APTIM’S Research and Development Efforts Focus on PFAS Treatment

For those of you unfamiliar with BDAG, the group consists of 11 scientists and engineers housed in a 17,000 sq. ft. laboratory and pilot plant facility. The core mission of BDAG is to conduct “flask to field” research on treatment of pollutants and to provide technical assistance to projects within both the commercial and federal sectors. BDAG is also the largest producer of bioremediation cultures in the industry, an example of successful commercialization of previous research efforts. Our primary focus has been on emerging contaminants. Today, PFAS clearly tops the list of those contaminants.

Current Treatment Approaches. PFAS represent a wide range (thousands) of fluorinated compounds with a multitude of uses, the most significant of which is their presence in aqueous film forming foams (AFFF). These foams have been used for decades for fire training and firefighting activities. The chemical nature of many PFAS in AFFF makes them recalcitrant to typical biological and abiotic treatment approaches (e.g., bioremediation, chemical oxidation, chemical reduction) and very mobile, resulting in large dilute plumes emanating from AFFF source areas. Of the thousands of different PFAS, only a few such as perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS), have garnered significant regulatory attention to date. However, based on current toxicological evidence, concentrations of these compounds in the part-per-trillion (ng/L) range are likely to be of regulatory concern, showing the potentially enormous scope of this problem. Over the past several years, the primary means to remove PFAS from water sources has been pump-and-treat (P&T) through adsorptive media, primarily granular activated carbon (GAC) or, more recently, ion exchange (IX) resin. Often, vessels of GAC or IX resin have been added to existing P&T systems designed for chlorinated solvents after PFAS was discovered in the solvent plume. APTIM has designed and built several GAC-based systems for removing PFAS from groundwater and drinking water.

APTIM PFAS Research and Development

Ex Situ Treatment. There are clearly a wide range of research needs surrounding PFAS treatment. With respect to ex situ treatment, current approaches (largely P&T with GAC or IX as noted) are not destructive, but rather result in media with adsorbed PFAS that require disposal and/or further treatment. Additionally, while IX resin has far greater sorptive capacity than GAC for most PFAS, it is also more expensive, so reducing the cost of this approach is important. One clear research need is to develop destructive approaches for PFAS in general, and specifically for PFAS adsorbed to GAC or IX resin.

APTIM scientist Mark Fuller has been leading an effort with Temple University and Purolite (IX resin manufacturer) to test new IX resins for PFAS treatment, to develop approaches to regenerate those resins for reuse, and to destroy PFAS in the regenerant solution(s). The project team has been evaluating sonochemical and electrochemical treatment of PFAS in the regenerant solutions, each of which has been showing promise. This project, which is funded through the DoD Strategic Environmental Research and Development Program (SERDP) (https://www.serdp-estcp.org/) will culminate in a field demonstration at the former Willow Grove Naval Air Station (PA) in 2021. In addition to GAC and IX sorbents, alternative media for PFAS sorption are of broad interest. An exploratory project led by APTIM engineer Paul Koster van Groos in collaboration with the University of Waterloo (Canada) was recently selected by SERDP to explore use of layered double hydroxide (LDH; i.e., “anionic clay”) materials for PFAS sorption. This project will begin in mid-2021.

An alternative approach widely used in the past to destroy PFAS sorbed to GAC, IX resin or other solid media is high temperature thermal treatment. However, in recent years, questions have arisen concerning the conditions necessary for thermal PFAS destruction (e.g., temperatures required, residence times) as well as the potential products emitted to the air. While these questions remain unresolved, use of thermal treatment for PFAS is increasingly being restricted. Paul Koster van Groos received a SERDP exploratory grant in 2018 to assess small-scale thermal treatment of PFAS in investigation derived wastes (e.g., drilling spoils). His initial studies showed that calcium hydroxide addition lowered PFAS thermal decomposition temperatures and reduced emissions of volatile organic fluorine (VOF) gases. However, the study also confirmed that there is a large data gap in our understanding of VOF species in off gas from thermal treatment processes as well as our ability to measure these species. APTIM submitted a SERDP proposal with scientists from Pacific Northwest National Labs (PNNL) in 2020 to specifically address these data gaps. This project, which was selected for award in 2021, will assess the ability of a number of different amendments to lower PFAS decomposition temperatures and will utilize state-of-the art infrared spectroscopic analysis (conducted at PNNL) to identify volatile species potentially emitted from the process. These studies are important for understanding the potential impacts of thermal treatment approaches for PFAS, as well as improving its safety and efficiency.

