Enhancing long-term As immobilization by NO₃-MgFe LDH coupling with Acidovorax sp. BoFeN1

Abstract

Arsenic (As) contamination of groundwater is a serious global issue requiring effective and sustainable remediation strategies. For long-term As immobilization, this study explores the potential of in-situ magnetite precipitation, induced by anaerobic nitrate-reducing Fe(II) -oxidizing (NRFO) bacteria. A nitrate-intercalated layered double hydroxide (NO₃-MgFe LDH) was introduced to provide nitrate as an electron acceptor for Fe(II) bio-oxidation and serve as an iron-based precursor in magnetite formation. The experimental results showed that NO₃-MgFe LDH was transformed into green rust (GR) in the presence of Fe(II) and HCO₃⁻. Meanwhile, 0.5 g/L of NO₃-MgFe LDH released cumulatively about 1.21 mM of nitrate within 12 h, promoting the transformation of GR into magnetite induced by Acidovorax sp. BoFeN1. As a result, the aqueous As concentration decreased from 2 mg/L to <0.008 mg/L, with approximately 70% of As confined in recalcitrant Fe oxides, suggesting high potential for long-term As immobilization. Environmental factors influenced the transformation process: a lower Fe(II) concentration (0.5 mM) delayed GR formation, while varying HCO₃⁻ concentrations (2.5–10 mM) had minimal effect. Subsequently, an elevated As level (5 mg/L) inhibited the bio-formation of magnetite, leading to lepidocrocite as the dominant mineral phase. Given the stability of magnetite, this study provides a cost-effective and environmentally friendly strategy for the durable in-situ remediation of As-contaminated groundwater.

Keywords

NO₃-MgFe LDH / green rust / magnetite / Acidovorax sp. BoFeN1 / long-term As immobilization

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