Operation and Maintenance Best Practices for MBR Systems

Membrane Bioreactors (MBRs) are a powerful wastewater treatment technology combining biological treatment with membrane filtration. While they offer superior effluent quality and a smaller footprint compared to conventional systems, optimal performance relies heavily on proper operation and maintenance (O&M). This post explores key O&M best practices to ensure long-term membrane health, energy efficiency, and minimized downtime.

A stable biological process is essential for membrane longevity and system efficiency.

• Target MLSS: Maintain Mixed Liquor Suspended Solids (MLSS) typically between 8,000–12,000 mg/L. Overloading can lead to fouling.
• SRT Control: Use long sludge retention times (20–30 days) to reduce sludge production and support nitrification.
• DO Monitoring: Ensure sufficient dissolved oxygen (>2 mg/L) in the bioreactor to support aerobic microbial activity and prevent fouling by filamentous bacteria.

Membrane fouling is the primary challenge in MBR systems. Routine prevention is more effective than reactive cleaning.

• Physical Cleaning (Relaxation and Backflushing): Follow manufacturer recommendations for relaxation intervals and air scouring.
• Chemical Cleaning: Perform regular Clean-In-Place (CIP) with hypochlorite or citric acid based on flux decline or TMP rise.
• Monitor Transmembrane Pressure (TMP): An increasing TMP trend is an early indicator of fouling.

Operating at appropriate flux (flow per membrane area) levels extends membrane life and improves energy efficiency.

• Design Flux: Stay within 15–30 L/(m².h) for municipal applications in i-MBRs (follow the recommendation by supplier). Always operate below critical flux which is the maximum flux below which a membrane can operate without experiencing significant or irreversible fouling [2].
• Adaptive Flux Control: Use flux stepping or automated control systems to adjust to influent variability.

Proper aeration not only supports biological processes but also controls fouling through membrane scouring.

• Intermittent Aeration: Use cyclic or pulse aeration to reduce energy while maintaining cleaning efficiency.
• Airflow Rate: Ensure scouring air rates are maintained per membrane supplier guidelines, typically 0.3–0.6 Nm³/h per m² of membrane [3].

Establish a robust monitoring program to catch issues early.

• Key parameters to log:
  • TMP (daily)
  • Permeate flow and flux
  • MLSS/MLVSS
  • pH, DO, temperature
  • Cleaning frequency and chemical usage
• Trend analysis of TMP and flux can reveal gradual fouling or equipment degradation.

MBR produces less sludge than CAS, but handling still requires attention.

• Waste Activated Sludge (WAS) withdrawal: Schedule regular wasting based on SRT and MLSS trends.
• Sludge thickening or dewatering: Coordinate with downstream handling systems for efficiency.

Be prepared for unexpected issues like membrane damage, power loss, or sudden loading increases.

• Spare parts inventory: Keep critical spares like blower components, valves, and a few spare membrane cassettes.
• Bypass systems: Design and maintain emergency bypass or overflow routes.

Trained operators are the backbone of reliable MBR operation.

• Regular training on biological process control, membrane maintenance, and troubleshooting.
• Maintain SOPs and cleaning logs for consistency and accountability.

Effective operation and maintenance of MBR systems hinges on a balance between biological process control and membrane care. By implementing proactive monitoring, cleaning, and optimization strategies, operators can extend membrane life, reduce energy and chemical use, and maintain consistent high-quality effluent.

1. Membrane Biological Reactors – Edited by Faisal I. Hai, Kazuo Yamamoto, and Chung-Hak Lee
   📖Chapter 2: Process Fundamentals: From Conventional Biological Wastewater Treatment to MBR
   Authors: V. Jegatheesan & C. Visvanathan

           📖 Chapter 4: Monitoring, characterization and control of membrane biofouling in MBR

           Authors: Katsuki Kimura, Fangang Meng, In-Soung Chang and Chung-Hak Lee

2. Metcalf & Eddy – Wastewater Engineering: Treatment and Resource Recovery (5th Edition)
   📖Chapter 14: Membrane Biological Reactors
3. The MBR Book – Simon Judd
   📖Principles and Applications of Membrane Bioreactors for Water and Wastewater Treatment
   A comprehensive guide covering MBR fundamentals, design, operation, and case studies.