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SUSTAINABILITY LIBRARY 2023 Circularity Sludge

Sludge

Collecting sludge from our farming operations - a new resource

Lerøy Sjøtroll has installed the world's first collection system for sludge in fish cages.

In collaboration with technology companies Lerøy Sjøtroll developed a completely new sludge collection technology to remove natural waste substances, such as feed residues and faeces, from fish cages.

The natural ecosystem on the seabed benefits from a little discharge of organic materials from the cages, it acts as fertiliser. The problem arises when the amount of sludge exceeds nature's own tolerance, which can happen in threshold fjords with low oxygen levels.

The sludge from the fish is collected in a fine-mesh groove installed at the bottom of the cage. It is then pumped up through a filtration system and into a tank located on the surface. The sludge is then transported away from the facilities in boats. The sludge is then converted into biogas.

The sludge contains resources that can be fed back into the value chain. Exciting projects range from soil improvement, gas production, extraction of minerals and production of larvae and insects.

Lerøy Sjøtroll has sludge collection on 2 farm locations.