The reverse osmosis membrane is the core component for realizing reverse osmosis, and is an artificial semipermeable membrane with certain characteristics made by simulating a biological semipermeable membrane. Generally made of polymer materials. For example, a cellulose acetate film, an aromatic polyhydrazide film, or an aromatic polyamide film. The membrane pore size of the reverse osmosis membrane is very small, so that dissolved salts, colloids, microorganisms, organic matter, and the like in the water can be effectively removed. The system has the advantages of good water quality, low energy consumption, no pollution, simple process and easy operation.
  Reverse osmosis membrane selection
Frequent customers often ask which performance indicators to consider when choosing a reverse osmosis RO membrane. Usually divided into three: salt rejection rate, water production, recovery.
I. Desalting rate and permeation rate of RO reverse osmosis membrane The desalination rate of RO reverse osmosis membrane element has been determined at the time of its manufacture, and the degree of desalination depends on the density of the ultra-thin desalination layer on the surface of the reverse osmosis RO membrane element. The denser the desalination layer, the higher the salt rejection rate and the lower the water production. The desalination rate of different substances in reverse osmosis membrane is mainly determined by the structure and molecular weight of the substance. The salt rejection rate of high-valent ions and complex monovalent ions can exceed 99%, and the salt rejection rate of monovalent ions such as sodium ion, potassium ion and chloride ion is slightly. Low, but can also exceed 98% (the longer the reverse osmosis membrane is used, the more chemical cleaning times, the lower the desalination rate of the reverse osmosis membrane). The removal rate of organic matter with molecular weight greater than 100 can also reach 98%, but The removal rate of organic matter having a molecular weight of less than 100 is low.
Calculation method of salt rejection rate and salt permeability of reverse osmosis membrane:
Salt permeability of RO membrane = RO membrane water concentration / influent concentration × 100%
Desalting rate of RO membrane = (1 - RO membrane water content / influent salt content) × 100%
Permeability of RO membrane = 100% - desalination rate
Second, RO reverse osmosis membrane water production and percolation rate
RO membrane water production - refers to the water production capacity of the reverse osmosis system, that is, the amount of water per unit time through the RO membrane, usually expressed in tons / hour or gallons / day.
The permeate flow rate of the RO membrane is also an important indicator of the amount of water produced by the reverse osmosis membrane element. Refers to the flow rate of permeate over a unit membrane area, usually expressed in gallons per square foot per day (GFD). Excessive permeate flow rates will result in faster water flow rates perpendicular to the surface of the RO membrane, exacerbating membrane fouling.
Third, the RO reverse osmosis membrane recovery rate
RO membrane recovery - refers to the percentage of feed water converted to water or permeate in a reverse osmosis membrane system. According to the influent water quality and water requirements of the pre-treatment in the reverse osmosis system. The recovery rate of the RO membrane system has been determined at the time of design.
(1) RO membrane recovery rate = (RO membrane water production flow rate / influent flow rate) × 100%
(2) The recovery formula, salt permeability and desalination rate of the reverse osmosis (nanofiltration) membrane module are as follows:
Recovery rate of reverse osmosis membrane module = RO membrane module water production / water intake × 100%
Salt permeability of reverse osmosis membrane module = RO membrane module water production concentration / influent concentration × 100%
Storage Conditions
Storage conditions of reverse osmosis membrane elements
First, the new film (before use)
1. The membrane element must be kept in a wet state at all times. Even if it is necessary to temporarily open it in order to confirm the number of the same package, it must be in a state where the plastic bag is not broken, and this state should be saved until use.
2. Avoid direct sunlight when storing in an atmosphere of more than 10 ° C. Choose a well ventilated place. At this time, the storage temperature should not exceed 35 °C.
3. Physical damage will occur if freezing occurs, so take insulation measures and do not freeze them.
Second, the membrane element after water
1. The membrane element must be kept in a dark place at all times, the storage temperature should not exceed 35 °C, and direct sunlight should be avoided.
2. If the temperature is below 0 °C, there is a possibility of freezing. Anti-freezing measures should be taken.
3. The composite membrane element should be soaked with pure water containing reverse drug or reverse osmosis filtered water.
4. The film should not be in a dry state under any circumstances.
5. The concentration and pH of the preservation solution should be kept within the above range and should be checked regularly. If it is possible to deviate from the above range, the preservation solution should be prepared again.
maintenance
With the wide application of water purification equipment in the water treatment industry, reverse osmosis membranes have gradually gained attention. The cost of the reverse osmosis membrane is one of the concerns of consumers. The good maintenance helps to prolong the service life of the reverse osmosis membrane.
After the equipment is tested, we have two methods to protect the reverse osmosis membrane. The equipment is tested for two days (15~24h), then maintained with 2% formaldehyde solution; or after 2~6h, the reverse osmosis membrane is maintained with 1% aqueous solution of NaHSO3 (the air in the equipment pipeline should be drained) To ensure that the equipment does not leak, close all inlet and outlet valves). Both methods can achieve satisfactory results, * the method is more expensive, and is used when the idle time is long, and the second method of maintaining the reverse osmosis membrane is used when the idle time is short.
Application range
Reverse osmosis membrane is widely used in electric power, petrochemical, steel, electronics, medicine, food and beverage, municipal and environmental protection, in seawater and brackish water desalination, boiler feed water, industrial pure water and electronic grade ultra-pure water preparation, drinking pure Water production, wastewater treatment and special separation processes play an important role.
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