Iron (hydr)oxide minerals-microbe interaction associated retention capacity boost and reaction rate fluctuation for perfluorooctanoic acid in an in-situ iron-based and microbe-based sustained-release system

Abstract

Based on the inefficient elimination of emerging contaminant perfluorooctanoic acid (PFOA) and the unpredictable performance of the filed-scale system, a novel in-situ iron-based and microbe-based sustained-release system and filed-scale model were developed to address the above issues in this study.

Especially, the PFOA-microbe-mineral interaction in various types of groundwater and the relevant mechanism were quantitatively and deeply studied. The results showed that the sustained-release interaction system in HCO₃⁻ type groundwater exhibited a greater retardation effect (K_d = 0.73 cm³ g⁻¹) on PFOA compared to the interaction system under no ions condition (K_d = 0.49 cm³ g⁻¹) or microbe system (K_d = 0.43 cm³ g⁻¹). Moreover, the reaction rate λ of PFOA exhibited minimal fluctuation in HCO₃⁻ type groundwater, indicating lower competition from HCO₃⁻ ions for occupancy site and resulting in less PFOA repulsed to the lower reactive region (with lower Fe²⁺ and microorganism cells concentrations). Furthermore, the retardation effect for PFOA was boosted by secondary minerals-microbe interaction and joint adsorption. HCO₃⁻ facilitated the minerals-microbes interaction, leading to increased formation of β-FeOOH and improved retardation effect for PFOA. Additionally, the functional microorganisms Pseudomonas and Delftia were combined to drive the Fe³⁺/Fe²⁺ cycle and PFOA biochemical transformation. The two-dimensional spatiotemporal evolution simulation results showed that pollutant flux (transport risk) of PFOA in HCO₃⁻ type groundwater system (0.124 × 10⁻³ mg·(m²·s)⁻¹) can be reduced by 23.0% compared to that in NO₃⁻ type groundwater system (0.161 × 10⁻³ mg·(m²·s)⁻¹). This study quantitatively revealed the coupling effect of minerals, microbes, and ions on PFOA, contributing to optimizing the sustained-release system for effectively remediating different types of PFOA-contaminated groundwater.