Development of a Novel Perfluoroalkyl Substance Sequestration Scheme Using Alginate Macrobeads and Common Water Treatment Polymers

Abstract

Groundwater contamination by perfluoroalkyl substances (PFASs) is a topic of growing concern. Preventing transport via sorption-enhancement to aquifer material is a potential solution to this problem. Two models of osmotic surgical implant pumps were used to demonstrate that the cationic polymers poly(diallyldimethylammonium chloride) (polyDADMAC) and epichlorhydrin dimethylamine (EpiDMA) could be reliably and passively delivered to promote sequestration of PFASs. It was found that pumps behaved as expected with one failure near the end of pump lifespan. Next, alginate was investigated as an encapsulation media for EpiDMA and polyDADMAC to develop a bead-like vector for delivery of these compounds in a time release manner. Bead experiments examined alginate synthesis concentration, membrane thickness, and alginate composition. Synthesis concentration had no effect on mass transfer. Beads synthesized with greater membrane thickness may be characterized by slower polymer release, and alternative alginate composition results were promising. A loss on ignition scheme was also used to evaluate the effectiveness of polyDADMAC as a sorption enhancer for the PFASs perfluoroctanesulfonate (PFOS), perfluorooctanoate (PFOA), and perfluorononanoate (PFNA) and to elucidate potential removal mechanisms. In all cases, sorption of compounds increased beyond what can be explained by hydrophobic partitioning indicating the presence of coulombic attraction between the contaminant and cationic polymer. Finally, sand and soil column studies were used to assess the behavior of beads containing polyDADMAC and the transport potential of PFOS in a dynamic environment with sorption enhancer present. PolyDADMAC exhibited little retention on Ottawa sand but significant retention on soil excavated from Tinker Air Force Base. Polymer retention, however, was less than indicated by batch studies and is likely inhibited by steric and kinetic factors.