Enhancing longevity and reactivity of sulfidated nanoscale zero-valent iron by Methanosarcina barkeri for sustainable remediation of p-chlorophenol in groundwater

A coupled system integrating M. barkeri with S-NZVI was developed for p-CP removal. • Microbially mediated iron cycling is the core mechanism of the synergistic system. • M. barkeri regenerates reactive Fe²⁺ sites by reducing the Fe(III) passivation layer. • Microbial activity effectively promotes electron transfer processes. • This work provides a bio-enhanced strategy to maintain long-term reactivity of S-NZVI. Chlorophenols are persistent and toxic pollutants frequently detected in contaminated groundwater. Sulfidated nanoscale zero-valent iron (S-NZVI) has been widely applied for chlorophenol remediation; however, its performance is limited by rapid surface passivation and a short service life. In this study, a coupled system integrating the methanogenic archaeon Methanosarcina barkeri with S-NZVI was developed to enhance both the degradation efficiency and long-term reactivity toward p-chlorophenol (p-CP). The coupled system achieved a removal efficiency of 85.5 % within 15 days, significantly outperforming the single S-NZVI system (44.2 %) and the single M. barkeri system (34.5 %). The interfacial electron transfer, material transformation, and microbial responses were systematically investigated through electrochemical analysis, multiple characterization techniques, and transcriptomic profiling. Mechanistic analysis reveals that M. barkeri plays a dual role: (1) reducing the Fe(III) passivation layer on S-NZVI, thereby regenerating reactive Fe⁰/Fe²⁺ sites; (2) facilitating electron transfer between the microorganism and the material, thereby promoting the efficient reductive dechlorination of p-CP. Transcriptomic results further show the upregulation of genes associated with electron transport and methanogenesis, indicating metabolic adaptation to the coupled system. For the first time, this study proves that methanogenic archaea can reactivate passivated S-NZVI biologically and preserve its long-term reductive dechlorination capacity. This work puts forward a bioaugmentation strategy against S-NZVI passivation, reveals new mechanisms of microbe-material interactions, and presents a feasible method for in situ remediation of groundwater contaminated with chlorophenols. Download: Download high-res image (211KB) Download: Download full-size image