Abstract

Tetracycline resistance genes (TRGs) are key mediators of antibiotic resistance genes dissemination, and their proliferation in waste treatment systems poses potential risks to environmental and public health. In this study, the effects of thermal alkali pretreatment and magnetite addition on anaerobic sludge digestion were investigated, also, the suppression on TRGs was investigated when polystyrene (PS) microplastic simultaneously exited in the system. The results showed that PS microplastics significantly reduced methane production by up to 57.41% and increase the TS value to 1.61 times its original value. Thermal alkali pretreatment of the sludge-PS mixture alleviated the accumulation of recalcitrant organic matter and mitigated biogas inhibition, while magnetite addition further restored methane production to 1.33 times of the original level, and reduced the absolute abundance of most TRGs, altered the relative abundance of intI1 and intI2. Microbial community analysis revealed that the combined strategy increased the relative abundance of Methanothrix and Methanomassiliicoccus , contributing to improved gas production and TRG suppression. Fourier transform infrared spectroscopy and scanning electron microscopy confirmed that thermal alkali pretreatment promoted PS microplastic aging and degradation, effects that were further intensified by magnetite addition.