1. How many years can reverse osmosis membrane elements generally be used?

The service life of the membrane depends on the chemical stability of the membrane, the physical stability of the components, the cleanability, the water source, pretreatment, cleaning frequency, operation management level, etc. According to economic analysis, it is usually more than 5 years.

2. What is the difference between reverse osmosis and nanofiltration?

Nanofiltration is a membrane liquid separation technology located between reverse osmosis and ultrafiltration. Reverse osmosis can remove the smallest solutes with a molecular weight of less than 0.0001 microns, and nanofiltration can remove solutes with a molecular weight of about 0.001 microns. Nanofiltration is essentially a low-pressure reverse osmosis, which is used in occasions where the purity of the produced water after treatment is not particularly strict. Nanofiltration is suitable for the treatment of well water and surface water. Nanofiltration is suitable for water treatment systems where there is no need for a high desalination rate like reverse osmosis, but it has a high ability to remove hardness components, sometimes called “softening membrane”. The nanofiltration system has low operating pressure and lower energy consumption. The corresponding reverse osmosis system.

3. What kind of separation ability does membrane technology have?

Reverse osmosis is currently the most sophisticated liquid filtration technology. Reverse osmosis membranes can retain inorganic molecules such as soluble salts and organic substances with a molecular weight greater than 100. On the other hand, water molecules can freely pass through the reverse osmosis membrane, which is typically soluble The salt removal rate is >95~99%. The operating pressure ranges from 7 bar (100 psi) when the inlet water is brackish water to 69 bar (1,000 psi) when the water is seawater.
Nanofiltration can remove impurities with particles at 1nm (10 angstroms) and organic matter with a molecular weight greater than 200-400. The removal rate of soluble solids is 20-98%, and the removal rate of salts containing monovalent anions (such as NaCl or CaCl2) is 20-80%, while the salt containing divalent anions (such as MgSO4) has a higher removal rate of 90-98%.
Ultrafiltration can separate macromolecules larger than 100-1,000 angstroms (0.01-0.1 microns). All soluble salts and small molecules can pass through the ultrafiltration membrane, and the removable substances include colloids, proteins, microorganisms and macromolecular organics. The molecular weight cut-off of most ultrafiltration membranes is 1,000 to 100,000.
Microfiltration removes particles in the range of about 0.1 to 1 micron. Under normal circumstances, suspended solids and large colloids can be retained, while macromolecules and soluble salts can freely pass through the microfiltration membrane. The microfiltration membrane is used to remove bacteria and micro For flocs or total suspended solids TSS, the typical pressure on both sides of the membrane is 1 to 3 bar.

4. How to prevent the growth of microorganisms in the original packaging of the membrane element?

When the protective liquid appears turbid, it is probably due to the growth of microorganisms. Membrane elements protected with sodium bisulfite should be checked every three months. When the protection solution appears turbid, the components should be taken out of the storage sealed bag and re-immersed in fresh protection solution. The concentration of the protection solution is 1% (weight) food grade sodium bisulfite (not activated by cobalt), soak for about 1 hour , And reseal it for storage, and drain the components before repackaging.

5. What are the water inlet requirements for RO membrane elements and IX ion exchange resin?

In theory, entering the RO and IX system should not contain the following impurities:

  • Suspended matter,
  • Colloid,
  • Calcium sulfate,
  • Algae,
  • germ,
  • Oxidizers, such as residual chlorine, etc.,
  • Oil or lipid substances (must be lower than the lower detection limit of the instrument),
  • Organics and iron-organic complexes
  • Metal oxides such as iron, copper, aluminum corrosion products

Influent water quality will have a huge impact on the life and performance of RO components and IX resins.

