RAS Biofilter Media and TAN Capacity Calculator

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Enter peak feed, feed-label protein, and supplier capacity to estimate TAN-N load and biofilter media volume with a chosen margin.

Media performance and sizing margin

Enter a volume-based rating. Do not enter an area-based rating such as g/m2/day.

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How to use our RAS Biofilter Media and TAN Capacity Calculator

  1. Enter Peak daily feed from the highest planned ration, then choose the matching Feed amount unit.
  2. Copy Crude Protein (min.) from the guaranteed analysis on the feed bag.
  3. Enter Feed nitrogen released as TAN-N, Supplier TAN-N removal capacity, its exact unit, and Extra media margin from the project design basis.
  4. Click Calculate. Start with Planned installed media after margin, then compare the shown capacity and media units with the supplier datasheet.
  5. Sanity-check the result by changing feed or capacity: more peak feed should require more media, while a higher valid capacity should require less media.
Example inputs for RAS Biofilter Media and TAN Capacity Calculator
Example inputs for RAS Biofilter Media and TAN Capacity Calculator

Definitions

TAN-N: Total ammonia nitrogen stated as the mass of nitrogen. It is a daily mass load here, not an ammonia concentration or a fish-toxicity reading.

Crude Protein (min.): The minimum protein percentage by weight printed in a feed's guaranteed analysis.

Feed nitrogen released as TAN-N: The planning share of feed nitrogen expected to become TAN-N. It is separate from the crude-protein percentage.

Supplier TAN-N removal capacity: The amount of TAN-N a cubic meter or cubic foot of media can remove per day under stated operating conditions.

Extra media margin: Added media above the calculated base requirement. It does not increase the demonstrated performance rating of the media.

Normalized capacity: The supplier capacity converted to g TAN-N/m3/day so both supported capacity units use one sizing calculation.

Media Volume Before and After MarginWorked example: 100 lb/day feed, 40% protein, 50% TAN-N release, and 350 g TAN-N/m3/day capacity.. The added volume is a planning margin above the calculated mature-capacity requirement.Media Volume Before and After MarginWorked example: 100 lb/day feed, 40% protein, 50% TAN-N release, and 350 g TAN-N/m3/day capacity.Base required4.15 m3Installed with margin5.18 m3Media volume
Media Volume Before and After Margin
The added volume is a planning margin above the calculated mature-capacity requirement.

Common mistakes and quick fixes

Mistake: Entering average feed instead of Peak daily feed.
Fix: Use the highest planned daily ration that the biofilter must support.

Mistake: Copying a feed bag value into Feed nitrogen released as TAN-N.
Fix: Put the bag's protein value in Crude Protein (min.) ; use an approved biological assumption for TAN-N release.

Mistake: Entering a surface-area rating for Supplier TAN-N removal capacity.
Fix: Use only a volumetric rate in g TAN-N/m3/day or g TAN-N/ft3/day. An area-based rate cannot size media volume in this calculator.

Mistake: Choosing g TAN-N/ft3/day under Supplier capacity unit while leaving a value copied in g TAN-N/m3/day.
Fix: Select the unit printed on the supplier sheet before entering or checking the capacity value.

Mistake: Treating Planned installed media after margin as proof that a new filter is ready to carry the load.
Fix: Confirm start-up, water chemistry, oxygen, solids control, and mature media performance with the supplier or engineer.

Limitations & Key Assumptions / Boundary Conditions

  • This is a preliminary feed-based media estimate. It does not design a vessel, pump, aeration system, solids filter, oxygen supply, or alkalinity addition.
  • The calculation uses the entered mature-media capacity. Actual capacity can change with temperature, dissolved oxygen, pH, alkalinity, salinity, hydraulic loading, solids control, media type, and biofilm condition.
  • A new, recently cleaned, or stressed biofilter may remove less TAN-N than a mature system. Do not treat a margin as a substitute for commissioning and monitoring.
  • Use peak planned feed for sizing. A lower routine average can understate the required media volume.
  • The protein-to-nitrogen divisor of 6.25 is a conventional crude-protein conversion factor. Feed-specific composition and fish metabolism can differ from this simplified mass balance.
  • Zero peak feed correctly returns zero estimated TAN-N and media demand, but it does not mean an operating RAS can run safely without biofiltration.

Methodology

Calculation steps

The calculator first converts feed to kg/day. It estimates feed nitrogen from crude protein using the conventional 6.25 protein-to-nitrogen divisor, then applies the entered TAN-N release percentage.

feed_kg_day = feed_amount for kg/day, or feed_amount * 0.45359237 for lb/day

feed_nitrogen_g_day = feed_kg_day * 1000 * (crude_protein_percent / 100) / 6.25

daily_tan_g_day = feed_nitrogen_g_day * (tan_excretion_percent / 100)

The supplier capacity is converted to g TAN-N/m3/day before the media volume is calculated. A capacity entered in g TAN-N/ft3/day is multiplied by 35.3146667 because one cubic meter contains that many cubic feet.

normalized_capacity_g_m3_day = media_capacity, or media_capacity * 35.3146667

required_media_m3 = daily_tan_g_day / normalized_capacity_g_m3_day

installed_media_m3 = required_media_m3 * (1 + safety_margin_percent / 100)

installed_media_ft3 = installed_media_m3 * 35.3146667

Worked example

For 100 lb/day of feed at 40% crude protein and 50% TAN-N release, the estimated load is 1,451.50 g TAN-N/day. At 350 g TAN-N/m3/day, base media is 4.147 m3. A 25% margin raises planned media to 5.184 m3, or 183.07 ft3.

Calculation choices

The result is a media-volume calculation, not a reactor-volume calculation. It uses only the feed, protein, TAN-N release fraction, supplier volumetric capacity, and added margin entered in the calculator. Capacity must be greater than zero; protein and TAN-N release must each be from 0% through 100%.