Requirements of reverse osmosis membranes for water quality

As a new type of purely physical desalination process, reverse osmosis equipment has high requirements for feed water due to the structure, material and desalination mechanism of the reverse osmosis membrane element and other conditions.

• Temperature conditions between 1 and 45°C;

• The pH value must be within the range of 2 to 11;

• The organic matter content (COD, mg/L) should be less than 1.5;

• Turbidity (NTU) should be controlled to less than 1.0;

• Sludge density index (SDI value) <4.0;

• Residual chlorine content <0.1mg/L (actual control is 0);

• Iron content (mg/L): Fe<0.05 for dissolved oxygen >5mg/L;

• Silicon dioxide content (mg/L): SiO2<100 in concentrated water; LSI: pHb-pHs<0;

• Sr, Ba and other ions that can easily form insoluble salts: Ipb<0.8Ksp.

The latter three can be appropriately increased by adding scale inhibitors.

If one or several of the above indicators are not up to standard, the following effects will be caused to the reverse osmosis membrane: 1.

    1. RO reverse osmosis membrane contaminated by metal oxides;

    2. Colloid contamination;

    3. RO reverse osmosis membrane fouling;

    4. RO reverse osmosis membrane fouling with suspended matter;

    5. organic matter and microbial contamination, resulting in higher COD in the effluent.

　　Reduce the amount of water produced by the reverse osmosis pure water system; reduce the quality of water produced by the reverse osmosis pure water system; increase the energy consumption of reverse osmosis equipment operation, including raw water, electricity consumption; increase the operating costs of water treatment, including reverse osmosis scale inhibitor, resin regeneration salt, other water treatment chemicals, etc.

　　Reverse osmosis pretreatment plays an irreplaceable role in it. When the pretreatment is not done, reverse osmosis feed water quality is seriously substandard and too long, it will lead to irreversible physical and chemical damage to the reverse osmosis membrane element, greatly shortening the life of the reverse osmosis membrane element.

The purpose of reverse osmosis pretreatment is to solve the following problems in order to ensure the stable operation and service life of reverse osmosis equipment.

　　1.To prevent membrane surface fouling (including CaCO3, CaSO4, SrSO4, CaF2, SiO2, iron and aluminium oxides, etc.);

　　2.To prevent the fouling of organic substances;

　　3.To prevent fouling by microorganisms;

　　4.To prevent the fouling of colloidal substances and suspended solid particles;

       5.To maintain the stability of water production in the reverse osmosis unit.