Multi-objective optimization in waste plastics - recycling vs thermo-valorization

In the past few years, waste management has received increasing attention not only from industry but also from academics. With an increase in plastic content, motivated by China’s ban on its import, waste composition is expected to change in the near future. Plastic is also considered a major pollutant if not handled properly, particularly for soils and oceans. Although recycling of plastics is well established for PET, a whole range remains that needs handling and treatment. Waste plastics are incorporated in a much wider treatment system and are decisive in contributing to waste calorific value. By providing separate collection routes and by increasing recycling, lower amounts are available for combined heat and power in typical thermo-valorization units, which demands the use of conventional fossil fuel alternatives to supply the needs. In this study, a multi- functional economic and environmental optimization is performed, covering the treatment of waste plastics by means of mixed integer linear programming. Multi-objective optimization was conducted to evaluate various designs. Solutions result in a trade-off between costs and emissions, with 8 designs beating current waste management solutions, with proper thermo-valorization challenging recycling processes in environmental impact assessment. Furthermore, costs can be reduced up to 20-fold, while environmental impact showed a potential for up to 20% reduction compared to the BAU scenario. This research allows new ways of considering the benefits and disadvantages of recycling and thermo- valorization, as it pretends to be closer to real systems considering real world trade-offs and decisions, challenging current views and beliefs.