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

[Display omitted] • Adding KWCL to compost led to the highest N 2 O emissions, reaching 121.66 mg m−2. • KWCL exerted the greatest impact on the community structure of bacteria and fungi. • Denitrification was the key way for N 2 O emissions in thermophilic stage of compost. • Bacteria were identified as the main key taxa for N 2 O emissions during composting. • Environmental factors emerged as the most critical drivers of N 2 O emissions. 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 (N 2 O) 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 N 2 O 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 N 2 O 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 N 2 O 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 nos Z gene in T1 (3.39 %) was lower than that in CK (4.18 %) and T2 (4.51 %), contributing to higher N 2 O emissions. Correlation analysis revealed the vital role of bacteria in N 2 O 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 N 2 O emissions (r = 0.837, P < 0.05). These findings provided valuable insights for the sustainable management and recycling of KW. [ABSTRACT FROM AUTHOR]