Low-Cost, Passive In Situ Treatment of PFAS-Impacted Groundwater Using Foam Fractionation In an Air Sparge Trench
Dung Nguyen | CDM Smith
The overarching goal of this project is to demonstrate and validate the use of a novel remedial technology capable of passively treating per- and polyfluoroalkyl substance (PFAS)-impacted groundwater in situ. This project's approach utilizes conventional sparge trench technology coupled with the recent development of foam fractionation technology and foam recovery/reconstitution to remove PFAS from groundwater. The specific demonstration objectives include:
- Confirm PFAS removal from groundwater using the coupled air sparge trench and in situ foam fractionation process;
- Verify the treatment system properly intercepts the target portion of the plume without mounding or flow bypass issues;
- Demonstrate foam recovery;
- Assess PFAS destruction in collected foam fractionates using novel destructive technologies including electrochemical oxidation (ECO) and enhanced contact plasma (ECP); and
- Determine life cycle costs of the treatment approach relative to conventional ex situ extraction and adsorption technologies.
The approach for this project employs the use of a conventional air sparge trench to intercept a shallow PFAS-impacted groundwater plume, which is often observed emanating from former fire training areas that employed the use of aqueous film forming foam (AFFF). For PFAS, the sparging bubbles provide a high air-water interfacial area that facilitates “stripping” of the surface-active PFAS from the groundwater. This sparging process results in formation of a foam on the water surface, which can be subsequently removed via a vacuum and/or skimming system, resulting in orders of magnitude decreases in bulk groundwater PFAS concentrations. This PFAS removal process has been well demonstrated, including in an ex situ field-scale foam fractionation system. PFAS concentration factors are typically in the range of 1-L of reconstituted foam to 5000-L of groundwater. This low volume, high concentration recovered PFAS can then be treated via conventional high temperature incineration, or treated via promising technologies such as ECO and ECP. The treatment approach has the potential to treat PFAS-impacted groundwater in situ, passively, and economically with very little energy consumption, waste generation, and little to no chemical additives.
Passive and in situ PFAS treatment approaches have yet to be demonstrated at the field-scale settings. Currently available ex situ treatment approaches involving groundwater extraction and conventional sorption-based treatment of the extracted groundwater are generally inadequate in removing residual PFAS from AFFF-impacted groundwater, require extensive above- and under-ground infrastructure, and generate a large volume of PFAS-impacted waste that also requires disposal or treatment. On the contrary, the approach of using in situ foam fractionation technology in a conventional air sparge trench has the potential for rapidly removing PFAS from impacted groundwater in situ in a passive, economical, low-energy, and sustainable manner. With proper optimization, it is foreseeable that the approach can be scaled up and implemented at multiple Department of Defense installations at a fraction of the life-cycle cost of conventional ex situ treatment and including on-site PFAS destruction in the very near future. (Anticipated project completion - 2024)