In industrial applications where the wastewater carries significant fats, oils, grease (FOG) or fine suspended solids that do not settle well, a dissolved air flotation (DAF) unit upstream of the MBBR is often the most effective pretreatment. DAF injects micro-bubbles that attach to particles and float them to the surface for removal, protecting carriers and biofilm from coating and clogging.
Why DAF suits MBBR pretreatment
FOG and fine colloidal solids are not removed effectively by gravity sedimentation but are lifted efficiently by DAF. Removing them upstream protects the carrier surface from coating (which reduces active biofilm area), prevents grease from accumulating on retention screens and reduces the total organic load reaching the biological stage. For food, dairy, meat-processing and similar industries, DAF + MBBR is a proven and compact combination.
DAF units are typically dosed with coagulant and/or polymer to aggregate the fine particles before flotation. The floated sludge (float) is high in organic matter and must be handled separately. The clarified underflow feeds the MBBR at a much lower FOG and TSS concentration, which lets the biofilm develop on clean carrier surfaces.
DAF pretreatment design
DAF + MBBR design factors (indicative — confirm per project)
| Parameter | Typical Value | Unit | Notes |
|---|---|---|---|
| Target removal | FOG + fine TSS | — | Protects carriers and screens. |
| Chemistry | Coagulant ± polymer | — | Aggregates fine particles for flotation. |
| Float handling | High-strength waste | — | Must be managed separately. |
| Industries | Food, dairy, meat, etc. | — | Where FOG is significant. |
Frequently Asked Questions
When is DAF needed before an MBBR?
Can the MBBR work without DAF pretreatment?
Does DAF reduce the MBBR size?
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