Recirculating aquaculture systems (RAS) reuse water to grow fish intensively, which means the ammonia excreted by the fish must be removed continuously to keep the water safe. This water is low-strength and has a low carbon-to-nitrogen ratio, so nitrification — not carbon removal — is the priority. MBBR biofilters are a mainstay of RAS because their carriers hold a stable nitrifying biofilm that reliably converts ammonia and nitrite to the far less toxic nitrate.
Nitrification for Fish Health
Ammonia and nitrite are toxic to fish even at low concentrations, so the biofilter must keep them consistently low. Because RAS water carries little organic carbon, the MBBR biofilm is dominated by nitrifiers, giving efficient ammonia conversion. The low-strength, low-C:N conditions and the need for stable operation at controlled temperatures make the moving-bed biofilter well suited to this duty, and the moving carriers resist clogging while presenting a large surface for nitrifiers.
Design accounts for temperature (which affects nitrification rate), dissolved oxygen and alkalinity, since nitrification consumes alkalinity that must be replenished to hold a stable pH.
Aquaculture / RAS Design Context (indicative literature ranges — confirm per project)
| Parameter | Typical Value | Unit | Notes |
|---|---|---|---|
| Primary duty | nitrification | — | Ammonia + nitrite control |
| Water strength | low | — | Low C:N ratio |
| Key controls | temperature, DO, alkalinity | — | Replenish alkalinity |
| Carrier benefit | clog-resistant | — | Large nitrifying surface |
A Different MBBR Duty
Aquaculture is a distinctive MBBR application: rather than removing a heavy organic load, the biofilter maintains water quality in a closed loop. The same nitrification principles that apply to municipal and industrial ammonia removal underpin RAS biofilter design, adapted to low-strength, temperature-controlled conditions.
Frequently Asked Questions
Why do RAS systems use MBBR biofilters?
Is carbon removal important in aquaculture?
What controls RAS biofilter performance?
Related Pages
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