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- ASSESSMENT OF WATER TREATMENT TECHNOLOGIES FOR PER-AND POLYFLUOROALKYL SUBSTANCES (PFAS) IN MULTIPLE MATRICES
- Maldonado , Vanessa
- Electronic Theses & Dissertations
The ubiquitous presence of per-and polyfluoroalkyl substances (PFAS) in the environment resulted in extensive water contamination that poses a significant risk to human health and biota. Continuous research efforts aim to develop efficient treatment technologies to treat PFAS in water, break the PFAS accumulation cycle in the environment, and improve the efficiency of emerging technologies. In this thesis work, selected treatment technologies including electrochemical oxidation and...
Show moreThe ubiquitous presence of per-and polyfluoroalkyl substances (PFAS) in the environment resulted in extensive water contamination that poses a significant risk to human health and biota. Continuous research efforts aim to develop efficient treatment technologies to treat PFAS in water, break the PFAS accumulation cycle in the environment, and improve the efficiency of emerging technologies. In this thesis work, selected treatment technologies including electrochemical oxidation and dielectrophoresis-enhanced adsorption were used to assess and advance the state-of-the-art for PFAS remediation in multiple matrices, not previously addressed. A boron-doped diamond (BDD) flow-through cell was used to evaluate the electrochemical oxidation of perfluoroalkyl acids (PFAAs) in landfill leachates. Multiple leachates with a concentration of individual PFAAs in the range of 10^2 -10^4 ng/L were treated. The effect of current density and variability of the composition of leachates was investigated. Non-detect levels and >90% removal of perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) were reached for all leachates tested after electrochemical treatment. Although high removal efficiencies for long-chain PFAAs were obtained, high concentrations of short-chain PFAAs were generated and associated with the transformation of perfluoroalkyl acid (PFAA) precursor compounds.In the second part of this thesis research, the oxidative transformation of PFAA-precursors typically present in leachates was addressed for the first time. Target and suspect PFAS were identified in a landfill leachate and their concentrations during electrochemical treatment were quantified over time. Liquid chromatography quadrupole time-of-flight mass spectrometry (LC-QToF) measurements of the leachate identified 53 PFAS compounds and 19 PFAS classes. Multiple PFAS were reported for the first time in landfill leachates. The evaluation of the intermediate and final products generated during the electrochemical treatment showed evidence of known electrochemical degradation pathways.Coupling destructive technologies (e.g., electrochemical oxidation) with concentration technologies (e.g., ion exchange (IX), adsorption) in a treatment train approach could reduce the treatment cost of destructive technologies and increase their feasibility. Therefore, in the next part of this work, electrochemical oxidation of PFAAs from the concentrated waste of IX still bottoms was assessed at laboratory and semi-pilot scales. The concentrated waste resulted from the treatment of PFAAs-impacted groundwater with IX resins. Multiple current densities were evaluated at laboratory scale and the optimum current density was used at the semi-pilot scale. The results at the laboratory and semi-pilot scales allowed for >99% and >94% removal of total PFAAs with 50 mA/cm^2, respectively. Defluorination values, energy consumption, and implications were discussed.The third matrix addressed for PFAS remediation was drinking water. Dielectrophoresis-enhanced adsorption was used for the removal of low concentrations of PFOA. This study introduced a coaxial-electrode cell (CEC) that allowed for the generation of a non-uniform electric field to enhance the adsorption of PFOA. Experiments were performed in batch and continuous-flow modes. The dielectrophoretic-enhanced adsorption in batch mode resulted in a 4, 7, and 8-fold increase in the removal of PFOA with 5, 25, and 50 V when compared to adsorption only. The performance of the CEC in continuous-flow mode allowed for an increase of up to 2.4-fold in the PFOA removal with 25 V. The results highlighted the benefits of using a dielectrophoresis-enhanced adsorption process for the removal of PFOA from water. Overall, results from this thesis contribute to the understanding of the electrochemical degradation of PFAS in multiple matrices and introduce an alternative process to enhance the widely used adsorption technology for PFAS removal. Treatment implications of each matrix are discussed and provide a clear baseline for future research, development, and scale-up of treatment technologies for PFAS remediation.