In Situ Treatment. Another critical research need with PFAS is the development of effective technologies for in situ treatment in groundwater. As noted in the introduction, PFAS are resistant to most traditional treatment approaches, such as chemical oxidation or bioremediation. Many different scientists are trying to develop approaches for destroying PFAS in groundwater, but to date, no approach has proven to be being both effective and practical. One alternative approach to this problem is to greatly enhance the adsorption of PFAS in situ to retard their transport toward new receptors. My own research in this area, in conjunction with geologist Dave Lippincott and engineer Graig Lavorgna of APTIM, concerns the application of colloidal activated carbon (CAC) in groundwater aquifers to immobilize PFAS in the presence or absence of co-contaminants such as chlorinated solvents. Separate research projects have been awarded to APTIM by both the Navy Environmental Sustainability Development Integration Program (NESDI) and the Environmental Security Technology Certification Program (ESTCP) to field test different applications of this approach. Along the same vein, Dave Lippincott received a recent award from ESTCP to develop a funnel-and-gate approach with an adsorptive IX barrier to remove PFAS from groundwater. This novel approach uses an in situ sheet-pile barrier to “funnel” groundwater through a small area that contains IX resin, subsequently cleaning the groundwater as it passes. The IX resin can be removed and replaced when PFAS breaks through the barrier. These three projects are in early phases of execution, with field trials set to commence in late 2021 through early 2022.

Fate and Transport. The behavior of PFAS in unsaturated and saturated environments is proving to be unlike most traditional contaminants (e.g., chlorinated solvents) and very hard to predict. In order to improve our understanding in this area, APTIM scientists are participating in two separate research projects. The objective of the first project, funded by ESTCP, is to develop better insight concerning the fate of PFAS in AFFF source areas. The particular focus is on the distribution and sorption of PFAS in vadose (unsaturated) soils at AFFF sites and the extent to which they mobilize to groundwater during recharge events. APTIM’s Dave Lippincott and Graig Lavorgna installed a highly instrumented study cell in an AFFF source area at Joint Base McGuire-Dix-Lakehurst (NJ) and collected pore water and groundwater samples before and after artificial rainfall events. The project data indicated that many PFAS are highly adsorbed near the ground surface (top few feet) but will desorb and move to groundwater during rainfall events. Importantly, the data suggest that these AFFF source areas will contribute to groundwater contamination with PFAS for decades to come. A second ESTCP project, which was selected for award in 2021, will evaluate the distribution of PFAS in groundwater and lake sediments using a high-resolution passive profiler (HRPP) developed at Texas Tech University (TTU). The team of APTIM and TTU has previously developed and field-tested similar devices for evaluating the distribution of other contaminants such as chlorinated solvents and metals in aquifers and sediments. This project will expand the utility of the HRPP as well as our understanding of the fate and transport of PFAS in the environment.

Final thoughts. Over my 25-year career in environmental R&D, there have been a wide variety of different contaminants that have taken the research spotlight for a period of time, some longer than others. These include chlorinated solvents, traditional and insensitive munitions compounds, methyl tert-butyl ether (MTBE), ethylene dibromide (EDB), 1,4-dioxane, and perchlorate among others. Universally, new solutions have been developed to address these contaminants, and APTIM scientists have played a role in the advancing these solutions. PFAS represent a unique challenge for many reasons, not the least of which is their diverse nature (thousands of individual compounds), recalcitrance, analytical challenges, overall ubiquity and exceedingly low regulatory levels. This is going to be a long haul! However, I am confident that solutions to this issue will be developed with time and that APTIM scientists will take a leading role in this area. The large number of current APTIM R&D projects shows our commitment to this end.