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PUREFLOW BIO / ENGINEERING FIELD GUIDE

Biological FiltersNitrification, Media and Sizing

Biological filters explained: how bacteria turn ammonia into nitrate, types of biofilter, how to choose, maintenance and why biofiltration matters in aquaculture.

Explore the process ↗Open the workbench
8 MIN GUIDEUPDATED NOVEMBER 2026
Reference illustration for Biological Filters: Nitrification, Media and SizingEQUIPMENT 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

  • Bacteria convert ammonia to nitrite and then to nitrate.
  • Surface area and oxygen set how much a biofilter can do.
  • Main types: moving bed, trickle and static media.
  • Nitrate still builds up and needs managing.
Reference illustration for Biological Filters: Nitrification, Media and Sizing
Equipment reference visual; not evidence of a completed installation.
THE SHORT ANSWER

How does a biological filter work?

  1. Ammonia productionFish excrete it.
  2. Ammonia to nitriteOne bacteria group.
  3. Nitrite to nitrateAnother group.
  4. Nitrate managementWater exchange, plants, denitrification.
Biological Filters - Pureflow Bio
Reference visual. Equipment configuration and project details must be confirmed separately.
Biological Filters - Pureflow Bio
Reference visual. Equipment configuration and project details must be confirmed separately.
BIOFILTERS

Types of biological filters

TypeHow it worksBest for
Moving bed (MBBR)Media kept moving by airPonds, RAS, aquariums. See MBBR
Trickle filterWater rains over media in airCooling and degassing. See trickle filters
Static mediaFixed blocks under waterSimple small systems
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

Which biofilter do i need?

Size it from daily feed, not from volume. See biofilter sizing and media types.

BIOFILTERS

Maintenance

Keep it aerated, avoid cleaning in chlorinated water and protect from toxins and sudden changes.

BIOFILTERS

Why biofiltration matters in aquaculture

In a recirculating farm, fish waste would quickly poison the system. Biofilters keep ammonia and nitrite near zero so fish can be stocked densely.

Pureflow Bio equipment for this

MBBR biofilters →Moving bed biofilters.Trickle filters →Biological stage with degassing.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

Biological Filters FAQ

How long does a biofilter take to start?

Usually several weeks.

Can I clean the media?

Rinse lightly in system water, never in tap water.

Does it need oxygen?

Yes. Bacteria use oxygen continually.

KEEP READING
Nitrification→Biofilter sizing→Biofilter start-up→Media types→

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