Biofilters

Biofiltration in aquaculture is a key process in managing water quality, especially in recirculating aquaculture systems (RAS). It allows for the removal of nitrogenous waste produced by fish, particularly toxic ammonia, by biologically converting it into less harmful compounds (nitrates).

Definition of Biofiltration
Biofiltration is a natural process that uses nitrifying bacteria to transform ammonia (NH₃), excreted by fish, into nitrites (NO₂⁻), and then into nitrates (NO₃⁻), which are much less toxic. This process is known as nitrification.

Steps of Nitrification:

Ammonia (NH₃/NH₄⁺) → Nitrites (NO₂⁻)
Carried out by bacteria of the genus Nitrosomonas.
Nitrites (NO₂⁻) → Nitrates (NO₃⁻)
Carried out by bacteria of the genus Nitrobacter or Nitrospira.

How Does a Biofilter Work?
A biofilter is typically made up of a medium (such as plastic beads, foam, sand, or ceramic) that offers a large surface area for bacterial colonization. Water passes through this medium, allowing the bacteria to process nitrogenous compounds.

Advantages of Biofiltration:

Controls toxic compounds (ammonia and nitrites)
Maintains water quality
Reduces the need for water changes
Provides a stable environment for fish

Integration into Aquaculture Systems:
Biofiltration is essential in:

Aquaponic systems
Closed or recirculating systems
Intensive pond farming
Systems sensitive to water quality (fry rearing, nurseries, hatcheries)
Aquariums

AQUACULTURE France designs, sizes, and manufactures a full range of biofilters adapted to all needs (gravity-fed or pressurized systems).

Subcategories

Aerobic biofiltration...
The pressurized biofilter is a biological water treatment device used in aquaculture to maintain optimal water quality, especially in Recirculating Aquaculture Systems (RAS). Unlike gravity-fed filters, it operates in a closed, pressurized loop, allowing for a compact, versatile, and high-efficiency installation.

How It Works

Water loaded with nitrogenous waste (mainly ammonia NH₃) is pushed under pressure through a filtering medium (e.g., plastic beads, ceramic media, or foam). Nitrifying bacteria colonize this media and carry out nitrification:
- Ammonia (NH₃/NH₄⁺) → Nitrites (NO₂⁻) (Nitrosomonas)
- Nitrites (NO₂⁻) → Nitrates (NO₃⁻) (Nitrobacter, Nitrospira)
Advantages
- Operates under pressure, ideal for closed-loop systems
- Suitable for compact installations
- Compatible with other filtration systems (UV, mechanical)
- Easy maintenance
- Excellent biological efficiency
Applications
- RAS (Recirculating Aquaculture Systems)
- Hatcheries, nurseries, fry rearing
- Aquaponics
- Public or professional aquariums
- Intensive fish farming tanks
Gravity Aerobic Biofilter
The gravity biofilter is a biological filtration system used in aquaculture to maintain optimal water quality, especially in recirculating systems or low water consumption setups. It relies on gravity to circulate the water through a filtering medium where nitrifying bacteria break down nitrogen compounds such as ammonia.

How It Works

Water containing nitrogenous waste (such as ammonia produced by fish) naturally flows under gravity through a filtering medium. This medium may consist of materials like plastic beads, ceramic supports, or special foam. Nitrifying bacteria settle on the medium and convert ammonia into nitrites and then nitrates, a process known as nitrification.

Advantages
- Gravity-powered: Operates without additional energy, reducing operational costs.
- Easy maintenance: Fewer moving parts and simple system cleaning.
- Biological efficiency: Helps maintain stable water quality by reducing ammonia and nitrite levels.
- Durability: Resistant materials with long system lifespan.
Applications
- RAS (Recirculating Aquaculture Systems): Used to treat water in controlled environments.
- Hatcheries and nurseries: Ideal for young fish or fry installations.
- Aquaponics: Used in systems combining aquaculture and plant cultivation.
- Extensive fish farming and aquaculture: Suitable for less intensive setups.
Anaerobic biofiltrer
Anaerobic biofiltration in aquaculture is a biological treatment process that uses microorganisms in the absence of oxygen (anaerobic conditions) to remove organic waste and certain nitrogen compounds (such as nitrates) from aquaculture water.

Detailed Description:

Operating Principle:
- Unlike aerobic biofiltration (which requires oxygen), anaerobic filtration relies on bacteria that break down organic matter in an oxygen-free environment.
- These bacteria perform fermentation or denitrification reactions.
- Denitrification is especially useful in aquaculture to convert nitrates (NO₃⁻), which accumulate in closed systems, into gaseous nitrogen (N₂), which is harmless and released into the atmosphere.
Required Conditions:
- Low-oxygen environment (confined zones, substrates with low porosity).
- Presence of organic carbon (often added in the form of sugar or methanol) to support the growth of denitrifying bacteria.
- Temperature, pH, and other parameters must be controlled to optimize bacterial performance.
Benefits for Aquaculture:
- Reduction of nitrates, improving water quality and fish health.
- Lower sludge production compared to aerobic systems.
- Can operate in low-energy environments (no need for aeration).
Drawbacks / Challenges:
- Slower process compared to aerobic filtration.
- Possible production of foul-smelling gases (e.g., H₂S).
- Requires careful monitoring to avoid imbalances (pH, accumulation of by-products).