Effects of struvite-humic acid loaded biochar/bentonite composite amendment on Zn(II) and antibiotic resistance genes in manure-soil

In this study, struvite-humic acid loaded biochar/bentonite composite (HMCC), a recovery product of humic acid, nitrogen and phosphorus from biogas slurry, was prepared and used for simultaneous control of Zn(II) and antibiotic resistance genes (ARGs) pollution in manure-soil. The adsorption performance and mechanism of Zn(II) on HMCC were first studied in aqueous solution. The adsorption data fitted well to the Freundlich isotherm model, and the primary mechanisms of Zn(II) absorbed by HMCC involved the formation of Zn-3(PO4)(2)center dot 4H(2)O and humic acid-metal complex. The changes of Zn(II) content, antibiotic resistance genes (ARGs) and bacterial communities during the remediation of Zn(II) contaminated manure-soil were analyzed simultaneously. With HMCC amendment, the content of bio-available Zn(II) (bio-Zn) efficiently reduced from 847.4 mg/g to 739.2 mg/g and the total relative abundance of ARGs accordingly decreased by 37.18%. RDA analysis indicated that soil pH and bio-Zn were the main contributors to the fluctuations of soil ARGs. Spearman correlation analysis revealed that the potential hosts for ARGs mainly belonged to the phylum Actinobacteria. In addition, HMCC addition increased the diversity of bacterial community but significantly reduced the abundance of an antibiotic resistant bacteria-Actinobacteria. It is the first study to demonstrate the feasibility of HMCC as an environmentally friendly amendment to immobilize Zn(II) and mitigate the dissemination of ARGs in manure-soil.