Synergistic effects of microbial EPS and iron-reducing bacteria on arsenate immobilization via Ferrihydrite transformation

The environmental behavior of arsenic (As) is closely coupled with iron mineral transformation and microbial activity;however, the stability of As immobilization in extracellular polymeric substances (EPS)–ferrihydrite (Fh) systems under iron-reducing conditions remains unclear. In this study, an As-resistant bacterium (Pseudomonas putida YT-1) and iron-reducing bacterium (Shewanella oneidensis MR-1) were employed to investigate As(V) immobilization in EPS–Fhy systems. Bacth experiments combined with confocal laser scanning microscopy (CLSM), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD) were conducted to elucidate the interactions among EPS, iron minerals, and arsenic. The results showed that EPS significantly enhanced As(V) removal (20.34–58.76%) compared to ferrihydrite alone (15.00–25.44%) by modifying mineral surface properties and introducing reactive functional groups (–COOH, –OH, and –NH₂) that facilitate surface complexation. In the presence of MR-1, the As(V) removal efficiency further increased to 21.85–82.86%, suggesting a synergistic effect between microbial activity and EPS–mineral interactions. Spectroscopic analyses indicated that protein- and phosphate-related functional groups in EPS played key roles in arsenate binding. XRD results suggested possible mineral phase changes during the reaction, although direct evidence for Fe(III) reduction and secondary Fe(II)-bearing mineral formation remains limited. Overall, As immobilization in the EPS–Fh–MR-1 system appears to be governed by the combined effects of surface complexation, microbial mediation, and mineral transformation. These findings highlight the potential role of EPS–mineral associations in enhancing arsenic stabilization while emphasizing the need for further studies to directly resolve Fe redox processes and mineral transformation pathways.