Aug 10, 2026

MBR vs MBBR · differences explained

Content

1 1. First, understand the core of wastewater treatment
2
3 2. MBR: membrane replaces the secondary clarifier
4
5 3. MBBR: more “living area” for microbes
6
7 4. MBR vs MBBR: how to choose?
8
9 5. More projects now use a “combined approach”
10 6. Final summary

One letter apart: MBR and MBBR — what’s the real difference? Read this article and you’ll understand

Anyone who has worked in wastewater treatment for a while has certainly heard the two names: MBR and MBBR. Many newcomers feel confused: only one letter apart, both sound like “advanced processes”, but what’s the actual difference? When I first encountered MBBR around 2016, I thought it was just an upgraded version of MBR.

MBR uses a membrane for filtration.

MBBR gives microbes extra “living space”.

One strengthens sludge-water separation, the other strengthens biological treatment.

1. First, understand the core of wastewater treatment

Most wastewater treatment essentially does two things:

Step 1: microbes consume the pollutants
Step 2: separate microbes from water

biological treatment sludge-water separation

The conventional activated sludge process is simple: aeration tank → secondary clarifier. MBR and MBBR are enhancements in these two steps.

2. MBR: membrane replaces the secondary clarifier

MBR stands for Membrane Bioreactor. The biggest change: replace the secondary clarifier with membrane filtration.

Imagine: traditional process “waits for sludge to settle”. MBR is like placing a very fine filter mesh in the water. Pore size 0.01~0.4 µm, much smaller than bacteria.

Sludge is completely retained
Suspended solids nearly zero
Very clear effluent – many MBR effluents can be reused as reclaimed water

MBR operation feature: extremely high sludge concentration.

Conventional activated sludge: MLSS ~2000–4000 mg/L.

MBR: MLSS usually 6000–12000 mg/L → more microbes, higher efficiency, smaller tank volume.

MBR advantages

Excellent effluent quality, SS ~0, very low turbidity
Stable compliance with Class 1A or higher
Small footprint (no secondary clarifier)
Stable system – no sludge washout
Good nitrogen removal (long SRT allows nitrifiers to thrive)

MBR challenges

Membrane fouling – leads to: lower flux, higher suction pressure, increased energy use
Requires: air scouring, backwashing, chemical cleaning
Membrane replacement every 3–5 years
Higher energy consumption (membrane scouring + suction)

3. MBBR: more “living area” for microbes

MBBR stands for Moving Bed Biofilm Reactor. This approach does not change sludge-water separation; instead, it increases the microbial population.

How? By adding suspended carriers (plastic media) into the aeration tank. They move and tumble with aeration, and each carrier grows a biofilm.

Think of it this way: Conventional activated sludge – microbes are “suspended in water”. MBBR has two parts: suspended sludge + biofilm on carriers → total biomass increases significantly.

Why MBBR is shock-resistant: biofilm on carriers is not easily washed out. When water quality fluctuates, the attached biofilm stabilises the system. That’s why many industrial projects prefer MBBR.

MBBR advantages

Strong shock-load resistance
Biofilm not easily lost → stable system
Easy retrofit – just add carriers in existing tanks
Simple operation, no membrane equipment
Lower energy consumption (similar to conventional aeration)

MBBR limitations

Effluent quality ceiling – still uses secondary clarifier
Effluent SS and turbidity usually higher than MBR
Potential issues: carrier accumulation, uneven aeration

4. MBR vs MBBR: how to choose?

Focus on three questions:

Effluent requirements – if reuse / high standard / surface water standards → MBR is better (membrane removes almost all SS).
Footprint – if space is tight → MBR has an advantage (no clarifier).
Investment & operation – if stability, cost, and simple management are priorities → MBBR is often more suitable, especially for upgrading old plants.

5. More projects now use a “combined approach”

In some projects, the two are combined: MBBR + MBR – carriers are added to the MBR bioreactor. Benefits: higher biomass and reduced membrane fouling. Many high-standard WWTPs adopt this concept.