Leister extruders in use – Marine Donut in Norway

Authors: Gregor Studer, Manager Marketing Services, and Reto Britschgi, Product Manager Plastic Fabrication, Leister Technologies AG

Aquaculture is an important part of the solution to world hunger and the growing global population. Because fresh fish provide nutritious proteins and generate considerably lower CO₂ emissions than conventional meat. However, to ensure commercial fish farming remains sustainable from all points of view, new innovative concepts are called for to factor in the challenges facing the sector. Norway’s Bluegreen has assumed this mission and will soon be unveiling the Marine Donut to the world.

A pioneering construction for fish farming of the future

The Marine Donut is a closed fishery designed in the form of a donut. The fish farm is suitable for both young and food fish rearing. The construction offers an ingenious solution for freshwater supply to ensure fish well-being: The flow system inside the Marine Donut was designed based on a fish’s natural habitat in rivers and the inflow is cleaned with a Bernoulli® filter* and UV lamp.

*Bernoulli® filters are used to remove solid waste in natural liquids such as sea or river water, including process water with moderate contamination. Bernoulli® is a registered trademark of Sweden’s Krone Filter Solutions GmbH.

The donut shape offers many benefits

The Marine Donut’s closed shape guarantees commercial and environmental benefits for fish farmers: Integrated sensors ensure digital control and monitoring of the entire circuit. So efficient feeding can be precisely scheduled, reducing costs. The ring-shaped main construction also forms a sealed barrier. This prevents fish from escaping and reduces the risk of disease or contamination with algae and sea lice. This considerably facilitates maintaining a healthy fish stock.

Resilient and sustainable

The Marine Donut is designed to withstand waves and ocean currents. The construction can be raised and lowered with floating tubing on the top, strut tubing below and vertical ballast tanks. There is a working platform on top of the construction with solar panels for sustainable power generation. The construction is also fitted with a system for collecting fish excrement. Excrement is recycled to be used as organic fertilizer or as a base product for natural gas production.

Leister supports pioneering work with high-performance extruders

The construction’s huge dimensions – the finished Marine Donut weighs 540 tons – presented Bluegreen’s engineers with massive challenges. This included meticulous and watertight welding of the ring-shaped main construction made up of individual 1-ton plastic HDPE (High Density Polyethylene) components. For this undertaking, Bluegreen CEO Nils-Johan Tufte and his team turned to the plastic welding experts at Inter-Supply AS. Eirik Tveitdal from Inter-Supply AS, official representative of Leister products in Norway, quickly and expertly responded to the unusual request.

Welding a combined distance of 20,000 m with WELDPLAST S2 and WELDPLAST 600

Between 8 and 10 tons of welding rod were needed for joining the HDPE components for welding a combined distance of 20,000 m. In order to ensure perfect seam quality, agile Leister WELDPLAST S2 and powerful WELDPLAST 600 extruders were used. The smaller and lighter WELDPLAST S2 with its arrow-shaped body is perfect for working in corners and hard to access places. The powerful WELDPLAST 600 and its large output volume of 6 kg/h is particularly suited to the construction of large polyethylene objects. Elg Ragnar Thunes, Bluegreen partner, confirms: “Leister devices are focused on quality and practical application. Both these factors help our welders achieve high quality welds. We use reliable Leister extruders for all manual welding work and we have virtually no downtime.”

Estimated water baptism: early summer 2023

If everything goes to plan, the world’s first Marine Donut should have its water baptism in early summer 2023. With its Donut, Bluegreen is looking forward to making an important contribution to sustainable fish farming to supply the world’s population.

Technical information

• Material: Polyethylene (HDPE)
• Total height: 14.64 m internal and 17.51 m external
• Diameter: 55 m plus walkway
• Width (shell cross section): 16.2 m
• Volume: 22,000 m³
• Water flow speed: <0.8 m/s
• Water inflow depth: 15 to 40 m
• Inflow water UV cleaning
• Construction work started: April 2022
• Completion and fish introduction: < June 2023

About Bluegreen

Bluegreen is a Norwegian company with leading expertise in thermoplastic constructions. Bluegreen’s vision is to provide the most environmentally friendly solutions worldwide for and in water – hence the name Bluegreen: “Green solutions for blue water and blue air”. Source Bluegreen website: https://bluegreengroup.no/en