We know that osmosis is the flow of water molecules from the dilute solution side through the membrane into the concentrated solution side. Reverse osmosis and nanofiltration technologies apply operating pressure on the incoming water stream side to overcome the natural osmotic pressure.
When an operating pressure above the osmotic pressure is applied to the concentrated solution side, the natural permeate flow direction of the water molecules is reversed and part of the incoming water (concentrated solution) passes through the membrane to become the purified produced water on the dilute solution side.
As shown in the diagram, there is a linear relationship between the increase in water flux through the membrane and the increase in feed water pressure, increasing the feed water pressure also increases the desalination rate, but there is no linear relationship between the two changes, and after a certain point the desalination rate will no longer increase.
