Precious raw material from sewage sludge

Waste is raw material - this is the guiding principle of waste and resource management in the Canton of Zurich. As a pioneer in so-called "urban mining," the Canton of Zurich consistently focuses on recovering valuable materials from the legacies of our society, thus making the Canton of Zurich a productive resource mine.

Closing a broken circuit again
One precious raw material that still ends up in waste today is phosphorus - an indispensable and irreplaceable substance for food production. Since 2006, sewage sludge from wastewater treatment plants may no longer be spread on fields as fertilizer because it contains too many pollutants. As a result, the phosphorus contained in the sewage sludge can no longer be returned to the natural material cycle. The canton of Zurich has therefore completely reorganized its sewage sludge disposal within a few years. With the commissioning of the new, central sewage sludge recycling plant in Zurich, practically 100 percent of the phosphorus present in the sewage sludge is available for recovery and the sewage sludge disposal costs in the Canton of Zurich have been reduced by more than half. In addition, the canton of Zurich has set itself the goal of developing a process that extracts the phosphorus from the sewage sludge ash in an environmentally friendly manner so that it is available in pure form as a raw material and commodity for industrial processes, such as the production of plant fertilizers. In this way, the natural phosphorus cycle will be closed again and Switzerland will become independent of phosphorus imports in the long term.

Successful in the laboratory
Now the Canton of Zurich has taken a decisive step closer to this goal. Together with the renowned technology partner Técnicas Reunidas SA (Spain), the Center for Sustainable Waste and Resource Utilization (ZAR) Foundation in Hinwil and Zuchwil, which was co-founded by the canton of Zurich, succeeded for the first time in October 2015 in producing high-quality phosphoric acid from Zurich sewage sludge ash in the laboratory. This success is an important milestone on the way to recovering phosphorus from sewage sludge on an industrial scale.

Canton Zurich supports further development
The ZAR Foundation, together with Técnicas Reunidas SA, will now test the technical feasibility of the process in a pilot plant. The canton of Zurich is supporting this phase of development in the form of start-up financing with a contribution of 2 million Swiss francs or 60 percent of the costs, as the government council has now decided. The remaining 40 percent or 1.3 million Swiss francs will be borne by the technology partner Técnicas Reunidas SA. The upcoming clarifications will show what costs would be incurred by a commercial user. In return, the canton of Zurich will receive free access to the findings of further development work and will be entitled to a free license should the process be patented.
Government Council Decision No. 58/2016 .