Low-Cost, Passive In Situ Treatment of PFAS-Impacted Groundwater Using Foam Fractionation in an Air Sparge Trench
Dung "Zoom" Nguyen, Chemical and Environmental Engineer, CDM Smith, Inc.
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. Our proposed approach employs the use of a conventional air sparge trench to intercept a shallow PFAS contaminated groundwater plume, which is often observed emanating from former fire training areas that employed the use of 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. Typical 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 waste can then be treated via conventional high temperature incineration, or treated via promising technologies such as electrochemical oxidation (ECO) and enhanced contact plasma (ECP). The proposed 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. With proper optimization, it is foreseeable that the proposed approach can be scaled up and implemented at multiple DoD installations at a fraction of the life-cycle cost of conventional ex situ treatment and including onsite PFAS destruction in the very near future.
Zoom Nguyen is a chemical and environmental engineer from the CDM Smith Bellevue, Washington office with 13 years of experience in bench-, pilot-, and full-scale design and implementation of in situ and ex situ soil and groundwater treatment systems. Zoom also serves as the manager of CDM Smith’s Research and Testing Laboratory where he leads design support treatability studies and innovative research and development work on fate and transport, and treatment of traditional and emerging contaminants including PFAS. He has served as the principal investigator or the co-principal investigator for a number of SERDP and ESTCP projects.