Investigating nitrous oxide emissions and mechanisms in kitchen waste composting with leachate reuse

Solid-liquid mixed composting is a novel approach for handling kitchen waste (KW). In this study, KW was employed as composting materials to explore the nitrous oxide (N2O) emissions and corresponding mechanisms associated with the reuse of three supplementary liquids (CK: deionized water; T1: kitchen waste composting leachate (KWCL); T2: kitchen waste leachate (KWL)) during the composting process. The analysis included N2O emissions, microbial community dynamics, and nitrogen metabolism pathways. The findings demonstrated that the addition of KWCL (T1) and KWL (T2) significantly increased the nutrient content in the compost. Notably, T1 exhibited significantly higher cumulative N2O emissions than CK and T2 (P < 0.01). Both CK and T2 demonstrated more robust microbial safety, while the addition of KWCL (T1) led to more significant alterations in the structure of bacterial and fungal communities. Denitrification was identified as the primary pathway for N2O emissions during the thermophilic period. Nitrous oxide reductase activity was significantly lower in T1 than in T2 (P < 0.05), and the abundance of the nosZ gene in T1 (3.39 %) was lower than that in CK (4.18 %) and T2 (4.51 %), contributing to higher N2O emissions. Correlation analysis revealed the vital role of bacteria in N2O production, while bacterial and fungal communities exhibited positive correlations with variables such as carbon-to-nitrogen ratio and total carbon. Environmental factors were identified as key drivers of N2O emissions (r = 0.837, P < 0.05). These findings provided valuable insights for the sustainable management and recycling of KW.