Environmental impact of ashes used in a landfill cover construction

Sammanfattning: The landfilling ban for combustible waste in EU countries and the extended use of bio fuels in heat and electricity production will result in an increasing generation of incineration residues, such as fly ash and bottom ash. Instead of landfilling, ashes used as a construction material in, e.g., roads or landfill covers can result in saving natural resources and economical advantages. The main aim of this work is to assess how ashes used in landfill cover construction affect the environment and how the potential environmental impact can be assessed. The main pollution pathway of using ashes in landfill cover construction is leaching. Laboratory leaching tests can be used as a tool to assess the possible environmental impact of ashes before their use in a landfill cover. Solubility leaching tests, e.g. batch leaching test, pH-stat test and percolation test, can be useful tools to predict contaminants that can be released from ashes used in a protection and drainage layer. The diffusion leaching test together with the availability test are suitable to assess the release from ash used as liner material. However, predicting contaminant release in the field is difficult due to the complexity of the processes occurring in the field. Leachate and drainage water are two types of water generated in landfill cover. Leachate samples were mainly contaminated by As, Mo, Cl and N. Drainage water contained high concentrations of Ni, Cl and N with the addition of As, Cu, Mo, Pb and Zn in the areas where bottom ash is in the protection layer. Since leaching of most pollutants showed no clear tendency to decline over time, assessing how long leachate and drainage water need treatment is difficult. However, it is expected that salt forming elements will be depleted from ashes within some decades. A lower release of other trace elements, such as Cu, Pb and Zn, to ash leachate is expected due to immobilization by Al/Fe hydr(oxides) and clay minerals.