How to clean reverse osmosis membrane
Reverse osmosis membrane is the core component of water treatment system, and its performance directly affects water quality and system operation efficiency. As the use time increases, pollutants will accumulate on the membrane surface, resulting in a decrease in water flow and a decrease in salt rejection rate. This article will introduce in detail the cleaning methods, steps and precautions for reverse osmosis membranes, and attach relevant data for reference.
1. Types and manifestations of reverse osmosis membrane pollution
Common types of pollution in reverse osmosis membranes include inorganic salt scaling, organic pollution, microbial pollution and colloid pollution. The following are the performance characteristics of various types of pollution:
| Pollution type | Main performance | Common causes |
|---|---|---|
| Inorganic salt scaling | Water production decreases and pressure difference increases | Calcium, magnesium, silicate, etc. deposition |
| organic pollution | Desalination rate decreases and water production decreases | Grease, humic acid, etc. adhere to |
| microbial contamination | The pressure difference rises rapidly and there is a peculiar smell | Bacteria and algae reproduction |
| Colloidal contamination | Water production gradually decreases | Deposition of colloidal particles such as iron and aluminum |
2. Reverse osmosis membrane cleaning steps
1.preprocessing: Shut down the system, drain the water in the membrane shell, and record the operating parameters before cleaning (water production, pressure difference, desalination rate, etc.).
2.Configure cleaning fluid:Choose cleaning agents according to the type of pollution. The following are commonly used cleaning fluid recipes:
| Pollution type | Cleaning fluid ingredients | pH range | temperature |
|---|---|---|---|
| Inorganic salt scaling | 2% citric acid or 1% hydrochloric acid | 2-4 | 30-40℃ |
| organic pollution | 0.1%NaOH+0.025%SDS | 10-12 | 30-35℃ |
| microbial contamination | 1% hydrogen peroxide or 200ppm sodium hypochlorite | 6-8 | 25-30℃ |
3.Cycle cleaning: Use a cleaning pump to circulate the chemical liquid at low pressure for 1-2 hours, and control the flow rate at 1/3 of the value recommended by the membrane manufacturer.
4.Soak: Turn off the cycle and soak for 30-60 minutes to enhance the cleaning effect.
5.Rinse: Rinse with RO produced water or pre-treated water until the pH is neutral, and the drainage turbidity is <1NTU.
3. Cleaning precautions
1. The recommended cleaning frequency is once every 3-6 months, which is determined based on water quality and operating data.
2. The temperature of the cleaning fluid must not exceed 45°C, otherwise the membrane element may be damaged.
3. It is strictly prohibited to use strong oxidants (such as high-concentration sodium hypochlorite) to clean polyamide composite membranes.
4. Disinfection should be carried out after cleaning. You can use 1% sodium bisulfite solution to soak for 30 minutes.
4. Evaluation of cleaning effect
After cleaning is completed, the following parameters need to be compared to judge the effect:
| parameters | Qualification standards |
|---|---|
| Water production recovery rate | ≥85% initial value |
| Desalination rate | ≥95% of initial value |
| Pressure difference between sections | ≤1.2 times the initial value |
5. Daily maintenance suggestions
1. Improve the pretreatment system to ensure SDI <5 and residual chlorine <0.1ppm.
2. Record operating data every month and establish a performance change trend chart.
3. When out of service for a long time, 1% sodium bisulfite protective solution should be injected.
4. It is recommended to conduct professional testing every 2 years to evaluate whether the membrane element needs to be replaced.
With standardized cleaning and maintenance, the service life of the reverse osmosis membrane can be extended to 3-5 years. In actual operation, the technical manual of the membrane manufacturer should be strictly followed. For special water quality, it is recommended to consult a professional water treatment engineer.
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