The release of heavy metals in stabilised MSW by oxidation

Leaching experiments on partly stabilised MSW under oxic conditions have been carried out. The objective of the study was to investigate the effects on heavy metals in anaerobically stabilised MSW during the exposure to air. It was suspected that the oxidation could increase the mobility of heavy metals, and, thus, trigger a chemical time bomb CTB.. The experiments and similar investigations indicate that the initial oxidation of the most reactive compounds, such as some organic substances and acid volatile sulphides AVS., will not mobilise large amounts of the total amount of heavy metals. However, the concentration in the leachate might increase up to one order of magnitude due to complexation with dissolved organic matter. The mobilisation is restricted by the presence of buffering substances in the waste, which are able to buffer neutral to weak alkaline leachates. The high buffer capacity of partly stabilised MSW indicates that acid leachates and CTBs will be avoided for a long period of time. However, acid leachates may appear earlier than expected in heterogeneously structured media where oxidation processes are enhanced along channels, which constitute favourable pathways for water and intruding air