Impact of ISCO Treatment on PFAA Co-Contaminants at a Former Fire Training Area

408

268

The need for remediation of poly‐ and perfluoroalkyl substances (PFASs) is growing as a result of more regulatory attention to this new class of contaminants with diminishing water quality standards being promulgated, commonly in the parts per trillion range. PFASs comprise >3,000 individual compounds, but the focus of analyses and regulations has generally been PFASs termed perfluoroalkyl acids (PFAAs), which are all extremely persistent, can be highly mobile, and are increasingly being reported to bioaccumulate, with understanding of their toxicology evolving. However, there are thousands of polyfluorinated “PFAA precursors”, which can transform in the environment and in higher organisms to create PFAAs as persistent daughter products. Some PFASs can travel miles from their point of release, as they are mobile and persistent, potentially creating large plumes. The use of a conceptual site model (CSM) to define risks posed by specific PFASs to potential receptors is considered essential. Granular activated carbon (GAC) is commonly used as part of interim remedial measures to treat PFASs present in water. Many alternative treatment technologies are being adapted for PFASs or ingenious solutions developed. The diversity of PFASs commonly associated with use of multiple PFASs in commercial products is not commonly assessed. Remedial technologies, which are adsorptive or destructive, are considered for both soils and waters with challenges to their commercial application outlined. Biological approaches to treat PFASs report biotransformation which creates persistent PFAAs, no PFASs can biodegrade. Water treatment technologies applied ex situ could be used in a treatment train approach, for example, to concentrate PFASs and then destroy them on‐site. Dynamic groundwater recirculation can greatly enhance contaminant mass removal via groundwater pumping. This review of technologies for remediation of PFASs describes that: GAC may be effective for removal of long‐chain PFAAs, but does not perform well on short‐chain PFAAs and its use for removal of precursors is reported to be less effective; Anion‐exchange resins can remove a wider array of long‐ and short‐chain PFAAs, but struggle to treat the shortest chain PFAAs and removal of most PFAA precursors has not been evaluated; Ozofractionation has been applied for PFASs at full scale and shown to be effective for removal of total PFASs; Chemical oxidation has been demonstrated to be potentially applicable for some PFAAs, but when applied in situ there is concern over the formation of shorter chain PFAAs and ongoing rebound from sorbed precursors; Electrochemical oxidation is evolving as a destructive technology for many PFASs, but can create undesirable by‐products such as perchlorate and bromate; Sonolysis has been demonstrated as a potential destructive technology in the laboratory but there are significant challenges when considering scale up; Soils stabilization approaches are evolving and have been used at full scale but performance need to be assessed usin...

Section: Destructive Techniquesmentioning

confidence: 99%

A review of emerging technologies for remediation of PFASs

Ross

McDonough

Miles

et al. 2018

408

268

“…Competitive decomposition of persulfate and/or oxidizing free radical species may be a cause of reduced destruction of PFAS. Experiments performed with combined oxidant systems reported that chemical oxidation of PFAS could be successful when creating complex chemistries that generate various radical species (Eberle et al., ; ISOTEC, ; Kingshott, ; Pancras et al., ; Suthersan et al., ). However, experimental reactors in this study and other studies designed to enhance generation of multiple free radical species, including using more than one activation method for sodium persulfate, observed reduced degradation of PFOA and other PFAS.…”

Section: Discussionmentioning

confidence: 99%

“…Eberle, Ball, and Boving () reported on field and laboratory tests using a proprietary buffered solution of peroxone brand‐named OxyZone ® (a combination of ozone and hydrogen peroxide activated persulfate). The application also included hydroxypropyl‐β‐cyclodextrin, to promote the desorption of chlorinated volatile organic compound co‐contaminants.…”

Section: Chemical Oxidation Of Pfasmentioning

confidence: 99%

“…Eberle, Ball, and Boving (2017) Thermal activation of sodium persulfate Bruton & Sedlak, 2017;Hori et al, 2008;Liu et al, 2012b;Lutze et al, 2017;Park et al, 2016 Photochemical activation of persulfate Hori et. al., 2004;Hori et al, 2005 Peroxone activated persulfate (OxyZone) Eberle et al, 2017 treatability of PFOS and PFOA using a groundwater sample collected from a site where AFFF was historically used. The final pH of the system was 1.99 leading the authors to postulate that neither superoxide radical nor hydroperoxide anion were present in the system due to the pK a for perhydroxyl disassociation to superoxide (Reaction 4).…”

Section: Combination Of Oxidantsmentioning

confidence: 99%

“…The baseline groundwater pH in the field treatment area was acidic (3.5 to 5.8) and following the ISCO treatment the average pH within the treatment area dropped approximately 1 pH unit. As reported byEberle et al (2017), semi-batch laboratory scale studies (1.6 liter vessels) were performed at EnChem Engineering, Inc., including buffering the pH to approximately pH 9 with phosphate and then spiking with PFOS and PFOA. Prior to applying the OxyZone R solution, a mix of oxygen and ozone gas (6 percent ozone) was sparged through the reactor, and when oxidation-reduction potential (ORP) increased to greater than 1,000 mV+, a 3 percent hydrogen peroxide solution was injected every 3 minutes and repeated six times (200 L per injection, equivalent to 8.7 mg hydrogen peroxide…”

mentioning

confidence: 99%

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Technology review and evaluation of different chemical oxidation conditions on treatability of PFAS

