Contaminants of environmental concern in sewage sludge in the Nordic countries

Sewage sludge monitoring data on many harmful organic pollutants is scarce. In this study, 23 contaminants of environmental concern were identified, including: Per- and polyfluoroalkyl substances (PFAS), pharmaceuticals and personal care products, hormones, and flame retardants. First, concentration data in sludge from the Nordic countries, was compiled. Several data gaps on concentration data were found, particularly in personal care products and flame retardants groups. There were also large differences in data availability between the countries. Second, removal efficiency of the selected pollutants was reviewed. Three different treatment methods were considered: anaerobic digestion, composting, and pyrolysis. Pyrolysis emerged generally as the most efficient removal method, whereas there were large differences in the reported removal efficiencies in anaerobic digestion and composting. Overall, the most recalcitrant pollutants in sludge in this study were PFAS, certain antibiotics, and estrogens. Several factors behind the variation were identified, such as diversity in plant design, operational and seasonal parameters, and challenges in sampling and analysing the sludge matrix. Coherent study designs are needed to compare removal efficiencies more transparently. Legislative requirements are usually the main drivers for carrying out monitoring, andurrent EU legislation regulating hazardous substances in sewage sludge is outdated. There is great variation in national regulations between the Nordic countries. The lack of regulatory requirements hinders informed/science-based long-term decision-making to protect the environment. Sludge utilization is a complex question requiring consideration from regulative, technological, and societal perspectives. Monitoring contaminants is vital in both assessing risks of sludge-based fertilizers and contaminant removal efficiencies in sludge treatment.