Molecular Design of Effective and Versatile Adsorbents for Ex Situ Treatment of AFFF-Impacted Groundwater

Mandy Michalsen | U.S. Army Corps of Engineers



Per- and polyfluorinated alkyl substances (PFASs) are a diverse group of chemicals that have been used as components of aqueous film-forming foam (AFFF) for decades. Early formulations used PFOS in large proportion. Unfortunately, long-chain PFASs like PFOS have since been found to be bioaccumulative and toxic, prompting voluntary phase-outs, a recent establishment of drinking water guidelines by the U.S. EPA, and the need to remediate contaminated water for the protection of environmental and human health. Areas where AFFF was routinely deployed during firefighting exercises, including DoD sites, have accumulated a variety of PFASs in their groundwater and are now in need of cost effective remediation solutions. Many PFASs eventually degrade to form perfluorinated alkyl acids, which are extremely persistent and have varying levels of water solubility. Due to this, ex situ treatment technologies may be most suitable. However, currently available technologies such as adsorption with granular activated carbon (GAC) cannot effectively treat both short- and long-chain PFASs.

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Cartoon of PFOA sorbed to Liver Fatty Acid Binding Protein

This proof-of-concept project will address this gap by exploiting the propensity of PFASs to bind with proteins, and use a combination of molecular modeling and batch testing to explore whether PFAS-protein interactions can be tuned to efficiently adsorb a variety of PFASs. Researchers will achieve this through the following objectives:

  1. identification of candidate proteins based on reported interactions with PFASs and/or fatty acids;
  2. molecular modeling of protein-PFAS interaction to rank identified proteins by their interaction strength with targeted PFASs; and
  3. batch testing of most promising PFAS-protein pairs to evaluate their effectiveness as models for ex situ adsorbents, and taking presence of common co-contaminants (e.g. chlorinated solvents) into account.

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Technical Approach

Candidate proteins to serve as templates for bio-based sorbents will be identified from existing literature based on interactions with PFASs or with analogous ligands such as fatty acids and acidic drugs. Their affinity for a set of eight selected perfluorinated alkyl acids — PFOS, perfluorononanoic acid (PFNA), PFOA, perfluorohexane sulfonic acid (PFHxS), perfluoroheptanoic acid (PFHpA), perfluorohexanoic acid (PFHxA), perfluorobutane sulfonate (PFBS), and perfluorobutanoic acid (PFBA) — will be predicted using a multi-step molecular modeling framework. Finally, the most promising proteins will be experimentally evaluated for PFAS adsorption through a series of batch tests at the bench scale, using equilibrium dialysis (EqD) to measure a suite of sorption parameters alone and in the presence of co-contaminants. The range of PFAS concentrations and water chemistries used in these batch experiments will allow accurate estimation of binding affinity and provide information on how selected proteins may respond to concentrations and conditions (e.g. pH, ionic strength) relevant for actual DoD site groundwater conditions. Researchers envision an expanded follow-on effort to test the scale-up potential and commercial viability of this approach through systematic evaluation of novel bio-based sorbent molecules immobilized onto robust support sorbents (e.g., activated carbon, nanoclays) for field deployment.

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Dissociation contant (KD) measured directly using EqD techniques

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This project has the potential to open an entirely new area of sorbent design for PFAS remediation. Of particular benefit is the ability to tune an adsorbent, by incorporating multiple protein-based moieties, to address a wide variety of PFAS structures. The combination of molecular modeling and batch testing in this project could form the basis of a robust and powerful design framework for remediation technology. An additional benefit of this approach is that it will rely on a benign (protein-based) substance to remove AFFF contaminants without introducing additional harmful substances (e.g. harsh oxidants) into the environment.

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Points of Contact

Principal Investigator

Dr. Mandy Michalsen

U.S. Army Corps of Engineers

Phone: 206-764-3324

Fax: 206-764-3706

Principal Investigator

Dr. Jennifer Field

Oregon State University

Phone: 541-737-2265

Fax: 541-737-0497

Principal Investigator

Dr. Carla Ng

University of Pittsburgh

Phone: 412-383-4075

Program Manager

Environmental Restoration