Every MBBR needs adequate pretreatment upstream. Rags, fibres, hair and large solids can blind retention screens; grit can abrade carriers and accumulate on the reactor floor; fats and grease can coat carriers and smother biofilm. The minimum pretreatment typically includes screening and, for municipal applications, grit removal.
Why pretreatment matters for MBBR
The retention screens at the reactor outlet are the most vulnerable component. If fibrous material accumulates on them, head loss rises, flow is restricted and — in the worst case — the reactor backs up. Grit settles in dead zones and gradually reduces effective reactor volume. Fats coat the carrier surface and reduce the area available for active biofilm.
For industrial effluents, pretreatment may also include equalisation, pH correction, temperature control, oil/grease removal (by DAF or similar) and, for very high-strength streams, load equalisation. The exact pretreatment train depends on the wastewater and should be confirmed per project.
Minimum pretreatment steps
Pretreatment before MBBR (indicative — confirm per project)
| Parameter | Typical Value | Unit | Notes |
|---|---|---|---|
| Screening | Fine screens | — | Removes rags, fibres and large solids. |
| Grit removal | Required (municipal) | — | Prevents accumulation on reactor floor. |
| FOG removal | Where significant | — | DAF or grease trap for fat/oil/grease. |
| Equalisation | Where loads vary | — | Dampens peak loads and concentration spikes. |
Frequently Asked Questions
What happens if pretreatment is skipped?
What screen size is needed before an MBBR?
Does industrial wastewater need more pretreatment?
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