A multi-objective model to optimize country-scale municipal solid waste management with economic and environmental objectives: A case study in Malaysia

Municipal solid waste (MSW) is a universal issue affecting all countries. In Malaysia, almost 90% of the MSW is disposed of in open landfills with no energy recovery system. Due to the heterogeneous characteristics of MSW, it is essential to develop a combination of different waste processing facilities with simultaneous cost and greenhouse gas (GHG) minimization. A novel multi-objective mixed-integer linear programming with the augmented e-constraint method is developed to assess the optimum MSW allocation on seven conventional waste processing facilities, including open landfills, material recycling facility, sanitary landfills, anaerobic digestion, composting, incineration, and plasma gasification. The avoided emissions of the valuable products valorized from MSW, which have been often neglected in the optimization model, are included in the study to investigate the extent of emissions reduction in the MSW management system. Compared to the current scenario in Malaysia (total cost: 66.66 MYR/tonne MSW, net GHG emissions: 0.42 tonne CO2-eq/tonne MSW), the least-cost solution (i.e., 74% open landfill, 10% sanitary landfill, and 15% material recycling facility) shows 26% reduction for both cost and GHG emissions, while the least GHG emissions solution (i.e., 20% sanitary landfill, 21% anaerobic digestion, 21% composting, 21% plasma gasification, and 17% material recycling facility) indicates 159% reduction of GHG emissions with 15% increase in cost. Among the 11 Pareto-optimal solutions, the 10th solution (34% sanitary landfill, 21% anaerobic digestion, 21% composting, 17% material recycling facilities, and 8% plasma gasification) reduces 3% of national greenhouse gas emissions and is recommended for future MSW management in Malaysia. The sensitivity analysis indicates that plasma gasification is more favorable when the electricity price is higher. A change of waste separation rate from 30% to 90% reduces total MSW management cost and the net GHG emissions by 18.24 MYR/tonne MSW and 0.30 tonne CO2-eq/tonne MSW, respectively. This study provides quantitative information to policymakers in developing a sustainable and resource-efficient MSW management system in Malaysia.