Succession of Bacterial Community Function in a Continuous Composting System with Spent Mushroom Substrate and Sawdust as Bulking Agents

Composting is a reliable way for manure treatment and nutrient recycle, but the accumulation of pig manures is not effectively treated with the limited available lands. In this study, a continuous composting system was designed to increasing the treatment capacity by adding pig manure three times at the beginning of each composting cycle. The aim of the present study was to assess the composting parameters and bacterial community structure in this system. Physicochemical factors, bacterial community, and functional prediction of each composting cycles were evaluated. The result indicated that content of total nitrogen and NH4+-N increased, while the amount of carbon, cellulose, and hemicellulose decreased during the composting process. At the same time, the amount of lignin increased firstly, and then decrease to 17.3% after the last composting cycle. Furthermore, bacterial community structures were different among the three composting cycles. The correlation heatmap between environment factors and microbial community indicated that C/N ratio and pH were the main factors affecting the community structure. Additionally, bacteria participated in nitrogen cycles were found in the composting materials. Paracoccus denitrificans, Jonesia denitrificans, and Geobacillus thermodenitrificans were the main denitrifiers, and became the most abundance after the second composting cycle. The numbers of KEGG Orthology (KO) associated with ammonification, nitrification, and denitrification increased after the composting. The present study illustrated that more composting cycles might reduce the ability of nitrogen assimilation, but increases the degradation of lignin, cellulose, and hemicellulose in continuous composting system.

Automated summary

A continuous composting system was designed to increase the treatment capacity, and the composting parameters and bacterial community structure were evaluated. The results showed that nitrogen increased, while carbon, cellulose, and hemicellulose decreased during the composting process. The bacterial community structure varied among the composting cycles, and the C/N ratio and pH were identified as the main factors affecting the community structure. Bacteria participating in nitrogen cycles were found in the composting materials, and the abundance of denitrifying bacteria increased after the second composting cycle.