MBR membrane integrity detection

The integrity of the membrane affects the quality of MBR produced water. When the hollow fiber membrane filament breaks for some reason, the raw water on the inlet side will enter the water-producing side directly through the broken membrane filament, resulting in the decline of the water-producing quality. Therefore, effective measures should be established to detect the integrity of the film in practical applications.

There are two types of measures to detect membrane integrity: direct method and indirect method. The direct method is based on the principle of bubble point test. After the film is completely wetted, compressed air below the bubble point pressure is passed into one side of the film filament (the water producing side). Due to the surface tension of the liquid in the film hole, there is no obvious air flow through the wet film hole except for a very small amount of air through the diffusion effect. If the membrane is defective or the membrane filament is broken, a large amount of compressed air will pass through the defect to the other side of the membrane, then if the other side is filled with liquid, continuous bubbles will be observed. The indirect method is to install a turbidity meter (or particle counter, automatic SDI tester) on the production pipe of the ultrafiltration system, and indirectly monitor the integrity of the membrane by monitoring the quality of the produced water.

The direct method is highly sensitive, and the fracture of a single or a few membrane filaments can be detected, but the disadvantage is that the device must stop running during detection, and it is not suitable for continuous detection. The advantage of indirect method is that continuous detection can be carried out, but the sensitivity is low. If the fracture of a small number of membrane filaments does not cause a sudden change in water quality, the turbidimeter can not distinguish and alarm. Therefore, in practical applications, the direct method can be used as a means of daily testing and maintenance in situations with low requirements, and the direct method and indirect method can be combined in situations with high requirements, the indirect method is used for continuous testing, and the direct method is used regularly for testing and maintenance.

5.2 Integrity detection Method

The indirect integrity test method belongs to the category of water quality monitoring. You can consult the water quality instrument supplier or Beenerg engineers. Only the direct integrity test method is introduced here. There are two methods for direct integrity test: bubble observation method and pressure attenuation method. The bubble observation method is suitable for manual detection, and the pressure attenuation method is suitable for manual detection or automatic detection.

Bubble observation method

1. Completely immerse the membrane component in water to fully wet the membrane filament;

2. Adjust the intake pressure reducing valve to 1Bar after the valve;

3. Slowly open the air intake valve and pass the compressed air into the water-producing side of the film filament. At the same time, observe the water surface. If there are continuous bubbles overflow, the film filament has a leakage point; if there are no continuous bubbles overflow, the film filament has good integrity;

4. If there is a leak point in the film wire, it is necessary to repair the film wire, and re-detect it after repair until the detection is passed;

5. Restore the valve status and enter normal operation.

Note: A single bubble that appears over a long period of time is a diffusible bubble and is not considered as a standard for determining the leakage of film filaments.

Pressure attenuation method

1. Completely immerse the membrane component in water to fully wet the membrane filament;

2. Adjust the intake pressure reducing valve to 1Bar after the valve;

3. Slowly open the intake valve, gradually increase the intake pressure to 1Bar, and close the intake valve when the pressure is stable;

Note: At the beginning, part of the undrained water on the intake side will enter the water production side under pressure, and the pressure stabilization time may take 2 ~ 3min;