Recirculating Aquaculture Systems

A functioning bioreactor enables the well-being and rapid growth of fish. The operations of a recirculating aquaculture system (RAS) are based on maintaining a consistent temperature optimal for the growth of the fish around the year.

In a recirculating aquaculture system, the growth rate of the fish and the water quality can be optimised according to the species being cultured. For the economic efficiency of the system, the amount of fish biomass should be kept as consistent as possible around the year. This enables the maintaining of the end products delivery to the market at a consistent rate. The system is measured according to the largest feeding, growth, and metabolic products of the fish. This requires careful production and equipment planning.

Recirculating aquaculture systems are particularly suited for areas where the amount or temperature of available water limits farming activities. Recirculating aquaculture system brings food production closer to the consumers and decreases the length and duration of the delivery chain.

Clewer’s bioreactors have been tested in a laboratory for coldwater fish (13—18°C) and warmwater fish (18—22°C). In each fish farming project, the water source and the cultured product are individually designed so that the fish farm concept can be optimised for the existing conditions. The design pays special attention to the well-being of the fish, the water quality, and the resulting cost-efficiency of the fish farm.

Biological Filter Constitutes a Substantial Part of the Filter

The recirculating aquaculture system accumulates ammonium due to the metabolism of the fish. Some of the nitrogen contained in the fish fodder is released from the gills to the recirculating water as ammonium. The released ammonia, whose share of the total ammonium depends on the pH value of the water, is dangerous to fish even in small quantities.

The nitrogen can be transformed into a less dangerous form with the help of biological treatment. This is carried out with nitrification (aerobic) by changing ammonium first into nitrite and then into nitrate with the bioreactor.

Water is changed in the system so that the amount of nitrate stays optimal, depending on the species of the fish. If the recycling ratio of the water is high and the amount of changed water is small compared to the total water mass, a denitrification reactor is installed in the system in order to remove nitrogen in anoxic conditions as well. The reactor reduces nitrate into nitrogen gas and releases it into the air.

The efficiency of the biological purification is influenced by a number of physical and chemical conditions. The efficiency of the biological filter depends on the amount and species of bacteria growing on the surfaces of the filter and their ability to utilise the ammonium entering the filter.


Clewer Aquaculture Oy is specialised in RAS

Clewer Aquaculture Oy combines the over 30 years’ experience in planning, constructing and project management of aquaculture systems of Kalavesi Consultants Ltd* with strong experience in modern water treatment systems of Clewer Oy.

Kalavesi Consultants Ltd was founded in 1984 to offer consultation and design services to aquaculture. Since then there has been a wide variety of fish farming projects and different design work for fish research stations and commercial farms.

Our skills have been used for designing and constructing both coldwater systems using recycling and warmwater systems utilising excess energy to heat the recycled water. Heat pump and heat exchanger systems are used, if waste energy or heat is not available on site. Cooling of water can be done easily by the same heat pump by only changing some of the water pipe line assembly.

Experience of RAS has been gained at first by building a test system in own hatchery for trout (later arctic char farming). Besides working as a commercial fish farm we have carried out research projects connected to developing the RAS systems. Our latest test experience is with Clarias anguillaris, which is cultured in a warmwater RAS.

Designs for commercial farms and research stations

We have designed and constructed commercial aquaculture farms in Finland, Sweden, the Baltic countries and Russia for several different species (e.g. rainbow trout, arctic char, pikeperch, sturgeon, eel and salmon). Some of the farms have been new, some have been transferred from flow-through farms into RAS farms. Technology in farms has included sand filters, moving bed reactors, trickling filters and combinations of these. UV and ozone have been used for disinfection and water quality improvement purposes.

We have also designed and constructed several research and aquarium systems for research laboratories of universities and research centres. We co-operate with several well-known manufactures to provide our projects and sale with high quality equipment for filtration, sterilizing water and pumping water and air. We also use the optimal materials for pipe lines, tank constructions and water treatment to sell safe and reliable RAS and other systems to customers. Fish handling is done by pumps, screws and grading machines on farms, where they help specially to handle big volumes of fish. For fish feeding we use different equipment produced by the Nordic suppliers.

Wide experience and strong expertise

Our personnel includes experts in different sectors of aquaculture – consulting including planning and project management, practical fish farming experience, teaching in aquaculture studies as well as experience in fish processing (e.g. hot and cold smoked fish).

Our personnel:

  • Managing Director Jouni T. Laine
  • M.Sc. Tech. Martti Naukkarinen
  • M.Sc. Fish Biologist Riitta Myyrä
  • B.Sc. Natural Resources, Fisheries and Environment Pasi Korvonen
  • Technical Installer Janis Austers

*Kalavesi Consultants Ltd is owned by Clewer Aquaculture Oy through business acquisition in February 2017.