Ammonia (measured as NH₄-N) is a priority pollutant: it is toxic to fish at low concentrations, exerts a nitrogenous oxygen demand in receiving waters, and contributes to eutrophication. MBBR removes ammonia biologically through nitrification — the oxidation of ammonia to nitrite and then nitrate by autotrophic nitrifying bacteria retained in the biofilm. This page focuses on ammonia as the pollutant; the nitrification process itself is covered in detail on its own page.
Why Ammonia Must Be Removed
Discharge consents commonly set tight ammonia limits because of its aquatic toxicity, especially in the un-ionised form whose proportion rises with temperature and pH. Ammonia also consumes dissolved oxygen in rivers as it nitrifies naturally, depressing oxygen levels downstream. Removing ammonia before discharge protects the receiving water and is frequently the objective that governs the biological design.
MBBR is well suited to ammonia removal because nitrifiers, which grow slowly, are retained on the carriers regardless of flow — so nitrification is more stable than in suspended-growth systems, particularly under variable load.
Ammonia Removal Context (indicative literature ranges — confirm per project)
| Parameter | Typical Value | Unit | Notes |
|---|---|---|---|
| SALR — nitrification | 0.4 – 1.0 | g NH₄-N/m²·d | Temp & DO dependent |
| Oxygen demand | ~4.3 | g O₂/g NH₄-N | Ammonia → nitrate |
| Design DO | 4 – 6 | mg/L | Overcomes diffusion limit |
| Prerequisite | low organic load | — | Carbon removed first |
Ammonia Removal vs. Total Nitrogen Removal
Removing ammonia by nitrification converts it to nitrate but does not remove nitrogen from the water. Where a consent limits total nitrogen, nitrification must be followed by denitrification, which converts nitrate to nitrogen gas. Ammonia removal alone is sufficient only where the consent limits ammonia (and possibly nitrite) but not total nitrogen. Clarifying which limit applies is essential before fixing the process configuration.
Frequently Asked Questions
How does MBBR remove ammonia?
Does removing ammonia remove nitrogen from the water?
Why is MBBR good for ammonia removal?
Related Pages
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