1. School of Environmental and Municipal Engineering, Lanzhou Jiaotong University, Lanzhou 730070, China; 2. Key laboratory of Yellow River Water Environment in Gansu Province, Lanzhou 730070, China; 3. Goldwind Environmental Protection Co., LTD, Beijing 102600, China
Abstract：The higher content of antibiotics resistance genes (ARGs) accumulated in excess sludge lowers its agricultural value of vermicompost. To eliminate the content of ARGs in sludge vermicompost, this study aimed to reveal the effects of corncob biochars added in sludge on microbial communities and ARGs of vermicomposting. For this, 1.25% and 5% of corncob biochars, were separately added to dewatered sludge, comparing with the counterpart without addition of biochars. The addition high content of corncob biochars significantly (P < 0.05) promoted the mineralization of organic matter, thus increasing the conductivity and pH of sludge vermicompost. In addition, the corncob biochars (P < 0.05) enhanced the gene abundances of bacterial 16S rDNA and eukaryotic 18S rDNA in the vermicompost, resulting in a significantly (P < 0.05) positive correlation between the microbial abundance and biochar concentration. Compared to control, the relative abundance of Proteobacteria, Bacteroidetes, Actinomycetes, and Planctomycetes in sludge vermicompost with high content of corncob biochar decreased by 11.8%, 7.1%, 33.3% and 20%, respectively. However, its abundance of Firmicutes significantly increased by 40% (P < 0.05). Besides, the absolute abundance of macrolide resistance genes (ermF) and tetracycline resistance genes (tetX) in vermicompost with corncob biochars significantly decreased by 32%~45% and 13%~31% (P < 0.05), respectively. But, the abundance of class 1integron (intI1) and sulfonamides resistance genes (sul2) significantly increased by 47%~135% and 9%~42% (P < 0.05) in the final vermciompost, respectively. The addition of corncob biochar in sludge can promote the mineralizaiton of sludge by enhancing microbial number and diversity of microbial, but this addition only selectively reduce the ARGs in vermicompost.
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