Per- and polyfluoroalkyl substances (PFASs) have permeated our minds with the recent discoveries that they are not only persistent, bioaccumulative, and toxic—as perfluorooctanesulfonic acid and perfluorooctanoic acid (PFOS and PFOA) are well-known to be—but also that many in this class are ubiquitous in the environment, water sources, and human serum. Although there are various studies reporting on improved analytical techniques, lab-scale removal efficiencies, and transformation and adsorption mechanisms of various PFASs, there are few studies looking at actual remediation of PFAS plumes. Such an undertaking entails testing the effectiveness of transformation techniques as well as addressing engineering and logistical challenges involved in implementation. In this talk, I will discuss a collaborative demonstration project at a naval air station (NAS) in Jacksonville, Florida with UC Berkeley, SERDP/ESTCP, and Geosyntec, where we are testing heat-activated persulfate in situ chemical oxidation (ISCO) coupled with ex situ adsorption to both transform PFCAs and their precursors, and to remove PFSAs, respectively. Heat-activated persulfate creates highly reactive sulfate radicals that can effectively transform PFCAs. These radicals, however, can be scavenged by aquifer constituents when the persulfate is injected into the aquifer for ISCO. Based on previous work done in our lab, we established this site as promising for persulfate chemical oxidation based on its low buffering capacity and chloride concentrations. PFASs at the NAS include approximately 2.5 uM PFCAs and 4.5 uM PFSAs, as measured by the total-oxidizable precursor (TOP) assay. We explored practical methods for heat-activating the persulfate in the field site as well as overcoming any radical scavenging that may occur in the aquifer. We evaluated a five-day peroxide pretreatment (0.01-12% by mass) with the dual effect of heating the groundwater during the decomposition of hydrogen peroxide and to oxidize organic constituents with the hydroxyl radicals formed. We then tested several ratios of peroxide to persulfate needed to completely transform PFOA and its transformation products. We found that a 12% peroxide pretreatment step coupled with a weekly dosing of high concentration persulfate achieved successful transformation of PFCAs. The Jacksonville demonstration will begin in the spring, testing the application of this process coupled with granular activated carbon adsorption to remove PFSAs.

Field demonstration design of heat-activated persulfate in situ chemical oxidation (ISCO) of PFASs in Jacksonville, FL

2019 Spring National Meeting

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