Technical standard analysis of reverse osmosis membrane performance

Reverse osmosis membrane is the core element to realize reverse osmosis, and it is an artificial semi-permeable membrane with certain characteristics made by simulating biological semi-permeable membrane. Generally made of polymer materials. Such as cellulose acetate film, aromatic polyhydrazide film, aromatic polyamide film. The diameter of the surface micropores is generally between 0.5 and 10 nm, and the permeability is related to the chemical structure of the membrane itself. Some polymer materials have good repellency to salt, but the water penetration rate is not good. The chemical structure of some polymer materials has more hydrophilic groups, so the water permeation rate is relatively fast. Therefore, a satisfactory reverse osmosis membrane should have an appropriate amount of permeation or salt rejection rate.

Technical standards for reverse osmosis membrane performance

1. Desalination rate and salt permeability

  • Desalination rate-the percentage of the concentration of soluble impurities removed from the influent water of the system through the reverse osmosis membrane.
  • Salt penetration rate-the percentage of soluble impurities in the influent water through the membrane.
  • Desalination rate=(1-Salt content of product water/Salt content of influent)×100%
  • Salt penetration rate = 100%-desalination rate

The desalination rate of the reverse osmosis membrane element is determined when it is manufactured and formed. The desalination rate depends on the density of the ultra-thin desalination layer on the surface of the reverse osmosis membrane element. The denser the desalination layer, the higher the desalination rate and the lower the water production. The removal rate of different substances by reverse osmosis is mainly determined by the structure and molecular weight of the substances.

2, water production (water flux)

  • Water production (water flux)-refers to the production capacity of the reverse osmosis system, that is, the amount of water permeating the membrane per unit time, usually expressed in tons/hour or gallons/day.
  • Permeate flow rate-Permeate flow rate is also an important indicator of the water production of reverse osmosis membrane elements. Refers to the flow rate of permeate per unit membrane area, usually expressed in gallons per square foot per day (GFD). An excessively high permeate flow rate will cause the water velocity perpendicular to the membrane surface to increase, which will aggravate membrane fouling.

3, recovery rate

  • Recovery rate–refers to the percentage of feed water converted into product water or permeate in the membrane system. The recovery rate of the membrane system is determined at the time of design and is based on the preset water quality. The recovery rate is usually hoped to be maximized in order to improve economic efficiency, but it should be the limit value that the membrane system will not precipitate due to the supersaturation of impurities such as salts.
  • Recovery rate = (product water flow/influent flow) × 100%

4, the main index to measure the performance of reverse osmosis membranes

  • Desalination rate = (1-salt content of product water / salt content of influent) × 100%
  • Water flux-refers to the water production capacity of the reverse osmosis system, that is, the amount of water permeating through the membrane per unit time, usually expressed in tons/hour or gallons/day.
  • Salt permeation rate-the amount of salt permeated per unit time and unit membrane area, also called salt permeation rate and salt flux.
  • Recovery rate-refers to the percentage of feed water converted into product water or permeate in the membrane system. Depends on the quality of pre-treated influent water and water requirements. The recovery rate of the membrane system has been determined at the time of design,
  • Recovery rate = (product water flow/influent flow)×100%

The desalination rate of the membrane element is determined when it is manufactured and formed. The desalination rate depends on the density of the ultra-thin desalination layer on the surface of the membrane element. The denser the desalination layer, the higher the desalination rate and the lower the water production. The desalination rate of different substances by reverse osmosis is mainly determined by the structure and molecular weight of the substance. The desalination rate of high-valent ions and complex monovalent ions can exceed 99%, and the desalination rate of monovalent ions such as sodium ions, potassium ions, and chloride ions is slightly lower. , But it can also exceed 98% (the longer the membrane is used, the more the number of chemical cleanings, the lower the salt rejection rate of the reverse osmosis membrane.); the removal rate of organic matter with a molecular weight greater than 100 can also exceed 98%, but for molecular weight The removal rate of organic matter less than 100 is lower.

8040 reverse osmosis membrane

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