Effect of auxiliary materials on the formation of humic acid carbon and nitrogen and bacterial dynamics in kitchen waste composting

This study investigated the impacts of different types of auxiliary materials on the humification process and bacterial dynamics during kitchen waste composting. Five types of auxiliary materials, including sawdust (SD), garden waste (GW), aquatic plants (AP), rice straw (RS), and rice husk (RH), were compared. The relationship between humic acid carbon and nitrogen components as well as bacterial community was analyzed by structural equation model and redundancy analysis. The results dindicated that SD and RS exhibited better thermophilic stage duration, germination index, and organic fractions degradation than other groups, which had higher degree of polymerization and the humification index of kitchen waste composting. AP, SD and RS had higher total nitrogen (TN) content and ammonia nitrogen accumulation, and RS had more humic acid nitrogen in TN with more amino acids and polyphenols precursors compared to other groups. High-throughput sequencing indicated that sawdust affected the variation of community structure and bacterial genera associated with lignocellulose degradation more than others. Redundancy analysis showed that Pseudoxanthomonas helped to the NH4+-N conversion to humic acid nitrogen for TN preservation. Structural equation modelling suggested that the conversion and utilization efficiency of microbes directly influenced the accumulation of humic acid carbon and nitrogen based on the types of intermediate metabolites. This study highlighted the role of auxiliary materials on improving the humification process of rapid kitchen waste composting.