Management and valorisation of sewage sludge to foster the circular economy in the agricultural sector

Sewage sludge, a by-product of wastewater treatment, is a potential source of energy and resources. Its use as raw material presents a promising perspective for waste management within the framework of the circular economy. Despite its potential benefits, the excessive production of sewage sludge poses environmental and socio-economic challenges, including the threat of contamination by heavy metals, pathogens and organic micro pollutants. Moreover, the European Directive regulating the agricultural use of sewage sludge (86/278/EEC) does not fully reflect current scientific knowledge and technological advancements, particularly in regard to emerging contaminants and harmonised reuse strategies among Member States. To date, only a limited number of comprehensive reviews have addressed the main impacts of sewage sludge in the agricultural sector, particularly regarding its effects on soil physical, chemical, and biological properties. Sewage sludge valorisation, including soil fertilization, plays a pivotal role in improving soil quality and long-term productivity. This is proven by an increased supply of organic matter and nutrients, as well as improvements in soil ecosystem health that promote crop growth. In addition, the application of sewage sludge makes the soil structure more stable and less vulnerable to erosion. Furthermore, through different physical-chemical processes, it is possible to recover materials and energy to be used as end products or included in other production processes, thus contributing to promote a sustainable and circular economy approach. The implications of this review point to the need for suitable EU laws and regulations, greater social acceptance, and continued research to exploit the full potential of sewage sludge for agricultural purposes.