Effect of zero-valent iron and magnetite on mitigating sulfate and lincomycin stress in anaerobic digestion: microbial succession and antibiotic resistant genes removal

This study investigated the enhancement performance of zero valent iron (ZVI) and Fe₃O₄ on sulfate, lincomycin and combination stressed anaerobic digestion. The cumulative methane yield were both promoted by ZVI and Fe₃O₄ under different stressed conditions. ZVI significantly elevated maximum methane production rate to 1.8 ± 0.1 mL/h under sulfate stress, which was 2.25-fold of control group. Fe₃O₄ revealed its superior performance on lincomycin degradation with a removal efficiency of 56.7 ± 1.3 % under combined stress. Besides, the formation of coenzyme F₄₂₀ and hydrogenotrophic methanogenesis were stimulated by ZVI. Regarding microbial community succession, Mesotoga and unclassified_f__Thermotogaceae were enriched by ZVI and Fe₃O₄, both of which profited propionate degradation. Iron-based materials similarly enriched hydrogenotrophic methanogens, especially with introduction of Fe₃O₄. Insight into metagenomic analysis, genes encoding hydrogenotrophic methanogenesis and direct interspecies electron transfer, such as pliA and chpA, were up-regulated by ZVI and Fe₃O₄ under different stress conditions. Moreover, Fe₃O₄ revealed its higher potential to decrease antibiotic resistant genes than ZVI. Overall, this study demonstrated the potential of ZVI and Fe₃O₄ to enhance anaerobic digestion under high sulfate/lincomycin conditions and provided fundamental basis for further researches.