Salt in circular value chains

Background

Fish sludge contains large amounts of carbon, phosphorus and other nutrients that are largely lost in sawmills. By converting the sludge into biochar through pyrolysis, one can both store carbon and return valuable nutrients to new cycles.

The project follows up on the results from the project 2023-0430 Industrial symbiosis from land-based aquaculture, which looked at the possibilities of building a regional circular value chain based on the pylorization of sludge from a land-based post-smolt facility. There, salt was identified as the biggest barrier to further utilization of biochar produced from sludge. While much research has been done on sludge from freshwater-based hatchery production, there is little documentation on how salt from the seawater phase affects biochar and various applications.

The aim of the project was to investigate

• How salt affects pyrolysis of fish sludge.
• How salt affects the quality of biochar.
• Whether biochar from saline fish sludge can be used in agriculture and plant production.
• What opportunities and limitations exist for the development of circular value chains around fish sludge.

The insight will contribute to better resource utilization, lower environmental footprint and new sustainable business opportunities in the aquaculture industry.

Progress
The project was completed in June 2026.