Appendix B Basic Principles - Culligan M2 Series Installation, Operation And Service Instructions

Appendix B Basic Principles

Reverse Osmosis
In order to understand reverse osmosis, we must first define osmosis. Osmosis is the passage of a liquid through a semi-
permeable membrane. A semi-permeable membrane is a membrane which allows one component of a solution to pass
through it and not the others. In osmosis, there is a tendency for a liquid to go from an area of less concentration to an
area of more concentration through a semi-permeable membrane. Figure 62 shows the osmotic process.
If pressure is applied to the concentrated solution, reverse osmosis will take place. The pressure causes a flow through
the semi-permeable membrane into the dilute solution. The semi-permeable membrane acts as a barrier to ions and does
not allow them to pass through into the dilute solution. When applied to water, this means that the product water has a
reduced total dissolved solids content as a result of the passage of water molecules through the membrane while the
mineral ions are rejected. See Figure 63.
Rejection and Recovery
Feed water entering the system is split into two streams, a product stream and a concentrate stream. See Figure 64.
Figure 64.
During the process of reverse osmosis, some of the water has its dissolved solids content reduced by approximately 99%.
This high quality product water is sent to service
Culligan® Series M2 Reverse Osmosis
102
Concentrated
Solution
Figure 62.
Pressure
Concentrated
Solution
Figure 63. Effect of pressure on reverse osmosis.
Feed
Feed water product stream and concentrate stream.
Semi-Permeable
Membrane
Dilute
Solution
Passage of
Water
Osmotic process.
Semi-Permeable
Membrane
Dilute
Solution
Passage of
Water
Concentrate
Product
102
Cat. No. 01023095