Environmental Sustainability Assessment of an Innovative Hydrothermal Treatment of Sewage Sludge

The European Union produces approximately 8 million tons (dry matter) of sewage sludge annually. Conventional management approaches, such as landfilling and incineration, pose significant environmental concerns, including greenhouse gas emissions and pollutant dispersion. This study evaluates the environmental sustainability of an innovative sludge recovery pathway, Hydrothermal Dewatering (HTD), developed and validated within the LIFE FREEDOM project. A Life Cycle Assessment (LCA) was conducted on a pilot plant treating 1000 tons of sewage sludge. The quantitative results reveal that the HTD process generates a total climate change impact of 8.95 × 104 kg CO2 eq per functional unit (1000 t). The heating and reaction phase represents the main environmental hotspot, accounting for 92.9% of the overall single-score impact. Crucially, comparative analyses indicate that the HTD process exhibits statistically comparable aggregated impacts to incineration and landfilling, while demonstrating distinct environmental advantages in specific midpoint categories. Furthermore, the assessment of the solid residue (HTD-cake) as a 10 wt% substitute for natural clay in brick manufacturing confirmed the absence of environmental burden shifting. Overall, the findings quantitatively validate HTD as a viable and competitive alternative to traditional end-of-life options.