Enhancing sludge management efficiency through thermal hydrolysis: A system-wide analysis from biogas production to dewatering

Thermal hydrolysis pre-treatment (THP) is increasingly applied to improve the energy and resource efficiency of sludge management. This study evaluates the system-wide impacts of THP at 60 °C, 80 °C, and 120 °C in a model wastewater treatment plant, integrating anaerobic digestion performance, digestate rheology, dewatering behaviour (including mass partitioning between cake and reject water), and auxiliary energy demand. At 120 °C, THP increased methane yield by 43 %, increased cake solids concentration by 33 %, and reduced energy consumption for pumps and agitators by 43 % and 11 %, respectively. Despite a 59 % increase in nitrogen content in the liquid fraction, the 120 °C configuration achieved a 43.4 % increase in net energy output, whereas the 60 °C and 80 °C scenarios produced 8.5–8.7 % less net energy than the reference. By explicitly linking THP-induced changes in digestion and rheology to dewatering performance and downstream mechanical energy demand within unified mass and energy balances, this work provides a system-wide assessment of how pre-treatment conditions propagate through sludge-processing systems, supporting improved interpretation of energy recovery and process performance in full-scale WWTPs. • THP at 120 °C increased methane production by 43 % compared to untreated sludge. • Solubilization and rheology post-THP correlate with higher methane yield. • Mass balances show improved solids removal and enhanced dewaterability. • THP led to 43.4 % higher energy efficiency via pumps, agitators, and dewatering. • Digestate after THP has higher soluble nitrogen, enabling recovery.