Basic Principles of Penetration

When pure water and salt water are separated by an ideal semipermeable membrane, which allows only water to pass through while blocking salt, water on the pure water side of the membrane will spontaneously flow through the membrane into the salt water side. This phenomenon is called osmosis. If pressure is applied to the salt water side of the membrane, the spontaneous flow of water will be inhibited and slowed down. When the applied pressure reaches a certain value, the net flow rate of water through the membrane is zero. This pressure is called osmotic pressure. When the pressure applied to the salt water side of the membrane is greater than the osmotic pressure, the flow of water will reverse. At this time, water in the salt water will flow into the pure water side. The above phenomenon is the basic principle of reverse osmosis (RO) water treatment.