in areas with known serious pollution problems.

Gases that are dissolved in the feed water will generally not be rejected to any significant extent. If the feed water has an odor problem, it is best to treat the problem separate from the R.O. system. Consult with a water treatment professional for specific solutions to unusual feed water situations.

Rejection characteristics of membranes are influenced by the particular mix of solutes in the water. The rejection will decrease at lower pressures, so use the numbers shown as a guideline only.

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