Sonochemical degradation of perfluorooctane sulfonate and perfluorooctanoate in groundwater

Abstract

Ultrasonic irradn. has been shown to effectively degrade perfluorinated chems. (PFCs) such as perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) in aq. soln. Reduced PFC sonochem. degrdn. rates in org.-rich groundwater taken from beneath a landfill, however, testify to the neg. kinetic effects of the org. groundwater constituents. In this study, the PFOX (X = S or A) sonochem. degrdn. rates in a groundwater sample with org. concns. 10 times lower than those in the groundwater taken from beneath a landfill are found to be 29.7% and 20.5% lower, resp., than the rates in MilliQ water, suggesting that inorg. groundwater constituents also neg. affect PFC sonochem. kinetics. To det. the source of the groundwater matrix effects, we evaluate the effects of various inorg. species on PFOX sonochem. kinetics. Anions over the concn. range of 1 to 10 mM have dissimilar effects on the sonochem. degrdn. rates of PFOX that follow the Hofmeister series. In contrast, the presence of 5 mM of various cations has negligible effects. Initial soln. pH enhances the degrdn. rates of PFOX at 3, but has negligible effects over the range of 4 to 11. The obsd. inorg. effects on sonochem. kinetics are hypothesized to be due to ions' partitioning to and interaction with the bubble-water interface. Finally, it is shown that the rate redn. in the groundwater is primarily due to the presence of bicarbonate and thus can be fully rectified by pH adjustment prior to sonolysis.