Theme: 07. Per- and Polyfluorinated Alkyl Substances (PFAS)

Topic Area: 7p. PFAS: Groundwater Treatment Case Studies

Formatted Title:

A Successful Case of In Situ Electrochemical Nanoremediation for PFAS-Contaminated Groundwater

Background/Objectives:

The unique stability and surfactant properties of PFAS in combination with its extensive industrial adoption have created an environmental remediation challenge. With an increasingly stringent regulatory landscape, combined with social and environmental awareness, priority has shifted towards in situ immobilization, removal, and destruction in support of traditional and ex situ PFAS technologies. With a focus on potable and groundwater, effective in situ technologies will support the pragmatic risk-based combination of synergetic approaches required.

The following abstract delineates a successful application of one such emerging in situ solution within a contaminated aquifer hotspot. The global first field application of electrochemical nanoremediation of PFAS was delivered with the support of the Australian Government Department of Defence with the objective to empirically demonstrate the technology’s efficiency in achieving mass reduction in concentration and flux of PFAS contaminated groundwater. The successful operation of this pilot project has provided a platform for further investigation and research in soil documented below, in addition to constitute scaled-up opportunities in groundwater remediation.

The Australian field trial was positioned within PFAS contamination hotspot in a historic firefighting training facility. The reactive trial area features an upper aquifer into which in situ electrochemical nanoremediation was applied. The site is situated within a highly sensitive geographic location, with documented influence on nearby communities. The site owner has diligently undertaken an extensive remediation options and action plan and continues to engage community stakeholders, supporting the application of proven technology and this emerging in situ electrochemical approach.

The project aim was to confirm the applicability of electrochemical nanoremediation (ECNR) to reduce the concentration and mass of PFAS present in the aquifer groundwater and to prevent further migration of PFAS contaminated groundwater from this hotspot. The collected data from both sampling and ongoing real-time monitoring was used to assess the efficacy of the technology, characterized by physical and chemical trial observations. These findings form lessons learned and provided critical foundations for engineering optimisation and future scaling activities. The project was designed to address data gaps and verify process assumptions. Verification that environmental controls performed as designed was critical to address within the project scope.

Approach/Activities:

The project involved installing and subsequently operating 10 groundwater monitoring and injection wells at 4 m depth, a DC-powered system comprising 49 powered electrodes, 203 monitoring electrodes, and an autonomous water sampling and analysis system. In the 7 by 7 m reactive trial site, through the wells installed in the upper aquifer, a liquid suspension including zero valent iron was injected into the groundwater. Low direct current and voltage applied to the application electrodes, supported a voltage differential between an anode and cathode. Within the trial-specific and identified groundwater conditions, PFAS compounds underwent reduction reactions (forming complexes with nZVI), while iron particles and the electrodes were oxidized within the treatment area.

The technology efficiency was measured empirically through concentration reductions of PFAS in the groundwater (total and individual analytes) and physicochemical parameters in soil and water. Concentrations prior to the injection, during, and at the completion of the sampling analysis quality plan (SAQP) were compared, analyzed, and modelled through standard data analytical procedures including principal component analysis and least squares regression modelling. All data were compared to initial laboratory reactor testing and has subsequently been developed in further reactor studies in soil and water.

Additional investigative enquiries assessed the potential for phase change, partitioning and PFAS soil concentrations and have reconfirmed the absence of precursor and intermediate species, verifying (where practicable) byproducts, volatile compounds, and potentially more harmful byproducts.

Results/Lessons Learned:

Under strict sampling and analysis quality criteria, and across the reactive site area, an average concentration reduction of 79% was documented. This included hydraulically disconnected wells, and locations with inadequate applied voltage due to design and corrosion. Aquifer locations that reflected a more optimum influence of direct current and nano zero-valent iron (nZVI) suspension, delivered an average PFAS concentration reduction of 95% across the trial duration, from an average of 42.65 µg/L to 2.15 µg/L. PFAS mass concentration reduction of up to 100% at specific well locations was detected and represented the lowest concentrations recorded over the sampling regime. The treatment efficiency which can be support by of grid photovoltaic capability was low at 75W-h/L.

Separate from the concentration reduction delivered, compliance with drinking and recreational water standards was made with reference to the Australian EPA Version 3.0 (Draft) PFAS National Environmental Management Plan. The reactive site area for PFOA all complied with the 0.56 µg/L drinking water guideline concentration value. PFOS & PFHxS concentrations significantly reduced towards the 2.0 µg/L recreational water guideline levels.

An analogous reduction in mass flux off the site was noted at the control downstream well displaying a similar 72% mass concentration reduction. The upstream control well 243 µg/L remained consistent during the trial operation.

No related PFAS byproducts of degradation were noted through water quality sampling and discrete analysis. Statistically significant positive correlations for all PFAS species were observed. Additional laboratory reactor testing was undertaken in late 2022 to further define the PFAS migration mechanisms, quantify degradation products, and to support technical conclusions. These results displayed a similar 93% concentration reduction in a single closed reactor test with direct current and zero valent iron. These tests reinforced the safety of the solution technology with no evidence of the formation of short more hydrophilic species. Reactor mass balances showed no evidence of soil or solid adsorption or volatile production. The comparison of soil samples obtained before and after the trial, present preliminary data of PFAS mass reduction in accordance with the research of (Ganbat, et al., 2022). This finding has prompted further study into the feasibility and upscaling of Photon’s patented PFAS electrochemical nanoremediation solution in in situ and ex situ PFAS contaminated soil application.

Development of further groundwater remediation projects within the Australian Government Department of Defence and Australian Airservices are currently underway. At the time of writing, a proposal for an in situ electrochemical nanoremediation is being explored with the United Kingdom Environment Agency and CLAIRE in the context of a current zero valent iron moratorium in place. Key collaborative partnerships and business development activities with American Certified Womens Business Enterprise, Brownfield Science & Technology Inc (BTSI) are currently underway to identify an applicable pilot project for application within the US in early 2024. These case studies may supplement this submission by Q2-2024.

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Jaroslav Nosek