Introduction to reverse osmosis technology

Reverse osmosis and osmosis is a physical phenomenon. The water containing salt has a natural osmotic pressure. When the brine (raw water) and pure water are separated by a semi-permeable membrane with a micropore diameter of one ten thousandth of a micron, pure Water will enter the raw water side through the semipermeable membrane due to the action of osmotic pressure. On the contrary, if a pressure higher than its own osmotic pressure is applied to the raw water side, the molecules in the raw water will pass through the semi-permeable membrane and enter the pure water side, but the salt, fine impurities, organic matter and other components in the raw water cannot enter the pure water side. On the water side, this is reverse osmosis. Based on this principle, people invented reverse osmosis membrane and reverse osmosis technology and applied them to water treatment. Application of reverse osmosis technology Reverse osmosis technology can be used for desalination of brackish water, production of pure drinking water, production of high-quality drinking water, production of industrial water with low salt content and low hardness, preparation of industrial pure water and high-purity water, recycling of industrial wastewater, etc. Main features of reverse osmosis water treatment Desalination by physical method, stable effluent quality, continuous production, simple operation, low operating cost, less waste water discharge, small footprint, and wide range of applicable water quality.

The application status of reverse osmosis technology

In foreign countries, research on reverse osmosis technology has been started as early as the 1940s. From testing to production, it is mainly used in the fields of seawater chemistry and pure water preparation. By the 1980s, with the application of cathodic electrophoresis technology, reverse osmosis technology has been widely used in It is widely used in the field of coating. In China, due to the late start, the application of reverse osmosis technology in coating production is limited. At present, most of the pure water used in coating production is produced by ion exchange method.

Basic principles and characteristics of reverse osmosis

Fresh water and salt water are separated by a semi-permeable membrane that can only permeate water but not solutes. Fresh water will naturally pass through the semi-permeable membrane to the salt water side. This phenomenon is called osmosis. When the liquid level on the brine side reaches a certain height, a pressure H is generated, which inhibits the further infiltration of fresh water to the brine side, and the natural tendency of infiltration is offset by the pressure H and reaches a balance. This equilibrium pressure H is called Osmotic pressure, in this case, if a pressure greater than osmotic pressure is added to the salt water side, the water in the salt water will pass through the semipermeable membrane from the salt water side to the fresh water side (the concentration of the salt water side will increase. large, that is, concentrated), a phenomenon called reverse osmosis.

Reverse osmosis is to use sufficient pressure to separate the solvent (usually water) in the solution through the reverse osmosis membrane, which is opposite to the natural osmosis direction. According to the different osmotic pressures of various materials, the reverse osmosis method that is greater than the osmotic pressure can be used for separation, purification and concentration.

The main separation object of the reverse osmosis membrane is to separate the ion range in the solution. The separation process of reverse osmosis does not require heating, has no phase change, has the advantages of less energy consumption, small equipment volume, simple operation, strong adaptability and wide application range, and has become one of the important water treatment methods.

Reverse osmosis membrane separation technology (referred to as R0 technology) is a new and practical water treatment technology. Reverse osmosis is the most fine filtration system at present. RO membrane can block all solutes and inorganic molecules and any organic matter with a molecular weight greater than 100, water. Molecules can be purified by freely passing through the R0 membrane, and the desalting rate of dissolved salts can reach 95% or even 99%. Therefore, the application of reverse osmosis is quite extensive, and reverse osmosis is gradually adopted in the production of seawater and brackish water, domestic drinking water and industrial pure water.

Structure

The reverse osmosis device is composed of a roll-type membrane module, and the roll-type membrane module is composed of a roll-type membrane element. The roll-type membrane element is based on the principle of the reverse osmosis method. Glued and rolled onto a central tube with rows of holes to form the element. The raw water enters the separator layer from one end of the element. When passing through the separator layer, under the external pressure, part of the water passes through the pores of the membrane and penetrates into the diversion layer. It flows out through the central pipe, and the remaining part (concentrated water) is discharged from the other end of the separator. An assembly is formed by placing one or more reverse osmosis elements in a pressure-resistant container. When working, the raw water flows into the components from one end, and then flows through each component one by one. All raw water enters the first element, the effluent of the first element is used as the inlet water of the second element, the effluent of the second element is used as the inlet water of the third element… until the final concentrated water is discharged from the assembly: put several The components are combined in series and parallel, together with the necessary pipelines and instruments to form a device.

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Further reading:

25TPH RO water treatment

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