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

The service life of reverse osmosis membrane elements depends on the chemical stability of the reverse osmosis membrane, the physical stability of the membrane elements, cleanability, influent water source, pretreatment, cleaning frequency, operation and management level, etc. Under the premise that the influent water quality meets the requirements of the membrane element system, the service life of reverse osmosis membrane elements can usually reach more than 5 years.

2. What separation capacity does reverse osmosis membrane technology have?

Reverse osmosis membrane technology is currently a precise liquid filtration technology. Reverse osmosis membranes have a retention effect on soluble inorganic salt molecules and organic matter with a molecular weight greater than 100. At the same time, water molecules can freely pass through the reverse osmosis membrane. The typical soluble salt removal rate is 95-99%.

3. What kind of pretreatment is generally required for reverse osmosis membrane systems?

The usual pretreatment system consists of the following: coarse filtration (~80 microns) to remove large particles, adding oxidants such as sodium hypochlorite, and then fine filtration through a multi-media filter or clarifier, and then adding sodium bisulfite to reduce residual chlorine and other oxidants, and installing a safety filter before the high-pressure pump inlet.

The role of the safety filter: As the name suggests, it is an indispensable 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 soften or add acid and scale inhibitors, etc. For water sources with high microbial and organic content, activated carbon or anti-pollution membrane elements are also required.

4. Can reverse osmosis membrane technology remove microorganisms such as viruses and bacteria?

The reverse osmosis membrane is very dense and has a very high removal rate for viruses, bacteriophages and bacteria, at least above 3log (removal rate>99.9%). However, it should be noted that in many cases, microorganisms may still grow again on the membrane water production side, which mainly depends on the way of assembly, monitoring and maintenance. That is to say, the ability of a system to remove microorganisms mainly depends on whether the system design, operation and management are appropriate, rather than the properties of the membrane element itself.

5. What is particle and colloid pollution? How to judge?

Once the reverse osmosis or nanofiltration membrane system is blocked by particles and colloids, the water production of the membrane will be seriously affected, and sometimes the desalination rate will be reduced.

The early symptom of colloid fouling is the increase of system pressure difference. The source of particles or colloids in the water source of the membrane system varies from place to place, often including bacteria, sludge, colloidal silicon, iron corrosion products, etc. The chemicals used in the pretreatment part, such as polyaluminum and ferric chloride or cationic polyelectrolyte, may also cause fouling if they cannot be effectively removed in the clarifier or medium filter.

6. Can the reverse osmosis membrane pure water system be started and stopped frequently?

The membrane system is designed based on continuous operation, but in actual operation, there will always be a certain frequency of startup and shutdown.

When the membrane system is shut down, it must be flushed at low pressure with its produced water or qualified pre-treated water to replace the high-concentration concentrated water containing antiscalant from the membrane elements; measures should also be taken to prevent water leakage in the system and the introduction of air, because if the elements dry up due to water loss, irreversible water flux loss may occur.

If the shutdown is less than 24 hours, there is no need to take measures to prevent microbial growth. However, if the shutdown time exceeds 24 hours, a protective liquid should be used to preserve the system or the membrane system should be flushed regularly.

7. What is the effect of pH on removal rate, water production and membrane life?

The pH range used for reverse osmosis membrane products is generally 2 to 11. The effect of pH on the performance of the membrane itself is small, but the characteristics of many ions in water are greatly affected by pH. For example, when weak acids such as citric acid are under low pH conditions, they are mainly non-ionic, but dissociate and become ionic under high pH values. For the same ion, the removal rate of the membrane is high when the charge is high, and the removal rate of the membrane is low when the charge is low or uncharged. Therefore, pH has a huge impact on the removal rate of certain impurities.

8. How do I know if the membrane has been contaminated?

The following are common symptoms of contamination:

(1) Water production decreases at standard pressure;

(2) In order to achieve standard water production, the operating pressure must be increased;

(3) The pressure drop between the inlet water and the concentrate increases;

(4) The weight of the membrane element increases;

(5) The membrane removal rate changes significantly (increases or decreases);

(6) When the membrane element is taken out of the pressure vessel, water is poured on the inlet side of the erected membrane element. The water cannot flow through the membrane element and only overflows from the end face (indicating that the inlet flow channel is completely blocked).

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

When the protective solution becomes turbid, it is likely due to microbial growth. Membrane elements protected with sodium bisulfite should be checked every three months.

When the protective solution becomes turbid, the element should be taken out of the sealed bag and re-immersed in fresh protective solution. The concentration of the protective solution is 1% (weight concentration) food-grade sodium bisulfite (not activated by cobalt). Soak for about 1 hour and reseal it. The element should be drained before repackaging.

10. How do you know what cleaning method should be used for your membrane system?

In order to achieve the cleaning effect, it is very important to choose the cleaning agent and cleaning steps that can be symptomatic. Incorrect cleaning will actually deteriorate the system performance. Generally speaking, for inorganic scaling pollutants, it is recommended to use acidic cleaning solution, and for microbial or organic pollutants, it is recommended to use alkaline cleaning solution.