Reverse osmosis technology is the most advanced, energy-saving and effective membrane separation technology. Its principle is that under the action of osmotic pressure higher than that of solution, other substances and water are separated according to the fact that they cannot penetrate the semi-permeable membrane. Because the membrane pore size of reverse osmosis membrane is very small (only about 10A), it can effectively remove dissolved salts, colloids, microorganisms, organic substances and so on in water (the removal rate is as high as 97-98%). The system has the advantages of good water quality, low energy consumption, no pollution, simple process and easy operation.
Reverse osmosis technology is usually used in seawater and brackish water; Softening treatment of water; Wastewater treatment and purification, concentration and separation in food, pharmaceutical and chemical industries. In addition, the application of reverse osmosis technology in pre-desalination treatment has also achieved good results, which can reduce the load of ion exchange resin by more than 90% and the dosage of resin regenerant by 90%. Therefore, it not only saves the cost, but also is beneficial to environmental protection. Reverse osmosis technology can also be used to remove particles, organic matter and colloid in water, which has a good effect on reducing the pollution of ion exchange resin and prolonging the service life.
Reverse osmosis is the most widely used desalination technology to prepare high-purity water at present, and its separation object is the organic matter with ionic range and molecular weight of several hundred in the solution. Reverse osmosis, ultrafiltration, microporous membrane filtration and electrodialysis are all membrane separation technologies.
In recent 30 years, reverse osmosis, electrodialysis, ultrafiltration and membrane filtration have entered industrial applications and developed rapidly. In semiconductor and integrated circuit manufacturing processes, food and pharmaceutical industries, reverse osmosis is usually used for desalination of high-purity water, ultrafiltration is mostly used for post-treatment of water-making systems, and membrane filtration is used for pretreatment and post-treatment of water treatment to filter particles and bacteria.
Working principle:
The desalination rate of reverse osmosis equipment system is generally 98-99%. This desalination rate can meet the requirements in most cases. Electronic industry, extra-high pressure boiler make-up water and individual pharmaceutical industry may have higher requirements for pure water. At this time, single-stage reverse osmosis equipment can not meet the requirements.
Infiltration is common in nature. For example, if a cucumber is put into salt water, it will become smaller because of water loss. The process of water molecules in cucumber entering salt solution is osmotic process. If a water tank is divided 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 at the same height. After a period of time, it can be found that the water level of pure water has decreased, while the water level of salt water has increased. We call the phenomenon that water molecules permeate and migrate into brine through this diaphragm. The rise of salt water level is not endless, reaching a certain height will reach a balance point. At this point, the pressure represented by the liquid level difference at both ends of the diaphragm is called osmotic pressure. Osmotic pressure is directly related to the concentration of brine.
After the device reaches equilibrium, if a certain pressure is applied to the liquid level at the salt water end, water molecules will migrate from the salt water end to the pure water end. The phenomenon that liquid molecules migrate from dilute solution to concentrated solution under pressure is called reverse osmosis. If salt water is added to one end of the above-mentioned equipment and a pressure exceeding the osmotic pressure of salt water is applied to one end, we can get pure water at the other end. This is the principle of reverse osmosis water purification. There are two keys to producing pure water by reverse osmosis equipment. One is selective membrane, which we call semi-permeable membrane, and the other is certain pressure. Simply put, there are many holes in the reverse osmosis semipermeable membrane, and the size of these holes is equivalent to the size of water molecules. Because bacteria, viruses, most organic pollutants and hydrated ions are much larger than water molecules, they cannot penetrate the semi-permeable membrane of reverse osmosis and are separated from the water phase that penetrates the reverse osmosis membrane. Among many impurities in water, soluble salts are the most difficult to remove. Therefore, the water purification effect of reverse osmosis is often determined by the desalination rate, which is mainly determined by the selectivity of reverse osmosis semi-permeable membrane. At present, the desalination rate of high selectivity reverse osmosis membrane elements can reach 99.7%.