Transformation impacts of dissolved and solid phase Fe(II) on trichloroethylene (TCE) reduction in an iron-reducing bacteria (IRB) mixed column system: A mathematical model

In this research, we conducted trichloroethylene (TCE) reduction in a column filled with iron and iron-reducing bacteria (IRB) and developed a mathematical model to investigate the critical reactions between active species in iron/IRB/contaminant systems. The formation of ferrous iron (Fe(II)) in this system with IRB and zero-valent iron (ZVI, Fe(0)) coated with a ferric iron (Fe(III)) crust significantly affected TCE reduction and IRB respiration in various ways. This study presents a new framework for transformation property and reducing ability of both dissolved (Fe(II)dissolved) and solid form ferrous iron (Fe(II)solid). Results showed that TCE reduction was strongly depressed by Fe(II)solid rather than by other inhibitors (e.g., Fe(III) and lactate), suggesting that Fe(II)solid might reduce IRB activation due to attachment to IRB cells. Newly exposed Fe(0) from the released Fe(II)dissolved was a strong contributor to TCE reduction compared to Fe(II)solid. In addition, our research confirmed that less Fe(II)solid production strongly supported long-term TCE reduction because it may create an easier TCE approach to Fe(0) or increase IRB growth. Our findings will aid the understanding of the contributions of iron media (e.g., Fe(II)solid, Fe(II)dissolved, Fe(III), and Fe(0)) to IRB for decontamination in natural groundwater systems.

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► A mathematical model was developed to investigate TCE reduction filled with IRB and iron media.
► The majority of the Fe(II) produced by IRB respiration was Fe(II)solid rather Fe(II)dissolved.
► Formation of Fe(II)solid negatively affected TCE reduction in iron/TCE/IRB system.
► In condition of IRB and Fe(0) coated with Fe(III), TCE reduction strongly depends on exposed Fe(0).
► Regulating Fe(II)solid formation might ease TCE approach to Fe(0) or Fe(0) exposition.