Effects of torrefaction pretreatment on the composting of tetracycline mycelial residues: Antibiotic resistance

The persistence of tetracycline (TC) and antibiotic resistance genes (ARGs) in tetracycline mycelial residue (TMR) has emerged as a concern. Torrefaction has been demonstrated as an effective treatment for reducing both contaminants. However, the effect of torrefaction as a pretreatment on controlling antibiotic resistance during composting remains unclear. Thus, the dynamics of residual TC, ARGs, and the microbial community succession were compared during composting of raw and torrefied TMR. The results indicate that torrefaction at 200.0 °C for 60.0 min is an effective pretreatment for improving the safety of TMR composting without negatively affecting its performance. No TC was detected in the compost derived from TMR torrefied under these conditions, while ARG relative abundance (RA) remained consistently low throughout the process. Compared with the control group, torrefaction at 200.0 °C for 60.0 min reduced ARG RA in the fertilizer by 10.4 %. Furthermore, the RA of ARGs associated with potential human pathogenic microorganisms (HPMs) decreased by 58.9 % in the final product. The limited mobility of residual ARGs ( rsmA , mexK , and vanRO ) in compost products and the non-pathogenic phenotype of their hosts collectively indicate limited environmental risks. The persistence of these ARGs was attributed to the high-temperature, oxidative composting environment and dynamics secondary metabolites. These findings demonstrate that torrefaction combined with composting is a promising strategy for mitigating antibiotic resistance risks and facilitating the resource reutilization of TMR.