A RAS biofilter carries more biomass per cubic metre than a municipal plant and is far less forgiving of a bad week. The carrier decision is really a decision about protected surface versus the risk of the bed clogging with biosolids.
Also searched as: biofilter media aquaculture · RAS moving bed biofilter media · K1 media aquaculture · mbbr media fish farm · recirculating aquaculture carrier media
Three differences drive the media choice, and none of them is about the product being "for aquaculture".
| Solids are organic and sticky | Fish biosolids and uneaten feed bind carriers together. Protected internal surface is where nitrifiers live, and it is also the first place to clog - which sets a practical limit on how fine a carrier you can run |
| Load changes fast | Feeding rate, stock size and mortality events move the ammonia load within days, not seasons. Fill fraction has to be chosen with headroom, not sized to the average |
| Salinity and temperature | HDPE carriers are unaffected by seawater, and our published working range is 5–60 °C. Cold-water species run at the bottom of that range, where nitrification slows sharply |
The moving bed principle is the same as in municipal MBBR: carriers are kept fluidised by aeration (or by a mechanical mixer in a denitrification stage), the biofilm builds on the protected surface, and the bed self-cleans as the carriers collide. What changes is the hydraulic design margin.
Use the published figures rather than a rule of thumb. Our K-series carriers run from over 800 to over 1000 m²/m³ of specific surface with void fractions of 85–90 %, a published piece count from roughly 76,000 to 850,000 per cubic metre depending on grade, and nitrification rates of 400–1200 gN/m³·d. Fill fraction for municipal duty is published as 15–67 % of reactor volume.
In practice the aquaculture question is where in that band to sit. A cold-water smolt tank with a generous biofilter can sit low in the band; a warm-water system running close to its feed limit needs the upper end and the oxygen budget to support it. Adding carriers to a bed that has run out of oxygen moves the constraint from media to aeration and changes nothing.
Fine, high-surface carriers give more nitrification per cubic metre and clog faster with organic solids. Coarse, high-void carriers are easier to keep clean and need more volume for the same removal. Our published range runs from the K1 grade at around 10 mm through K5 at 25 mm with 64 protected chambers - the coarse end is the safer choice where the pre-filter is the weak point in the system.
For denitrification stages, the same carriers work in a mechanically mixed anoxic tank; the difference is that without air the bed is mixed by the mixer and the media must be dense enough not to float. Published bulk density for the K-series is 0.96.
Product data and piece counts: MBBR media K1–K5 · technical details · calculators: carrier volume · top-up or replace.
Yes - the carriers are the same HDPE products. What differs is the sizing: an aquaculture biofilter is usually designed with less safety margin on ammonia and a tighter oxygen budget, so the fill fraction and the aeration design are worked out differently rather than the media being different.
HDPE is unaffected by seawater, and our published working temperature range is 5-60 degrees C. The material is not the constraint in marine systems; the cold end of the range is, because nitrification rates fall there.
Two things: keep the pre-filter doing its job, and choose a coarse, high-void carrier if the pre-filter is unreliable. Protected internal surface is where nitrifiers live and where biosolids collect, so the finer the carrier, the more the system depends on upstream solids removal.
Start from the TAN load at maximum feed and maximum biomass, then convert using the published nitrification rate per cubic metre for the grade and temperature you are running, and check the result against the published fill band of 15-67 percent of reactor volume. We will do that with you if you send the system data.
We return the carrier grade, the volume and the fill-fraction check against the aeration you have.
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