Effect of leaching behaviour by quenching of bottom ash from MSW incineration

Bottom ashes (BA) obtained from a municipal solid waste incineration plant, have shown different pH and lead concentrations in leachate for different lines. In order to explain this behaviour, combustion tests were performed concerning the lines and the effect of the type of wastes. The BA obtained from the same waste has shown the same raw chemical composition, but different leachate characteristics for the different lines. The bottom ash from different wastes burned on the same line instead showed very similar leachate behaviour. The results suggest that the quality of leach ate depends on the plant and process conditions (in particular the ash quenching phase) and not on the composition of the waste. During ash quenching, the formation and dissolution of soluble alkalis depends on the washing ratio and on the residence time. A different washing degree leads to a different residual alkalinity in the bottom ash, and consequently to a different value of leachate pH with different metal releases. Therefore, with the practical aim of establishing the best conditions for the final disposal of bottom ash, a careful planning of this phase could be proposed as an alternative to a weathering process.