Decentralised treatment versus integrated biorefinery recovery of polyhydroxyalkanoates and struvite from urban and organic waste: A life cycle assessment approach

Abstract

Despite being a well-known alternative for the valorisation of organic wastes, anaerobic digestion needs to evolve toward the synthesis of higher-value products ensuring higher organic matter yield and economic profits. Large-scale implementation and robust environmental assessments of such integrated systems remain limited. This study compares two waste management scenarios for the Lombardy region (Italy): the current decentralised system (Actual Scenario) and a novel centralised biorefinery configuration (Biorefinery Scenario) designed to recover polyhydroxyalkanoates (PHA), struvite, heat and electricity. Following Life Cycle Assessment principles, the Product Environmental Footprint method was applied to quantify environmental impacts and identify key contributors to system performance. The results show that implementing a biorefinery at the Italian facility can reduce climate change (CC) impacts by 22 %. However, these benefits depend strongly on the PHA extraction method: only mechanical disruption and sodium hydroxide extraction keep CC impacts below those of the Actual Scenario (177.8 kg CO₂eq/t input waste). Biogas purification, sludge incineration and struvite recovery are identified as major hotspots requiring optimisation. Reducing energy demand (responsible for 31 % of CC impacts) and improving the management of direct emissions from biogas combustion are key priorities for enhancing environmental performance. Overall, this study provides one of the first integrated MFA–LCA assessments of a regional biorefinery simultaneously treating sewage sludge, agri-food residues and OFMSW using real operational data. By demonstrating both the potential and the critical limitations of multi-output resource-recovery systems, the work offers new scientific evidence to support the design, optimisation and policy development of future circular biorefineries