Identifying the critical intermittent aeration window in composting: Thermophilic-stage intensification via temperature-based control enhances humification and nitrogen retention

Despite the recognized importance of aeration in composting, the systematic optimization of aeration intensity across different stages, as well as the underlying mechanisms governing humification pathways and nitrogen transformation, remain poorly understood. This study addressed this gap by systematically comparing stage-specific aeration intensification during either the thermophilic (TAI) versus cooling (CAI) stage within an intermittent aeration framework, using temperature as a simple and reliable indicator for stage identification. Compared with moderate aeration (MA), TAI significantly enhanced compost maturity, increasing the degree of polymerization (DP) by 24.44 % and total nitrogen (TN) retention by 17.01 %. In contrast, CAI was less effective than MA in promoting humification, resulting in a 14.44 % lower DP; nevertheless, it still outperformed low aeration (LA) and achieved satisfactory maturity, while also improving nitrogen retention by 11.15 % relative to MA. Mechanistic evidence suggests that TAI promoted lignin degradation, generating aromatic skeletons that may couple with bioavailable organic nitrogen (BON) potentially through lignin-related humification processes, thereby contributing to the transformation of BON into stable humus. Furthermore, TAI optimized the microbial community, enriching thermophilic genera (e.g., Thermobacillus, Ureibacillus), enhanced the electron transfer capacity of dissolved organic matter, and reinforced nitrification and ammonia assimilation while suppressing denitrification. These synergistic effects under TAI produced a highly humified and nitrogen-rich compost. This work provides an efficient and easily implementable aeration strategy that simultaneously advances humification and nitrogen conservation, leveraging widely available temperature sensors already standard in composting facilities, with significant promises for improving the quality and agronomic value of kitchen waste compost.