Thermal-assisted aerobic composting: a sustainable approach to sludge dewatering and process optimization

Thermal-assisted aerobic composting is a novel process for treating municipal dewatered sludge (MDS), the core of which is effective moisture removal from MDS through the synergistic action of thermal treatment and microorganisms. In this study, the operational condition combination of the thermal-assisted aerobic composting process was effectively optimized through the implementation of an orthogonal experiment. On the basis of these findings, the technical superiority of this process was confirmed by comparing it with traditional drying processes and by exploring the material and energy changes during the thermal-assisted aerobic composting process. The results revealed that the optimal process conditions for thermal-assisted aerobic composting were as follows: a heating temperature of 50 °C, a ratio of MDS to auxiliary materials (AM) of 4:1, and continuous turning. Thermal assistance significantly shortened the initiation time of aerobic composting, reducing the entire composting cycle to 7 days. The mixture of MDS and AM after completing the process presented a low moisture content (21.8 ± 2.2 %) and high calorific value (19583.1 ± 42.4 kJ/kg), indicating that the mixture has excellent performance in subsequent thermal treatment. Process analysis revealed that moisture removal primarily occurred during the 0st–10th days of operation, whereas organic matter degradation mainly took place between the 10–20th hours. The process heat changes revealed that the heat input exceeded the heat output, demonstrating that rapid moisture content reduction could spontaneously proceed in a positive direction. This study provides a theoretical basis and foundation for an inventive path for the drying MDS.