Aeration intensity drives dissolved organic matter transformation and humification during composting by regulating the organics metabolic functions of microbiome

Oxygen levels are critical for composting success and improving humification. Whereas aeration intensity driving the structural heterogeneity and formation mechanism of humus in the dissolved organic matter (DOM) transformation process during kitchen waste with hydrothermal pretreatment composting remains unclear. In this study, the potential mechanisms of aeration intensity on humification were explored by Fourier transform infrared spectroscopy and fluorescence spectroscopy combined with functional microbial prediction analysis. The results showed that moderate aeration intensity (AR_0.05, 0.05 L min⁻¹ kg⁻¹ DM) achieved a highly matured fertilizer with a humification index of 0.83 and a humic acid / fulvic acid (HA/FA) of 1.99. Partial least-squares path model demonstrated that environmental factors and humus-like substances were the two most critical factors to improve humification levels. According to the heterogeneous-2DCOS analysis, the biopolymers in DOM were preferentially decomposed into low molecular weight HA precursors through a series of biochemical reaction processes, and then formed the carbon skeleton of HA through condensation reactions, and finally polymerized into complex macromolecular HA. Bugbase analysis showed that AR_0.05 treatment reduced 58.52 % of potentially pathogenic bacteria in the thermophilic phase. Moreover, functional bacterial communities in composting systems with AR_0.05 were more favorable to drive the organic matter decomposition and HA formation. The mantel test revealed temperature and pH were key drivers in the composition of phenotypic and functional bacterial communities. This study provided unique insights into a deeper understanding of the aeration intensity on the humification pathways of kitchen waste composting.