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Replacement steps and cleaning precautions of RO membrane
The pore size of RO RO membrane is as small as nanometer (1 nm = 10 * - 9 m). Under certain pressure, water molecules can pass through the RO membrane, while inorganic salts, heavy metal ions, organics, colloids, bacteria, viruses and other impurities in the source water can not pass through the ro membrane, so that the permeable pure water can be strictly distinguished from the impermeable concentrated water.
The pure water conductivity of general tap water after RO membrane filtration is 5 μ s / cm (the effluent conductivity after RO membrane filtration = influent conductivity × desalination rate. Generally, the desalination rate of imported reverse osmosis membrane can reach more than 99%, and the operation can guarantee more than 97% within 5 years. For the outlet water with high electrical conductivity requirements, two-stage reverse osmosis can be used, and after simple treatment, the hydraulic conductivity is less than 1 μ s / cm), which meets the national laboratory level III water standard. The water resistivity can reach 18.2 m · cm after circulating filtration by atomic level ion exchange column, which is higher than the first grade water standard of National Laboratory (GB 6682-92).
The working principle of RO membrane is as follows
Infiltration is a physical phenomenon. When two kinds of water containing different salts are separated by a semi permeable membrane, it will be found that the water on the side with less salt content will penetrate through the membrane into the water with high salt content, while the salt content will not penetrate. In this way, the salt concentration on both sides will be gradually integrated to an even level. This process is called infiltration. However, it will take a long time to complete this process. However, if a pressure is applied to the water side with high salt content, the result can also stop the above-mentioned infiltration, and the pressure is called osmotic pressure. If the pressure is increased again, the opposite direction of penetration can be made, and the salt remains. Therefore, the principle of reverse osmosis desalination is to apply a greater pressure than the natural osmotic pressure in salty water (such as raw water), so as to make the infiltration proceed in the opposite direction, so that the water molecules in the raw water are pressed to the other side of the membrane to become clean water, so as to achieve the purpose of removing impurities and salts in water.
Reverse osmosis, also known as reverse osmosis, is a kind of membrane separation operation with pressure difference as driving force to separate solvent from solution. When the pressure exceeds its osmotic pressure, the solvent will reverse the direction of natural penetration. Thus, the permeated solvent, namely osmotic solution, is obtained at the low pressure side of the membrane, and the concentrated solution is obtained at the high pressure side. If seawater is treated by reverse osmosis, fresh water is obtained at the low pressure side of the membrane and brine is obtained at the high pressure side.
In reverse osmosis, the permeation rate of solvent, i.e. liquid flow energy N, is: n = KH (Δ p - Δπ) (where KH is the hydraulic permeability coefficient, slightly increased with the increase of temperature; Δ P is the static pressure difference between the two sides of the membrane; Δπ is the osmotic pressure difference of the solutions on both sides of the membrane). The osmotic pressure of dilute solution π is: π = ICRT (where I is the number of ions generated by the ionization of solute molecules; C is the molar concentration of solute; R is the molar gas constant; t is the absolute temperature. )
Asymmetric membrane and composite membrane are usually used in reverse osmosis, and the main equipment used is hollow fiber type or roll type membrane separation equipment. Reverse osmosis membrane can intercept all kinds of inorganic ions, colloidal substances and macromolecular solutes in water, so as to obtain purified water. It can also be used for preconcentration of macromolecular organic solution. Because of its simple process and low energy consumption, reverse osmosis has been developed rapidly in recent 20 years. It has been widely used in seawater and brackish water (see brine) desalination, boiler water softening and wastewater treatment, and combined with ion exchange to produce high-purity water. At present, its application scope is expanding, and it has been used in the concentration of dairy products and fruit juice, as well as the separation and concentration of biochemical and biological agents.
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August 02, 2022
August 02, 2022
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