Alkaline Cleaning Followed by Acid Cleaning
RO membrane cleaning is essential for maintaining stable performance and extending the service life of reverse osmosis membranes. In industrial and municipal water treatment systems, the most effective method is alkaline cleaning first, followed by acid cleaning.
Why Reverse Osmosis Membrane Cleaning Is Required
During continuous operation, RO membranes accumulate organic fouling, biological contaminants, and inorganic scaling. Without proper reverse osmosis membrane cleaning, system efficiency will continuously decline.
Common Types of RO Membrane Fouling
- Organic fouling (oil, grease, natural organic matter)
- Biological fouling (biofilm, bacteria, microorganisms)
- Inorganic scaling (calcium carbonate, metal oxides)
RO Membrane Cleaning Sequence Overview
| Cleaning Step | Cleaning Type | Main Purpose | Recommended Chemical |
|---|---|---|---|
| Step 1 | Alkaline Cleaning | Remove organic & biological fouling | Caustic Soda (NaOH) |
| Step 2 | Acid Cleaning | Remove inorganic scale | Citric Acid |
Recommended RO Membrane Cleaning Procedure
Step 1: Alkaline Cleaning for RO Membrane
Alkaline cleaning targets organic and biological fouling that blocks membrane pores and reduces water flux.
Recommended Chemical: Caustic Soda (NaOH)
Caustic soda (sodium hydroxide, NaOH) is widely used for alkaline RO membrane cleaning due to its strong ability to dissolve organic matter and biofilm.
Typical RO Membrane Cleaning Parameters
| Parameter | Alkaline Cleaning | Acid Cleaning |
|---|---|---|
| Chemical | Caustic Soda (NaOH) | Citric Acid |
| pH Range | 10.5 – 12 | 2 – 4 |
| Temperature | 25 – 35°C | 20 – 30°C |
| Circulation Time | 30 – 60 minutes | 30 – 60 minutes |
Step 2: Acid Cleaning for RO Membrane
After alkaline cleaning, acid cleaning is applied to dissolve inorganic scale and mineral deposits on the membrane surface.
Recommended Chemical: Citric Acid
Citric acid is a mild organic acid commonly used in RO membrane acid cleaning. It effectively removes calcium carbonate and metal scaling while remaining safe for most reverse osmosis membranes.
Citric Acid vs Other Acids for RO Membrane Cleaning
| Acid Type | Cleaning Efficiency | Membrane Safety | Industry Usage |
|---|---|---|---|
| Citric Acid | High | Excellent | Widely used |
| Hydrochloric Acid | Very High | Risky | Limited |
| Sulfuric Acid | High | Medium | Limited |
Why Alkaline Cleaning Must Be Done Before Acid Cleaning
- Organic fouling blocks acid contact with inorganic scale
- Alkaline cleaning opens membrane pores
- Acid cleaning becomes more effective afterward
- Overall chemical consumption is reduced
Conclusion
A professional reverse osmosis membrane cleaning program should follow alkaline cleaning with caustic soda (NaOH) and then acid cleaning with citric acid. This proven two-step process ensures maximum cleaning efficiency, stable system operation, and extended membrane lifespan.
