Enhanced Adsorption of Perfluoro Alkyl Substances in Groundwater; Development of a Novel In-Situ Groundwater Remediation Method

Abstract

Per- and poly- fluoro alkyl substances (PFAS) are a class of highly persistent, toxic and bio-accumulative anthropogenic chemicals. Due to their wide range of application including non-stick cookware, water and stain resistant coatings, chrome plating and aqueous film forming foams (AFFF), the potential exposure pathways for humans are numerous. AFFF use and subsequent release often leads to groundwater contamination, which poses a risk for human health. Currently, there is a wide array of remediation methods capable of treating PFAS contamination. These pump and treat methods, however, face many limitations including inhibitory costs, harmful byproducts, feasibility and ease of deployment. An in place (in-situ) remediation method holds the advantage of being more cost-effective, easier to deploy and cope with post remediation. Current in-situ PFAS remediation is limited. This thesis explores the amendment of a natural soil by two cationic coagulants (polydiallyldimethylammonium chloride [PDM] and poly(epichlorohydrin-dimethyl) amine [PA]) in order to increase adsorption, and thus retention, of PFAS in groundwater, and possibly sequestering a plume. PFAS adsorption onto natural soil was increased significantly based on batch and column tests. The increase in PFAS adsorption was not due solely to increases in organic matter from the addition of adsorption enhancers. Therefore, the mechanism of PFAS-enhancer interaction was explored. 19Fluorine-NMR spectra indicated that perfluoro carboxylates (PFCAs) were strongly bound in solution when in a solution of PA and PDM. The use of a PFOS ion specific electrode (ISE) found the same result. Given that this is a proposed in-situ remediation method; the long term behavior of PFAS-enhancer binding interactions is an important question that needs answering. Weathering and biodegradation by bacteria native to natural soil were not capable of degrading PA and PDM. However, activated sludge was able to degrade enhancers. There was little PFAS release detected indicating again that PFAS are strongly bound in solution and that this binding interaction potentially reduces bioavailability of enhancers when bound with PFAS.