Potential of industrial composting and anaerobic digestion for the removal of antibiotics, antibiotic resistance genes and heavy metals from chicken manure

Composting and anaerobic digestion techniques are widely used for manure recycling, but these methods have shown conflicting results in the removal of antibiotics, antibiotic resistance genes (ARGs), and heavy metals. In the present study, anaerobically digested chicken manure and various types of composted chicken manure were investigated on an industrial scale. Antibiotics, ARGs, and heavy metals had shown inconsistent results for anaerobic digestion and composting. The different composting processes either declined or completely removed the blaCTX-M, intl1 and oqxB genes. In addition, composting processes decreased the absolute abundance of aac6'-Ib and aadA genes, while increased the absolute abundance of qnrD, sul1, and tet(A) genes. On the other hand, anaerobic digestion of chicken manure increased the absolute abundance of ere(A) and tet(A). High throughput sequencing showed that Firmicutes, Proteobacteria, Bacteroidetes, and Actinobacteria dominated the total bacterial composition of composted and anaerobically digested samples. Network analysis revealed the co-occurrence of ARGs and intl1. The redundancy analysis showed a significant correlation between some heavy metals and ARGs. Similarly, the bacterial composition showed a positive correlation with the prevalence of ARGs in treated manure. These findings suggest that bacterial community, heavy metals, and mobile genetic elements can play a significant role in the abundance and variation of ARGs during composting and anaerobic digestion. In conclusion, anaerobic digestion and composting methods at industrial scale need to be improved for the effective removal of antibiotics, ARGs and heavy metals from chicken manure. (C) 2020 Elsevier B.V. All rights reserved.