Recycling of contaminated dewatered sludge from the Gotthard Base Tunnel

The water flowing out of the tunnel during the construction period must be processed through a water treatment facility, creating the bi-product “sludge”. This sludge is then dewatered, and what remains is a filter cake that is contaminated with hydrocarbons (up to 10,000 mg/kg), nitrite (up to 5 mg/l) and chromate (up to 0.1 mg/l). The contamination originates from the employment of lubricants, fuels and hydraulic fluids, as well as explosives, and wash-out from shotcrete waste. The contaminated filter cakes had to be disposed of in appropriate landfills by the spring of 2006. An amendment to the Swiss laws led to higher standards for the disposal of these contaminated filter cakes. This caused substantial extra costs for the railway construction project. Therefore a new concept for an economic and legally compliant disposal and/or utilization of these filter cakes was established. As a result of an international invitation to tender, the heavily contaminated filter cakes are now used as raw material in the cement and/or brickyard industry. The article describes how a problematic construction waste became a construction material and thereby natural resources and landfill capacity could be preserved and costs could be saved. The solution is environmentally and economically sound.