Infiltration is common in nature. For example, if a cucumber is put into salt, the cucumber will become smaller due to water loss. The process of water molecules in Cucumber entering saline solution is the infiltration process. If a water tank is separated into two parts by a film that only water molecules can penetrate, inject pure water and salt water to the same height on both sides of the diaphragm. After a period of time, it can be found that the liquid level of pure water decreases and the liquid level of brine increases.
We call the phenomenon that water molecules migrate into salt water through this membrane permeation. The rise of brine level is not endless. At a certain height, it will reach an equilibrium 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.
Reverse osmosis technology is the most advanced and energy-saving membrane separation technology. The principle is to separate these substances from water under the action of higher than the osmotic pressure of the solution according to the fact that other substances cannot pass through the semi permeable membrane. Because the pore size of the reverse osmosis membrane is very small (only about 10a), it can effectively remove dissolved salts, colloids, microorganisms and organic matter 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 simple operation.
The system desalination rate of reverse osmosis equipment is generally 98-99%, which can meet the requirements in most cases. In the electronic industry, ultra-high pressure boiler make-up water and individual pharmaceutical industries, the requirements for pure water may be higher. At this time, the single-stage reverse osmosis equipment can not meet the requirements.
Reverse osmosis technology is usually used for fresh water of seawater and brackish water; Softening treatment of water; Wastewater treatment and purification, concentration and separation of food, pharmaceutical industry and chemical industry. In addition, the application of reverse osmosis technology in pre desalting treatment has also achieved good results, which can reduce the load of ion exchange resin by more than 90%, and the amount of resin regenerant can also be reduced by 90%. Therefore, it not only saves costs, but also is conducive to environmental protection. Reverse osmosis technology can also be used to remove particles, organic substances and colloids in water and reduce the pollution of ion exchange resin. Prolonging the service life has a good effect.
Reverse osmosis (RO), ultrafiltration (UF), microporous membrane filtration (MF) and electrodialysis (ED) are all membrane separation technologies.
In the past 30 years, reverse osmosis, electrodialysis, ultrafiltration and membrane filtration have entered industrial applications and developed rapidly. In semiconductor, integrated circuit manufacturing process, food and pharmaceutical industry, reverse osmosis is usually used as desalination in the preparation of high-purity water, and more than filtration is used as post-treatment of water system. Membrane filtration is used for pretreatment and post-treatment of water treatment, as well as filtration of particles and bacteria.