Innovative Treatment of Municipal Sewage Sludge Using Hydrothermal Carbonization and Nutrient Recovery Technologies

Phosphorus (P) is an essential and at the same time critical resource, as there are barely any available reserves in the European Union, which means that there is a dependence on imports from non-EU countries. In these countries, there are critical working and environmental conditions for which social responsibility must be taken. To address these challenges, municipal sewage sludge has to be utilized since it has a huge potential to produce sustainable P- fertilizers. Hydrothermal Carbonization (HTC) is an energy-improved treatment of sewage sludge and enhances the dewatering properties. The remaining process water contains a significant nutrient content, especially nitrogen (N) and phosphorous (P). For a future project, the recovery potential of P was investigated for Germany, Austria and Switzerland (DACH region). The forecasted P recovery potential in the DACH region until 2030 covers 25% of the annual P demand and the environmental impact due to the conventional industrial production of P fertilizer could be reduced dramatically (up to 63 t of CO₂ emissions can be saved per year). To identify the sustainable development goals (SDGs) which are primarily addressed by the project, the following question was formulated: What effects does the technology have in terms of sustainability (social, ecological, economic)? The investigation showed that SDGs 8, 11, 12, and 13 are mainly focused. The investigations serve as a basis for a future project, which is shortly introduced in this work, where the nutrients, as well as heavy metals, will be recovered by an innovative combination of three novel processes.