In the ZAV Recycling plant in Hinwil, Switzerland, materials from the bottom ash are recovered thanks to new technologies and shared solutions.

In Hinwil, a small Swiss town in the Canton of Zurich, every year 16,000 tons of metals get recycled, saving up both precious resources and up to 100’000 tons of CO₂ emissions.

This process takes place in the ZAV Recycling plant, where dry incineration bottom ashes (IBA), the solid residues of the thermal treatment of municipal solid waste, are sorted, treated and turned into new resources.

Waste-to-Energy is an efficient way to treat non-recyclable waste, a fraction of our waste that cannot directly be reused or recycled. However, for each 1000 kg of thermally treated waste, 230 kg remains in the form of bottom ash, and every year European Waste-to-Energy plants generate roughly 19 million tons of IBA. Often considered as residues, IBA is much more than that, and maybe not everyone knows that there’s a treasure hiding in this dust.

(Inside ZAV Recycling plant)

Built in 2016, the ZAV Recycling plant quickly became world excellence when it comes to dry IBA recovery. Motivated by environmental and economic advantages, the five WtE plants that are operational in the Canton of Zurich decided to join forces and build one large, joint processing plant instead of five separate units. The bottom ash treatment plant that was born from this collaboration currently processes successfully around 100,000 tons of dry bottom ash per year, extracting a wide array of different metals, like iron, copper and aluminium down to a particle size of 0.2 mm.

Now you’re probably wondering, what can be found in these ashes?

Important quantities of metals and minerals are present in incineration bottom ashes and offer many opportunities for recycling. Bottom ash is composed of inert, non-combustible materials that are left over after the combustion process: sand, stones, and ash from burnt material, this is the so-called mineral fraction, which makes up 80-85% of IBA, and can be utilised as filling material for construction purposes (as a sub-base material in road construction substituting virgin gravel material, or concrete products, decreasing demand for energy-intensive concrete production).

IBA also contains metals that come from composite products, which makes them difficult to recycle such as nails in wooden objects, zippers in clothes, copper wire bits, and stainless-steel ballpoint pen tips. In fact, 10-12% of IBA is composed of ferrous metals and the remaining 2-5% is non-ferrous metals (of which 2/3 aluminium) (More in CEWEP Factsheet on Incineration Bottom Ash). All these materials can be extracted from the ash and further used as raw material at a lesser environmental cost than the production of virgin materials.

As pointed out by the Global Resources Outlook (IRP, 2019) resource extraction and processing are activities associated with large environmental impacts and costs, as the extractive processes of raw metals are highly energy-consuming, emit a great number of greenhouse gases, and can negatively impact natural habitats as they cause soil, air, and water pollution. The recovery of materials from the European Waste-to-Energy plants can contribute to lessening these negative environmental impacts and saving CO₂ emissions.

So, all in all, the positive example of the ZAV recycling plant highlights the unexpected ways in which the recovery of incineration bottom ash can contribute to the circular economy, and how fostering the enhanced recovery of secondary raw materials from Waste-to-Energy contributes to saving GHG emissions and reducing the reliance on third countries for raw materials. The recycling potential of metals and minerals from IBA is fully aligned with the EU objective of carbon neutrality by 2050.

To increase the knowledge of IBA and its environmental benefits, the ESWET secretariat is launching a new working group on this topic. For more information, please contact Manon Roussel at m.roussel@eswet.eu