The behavior of antibiotic resistance genes and arsenic influenced by biochar during different manure composting.

The effect of two different biochar types, rice straw biochar (RSB) and mushroom biochar (MB), on chicken manure composting was previously examined by monitoring the fate of antibiotic resistance genes (ARGs) and arsenic. The behavior of ARGs and arsenic in other kinds of manure composting with the same biochar types had not been examined. In this study, we added either RSB or MB to pig and duck manure composts to study the behavior of ARGs (tet genes, sul genes, and chloramphenicol resistance genes) and arsenic under the same experimental condition. The results showed that the average removal values of selected ARGs were respectively 2.56 and 2.09 log units in duck and pig manure compost without the addition of biochar. The effect of biochar addition on the average removal value of ARGs depended on the type of biochar and manure. For instance, in pig manure compost, MB addition increased the average removal value of ARGs, while RSB addition decreased. And both biochar additions had a negative influence on the average removal value of ARGs in duck manure compost. Analytical results also demonstrated that MB addition reduced total arsenic and the percentage of bioavailable arsenic more than RSB.