Optimizing green waste composting with Bacillus siamensis inoculant: Impacts on decomposition and microbial dynamics

The use of microbial inoculants has emerged as a promising strategy to improve the efficiency of green waste (GW) composting. This study evaluated the effects of inoculating compost with an indigenous Bacillus siamensis inoculant (T1), a commercial effective microorganism (EM) inoculant (T2), and a non-inoculated control (T3), under light conditions excluding blue light. The T1 treatment resulted in a significantly higher peak temperature (65.8 °C) and an extended thermophilic phase (12 days), reducing the overall composting duration to 35 days, compared with 37 days for T2 (61.2 °C; 9 days) and 39 days for T3 (58.4 °C; 6 days). The T1 also markedly enhanced the degradation of key organic components (achieving reductions of 60.6 % in organic matter, 43.2 % in lignin, 51.0 % in cellulose, and 44.5 % in hemicellulose), outperforming both T2 and T3 by 6.9-37.6 percent. Compost quality under T1 was significantly enhanced, with elevated levels of total nitrogen, nitrate nitrogen, total and available phosphorus, and total and available potassium, alongside enhanced structural stability, water-holding capacity, and porosity. High-throughput microbial analyses revealed that T1 significantly enriched functional microbial taxa such as Bacillus, Aspergillus, and Thermomyces, resulting in a more functionally optimized community structure. Functional prediction further indicated phase-specific enhancement of enzymatic activity, with bacterial enzymes predominantly enriched during the mesophilic phase and fungal enzymes during the thermophilic phase. These findings provide mechanistic insights into the synergistic effects of microbial inoculation on organic matter decomposition and nutrient transformation, offering a practical framework for value-added GW composting through targeted microbial intervention.