Insights into acid-base properties of hydrotalcite materials during hydrothermal carbonization of sewage sludge

Based on proteins hydrolysis requiring alkaline conditions while polysaccharide hydrolysis requiring acidic conditions during hydrothermal carbonization (HTC) of sewage sludge (SS), different types of layered double oxides (LDOs) were introduced as catalysts to understand their role and structural alterations due to its containing acidic and basic sites. Results indicated that the structure of LDOs changes during HTC of SS with structural reconstruction influenced by properties of the aqueous phase, including anions and organic matter. As a result, the properties of the resulting hydrochar are also altered. Structural reconstruction of LDOs is a key factor that influences the HTC of SS. Basic sites of Mg/Al/Zn LDOs are slightly reduced, while acidic sites are remarkably enhanced, leading to an improvement in nitrogen removal and the recovery of organic matter from the HTC aqueous phase. © 2023