The two-stage reverse osmosis system is composed of a reverse osmosis body device and a cleaning device, which mainly completes the desalination treatment of the pretreated effluent, and uses the characteristics of the reverse osmosis membrane to remove most of the soluble salts, colloids, organic matter and microorganisms in the water. In order to improve the water utilization rate, the concentrated water of the secondary reverse osmosis is reused, and the design can increase the water utilization rate of reverse osmosis to 6775 or more, and at the same time, it can also extend the service life of reverse osmosis.
Reverse osmosis principle:
Reverse osmosis is a high-tech membrane separation technology invented by Loeb and Sourirtajan of the University of California in 1960, its pore size is very small, mostly 10 10 10 (10A), it can remove organic matter with a small ionic range and molecular weight in the filtrate, such as bacteria, viruses, heat sources, etc. It has been widely used in the production of seawater or brackish water desalination, electronics, pharmaceutical pure water, drinking distilled water, space water, and also used in biological and medical engineering.
Reverse osmosis is also known as reverse osmosis (RO). It is to use a certain pressure to separate the solvent in the solution through a reverse osmosis membrane (or semi-permeable membrane). Because it is in the opposite direction of natural osmosis, it is called reverse osmosis. According to the different osmotic pressure of various materials, the reverse osmosis method greater than the osmotic pressure can achieve the purpose of separation, extraction, purification and concentration.
Osmosis is common in nature, such as when a cucumber is placed in salt water, the cucumber becomes smaller due to water loss. The process by which the water molecules in the cucumber enter the brine solution is the osmosis process. As shown in the figure, if a pool is divided into two parts with a membrane that only water molecules can penetrate, pure water and salt water are injected to the same height on both sides of the diaphragm. After a while, you can see that the level of pure water is lowered, and the level of brine is raised. We call the migration of water molecules through this diaphragm into the brine as osmosis. The rise in the brine level is not endless, and an equilibrium point will be reached at a certain height. At this time, the pressure represented by the difference in liquid levels at both ends of the diaphragm is called osmotic pressure. The magnitude of osmotic pressure is directly related to the concentration of saline.
After the above devices reach equilibrium, if a certain pressure is applied to the liquid surface at the brine end, the water molecules will migrate from the brine end to the pure water end. The process of migration of liquid molecules from dilute solution to concentrated solution under pressure is called reverse osmosis. If brine is added to one end of the above facility and a pressure is applied to that end that exceeds the osmotic pressure of that brine, 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 in a reverse osmosis facility, one is a selective membrane, which we call a semi-permeable membrane, and the other is a certain pressure. To put it simply, there are numerous pores on a reverse osmosis semi-permeable membrane, and these pores are about the size of a water molecule, and because bacteria, viruses, most organic pollutants, and hydrated ions are much larger than water molecules, they cannot be separated from the water through the reverse osmosis membrane. Among the many impurities in water, dissolved salts are the most difficult to remove. Therefore, the water purification effect of reverse osmosis is often determined according to the level of desalination rate, and the level of reverse osmosis desalination rate is mainly determined by the selectivity of reverse osmosis semi-permeable membrane. At present, the salt removal rate of reverse osmosis membrane elements with high selectivity can be as high as 996%。