Abstract:
Antibiotic resistance genes (ARGs) can pose a serious threat to public health and the ecological environment. This study aims to effectively remove the wide transmission of the ARGs during composting. A 35-day chicken manure composting experiment was also conducted with the corn straw biochar (CSB) and corn straw biochar-nZVI (CSBN) amendment. The results indicated that the compost temperature reached above 55 ℃ within 4 to 5 days, and then remained at a high level for 5 to 7 days before starting to decline. The high-temperature period of compost in the CSB and CSBN treatments was 2 days longer than that of the control (CK) treatment. The pH values of all three treatments first rose and then fell, thus varying between 7.39 and 8.48. The NH
4+-N content in each treatment increased rapidly at first and then gradually decreased to a relatively low level (<50 mg/kg). The NO
3−-N content in each treatment slightly decreased in the early stage, and then gradually increased. The NO
3−-N content in the compost products increased obviously after adding CSB and CSBN, respectively. The seed germination index (GI) in each treatment continuously rose. The GI of compost products was all above 80 %. The addition of CSB and CSBN increased the C/N ratio of the compost products in each treatment, and then reached the standard of the mature compost. After composting, the abundances of aminoglycoside, sulfonamide, multidrug, tetracycline, beta-lactamase and chloramphenicol resistance genes in CSB treatment were 35.13 %, 37.98 %, 52.45 %, 34.53 %, 86.23 % and 83.56 % lower than those in the CK treatment, respectively; The abundances of these ARGs in the CSBN treatment were 52.77 %, 57.44 %, 57.94 %, 65.23 %, 85.36 % and 61.26 % lower than those in the CK treatment, respectively. The abundance of the MLSB resistance gene in the CSB treatment was 92.93 % higher than that in the CK treatment. While the CSBN treatment showed a 43.65 % lower to the CK. The CSB and CSBN treatments shared particularly the significant removal effects for the high-risk ARGs dfrA1 and dfrA12, with the removal rates ranging from 56.00 % to 90.34 %. In addition, the total abundances of the ARGs and mobile genetic elements (MGEs) in the CSB and CSBN treatments were 40.42 % and 57.56 % lower than those in the CK treatment, respectively. The CSBN treatment was more effectively eliminated from the ARGs and MGEs than the CSB. The main potential host bacteria for the ARGs were Bacillus, Sporosarcina, Jeotgalicoccus, Pusillimonas, and Corynebacterium. The addition of the CSB and CSBN reduced the abundance of the host bacteria, especially the CSBN. Structural equation modeling demonstrated that the MGEs played a dominant role in the removal of ARGs. Therefore, the CSBN addition significantly reduced the abundance of the host bacteria for the ARGs. The horizontal gene was inhibited to transfer mediated by the MGEs. Thus, the ARGs were effectively removed in the chicken manure compost. These findings can also provide an important theoretical basis and practical reference for the safe and efficient composting, in order to control the environmental spread of the ARGs in chicken manure.