A Moving Bed Biofilm Reactor (MBBR) is a biological wastewater treatment technology in which specially designed polyethylene carriers, each typically 10–25 mm in size, are kept in continuous motion inside a reactor by aeration or mechanical mixing. Microorganisms colonize the protected interior surfaces of the carriers, forming a thin, active biofilm that removes organic pollutants (BOD/COD) and nutrients (ammonia, nitrogen) from wastewater.
Definition and Core Concept
The term "Moving Bed Biofilm Reactor" describes the fundamental operating principle: the biofilm "bed" (the mass of plastic carriers) moves freely inside the reactor rather than being fixed to a static support structure. This distinguishes MBBR from other biofilm processes such as trickling filters, rotating biological contactors (RBCs), or fixed-bed reactors.
Invented by Professor Hallvard Ødegaard and colleagues at the Norwegian University of Science and Technology (NTNU) in the late 1980s, the MBBR concept was first commercialized by Kaldnes Miljøteknologi (now Veolia Water Technologies / AnoxKaldnes). Since then, multiple vendors have developed proprietary carrier designs, but the underlying process principle remains the same.
The core innovation of MBBR is that it achieves high biomass concentrations (5–20 g VSS/L of carrier volume) without requiring sludge recirculation or large settling tanks. The biofilm is self-regulating: excessive growth is sheared off by hydrodynamic forces, maintaining an optimal active thickness of approximately 50–300 µm.
Key Terminology
Biofilm Carrier
Small plastic element (HDPE/PP) with internal voids providing protected surface area for biofilm growth.
Fill Ratio
Volume of carriers / total reactor volume, typically 30–67%.
Protected Surface Area
Internal carrier area accessible to biofilm, measured in m²/m³ of carrier.
SALR
Surface Area Loading Rate — substrate load per m² of biofilm surface per day (g/m²·d).
Retention Screen
Sieve at the reactor outlet that keeps carriers inside while passing treated effluent.
IFAS
Integrated Fixed-Film Activated Sludge — MBBR carriers added to an existing CAS reactor.
MBBR vs. Activated Sludge — Key Differences
| Parameter | Typical Value | Notes |
|---|---|---|
| Biomass Attachment | Attached biofilm on carriers | MBBR |
| Biomass Retention | Carriers + retention screen | No sludge recirculation |
| Footprint | 50–70% of CAS | Higher volumetric rates |
| Sludge Return | Not required | Simpler operation |
| Shock Load Tolerance | High | Biofilm is protected |
| MLSS Control | Not applicable | No suspended biomass target |
Process Overview
In a typical MBBR system, raw or pre-treated wastewater enters a reactor tank filled with biofilm carriers at 30–67% fill ratio. Aeration diffusers at the bottom of the tank provide oxygen for aerobic treatment and keep the carriers in suspension through the rising air pattern. The carriers tumble and circulate, exposing the biofilm to the wastewater and oxygen.
As wastewater flows through the reactor, dissolved organic compounds and ammonia diffuse into the biofilm, where they are metabolized by heterotrophic bacteria (for carbon removal) and autotrophic nitrifiers (for ammonia oxidation). The treated effluent exits through a retention screen and proceeds to secondary clarification or direct filtration.
For anoxic applications (denitrification), carriers are kept in motion by slow-speed mechanical mixers instead of aeration. The anoxic zone is typically placed before the aerobic zone, with nitrate-rich recirculation from the aerobic stage providing the electron acceptor for denitrifying bacteria.
Where MBBR Is Used
MBBR technology is deployed in municipal wastewater treatment plants (secondary treatment, nitrification, tertiary polishing), industrial pretreatment (food & beverage, dairy, brewery, pharmaceutical, petrochemical), aquaculture (recirculating aquaculture systems), and decentralized or small-scale treatment installations. Its ability to operate in existing tanks without new civil construction makes it particularly attractive for plant upgrades and capacity expansions.
Frequently Asked Questions
What does MBBR stand for?
Who invented MBBR?
Is MBBR the same as IFAS?
Does MBBR require sludge recirculation?
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