Effects of chicken manure-modified biochar on the adsorption capacity of tetracycline and abundance of antibiotic resistance genes in soil

Large quantities of livestock manure not only occupy farmland but also serve as the primary source of antibiotics and antibiotic resistance genes (ARGs) in agricultural soil. To enhance the resource utilization of animal manure and mitigate ecological risks associated with antibiotics in agroecosystems, chicken manure was used as a raw material for biochar production. The manure derived biochar (MB) was modified with an alkali-acid two-step modification process. The results showed that the total pore volume and surface area of alkali-acid modified MB (AMMB) was significantly increased about three and five times, respectively after modification. The SEM images showed that the surface of AMMB had a more regular and clearer structure with fewer impurities. The improvement of surface properties of AMMB significantly increased its adsorbing capacity of tetracycline in the soil. The adsorption kinetics of tetracycline by AMMB were better fitted by the pseudo-second-order kinetic model, suggesting that the adsorption of tetracycline on biochar followed the process of chemisorption. The adsorption mechanisms mainly involved the pore filling, hydrophobic effect, and pi-pi EDA interaction. Moreover, after a 60 days amendment of AMMB, the total relative abundances (RAs) of tested tetracycline resistance genes (TRGs) in soil decreased significantly, which suggested that AMMB can be a potential material to reduce risks of antibiotics and its resistance genes.