MBBR technology for sewage treatment plant

MBBR (Moving Bed Biofilm Reactor) is a wastewater biological treatment technology that combines the advantages of traditional activated sludge processes with biofilm processes. Its application in municipal and industrial wastewater treatment plants has grown rapidly over the past 20 years. Its core concept is to add a plastic carrier with a density of ≈1 g cm⁻³ to an aeration tank (or anoxic/anaerobic tank), allowing microorganisms to grow a biofilm on the carrier surface. The carrier rolls freely with the water flow and air bubbles, eliminating the need for backwashing and reducing clogging. Because the biomass is mainly fixed on the carrier, the system retains the mixed liquor suspension characteristics of activated sludge while achieving the high biomass concentration of fixed membrane processes, resulting in a small footprint, shock resistance, and rapid start-up.

 

 

* Biological Carrier: Commercially available K1, K3, Bio-Portz, Bio-Chip M, etc., with a specific surface area of ​​350–650 m² m⁻³, mostly made of HDPE/PP, with a filling rate typically 30–70% (volume fraction).

Tank Structure: Can be newly built, or existing primary sedimentation tanks, aeration tanks, or sludge tanks can be modified; water depth 3–8 m.

Aeration/Agitation: Coarse-medium bubble aerators are used in the aerobic zone to supply oxygen and fluidize the carrier; submersible or side-entry mechanical agitators are used in the anoxic/anaerobic zone.

Post-Separation: Secondary sedimentation tanks, dissolved air flotation, or filters are all acceptable; because the effluent SS is slightly higher than that of MBR, sand or cloth filtration is often added if <10 mg L⁻¹ is required.

 

 

BOD₅ Removal Rate ≥ 90%, Effluent < 10 mg L⁻¹

COD Removal Rate 80–92%, Effluent 60–120 mg L⁻¹

NH₄-N Removal Rate 90–99%, Effluent < 5 mg L⁻¹ (DO > 2 mg L⁻¹, HRT 2–4 h)

TN Removal: Pre-anaerobic MBBR + aerobic MBBR, TN < 10–15 mg L⁻¹, no external carbon source required (C/N > 4)

Total HRT 1.5–4 h (aerobic stage only 1–2 h), sludge production 0.15–0.25 kg VSS kg⁻¹ BOD, 20–30% lower than CAS
Biofilm thickness controlled at 50–150 mm µm; excessive thickness will cause the inner layer to detach due to oxygen deficiency, automatically "shedding" and renewing.

 

 

* High load, small footprint: Effective biomass concentration 8–15 g L⁻¹, footprint is 30–50% of traditional processes.

* Shock Resistance and Rapid Recovery: Biofilm retention time is 20–60 days, providing strong buffering against sudden changes in toxins, pH, salinity, and flow rate; the system recovers within 24 hours after a laboratory salt shock (15 g L⁻¹ NaCl).

* Modular and Easily Expandable: Carriers can be added in batches, allowing CAS to be upgraded to IFAS (Integrated Fixed-film Activated Sludge) or a pure MBBR without interrupting water flow.

* Fast Start-up: New units can reach full capacity in 1–2 weeks; expansion and modification require only a few days of carrier introduction.

* Simple Operation: No sludge return requirement; biofilm detaches naturally, resulting in low secondary sedimentation tank load; aerators are less prone to clogging, requiring minimal maintenance.

* Lower Energy Consumption than MBR: Only 0.5–1 kWh more for aeration and kg⁻¹ N removal, with no membrane suction energy consumption; 30–50% energy saving compared to MBR.

 

 

* High effluent SS: Subsequent filtration or flocculant addition is required to reduce SS to <10 mg L⁻¹. For applications with high reuse requirements, sand filtration/MF is necessary.

* Carrier loss: Fine screens (≤ 6 mm) or perforated plates are required for interception; hydraulic calculations should be strengthened during sudden changes in water flow.

* Simultaneous nitrogen and phosphorus removal requires staged processes: Pre-anoxic + aerobic + post-anoxic + chemical phosphorus removal, resulting in a longer process than CAS; however, it still requires less land.

* Industrial wastewater requires acclimatization: Recalcitrant, high-oil, or high-temperature wastewater requires gradual biofilm formation, with the addition of specific microbial agents if necessary.

* Limited operational experience: Training is needed on carrier management (replenishment, replacement, fire prevention) and biofilm thickness control.

 

 

* Municipal: Lillehammer, Norway, 55,000 m³ d⁻¹, originally overloaded with CAS (Clean Air Supply), after adding K1 carrier, NH₄-N < 1 mg L⁻¹, no additional tank volume required.

* Industrial: 15,000 m³/d⁻¹ of paper mill wastewater from Shandong, China, COD 1800→150 mg L⁻¹, A/O MBBR + air flotation, saving 40% of floor space.

* Containerized: MBBRPAC™ 50–330 m³/d⁻¹ modules, BOD < 15 mg L⁻¹, TSS < 15 mg L⁻¹, on-site installation completed in 3 days.

 

 

1. Loading: Organic 0.3–1.2 kg BOD m³ d; Nitrification 0.15–0.4 kg NH₄-N m³ d; Denitrification 0.3–0.8 kg NO₃-N m³ d.

2. Filling ratio: 40–60% in aerobic zone, 50–70% in anoxic zone; overfilling will hinder fluidization.

3. DO: 2–4 mg L⁻¹ in aerobic zone; < 0.3 mg L⁻¹ in anoxic zone, ensuring a stirring power of 8–12 W m⁻³.

4. Screen: A 0.5–1 mm wedge screen is installed in the effluent zone to prevent carrier loss.

5. Secondary sedimentation tank: Surface loading ≤ 0.8 m³ m⁻² h, solids loading ≤ 120 kg SS m⁻² d; or use air flotation instead.

6. Lifespan: Carrier 10–15 years, aerator 5–8 years; 5% carrier replenishment is required every 3–5 years.

 

Conclusion: With its core selling points of "small footprint, high load capacity, shock resistance, and easy expansion," MBBR has become one of the preferred biological treatment technologies for new wastewater treatment plants, upgrades and expansions of existing plants, and the treatment of highly challenging industrial wastewater. With the right post-separation and filtration units, it can stably achieve Class A or even Class IV surface water quality according to the "Urban Wastewater Treatment Plant Pollutant Discharge Standard" while consuming significantly less energy than MBR. It is especially suitable for projects with limited land, large fluctuations in water volume, or those requiring rapid commissioning.

 

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