Have you noticed that your MBR membrane system is producing colored effluent? If so, you’re not alone. The MBR membrane color issue is common in wastewater treatment plants, especially those handling textile, dye, or chemical wastewater. In this article, we’ll break down the main causes and show you simple solutions to improve water clarity and meet discharge standards.
1. What Causes the MBR Membrane Color Issue?
Even though MBR membranes do a great job removing suspended solids and bacteria, they are typically classified as ultrafiltration (UF) or microfiltration (MF) membranes. These membranes are porous and cannot block small colored molecules, known as color-causing agents. These agents can include:
A. Incomplete ammonia removal
If ammonia (NH₃) is not properly treated in the AO (Anaerobic-Oxic) biological system, it may cause the water to turn yellowish.
B. High levels of metal ions
Excessive iron (Fe), copper (Cu), or chromium (Cr) ions in the water can lead to a stronger color due to ionized compounds.
C. Small dye molecules
Industries like printing and dyeing or ink production often use colorants that are too small for MBR membranes to filter out.
D. Hidden colored compounds activated during aeration
Some colorless organic compounds can turn colored after oxidation or during the aerobic stage, especially chelates or complex molecules
2. What Can You Do to Remove the Color?
Depending on the specific source of the color, you can try one or more of these solutions:
A. Improve biological treatment
Strengthen the AO system and control ammonia levels to reduce yellowing caused by leftover NH₃.
B. Add post-treatment filtration
Use activated carbon filters, coagulants, or decolorizing agents after the membrane stage.
C. Enhance oxidation
For small, hard-to-remove organics, consider adding advanced oxidation processes (AOPs) like:
- Ozone (O₃)
- Sodium hypochlorite (NaClO)
- Fenton reaction
C. Use NF/RO membranes for deep decolorization
- Add a Nanofiltration (NF) or Reverse Osmosis (RO) system after the MBR stage.
- his is becoming more common in high-demand applications like landfill leachate treatment, dye wastewater reuse, or chemical wastewater recovery.
Conclusion
Color in MBR-treated water doesn’t necessarily mean poor performance. In many cases, the turbidity is low and the water is safe — it just looks a little off. But if aesthetics, reuse, or specific industry standards matter, you’ll want to consider one or more of the methods above.
Need help selecting the right MBR membranes or designing a post-treatment process? Feel free to reach out, we’re happy to support your project.
