Mowi has been granted two of the eight development licences it wanted for ØPD's Marine Donut. Image: Mowi.

Mowi offered just a small bite of the Marine Donut

Norway’s fisheries directorate has granted Mowi two development licences to test the Marine Donut floating closed salmon farm concept. It had applied for eight.

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It means Mowi will be allowed to grow a maximum biomass of 1,100 tonnes in the Donut for seven years.

The concept is a closed fish farming unit that is shaped like a torus or ‘donut’. It will be made from high density polyethylene (HDPE) and will act as a closed barrier to the external environment.

The relative size of the Marine Donut. Click in image to enlarge. Illustration: ØPD.

Below the lice layer

Water will be pumped into the plant from a depth below the lice layer to prevent lice and other diseases and to achieve a more even temperature throughout the season. 

Inlets and outlets will have dual barriers and in addition the facility will be equipped with emergency power units and emergency oxygenation equipment in case circulation stops. 

The inlets will be able to be adjusted to different water depths in the sea by means of a winch inside the inlet pipe.

Water exchange will be up to 100% of the total water volume in the plant within one hour. The seawater inside the Marine Donut will have oxygen added via a venturi valve at the inlet or in the construction itself. According to the applicant, the facility will be able to be isolated, if necessary, by running circulating pumps with oxygenation (for example in the case of oil spills or acute pollution). There will be continuous flow inside the closed system.

Look familiar? The concept's torus or 'donut' shape should provide a good hydrodynamic flow.

Good hydrodynamic flow

The torus shape of the concept will, according to the applicant, provide a good hydrodynamic flow pattern and give the fish the opportunity to continuously swim against the current. The current will be adjustable and independent of the water intake.

Mowi states that in operation, 90% of the plant will be submerged to provide good stability and have less of a visual impact. The plant will be able to be raised and lowered in order to efficiently carry out cleaning and maintenance.

Pumps will be able to rotate 180 degrees in the inlet pipe and pump out water so that the unit is emptied and raised. Remaining water in the plant below the water intake level will be discharged via a submersible pump. The plant will be able to be lowered again by pumping in water.

From 3kg to slaughter

The Marine Donut will produce fish from 3kg to slaughter. In order to clear the plant for fish, two sliding bulkheads that collect the fish must be used.

The plant will have the following main dimensions: 16.5m height, 54.5m diameter, and total internal volume equal to 22,000m³. The applicant states that the Marine Donut concept is intended to lie in Norwegian fjords. The design life of the concept should be 20 years.

The technology is developed and owned by Norwegian firm ØPD, which specialises in the installation of both submarine polyethylene (HDPE) pipelines and onshore HDPE pipes, and using its HDPE expertise to develop innovative solutions to real world challenges.