Assessing and Mitigating Risks of Emerging Contaminants in Fertilizer Production from Sewage Sludge: Challenges and Opportunities

The increasing production of sewage sludge (SS) poses a major challenge for sustainable waste management, particularly when SS is considered for agricultural use as a source of fertilizer components. Although SS contains valuable nutrients and organic matter, its agricultural application may also introduce contaminants that pose risks to soil quality, water resources, ecosystems, and human health. This study presents a structured narrative review of the safety-related challenges associated with the agricultural use of SS, with particular emphasis on the occurrence of contaminants, related environmental and health risks, treatment and stabilization options, and the regulatory context governing SS-derived materials. The review addresses major contaminant groups discussed in the literature, including heavy metals, pathogens, microplastics, pharmaceuticals, and other contaminants of emerging concern. It also examines the main approaches used to improve the safety of SS before agricultural use, such as composting, anaerobic digestion, thermal and chemical treatment, and dewatering with granulation or palettization. The analysis highlights that the safe use of SS in agriculture depends not only on its fertilizing value, but also on effective treatment, continuous monitoring, and a clearer regulatory framework. In particular, the review identifies important legal and regulatory gaps regarding treatment requirements, permissible contaminant levels, and criteria for agricultural application. Overall, the findings indicate that SS can remain a valuable source of fertilizer components, provided that its use is supported by appropriate risk mitigation strategies and science-based regulation. Sewage sludge offers fertilizer value, but raises major safety concerns. Heavy metals, pathogens, and microplastics remain key barriers to reuse. Treatment and stabilization are essential before agricultural application. Continuous monitoring is required to control environmental and health risks. Regulatory gaps still limit the safe use of sludge-derived fertilizers.