Recycling of phosphorous and valuable metals from sewage water and sludge

Sewage sludge has a high content of phosphorus but it frequently contains high enough concentrations of environmentally hazardous compounds, e.g. transition metals, to make it unsuitable as fertilizer for crop production. Some of the metals are not only toxic but they also have a commercial value. Most efforts to remove either the phosphorous or the metals have been directed to the sludge which is a highly complex material. In this study we also include treatment of the sewage water before the conventional treatment. The aim is to specifically enrich the phosphorous and the metals to allow for recycling and to use the sludge for production of gas or extract its energy content.