Date of Award
12-2023
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Environmental Engineering and Earth Science
Committee Chair/Advisor
Dr. Ezra Cates
Committee Member
Dr. Elizabeth Carraway
Committee Member
Dr. Brian Powell
Committee Member
Dr. Sudeep Popat
Abstract
The main objective of this study is to evaluate the practical applicability of heterogeneous photocatalysis technology powered by ultraviolet (UV) photons for the degradation of per and -polyfluoroalkyl substances (PFAS) in contaminated groundwater samples. For this purpose, bismuth oxyhydroxy phosphate (BOHP) and hexagonal boron nitride (hBN) were utilized as the main photocatalysts in slurry photodegradation systems. BOHP (Bi3O(OH)(PO4)2) is a wide bandgap semiconductor with high activity for degrading long-chain perfluorocarboxylic acids (PFCAs) in mild operational conditions. Boron nitride (BN) is another wide bandgap semiconductor material that was used in this study due to its ability to degrade a wide variety of PFAS at environmentally relevant concentrations. Perfluorooctanoic acid (PFOA) was selected as the primary target contaminant, but the degradation of other PFCAs and perfluorooctane sulfonate (PFOS) was also investigated.
In the first section of this study, the degradation mechanisms of PFOA in the UVC/BOHP system and the effect of major water constituents on the degradation efficiency were investigated. Degradation intermediates of PFOA and the extent of mineralization were determined by using liquid chromatography-tandem mass spectrometry (LCMS) and ion chromatography (IC), respectively. The role of different reactive species in the degradation process was unraveled by the addition of scavenger agents to the reaction solution. The performance of the UVC/BOHP photocatalytic process for degrading other PFCAs was examined, and the chain-length dependency of the degradation rate was discussed. In more realistic conditions, the capability of the degradation system was evaluated in the presence of major groundwater constituents, such as chloride and natural organic matter. Furthermore, the effect of the reactor configuration on the degradation efficiency was studied. In addition to the typical mixed tank reactors, the degradation rate of PFOA in bench-top plug flow reactors was tested, and the effect of the reactor parameters was evaluated.
In the second section, the capability of the hexagonal phase of boron nitride (h-BN) for photocatalytic degradation of PFOX (X: S and A) in more realistic scenarios was explored. The effect of the initial concentration of PFOX on the degradation rate was investigated, and the results were discussed in terms of PFAS-PFAS and PFAS-solid surface interactions. The mineralization efficiency and the concentration of degradation intermediates were evaluated using IC and LCMS analyses, respectively. By utilizing lamps that emit both 245 and 185 nm photons in photolytic/photocatalytic degradation experiments of PFOX, the contribution of 185 nm photons to the degradation reaction was evaluated. Finally, in a 5 L pilot-scale reactor, the performance of the UV/hBN photocatalytic system for degrading the ppb range of PFAS concentrations in real groundwater samples was evaluated. The energy efficiency and scalability of the system are discussed and compared to other proposed technologies.
Finally, the third section explores the mixing rate's effect on PFOA's degradation efficiency in mixed-tank slurry photocatalytic reactors. Three metal oxide photocatalysts (BOHP, β-Ga2O3, and In2O3), as well as hexagonal boron nitride, were utilized as photocatalysts for PFOA degradation and the effect of mixing on the degradation rate was discussed in terms of fluid shear and PFAS-surface interactions. The mixing dependency of the degradation rate of perfluorocarboxylic acids (PFCAs) with different chain lengths was also investigated. Finally, the response of the degradation system to mixing rate at different initial concentrations of PFOA and ionic strength values was evaluated.
Recommended Citation
Qanbarzadeh, Mojtaba, "Influence of Photoreactor Design Parameters on the Performance of Ultraviolet Light-Induced Degradation of Per-and Polyfluoroalkyl Substances by Bismuth Oxy Hydroxy Phosphate and Hexagonal Boron Nitride Photocatalystsinfluence of Photoreactor Design Parameters on the Performance of Ultraviolet Light-Induced Degradation of Per-and Polyfluoroalkyl Substances by Bismuth Oxy Hydroxy Phosphate and Hexagonal Boron Nitride Photocatalysts" (2023). All Dissertations. 3529.
https://open.clemson.edu/all_dissertations/3529