Using biochar to strengthen the removal of antibiotic resistance genes: Performance and mechanism

Abstract

In this study, the excess activated sludge was used for pyrolysis to produce biochar with Ce modification. The removal process and mechanism of ampicillin resistance gene (ARGAmp) by biochar was investigated. The results showed that when pyrolyzing the excess sludge at 400 °C, the organic components in the sludge could be partially pyrolyzed and complexed with Ce. By accepting electrons from phenol or quinone, persistent free radicals (PFRs) were formed on the surface of biochar. On the optimized conditions with the initial ARGAmp concentration of 41.43 mg/L, the removal ratios of ARGAmp by adsorption, PFRs, hydroxyl free radicals (·OH) by adding H2O2 were 28.37%, 8.26%, and 27.56%. No melted DNA was detected in the treated samples. The oxidation process by PFRs and ·OH can directly destroy the ARGAmp structure. The phosphodiester bond in the base stacking structure and the phosphate bond in the nucleotide are the possible action sites of PFRs. Treated ARGAmp products were in the form of base pair residues or short-chain double helix structures. ·OH can be added to the bases of nucleotide molecules to form highly active free radical adducts. They can initiate molecular dehydrogenation and intermolecular proton transfer, resulting in oxidation of the base to the scission of the phosphate sugar backbone.