Effect of biochar on antibiotic resistance genes in the anaerobic digestion system of antibiotic mycelial dreg

•Biochar improved the efficiency of anaerobic digestion of antibiotic residues.•BC and nZVI-BC increased the gas production efficiency by 20.75% and 15.50%, respectively.•The effect of nZVI-BC was greater than BC in reducing ammonia nitrogen content.•nZVI-BC significantly enhanced the removal of aadA, ant (2″)-Ⅰ, qacEdelta1 and sul1. To address the problem of antibiotic mycelial dreg (AMD) treatment and removal of antibiotic resistance genes (ARGs), this study adopted anaerobic digestion (AD) technology, and added biochar (BC) and biochar loaded with nanosized zero-valent iron (nZVI-BC) to promote the AD of AMD and enhance the removal of ARGs. Results showed that nZVI-BC was better than BC in promoting AD due to the hydrogen evolution corrosion and the synergistic effect of nZVI and BC. In addition, BC and nZVI-BC can enhance the oxidative stress response and reduce ammonia stress phenomenon, which significantly reduces the abundance of aadA, ant(2″)-Ⅰ, qacEdelta1 and sul1. In conclusion, the enhance effect of nZVI-BC is greater than BC. The removal efficiency rates of nZVI-BC on the above-mentioned four ARGs were improved by 33%, 9%, 24% and 11%.