Optimization and mechanistic analysis of high-temperature aerobic composting process for dynamic sludge in rotary drums

This study addresses challenges in high-temperature aerobic sludge composting using a rotary drum, particularly material adhesion to the drum wall and low efficiency. Response surface methodology (RSM) was used to develop predictive models for composting period time and seed germination index (GI). The models showed high reliability (R²≥ 0.95, p < 0.001) with validation errors of 6.67% for composting period and 1.04% for GI. The optimal conditions identified were 55% moisture content, 10 mm auxiliary material dimensions, 7 L·min⁻¹·kg⁻¹ TS aeration rate, and 1.5 r·min⁻¹ rotational speed. These conditions reduced the composting period to 15 days, increased GI to 86%, and met the GB/T 23,486 − 2009 standards for heavy metal concentrations. The bioavailability of heavy metals decreased significantly, ensuring environmental safety. Microbial community analysis revealed a two-stage succession pattern, with thermophilic Bacillus and Aspergillus dominating the high-temperature phase. The process efficiency was influenced by synergistic parameter interactions. Through comparative analysis of processes, it was found that rotating drum composting achieves an optimal balance among efficiency, environmental performance, and engineering feasibility, making it highly suitable for large-scale municipal sludge valorization.