Grønn Gjødsel has taken over the task of fermenting fish sludge with bokashi method in large volume. To collect sludge has been difficult, both in terms of finding a relevant source and the practical sides of it. Today most fish sludge is dried immediately without storage and either sent to cement furnaces or to agricultural use.

Grønn had an agreement with company Bremnes Seashore to collect sludge after sedimentation and pressing, with a dry matter content of 20-25 %, that is before going into the dryer. However there was technical issues, the plant had to be repaired, so we found another supplier close to Bodø. There was an issue with this sludge, it went bacterial and developed gases, so we came back to Bremnes Seashore at Trovik, north of Haugesund.

On the 24 of november director Lars Evju and biologist Tommy C. Olsen went to the plant at Trovik, to start fermentation of sludge with bokashi, the idea was to collect from stream after pressing at 20 % dry matter  and mixing batches with bokashi culture base. The smolt plant is one of the most modern in Europe, with high degree of recirculation of water.

However the sludge was apparently too solid to be mixed, the consistency can be compared to wet bread, see picture, so we had to go further into the processes of the smolt plant. We identified a liquid sludge tank with 5 % dry matter, a stable materiel, according to the plant manager. We were able to collect two IBC containers with this material and have the sent to Grønn i Rakkestad for further work and analysis. The containers will be stored cold until the work proceeds. See pictures:

Processing plant for sludge.


Sludge at 20 % dry matter.


Collecting 5 % dry matter sludge.