Biogenic sulfidation-mediated de-passivation and reactivation of zero-valent iron: Synergism of sulfate-reducing bacteria and Shewanella towards trichloroethylene degradation.

Zero-valent iron (ZVI) for groundwater remediation is severely limited by surface passivation, while biogenic sulfidation is a promising eco-friendly modification. However, research on biogenic sulfidated ZVI (BS-ZVI) mainly focuses on sulfate-reducing bacteria (SRB), neglecting multi-strain synergism. Herein, we constructed BS-ZVI systems with SRB (denoted as BS-ZVISRB) and Shewanella oneidensis MR-1 (denoted as BS-ZVIMR-1) to compare their trichloroethylene (TCE) degradation performance, and develop a "SRB-Shewanella" synergistic system. 95.7% and 96.2% of TCE were degraded by BS-ZVISRB (0.43 d-1) and BS-ZVIMR-1 (0.45 d-1), respectively. BS-ZVISRB had a higher sulfidation degree and the polysulfides inhibited the hydrogen evolution reaction (HER). The active dissimilatory iron reduction (DIR) behavior in the BS-ZVIMR-1 system suppressed the surface passivation. Notably, the "SRB-Shewanella" maintained 95.2%-98.8% TCE degradation efficiency under oligotrophic conditions (chemical oxygen demand (COD) = 45.7 mg/L-47.3 mg/L), with improved carbon-source utilization and enzymatic activity. Overall, this study offers fundamental theoretical insights and parametric references for the development of in-situ BS-ZVI remediation technology.