Agricultural use of sewage sludge faces nutrient efficiency challenges

Research and environmental reports highlight challenges regarding the use of sewage sludge as fertilizer in Scandinavian agriculture. In Norway, a NIBIO study led by researcher Eva Brod indicates that much of the phosphorus in sewage sludge is not effectively utilized by plants. This inefficiency is partly due to sludge being applied in quantities exceeding plant uptake capacity. New regulations set for 2030 will shift limits from sludge volume to phosphorus content, introducing a cap of 25 kilograms of total phosphorus per decare over a ten-year period. However, researchers warn that these rules may create a paradox where sewage treatment plants benefit from low plant-available phosphorus to meet regulatory limits, potentially hindering optimal resource utilization.

In Denmark, over 50,000 tons of sewage sludge were spread on agricultural land in 2024, according to the Danish Environmental Protection Agency. While the practice recycles vital nutrients like phosphorus, it has caused local concerns regarding odors and the presence of heavy metals or medicinal residues. Experts from Aarhus University note that while sludge is highly regulated and contains environmental risks, the benefits of nutrient recycling generally outweigh the drawbacks, provided the sludge is properly treated and controlled.