The Effect Of Biochar Addition On Antibiotic Resistance Genes During Manure Composting

In recent years, antibiotic resistance genes (ARGs), as being a new pollutant, have been considered as a threat for human health. Animal manure has been detected with high abundance of antibiotic resistance genes, thus animal manure has become the reservoir for antibiotic resistance genes. Rice straw biochar (RSB) and mushroom biochar (MB) were added to lab-scale manure composting to evaluate their effects on the behaviors of antibiotic resistance genes (ARGs) and on total and bio-available heavy metals (Cu, Zn and As). Taking chicken manure composting as an example, the associated bacterial community was characterized by 16S rRNA gene high-throughput sequencing, and then investigated the correlation between bacterial community and ARGs. The main conclusions are as follows:(1) The order of the total abundance of quantified ARGs was chicken manure> duck manure> pig manure before composting, whereas the order of the average removal rate of ARGs was DM> PM> CM with the value of 2.58 log units,2.19 log units and 0.80 log units. In pig manure composting and chicken manure composting, generally speaking, addition of MB increased the average removal rate of the selected ARGs, but addition of RSB decreased. However, in duck manure composting, addition of RSB and MB decreased the average removal rate of all ARGs.(2) In pig manure composting, chicken manure composting and duck manure composting, the concentrations of total As and the percentage of bioavailable fraction of As decreased. The reduction of the percentage of bioavailable fraction of As was enhanced by biochar addition. Chicken manure composting could reduce the concentrations of total Cu and Zn, but increase the percentage of bioavailable fraction of Cu and Zn. Biochar addition significantly reduced the the percentage of bioavailable fraction of Cu and Zn(p< 0.05). Compoared with the correlations between total heavy metals and ARGs, the correlations between bio-available heavy metals and ARGs were more obvious.(3) During the three kind of chicken manure composting process, Fimicutes, Bacteroidetes, Proteobacteria and Actinobacteria were the most dominant phyla. However, their relative abundance varied significantly during the composting process (p< 0.05). The decrease in abundance of Firmicutes might explain the removal of most ARGs during the composting process. The abundance of three bacteria (belonging to Firmicutes) in chicken manure composting with RSB was much higher than composting without biochar. In addition, the result of redundancy analysis (RDA) revealed that these three bacteria had positive influence on most ARGs. Therefore, the higher abundance of these bacteria was responsible for the lower removal rate of ARGs in chicken manure composting with RSB. What’s more, the order of removal rate of pathogenic bacteria was comparable with that of ARGs.