Dissertation title: 

Production of Light-independent Reactive Oxygen Species during Microbially-mediated Fe(II)/Fe(III) Redox Cycling and its Application in the Degradation of Organic Contaminant 

Abstract: 

Reactive oxygen species (ROS), such as superoxide (O2•−), hydrogen peroxide (H2O2), and the hydroxyl radical (•OH), represent transient reactants that are redox active and ubiquitous in aquatic systems. In the presence of Fe(II), H2O2 represents a potential source of •OH via the Fenton reaction, which is commonly used in remediation for organic contaminant degradation. The degradation of various organic contaminants during aerobic oxidation of Fe(II) species without addition of exogenous peroxide has also been demonstrated, suggesting that oxidation of natural organic matter and organic contaminants may occur naturally at redox interfaces. In redox-dynamic environments, facultative anaerobic microorganisms such as Shewanella species may alternate between respiration of O2 and Fe(III) oxides as terminal electron acceptor and potentially produce ROS during redox oscillations. Although these processes have been proposed, and the formation of ROS has been increasingly documented in natural environments, a mechanistic investigation of the processes regulating the generation of ROS during redox oscillations with Fe(III) oxides is lacking. The overall objective of this research was to investigate the mechanism of light-independent ROS production during microbially-mediated Fe(III)/Fe(II) redox cycling with iron oxides and its potential application for field remediation of organic contaminants. The role of nutrients, organic ligands, and redox conditions on ROS generation in the presence of Fe(III) oxides was investigated in both batch and flow-through reactors to gain insights into the complex mechanism of ROS production and consumption and its effect on organic carbon degradation, using 1,4-dioxane as a recalcitrant model organic contaminant. Overall, this dissertation contributes to our understanding of the light-independent production and role of ROS in natural environments by: 1) providing new insights into the importance of nutrients in the production of ROS during Fe redox cycling; 2) highlighting the importance of ligands in promoting both Fe redox cycles and •OH production in subsurface environments; 3) demonstrating that the production of ROS is sustainable at redox interfaces without high frequency redox oscillations; and 4) providing a new process that could be exploited in in situ bioremediation strategies aimed at using •OH for contaminant remediation. 

Thesis Committee Members:  

Dr. Martial Taillefert (Advisor), Dr. Thomas J. DiChristina, Dr. Yuanzhi Tang, Dr. Ching-Hua Huang, Dr. Aaron Thompson (UGA) 

Time and Date: 2:00 p.m. Tuesday, November 22nd 2022 

Location: ES&T L1114