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PUREFLOW BIO / ENGINEERING FIELD GUIDE

How to Size a BiofilterTAN Load, Media and Reactor Volume

Work out biofilter size from daily feed, ammonia production and media conversion rate, with a worked example for trickling and moving bed filters.

Explore the process ↗Open the workbench
8 MIN GUIDEUPDATED NOVEMBER 2026
Reference illustration for How to Size a Biofilter: TAN Load, Media and Reactor VolumeEQUIPMENT REFERENCE
Equipment reference illustration. Confirm the supplied model configuration and installation arrangement from its approved documentation.
01Understand the mechanismInspect the relevant process stages.
02Review the operating dutyKeep assumptions and measured values visible.
03Prepare the next decisionUse the guide, tools and project checks.
INTERACTIVE PROCESS ATLAS

See the mechanism.
Understand the duty.

Select a route or a stage to inspect the process. The cutaway explains the equipment and water environment; it is a teaching illustration, not a project drawing.

Swipe horizontally to inspect the equipment. Stage buttons below also centre the selected component.
Aerated biological treatment and samplingPUREFLOW / INTERACTIVE PROCESS ATLASCONCEPT LAYOUT · NOT TO SCALETAN-NpH°CPRE-SCREENED SUPPLYBIOFILM ON MOVING CARRIERSMEASURE THE PROCESSAIR DISTRIBUTIONNH₄⁺ → NO₂⁻ → NO₃⁻Motion explains the process; it is not a measured flow rate or biological time model.
Pre-screened water reaches the biological stage and continues through the retained-media outlet.
Selected process stage

Feed the reactor

Define peak feed and the nitrogen load.

How it works

Pre-screened water enters the biological stage. Effective upstream solids removal helps protect the reactor.

What to establish
  • Define peak feed and the nitrogen load.
  • Check oxygen, pH, alkalinity and temperature.
  • Use supported media performance and the specified fill arrangement.

Continue this guide ↗

Motion explains direction and mechanism; it does not represent measured performance. Geometry, stage order, pipe routes and equipment configuration are conceptual. Use the approved project design, operating instructions and verified model data.

Key takeaways

  • Step 1: estimate TAN: A common design estimate is that each kilogram of feed with 40 percent protein produces roughly 38 g of total ammonia nitrogen (TAN).
  • Step 2: choose a conversion rate: Media is rated by how much TAN a cubic metre removes each day.
  • Step 3: divide: Take 60 kg of feed a day at 40 percent protein.
  • Why moving bed is popular: You can see from the example: far less volume for the same load.
Reference illustration for How to Size a Biofilter: TAN Load, Media and Reactor Volume
Equipment reference visual; not evidence of a completed installation.
THE SHORT ANSWER

Step 1: estimate tan

A common design estimate is that each kilogram of feed with 40 percent protein produces roughly 38 g of total ammonia nitrogen (TAN). Your own feed and species will change this, so use it as a start.

How to Size a Biofilter - Pureflow Bio
Reference visual. Equipment configuration and project details must be confirmed separately.
BIOFILTERS

Step 2: choose a conversion rate

Media is rated by how much TAN a cubic metre removes each day. Published design values at around 25 °C and good oxygen are about 90 g TAN/m³/day for a trickling filter media of 200 m²/m³, and about 350 g TAN/m³/day for conservatively-rated moving bed media. These vary with media, temperature and water conditions, so verify with your supplier.

PLANNING WORKBENCH

Work with your own numbers.

Use the tools below to explore the relevant arithmetic. Enter measured values or declared assumptions. An estimate does not establish equipment capacity, biological performance or a safe operating limit.

Biofilter media planning scenario

Relate a defined nitrogen load to an explicitly supplied media conversion rate and fill share.

Assumptions and limits

Use a conversion rate verified for the media, water chemistry, oxygen, temperature and load. Example numbers are arithmetic inputs, not approved biological capacities or fill recommendations.

—TAN-N load · g/day
—Media volume · m³
—Nominal reactor volume · m³
Enter your values, or load the labelled arithmetic example. No design values are pre-filled.
FormulaMedia m³ = feed × TAN-N yield ÷ conversion rate. Reactor m³ = media m³ ÷ fill fraction.
Convert units before you calculate
Choose units and enter a value.

Planning arithmetic · inputs remain visible for review · example values are not operating recommendations

BIOFILTERS

Step 3: divide

Take 60 kg of feed a day at 40 percent protein. TAN is about 2.3 kg per day, or 2,300 g. At 90 g/m³/day you need about 25 m³ of trickling media. At 350 g/m³/day you need about 6.6 m³ of moving bed media, and, if the media can fill 70 percent of the reactor, a reactor of around 9 to 10 m³.

BIOFILTERS

Why moving bed is popular

You can see from the example: far less volume for the same load. That is why moving bed reactors dominate modern RAS. See moving bed biofilters.

BIOFILTERS

Add margin

Allow for growth in feed, cold weather, and a sudden jump in load. Leave headroom so the biofilter is never at its limit.

BIOFILTERS

Get help

Send your feed rate, protein and temperature to our team via the enquiry form and we will check the size with you. See our MBBR biofilters.

Pureflow Bio equipment for this

MBBR biofilters →Moving bed biofilters.Standard drum filters (RDF) →Automatic solids removal.
PROJECT REVIEW

Check the biological assumptions

Use these questions to prepare a project brief or an operating review. Check an item only when the information has been recorded for your installation.

0 of 3 checked

This checklist is a working aid in the current page session, not a saved maintenance record.

QUESTIONS

How to Size a Biofilter FAQ

Is the TAN estimate exact?

No. It is a design estimate. Measure your own system once it is running.

What about temperature?

Cold water slows nitrification, so size with margin if your water is cool.

KEEP READING
MBBR biofilters→Biological filters→Moving bed biofilters→Biofilter Media Types: Plastic Carriers, Sand, Ceramic and Brushes ↗Biofilter Start-Up and Cycling: How Long and What to Watch ↗

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