Scandinavian sewage sludge and nutrient recycling research

Research in Scandinavia has highlighted inefficiencies in using sewage sludge as agricultural fertilizer. In Norway, a NIBIO study led by Eva Brod found that much of the phosphorus in sludge is not effectively utilized by plants, often because application quantities exceed plant uptake capacity. This issue is compounded by upcoming 2030 regulations that will shift limits from sludge volume to a phosphorus cap of 25 kilograms per decare over ten years. Researchers warn this could create a paradox where treatment plants benefit from low plant-available phosphorus to meet regulatory limits.

In Denmark, the use of over 50,000 tons of sludge in 2024 has raised local concerns regarding odors and residues, though experts suggest nutrient recycling benefits generally outweigh these risks if properly controlled.

Further research by NIBIO is exploring the repurposing of fish sludge from land-based cod production. Rather than burning or using it for biogas, new projects aim to use the sludge as a microbial substrate to produce fats and proteins for fish feed, aiming to transform waste into a resource.