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Recirculating Aquaculture Systems (RAS)

Recirculating Aquaculture Systems (RAS) incorporate additional treatment technologies beyond those used in Partial Reuse Aquaculture Systems (PRAS), allowing for significantly greater quantities of water to be reused. Recirculation systems afford a level of control well beyond any other technology application in aquaculture and provide significant production and economic benefits.

Recirculation systems are usually used where new water supplies are limited or expensive to achieve (i.e. high pumping costs), the risk of introducing pathogens or contaminants into the system with influent water is high, effluent disposal capacity is limited, or where operators want to practice strict control over the water quality and temperature within the fish culture system. Such systems are characterized by increased technical complexity, capital costs, and in some applications, operating costs. However, because RAS allow optimum culture conditions to be maintained year round, independent of fluctuations in water supply quality and ambient temperatures, fish growth rates may be accelerated allowing more fish or larger fish to be produced in the same amount of time. In a well designed system, the production benefits will outweigh the additional costs resulting in a net lower cost of production.

Recirculating Aquaculture Systems maximize water re-use by employing a comprehensive water treatment system. Water treatment processes typically include solids removal, biofiltration, gas balancing, oxygenation, and disinfection. By addressing each of the key water quality concerns through treatment, rather than flushing as is used in flow-through and partial reuse systems, ultimate control over culture conditions and water quality is provided.

Water quality in recirculation systems is highly dependant on the complexity and cost of the water treatment system used. Better water quality may be provided and higher recirculation rates may be achieved through the use of additional treatment processes or with greater intensity of treatment. A typical recirculation system will provide a maximum recirculation rate of 95% – 99% of the system flow rate while maintaining optimal water quality for the fish. However, with the addition of denitrification technologies, and by capturing water extracted from sludge thickening processes, some systems may become effectively “closed” with very little to no exchange of water. A balance must be achieved in design between water quality objectives and treatment system complexity and cost.

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Recycling has become an economic imperative in many industries and aquaculture is no exception. Recirculation technology has allowed aquaculture facilities to evolve to meet the growing need for economic and environmental sustainability. PR Aqua is a world leader the large-scale in­tegration of water recirculation and partial reuse technologies in the design and construction of aquaculture facilities. Please contact us to see how recirculation technologies can help you in meeting your production and profitability objectives.

Recirculation Facts

  • Significantly reduced water consumption and effluent volumes (95%-99.9%).
  • Minimal influent water consumption allows for cost effective treatments to improve water quality and prevent the ingress of disease.
  • Minimal effluent volumes result in the ability to treat both effluent water and sludge to meet sustainability objectives.
  • Full control of culture temperature is possible, allowing for year-round production independent of fluctuating environmental or influent water conditions.
  • A high degree of control over culture conditions enables operators to optimize fish growth and feed conversion, increased production, and improve product quality.
  • Are often mechanically and operationally less complex than other types of culture systems.
  • Initial capital investment is typically higher but cost of production is typically lower than in other culture systems.
  • Therapeutic treatments are efficient and economical as dosage is maintained in the system due to minimal water exchange.
  • Facilities can be located almost anywhere. Site selection is not tied to access to large volumes of water.
  • System and technology performance have been proven by successful facilities in a wide range of aquaculture applications.