Effect of Source-Classified Collection of Municipal Solid Waste on Heavy Metals and Pozzolanic Properties of Incineration Residues

Abstract

The adoption of source-classified collection of municipal solid waste (MSW) systems has improved waste management and resource conservation in developing countries, including China. Here, we evaluated the effects of a new MSW source-classified collection system on the distribution and leaching of heavy metals in incineration residues as well as on the pozzolanic properties of residues used as additives in cement production. Cu, Cr, and Mn were found primarily in bottom ash, while the volatile metals Zn, Pb, and Cd became enriched primarily in fly ash during combustion. However, effective presorting of MSW prior to incineration reduced the heavy metal content of the MSW source material and increased the combustion efficiency and heat values of MSW. The system of source-classified collection of MSW resulted in decreased concentrations of heavy metals in bottom ash, as well as decreased leachate toxicity, which improved the viability of bottom ash for use as a non-hazardous raw material in cement production. The consistently high temperatures sustained during incineration of source-classified MSW increased the concentrations and leachate toxicity of Cd, Pb, Cu, Zn, and Cr in fly ash. Pozzolanic activity testing revealed that bottom ash may be used as a pozzolanic material in cement production, but that fly ash is not suitable. In contrast to bottom ash from the incineration of mixed MSW, bottom ash from the incineration of source-classified MSW fully satisfies China’s “Pozzolanic materials used for cement production” standards due to its low loss on ignition, high grindability, and the desired rupture strength, compressive strength, and stability that it adds to mortar mixtures.