Why Sequencing Matters in Multi-Stage Plastic Waste Sorting: A Techno-Economic Comparison

The design of multi-stage plastic waste sorting systems plays a decisive role in determining operating cost and overall process performance. In such systems, the sequencing of individual separation technologies strongly influences the economic feasibility of the recycling process, yet this effect has rarely been evaluated in a systematic and comparative manner. In this study, a techno-economic comparison of alternative multi-stage sorting pathways was conducted using total annualized cost (TAC) as a unified economic metric. Five widely applied separation technologies are combined to construct sixteen sorting pathways by permuting the order of separation stages. A representative case study was performed for a mixed plastic waste stream (PET, PE, PP, PS and PVC) at a processing capacity of 3000 kg/h. The results show that sorting pathways employing froth flotation as the final separation stage consistently exhibit lower TAC values than configurations terminating with tribo-electrostatic separation. The most favorable sequence achieved approximately a 40% reduction in annualized cost relative to representative baseline configurations employing tribo-electrostatic separation as the final stage under identical operating conditions. Scenario-based analyses under different processing capacities (1000–5000 kg/h) and alternative electricity cost assumptions further demonstrate that the relative economic ranking of sorting pathways remains unchanged, confirming the robustness of favorable separation sequences. The results highlight that strategic sequencing of existing separation technologies can significantly improve the economic performance of plastic waste sorting systems without increasing process complexity, thereby providing practical guidance for process design and technology selection.