Dombrowski¹,

Kakarla²,

Caldicott³

et al. 2018

Per‐ and polyfluoroalkyl substances (PFAS) are a class of stable compounds widely used in diverse applications. These emerging contaminants have unique properties due to carbon–fluorine (C–F) bonds, which are some of the strongest bonds in chemistry. High energy is required to break C–F bonds, which results in this class of compounds being recalcitrant to many degradation processes. Many technologies studied that have shown treatment effectiveness for PFAS cannot be implemented in situ. Chemical oxidation is a demonstrated remediation technology for in situ treatment of a wide range of organic environmental contaminants. An overview of relevant literature is presented, summarizing the use of single or combined reagent chemical oxidation processes that offer insight into oxidation–reduction chemistries potentially capable of PFAS degradation. Based on the observations and results of these studies, bench‐scale treatability tests were designed and performed to establish optimal conditions for the formation of specific free radical species, including superoxide and sulfate radicals, via various combinations of oxidants, catalysts, pH buffers, and heat to assess PFAS treatment by chemical oxidants. The study also suggests the possible abiotic transformations of some PFAS when chemical oxidation is or was used for treatment of primary organic contaminants (e.g., petroleum or chlorinated organic compounds) at a site. The bench‐scale tests utilized field‐collected samples from a firefighter training area. Much of the available data related to chemical oxidation of PFAS has only been reported for one or both of the two more commonly discussed PFAS (perfluorooctane sulfonic acid and/or perfluorooctanoic acid). In contrast, this treatability study evaluates oxidation of a diverse list of PFAS analytes. The results of this study and published literature conclude that heat‐activated persulfate is the oxidation method with the best degradation of PFAS. Limited reduction of reported PFAS concentrations in this study was observed in many oxidation reactors; however, unknown mass of PFAS (such as precursors of perfluoroalkyl acids) that cannot be identified in a field collected sample complicated quantification of how much oxidative destruction of PFAS actually occurred.

Six pilot‐scale studies evaluating the in situ treatment of PFAS in groundwater

McGregor¹

2020

Per‐ and polyfluoroalkyl substances (PFAS) have been identified by many regulatory agencies as emerging contaminants of concern in a variety of media including groundwater. Currently, there are limited technologies available to treat PFAS in groundwater with the most frequently applied approach being extraction (i.e., pump and treat). While this approach can be effective in containing PFAS plumes, previous studies of pump and treat programs have met with limited remedial success. In situ treatment studies of PFAS have been limited to laboratory and a few field studies. Six pilot‐scale field studies were conducted in an unconfined sand aquifer coimpacted by petroleum hydrocarbon along with PFAS to determine if a variety of reagents could be used to attenuate dissolved phase PFAS in the presence of petroleum hydrocarbons. The six reagents consisted of two chemical oxidants, hydrogen peroxide (H2O2) and sodium persulfate (Na2S2O8), and four adsorbents, powdered activated carbon (PAC), colloidal activated carbon (CAC), ion‐exchange resin (IER), and biochar. The reagents were injected using direct push technology in six permeable reactive zone (PRZ) configurations. Groundwater concentrations of various PFAS entering the PRZs ranged up to 24,000 µg/L perfluoropentanoic acid, up to 6,200 µg/L pentafluorobenzoic acid, up to 16,100 µg/L perfluorohexanoic acid, up to 6,080 µg/L perfluoroheptanoic acid, up to 450 µg/L perfluorooctanoic acid, and up to 140 µg/L perfluorononanoic acid. Performance groundwater sampling within and downgradient of the PRZs occurred for up to 18 months using single and multilevel monitoring wells. Results of groundwater sampling indicated that the PFAS were not treated by either the persulfate nor the peroxide and, in some cases, the PFAS increased in concentration immediately following the injection of peroxide and persulfate. Concentrations of PFAS in groundwater sampled within the PAC, CAC, IER, and biochar PRZs immediately after the injection were determined to be less than the method detection limits. Analyses of groundwater samples over the 18‐month monitoring period, indicated that all the PRZs exhibited partial or complete breakthrough of the PFAS over the 18‐month monitoring period, except for the CAC PRZ which showed no PFAS breakthrough. Analysis of cores for the CAC, PAC, and biochar PRZs suggested that the CAC was uniformly distributed within the target injection zone, whereas the PAC and biochar showed preferential injection into a thin coarse‐sand seam. Similarly, analysis of the sand packs of monitoring wells installed before the injection of the CAC, PAC, and biochar indicated that the sand packs of the PAC and biochar preferentially accumulated the reagents compared with the reagent concentrations within the surrounding aquifer by up to 18 times.