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Why Reverse Osmosis?

By: Gil K. Dhawan Ph.D., P.E., Applied Membranes, Inc.

To Remove Dissolved Solids

  • Calcium (Hardness)

  • Sodium

  • Sulfates

  • Others

Dissolved Solids

  • Evaporate Water

  • Residue Left

 REVERSE OSMOSIS VS. CONVENTIONAL FILTER      

 

RO

FILTER

Cross-Flow   

Yes

No

Dead-end

No

Yes

One liquid stream comes out

No

Yes

Dissolved solids      

Yes

No

Flushing action

Yes

No

Useful life

Long

Short

Pore Size

0.0001 micron

0.1 Micron (smallest)

* Although not a good use of RO for this purpose

What does RO do?

  • Permeate (Product)

  • Concentrate (Reject)

  • Impurities Are Concentrated

Osmotic Pressure

  • Created by ionic content of dissolved solids

  • Organics do not contribute significantly to the Osmotic Pressure

  • Rule of thumb:

                             Osmotic Pressure  =    TDS in PPM

                                   (PSI)                                100

 

                   OSMOTIC PRESSURE VS. CONCENTRATION

                                        Assume Feed TDS = 1000 PPM

      Reject Concentration =

100

× Feed Concentration

(100-R)

 

Feed Flow
(GPM)

Permeate Flow (GPM)

Reject Flow (GPM)

Recovery (%)

Reject Conc. (PPM)

Osmotic Press. (PSI)

10

1

9

10

1,110

11.1

10

2

8

20

1,250

12.5

10

3

7

30

1,430

14.3

10

4

6

40

1,670

16.7

10

5

5

50

2,000

20

10

6

4

60

2,500

25

10

7

3

70

3,333

33.3

10

8

2

80

5,000

50

 

 
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