Torrefaction: A promising approach for the harmless treatment of low-moisture tetracycline mycelial residue

Abstract

Tetracycline mycelial residue (TMR), a byproduct derived from the tetracycline fermentation process, is rich in organic matter, making it a promising resource. However, the presence of residual tetracycline and antibiotic resistance genes (ARGs) limits its potential for resource utilization. In this study, torrefaction was employed for the harmless treatment of low-moisture TMR, and the optimized condition was 200.0 °C for 30.0 min. Under this condition, 97.2% of tetracycline (TC) in TMR could be efficiently removed, with more organic matter reserved for resource utilization. The plausible degradation pathway was proposed, involving the formation of lactone structure and anhydro-tetracycline (ATC) during TC degradation, followed by a series of reactions among main functional groups, including concerted reactions, retro-Diels-Alder (RDA), cleavage reactions, and rearrangement. Furthermore, the antibacterial efficacy of degradation products from TC has significantly diminished, and the structure of ARGs and bacteria was disrupted during the torrefaction of TMR. After the treated TMR was amended into the soil as fertilizer, the dissemination of ARGs could also be effectively controlled. Therefore, torrefaction could be recommended as a promising harmless treatment for the resource utilization of low-moisture TMR.