What are the water quality requirements for the reverse osmosis system?

As a new type of pure physical desalination process, reverse osmosis system has higher requirements for influent water due to the limitations of the structure, material and desalination mechanism of reverse osmosis membrane elements:

Parameters of reverse osmosis system

  1. Temperature (℃): 1-45.
  2. pH value: 2-11.
  3. Silt density index (SDI value) <4.0.
  4. Turbidity (NTU) <1.0.
  5. Organic matter content (COD, mg/L) <1.5.
  6. Residual chlorine content (mg/L) < 0.1 (actually controlled at 0).
  7. Iron content (mg/L): when dissolved oxygen is >5mg/L, Fe<0.05.
  8. SiO2 (mg/L): SiO2<100 in concentrated water.
  9. LSI: pHb-pHs<0.
  10. Ions that are easy to form insoluble salts such as Sr and Ba: Ipb<0.8Ksp.
    The last three items can be properly increased by adding scale inhibitors.

What harm will the reverse osmosis system cause if the reverse osmosis inlet water requirements are not up to standard?

(1)If one or more of the above indicators do not meet the standard, it will have the following effects on the reverse osmosis membrane

  1. Fouling of RO reverse osmosis membrane.
  2.  The RO reverse osmosis membrane is contaminated by metal oxides.
  3. Suspended solids foul the RO reverse osmosis membrane.
  4. Colloidal pollution.
  5. The pollution of organic matter and microorganisms leads to the increase of COD in the effluent.

(2)Then it will have the following effects on the entire reverse osmosis pure water system:

  1. Reduce the water production of the reverse osmosis pure water system.
  2. The quality of the product water of the reverse osmosis pure water system is low.
  3. Increase the energy consumption of reverse osmosis equipment operation, including raw water and electricity consumption.
  4. Increase the operating cost of water treatment, including reverse osmosis scale inhibitor, resin regeneration salt, and other water treatment chemicals.
    When the pretreatment is not done well, the quality of the reverse osmosis influent is seriously substandard, and the time is too long, it will cause irreversible physical and chemical damage to the reverse osmosis membrane element, and greatly shorten the service life of the reverse osmosis membrane element.

The role of reverse osmosis pretreatment

The pretreatment of the reverse osmosis unit plays a very important role in ensuring the safety, reliability and economy of the operation of the reverse osmosis unit. The purpose of reverse osmosis pretreatment is to solve the following problems to ensure the stable operation and service life of the reverse osmosis device.

  1. Prevent scaling on the membrane surface (including CaCO3, CaSO4, SrSO4, CaF2, SiO2, iron and aluminum oxides, etc.).
  2. Prevent the fouling of colloidal substances and suspended solid particles.
  3. Prevent the fouling of organic substances.
  4. Prevent microbial fouling.

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Further reading:

water quality requirements for the reverse osmosis system

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