Net pen collection system trapped 60% of sludge
A cage system designed to reduce sludge accumulation beneath fish farms collected about 60% of the fish faeces and uneaten feed at a site during a long-term trial in Norway.
Scottish Sea Farms co-owner Lerøy Seafood has tested the Mørenot Collect system since August 2020, covering a whole generation of rainbow trout at the Blom fish farm in the Oster Fjord.
The facility, with 14 square cages each measuring 25 x 25 metres, has a maximum permitted biomass of 3,120 tonnes. The test has documented solids collection estimated at about 60% of the particulate discharge.
The sludge is converted to green energy and fertiliser.
Circular cages
Lerøy now wants to verify and adapt the cage concept for circular pens and is due to get the first circular collector cage – measuring 160 metres in diameter – from Mørenot in the water this month.
“We want to adapt the cage concept technically and operationally to our traditional farm with 160-metre cages,” explained Sven-Åge Hauge, project manager for aquaculture technology development at Lerøy Sjøtroll. “The trial has shown substantial environmental gains.”
Mørenot and Lerøy collaborated with Framo Lift-Up, which adapted its well-known mort collection pump to create the Combi Cone, which sucks up both morts and sludge through separate tubes.
350 tonnes
During the test period, the collection cage gathered 350 tonnes of sludge (weighed as 100 per cent dry matter), which will be converted to renewable energy and fertiliser using the Framo Lift-Up technology and the Ragn-Selles Havbruk logistical solution.
“The dry matter collected at the farm provides about 800,000 kilowatt-hours of renewable energy,” said product developer Jarle Ragnhildstveit at Framo Lift-Up. “That corresponds to power consumption by 40 Norwegian households for a whole year.”
Read more details about the Lift-Up sludge collection method in the March 2021 edition of Fish Farming Expert online magazine.
