Revealing carbon-iron interaction characteristics in sludge-derived hydrochars under different hydrothermal...

Hydrothermal conversion is seen as a potential sustainable solution for the disposal and utilization of sewage sludge. One-step hydrothermal carbonization was used to prepare iron-based sludge hydrochars, and the microstructure properties of hydrochars under different hydrothermal conditions were investigated, with emphasis on the inherent interaction mechanisms between carbon and iron. The aromaticity of hydrochars increased with increasing hydrothermal temperature and time, whereas the specific surface area and pore volume as well as magnetic characteristics of hydrochars were only contingent on temperature. Once the temperature reached 160 °C, Fe₂O₃ in sludge was completely transformed into Fe₃O₄ in hydrochars. Simulated experiments suggest that glucose is more advantageous than protein in the iron transformation and mesopore formation. The coexistence of glucose, protein, and FeCl₃ improved the aromaticity as well as specific surface area and pore volume of hydrochars. This study provides a basis for designing high performance iron-based sludge hydrochars.