Effects of steam-explosion pretreatment on humification and microbial communities during aerobic composting

The goal of this study was to investigate the effect of steam-explosion pretreatment on humification performance during sawdust composting. To achieve this, an aerobic composting experiment was conducted using sawdust, chicken manure, and spent mushroom substrate as feedstocks. Two treatments were established: a steam-explosion-pretreated sawdust group (SEW) and an untreated sawdust control group (CK). The results indicated that, compared to the CK group, the SEW group entered the thermophilic phase earlier, reached a higher peak temperature (65C), and prolonged the thermophilic phase for 13 days. Additionally, the SEW treatment significantly increased cellulase and polyphenol oxidase activities during the thermophilic phase and enhanced laccase and peroxidase activities during the cooling/maturation phase. Relative to CK (75.30 g/kg of humic substances), SEW promoted a significant increase in the accumulation of humic substances (120.80 g/kg) and soluble organic carbon synthesis. The co-occurrence network in SEW (50 nodes and 602 edges) was notably more complex than in CK (49 nodes and 440 edges), suggesting a more interconnected community network with stronger interactions. Path analysis further revealed that in CK, humic substances (HS) were primarily influenced by dissolved organic carbon (DOC) and temperature, with DOC negatively correlated with HS. In contrast, in SEW, HS were associated with enzyme activities, community diversity, and the presence of Pseudogracilibacillus. Overall, the findings highlight that steam-explosion pretreatment accelerates the transformation of organic matter into humic substances and enhances the humification process.