Environmental safety evaluation of organic fertilizer produced from spiramycin fermentation residue via thermally activated persulfate integrated with aerobic composting: Effects on antibiotic resistance genes, microbial communities, and soil quality

Spiramycin fermentation residue (SFR), an organic waste generated during spiramycin production, is classified as hazardous waste due to the antimicrobial resistance risks posed by residual antibiotics. This study develops and evaluates an innovative recycling strategy that integrates thermally activated persulfate (TAP) pretreatment with aerobic composting to convert SFR into a value-added organic fertilizer (SC). However, the environmental safety of SC application in agriculture requires further investigation. This study evaluated the impact of SC application on soil physicochemical properties, microbial communities, and antibiotic resistance genes (ARGs) through soil incubation experiments. Results demonstrated that SC significantly enhanced soil physicochemical properties and stimulated enzyme activities. Parallel factor analysis combined with the Random Forest modeling revealed that humic substances play a dual role in promoting enzyme activities and sustaining soil fertility. Furthermore, network analysis indicated that SC application increased bacterial modularity and enhanced community stability. Most importantly, the integrated TAP-composting process critically reduced the antimicrobial resistance risk, achieving a profound 939-fold reduction in the absolute abundance of ARGs compared to untreated SFR—a effectiveness not attainable by composting alone. Partial Least Squares Path Modeling (PLS-PM) identified that physicochemical properties primarily influence ARG abundance indirectly through microbial processes, specifically by modulating microbial diversity and facilitating horizontal gene transfer. These findings provide critical insights for the safe utilization of SFR-derived fertilizer and its environmental risk assessment upon soil application. • An integrated TAP-composting process was developed for safe recycling of SFR. • The derived organic fertilizer critically reduced absolute ARG abundance by 939-fold. • SC enhanced soil enzyme activity and stabilized the bacterial community network. • Humic substances were key in sustaining soil fertility and enzymatic functions. • Soil properties influence ARGs indirectly by modulating microbial diversity and HGT.