Enhancing compost safety: Simultaneous reduction of antibiotic resistance genes and bioavailable heavy metals by microbial additives

The continuous accumulation of antibiotic resistance genes (ARGs) and heavy metals (HMs) during sludge composting poses increasing environmental risks, highlighting the urgent need to explore effective remediation strategies. However, the mechanisms by which microbial additives simultaneously mitigate these two types of pollutants during sludge composting remain unclear. Different doses (0, 0.03 %, 0.09 %, and 0.15 %) of a commercial microbial agent were added during co-composting of sludge and garden waste to evaluate their impacts on the bioavailability of HMs and the abundance of ARGs. The results showed that the addition of the highest dosage (0.15 %) of microbial agent significantly promoted humus formation, increased the content of phosphorus (P) and potassium (K) on a dry weight basis, reduced the bioavailable fractions of Zn, Mn, and Pb by 19.21 %-26.17 %, and markedly inhibited ARGs, such as sul2 and gyrB, with removal rates exceeding 78.92 %. The microbial agent significantly altered the microbial community structure, with the relative abundance of Actinobacteria reaching 60.42 %. Redundancy analysis (RDA) and network analysis revealed that temperature, pH, and the relative abundance of Firmicutes were key factors regulating the variations in ARGs. This study provides theoretical support for enhancing compost safety through microbial regulation.