Research Abstract

Poly- and perfluoroalkyl substances (PFAS) are a large group of organic contaminants that have been detected nationally in the aquatic environment. Two eight-carbon PFAS compounds, perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS), have been observed in >95% of the blood samples collected during multiple U.S. national surveys at health-relevant concentrations. Contaminated drinking water is a major source exposure to PFAS for the general public.

In a previous ND WRRI-supported project (to another graduate student), we have identified PFAS in the Red River that is the drinking-water source of the city of Grand Forks. The goal of this project is to develop an innovative treatment system that can effectively and practically remove PFAS from water. The results of this project have important implications for technological improvements in water purification. Water treatment plants, the water industry, water resources personnel, and the broader education and research communities who are concerned about PFAS contamination would benefit from the results of this proposal.

Research Highlights

To get a better understanding of PFAS decomposition, we studied five perfluoroalkyl carboxylic acids (PFCAs) and one perfluoroalkyl ether carboxylic acid (PFECA) in three different conditions (PFAS only, PFAS with GAC, and PFAS adsorbed on GAC) in a closed system. We found that the destabilization of studied compounds during thermal treatment followed the first-order kinetics. The temperature needed for thermally desta-bilizing PFCAs increased with the number of perfluorinated carbons (nCF2) when PFAS were adsorbed on to GAC. Decomposition of PFCAs such as perfluorooctanoic acid (PFOA) on GAC initiated at temperatures as low as 200 °C. The PFECA was even more readily decomposed than PFCA with the same nCF2. The degradation temperature of PFAS decreased with the presence of GAC and on PFAS laden GAC compared to its absence. In addition to the volatile organofluorine species identified in previous studies, we found evidence for the formation and then decomposition of short-chain compounds during thermal degradation of four PFCAs. Efficient mineralization to fluoride ions (>80%) of PFOA and PFOS on GAC occurred at 700 °C or higher, accompanied by near complete PFOA and PFOS decomposition (>99.9%). Thermal decomposition pathways of PFOA were proposed. We have also identified that ammonium acetate is the most suitable amendment for methanol to achieve higher PFAS extraction efficiencies. Orga-nofluorine and short-chain compounds generated from thermal decomposition of PFAS at low to moderate temperatures (≤600 °C) warrant studies on the exposure to these compounds during cooking, baking, firefighting, and other relevant thermal processes involving PFAS.