Efficiency and mechanisms for enhancing nitrogen retention in distilled grain waste compost through a composting-biofiltration approach.

Composting is an effective method for recycling resources in waste management. However, significant nitrogen loss can hinder the overall effectiveness of the composting process. Biofiltration is a promising method for conserving nitrogen in composting owing to its ability to efficiently trap and convert gaseous emissions. This study investigated the efficiency and mechanisms of a composting-biofiltration system to enhance nitrogen retention in distilled grain waste (DGW) compost using pre-composted DGW as biofilter media. The DGW composting-biofiltration system exhibited a lower nitrogen loss (24.9%) than the mono-composting system (40.1%). Additionally, this DGW system achieved a high NH removal efficiency of 94.7%-97.7%, while NO- concentration continuously increased in the biofilter, indicating that biofiltration mainly conserved nitrogen through the conversion of NH emitted from the composter. The analysis of the microbial community and key functional enzymes involved in nitrogen metabolism revealed a significant increase in both nitrification and ammonia assimilation within the biofilter. This resulted in the accumulation of NO- and the formation of organic nitrogen, thereby facilitating nitrogen retention. Genera such as Chryseolinea, Anseongella, Parapusillimonas, Bacillus, and Urebacillus mainly contributed to the generation of NO- and organic nitrogen. The structural equation model analysis revealed that nitrogen retention in DGW compost was mainly facilitated by enhanced nitrification and ammonia assimilation in the biofilter. These results provide insights into underlying mechanisms for enhancing nitrogen retention through a composting-biofiltration approach and present guidance for improving compost quality.