Reverse osmosis technology is today's most advanced and most energy efficient membrane separation technology. Its principle is higher than the osmotic pressure of the solution under the action, based on other substances can not pass through the semi-permeable membrane and these substances and water to leave. Due to the reverse osmosis membrane pore size is very small (only 10A or so), so can effectively remove dissolved salts, colloids, microorganisms, organic matter, etc. in water (removal rate of up to 97% -98%). Reverse osmosis is currently the most widely used in high-purity water equipment, a desalination technology, which separates the object of the solution of the ionic range and molecular weight of a few hundred organic matter; reverse osmosis (RO), over the filtration (UF), microporous membrane filtration (MF) and electrodialysis (EDI) technology are all belong to the membrane separation technology.
In the past 30 years, reverse osmosis, electrodialysis, more than filtration and membrane filtration has entered the industrial applications, mainly in the field of electronics, chemical industry, food, pharmaceuticals and drinking water.
Reverse osmosis working principle
1. Osmosis and osmotic pressure
Osmosis phenomenon is common in nature, for example, when a cucumber is put into salt water, the cucumber becomes smaller due to water loss. The process by which the water molecules in the cucumber enter the saline solution is osmosis. If a pool of water is partitioned into two parts by a membrane through which only water molecules can pass, pure water and saline water are injected to the same height on each side of the diaphragm. After a while it can be noticed that the level of pure water decreases, while the level of salt water increases. We call the phenomenon of water molecules migrating through the diaphragm into the brine osmosis. Salt water level rise is not endless, to a certain height will reach an equilibrium point. The pressure represented by the difference in liquid level between the two ends of the diaphragm at this point is called osmotic pressure. The magnitude of osmotic pressure is directly related to the concentration of saline.
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 level at the brine end, at this time, water molecules will migrate from the brine end to the pure water end. Liquid molecules under pressure from a dilute solution to a concentrated solution migration process this phenomenon is known as reverse osmosis phenomenon. 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 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: a selective membrane, which we call a semi-permeable membrane, and a certain pressure. Simply put, reverse osmosis semi-permeable membrane has numerous holes, the size of these holes and the size of the water molecule is comparable to the size of the water molecule, due to bacteria, viruses, most organic pollutants and hydrated ions are much larger than the water molecule, and therefore can not pass through the reverse osmosis semi-permeable membrane and through the reverse osmosis membrane of the water phase separation. In the many kinds of impurities in the water, dissolved salts are the most difficult to remove. Therefore, often based on the salt removal rate to determine the reverse osmosis water purification effect. Reverse osmosis salt removal rate is mainly determined by the selectivity of the reverse osmosis semi-permeable membrane. At present, the higher selectivity of the reverse osmosis membrane element salt removal rate can be as high as 99.7%.