Influence of the classification of municipal solid wastes on the reduction of greenhouse gas emissions: A case study of Qingdao City, China

Municipal solid waste (MSW) is an important source of greenhouse gas (GHG) emissions. Reduction of GHG emissions and resource recovery from MSW disposal units is vital for China's dual carbon strategy. Carbon emissions during the treatment of MSW from Qingdao City under different disposal modes including the classification of MSW were investigated using the life-cycle assessment (LCA) methodology and life-cycle inventory (LCI) with material flows. It was found that the carbon emissions during MSW disposal depended on the disposal modes. The traditional mode of mixed domestic waste collection + landfill had the largest carbon emission (568.98 kgCO₂-eq/t MSW), while the mode of mixed domestic waste collection + incineration served as a carbon sink with a net carbon emission of −28.56 kgCO₂-eq/t MSW. The carbon emissions of classification of MSW + anaerobic digestion of kitchen waste + incineration of other wastes and ideal classification of MSW modes (classification of MSW, anaerobic digestion of food wastes, resource utilization of recyclable wastes, and incineration of dry wastes.) were 4.27 and −269.34 kgCO₂−eq/t MSW, respectively. Further, it was determined that improving the classification efficiency of food waste had no significant impact on carbon emissions and the reduction of carbon emission increased linearly with the improvement of waste recycling efficiency. When the recovery efficiency reaches 5%, the MSW disposal sector can be expected to achieve near carbon neutralization. This study show that appropriately separating food waste, improving the recycling efficiency of recyclable waste, and reducing the leakage rate of biogas from anaerobic digestion are three feasible strategies to reduce carbon emission from MSW disposal units through the classification of MSW.