If waste cannot be avoided, it must be optimally recycled. New technologies and shared solutions are setting new standards. Thermo-Recycling combines proven thermal processing of waste with a new treatment and separation process.
In Switzerland, the 2-pillar principleapplies to waste management: thermal as well as material recycling. As early as 1986, the Federal Office for the Environment's mission statement defined that waste disposal systems shall produce only two types of material classes from waste, namely recyclable materials and residual materials suitable for final disposal. With a recycling rate1 of around 55%, the Swiss are among the leaders in Europe. Today, many products are so-called composite materials, which are preferably recycled thermally.
For each 100 kg of thermally recycled waste, 23% remains in the form of bottom ash.
Thermal recycling is very energy efficient and the emission values are subject to strict limitations. Nevertheless, about 23% of 100 kg of waste remains in the form of bottom ash, which is disposed in landfills. The federal regulations require that waste-disposal needs to be done within the country of origin.2
Metals in the bottom ash of waste incineration plants
Efforts have been done for many years to minimize the volume of the residual bottom ash. The approach was to separate coarse iron and aluminium prior to landfill disposal.
As from 2008, the focus was increasingly on the small and smallest metal particles in the bottom ash. It was not about reducing the volume of the landfills only. The main objective was to directly recycle these ferrous and non-ferrous metals in the form of marketable products, thereby reducing primary production with all its associated environmental impact.
Pioneers at KEZO Hinwil took a significant step in 2007 by modifying the bottom ash discharge after the incinerator. The bottom ash no longer needed to be extinguished with water. This “dry bottom ash discharge” delivered dry bottom ash containing all substances and particles in their original form. This modification opened up a “no limits” approach regarding separation either by particle size, weight, colour, conductivity, etc. of the bottom ash.
In close cooperation with representatives of the waste treatment industry, the raw materials and recycling industries as well as cantonal and national environmental authorities, the ZAR Foundation developed a process for processing this dry bottom ash and successfully pioneered operations at the KEZO plant. It was possible to separate metals down to a particle size of 0.2 mm with high efficiency and high quality and to feed them back into the material cycle.
Synergies to be exploited
The Canton of Zurich operates five municipal waste incineration (MSW) plants that have been carrying out joint capacity planning and close cooperation for many years.
The ecological and economic advantages convinced the MSWs to join forces within the canton and to build one large, joint processing plant instead of five separate units. To this end, ZAV Recycling AG was founded in 2013 with the following shareholders:
- Intercommunal institution Limeco, Dietikon,
- Zurich Oberland Waste Disposal Association, KEZO, Hinwil,
- Municipal waste disposal association in Horgen district, Horgen
- City of Zurich, represented by ERZ Entsorgung + Recycling Zürich
The joint bottom ash processing plant with an annual capacity of 200,000 tons was commissioned in 2016. Currently, around 100,000 tons of dry bottom ash per year are processed successfully.
2 Mission Statement for Swiss Waste Management No. 51, Berne June 1986, FOEN