Reshaping heavy metal pathways: A long-term field study on emissions and partitioning in municipal solid waste (MSW)...

China is vigorously implementing municipal solid waste (MSW) classification, which significantly alters the composition of MSW entering incinerators and influences the migration and transformation of heavy metals (HMs). However, long-term comparative research based on full-scale plants examining HMs behavior before and after MSW classification remains lacking. This study investigates how MSW classification affects HMs evolution along the flue gas flow in the post-combustion zone, removal efficiencies, and partitioning characteristics in a modern MSW incineration (MSWI) plant. A continuous field study, spanning the pivotal transition before and after the mandatory implementation of MSW classification, was conducted at an MSWI plant in South China equipped with advanced air pollution control devices (APCDs). Flue gas samples and ashes were collected and analyzed before and after implementing MSW classification. Results show that MSW classification reduced HMs input at the source and separated food waste, the latter lowering chlorine input and thus suppressing HMs volatilization. Consequently, incinerating classified MSW significantly decreased total HMs content in residues and altered partitioning patterns. Specifically, incinerating classified MSW led to lower Cr and Cu concentrations in fly ash. Compared to before classification, fractions of Pb, As, Sb, Zn, Cd, and Hg partitioned into fly ash increased, while their shares in bottom ash and flue gas decreased. Moreover, HMs concentrations in flue gas, both before and after APCDs, were markedly lower than pre-classification levels; except for Mn and Hg, removal efficiencies for all HMs exceeded 97%. This study demonstrates that MSW classification is an effective strategy to reduce environmental risk by cutting HMs input at the source and concentrating HMs in fly ash.