Converting an activated sludge plant to MBBR or IFAS is one of the most common retrofit routes. Adding biofilm carriers to an existing aeration basin introduces attached biomass that is independent of the sludge return, which increases capacity and makes the process more resilient to load peaks and to washout. Whether the result is a hybrid IFAS system (carriers plus suspended sludge) or a pure MBBR depends on how the conversion is configured and on the treatment objective.
What changes in the conversion
The aeration basin gains carriers and retention screens. Aeration is reviewed because carriers add oxygen demand and require enough turbulence to circulate. The secondary clarifier remains in service to separate sloughed biofilm and any suspended solids. In an IFAS conversion the sludge age and return are still managed; in a full MBBR conversion the process relies on attached growth and the downstream separation stage handles the detached biomass.
The main benefits sought are added capacity in the same footprint, more reliable nitrification, and greater tolerance of hydraulic and organic peaks.
Conversion Considerations (site-specific — confirm per project)
| Parameter | Typical Value | Unit | Notes |
|---|---|---|---|
| Resulting process | IFAS or MBBR | — | Hybrid vs attached-only |
| Aeration | review | — | Added O₂ demand + mixing |
| Clarifier | retained | — | Separates sloughed biomass |
| Benefit | capacity + stability | — | Resilient to load peaks |
Frequently Asked Questions
Is converting activated sludge to MBBR the same as IFAS?
Why convert an activated sludge plant?
Is the secondary clarifier still needed?
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