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Mitigation of polyethylene microplastic-induced estrogen degradation inhibition in anaerobic digestion by zero-valent iron: Mechanisms linking microbial community succession to metabolic pathway regulation
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In lab tests of anaerobic digestion systems, adding iron particles alongside polyethylene microplastics reduced hormone residues (estrone and estradiol) compared to microplastics alone. The iron changed microbial community makeup and increased activity of genes linked to hormone breakdown and electron transfer between microbes.
Zero-valent iron (ZVI) has shown promise in enhancing pollutant removal, yet its multi-scale mechanism for alleviating polyethylene microplastics (PE-MPs)-induced inhibition of estrogen degradation during anaerobic digestion (AD) remains unclear. Therefore, three treatment groups (T1, T2 and T3) were established in this study, including ZVI addition (1.0 g/L ZVI, T1), PE-MPs addition (150 particles/g TS, T2) and PE-MPs + ZVI addition (150 particles/g TS and 1.0 g/L ZVI, T3). After 60 days of AD, PE-MPs + ZVI addition (T3) reduced estrone (E1) and estradiol (E2) residues to 21.64 ± 0.23 μg/kg and 15.77 ± 0.05 μg/kg, increasing their removal efficiencies by 12.02% and 9.04% compared to T2. Specifically, ZVI reduced the relative abundance of Firmicutes and increased the relative abundance of the electroactive bacterium Desulfovibrio (21.74-fold vs T2), as well as methanogens. Metagenomic analysis revealed ZVI upregulated quorum sensing (QS) genes ( LuxQ , LuxS 1.14-fold and 1.13-fold vs T2) and direct interspecies electron transfer (DIET)-related genes ( ubiE , pilW , 6.98-fold and 7.66-fold vs T2), enhancing the connectivity between key estrogen-degrading genes and microorganisms (154 edges in T3 vs 120 edges in T2), particularly genes annotated to 17β-estradiol dehydrogenase and the EmtABCD system. Additionally, ZVI mitigated SOD activity and restored acetate kinase activity. PLS-PM modeled estrogen degradation genes as the primary drivers of estrogen degradation. This study provided multi-scale evidences for ZVI’s application in remediating combined PE-MPs and estrogen pollution in AD systems.
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