Fish Sludge for Fertilizer

Picture: Osland Settefisk

Osland Settefisk invests NOK 12 million in drying facilities for fish sludge in connection with the expansion of the smolt plant. The end product will have high nutritional value and will be used in pelleted fertilizers.

Osland Settefisk at Sørebø in Sogn is one of the country’s oldest fish farming businesses. Established in 1963 and locally owned by the third generation Osland, it has clear ambitions for sustainable operations. In connection with the expansion of the setfish plant, full recovery of the cleaning sludge is planned. The end product, dried granules will go to fertilizer production.

RAS plant
The plant at Sørebø was early in the process of switching to reuse of water (RAS) and collection of effluent sludge. The sludge contains about 90 percent water, and has so far been transported to a sewage sludge treatment. Some have also been delivered to agriculture, after curing with lime.

In order to be able to supply a more robust smolt, the facility is now being further expanded, from an annual production of 250 tonnes to 1,000 tonnes, within a five million smolt license. This is done with RAS technology, where the investment come to NOK 120 million, with full production in the plant in two years.

– A larger smolt provides a better starting point for growth in the sea and less loss of fish, says Kjetil Rørtveit, operations manager at the plant.

More sludge
The expansion will lead to an increase in the amount of sludge, and after careful considerations it has been decided to invest in a plant for drying this sludge into granules.

– Instead of moving large amounts of thin sludge with about 90 percent water, we dry it to over 90 percent dry matter, and then deliver it for agricultural purposes. In line with a circular mindset, we thus treat the sludge as a resource, says Rørtveit.

The thin  sludge is collected during filtration of the waste water from the RAS plant, thickened and dried at low temperature. Thus, the nitrogen that would otherwise evaporate is not lost, and the granulate receives the greatest possible benefit as fertilizer. The fact that it is dry makes it easy to pellet for so-called “smart fertilizers”.

In total, it is estimated that approximately 100 tonnes of dried sludge will be produced annually when the plant is fully operational. Sterner will supply sludge treatment and drying plants, and the plant will be operational in February next year.

– Obviously it is a significant investment, but we choose to see this as part of the whole, we want to operate sustainably and environmentally friendly, then there is no other way to go. Instead of using large amounts of diesel to carry the gross sludge as waste, we choose to use some electrical energy, reduce the volume to a tenth and make it usable. The sludge has a high nutritional value, so we think that this is future-oriented, says Rørtveit.

Operating expenses
Sterner has ensured that the dried granules are retrieved free of charge for Osland Settefisk and that both transport and further use are in accordance with current requirements. Energy costs including cooling will amount to approximately NOK 300,000 per year. Sterner will be responsible for the costs of polymer, large bags and spare parts.

– We chose to go for the simplest solution in the market, where high ease of use and low energy costs have been crucial to the choice. With this solution, operating costs are kept as low as possible. We have good experiences with Sterner from the past, says Rørtveit.

The drying plant will be operational in the spring of 2020, and the investment in the plant will amount to approximately NOK 12 million. The granulate is scheduled to be delivered to Grønn Gjødsel at Rakkestad.

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