Graduate Thesis Or Dissertation
 

Poly- and perfluorinated alkyl substance release from landfills and landfill model reactors

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/7p88ck20f

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  • Research and public concern of poly and perfluoroalkyl substances (PFASs) as environmental contaminants has increased significantly due to the increasing number of reports of their detection in humans and wildlife. PFASs have a number of commercial applications including surfactants, coatings, polymers, and levelers, which are used on consumer products like papers and textiles that are often discarded into landfills. The landfill leachate is highly concentrated with PFASs and acts as a point source of PFASs to the environment. However, the factors impacting the movement of PFASs from commercial products to leachate remain elusive. It is important to understand the load of PFAS in landfill leachates and how conditions within a landfill contribute to the composition and concentration of PFASs observed in leachates. To answer this question, a reliable analytical method was needed to analyze the diverse PFASs potentially in leachate, including newly identified compounds that expand on the few (typically <15) PFASs typically analyzed in leachate. Chapter 2 describes how micro liquid-liquid extraction was combined with large volume injection (LVI, 900 µL) and orthogonal liquid chromatography/tandem mass spectrometry to measure 70 PFASs in leachate. This methodology used over seven times more of the generated extract by volume, was faster, and produced less solvent and solid waste than previous methods. Method accuracy and precision for PFASs with analytical grade reference materials ranged from 81-120 % and 5.5-33 %, respectively. Estimated method detection limits were low to sub-ng/L. For the purposes of demonstrating the developed method, seven leachates were analyzed and 37 PFASs were identified in leachate that had been previously unreported in landfill leachates. One limitation identified in Chapter 2 is the inability of the orthogonal chromatographic system to retain and separate neutral PFASs. Chapter 3 then discusses alternative LVI approaches for the retention and separation of neutral PFASs along with charged PFASs in clean and complex matrices. Additional demonstrations of alternative LVI techniques for other matrices and analytes are also described, ending with injection and online-dilution strategies that require little to no hardware changes to analyze neutral PFASs in landfill leachate. The practical benefits of the LVI approaches discussed include faster sample preparation times, lower detection limits, and minimal waste generation. Chapter 4 then describes the measurement of PFASs in leachate collected from lab-scale reactors that are operated to simulate the geochemical conditions in landfills and to investigate the processes that control the temporal trends in PFAS composition and concentration in landfills. Four lab-scale reactors were filled with shredded municipal solid waste (MSW) and operated under methanogenic conditions at 37 °C for 273 days. An antibiotic and antimicrobial were added to two of the four reactors to inhibit biological activity. Temporal trends in PFAS concentrations in biologically-active and abiotic (biologically-inactive) reactors were interpreted as resulting from processes including abiotic leaching, MSW substrate degradation, biotransformation, pH, degradation and sorption impacts. At the onset of reactor operation, PFAS concentrations were controlled by abiotic leaching from discarded commercial products and partitioning onto MSW during recirculation of leachate during sampling. Substrate degradation and desorption at a higher pH led to increased concentrations of PFASs with longer chain-lengths within selected PFAS classes. Additionally, biotransformation led to the formation of the 5:3 fluorotelomer carboxylate, the most abundant compound in reactor leachates. Generation of significant concentrations of fluorotelomer carboxylates substantiates the higher concentrations observed in actual landfill leachates and highlights landfill leachates as important point sources of these little-studied PFAS compounds.
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