What is an MBBR? Moving Bed Biofilm Reactor Explained

Introduction

The Moving Bed Biofilm Reactor (MBBR) is one of the most significant advances in biological wastewater treatment in the last 30 years. Originally developed in Norway in the late 1980s by Professor Hallvard Ødegaard at NTNU, the technology has become a global standard for municipal and industrial treatment plants that need high performance in a compact footprint.

At its core, MBBR combines the best elements of activated sludge (the microorganisms do the work) with fixed-film media (the microorganisms stay put). The result is a system that handles load variations, resists toxic shocks, and doesn't require recycle streams — with no moving parts in the reactor itself.

How Does MBBR Work?

The MBBR process uses small plastic carrier elements — typically polyethylene or high-density polyethylene — that move freely through the reactor tank. Each carrier has a protected surface area on its interior, where a biofilm of microorganisms grows and is retained regardless of hydraulic conditions.

The carriers are typically about the size of a bottle cap (25-50mm diameter) and have a specific gravity slightly less than or equal to water, allowing them to move through the tank without settling. Aeration or mixing keeps the carriers in suspension, ensuring contact between wastewater and the biofilm.

Key process steps:

1. Wastewater enters the MBBR reactor
2. Carriers circulate freely, driven by aeration (aerobic process) or mixing (anoxic/anaerobic zones)
3. Microorganisms in the biofilm on the carriers consume organics, ammonia, or other target compounds
4. Effluent screens (1-3mm openings) retain the carriers while treated water passes through
5. Excess biomass sloughs off naturally — no sludge recycle needed

The biofilm naturally maintains the right thickness through sloughing — when it gets too thick, shear forces from carrier-on-carrier contact remove the outer layer. This self-regulating mechanism eliminates the need for wasting mechanisms or RAS (return activated sludge) control.

MBBR vs. Activated Sludge: Key Differences

When to Use MBBR

MBBR is the right choice when:

• Space is limited. The process produces significantly higher volumetric loading rates than conventional activated sludge. MBBR reactors treating the same flow require 30-60% less tank volume.

• Upgrading an existing plant. Converting an existing activated sludge tank to MBBR is a common upgrade path. Add carriers and effluent screens — no new tanks required.

• Nitrification is the primary goal. MBBR is extremely well-suited to nitrification (ammonia to nitrate conversion). The biofilm retains slow-growing nitrifiers that are often washed out of activated sludge systems.

• Flows vary widely. The attached biomass on carriers is not washout-sensitive the way suspended biomass is. MBBR handles diurnal and seasonal peaks well.

• You need a high-rate BOD removal system. In a combined MBBR/activated sludge (IFAS) configuration, MBBR carriers handle the high-rate BOD removal zone, freeing up the aeration basin for nitrification.

MBBR is typically not the right choice for:

• Very large plants (>10 MGD) where conventional activated sludge with optimized controls may be more cost-effective
• Applications requiring biological phosphorus removal in a single reactor (EBPR in MBBR is possible but complex)

MBBR for Nitrification

Nitrification — converting ammonia (NH4-N) to nitrate (NO3-N) — is one of MBBR's strongest applications. The nitrifying bacteria Nitrosomonas and Nitrobacter are slow-growing organisms that struggle in activated sludge systems with short SRTs (solids retention times) or at low temperatures.

In MBBR, nitrifiers colonize the protected inner surface of the carriers where they're shielded from high shear. A well-designed nitrification MBBR can reliably produce effluent with <1 mg/L NH4-N even at water temperatures as low as 10°C.

Typical nitrification MBBR design parameters:

• Surface area loading: 0.5-1.5 g NH4-N/m²·day
• Carrier fill fraction: 40-67% typical, ~70% practical max
• DO: >2 mg/L
• Hydraulic retention time: 30-90 minutes (reactor volume only)

MBBR for Lagoon Upgrading

One of the most compelling MBBR applications in the municipal market is lagoon upgrading. Thousands of small communities operate stabilization lagoons that were designed 30-50 years ago to meet older standards. Today's nutrient limits — particularly for ammonia and total nitrogen — require those lagoons to be upgraded.

Adding MBBR carriers to an existing lagoon cell can dramatically improve performance without building new tanks. The carriers provide the attached biomass surface for nitrification, while the lagoon volume provides adequate HRT for BOD removal and settling.

Entex Technologies (Chapel Hill, NC) and Triplepoint Environmental have both done significant work in this application.

Pros and Cons of MBBR

Pros:

• No sludge recycle required — simpler operation
• High volumetric efficiency — smaller footprint
• Excellent nitrification performance
• Resilient to load shocks and toxic influent
• Retrofit-friendly — add to existing tanks
• Reliable, low-maintenance media (20+ year lifespan)

Cons:

• Requires secondary clarification (not a standalone process)
• Effluent screens require maintenance
• Higher upfront media cost than activated sludge alone
• Not optimal for biological phosphorus removal without additional zones

MBBR Manufacturers

Several manufacturers offer MBBR carrier media and process systems. Leading providers include:

• Entex Technologies — WavTex, Webitat (BioWeb), and BioBloc MBBR/IFAS media (lagoon upgrades and municipal)
• Veolia (AnoxKaldnes) — commercialized MBBR (invented by Prof. Ødegaard, NTNU); K-series carriers
• Nexom — North American MBBR/IFAS specialist
• Biowater Technology — Norwegian manufacturer, strong US presence
• Ecologix Environmental Systems — industrial and municipal
• Nviro — combined SBR/MBBR systems

Browse MBBR equipment manufacturers on WER →

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