An aerobic MBBR is the most widely applied configuration: carriers move freely in an aerated reactor where the biofilm oxidises organic carbon (BOD/COD) and, if the reactor is sized and loaded for it, converts ammonia to nitrate (nitrification). Coarse-bubble aeration serves the dual purpose of supplying dissolved oxygen and keeping the carriers circulating.
How the aerobic process works
Wastewater flows through the reactor continuously. Bacteria colonise the protected surfaces of the carriers, forming a biofilm that absorbs and metabolises dissolved organic matter and — in the outer, oxygenated biofilm layer — oxidises ammonia. Because the biofilm is attached, the process retains a large, active biomass without needing sludge return, making it inherently resistant to washout.
Oxygen supply is usually the limiting factor, especially when both carbon removal and nitrification must occur in the same reactor. Carbon-oxidising heterotrophs grow faster and thicker than the slower nitrifiers, so at high organic loads the nitrifiers are outcompeted for space and oxygen. This is why high-rate carbon removal and deep nitrification are often separated into stages — the first reactor takes the organic load, the second, lower-loaded reactor supports a thin nitrifying biofilm.
Key design considerations
Aerobic MBBR design factors (indicative — confirm per project)
| Parameter | Typical Value | Unit | Notes |
|---|---|---|---|
| Aeration purpose | O₂ supply + carrier mixing | — | Coarse-bubble grid drives both functions. |
| Limiting factor | Dissolved oxygen | — | Especially when nitrification is required. |
| Carbon vs nitrification | Staging helps | — | Separate high-rate C and low-load nitrification. |
| Biofilm | Self-cleaning | — | Carrier collisions control thickness. |
Frequently Asked Questions
Can aerobic MBBR remove carbon and nitrify at the same time?
What type of aeration does aerobic MBBR use?
Does aerobic MBBR need sludge return?
Related Pages
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