Figure 1.2

Typical Membrane Element

Rejections/Passages

SALTS

CATIONS

 

 

Percent

Maximum

 

 

 

 

 

Percent

Passage

Concentration

Name

Symbol

Rejection

(Avg)

Percent

Sodium

Na+

94-96

5

5-10

Calcium

Ca+2

96-98

3

*

Magnesium

M g+2

96-98

3

*

Potassium

K+1

94-96

5

5-10

Iron

Fe+2

98-99

2

*

Manganese

M n+2

98-99

2

*

Aluminum

Al+3

99+

1

10-20

Ammonium

N H4+1

88-95

8

3-8

Copper

Cu+2

98-99

1

10-20

Nickel

Ni+2

98-99

1

10-20

Zinc

Zn+2

98-99

1

10-20

Strontium

Sr+2

96-99

3

-

Hardness

Ca & Mg

96-98

3

*

Cadmium

Cd+2

96-98

3

10-20

Silver

Ag+1

94-96

5

*

Mercury

Hg+2

96-98

3

-

To estimate passage of salts for membrane elements other than SEPA- HR, take the passage for the SEPA-HR and multiply by the factor for the passage for the particular membrane element. The factors are:

SEPA-SR is 1.6 times SEPA-HR passage

SEPA-PR is 2.5 times SEPA-HR passage

Operation of the SEPA-HR membrane element at pressures over 400 psig (27.6 barg) will reduce salt passage slightly. Operation at 200 psig (13.8 bar) will increase the passage of monovalent ions by approximately 2.0 times and the passage of multivalent ions will increase by 1.5 times the 400 psig (27.6 bar) passage.

For SEPA membrane elements with larger pores than the SEPA-PR it is recommended that actual tests be run prior to estimating the permeate quality.

The maximum concentrations given in the table are the approximate concentrations resulting in an osmotic pressure of 500 psi (34.5 barg) for the solution.

Compounds such as CaSO4 which have specific solubility limits can be controlled with proper addition of dispersants. Check with the factory for more information on Osmonics special line of dispersants.

ORGANICS

ANIONS

Chloride

Cl-1

94-95

4

5-8

Bicarbonate

H C O3-1

95-96

4

5-10

Sulfate

S O4-2

99+

1

5-15

Nitrate

N O3-1

85-95

10

3-6

Fluoride

F-1

94-96

5

5-8

Silicate

SiO2-2

80-95

10

-

Phosphate

P O4-3

99+

1

10-20

Bromide

Br-1

94-96

5

5-8

Borate

B4O 7-2

35-70**

-

-

Chromate

CrO4-2

90-98

6

8-12

Cyanide

C N-1

90-95**

-

4-12

Sulfite

S O3-2

98-99

1

5-15

Thiosulfate

S2O 3-2

99+

1

10-20

*Must watch for precipitation; other ion controls maximum concentration

*Extremely dependent on pH; tends to be an exception to the rule

The following are typical rejections and passages for various salts and organics using the SEPAfi -HR membrane at 400 psig (27.6 bar) operating pressure. Modules made with this membrane, such as the OSMOfi - HR, can be expected to give these same passages. As can be seen, multivalent ions tend to have less passage than do monovalent ions. If monovalent ions are combined with multivalent ions to form a salt, the passage will be controlled by the multivalent ion. In RO all ions must be combined as the salt form before passages can be considered.

For estimating purposes, to obtain the expected permeate quality when handling a solution of salts,take a simple average of the feed concentration and the

concentrate concentration and multiply this figure by the average percent passage to calculate the average concentration of the permeate.Salts or organics that are complexed with organics of large molecular weights will tend to act like the organics with which they are complexed.

 

 

 

Maximum

 

Molecular

Percent

Concentration

 

W eight

Rejection

Percent

Sucrose Sugar

342

99.9

30-35

Lactose Sugar

360

99.9

30-35

Protein

10,000 Up

99.9

50-80

Glucose

180

99.0

15-20

Phenol

94

***

-

Acetic Acid

60

***

-

Formaldehyde

30

***

-

Dyes

400 to 900

99.9

-

Biochemical

 

 

 

Oxygen Demand

(BOD)

90.0-99.9

 

Chemical

 

 

-

Oxygen Demand

(COD)

99.9

 

Urea

60

40-60 Reacts similar to

 

 

 

a salt

Bacteria & Virus

50,000 to

99.9+

 

 

500,000

 

-

Pyrogen

1,000

99.9+

-

 

to 5,000

 

 

***Permeate is enriched in material due to preferential pas- sage through the membrane.

GASES, DISSOLVED

Carbon Dioxide

C O2

30-50%

 

 

 

Oxygen

O 2

Enriched in permeate

 

 

 

Chlorine

Cl2

30-70%

NOTE: The actual permeate water quality will vary with the inlet water quality and can only be verified by actual analysis of the permeate stream.

9