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Final Report: Electrochemical Extraction and Remediation of PFAS in Soils

EPA Contract Number: 68HERD19C0023
Title: Electrochemical Extraction and Remediation of PFAS in Soils
Investigators: Lee, Katherine
Small Business: Faraday Technology, Inc.
EPA Contact: Richards, April
Phase: I
Project Period: May 1, 2019 through October 31, 2019
Project Amount: $100,000
RFA: Small Business Innovation Research (SBIR) - Phase I (2019) RFA Text |  Recipients Lists
Research Category: Small Business Innovation Research (SBIR): Phase 1 (2019) , Small Business Innovation Research (SBIR) , SBIR - Cleanup of Contaminated Sediments

Description:

The purpose of the research conducted in this program was to demonstrate the feasibility of two technologies in tandem for remediation of per-/polyfluorinated alkyl species (PFAS) in soils/groundwater: electrokinetically-induced transport for concentration/extraction of PFAS, and pulsed-waveform FARADAYIC® ElectroCatalysis for destruction of PFAS. PFAS are used across a broad range of industries for a wide variety of applications, including carpeting, apparel, upholstery, metal plating and firefighting foams. However, research has demonstrated that these compounds are highly refractory and bio-accumulative when released to the environment, and have the potential to cause adverse health effects, such as low birth weight, accelerated puberty, cancer, and skeletal, liver, kidney and other problems. The technologies at the focus of this program are needed due the presence of PFAS soil/groundwater contamination at various sites around the Nation, and the current complete lack of effective, cost-efficient remediation methodologies. Electrokinetic methods are well validated for remediation of other soil contaminants, and the use of pulsed FARADAYIC® waveforms for electrocatalytic destruction of PFAS was anticipated to provide significant techno-economic improvements due to the finer control afforded over mass transport of the PFAS to the catalytic electrodes.
 
In this Phase I SBIR program, Faraday Technology and our collaborators at Terran Corporation implemented electrokinetic PFAS extraction tests under direct-current waveform conditions, and FARADAYIC® ElectroCatalysis in two electroreactor form factors, a custom beaker-scale stirred configuration and a commercial flow-through configuration. Electrokinetic tests were performed with three soil materials: sand, kaolin clay and local Dayton, OH till, with injection of a spike of perfluorooctanesulfonate (PFOS, a representative PFAS) in the center of the electrokinetic cell at the outset of each test.  Soil samples were extracted and sent for EPA-standard LC-MS analysis to evaluate the direction and magnitude of electrokinetic PFOS transport.
 
FARADAYIC® ElectroCatalysis tests were performed with multiple anode electrocatalyst materials (nickel, titanium, boron-doped diamond) at the beaker scale, and at the bench scale with a flow reactor procured from vendor Element Six Technologies (Santa Clara, CA), a potential commercialization partner. This reactor was equipped with a four-cell stack of monolithic boron-doped diamond electrodes. In order to reduce the complexity of the experimental work in this Phase I program, PFOS was selected as a model compound for study.  Work in a synergistic program (USEPA 68HERD-19-C-0011) provided reference data for PFOS destruction by FARADAYIC® ElectroCatalysis in a monopotassium phosphate electrolyte, which was compared to the destruction performance observed in this program with a simulated soil-derived electrolyte (containing CaCl2, MgCl2, KCl, Na2SO4, KH2PO4, NaH2PO4, NaNO3, and NaCl).  While the actual composition of a true soil-derived electrolyte will almost certain vary appreciably from that used here, these tests allowed investigation of the efficacy of FARADAYIC® ElectroCatalysis in the presence of a combination of relevant ions.  The extent of FARADAYIC® ElectroCatalysis destruction of PFOS was evaluated by two methods, (i) accumulation of the fluoride ion byproduct via ion-specific electrode (ISE) and (ii) standardized LC-MS analysis, via a Modified EPA 537 method. The fluoride ISE provides a semi-quantitative but extremely rapid analytical method, which was used for initial screening of anode electrocatalysts and FARADAYIC® ElectroCatalysis operating parameters.  Results from selected FARADAYIC® ElectroCatalysis tests were confirmed via subcontracting the fully quantitative LC-MS method to a third-party vendor.
 
