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In order to explore the enhancement effect of biochar on anaerobic digestion, oxytetracycline residue was used as the substrate for anaerobic digestion, and biochar was added to solve the problems of low efficiency and weak stability of traditional anaerobic digestion. The strengthening effects of biochar and zero-valent iron modified biochar were illustrated by the changes of gas production, stability and microbial community. The results show that adding biochar alone and nano-scale zero-valent iron modified biochar can reduce the concentration of ammonia nitrogen in the system, reduce the influence of ammonia inhibition on anaerobic digestion, promote the transformation and consumption of VFAs, and improve the stability of the system. The gas production efficiency increased by 20.74% and 15.49% respectively, reaching above 115.20 mL/g. In addition, biochar can also strengthen the removal of residual oxytetracycline, and its removal efficiency is increased by 2.37% and 4.82% respectively compared with the control group, and the content of residual oxytetracycline in the final system can be reduced to below 10 mg/L. After adding zero-valent iron to biochar, the abundance of acid-producing bacteria and methano-genic archaea increased in different degrees, thus strengthening the process of anaerobic digestion and methanogenesis. [ABSTRACT FROM AUTHOR]

• The property of AMRs biochar has been improved by H 3 PO 4 -modification. • The using of PBC as carrier to load nZVI improved the agglomeration of Fe particles. • PBC and nZVI/PBC enhanced biogas yield by more than 20% in AD of corn straw. • The nZVI/PBC exhibited higher ability in maintaining the stability of AD system. Antibiotic mycelial residues (AMRs), as recyclable hazardous waste, can realize efficient utilization by reasonable treatment. To solve the problems of undeveloped pore structure and low specific surface area existed in AMR biochar, this study first modified biochar by phosphoric acid (H 3 PO 4) to prepare PBC (H 3 PO 4 -modified biochar). Then, PBC was used as carrier to load nano zero-valent iron (nZVI) for preparation of nZVI/PBC. Finally, the biochar materials were used to promote anaerobic digestion (AD) of corn straw. The results showed that H 3 PO 4 -modification can effectively improve the specific surface area, pore structure, and electron donating capacity of AMRs biochar. The using of PBC as carrier to load nZVI attenuated the agglomeration of nZVI particles. Both PBC and nZVI/PBC improved the AD process, with biogas yield enhanced by 29.63% and 29.26%, respectively. The nZVI/PBC exhibited higher ability in maintaining the stability of AD system and promotion of fiber degradation than PBC. [ABSTRACT FROM AUTHOR]

• 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 aad A, ant (2″)-Ⅰ, qacEdelta 1 and sul 1. 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 aad A, ant(2″) -Ⅰ, qacEdelta 1 and sul 1. 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%. [ABSTRACT FROM AUTHOR]