Leachability and metal-binding capacity in ageing landfill material.

In order to study the stability of landfilled heavy metals, landfill material from a combined household and industrial waste landfill was aerated for 14 months to simulate the natural ageing processes as air slowly begins to penetrate the landfill mass. During aeration, the pH of the landfill material decreased from around 8.6 to 8.1 and the carbon content also decreased. In order to investigate the possible fate of metals in ageing landfills, a four-stage sequential extraction technique was applied. The ability of the materials to bind metal ions by electrostatic attractions and to form stronger complexes was studied separately. The amount of exchangeable cations, the capacity to bind metal ions by electrostatic attraction and the capacity of the landfill material to complex copper ions were increased by the aeration process. However, results from the sequential analysis showed an increased solubility of sulphur and some metals (Cd, Co, Cu, Ni and Zn). Equilibrium speciation models (Medusa) indicated that the organic matter deposit had a significant capacity to bind metal ions provided that pH was sufficiently high. However, as carbonates are consumed over time, the risk for metal mobility increases. Therefore, the landfills can become an environmental risk, depending on variations in the solubility of metal ions due to changes in pH, redox status and the availability of organic material.

Metal and organic matter contents in a combined household and industrial landfill.

A combined household/industrial landfill in a humid and cold temperate climate was characterised with respect to its chemical composition. Cores taken at three randomly chosen sites on the landfill and at different depths at each site were analysed. Carbon, nitrogen and pH were measured by standard laboratory methods. The chemical elements analysed included metals and the non-metals B, P and S. pH ranged between 8.0 and 8.5. The total carbon content was in the interval 4.5-26.9% and the total nitrogen content in the interval 0.05-0.48%. The C/N ratio was high, indicating that there was not enough nitrogen available to ensure the stabilisation of carbon. The metal contents varied substantially. The water and carbon contents were related to each other as well as to the metal content, which increased with the content of water. Based on the results obtained regarding the chemical composition of the landfill, it is evident that the landfill consists of two layers. This indicates that the landfill body might have different levels of chemical development, due to water content, and different long-term leachability in the future.