Sewage sludge valorization process: study of contaminants mobility

This thesis investigates the organic and inorganic parameters in sewage sludge from the Cross-Life Project pilot plant. The Cross-Life Project focuses on sludge treatment for the production of polyhydroxyalkanoates (PHA), biopolymers that are gaining increasing importance in today’s market. Within this framework, sewage sludge was analysed after the initial treatment steps to evaluate how the digestates change from a chemical–physical perspective. The quality of the treated sludge was assessed, with particular attention to the migration of heavy metals between soluble and insoluble fractions. In addition, the presence of polycyclic aromatic hydrocarbons (PAHs) is verified. The main variations were observed after the hydrothermal carbonization (HTC) stage, which led to an increase in all parameters in the soluble fractions. Anaerobic digestion (AD) was also found to influence pollutant concentrations, although the specific effects varied depending on the parameter considered. A mass balance was performed for Cupper, Chromium, Nickel, Total Organic Carbon (TOC), Total Nitrogen (TN), and Ammonium (NH₄⁺), which showed that contaminants were predominantly distributed in the insoluble phase, with a subsequent increase in the soluble fraction after HTC. The findings of this study could be useful for optimizing the different steps of the process, as fluctuations in various parameters may influence microbial activity within the reactor.