Reactive oxygen species (ROS) are potent reactants that are responsible for a variety of environmentally relevant reactions in aquatic systems, including degradation of natural organic matter and organic contaminants, oxidative damage of cellular material, and Mn(II) oxidation. ROS production in surface environments exposed to light irradiation is relatively well known, but ROS production under dark conditions in subsurface environments has been mostly overlooked. Recent studies indicate that dark extracellular ROS production from aerobic microorganisms and dark ROS production from the oxygenation of Fe(II) and the oxidation of natural organic matter may be significant at redox interfaces in sedimentary environments. In fact, a microbially-driven Fenton reaction system was designed in flow-through reactors (FTRs) with the Fe(III)-reducing facultative anaerobe Shewanella oneidensis to simultaneously produce Fe(II) and hydrogen peroxide (H2O2) in the presence of 2L-ferrihydrite-coated sand. Dark production of ROS by this microbially-driven Fenton reaction in FTRs is sustained along a redox transition zone maintained by continuously supplying aerated medium to the reactors. Although the secondary mineralization of ferrihydrite is promoted during microbial Fe(III) reduction, the effect of iron crystallinity on ROS production via microbially-driven Fenton reaction has not been investigated. In this study, dark ROS production via microbially-driven Fenton reaction was investigated in batch reactors with different Fe(III) minerals to determine in what conditions ROS production is regulated by the redox transformation of Fe(III) oxides. These experiments provide new information on the microbially-driven Fenton reaction mechanism and more insights into dark ROS production during water table fluctuations in subsurface environments, when the metabolic activity of iron reducing bacteria alternates with aerobic respiration.

Effect of secondary mineralization of ferrihydrite on dark production of ROS via microbially-driven Fenton reaction

2019 Fall National Meeting

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