6. Why is the pH value of RO product water lower than that of influent water?

When you understand the balance between CO2, HCO3- and CO3=, you can find the best answer to this question. In a closed system, the relative content of CO2, HCO3- and CO3= changes with the pH value. Under the condition of low pH value, CO2 accounts for the main part, in the medium pH value range, it is mainly HCO3-, and in the high pH value range, it is mainly CO3=.
Because the RO membrane can remove soluble ions but not soluble gases, the CO2 content in the RO product water is basically the same as the CO2 content in the RO feed water, but HCO3-and CO3 = can often be reduced by 1 to 2 orders of magnitude , This will break the balance between CO2, HCO3- and CO3= in the influent water. In a series of reactions, CO2 will combine with H2O to transfer the following reaction balance until a new balance is established.
HCO3- CO2 +à+ H+ H2O
If the influent water contains CO2, the pH value of the RO product water will always decrease. For most RO systems, the pH value of the reverse osmosis product water will have a drop of 1 to 2 pH values. When the alkalinity and HCO3 of the influent water are high At that time, the pH value of the produced water drops even more.
Very few influent water, containing less CO2, HCO3-or CO3 = so that there is less change in the pH value of the produced water. Some countries and regions have regulations on the pH value of drinking water, generally 6.5 to 9.0. According to our understanding, this is to prevent corrosion of the water pipeline, and drinking water with a low pH value itself will not cause any health problems. As we all know, many commercial carbonated beverages have a pH value between 2 and 4.

7. What is the maximum allowable silica concentration in the reverse osmosis membrane?

The maximum allowable concentration of silica depends on temperature, pH value and scale inhibitor. Usually, the maximum allowable concentration at the concentrated water end is 100 ppm when no scale inhibitor is added. Some scale inhibitors can allow the highest concentration of silica in concentrated water. 240ppm, please consult the scale inhibitor supplier.

8. What effect does chromium have on RO membrane?

Some heavy metals, such as chromium, can catalyze the oxidation of chlorine, which in turn causes the irreversible performance degradation of the diaphragm. This is because Cr6+ is less stable than Cr3+ in water. It seems that for metal ions with high oxidation valence, this destructive effect is even stronger. Therefore, the chromium concentration should be reduced in the pretreatment part or at least Cr6+ should be reduced to Cr3+.

9. What kind of pretreatment does RO system generally need?

The usual pretreatment system consists of the following: coarse filtration (~80 microns) to remove large particles, adding sodium hypochlorite and other oxidants, and then precision filtration through a multi-media filter or clarifier, and then adding sodium bisulfite to reduce residual chlorine and other oxidants. Finally, install a security filter before the inlet of the high-pressure pump. The role of the security filter is as the name suggests, it is used as a final insurance measure to prevent accidental large particles from damaging the impeller and membrane elements of the high-pressure pump. Water sources with more suspended particles usually require a higher degree of pretreatment to meet the specified water inlet requirements; for water sources with high hardness content, it is recommended to use softening or adding acid and adding scale inhibitors, etc., for the content of microorganisms and organic matter High water sources also require the use of activated carbon or anti-pollution membrane elements.

10. What kind of pretreatment does RO system generally need?

The usual pretreatment system consists of the following: coarse filtration (~80 microns) to remove large particles, adding sodium hypochlorite and other oxidants, and then precision filtration through a multi-media filter or clarifier, and then adding sodium bisulfite to reduce residual chlorine and other oxidants. Finally, install a security filter before the inlet of the high-pressure pump. The role of the security filter is as the name suggests, it is used as a final insurance measure to prevent accidental large particles from damaging the impeller and membrane elements of the high-pressure pump. Water sources with more suspended particles usually require a higher degree of pretreatment to meet the specified water inlet requirements; for water sources with high hardness content, it is recommended to use softening or adding acid and adding scale inhibitors, etc., for the content of microorganisms and organic matter High water sources also require the use of activated carbon or anti-pollution membrane elements.

5TPH~20TPH commercial reverse osmosis equipment

Do you have a water treatment project we can help with

Designing,machining,installing,commissioning, customize and one-stop service

    We will answer your email shortly!

    FOLLOW US