Nitrification is often the parameter that pushes a plant into non-compliance, because nitrifying bacteria grow slowly and are the first to be lost when a suspended-growth plant is overloaded or runs at a short sludge age. MBBR addresses this directly: nitrifiers colonise the carriers and are retained on the biofilm regardless of the suspended sludge age. Adding a nitrifying MBBR stage — or converting part of an existing basin — provides dedicated nitrification capacity. The required carrier surface area depends on the ammonia load and the design temperature.
Why MBBR suits nitrification upgrades
Because attached biomass is decoupled from the sludge return, nitrifiers are not washed out during load or flow peaks. Nitrification is strongly temperature-dependent and requires sufficient dissolved oxygen and alkalinity, so a nitrification upgrade is sized for the coldest design condition and checked against the available oxygen and alkalinity. Carbon must be sufficiently removed upstream so that nitrifiers are not outcompeted by faster-growing heterotrophs.
A dedicated nitrification MBBR is typically placed after a carbon-removal stage to give the nitrifiers a low-BOD environment.
Nitrification Upgrade Drivers (indicative literature ranges — confirm per project)
| Parameter | Typical Value | Unit | Notes |
|---|---|---|---|
| Design temperature | coldest case | °C | Nitrification rate falls with T |
| Dissolved oxygen | ≥ ~2 | mg/L | Higher DO aids nitrification |
| Alkalinity | sufficient | — | Consumed during nitrification |
| Upstream BOD | low | — | So nitrifiers are not outcompeted |
Frequently Asked Questions
Why is MBBR good for adding nitrification?
What limits nitrification in an MBBR upgrade?
Where is a nitrification MBBR placed?
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