Process Technology
Moving Bed Biofilm Reactor (MBBR)
Attached-growth process using plastic carrier media. Compact, scalable, and uniquely suited for retrofitting existing aeration tanks.
Process Description
The MBBR process uses specially designed plastic carrier elements that move freely within the aeration tank. Biofilm grows on the protected internal surfaces of these carriers, providing a high specific surface area for biological treatment.
Unlike activated sludge, the MBBR does not rely on sludge recirculation for biomass retention. The biofilm carriers are kept in the reactor by sieves at the outlet, while excess biofilm sloughs off naturally and is removed in downstream solids separation.
Key Design Parameters
Specific Surface Area
Protected surface of carriers
Fill Fraction
Volume of carriers in reactor
Surface Loading Rate
For BOD removal
Nitrification Rate
At 15°C
Retrofit Potential
One of the key advantages of MBBR technology is its retrofit capability. Carrier media can be added to existing aeration tanks, converting them from a pure activated sludge system to a hybrid IFAS (Integrated Fixed-Film Activated Sludge) or standalone MBBR.
Can be installed in existing concrete or steel tanks
No additional land required for biological capacity increase
Minimal civil works — primarily sieves, aeration modifications, and carrier addition
Gradual capacity increase possible by adding carriers over time
Combined with existing activated sludge as IFAS for incremental upgrade
Engineering Note
When to Consider MBBR
| Condition | Potential Issue | What to Investigate |
|---|---|---|
| Need more biological capacity | Existing tanks at limit | Add carriers to existing tanks (IFAS retrofit) |
| No space for new tanks | Limited footprint | MBBR increases capacity within existing volume |
| Variable or peak loads | Seasonal or industrial variation | Biofilm is more resilient to load peaks than suspended growth |
| Nitrification required | Need to add nitrification | Dedicated MBBR nitrification stage post-BOD removal |
Frequently Asked Questions
An MBBR is an attached-growth process in which biomass grows as a biofilm on small plastic carrier media kept in suspension by aeration or mixing. Sieves at the outlet retain the carriers, while excess biofilm sloughs off and is removed in downstream solids separation.
MBBR is well suited to retrofits and capacity expansions because carriers can be added to existing tanks to increase biological capacity without enlarging the footprint. It is robust to hydraulic peaks and does not rely on sludge recirculation for biomass retention.
In activated sludge the biomass is suspended and must be separated and recirculated. In MBBR the biomass stays in the reactor on carriers, so there is no return sludge stream for biomass control. MBBR can also be combined with suspended growth as IFAS to boost an existing activated sludge plant.
Engineering Assessment
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