Resource recovery strategies and schemes: A regional case study on sewage sludge hub centres in Italy

The establishment of regional sludge treatment hubs has been proposed as a solution to achieve the necessary economic scale for sustainable resource recovery and safe reuse in non-metropolitan areas. However, existing literature provides limited insights into their sustainability and effectiveness, and inadequate legal frameworks often hinder efficient sludge treatment, leading to improper disposal and increased risks. This article addresses these gaps by evaluating the environmental impact of a centralised sludge treatment system through a real case study, highlighting the importance of selecting sewage sludge with minimal risks for centralised resource recovery and safe reuse, in line with the recent review of the Sewage Sludge Directive. Building on the Horizon 2020 SMART-Plant innovation action, a regional sludge hub has been designed to treat and valorise the sewage sludge from 52 municipalities in Treviso, serving around 500,000 residents. In the first phase, the potential for resource recovery and safe reuse was assessed by evaluating the long-term chemical and physical characteristics of the sewage sludge, while considering the replicability of this model. In the second phase, a Life Cycle Assessment (LCA) was conducted to evaluate the environmental impact of various valorisation pathways, including composting, biogas production, phosphorus salts, and biopolymer (PHA) recovery. The final environmental impacts were normalised using the revised ReCiPe 2016 normalisation values. The results indicated that phosphorus and biopolymer recovery was the most sustainable scenario, reducing emissions by an amount equivalent to 176 individuals per day compared to the decentralised system