1. Background of Process Development
Traditional activated sludge processes are mature and capable of achieving good treatment performance. However, they typically require large land areas, high capital investment, and exhibit poor adaptability to fluctuations in influent water quality and quantity.
Biofilm processes offer better stability, strong resistance to shock loads, smaller footprints, and effective removal of organic matter. Nonetheless, they face issues such as clogging of filter media and difficulties in maintenance.
The Moving Bed Biofilm Reactor (MBBR) process was developed in the late 1980s in Europe to combine the strengths of both technologies while overcoming their main limitations. It has since become a highly efficient hybrid wastewater treatment technology.
2. Process Principle
In MBBR systems, buoyant suspended carriers with a density close to that of water are added to the reactor. Through aeration and hydraulic mixing, these carriers remain in continuous motion, ensuring optimal contact between wastewater and biofilm.
Microorganisms attach to the internal and external surfaces of the carriers, forming zones with aerobic, anoxic, and anaerobic conditions. This enables simultaneous nitrification and denitrification, enhancing both organic matter removal and nitrogen reduction.
MBBR Tank-1
MBBR Tank-2
3. Technical Features
- Compact footprint: Requires only about 20% of the tank volume of a conventional activated sludge process.
- Low maintenance: No sludge recirculation or backwashing is required; carriers do not clog easily.
- High load tolerance: Can handle high organic loading rates while maintaining stable effluent quality.
- High efficiency: Low operational energy consumption and simple management, suitable for both new installations and retrofits.
4. Key Influencing Factors
Carrier properties: Should have a density close to water, large specific surface area, strong biofilm affinity, and good fluidization behavior.
Dissolved Oxygen (DO): Must be kept within optimal range (generally ≥2 mg/L) to balance nitrification and denitrification while avoiding unnecessary energy consumption.
Hydraulic Retention Time (HRT): Influences contact efficiency between organic matter and microorganisms; should be optimized based on influent characteristics.
Temperature & pH: Nitrifying bacteria perform best at 20–30°C, denitrifying bacteria at 20–40°C; optimal pH is 6.5–8.5.
Other factors: Air-to-water ratio, influent turbidity, COD load, nutrient balance, and presence of toxic substances can also affect performance.
5. Application Status
International: Widely used in municipal and industrial wastewater treatment, including pulp and paper, food processing, slaughterhouses, and oil refining. Over a hundred full-scale MBBR-based treatment plants have been built worldwide.
China: Research is mainly at the laboratory or pilot stage, with small-scale engineering applications more common. Development of
novel suspended carriers and scaling-up to full industrial application remain areas with significant potential.