Junki So  Yuchan Ahn

Vol. 31,  No. 4, pp. 274-284, Dec.  2025
10.7464/ksct.2025.31.4.274

Plastic waste Sorting Diversified machine capacity Economic Analysis Optimization

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Efficient sorting of plastic waste is essential for enhancing recycling rates and reducing environmental impacts. Conventional sorting systems depend on fixed-capacity machines. However, when there are fluctuations in feed volume, these machines can be inefficient and require excessive investment. To address these issues, this study develops an optimization model for a single-stage plastic sorting process with variable-capacity machines using mixed-integer linear programming (MIP). The model allows machine capacities between 100 and 1,000 kg/h to be selected in increments of 100 kg/h at each sorting spot to allow for flexible adaptation to feed variations. Seven serially connected sorting spots were modeled to separate resins, with unsorted residues transferred sequentially to maintain mass balance. The objective function was formulated to maximize daily profit by balancing revenues from recovered plastics with investment and operating costs, including the energy consumption proportional to machine capacity. The results showed that the variable-capacity configuration significantly reduces the investment costs compared to fixed-capacity systems. The variable-capacity configuration also maintains or enhances the throughput and profitability, achieving a net profit of 4,969 US$/day. These findings demonstrate that flexible capacity planning can improve both the economic and operational efficiency of plastic waste sorting facilities, and can offer a practical approach for sustainable resource management.