Biological Aerated Filter (BAF)

With 25 years of experience and over 160 references, Veolia Water Technologies, is the world leader on the biofilter market.


Biostyr™ - The compact biofiltration solution 

Biostyr™ is a simple and innovative process, enabling removal of pollution in a compact structure, thereby presenting a low environmental footprint.

Biostyr™ is able to eliminate all pollution, both organic (COD and BOD), nitrogenous (N-NH4 and N-NO3) and particulate compounds (TSS).

The modular design of Biostyr™ makes it a suitable tool in cases of variable load as part of the cells can be stopped and restarted quickly.

As a biofilter, Biostyr™ combines in a single structure:


  • a biological reactor
  • a physical filter to store the biomass and stop particulate pollution

Therefore, Biostyr ™ requires no final clarifier.

Features and Benefits


  • Adaptable to any kind of influent
  • Compact process: low surface required - low footprint
  • Combined biological and filtration process: no further clarification needed
  • Patented single stage treatment, including Total Nitrogen removal
  • Fully automated operation
  • Modular design, therefore quick response to high load variations
  • Buoyant media bed (Biostyrene™): backwashing by gravity (no pumping required)
  • Only treated water is in contact with the atmosphere, even during backwashes: thus lack of odor nuisance can be guaranteed with no need to treat the upper atmosphere inside the structure
  • Nozzles on treated water side, only in contact with clean water: no clogging and easy access


Biostyr™ exists in several versions, depending on the pollution to be treated:

  • Carbon removal only
  • Carbon removal and ammonia oxidation (nitrification)
  • Carbon removal and combined pre-denitrification, nitrification in separate structures
  • Carbon removal and simultaneous nitrification-denitrification
  • Tertiary nitrification, or tertiary denitrification with addition of a soluble carbon source (i.e. methanol)


Patented One-Stage Treatment

The advantages of simultaneous "Nit-Denit":

  • Less energy consumption due to:
       o Lower air consumption 
       o Reduced recirculation of treated effluent
  • Reduced equipment cost due to
       o Common air grid for scour and process air
       o Smaller pumps and blowers

Biostyr ™ is particularly suitable whenever compactness is sought, such as:

  • In tourist and resort areas, where land pressure and claims of neighbors are often experienced,
  • In mountainous areas where, due to the harsh climate, treatment installations have to be completely protected from bad weather, tolerance of the process to variations in load being another asset.


Biostyr™ is based on the use of light and floating filling material: Biostyrene™.

BIOSTYRENE ™ consists of polystyrene beads manufactured specifically and sized according to the required result. These beads are blocked under the ceiling of the concrete structure (the cell) which is fitted with nozzles which allow the treated water to flow out. Therefore, BIOSTYRENE ™ optimizes the cycle duration between washes, and avoids clogging.

Feeding from the base causes "self-compacting" of the filter bed, with a beneficial effect on its ability to retain suspended solids. The nozzles, located in the upper part of the filter, are easily accessible.

The aeration manifold is located in the lower part of the structure, thus optimizing the contact time between the wastewater and the process air.

Biomass and suspended solids accumulated inside the filter medium must be removed regularly by periodic backwashes. The lightweight of the material allows the system to be washed by simple gravity expansion of the filter medium using the treated water stored in the upper structure (flushing). This results in less equipment being installed (no wash pump), less maintenance and better energy efficiency.

Among our References

  • Achères BIOSAV (France): the largest biofiltration plant reference in the World (Pre-denitrification and nitrification in two stages) - 6,000,000 PE - 2016
  • Davyhulme, Manchester (UK): Wastewater treatment (Tertiary nitrification) - 1,500,000 PE - 2014
  • Les Grésillons (France): (Pre-denitrification and nitrification in two stages) - 1,200,000 PE - 2012
  • Lyon-Saint-Fons (France): (tertiary nitrification) - 980,000 PE - 2011
  • Hebei Shijiazhuang Qiaodong WWTP: Upgrading Project (tertiary denitrification) - nominal flow rate 20,833 m³/d - 2010
  • Patapsco, Baltimore (USA): 12,776 m³/d (tertiary treatment) - 2010
  • Blackburn (UK): Tertiary nitrification - 3,542 m³/d - 2009
  • Wigan (UK): Tertiary nitrification - 7,528 m³/d - 2009
  • Maidao (China): Plant upgrade (total nitrogen removal) - 140,000 PE - 2007
  • Montpellier (France): Plant refurbishing and upgrade (carbon removal) - 170,000 PE - 2007
  • Newham (UK): compact stainless-steel unit (total nitrogen removal) - 25,000 PE - 2006
  • Denver (USA): tertiary nitrification for the reuse of treated water (supplied to a power-plant cooling system) - 325,000 PE - 2005
  • Nanhai (China): WWTP (Carbon and nitrogen removal) - 125,000 PE - 2005
  • Songdo (Corea): WWTP (total nitrogen removal) - 33,000 PE - 2004
  • Geneva-Air (Switzerland): municipal WWTP (secondary treatment) - 600,000 PE - 2003
  • Helsinki (Finland): Viikinmäki WWTP (Tertiary denitrification) - 900,000 PE - 2003
  • Freeport (USA): WWTP (Tertiary nitrification) - 76,000 PE - 2001
  • Herford (Germany): WWTP (total nitrogen removal) - 250,000 PE - 1998
  • Alanya (Turkey): WWTP (secondary nitrification) - 145,000 PE - 1998
  • Nyborg (Denmark): WWTP (total nitrogen removal) - 60,000 PE - 1992
  • Cergy (France): municipal WWTP (secondary nitrification) - 200,000 PE - 1992