Manganese-oxidizing Priestia sp. Z-MLHA-1 drives biogenic Fe-Mn mineralization for synergistic As(V)/Cd(II) co-immobilization in groundwater: Experimental and DFT mechanisms with sustainability implications.

Arsenic (As) and cadmium (Cd) frequently co-occur in contaminated groundwater, yet their distinct geochemical behaviors make simultaneous immobilization challenging. Here, a newly isolated Mn-oxidizing bacterium, Priestia sp. Z-MLHA-1, drives the formation of biogenic Fe-Mn minerals (BFMMs) through microbial Mn(II) oxidation involving a transient Mn(III) intermediate. The resulting bacteria-mineral composites, comprising poorly crystalline Fe-Mn oxides and microbial organic components, provide hydroxyl, carboxyl, and metal-oxygen groups as binding sites. In binary As(V)-Cd(II) systems, BFMMs achieve immobilization efficiencies of 97% and 98%, substantially outperforming single-component systems (82% and 91%), with single-component Langmuir capacities of 94.33 and 120.16 mg/g for As(V) and Cd(II), respectively. Combined characterization and density functional theory calculations reveal that heterogeneous electrostatic interactions and surface complexation govern contaminant binding, while Cd(II) acts as a bridging cation to stabilize ternary As-Cd-surface complexes. This mechanism accounts for the synergistic, rather than competitive, immobilization of As(V) and Cd(II) on BFMM surfaces. Sustainability assessments confirm low phytotoxicity and identify optimization pathways for production costs and environmental impacts, supporting the practical applicability of BFMMs as adsorbents in fixed-bed systems for active remediation, while the underlying bacteria-mediated mineralization process can be harnessed for passive in-situ natural attenuation, offering a nature-based solution for co-contaminated groundwater remediation.