Phosphorus recovery from sewage sludge realistic

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.

One of the most precious raw materials that still ends up in waste today is phosphorus - an indispensable and irreplaceable substance for humans, animals and plants. 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 sewage sludge can no longer be returned to the natural material cycle. With the new sewage sludge disposal plan, the canton of Zurich has set itself the goal of designing the disposal routes for sewage sludge in such a way that the phosphorus can be recovered at a later date, in the interests of sustainable resource management. With the realization of the central sewage sludge utilization plant at Werdhölzli in Zurich, it was also possible to significantly reduce the costs of sewage sludge treatment and optimize the use of energy from sewage sludge. At present, however, there is still a lack of practical applications for returning the phosphorus from the sewage sludge ash to the recyclable material cycle.

Following the successful laboratory tests, the pilot now follows
To ensure that the set target can also be achieved with regard to phosphorus, the Canton of Zurich has made a significant contribution to the development of a new process that extracts the phosphorus from the sewage sludge ash in an environmentally friendly manner and makes it usable again. With the newly developed process, the phosphorus can be returned to the recyclable material cycle as high-quality phosphoric acid. In addition to fertilizer production, potential applications for phosphoric acid include the food and animal feed industries as well as other industrial processes.

Following the successful first-time production of high-quality phosphoric acid from Zurich sewage sludge ash in October 2015, the findings on the continuous operation of the so-called Phos4life process are now being deepened as part of the ongoing pilot operation. The aim is to make the industrial production of pure, heavy metal-free phosphoric acid from sewage sludge ash marketable.

Much more environmentally friendly
Compared with the conventionally produced phosphoric acids from raw phosphate used today, the environmental impact of Phos4life acid from domestic sewage sludge ash is significantly lower. On the other hand, it is already becoming apparent that economically viable implementation will only be possible if the ash from several sewage sludge utilization plants is treated together. In addition, a solution must be found as to how and by whom the costs not covered by the market will be borne.