The AshCycle Project: Utilizing ash instead of depositing it
Ash produced from the incineration of sewage sludge, other biomass and waste is not being utilised to its full potential. Changing this was the motivation behind the EU project AshCycle, which developed a range of new ways to utilize ash.
Across Europe, around 25 million tonnes of ash are produced annually from the incineration of municipal waste, sewage sludge or biomass. Most of this ends up in landfill. The only exception to this so far is the increasing use of technologies for phosphorus recovery from sewage sludge ash in Germany, Austria and Switzerland. This is because legal regulations are already in place there. The landfilling of untreated ash results in the loss of valuable nutrients, minerals, metals and rare earth elements.
A total of 27 partner organisations from seven European countries and South Africa spent four years working on the AshCycle project to develop solutions within the framework of the Industrial-Urban Symbiosis (I-US) initiative promoted by the EU.
The need for this work arose not only from an environmental perspective:
“Landfilling of ashes costs at least €100–500 per ton, and these costs are expected to rise further. Therefore, developing new utilization methods is important both economically and environmentally,” Tero Luukkonen notes. He is Associate Professor at the Fibre and Particle Engineering Research Unit at the University of Oulu.
16 pilots demonstrated the potential of ash utilization
The project, which received a total of €10.3 million in funding, involved 16 pilot projects in Denmark, Finland, Belgium, Croatia, Slovenia and the Netherlands. All the projects resulted in alternative building materials such as concrete materials with admixtures, cement alternatives, bricks and paving stones, and loose fill used as a base for paved areas. In most applications, the aim was to replace conventional components such as cement or sand, either entirely or in part.
Two pilot projects applied electrodialysis to remove particular ash components:
- Calcium, magnesium, chlorine were recovered from fly ash of wood combustion; the remaining ash was used to produce an alternative for cement,
- Phosphor was recovered from the ash of sewage sludge combustion, simultaneously heavy metals were removed.
Characteristics and environmental impacts of the new materials
The research work resulted in 36 peer-reviewed publications and 24 theses elaborated at the various participating universities. These publications reflect the breadth of the various work packages. The building materials produced in the pilot projects underwent extensive analysis of their mechanical and morphological properties. Their environmental impact and the leaching behaviour of pollutants such as heavy metals, sulphates and halides were examined. Some products derived from the ash were specifically developed and investigated for their suitability for CO2 sequestration.
Furthermore, as part of the AshCycle project, a digital tool was developed by the Finnish company AI4Value to facilitate the assessment of individual types of ash and decision-making regarding suitable applications.
Featured image: Photo by Volodymyr Hryshchenko at Unsplash