Mixed waste generated by households in the metropolitan area has been utilised for energy recovery in the waste-to-energy power plant in Vantaa since 2014. The combustion process in the waste-to-energy plant generates bottom ash, boiler and fly ash and APC (Air Pollution Control) waste. Bottom ash and boiler and fly ash of the abovementioned residues are treated in the Ämmässuo Waste Treatment Centre.
Bottom ash from the waste-to-energy plant is non-hazardous waste which is aged and treated at Ämmäsuo. Magnetic and non-magnetic metals are separated from bottom ash for further utilisation. The remaining mineral materials are utilised in the structures of the waste treatment centre according to the environmental permit.
Ash from the waste-to-energy power plant is classified as hazardous waste, first and foremost due to its high chloride content. Ash is stabilised and final-disposed of at Ämmässuo. Final-disposing takes place in the hazardous waste cell, built for this purpose, with a filling volume of ca. 40 000 m³. The concentration of harmful substances of ash is dependent on the quality of waste to be combusted. The more carefully waste is sorted (e.g. biowaste, metal and batteries) the fewer harmful substances there is in ash.