Principle of reverse osmosis equipment
Working principle of reverse osmosis
1. Penetration and osmotic pressure
Infiltration is common in nature. For example, if a cucumber is put into salt water, the cucumber will become smaller due to water loss. The process of cucumber water molecules entering into saline solution is the infiltration process. As shown in the figure below, if a water pool is separated into two parts by a membrane that only water molecules can penetrate, pure water and salt water are injected into both sides of the membrane to the same height. After a period of time, it can be found that the level of pure water has decreased, while the level of salt water has increased. The phenomenon that we transfer water molecules through this membrane into brine is called osmosis. Salt water level rise is not endless, to a certain height will reach a balance point. At this time, the pressure represented by the liquid level difference at both ends of the diaphragm is called osmotic pressure. The osmotic pressure is directly related to the concentration of brine. 2. Reverse osmosis phenomenon and reverse osmosis water purification technology
After the above device reaches equilibrium, if a certain pressure is applied to the liquid surface of the brine end, the water molecules will migrate from the brine end to the pure water end. The process of migration of liquid agent molecules from dilute solution to concentrated solution under pressure is called reverse osmosis. If salt water is added to one end of the above facilities and pressure is applied to that end beyond the osmotic pressure of the salt water, we can get pure water at the other end. This is the principle of RO water purification.
There are two key points to produce pure water in reverse osmosis facilities. One is a selective membrane, which we call semi permeable membrane, and the other is a certain pressure. In short, there are many pores on the reverse osmosis membrane. The size of these pores is the same as that of water molecules. Because bacteria, viruses, most organic pollutants and hydrated ions are much larger than water molecules, they cannot be separated from water through the reverse osmosis membrane. Among many impurities in water, soluble salts are difficult to be removed. Therefore, the water purification effect of reverse osmosis is often determined according to the desalination rate. The desalination rate of reverse osmosis mainly depends on the selectivity of reverse osmosis semi permeable membrane. At present, the desalination rate of high selective reverse osmosis membrane element can be as high as 99.7%.