Tertiary filtration is the final physical barrier in the treatment train. Placed after the MBBR and its primary solids-separation step (clarifier, DAF or filter), it captures residual suspended solids and, when combined with chemical phosphorus precipitation, reduces total phosphorus to very low levels. It is required when discharge limits are stringent or when the effluent is destined for reuse.
Filter types used after MBBR
Sand filters, cloth-media disc/drum filters and dual-media gravity filters are all used for tertiary polishing. Cloth-media filters (disc or drum) are increasingly popular because they combine small footprint, gravity operation and continuous backwash. For very low phosphorus targets, coagulant (e.g. ferric or aluminium salts) is dosed upstream of the filter so that precipitated phosphorus flocs are captured on the media.
In some compact process trains, the secondary solids separation and the tertiary filtration are combined into a single disc or drum filter step directly after the MBBR, avoiding the secondary clarifier entirely. Whether this is feasible depends on the solids load and the effluent targets — confirm per project.
Design considerations
Tertiary filtration after MBBR (indicative — confirm per project)
| Parameter | Typical Value | Unit | Notes |
|---|---|---|---|
| Target | Very low TSS + TP | mg/L | Reuse or sensitive-water discharge. |
| Chemistry | Coagulant for P removal | — | Precipitates phosphorus onto filter. |
| Filter types | Cloth (disc/drum), sand | — | Cloth media increasingly common. |
| Combined step | Possible | — | Single filter replaces clarifier + tertiary. |
Frequently Asked Questions
Is tertiary filtration always needed after MBBR?
Can tertiary filtration remove phosphorus?
Which filter type is best after MBBR?
Related Pages
Need MBBR Design Support?
Submit your wastewater data for a preliminary MBBR engineering assessment. Our team reviews every submission within 2 business days.