Central Hydroxide Sludge Treatment Plant with Metal Recovery


In filter ashes from  Municipal Solid Waste Incineration plant (MSWI) lays a big potential for recyclable metals. Particularly interesting for a recovery is the high content of zinc. In addition to this, the reduction of toxic heavy metals would make a big positive contribution to the environment.

Currently, about 55% of the Swiss filter ashes are washed with the so-called FLUWA process transferring the metals in a zinc-containing hydroxide sludge, which can so far only be treated as expensive hazardous waste abroad. The rising costs for the disposal of the hydroxide sludge are making the metal recovery from filter ashes increasingly difficult from an economic point of view, although the material content of zinc is in the range of 20%. Comparable ores which were conventionally mined can already be sold as raw materials successfully. The integration of hydroxide sludge into existing zinc smelteries fails due to the existence of suitable process technology, the acceptance by smeltery operators and the high costs involved.

The SwissZinc project tries to overcome these obstacles and will prove the technical and economic feasibility of direct materials recovery within Switzerland.

Project Fact Sheet No. 1 (in German only)

Project Fact Sheet No. 2 (in German only)


In the new VVEA (Verordnung zur Vermeidung und Entsorgung von Abfällen) the recovery of metals from incineration plant bottom ash as per 1.1.2021 is defined. The current situation of FLUWA-incineration plants with exports of zinc hydroxide sludge abroad as waste is not effective, as it’s neither economical nor ecological.


Development and establishment of a central processing method in Switzerland, similar to the FLUREC process for metal recovery from FLUWA-hydroxide sludge.


Development of an industry solution under the leadership of the Association of  Swiss Operators of thermal waste processing plants (VBSA) and the SwissZinc AG.

Extensive feasibility and design studies with an international engineering company with the goal of large-scale implementation.

Tasks ZAR

Technical project management, appraisal, monitoring and coordination of the basic and detail engineering. Support of clients in the implementation and commissioning of the new method.

Project Duration