Industrial aerobic composting and the addition of microbial agents largely reduce the risks of heavy metal and ARG transfer through livestock manure

Composting is an effective and necessary modality in the recycling of agricultural wastes such as livestock manure, furfural, and straw. However, the risks of heavy metals (HMs) and antibiotic resistance genes (ARGs) during industrial aerobic composting, especially with the addition of bacterial agents, have not been adequately assessed. In this study, changes in HMs toxicity, ARGs propagation and microbial community structure during industrial-scale aerobic composting of various substrates were investigated for the first time. Moreover, the effect of the addition of bacterial agents (Bacillus strains) was evaluated. The results showed that industrial aerobic composting had different effects on the immobilization of HMs and significantly suppressed the expression levels of ARGs such as intl1 and oqxB genes. The bioavailability of Cu and Cr was further reduced by the addition of bacterial agents and the absolute abundance of ereA and tetA was not detected. The main bacterial community structure after composting in different substrates were similar, irrespective of bacterial agents, indicating that composting was the main driver of the change in microbial community structure. This study expands the research related to the reuse of livestock manure and provides a scientific basis for the reuse of livestock manure.