Sustainable sludge management--what are the challenges for the future?

Sewage sludge is a serious problem due to the high treatment costs and the risks to environment and human health. Future sludge treatment will be progressively focused on an improved efficiency and environmental sustainability of the process. In this context a survey is given of the most relevant sludge treatment options and separate treatment steps. Special attention is paid to those processes that are simultaneously focused on the elimination of the risks for environment and human health and on the recovery or beneficial use of the valuable compounds in the sludge such as organic carbon compounds, inorganic non-toxic substances, phosphorus and nitrogen containing compounds. Also, a brief assessment is given of the specific future technological developments regarding the various treatment steps. Furthermore, it is discussed how to assess the various pathways which can lead to the required developments. In such an assessment the technical and economic feasibility, the environmental sustainability, the societal acceptance and the implementation route are important factors. The optimal approach also strongly depends on the local and regional situation of concern and the relevant current and future boundary conditions.