Prediction of the Degradation of Emerging Contaminants During Oxidative Treatment via Analysis of Reaction Rate Constants

Abstract

Prediction of the Degradation of Emerging Contaminants During Oxidative Treatment via Analysis of Reaction Rate Constants Kellie Cochran Globally, water supplies are diminishing in quality while demand is continually increasing. The municipal water and wastewater sector has been paying increased attention to unregulated emerging organic contaminants. Advanced oxidation processes (AOPs), which produce hydroxyl radicles (•OH), have been developed and implemented to remove recalcitrant emerging contaminants left by conventional treatment processes. The current understanding of the removal efficacy of AOPs for emerging contaminants is limited. This study analyzes the ability of an AOP involving ozone and multi-walled carbon nanotubes (MWCNTs) in removing three specific emerging contaminants: caffeine, atrazine, and phenytoin, which were selected based on their persistence and ubiquity in the environment and their potential to serve as AOP efficacy indicator compounds. Reaction rate constants were determined from batch reactor data and compared to the degradation trends observed for the different compounds after exposure to treatment. During exposure to ozone alone, caffeine degraded quickly (KO3 = 334 ± 67 M-1 s-1), atrazine degraded slightly (KO3 = 8.3 ± 1.0 M-1 s-1), and phenytoin did not respond to the treatment. Atrazine and phenytoin were exposed to •OH in the AOP treatment process, and the contaminants displayed greater removal v compared to ozone only. To simulate more realistic water systems, a mixture of caffeine and atrazine was subjected to ozone only and the AOP with ozone and CNTs. Competition for ozone and •OH resulted in lower atrazine degradation. This result reflects the expected degradation of these compounds based on their individually determined reaction rate constants. Atrazine behaved as expected when exposed to ozone and the AOP, and the reaction rate constants determined for atrazine reflect the observed degradation trend which qualifies atrazine as a potential indicator compound. Overall, this study demonstrates the ability of the AOP combining ozone and CNTs to degrade recalcitrant compounds, the potential for atrazine to serve as an indicator compound for AOPs, and the reliability of reaction rate constants to predict the degradation of contaminants in increasingly complex water systems. vi ACKNOWLEDGMENTS I would like to acknowledge the following people for their continued support and encouragement throughout this research project: Dr. Rebekah Oulton for sharing your excitement and extensive knowledge in this field of research, and for helping me develop a project centered around my interests and guiding me through every step in the process. I am grateful for the professional development and personal growth I have experienced through this project. Dr. Amro El Badawy for helping me develop my research question and for your guidance over the past year. Dr. Tryg Lundquist for your recommendations and support for my project throughout. The faculty, students, and staff of the Civil and Environm...