Phosphorous flow analysis and resource circularity at the province level in north Italy

Phosphorus is an essential element for living organisms, but its unequal distribution combined with the current anthropogenic activity make it a critical resource. To decrease the risks of future shortages, new techniques to manage phosphorous are needed to be mainstreamed under a Circular Economy approach to boost a sustainable transition. A full characterization of flows and stocks is necessary to measure the contribution of secondary materials to meet the overall demand in a system and support decision-making process towards potential improvements. This understanding is determinant for a successful implementation of phosphorous recovery at the regional level, where site-specific conditions dictate local constraints. In this study, material flow analysis has been applied to characterize the 2020 phosphorous cycle in the Province of Rimini (Italy) and the State of San Marino, which are served by a wastewater treatment plant with a 560,000 person-equivalent capacity. Our model shows that, about 236 ± 23 t P entered the system, while 155 ± 14 t P left it, resulting in a net accumulation of 81 ± 21 t P, mainly located in soil for crop production, water bodies, and sedimentation due to dissipative flows. The greatest potential for phosphorous recovery is embedded into the digested sludge from the wastewater treatment plant, which would ideally meet 96% of the annual local demand of mineral fertilizers. However, this flow is currently disposed of by landfilling. Further technical, economic, environmental, and regulatory valuations are ultimately needed to build a positive business case to recover phosphorous in the region.