Short answer: MBBR alone cannot achieve enhanced biological phosphorus removal (EBPR). EBPR requires alternating anaerobic and aerobic conditions with sludge recycling to enrich phosphorus-accumulating organisms (PAOs) — conditions that do not exist in a pure MBBR. When phosphorus removal is required, chemical precipitation (typically iron or aluminium salts) is added alongside the MBBR.
Why MBBR cannot do EBPR
EBPR relies on cycling PAOs through strict anaerobic conditions (where they release phosphorus and take up volatile fatty acids) and aerobic conditions (where they take up excess phosphorus). This cycling requires a defined sludge age (SRT) managed through sludge return. In a pure MBBR, there is no sludge return, no controlled SRT, and the biofilm is always exposed to the same reactor conditions — making PAO enrichment impossible.
Chemical phosphorus removal
The standard approach is to dose a metal salt (ferric chloride, ferric sulphate or aluminium sulphate) into the process. The metal ions react with dissolved phosphate to form insoluble precipitates that are removed with the sludge. Dosing can occur before, during or after the biological stage.
Chemical P removal with MBBR (indicative — confirm per project)
| Parameter | Typical Value | Unit | Notes |
|---|---|---|---|
| Iron salt (FeCl₃) | Most common | — | Molar ratio Fe:P typically 1.5–2.5 for low effluent P. |
| Aluminium salt (alum) | Alternative | — | Similar effectiveness; choice depends on local supply and sludge handling. |
| Dosing point | Pre- or simultaneous | — | Before or into the MBBR reactor, or ahead of the clarifier. |
| Achievable effluent TP | Below 0.5 mg/L | mg/L | With optimised dosing and good solids separation. |
Frequently Asked Questions
Can IFAS (hybrid MBBR) achieve EBPR?
Does chemical dosing affect biofilm performance?
Is chemical P removal expensive?
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.