Reasons and solutions for blocking reverse osmosis membrane

Published in:2020-10-20    Category:Common problem  

Reverse osmosis equipment in use
It is inevitable that there will be improper operation or improper cleaning
And the problem of blocking the reverse osmosis membrane
Let’s analyze these issues
And summarize the corresponding solutions

01/Reverse osmosis membrane blocked reasons and solutions

1. The system is equipped with pretreatment devices that are not suitable for the quality and flow of the raw water, or the necessary process devices and process links are not equipped in the system.

2. The pretreatment device is not operating normally, that is, the original pretreatment equipment of the system has a low ability to remove raw water SDI components, turbidity, colloids, etc., and the pretreatment effect is not ideal.

3. Inappropriate equipment is selected by the system or the equipment material is incorrectly selected (pumps, piping and others).

4. The system chemical injection device fails (acid, flocculation/coagulant aid, scale inhibitor/dispersant, reducing agent and others).

5. Appropriate protective measures are not taken after the equipment is running intermittently or the system is out of use.

6. Unreasonable equipment operation and use by operation management personnel (recovery rate, water production, concentrated water, pressure difference, cleaning, and others).

7. Long-term accumulation of insoluble sediments in the membrane system.

8. The raw water composition has changed greatly or the water source characteristics have undergone a fundamental change.

9. A considerable degree of microbial contamination has occurred in the reverse osmosis membrane system.

02/Performance of fouling and blocking of different pollutants

1. Carbonate scale
Performance after scaling: the standard permeate flow rate decreases, or the salt rejection rate decreases.
Reason: Concentration polarization on the membrane surface increased. 2. Iron/Manganese
Post-contamination performance: The standard pressure difference rises (mainly at the membrane element at the front end of the device), which may also cause a drop in water permeability. Usually manganese and iron will be present at the same time.
3. Sulfate scale
If deposition occurs, it will first affect the last membrane element of the system with the highest salt concentration, which is manifested as a significant increase in the pressure difference between the two stages. Need to use special cleaning agent.

4. Silicon
Granular silicon: fouling the water flow channel of the membrane element, causing the system pressure difference to rise. The use of 0.4% dichloramine is effective for dissolving seriously polluted silica scale.
Colloidal silicon: similar to granular silicon.
Dissolved silicon: the formation of silicate precipitation, should be washed with dichloramine.

5. Suspended matter/organic matter
Fouling performance: the water permeation rate decreases, and the pressure difference in a section increases significantly. If the feed water SDI is greater than 4 or the turbidity is greater than 1, the possibility of organic contamination is greater.

6. Microorganisms
Fouling performance: the standard pressure difference increases or the standard water permeability decreases. Non-oxidizing bactericide and alkali can be used for cleaning.

7. Iron bacteria
Fouling performance: the standard pressure difference rises. EDTA sodium salt and alkali can be used for cleaning.

03/The membrane should be cleaned when the following situations occur

1. The water output of the standardized equipment has been reduced by 10-15%;

2. The operating pressure of the standardized membrane system has increased by 15%;

3. The salt permeability of the standardized membrane system has increased by 10-15% compared with the initial normal value;

4. The operating pressure difference has increased by 15% compared to the initial operation.

04/Reverse osmosis membrane cleaning method

1. Negative pressure cleaning: Negative pressure cleaning can be said to be the pressure formed on the side of the reverse osmosis membrane through the vacuum suction of the equipment, which can effectively remove the contaminants on the membrane surface and inside;

2. Recoil: Recoil is the use of powerful gas or liquid to clean the surface of the membrane, so as to clean up the contaminants inside the membrane and restore the membrane. Recoil is currently one of the more common ways to clean reverse osmosis membranes. One;

3. Chemical cleaning: The chemical cleaning method is to use chemical cleaning agents to clean the reverse osmosis membrane. Because it is a chemical targeted cleaning that can also effectively clean the membrane, this method is also one of the commonly used cleaning methods.