The electrokinetic and FARADAYIC® ElectroCatalysis experimental data were used in combination with Terran Corp. data from prior activities relating to electrokinetic soil remediation to develop capital and operating expense estimates for tandem electrokinetic/FARADAYIC® ElectroCatalysis remediation of two hypothetical sites, one representing a diffuse PFAS contamination (700 ppt) across a larger volume (2 acres, 50 ft depth) and one representing a more-concentrated PFAS presence (10 ppb) in a smaller volume (0.5 acres, 10 ft depth). The scales of these two hypothetical sites were selected based upon literature data for recent soil/groundwater remediation activities focused on other contaminants, as minimal data on PFAS site remediation is yet available.

Summary/Accomplishments (Outputs/Outcomes):

The electrokinetics tests in the three soil types yielded data strongly suggesting that the two modes of electrokinetic transport, electromigration and electroosmosis, operate in opposite directions on PFOS (moving it toward the anode and cathode, respectively) and are nearly balanced in magnitude, leading to approximately zero net PFOS transport for the simple electrokinetics configuration tested.  Various approaches are available that should disrupt the balance of the two effects (e.g., introduction of cations likely to ion-pair with PFOS/PFAS, changing its electromigration properties; or, introduction of biodegradable cationic surface-active species to diminish or reverse the negative polarization of the soil particle surfaces. Work in the follow-on Phase II program will focus on identifying suitable adaptations of the electrokinetic technology to enable net transport of PFOS/PFAS.
 
The FARADAYIC® ElectroCatalysis tests revealed that, of the materials tested, the boron-doped-diamond (BDD) catalyst yielded markedly superior performance. Both BDD-equipped reactors (beaker-scale stirred and bench-scale flow configurations) demonstrated significant PFOS destruction within one hour of processing in multiple tests as inferred from adjusted fluoride ISE measurements, with the best-performing test in the flow reactor exhibiting an inferred 95% destruction of PFOS. The pulsed-waveform FARADAYIC® ElectroCatalysis destruction process exhibited favorable technoeconomic performance when operated with waveform parameters identified as preliminarily optimal, with best-performing specific energy inputs per log-reduction in PFOS of 5-6 kWh/m3-log (competitive with best-performing catalysts from literature) and area-normalized heterogeneous first-order destruction rate constants of 7.3-9.3 × 10-4 m/s (superior to best-performing catalyst/reactor configurations by approximately one order of magnitude).

Conclusions:

Based on the Phase I data and analysis, Faraday anticipates that the combination of electrokinetic methods for extraction of PFAS from soils and pulsed FARADAYIC® ElectroCatalysis for destruction of these PFAS embodies a revolutionary, novel capability for PFAS remediation in soils. The PFAS destruction technology based on FARADAYIC® ElectroCatalysis is compact, significantly more energy- and cost-efficient than the majority of competitor technologies, and can be adapted directly into electrokinetic apparatus in a variety of configurations. More work is required in order to establish specific operating parameters for both the electrokinetics and FARADAYIC® ElectroCatalysis technology components, and to demonstrate the tandem technologies in contexts of interest to Phase II/III commercialization partner(s), as part of a larger-scale demonstration of the technology.

Terran Corp. has executed multiple projects for soil remediation using its electrokinetics technology, and the associated costs are well known and reasonable.  The economic analysis performed as part of this Phase I SBIR program strongly supports the relevance of the FARADAYIC® ElectroCatalysis approach as an augmentation to electrokinetic PFAS extraction providing efficient, cost-effective PFAS destruction. For two hypothetical soil remediation case studies subjected to cost analysis, the 20-year annualized costs to reduce PFAS levels to below the 70-ppt EPA Lifetime Health Advisory limit seem reasonable for typical remediation applications.  The intrinsically scalable nature of electrochemical hardware makes it highly likely that both larger- and smaller-scale applications would also find the technology economically appealing. Discussions with our commercialization partners [Fraunhofer USA Center for Coatings and Diamond Technologies (East Lansing, MI), U.S. Ecology (Livonia, MI), Jacobs Engineering (Dallas, TX), Coventya (Brooklyn Heights, OH), and CONDIAS (Itzehoe, Germany)] all support the appeal of the tandem electrokinetic extraction and FARADAYIC® ElectroCatalysis technologies as a cost-effective, efficient, scalable technology solution for the remediation of PFAS in soils.

SBIR Phase II:

Electrochemical Extraction and Remediation of PFAS in Soils  | Final Report

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