ENVIRONMENTAL MANAGEMENT OF FLY ASH PRODUCED FROM THE INCINERATION OF MUNICIPAL SOLID WASTE

Incineration is a widely used and well established technology for the municipal solid waste (MSW) management. Modern MSW incineration plants are equipped with improved air pollution control (APC) systems, which reduce pollutants well below the established limits. The environmental concern has, thus, moved from the air emissions to the solid residues generated from the APC systems of the incineration plants. A detailed characterization of fly ash collected from a municipal solid waste incinerator, which involves both its physicochemical properties and its leaching behavior, is presented. The leaching test results indicate that leachate concentration of Pb and Total Dissolved Solids (TDS) exceed the regulation limits for non-hazardous waste landfilling, according to Council Decision 2003/33/EC. Therefore, this fly ash should be disposed off in a landfill for hazardous waste or it should be treated before landfilling. Two treatment techniques, chemical stabilization with phosphoric acid and water extraction (washing), were investigated for the treatment of fly ash. Phosphoric acid reduces the leachability of certain heavy metals contained in ash by promoting the formation of geochemically stable metal phosphate compounds, which are resistant to leaching. In addition, a very high part of soluble salts is removed from the ash during the washing process. Various parameters of the washing and stabilization process were experimentally tested in order to improve the leaching properties of the stabilized ash and the quality of the process wastewater.