Biostyr™ Duo

Biostyr™ Duo technology offers the most compact solution for carbon and nitrogen removal. Due to the unique combination of media within the process, biological treatment and suspended solids removal are achieved in one step.
Biostyr™ Duo

The Biostyr™ Duo features the combination of two well known compact technologies, the Biological Aerated Filter (BAF) and Moving Bed Biofilm Reactor (MBBR).

Biological treatment and filtration occur simultaneously within the system as two separate media types are contained within the same treatment cell.

Wastewater first flows through a dynamic AnoxK™5 MBBR media layer which provides a large surface area and an open void for biofilm growth and treatment.

Flow then passes through the BIOSTYRENE media layer, which provides additional fixed film treatment and filtration as the water flows up through the fixed bed.

The buoyant BIOSTYRENE media is retained by a concrete nozzle deck. The system uses a gravity-driven backwash for excess solids removal with no pumping. It offers significantly increased BOD and Ammonia loading rate capabilities compared to other BAF or MBBR systems without any need for additional sludge separation, while maintaining very low effluent BOD, TSS and Ammonia values.

One of the challenges of cities around the Globe is to find space for wastewater treatment plants. They often demand a No, Hear, No See, No smell solution.

Biostyr™ Duo technology offers the most compact solution for Carbon and Nitrogen removal, offering  the possibility to totally cover the plant, avoiding emissions and completely integrating it into the surroundings.



Secondary Treatment

Classical BAF solutions normally demand Chemical Enhanced Primary Treatment. Biostyr™ Duo enables more TSS loading and Biofilm growth due to void space in the K5 media, making it possible to install the system downstream of a traditional primary settler.

Biostyr™ Duo is an optimal solution for the removal of BOD, suspended solids, and ammonia following primary clarification. Typical effluent levels achieved are 10/10/1 (BOD, TSS, NH3-N).

As a compact, fixed-film process, Biostyr™ Duo offers a more reliable treatment than activated sludge at low influent temperatures and avoids the need for clarification.



Biostyr™ Duo is an ideal solution for existing activated sludge systems that provide limited or no nitrification as it can be used to expand existing secondary treatment processes to provide tertiary removal of ammonia while polishing suspended solids.

These facilities can easily meet new objectives by adding Biostyr™ Duo at the end of the existing process.

Compared to the traditional BAF nitrification filter, Biostyr™ Duo can accept higher organic loading and achieve high nitrification performance in the same volume since all easily degradable carbon will be removed by the heterotrophic biofilm on AnoxKaldnes K5 media. This gives maximum performance on the autotrophic biofilm on BIOSTYRENE with a very large surface area.



Biostyr™ Duo is an ideal choice for denitrifying filter applications. It can be applied downstream of the primary settler as pre-denite filter or following any proceeding nitrification process. It offers post-denitrification to very low levels. Effluent Total Inorganic Nitrogen from Biostyr™ Duo denitrification filters is typically < 1.5 mg/L. Due to the specific design combining two media types, Biostyr™ Duo denitrification filters operate at much higher loading rates than conventional BAFs or sand-based, denitrifying filter technologies, and occupy a fraction of the footprint.



  • Compact footprint; Ideal for constrained sites
  • Downstream clarifiers are not necessary, decreasing operation and maintenance requirements
  • Treated water of exceptional quality, even in very cold climates
  • Footprint allows for the process to be easily enclosed, neighborhood-friendly
  • No media escape from the process and no periodic replenishment or replacement of media required, decreasing maintenance costs
  • Biostyr™ Duo cells do not require dedicated screening; typical headwork screens only
  • Biostyr™ Duo is the only BAF working without Chemical Enhanced Primary Treatment
  • Add-on nitrification and/or denitrification in one process with minimal space required
  • Fully automated sensor-based controlled process reducing maintenance



AnoxKaldnes’ technologies are found in more than 1,200 treatment plants around the world. Contact us for references related to your specific needs.

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