- Recirculation Aquaculture Systems (RAS)


For land-based fish farms, Recirculation Aquaculture Systems (RAS) provide significant advantages towards flow through systems. Excellent water quality, rich water quantities and preservation of temperature are all key factors to provide good health and optimal growth conditions for fi sh. Kaldnes RAS plants are tailored for optimum conditions related to fish species, degree of recirculation, fish tank configuration and source of raw water. Components that typically will be removed in a Kaldnes RAS plant include organic matter, total ammonium nitrogen (TAN), suspended solids, CO2, N2 and harmful bacteria/ virus. They will also provide optimum conditions related to pH and alkalinity. Kaldnes RAS solutions are being used for both fresh- and saltwater systems.


The Moving Bed Biofilm Reactor  (AnoxKaldnes MBBR technologies)  is our own proprietary technology,  and the biological engine of Kaldnes  RAS. The MBBR technology allows the  microorganisms to grow on sheltered,  surfaces inside moving, plastic carriers  creating a continuous Biofilm process  without any risk for clogging and without  any need for back flushing. Advantages  like low head loss and high volumetric  capacity make the process compact  and well suited for treatment of large  water flows. The process is very  robust and easily operated  with a minimum need for  maintenance.


Biomass from the Kaldnes MBBR  process, fish faeces and excess  feed is efficiently separated with  Hydrotech drum filters, another  well known Veolia Water Solutions  & Technologies’ technology in the  industry.

The Hydrotech filters have a high  hydraulic capacity, are easy to operate  and provide apredictable results.  Typical mesh sizes are 40-90 micron,  but can be delivered with mesh sizes  down to 10 micron.

Kaldnes RAS offer systems for preparation of intake water where the treatment may typically include one or more of the following unit processes:

  • Solids removal (Filtration)
  • Disinfection
  • Alkalinity and pH adjustment
  • Biological treatment
  • CO2 and N2 stripping
  • Oxygenation

A full range of solutions:

  • Recirculating Aquaculture Systems (RAS) – up to 99.99% reuse
  • Treatment of intake water
  • Conditioning of water during production in flow through systems
  • Treatment of effluent water from fish farms


Water conditioning in flow through systems
Elevated CO2 concentrations and marginal O2 levels are the main challenge in flow through systems. This has a negative impact on fish welfare and growth rate. With more intensive and stable production, Krüger Kaldnes offers cost-effective systems for CO2 stripping and aeration.

Effluent water treatment from fish farms and abattoir waste
Wastewater from fish farms and production plants constitutes pollutants that may harm the receiving water resources. Treatment of discharges is hence often a necessity to ensure sustainability of fish production facilities. Effluent treatment will typically constitute processes for removal of major pollutants such as organic matter, suspended solids, ammonia nitrogen and bacteria/virus. Krüger Kaldnes offers a wide range of treatment solutions for these objectives.

Typical unit processes may include:

  • Biological treatment
  • Solids removal
  • Disinfection


Sludge and waste from fish farm facilities typically comprises biomass from biological treatment, fish faeces, feed waste, dead fish and abattoir waste.

Krüger Kaldnes offers solutions for:

  • Storage
  • Stabilization
  • Hygienization
  • Dewatering

Kriiger Kaldnes has developed a range of concepts for sludge handling at fish farms and fish processing sites. The different systems are adapted to each individual site based on quantity and quality of raw sludge, local regulations and transportation-and end user requirements. All of Kruger Kaldnes' sludge treatment! systems focus on high quality, low energy and simple operation with low requirements for maintenance.

Other processes provided in Kaldnes RAS plants may include oxygenation, ozonation, UV disinfection, CO2, removal, N2. removal and alkalinisation. Kaldnes RAS provides highly compact and energy efficient solutions with focus on easy operation and low maintenance requirements.

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