Temporal succession and spatial heterogeneity of humification, pathogens and bacterial community in facultative heap composting

The oxygen (O2) content of heap composting pile gradually decreased with depth, mainly because of limitations to air diffusion. Owing to uneven distribution of O2, composting was aerobic in upper layer, facultatively anaerobic in middle layer, and anaerobic fermentation occurred in bottom layer. Therefore, this study investigated temporal succession and spatial heterogeneity of humification, pathogens and bacterial community in facultative heap composting. In this study, pig manure alone or mixed with cornstalk was composted for 90 days without ventilation or turning. Different compost layers exhibited discrepancies in maturity and bacterial community due to differences in air diffusion during heap composting. From the compost pile's upper to lower levels, the maturity of both treatments decreased from 80.60% to 0%, and the Shannon index decreased from 4.09 to 2.08. Cornstalk regulation significantly improved compost maturity and humification, brought obvious improvements to bacterial diversity and cooperative interactions and accelerated transformation from anaerobic to aerobic bacteria by enhancing porosity and oxygen diffusion. Cornstalk addition would slow the rate of pathogen reduction but could inactivate more thoroughly. The structural equation model revealed oxygen content, temperature and bacterial community mainly influenced pathogen inactivation, and key factors affecting humification were dissolved organic carbon and bacterial community.

Automated summary

The oxygen content in the heap composting pile decreases with depth, leading to aerobic, facultatively anaerobic, and anaerobic fermentation in different layers. This study investigated the temporal succession and spatial heterogeneity of humification, pathogens, and bacterial community in facultative heap composting. Pig manure alone or mixed with cornstalk was composted for 90 days without ventilation or turning, and different compost layers exhibited discrepancies in maturity and bacterial community. Cornstalk addition improved compost maturity, humification, bacterial diversity, and cooperative interactions, as well as the transformation from anaerobic to aerobic bacteria by enhancing porosity and oxygen diffusion. However, it also slowed down pathogen reduction.