After incineration of residual household waste, a considerable amount of ash remains. This ‘incinerator bottom ash’ contains rather high concentrations of metals and salts, which are partly leachable. To be able to use bottom ashes as building material, Tauw developed a process called EquiAsh®. Through this process, bottom ashes are upgraded, making them usable as raw material. Results of a large-scale experiment on EquiAsh® was recently published in the scientific journal Waste and Biomass Valorization.
In the Netherlands, bottom ash has been used for more than 30 years as a building material in civil engineering constructions. But to prevent soil contamination, the application of bottom ash must meet strict requirements of the Soil Quality Decree. In practice, it turned out to be difficult to meet all the requirements.
Therefore, a ‘Green Deal’ agreement was concluded between the incinerator branch and the Dutch government. This deal involves upgrading the bottom ash to a freely applicable building material, with a much lower leaching level than the original material. This means a considerable effort for the incineration industry in the Netherlands.
In this framework, Tauw has developed a process called EquiAsh®. This process aims at upgrading incinerator bottom ash into a long-term environmentally safe and stable product. This is an important issue because, also after upgrading, bottom ash still contains high amounts of heavy metals, which could become available for leaching in the future.
EquiAsh®, which is a combination of carbonation, washing and further mineralisation, realises a safe and stable product now and in the future. The bottom ash is in equilibrium with the atmosphere and the pH is stabilised at values around 8.5. Large-scale experiments with 1,000 ton incinerator bottom ash are performed. After treatment, the bottom ash fulfils the Dutch leaching criteria for a freely applicable building material. Tauw has licensed the EquiAsh® process to Heros, a company which annually treats 650,000 ton bottom ash.
After successful experiments, Heros will decide about the realisation of a full scale plant in June 2020.
Results of large-scale experiments with EquiAsh® and reflections on the long-term stability of the pH are now published in the scientific journal Waste and Biomass Valorization. With this link, you can read the article online.