Remediation of Per- and Polyfluoroalkyl Contaminated Groundwater Using Cationic Hydrophobic Polymers as Ultra-High Affinity Sorbents

Reyes Sierra-Alvarez | University of Arizona

ER18-1052

Objective

Per‐ and polyfluoroalkyl substances (PFASs) such as PFOS and PFOA are persistent pollutants present in the subsurface at many DoD facilities, often due to the past use of aqueous film‐forming foam (AFFF) in firefighting. PFASs pose a human health threat, necessitating feasible technologies for their removal. At present, ex situ treatment of groundwater by granular activated carbon (GAC) adsorption is the most commonly used technology for treating PFAS‐contaminated water. However, this approach is very costly and relatively inefficient at removing PFOA and shorter length analogues. Ultra‐high affinity sorbents are promising for application in ex situ pump‐and‐treat adsorption systems. In addition, they offer further opportunities for in situ remedial technologies, including injection as a fine powder or use as filling in subsurface permeable adsorptive barriers.

The objective of this study is to determine the feasibility of utilizing an ultra‐high affinity sorptive remediation approach that exploits multiple, complementary bonding modes (e.g., electrostatic and hydrophobic interactions) for the remediation of PFAS‐contaminated groundwater. The innovative sorbents are cationic polyaniline (PANI) and polypyrrole (PPy) polymers containing hydrophobic moieties. The unique structure of these polymeric materials enables both strong electrostatic interaction with the functional head group of anionic PFAS and hydrophobic interactions with the fluorinated tail of PFAS, allowing them to be more selective than GAC and to adsorb a wider range of compounds than anion exchange resins. By using suitable polymer precursors, the charge density and hydrophobicity of these polymers can be tailored to enhance PFAS removal. 

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Technical Approach

The specific project objectives coincide with six research tasks as follows:

  1. Develop and evaluate cationic hydrophobic polymers as high affinity sorbents to sequester PFASs;
  2. Develop cationic hydrophobic polymers grafted on GAC and activated carbon fibers and evaluate the capacity of these composites to adsorb PFASs;
  3. Evaluate the impact of co‐contaminants and aqueous chemistry on the sorptive removal of PFASs;
  4. Assess the feasibility of regenerating cationic hydrophobic polymers;
  5. Elucidate the molecular‐scale adsorption mechanisms of PFASs on the most effective engineered sorbents; and
  6. With the most effective sorbents, demonstrate the continuous ex situ treatment of PFASs in contaminated groundwater and develop cost effective implementable ex situ and in situ remediation strategies for PFASs. 

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Benefits

This project will develop novel sorbents that are highly effective at sequestering PFASs at environmentally relevant concentrations and can reliably meet the very low advisory levels established for PFOS and PFOA. The remedial processes will immobilize and highly concentrate dilute PFASs onto an adsorptive, regenerative media more efficiently and effectively than the existing technology (GAC). Benefits of this approach could include a reduction in the cost of water treatment for PFASs, reduction in the volume of waste produced, and potential applications to in situ treatment. (Anticipated Project Completion - 2020)

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Points of Contact

Principal Investigator

Reyes Sierra-Alvarez

University of Arizona

Phone: 520-626-2896

Program Manager

Environmental Restoration

SERDP and ESTCP

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