Life cycle assessment of recycling food-contaminated polylactic acid packaging: net-energy, carbon emissions, and cost-based scenario assessment.

Abstract

This study presents a goal-oriented life cycle assessment of end-of-life strategies for food-contaminated polylactic acid (PLA) packaging, an increasingly prevalent waste stream driven by the growth of food delivery services. Using empirically measured contamination data from 100 delivery meals, four recycling pathways (five scenarios) were evaluated: thermal recycling, mechanical recycling, chemical recycling, and anaerobic digestion (AD)-based systems. Net energy balance, non-biogenic CO2 emissions (CO2E), and daily operational cost (OpCost) were quantified for a functional unit of one day of system operation. Multi-criteria decision-making methods were applied to determine integrated scenario rankings. The measured PLA-to-food waste ratio (2.9:1; 34.5% PLA) was significantly higher than values commonly assumed in previous studies. Full thermal recycling (Scenario 1-1) showed the poorest performance across all indicators. In contrast, chemical recycling combined with AD (Scenario 3) achieved the highest overall performance, driven by high-value ethyl lactate production, reduced CO2E, and stable net-energy recovery. Mechanical recycling combined with AD (Scenario 2) and dual AD processes (Scenario 4) also demonstrated robust mid- to high-level performance, with consistent rankings under uncertainty conditions. Across all scenarios, landfilled dehydrated sludge was the dominant contributor to CO2E and OpCost, highlighting the potential benefits of enhanced dewatering using surplus AD heat. By incorporating real contamination levels and complete downstream processes, including wastewater treatment and digestate management, this study provides practical and policy-relevant insights for transitioning from incineration-centered systems toward recycling-oriented management of mixed PLA-food waste streams.